CN105915156B

CN105915156B - Photovoltaic power generation system with power optimizer

Info

Publication number: CN105915156B
Application number: CN201610389129.5A
Authority: CN
Inventors: 张永; 应剑东
Original assignee: Fonrich Shanghai New Energy Technology Co ltd
Current assignee: Fonrich Shanghai New Energy Technology Co ltd
Priority date: 2016-06-03
Filing date: 2016-06-03
Publication date: 2020-07-07
Anticipated expiration: 2036-06-03
Also published as: CN105915156A

Abstract

The invention mainly relates to a photovoltaic power generation electric device, which adopts a scheme that each photovoltaic component uses a multi-stage photovoltaic cell string and a multi-stage voltage conversion circuit as a power optimizer, so that any one stage of voltage conversion circuit can independently execute independent maximum power point tracking calculation on one cell string corresponding to the voltage conversion circuit, and the stability of the output power of the whole solar power generation system is ensured. The power optimizer also includes a communication circuit for forming a communication carrier on the transmission line to enable the power optimizer to send out communication information.

Description

Photovoltaic power generation system with power optimizer

Technical Field

The invention mainly relates to a photovoltaic power generation electric device, in particular to a scheme that each photovoltaic module uses a multi-stage photovoltaic cell string and a multi-stage voltage conversion circuit as a power optimizer, so that any one stage of voltage conversion circuit can independently execute independent maximum power point tracking calculation on one cell string corresponding to the voltage conversion circuit, and the stability of the output power of the whole solar power generation system is ensured.

Background

With the shortage of energy and the development of science and technology, new energy is more and more widely applied, and due to the characteristics of safety, reliability, low operation cost, simplicity in maintenance, availability everywhere and the like of photovoltaic power generation, the photovoltaic power generation is rapidly developed in the world, and especially plays an indispensable role in solving the power utilization problem of remote areas. The output characteristics of the photovoltaic cell are greatly changed under the influence of the external temperature and the illumination radiation intensity, so that the photovoltaic cell can always output the maximum power, and the solar energy is more effectively utilized as the basic requirement of a photovoltaic power generation system. To output the desired maximum power from the solar panel, it is most important to find the Maximum Power Point (MPPT) at which the output voltage and output current of the panel are maintained. The change of the maximum power point is usually related to the irradiation intensity and the ambient temperature, so the problem to be solved is that when the environment of the solar panel changes, the parameters which need to be dynamically tracked change to eliminate the external environmental factors and ensure that the solar panel works at the maximum power point.

In current Photovoltaic power optimization approaches, optimization is almost always performed at the Photovoltaic module level, and in practice, each Photovoltaic module usually includes a plurality of Photovoltaic cell strings (Photovoltaic cell strings) formed by Photovoltaic cells connected in series, and optimization at the Photovoltaic module level means that each individual cell string is not optimized individually. When the same string of battery plates cannot normally generate electricity due to poor product consistency or shadow shielding and other factors, the efficiency loss of the whole string of photovoltaic cells is serious, and when inverters, particularly centralized inverters, access a plurality of battery plate arrays, the battery plates of all strings can not operate at the maximum power point of the inverters, which are losses of electric energy and generated energy. Therefore, the power optimizer described later in this application mainly solves or alleviates these problems, and implements power optimization at a battery string level to carry an active power optimizer for each photovoltaic battery string, and introduces maximum power point tracking to ensure stability of output power of the solar system and maximum optimization of power.

Disclosure of Invention

In one embodiment of the invention, a photovoltaic power generation system with a power optimizer is disclosed, comprising a multi-stage photovoltaic cell string and a multi-stage power optimizer, wherein each stage of the power optimizer comprises a multi-stage BUCK circuit; wherein, in each stage of the power optimizer: the first input end and the second input end of any stage of BUCK circuit are respectively coupled to the positive terminal and the negative terminal of the corresponding stage of photovoltaic cell string; an output capacitor of the BUCK circuit of any stage is connected between a first output node and a second output node of the BUCK circuit of any stage; setting a first output node of any back-stage BUCK circuit in the multi-stage BUCK circuits to be connected with a second output node of a front-stage BUCK circuit adjacent to the first output node; therefore, in the multi-stage BUCK circuits of each stage of power optimizer, a first output node of a first stage BUCK circuit is defined as a first equivalent output end of the stage of power optimizer, and a second output node of a last stage BUCK circuit at the tail end is defined as a second equivalent output end of the stage of power optimizer; the power optimizers are connected in series, and a first equivalent output end of any next-stage power optimizer in the power optimizers is connected with a second equivalent output end of a previous-stage power optimizer adjacent to the first equivalent output end; so as to form the total output voltage of the power optimizer in multiple stages between the first equivalent output end of the power optimizer in the first stage of the power optimizer and the second equivalent output end of the power optimizer in the last stage of the power optimizer.

In the photovoltaic power generation system with the power optimizer at any stage, the power optimizer at any stage further includes a communication circuit, which is used for forming a communication carrier on a transmission line connected to the first output node of the first-stage BUCK circuit of each power optimizer and/or on a transmission line connected to the second output node of the last-stage BUCK circuit, so as to realize that the power optimizer at each stage sends communication information outwards.

In the photovoltaic power generation system with the power optimizer, the communication circuit comprises a first switch, a bypass resistor and a bypass capacitor; the bypass resistor and the bypass capacitor are connected in parallel and then connected in series with the first switch between a first output node of a first-stage BUCK circuit and a second output node of a last-stage BUCK circuit of each stage of the power optimizer.

In the above photovoltaic power generation system with the power optimizer, each stage of the power optimizer further includes a first controller, and at the stage of sending the communication information by each stage of the power optimizer, the driving signal output by the first controller controls the first switch which is originally turned off to be turned on and then turned off, so that a carrier current flowing through the communication circuit is generated at the time when the first switch is turned on, and is injected onto a transmission line connected to the first output node of the first stage BUCK circuit of each power optimizer and/or injected onto a transmission line connected to the second output node of the last stage BUCK circuit to form a communication carrier.

In the photovoltaic power generation system with the power optimizer, each stage of the power optimizer further comprises a second switch which can be arranged in any stage of the BUCK circuit;

the second switch and the output capacitor of any stage of BUCK circuit in each power optimizer are connected in series between the first output node and the second output node of the BUCK circuit of any stage.

In the photovoltaic power generation system with the power optimizers, before each power optimizer sends the communication information, the driving signal output by the first controller in the power optimizer controls the originally-switched-on second switch to be switched off, and the second switch is not switched on until the power optimizer finishes the procedure of sending the communication information.

The photovoltaic power generation system with the power optimizer further comprises an inverter for converting direct current output by the power optimizer at multiple stages into alternating current.

In the photovoltaic power generation system with the power optimizer, the inverter further includes a detection module for extracting the communication carrier from the current flowing through the transmission line.

In the photovoltaic power generation system with the power optimizer, the detection module is any one of a high-frequency sensor, a band-pass filter and a codec.

The photovoltaic power generation system with the power optimizer further comprises an inverter for converting the dc power outputted by the power optimizer in multiple stages into ac power, the inverter has an energy storage capacitor and first and second circuit breaking modules, and the inverter further comprises: a first input node coupled to a first equivalent output of a first stage of said power optimizer of a plurality of stages of said power optimizer; a second input node coupled to a second equivalent output of a last stage of said power optimizer in said plurality of stages; the first disconnection module is connected between the first input node and the first end of the energy storage capacitor, the second disconnection module is connected between the second input node and the second end of the energy storage capacitor, and the connection or disconnection of the first and second disconnection modules is controlled by a second controller of the inverter.

In the photovoltaic power generation system with the power optimizer, the inverter further includes a command unit, which is configured to send a communication carrier on a transmission line connected to the first input node of the inverter and/or on a transmission line connected to the second input node of the inverter, so as to enable the inverter to send command information to the outside.

The photovoltaic power generation system with the power optimizer is characterized in that the command unit is provided with a resistor and a third switch which are connected between the first input node and the second input node of the inverter in series.

In the above photovoltaic power generation system with the power optimizer, at the stage when the instruction unit sends the instruction information, the driving signal output by the second controller controls the originally turned-off third switch to be turned on and then turned off, so that the carrier current flowing through the instruction unit is generated at the time when the third switch is turned on, and is injected into the transmission line connected to the first input node of the inverter and/or the transmission line connected to the second input node of the inverter to form a communication carrier.

When the inverter sends first instruction information to any one stage of the power optimizer, the power optimizer of any one stage extracts the communication carrier from the current flowing through the transmission line through a detection module, and the first instruction information is received by the first controller of the power optimizer of any one stage.

In the photovoltaic power generation system with the power optimizer, the detection module is any one of a high-frequency sensor, a band-pass filter, a codec and a shunt.

In the photovoltaic power generation system with the power optimizer, the first instruction information is a shutdown instruction, and before the inverter sends shutdown instruction information to any one stage of the power optimizer, the second controller controls the first and second disconnection modules to be switched to a shutdown state.

After the inverter sends the shutdown instruction information to any stage of power optimizer and after the plurality of sets of BUCK circuits enter the shutdown or sleep state, the second controller controls the third switch to be switched to the on state, and/or the first controller controls the first switch to be switched to the on state.

In the photovoltaic power generation system with the power optimizer, when the inverter controls the multistage power optimizer to start, the second controller firstly controls the first and second disconnection modules to be connected, and when the first controller of each stage of the power optimizer detects that the power optimizer of the stage of the first controller receives the voltage and/or the current transmitted by the inverter, the first controller controls the multiple groups of BUCK circuits of each stage of the power optimizer to start to execute the voltage conversion function so as to exit the shutdown or sleep state.

In the photovoltaic power generation system with the power optimizer, the power optimizer at any stage further includes a detection module, which is used for extracting the communication carrier wave sent by other power optimizers from the current flowing through the transmission line of the power optimizers connected in series to realize the mutual communication between different power optimizers.

In one embodiment of the invention, a power optimizer is disclosed for voltage conversion of one or more levels of photovoltaic cell strings, comprising one or more levels of BUCK circuitry, wherein: the first input end and the second input end of any stage of BUCK circuit are respectively coupled to the positive terminal and the negative terminal of the corresponding stage of photovoltaic cell string; one output capacitor of the BUCK circuit of any stage is connected between the first output node and the second output node of the BUCK circuit of any stage; when the number of the photovoltaic cell strings and the number of the BUCK circuits are both one stage, the output voltage of the single-stage photovoltaic cell string is provided between a first output node and a second output node of the single-stage BUCK circuit; or when the number of the photovoltaic cell strings and the number of the BUCK circuits are both in multiple stages, setting that a first output node of any one later stage BUCK circuit in the multiple stages of BUCK circuits is connected with a second output node of an adjacent previous stage BUCK circuit, and forming the total output voltage of the multiple stages of photovoltaic cell strings between the first output node of the first stage BUCK circuit and the second output node of the last stage BUCK circuit in the multiple stages of BUCK circuits.

The power optimizer described above, wherein said power optimizer further comprises a communication circuit; when the number of the photovoltaic cell strings and the number of the BUCK circuits are both one level, the communication circuit is connected between a first output node and a second output node of the single-level BUCK circuit; when the number of the photovoltaic cell strings and the number of the BUCK circuits are both multi-level, the single communication circuit is connected between a first output node of the first-level BUCK circuit and a second output node of the last-level BUCK circuit.

In the above power optimizer, the communication circuit includes a first switch, a bypass resistor and a bypass capacitor; when the number of the photovoltaic cell strings and the number of the BUCK circuits are both one level, the bypass resistor and the bypass capacitor are connected in parallel firstly and then connected in series with the first switch between a first output node and a second output node of the single-level BUCK circuit, and the communication circuit is used for forming a communication carrier on a transmission line connected with the first output node and/or the second output node of the single-level BUCK circuit; or when the photovoltaic cell strings and the BUCK circuits are in multiple stages, the bypass resistor and the bypass capacitor are connected in parallel and then connected in series with the first switch between a first output node of the first-stage BUCK circuit and a second output node of the last-stage BUCK circuit, and the communication circuit is used for forming a communication carrier on a transmission line connected with the first output node of the first-stage BUCK circuit and/or a transmission line connected with the second output node of the last-stage BUCK circuit.

In the above power optimizer, the power optimizer further includes a first controller, and in a stage where the power optimizer sends the communication information, the driving signal output by the first controller controls the first switch that is originally turned off to be turned on and then turned off, so that a carrier current flowing through the communication circuit is generated at a time when the first switch is turned on, and the carrier current is injected into the transmission line to form a communication carrier.

In the power optimizer, the power optimizer further comprises a second switch which can be arranged in any stage of the BUCK circuit; the second switch and the output capacitor of the BUCK circuit of any stage are connected in series between the first output node and the second output node of the BUCK circuit of any stage.

In the above power optimizer, before the power optimizer sends the communication information, the driving signal output by the first controller controls the originally turned-on second switch to be turned off, and the second switch is not turned on until the power optimizer finishes the procedure of sending the communication information.

In the above power optimizer, each stage of the BUCK circuit includes a main switch and an inductor connected between its first input terminal and a first output node, both the main switch and the inductor being connected at an interconnect node; and

a freewheeling switch is also connected between the interconnect node and the second input terminal, wherein the second input terminal of the BUCK circuit of each stage is connected to the second output node.

The power optimizer also comprises a detection module; when the number of the photovoltaic cell strings and the number of the BUCK circuits are both one level, the detection module extracts communication carriers from a transmission line connected with a first output node and/or a second output node of the single-level BUCK circuit; or when the number of the photovoltaic cell strings and the number of the BUCK circuits are both in multiple stages, the detection module extracts communication carriers from a transmission line connected with a first output node of the first-stage BUCK circuit and/or a transmission line connected with a second output node of the last-stage BUCK circuit.

The detection module is any one of a high-frequency sensor, a band-pass filter, a coder-decoder and a current divider.

In the power optimizer, after the detection module detects the shutdown or hibernation instruction information, the first controller of the power optimizer receives the instruction information, and when the first controller controls the BUCK circuit to enter the shutdown state, the first controller controls the first switch to be switched to the on state.

In one embodiment of the present invention, an inverter is disclosed, comprising an energy storage capacitor and first and second circuit breaking modules, wherein: the first circuit breaking module is connected between a first input node of the inverter and a first end of the energy storage capacitor, the second circuit breaking module is connected between a second input node of the inverter and a second end of the energy storage capacitor, and the connection or disconnection of the first circuit breaking module and the second circuit breaking module is controlled by a second controller of the inverter; the inverter further comprises a command unit, and the command unit is used for sending communication carriers on a transmission line connected with the first input node of the inverter and/or a transmission line connected with the second input node of the inverter so as to enable the inverter to send command information outwards.

In the inverter, the command unit has a resistor and a third switch connected in series between the first and second input nodes of the inverter.

In the inverter, at the stage when the command unit sends the command information, the driving signal output by the second controller controls the third switch, which is originally turned off, to be turned off after being turned on, so that the carrier current flowing through the command unit is generated at the time when the third switch is turned on, and is injected onto the transmission line connected to the first input node of the inverter and/or the transmission line connected to the second input node of the inverter to form a communication carrier.

In the inverter, before the inverter sends the instruction information, the second controller controls the first and second disconnection modules to be switched to the disconnection state, and the instruction unit is supplied with power by the voltage source loaded on the transmission line connected to the first input node of the inverter and the transmission line connected to the second input node of the inverter.

In the inverter, the instruction information is shutdown instruction information, and after the inverter sends the instruction information and an object receiving the shutdown instruction information is shutdown, the second controller controls the third switch to be switched to an on state, so as to release the residual electric quantity loaded on a transmission line connected to the first input node of the inverter and/or a transmission line connected to the second input node of the inverter.

In the inverter, the inverter further includes a detection module, configured to detect an external communication carrier that is sent by any harmonic source to a transmission line connected to the first or second input node, so that the inverter receives communication information from outside.

In the inverter, the detection module is any one of a high-frequency sensor, a band-pass filter, a codec and a shunt.

In the invention, the photovoltaic optimizers can communicate with each other, so that the working state of each photovoltaic assembly (even at the level of a cell string) and the voltage of the whole photovoltaic system are known. The inverter realizes the detection of each photovoltaic component through a Rogowski coil, a band-pass filter, demodulation and the like, and the circuit also integrates an arc detection function. The inverter can also realize the issue of commands to the photovoltaic optimizer, the photovoltaic optimizer can be intelligently shut down by adjusting interference current, and the photovoltaic optimizer can be informed of intelligent startup through slow loading voltage. In addition, the inverter informs the photovoltaic optimizer of shutdown or entering a protection mode in a current mode, and the circuit for loading current can also be used as a discharge circuit of the internal capacitance of the inverter. According to the invention, a long photovoltaic string mode can be realized, namely each photovoltaic optimizer controls the output voltage thereof, so that each whole photovoltaic string can be connected with more photovoltaic components in series, and the condition that the inverter needs more input voltage margin due to overhigh output voltage under the condition of low-temperature open circuit of the traditional photovoltaic string is avoided.

These solutions have advantages such as: the power generation efficiency of the whole power generation system is improved, negative factors such as local photovoltaic damage and shielding or inconsistency of photovoltaic cells and installation inconsistency have no influence on the power generation efficiency of the system, the cascade optimization of the cell pieces is realized, the system efficiency is deeply excavated, and the observability of various parameters of each cell component is achieved in a communication mode. The safety of the photovoltaic system is also realized, when a fault or maintenance occurs, the photovoltaic string can be switched off, and the output voltage is zero. The number of each photovoltaic group string in series connection is increased, and the wiring cost of the system is saved. The hot spot resistance of the photovoltaic module is improved, so that the service life of the cell is prolonged.

Drawings

The features and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the following drawings:

fig. 1 is a photovoltaic module containing a plurality of strings of photovoltaic cells.

Fig. 2 is a topology of a multi-stage optimizer with a BUCK circuit voltage converting a multi-stage battery string.

FIG. 3 is a schematic diagram of converting the voltage of a photovoltaic cell to power a load using a BUCK circuit.

Fig. 4 is a schematic diagram of an equivalent variable resistance based on the BUCK circuit and the load.

FIG. 5 shows a switch in series with an output capacitor between a pair of output terminals of the second stage BUCK circuit.

FIG. 6 shows a switch in series with an output capacitor between a pair of output terminals of the first stage BUCK circuit.

Fig. 7 shows that the shunt resistor and the shunt capacitor connected in parallel in the communication circuit can be reversed with respect to the shunt switch.

Fig. 8 is a schematic diagram of a BUCK circuit and battery string utilizing more stages.

Fig. 9 is a schematic diagram of grid-tie delivery of voltage sources to the same inverter using more photovoltaic modules.

Fig. 10 is a schematic diagram of a sensor employing a shunt rather than a rogowski coil.

Fig. 11 is a schematic diagram of a single-stage BUCK circuit performing voltage conversion on a single-stage photovoltaic cell string.

Fig. 12 is a schematic diagram of multiple optimizers connected in series with each other in output voltage/current to the inverter.

FIG. 13 is a schematic diagram of an alternative topology of the communication circuit and instruction unit.

Detailed Description

Referring to fig. 1, the CELL strings CELL-ST 1-CELL-ST 3 disposed on the photovoltaic module are taken as an example to illustrate the inventive spirit of the present invention, and it is noted that the specific number of the CELL strings on the photovoltaic panel is only for convenience of description, and does not represent that the present invention is limited to the specific number listed. The CELL string CELL-ST1 has a plurality of photovoltaic CELLs 10 connected in series with each other, typically in such a way that the anode of the latter photovoltaic CELL 10 is connected to the cathode of the adjacent former photovoltaic CELL 10, the anode of the first photovoltaic CELL 10 in the string is set as the equivalent anode a1 of the entire CELL string CELL-ST1, and the cathode of the last photovoltaic CELL 10 in the string is set as the equivalent cathode C1 of the entire CELL string CELL-ST 1. By the same token, CELL string CELL-ST2 has equivalent anode a2 and equivalent cathode C2, and CELL string CELL-ST3 has equivalent anode A3 and equivalent cathode C3. In conventional use, it is necessary to connect the equivalent cathode C1 of the battery string CELL-ST1 with the equivalent anode A2 of the battery string CELL-ST2 and to connect the equivalent cathode C2 of the battery string CELL-ST2 with the equivalent anode A3 of the battery string CELL-ST 3. Viewing the photovoltaic module as a whole, a positive terminal A thereof for connection to an external circuit_EQAn equivalent anode A1, a negative terminal C for connection to an external circuit_EQIs connected with an equivalent cathode C3 at the positive terminal A_EQAnd a negative terminal C_EQThe voltage drop therebetween charges the energy storage element.

Referring to fig. 1, in order to avoid that the entire photovoltaic module cannot work normally due to damage or other abnormal conditions of the panel inside any one of the CELL strings, a diode D1 is connected between the equivalent anode a1 and the equivalent cathode C1 of the CELL string CELL-ST1, the anode of the diode D1 is connected to the equivalent cathode C1, and the cathode is connected to the equivalent anode a1, so that the diode D1 is reversely biased. Similarly, a diode D2 has its anode connected to the equivalent cathode C2 and its cathode connected to the equivalent anode a2, and a diode D3 has its anode connected to the equivalent cathode C3 and its cathode connected to the equivalent anode A3. When the CELL strings CELL-ST 1-CELL-ST 3 are operating normally, the diodes D1-D3 are reverse biased, but when some of the photovoltaic CELLs 10 in one of the strings are damaged by physical trauma or are shaded, the string may experience a so-called hot spot effect, and the affected CELL pieces may be placed in a reverse biased state and consume power and cause overheating. However, if the diodes D1-D3 are adopted, most of the current of the shielded cell string will flow through the diodes connected in parallel with the cell string, so that the temperature of the hot spot cell string can be remarkably reduced, and the damage and the rejection of the whole photovoltaic module can be prevented.

The utilization of photovoltaic cells is mainly affected by two aspects: (1) the internal characteristics of the photovoltaic cell; (2) the ambient use environment of the photovoltaic cell such as solar irradiance, load conditions and temperature conditions. Under different ambient conditions, the photovoltaic cells may operate at different and unique Maximum Power points (Maximum Power points). Therefore, for a power generation system of a photovoltaic cell, the real-time optimal working state of the photovoltaic cell under any illumination condition should be sought so as to convert the light energy into electric energy to the maximum extent. For example, for the photovoltaic module shown in fig. 1, the maximum power point of the photovoltaic cell is optimized and tracked, and the general approach is to optimize the output voltage and the output current of the whole photovoltaic module, calculate the output power of the solar array, and realize the tracking of the maximum power point. The disadvantage of this optimization mode is that the output of the entire pv module is optimized only by considering the individual strings, but in practice, the strings CELL-ST1 to CELL-ST3 have differences in individual pv characteristics, for example, the voltage levels of their respective outputs are not necessarily identical under the same lighting conditions, and thus, the maximum power point tracking of the entire pv module is not necessarily the ideal power output state. The present application will in the following go to great lengths to overcome this doubt and to introduce how to optimize CELL-ST1 or CELL-ST2 or CELL-ST3 independently to maximize the conversion of light energy into electrical energy.

Referring to FIG. 2, a first CELL string CELL-ST1 generates a desired voltage output by using a first BUCK conversion circuit BUCK1, an inductor L1 and a capacitor cap1 in a BUCK1 circuit constitute a low pass filter, a first input node of a BUCK1 circuit is connected to an equivalent anode A1 of the CELL string CELL-ST1, a second input node of the BUCK1 circuit is connected to an equivalent cathode C1 of the CELL-ST1, and a switch S11 and the inductor L1 are connected in series between the first input node of the BUCK1 circuit and a first output node B1_N1In the meantime. Wherein one terminal of switch S11 is connected to a first input node of the BUCK1 circuit, but the opposite terminal of switch S11 is connected to a second input node (or second output node B1) of the BUCK1 circuit_N2) With another switch S12 connected therebetween. The capacitor cap1 is connected between the first output node and the second output node of the BUCK1 circuit. The basic principle of the conversion circuit is as follows: the first and second inputs of the BUCK1 circuit draw power from between the anode and cathode of the first CELL string CELL-ST1, during a switching cycle, switch S11 is turned on and off S12, inductor L1 current is increased and charges capacitor cap1, switch S11 is turned off and on S12, inductor L1 current is decreased and begins to discharge energy, and then S12 is turned on to freewheel.

In the same way, reference may be made to FIG. 8, which in a more representative illustration may be considered to be: AN arbitrary Nth battery string CELL-STN generates a desired voltage output (N is a natural number larger than or equal to 1) by using AN Nth BUCK conversion circuit BUCKN, AN inductor LN and a capacitor capN in the Nth BUCK circuit form a low-pass filter, a first input node of the Nth BUCKN circuit is connected to AN equivalent anode AN of the Nth battery string CELL-STN, a second input node of the Nth BUCKN circuit is connected to AN equivalent cathode CN of the Nth CELL-STN, and a switch SN1 and the inductor LN are connected in series to the first input node of the BUCKN circuitNode and first output node BN_N1In the meantime. Wherein one end of the switch SN1 is coupled to a first input node of the Nth BUCKN circuit, an opposite end of the switch SN1 and a first output node BN_N1The inductance LN is connected between and the opposite end of the switch SN1 and the second input node (or second output node BN) of the nth buck circuit_N2) There is also another switch SN2 connected between. The capacitor capN is connected to the first output node BN of the Nth BUCKN circuit_N1And a second output node BN_N2In the meantime. One of switches SN1 and SN2 is turned on while the other is turned off.

The photovoltaic optimizer of the present application can be summarized as: in the N-stage photovoltaic cell string and the N-stage BUCK circuit, any K-th stage BUCK circuit comprises an inductor L for low-pass filtering_KAnd a capacitor CAP_KThe natural number K satisfies N ≧ K > 1, and the capacitance CAP of any K-th stage BUCK circuit_KA first output node BK connected to the K-th stage BUCK circuit_N1And a second output node BK_N2In the meantime. The voltage provided by the photovoltaic cell string of the Kth stage is correspondingly output at a first output node BK of the BUCK circuit of the Kth stage_N1And a second output node BK_N2And (3) removing the solvent. In addition, a first output node BK of any subsequent stage BUCK circuit is also provided_N1And a second output node B (K-1) of the previous stage BUCK circuit adjacent thereto_N2Are connected so that we can be at the first output node B1 of the first stage BUCK circuit_N1And a second output node BN of a last Nth stage BUCK circuit at the end_N2And generating and providing a total output voltage of the N-level photovoltaic cell string. The total number of stages of the photovoltaic cell strings is equal to the total number of stages of the BUCK circuit. Viewed from the outside of the photovoltaic module, a first output node B1 of the first stage BUCK circuit_N1Connected positive terminal A_EQAnd a second output node BN of the Nth stage BUCK circuit_N2One negative terminal C connected with_EQAs a pair of output ports for the entire photovoltaic module.

Referring to fig. 2, the optimizer includes at least a first controller 110 such as an MCU in addition to the N-stage BUCK circuit, and for the first CELL string CELL-ST1 and the first stage BUCK1 circuit, the pulse width modulation signal PWM sent by the first controller 110 drives the switch S11 and the switch S12 to switch between off and on, and modulates the duty cycle of each of the switches S11 and S12 to achieve maximum power point tracking.

Referring to fig. 3-4, to understand the general process of maximum power point tracking, we roughly simulate the application scenario of a photovoltaic cell. If the photovoltaic cell includes a DC power supply U_SAnd an equivalent adjustable resistance R₁Voltage U₁Is to simulate the output voltage, voltage U, of the photovoltaic cell₁The output voltage of the BUCK BUCK circuit is U_OVoltage U of BUCK output_OApplied to an equivalent load R₂The current flowing through the load is I_OAverage input current of BUCK circuit is I₁And D is the duty cycle at which switch S1 is on. Substantially satisfying the relation U in BUCK circuits₁×I₁＝U_O×I_O＝(U_O)²/R₂And U is_O＝D×U₁And the BUCK converter and the load are ideally considered as an equivalent variable resistance R_EQ，R_EQ＝U₁/I₁Thus calculating R_EQ＝U₁/I₁＝R₂/D²This proves that the external equivalent resistance can be adjusted according to the adjustment duty ratio D. If the output power of the analog photovoltaic is described by P, then P-U₁×U_S/(R₁+R_EQ)，U₁＝R_EQ×U_S/(R₁+R_EQ) R in the functional relation_EQElimination then P ═ U₁)²/R₁+U_S×U₁/R₁In a more ideal approximation scheme, R is assumed_EQ＝R₁The maximum power output P can be obtained by the photovoltaic cell_MAX＝(U_S)²/4R₁. The adjustment of the duty ratio D is actually equivalent to the adjustment of the output load impedance, and also means that the duty ratio D determines the matching degree of the internal resistance and the external resistance, so that the duty ratio D can be adjusted in real time to realize the maximum powerAnd MPPT optimization tracking. It should be noted that the approximation processes of fig. 3 and fig. 4 are for proving that the PWM signal sent by the first controller 110 drives the switches S11 and S12 to realize maximum power point tracking by modulating the duty ratio of the switches S11/S12 when switching, but this does not indicate that the actual operating parameters of the BUCK circuit in the present invention are necessarily limited by the functional relationships of these approximation processes. In addition, since those skilled in the art already know various approaches for implementing maximum power MPPT optimized tracking by PWM, these approaches are considered as known techniques in the present application, as described in chinese patent applications CN202444444U and CN 201608672U.

Based on the above description, in the CELL strings CELL-ST1 to CELL-ST3 of a certain photovoltaic module, any CELL string can independently execute the maximum power point tracking command by using the BUCK circuit, so as to realize the power optimization at the CELL string level, which is obvious to those skilled in the art. In the prior art, the final output voltage of the photovoltaic module is mostly optimized in power, so that the efficiency of each battery string cannot be exerted to the maximum extent, but the invention well solves the problem. Particularly, the problem of low power generation efficiency caused by local photovoltaic damage or light shielding of the battery strings or negative adverse factors such as inconsistent characteristics and installation difference among the photovoltaic strings is solved, the power generation efficiency of the whole power generation system is improved, and the energy efficiency of the power generation system is deeply optimized.

In the field of photovoltaic inversion, a direct-current voltage source generated by a photovoltaic module needs to be converted into alternating current to realize grid connection, a photovoltaic inverter is used for converting direct-current electric energy provided by a solar cell into alternating-current electric energy so as to meet the requirements of alternating-current load or equipment power supply and grid connection, and the inverter usually has a single-phase or three-phase or even at most equal inversion mode. For the purpose of simple explanation of the function of the inverter, fig. 2 exemplarily shows a three-phase full-bridge main power converting circuit 170 (which may be a single-phase or two-phase or multi-phase), a conventional EMC filter used in a previous stage of the three-phase full-bridge main power converting circuit 170, a three-phase LC filter used in a subsequent stage, and the like are omitted, and the converting circuit 170 may be configured to omit a capacitor in the inverterC_DCThe stored dc voltage is converted into ac power, wherein the switching tubes of the converter circuit 170, which constitute an inverter bridge, are mainly driven and controlled by a PWM signal PWM sent from a controller 140 of the inverter. Since the Inverter circuit 170 of the Inverter (Inverter) is used for inverting and converting direct current into alternating current, alternative types thereof are well known to those skilled in the art and thus will not be described in detail.

The inverter often performs voltage conversion on a certain photovoltaic module with a plurality of photovoltaic strings, but performs voltage conversion on a plurality of different photovoltaic modules at the same time, so that in the invention, besides information interaction/communication between the optimizer and the photovoltaic inverter, information interaction/communication also exists between different optimizers. To implement this mechanism of communication between each other, FIG. 2 illustrates an example of a communication implementation, the first output node B1 of the first stage BUCK1 circuit_N1And a second output node B3 of the last stage 3 BUCK3 circuit_N2A communication circuit is connected in series between the two, and the communication circuit comprises a shunt capacitor C connected in parallel_BYAnd a shunt resistor R_BYAnd a switching device S_BYWherein a capacitor C is bypassed_BYAnd a shunt resistor R_BYFirst connected in parallel and then connected with the switching device S_BYConnected in series at a first output node B1_N1And a second output node B3_N2In the meantime. Such as a bypass capacitor C_BYAnd a shunt resistor R_BYEach having one end interconnected and connected to a first output node B1_N1Upper and bypass capacitor C_BYAnd a shunt resistor R_BYThe opposite ends of each are interconnected and then connected to a switching device S_BYA terminal of, a switching device S_BYIs connected to a second output node B3_N2Note that the switching device S_BYIs any type of electronic switch whose connection or disconnection between a pair of input/output terminals is driven or controlled by a signal applied to its control terminal. In the embodiment of FIG. 2, the first controller 110 of the optimizer sends driving signals other than the control signals S11S 12 of BUCK1Switches S21-S22 of BUCK2, and switches S31-S32 of BUCK3, the driving signal sent by the first controller 110 drives the switch S_BYOn or off. Although not shown, the first controller 110 can detect the output voltage and the output current of each of the BUCK 1-BUCK 3, and how the first controller 110 transmits the information to the second controller 140 of the inverter or how the first controller 110 receives the information sent by the second controller 140 will be discussed later in this document.

Referring to FIG. 2, a bypass capacitor C is included_BYA bypass resistor R_BYAnd switch S_BYIn the communication circuit of (3), the switch S may be held first_BYIn the off state, if the first controller 110 tries to exchange information with the outside, the driving signal sent by the first controller 110 rapidly jumps from the first logic state (e.g. low level) to the second logic state (e.g. high level) and then returns to the first logic state, so that the switch S which is switched on under the high level driving_BYIs turned on and off. Or the driving signal sent by the first controller 110 rapidly jumps from the first logic state (e.g. high level) to the second logic state (e.g. low level) and then returns to the first logic state, so that the switch S, which is switched on under the low level driving_BYIs turned on and off, the switch S_BYThe off-on-off process of (a) may be repeated multiple times. It can be considered that the control switch S_BYHas a rising or falling edge moment of a nearly transient jump, will turn on the switch S_BYGenerating a harmonic or carrier current through the communication circuit that is injected into the first output node B1_N1Or at a second output node B3_N2On the transmission line. Various carrier detection modules 120 (e.g., air coil sensors or high frequency transformers, band pass filters, de-encoders) may be used to extract the carrier signal sent by the communication circuit from the current information flowing through the transmission line for demodulation. For example, an inverter or other photovoltaic module may utilize the carrier detect module 120 to detect carrier information emitted by a particular photovoltaic module that utilizes the communication circuitry to transmit information. Such carrier information may beAnd converting the information into binary code elements according to various communication protocols specified currently for information interaction.

Referring to FIG. 2, in a preferred embodiment, except at the first output node B3 of the third stage BUCK3 circuit_N1And a second output node B3_N2In addition to a capacitor cap3, a switch S33 is connected in series with the capacitor cap3, both of which are connected in series at a first output node B3_N1And a second output node B3_N2One end of the capacitor cap3 is connected to the first output node B3_N1And its opposite end and a second output node B3_N2The switch S33 is connected, but in practice the positions of the switch S33 and the capacitor cap3 may be reversed, i.e. as an alternative, one end of the switch S33 is connected to the first output node B3_N1And its opposite end and a second output node B3_N2The capacitor cap3 is connected therebetween. In the normal operation stage of the optimizer, the BUCK1 circuit performs voltage reduction conversion on the voltage sources output by the anode A1 terminal and the cathode C1 terminal of the battery string CELL-ST1, and the generated output voltage falls on a first output node B1 of the BUCK1 circuit_N1And a second output node B1_N2A (c) is added; similarly, the BUCK2 circuit down-converts the voltage source output from the anode A2 terminal and the cathode C2 terminal of the battery string CELL-ST2 to generate an output voltage falling at the first output node B2 of the BUCK2 circuit_N1And a second output node B2_N2A (c) is added; and the BUCK3 circuit performs voltage reduction conversion on the voltage source output by the anode A3 terminal and the cathode C3 terminal of the battery string CELL-ST3, and the generated output voltage falls on a first output node B3 of the BUCK3 circuit_N1And a second output node B3_N2And (3) removing the solvent. In the topology design manner introduced above, the second output node B1 of the BUCK1 circuit of the first stage_N2And a first output node B2 of the BUCK2 circuit of the second stage_N1Connected to the second output node B2 of the BUCK2 circuit of the second stage_N2And a first output node B3 of the BUCK3 circuit of the third stage_N1Therefore, it can be considered that the capacitor cap1 of the first stage BUCK1, the capacitor cap2 of the second stage BUCK2, and the capacitor cap3 of the third stage BUCK3 are serially connected in turn at the first output node B1 of the first stage BUCK1_N1And a second output node B3 of the third stage BUCK3_N2In the above-mentioned manner,it may be that the switch S is in a communication circuit_BYWhen on/off switching is performed, the capacitor cap1, the capacitor cap2 and the capacitor cap3 are connected in series and then connected in parallel with the communication circuit, and the carrier signals caused by the overlarge voltages of the capacitors cap 1-cap 3 are weak or even cannot form effective carriers, so the switch S33 is additionally designed. The switch S33 is controlled by the first controller 110 to be in a state of being always on in a stage where the optimizer does not enable the communication circuit and the BUCK 1-BUCK 3 circuits are normally operated, and the switch S is turned on only when the optimizer is ready to enable the communication circuit_BYIn this case, the switch S33 is preferably turned off by the first controller 110 (communication phase), and the first output node B1, which is originally normally connected to the first stage BUCK1, is connected to the first output node B1_N1And a second output node B3 of the third stage BUCK3_N2The capacitor string cap 1-cap 3 between, from the first output node B1_N1And a second output node B3_N2Form a circuit break therebetween and then turn on the switch S_BYWill be at the first output node B1_N1Or second output node B3_N2The associated voltage transmission lines used to provide the voltage produce a carrier signal that is relatively distinct and easily captured by the detection module 120.

Referring to FIGS. 5-6, which are slightly modified topologies based on FIG. 2, in FIG. 2, a switch S33 and a capacitor cap3 are connected in series with a first output node B3 of the BUCK3 circuit_N1And a second output node B3_N2In the embodiment of FIG. 5, however, switch S33 of the BUCK3 circuit is eliminated and instead at the first output node B2 of the BUCK2 circuit_N1And a second output node B2_N2A switch S23 and a capacitor cap2 are connected in series. In the embodiment of FIG. 6, switches S23 and S33 of the BUCK 2-BUCK 3 circuits are eliminated instead of at the first output node B1 of the BUCK1 circuit_N1And a second output node B1_N2A switch S13 and a capacitor cap1 are connected in series. In either of the topologies of FIGS. 5-6, the switch S is turned on when the optimizer enables the communication circuit to prepare for_BYIn this case, the switch S13 (or S23 or S33) is preferably turned off by the first controller 110, and then the switch S is switched_BYLet it switch onAnd a shut-down program for executing a communication process of the communication circuit, and the communication circuit should shut down the switch S after completion of communication_BYAnd turns on the switch S13 (or S23 or S33). Referring to fig. 7, a slightly modified topology based on fig. 2 is shown, in which a bypass capacitor C is used_BYAnd a shunt resistor R_BYEach having one end connected to a second output node B3_N2Upper, and a bypass capacitor C_BYAnd a shunt resistor R_BYThe opposite ends of which are connected to each other and then connected to the switching device S_BYA terminal of, a switching device S_BYIs correspondingly connected to a first output node B1_N1The above. Equivalent to a bypass capacitor C in a communication circuit_BYAnd a shunt resistor R_BYBoth and a switching device S_BYThe position of (c) is reversed with respect to fig. 2. The optimizer of fig. 7 may also replace the freewheeling switches (e.g., S12, S22, S32 in fig. 2) in the BUCK circuits of the stages with freewheeling diodes. Note that S12 in BUCK1 is replaced with a diode D12, and a switch S11 and an inductor L1 are connected in series at a first input node and a first output node B1 of a BUCK1 circuit_N1A node where the switch S11 and the inductor L1 are connected to each other and a second input node (or second output node B1) of the BUCK1 circuit_N2) Between which is connected a diode D12. Wherein one terminal of the switch S11 is connected to a first input node of the BUCK1 circuit, the cathode of the diode D12 is connected to the opposite terminal of the switch S11, the cathode of the diode D12 is also connected to a node at which the switch S11 and the inductor L1 are interconnected, and the anode of the diode D12 is connected to a second input node (or a second output node B1) of the BUCK1 circuit_N2) The above. In the same way, diode D22 is used in the BUCK2 circuit to replace switch S22, and diode D32 is used in the BUCK3 circuit to replace switch S32, and since the circuit structures of BUCK 2-BUCK 3 are similar to that of BUCK1, the description is omitted.

As already mentioned above, the inverter needs to interact with the optimizer for various reasons, such as various commands issued by the optimizer to request the optimizer to execute corresponding commands, so the present invention also designs a command unit for the inverter. Referring to FIG. 9, the inverter includes, based on the power supply voltage supplied from the conversion three-stage battery string and the three-stage BUCK circuitAn energy storage capacitor C_DCWherein power is supplied at a first output node B1 of the first stage BUCK1 circuit_N1A voltage transmission line LINA connected to the last stage and a second output node B3 connected to the last stage BUCK3 circuit_N2The transmission is carried out on a voltage transmission line LINB connected to it, noting that the electrical energy transmitted here should be the photovoltaic supply voltage generated jointly by the series of CELLs CELL-ST1 to CELL-ST3, and the capacitance C of the inverter_DCThe two ends are correspondingly coupled to the pair of voltage transmission lines LINA-LINB and receive the electric energy transmitted by them. The command unit of the inverter comprises a resistor R_INSAnd switch S_INSResistance R_INSAnd switch S_INSAre connected in series and are connected in series with a first output node B1 of a first stage BUCK1_N1A voltage transmission line LINA connected to the first output node B3 of the third stage BUCK3_N2Between the connected voltage transmission lines LINB. In addition, it is assumed that the inverter has a first input node N_IN1And a second input node N_IN2First input node N_IN1A first output node B1 coupled to a first stage BUCK1 via a transmission line LINA_N1Corresponding second input node N_IN2Coupled to a second output node B3 of the last stage BUCK3 via a transmission line LINB_N2Resistance R_INSAnd switch S_INSIs connected in series to the first input node N_IN1And a second input node N_IN2And (3) removing the solvent. In addition, at the first input node N_IN1And a capacitor C of the inverter_DCIs connected with a first disconnection module 180A, and at a second input node N_IN2And a capacitor C of the inverter_DCAnd a second disconnection module 180B is connected between the opposite ends thereof. Wherein the first circuit breaking module 180A comprises a switch S_D1And switch S_D2And a resistance R_D1Is provided with a switch S_D2And a resistance R_D1Both are connected in series, then they are connected with another switch S_D1Parallel connection, corresponding to switch S_D1Directly connected to the first input node N_IN1And a capacitor C_DCBetween the first ends of the first and second switches S connected in series_D2And a resistance R_D1Is also connected to the first input node N_IN1And a capacitor C_DCBetween the first ends of the first and second ends.According to the same principle, the second breaking module 180B comprises a switch S_D3And switch S_D4And a resistance R_D2Is provided with a switch S_D4And a resistance R_D2Both are connected in series, then they are connected with another switch S_D3Parallel connection, corresponding to switch S_D3Directly connected to the second input node N_IN2And a capacitor C_DCBetween the second terminals of the first and second switches S connected in series_D4And a resistance R_D2Is also connected to the second input node N_IN2And a capacitor C_DCBetween the second ends. The turn-on or turn-off of the respective switches of the first and

second breaking modules

180A and 180B is driven by the second controller 140 of the inverter, and the switch S in the command unit_INSIs also driven by the second controller 140 of the inverter. Finally in the capacitor C_DCBetween the first and second terminals of the inverter, and a capacitor C for the inverter_DCIs connected with the direct current output terminal A_INVAnd a capacitor C_DCSecond end of the direct current output terminal C is connected with_INVThe conversion circuit 170 in fig. 2 is supplied with direct current, and the conversion circuit 170 inverts and converts the direct current into alternating current for grid connection.

It is possible to incorporate new PV modules into the inverter at any time, depending on the actual requirements, for example, in addition to the fact that in fig. 9 a PV module PV-Arr1 with a three-stage PV string is connected to the inverter, it is also possible to integrate a new PV module at the first input node N_IN1And a second input node N_IN2The other photovoltaic modules PV-Arr2 and PV-Arr3 or more are connected in series, and the photovoltaic module PV-Arr1, the photovoltaic module PV-Arr2 and the photovoltaic module PV-Arr3 are connected in series (or more). Although a new pv module can be connected in series with the inverter at any time, each time a new pv module is introduced, the first input node N may be potentially caused_IN1And a second input node N_IN2The high voltage at the inrush moment causes the components of the inverter to exceed the acceptable withstand voltage, so the first and

second shutdown modules

180A and 180B should be turned off first, for example, the second controller 140 drives their switches S_D1～S_D4Are all turned off and then will beThe output voltage of the photovoltaic component is connected in series to a first input node N of the inverter_IN1And a second input node N_IN2The above. Since the first and

second disconnection modules

180A and 180B are disconnected, the first input node N_IN1And a capacitor C_DCIs open, the second input node N_IN1And a capacitor C_DCSo that the second terminal of the capacitor C is open_DCIs not subjected to overpressure stress and is protected. After waiting for the output voltage of each newly introduced photovoltaic module to be incorporated into the inverter, the switch S in the first disconnection module 180A is switched on_D2And closing the switch S in the second disconnect module 180B_D4At this time, the resistance R_D1～R_D2The ballast function is realized, and the switch S in the first circuit-breaking module 180A is completely switched on subsequently_D1And closing the switch S in the second disconnect module 180B_D3Thereby completely ending the step of incorporating the new photovoltaic module into the inverter.

The photovoltaic cell/optimizer and the matched inverter as well as other electronic equipment may have faults and need to be repaired and maintained regularly, but the electric energy level of the photovoltaic cell/optimizer and the matched inverter belong to the heavy-current category and have safety threat to human bodies, and how to reliably shut down the optimizer or enter a protection mode is a pending problem. Referring to fig. 9, the command unit of the inverter includes a first input node N connected in series to the inverter_IN1And a second input node N_IN2R between_INSAnd switch S_INSThe switch S_INSIs driven by the second controller 140 of the inverter. When the inverter issues a command instructing the optimizer to shut down, the driving signal sent by the second controller 140 rapidly jumps from the first logic state (e.g., low level) to the second logic state (e.g., high level) and then returns to the first logic state, so that the switch S that will be turned on under the high level driving condition_INSIs turned on and off, the switch S_INSThe off-on-off process of (a) may be repeated multiple times. Or the driving signal sent by the first controller 140 rapidly jumps from the first logic state (e.g. high level) to the second logic state (e.g. low level) and then returns to the first logic state, so that the driving signal is switched on under the low level drivingSwitch S_INSIs turned on and off. Can be considered to be in the control switch S_INSHas a rising or falling edge moment of a nearly transient jump, switches S are closed_INSGenerating a harmonic or carrier current flowing through the command unit, which is injected into a first input node N connected to the inverter_IN1And/or connected at a second input node N_IN2Transmission line LINB on line, due to the first output node B1 of the first stage BUCK1 circuit in the optimizer_N1Coupled to a first input node N of an inverter via a transmission line LINA_IN1Second output node B3 of third stage BUCK3 circuit in optimizer_N2Coupled to a second input node N of the inverter via a transmission line LINB_IN2Therefore, the optimizer can extract the carrier signal sent by the command unit from the current information on the transmission line LINA or LINB by using various carrier detection modules (e.g., air coil sensor or high frequency transformer, band pass filter, de-encoder) for demodulation. The carrier information carrying the instructions can be converted into binary code elements according to various communication protocols specified currently for information interaction.

After the first controller 110 of the optimizer receives the carrier signal sent by the instruction unit, since the instruction tells the first controller 110 to turn off each BUCK circuit, the driving signal output by the first controller 110 can directly turn off the switches S11 to S12 in the first stage BUCK1, turn off the switches S21 to S22 in the second stage BUCK2, and turn off the switches S31 to S32 in the third stage BUCK 3. The BUCK 1-BUCK 3 circuits directly end the voltage conversion function and enter a shutdown or protection mode, namely, a first output node B1 of a first stage BUCK1_N1And a second output node B3 of the last stage BUCK3_N2No more power is delivered to the transmission line LINA or LINB. Therefore, the optimizer is safely and reliably shut down from the inverter side. In a preferred embodiment, after the first controller 110 receives the carrier signal sent by the command unit, the driving signal that should be output also turns on the bypass switch S_BYTherefore, the communication circuit can be used as a relief branch for releasing the voltage on the caps 1-3. In a preferred embodimentIn an embodiment, once the inverter intends to send a command to instruct the optimizer to shut down, the driving signal sent by the second controller 140 should first control the disconnection between the first disconnection module 180A and the second disconnection module 180B, that is, control the switch S of the first disconnection module 180A_D1And switch S_D2First turn off and control the switch S of the second disconnect module 180B_D3And switch S_D4First, the inverter is turned off, and the command unit of the inverter captures the first output node B1 of the first stage BUCK1 circuit_N1And a second output node B3 of the final stage BUCK3 circuit_N2The voltage between the two (provided by cap1, cap2 and cap3) is used as a power supply, so that a carrier signal is generated to send a shutdown command, and the capacitor C of the inverter_DCAnd the instruction unit is open-circuited.

The above discusses the mechanism of shutting down the optimizer by communication at the inverter side, and the optimizer in shutdown state may also be started at the inverter side. First, the driving signal sent by the second controller 140 should first control the first breaker module 180A and the second breaker module 180B to be connected to form a circuit, that is, control the switch S of the first breaker module 180A_D1And switch S_D2First on, and also controls the switch S of the second disconnection module 180B_D3And switch S_D4First, the first input node N of the inverter is connected_IN1A first output node B1 coupled to a first stage BUCK1 via a transmission line LINA_N1Second input node N of the inverter_IN2Coupled to a second output node B3 of the last stage BUCK3 via a transmission line LINB_N2At this time, the first output node B1 of the first stage BUCK1 circuit in the optimizer_N1And a second output node B3 of the final stage third stage BUCK3 circuit_N2The capacitors (cap1, cap2 and cap3) between receive the capacitor C of the inverter_DCThe charge transferred, note that the switch S33 (or S13 or S23 in FIGS. 5-6) may be on, meaning that the capacitor C is_DCThe capacitors (cap1, cap2, and cap3) are charged and the first controller 110 may be directly powered by the photovoltaic cells and when the first controller 110 detects the first output node B1_N1And a second output node B3_N2BetweenAfter the voltage of the first stage BUCK1 is increased, a start command can be issued, that is, the driving signal issued by the first controller 110 starts to switch on/off the switches S11-S12 in the first stage BUCK1, switch on/off the switches S21-S22 in the second stage BUCK2, and switch on/off the switches S31-S32 in the third stage BUCK3, so that the BUCK 1-BUCK 3 circuits start to enter a working state, and then the start-up procedure is completed. The startup detection process may be selected from a variety of options, and the startup command may be considered to be received as long as the first controller 110 detects that the optimizer is connected to the electric power transmitted from the inverter by the transmission lines LINA to LINB.

Referring to fig. 10, slightly different from fig. 9, the optimizer in fig. 9 can extract the carrier signal sent by the command unit from the current information on the transmission line LINA or LINB by using various carrier detection modules (e.g., air-core coil sensor or high-frequency transformer, band-pass filter, de-encoder) for demodulation, but the first output node B1 of the first stage BUCK1 circuit in the embodiment of fig. 10_N1And a first input node N of the inverter_IN1A shunt 121 or the second output node B3 of the last stage BUCK3 circuit can be connected between the two_N2And a second input node N of the inverter_IN2A shunt 121 is connected between the two terminals, and the shunt 121 can detect the current change on the voltage transmission lines LINA to LINB, so that the shunt 121 can replace the original coil sensor or high-frequency transformer and other elements as a detection module. For example, the first controller 110 may detect the first output node B1 through the shunt 121_N1And a second output node B3_N2Thereby starting to start or close the BUCK 1-BUCK 3 circuits to complete the on/off program.

With reference to fig. 11, in view of the explanation that the above summary of the present application is almost entirely directed to power optimization for multi-stage BUCK circuits and multi-stage photovoltaic cell strings, to avoid the reader from generating a misunderstanding that the summary of the present application seems to be unable to optimize for single-stage BUCK circuits and single-stage photovoltaic cell strings, refer to the scheme of fig. 11. A first input terminal of the first stage BUCK1 circuit is coupled to the positive terminal A1 of the battery string CELL-ST1, and a first input terminal of the first stage BUCK1 circuitA second input terminal coupled to the negative terminal C1 of the battery string CELL-ST1, a first stage BUCK1 circuit for generating a voltage source in response to the battery string CELL-ST1, and a first stage BUCK1 for converting the voltage source to a first output node B1_N1And a second output node B1_N2The output voltage and/or the output current. In addition, power is supplied at a first output node B1 which is in circuit with the first stage BUCK1_N1A voltage transmission line LINA connected with the first stage BUCK1 circuit and a second output node B1_N2The transmission takes place on a voltage transmission line LINB connected thereto, where the transmitted power is the photovoltaic supply voltage generated by the CELL string CELL-ST 1. Capacitor C of inverter_DCAre coupled to the pair of voltage transmission lines LINA-LINB and receive the electrical energy transmitted by them. Wherein the first input node N of the inverter_IN1Coupled to a first output node B1 of the first stage BUCK1 circuit via a transmission line LINA_N1And a second input node N of the inverter_IN2A second output node B1 coupled to the first stage BUCK1 via a transmission line LINB_N2. In addition, the first output node B1 of the first stage BUCK1 circuit_N1And a second output node B1 of the first stage BUCK1_N2A communication circuit is connected in series between the two, and the communication circuit comprises a shunt capacitor C connected in parallel_BYAnd a shunt resistor R_BYAnd a switching device S_BYWherein a capacitor C is bypassed_BYAnd a shunt resistor R_BYFirst connected in parallel and then connected with the switching device S_BYConnected in series at a first output node B1_N1And a second output node B1_N2In the meantime. The mechanism of the single-stage BUCK circuit for performing power conversion on the voltage output by the single-stage photovoltaic cell is not greatly different from the mechanism of the multi-stage BUCK circuit for performing power conversion on the voltage output by the multi-stage photovoltaic cell, the mechanism and the mechanism are only slightly different in topological structure, and only in a multi-stage scheme, the inverter is used for converting the first output node B1 of the first-stage BUCK1 circuit of the power optimizer_N1And a second output node B3 of the last stage BUCK3 circuit_N2While the dc power output in between is converted to ac power, in a single stage scheme, the inverter converts the first output node B1 of the first stage BUCK1 circuit of the power optimizer_N1And a second input of the first stage BUCK1 circuitEgress node B1_N2The dc power output therebetween is converted to ac power, and thus the various embodiments and features discussed above with respect to fig. 1-10 are equally applicable to fig. 11.

Referring to fig. 12, the photovoltaic power generation system includes multi-stage power optimizers OPT1, OPT2, … … OPT, where the natural number M is greater than 1. In the multi-stage BUCK 1-BUCK 3 circuit of each stage of power optimizer (such as OPT1), the first output node B1 of the first stage BUCK1 circuit_N1Defined as the first equivalent output terminal OUT1 of the power optimizer OPT1 of this stage and the second output node B3 of the last stage BUCK3 circuit of the end_N2Defined as the second equivalent output end OUT2 of the power optimizer OPT1 of this stage, when the power optimizers OPT1, OPT2 and … … OPT are connected in series in sequence, the first equivalent output end OUT1 of any subsequent stage (e.g., OPT2) of the power optimizers (OPT1, OPT2 and … … OPT) of the multiple stages is connected to the second equivalent output end OUT2 of the previous stage (e.g., OPT1) adjacent to the subsequent stage, according to the rule, all the power optimizers OPT1, OPT2 and … … OPT are connected in series, so that a total output voltage can be formed between the first equivalent output end OUT1 of the first stage power optimizer OPT1 of the multiple stages and the second equivalent output end OUT2 of the last stage power optimizer OPT and transmitted to the inverter as a dc power source. In fig. 12, the multi-stage power optimizers OPT1, OPT2, … … OPT are shown as examples of dc power supplies, and the first equivalent output OUT1 of the first stage power optimizer OPT1 (i.e. the positive terminal of the series of multi-stage optimizers for connection to the external inverter circuit) is coupled to the first input node N of the inverter via a transmission line LINA_IN1The second equivalent output OUT2 of the last power optimizer stage OPTM (i.e. the negative terminal of the cascade of multistage optimizers for connection to an external inverter circuit) is coupled by a transmission line LINB to the second input node N of the inverter_IN2。

Referring to fig. 13, unlike the above embodiments, the circuit configuration of the communication circuit and/or the instruction unit is slightly modified from that described above. In the communication circuit of fig. 13, first, power is suppliedContainer C_BYAnd a first resistor R_BYIn parallel, e.g. capacitor C_BYAre connected in parallel with a first resistor R_BYAnd a capacitance C_BYAnd a first output node B1 of the first stage BUCK1 circuit_N1A second additional resistor R is connected between the two (or first equivalent output ends)_BY1And the capacitor C_BYAnd a second output node B3 of the last stage BUCK circuit (in this case, the third stage BUCK3 circuit) at the end_N1(or second equivalent output) between which is connected a switch S_BY. In fact the capacitance C_BYAnd a second resistor R_BY1And a switch S_BYThe positions of any two of the three can be changed arbitrarily as long as they are connected in series.

Further alternative topologies of communication circuits may not adopt the scheme of fig. 13 but may achieve the same functionality. For example, by applying a second resistor R_BY1And switch S_BYThe position of (2) is exchanged: i.e. the capacitance C_BYAnd a first output node B1 of the first stage BUCK1 circuit_N1Is connected with a switch S_BYCapacitor C_BYAnd a second output node B3 of the last stage BUCK circuit_N1A second resistor R is connected between the two_BY1Then, again, at the capacitor C_BYIs connected with a capacitor C between one end and the opposite end_BYFirst resistors R connected in parallel_BY(this scheme is not shown in the figure).

Or in the communication circuit: capacitor C_BYAnd directly with the first output node B1 of the first stage BUCK1 circuit_N1Connected to a capacitor C_BYAnd a second output node B3 of the last stage BUCK circuit_N1A switch S connected in series between_BYAnd a second resistor R_BY1At this time, the switches S are connected in series_BYAnd a second resistor R_BY1The positions of the two can be reversed. Then, it is applied to the capacitor C_BYIs connected with a capacitor C between one end and the opposite end_BYFirst resistors R connected in parallel_BY(this scheme is not shown in the figure).

Or in the communication circuit: capacitor C_BYAnd a second output node B3 of the last stage BUCK circuit_N1Directly connected, capacitor C_BYAnd a first output node B1 of the first stage BUCK1 circuit_N1A switch S connected in series between_BYAnd a second resistor R_BY1At this time, the switches S are connected in series_BYAnd a second resistor R_BY1The positions of the two can be reversed. Then, it is applied to the capacitor C_BYIs connected with a capacitor C between one end and the opposite end_BYFirst resistors R connected in parallel_BY(this scheme is not shown in the figure).

Referring to FIG. 13, in the command unit circuit, first, a first resistor R is first applied_INSAnd a capacitor C_INSIn parallel, e.g. first resistor R_INSAre connected in parallel with a capacitor C_INSAnd a first resistance R_INSAnd a first input node N of the inverter_IN1Another second resistor R is connected between the two_INS1The first resistor R_INSAnd a second input node N of the inverter_IN2Between which a switch S is connected_INS. As long as the first resistor R is actually used_INSAnd a second resistor R_INS1And a switch S_INSThe three are connected in series, and the positions of any two of the three can be changed arbitrarily.

Further alternative topologies for instruction units may not adopt the scheme of fig. 13 but may achieve the same functionality. For example, by applying a second resistor R_INS1And switch S_INSThe position of (2) is exchanged: i.e. the first resistor R_INSAnd a first input node N of the inverter_IN1Is connected with a switch S_INSFirst resistance R_INSAnd a second input node N of the inverter_IN2A second resistor R is connected between the two_INS1Then again through the first resistor R_INSIs connected with a first resistor R between one end and the opposite end_INSParallel capacitors C_INS(this scheme is not shown in the figure).

Or in the instruction unit circuitry: a first resistor R_INSIs at one end directly andfirst input node N of inverter_IN1Connected to a first resistor R_INSAnd a second input node N of the inverter_IN2Is connected with a switch S in series_INSAnd a second resistor R_INS1At this time, the switches S are connected in series_INSAnd a second resistor R_INS1The positions of the two can be reversed. Then the first resistor R_INSIs connected with a first resistor R between one end and the opposite end_INSParallel capacitors C_INS(this scheme is not shown in the figure).

Or in the instruction unit circuitry: a first resistor R_INSAnd a second input node N of the inverter_IN2Directly connected, first resistor R_INSAnd a first input node N of the inverter_IN1A switch S connected in series between_INSAnd a second resistor R_INS1At this time, the switches S are connected in series_INSAnd a second resistor R_INS1The positions of the two can be reversed. Then the first resistor R_INSIs connected with a first resistor R between one end and the opposite end_INSParallel capacitors C_INS(this scheme is not shown in the figure).

While the present invention has been described with reference to the preferred embodiments and illustrative embodiments, it is to be understood that the invention as described is not limited to the disclosed embodiments. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above description. Therefore, the appended claims should be construed to cover all such variations and modifications as fall within the true spirit and scope of the invention. Any and all equivalent ranges and contents within the scope of the claims should be considered to be within the intent and scope of the present invention.

Claims

1. A photovoltaic power generation system with a power optimizer is characterized by comprising a multi-stage photovoltaic cell string and a multi-stage power optimizer, wherein each stage of power optimizer comprises a multi-stage BUCK circuit;

wherein, in each stage of the power optimizer:

the first input end and the second input end of any stage of BUCK circuit are respectively coupled to the positive terminal and the negative terminal of the corresponding stage of photovoltaic cell string;

an output capacitor of the BUCK circuit of any stage is connected between a first output node and a second output node of the BUCK circuit of any stage;

setting a first output node of any back-stage BUCK circuit in the multi-stage BUCK circuits to be connected with a second output node of a front-stage BUCK circuit adjacent to the first output node;

therefore, in the multi-stage BUCK circuits of each stage of power optimizer, a first output node of a first stage BUCK circuit is defined as a first equivalent output end of the stage of power optimizer, and a second output node of a last stage BUCK circuit at the tail end is defined as a second equivalent output end of the stage of power optimizer;

the multiple stages of power optimizers are connected in series, and a first equivalent output end of any next-stage power optimizer in the multiple stages of power optimizers is connected with a second equivalent output end of a previous-stage power optimizer adjacent to the first equivalent output end;

thereby forming a total output voltage of the plurality of stages of the power optimizer between a first equivalent output terminal of a first stage of the power optimizer and a second equivalent output terminal of a last stage of the power optimizer;

the power optimizer at any stage further comprises a communication circuit, which is used for forming a communication carrier on a transmission line connected with the first equivalent output end of each power optimizer and/or a transmission line connected with the second equivalent output end, so as to realize that the power optimizer at each stage sends communication information outwards;

the communication circuit comprises a first switch and a bypass capacitor which are connected in series, wherein the first switch and the bypass capacitor are connected between a first equivalent output end and a second equivalent output end of each stage of power optimizer in series; or

The communication circuit comprises a resistor, a first switch and a bypass capacitor which are connected in series, wherein the resistor, the first switch and the bypass capacitor are connected between a first equivalent output end and a second equivalent output end of each stage of power optimizer in series, and a bypass resistor is connected at two ends of the bypass capacitor in parallel;

each stage of the power optimizer further comprises a first controller;

the power optimizer of each stage also comprises a second switch which can be arranged in any one or more stages of BUCK circuits; in any stage of BUCK circuit with a second switch, an output capacitor and the second switch are connected in series between a first output node and a second output node of the BUCK circuit;

the second switch is used for being controlled to be in an off state by the first controller at the stage that each power optimizer sends communication information, the second switch is used for disconnecting the branch circuit formed by connecting the first equivalent output end and the second equivalent output end of the power optimizer at the stage by the output capacitors in series, and the second switch is controlled to be in an on state by the first controller after the power optimizer finishes sending the communication information.

2. The photovoltaic power generation system with the power optimizer of claim 1, wherein the first switch is configured to be switched between an off state and an on state under control of the first controller during a phase in which the power optimizer of each stage transmits the communication information, so as to generate a carrier current flowing through the communication circuit at a time when the first switch is turned on, and the carrier current is injected into the transmission line connected to the first equivalent output terminal and/or the transmission line connected to the second equivalent output terminal to form a communication carrier.

3. The photovoltaic power generation system with the power optimizer of claim 1, further comprising an inverter for converting the dc power output by the multiple stages of the power optimizer to ac power.

4. The photovoltaic power generation system with power optimizer of claim 3 wherein the inverter further comprises a detection module for detecting and extracting the communication carrier from the current flowing through the transmission line and a second controller of the inverter receives the communication from the detection module to enable communication between the power optimizer and the inverter.

5. The photovoltaic power generation system with the power optimizer of claim 4, wherein the detection module is any one of a high frequency sensor, a band pass filter, a codec, and a shunt.

6. The photovoltaic power generation system with power optimizer of claim 1, further comprising an inverter for converting the dc power output by the power optimizer in multiple stages to ac power, the inverter having an energy storage capacitor and first and second trip modules, and further comprising:

a first input node coupled to a first equivalent output of a first one of said power optimizers of said plurality of stages, a second input node coupled to a second equivalent output of a last one of said power optimizers of said plurality of stages;

wherein the first disconnection module is connected between the first input node and the first terminal of the energy storage capacitor, the second disconnection module is connected between the second input node and the second terminal of the energy storage capacitor, and the switching on or off of the first and second disconnection modules is controlled by a second controller of the inverter.

7. The photovoltaic power generation system with the power optimizer of claim 6, wherein the inverter further comprises a command unit for sending a communication carrier on a transmission line connected to the first input node of the inverter and/or on a transmission line connected to the second input node of the inverter to enable the inverter to send command information out.

8. The photovoltaic power generation system with the power optimizer of claim 7, wherein:

the command unit has a third switch and a first resistor connected in series between first and second input nodes of the inverter; or

The command unit includes a third switch and a first resistor and a second resistor connected in series between first and second input nodes of the inverter.

9. The photovoltaic power generation system with the power optimizer of claim 8, wherein a capacitor is connected in parallel across the first resistor.

10. The photovoltaic power generation system with the power optimizer of claim 8, wherein the third switch is configured to be switched between an off state and an on state under control of the second controller in a phase in which the inverter sends out the command information, so that the carrier current flowing through the command unit is generated at a time when the third switch is turned on, and injected into the transmission line connected to the first input node of the inverter and/or the transmission line connected to the second input node of the inverter to be used for generating the communication carrier.

11. The pv power generation system according to claim 10, wherein, in the step of sending the command information to the power optimizer of any stage, the power optimizer of any stage detects and extracts the communication carrier from the current flowing through the transmission line through a detection module, and the first controller of the power optimizer of any stage receives the command information from the detection module.

12. The photovoltaic power generation system with power optimizer of claim 11, wherein the detection module is any one of a high frequency sensor, a band pass filter, a codec, and a shunt.

13. The pv power generation system according to claim 11, wherein the command information includes a shutdown command, and the first and second disconnection modules are further configured to be controlled by the second controller to be in a shutdown state when the inverter sends the shutdown command information to any of the power optimizers, so as to disconnect the connection between the energy storage capacitor and the power optimizers.

14. The system of claim 13, wherein the first switch is further configured to be turned on by the first controller after the power optimizer enters the shutdown or sleep state, so as to convert the communication circuit into a bleeding branch of the residual charge on each of the cascaded output capacitors between the first and second equivalent outputs of each stage of the power optimizer;

and/or the third switch is also used for being controlled to be in a connection state by the second controller after the power optimizer enters a shutdown state or a dormant state, and is used for converting the instruction unit into a discharge branch circuit of residual electric quantity on each series-connected output capacitor between the first equivalent output end of the first-stage power optimizer and the second equivalent output end of the last-stage power optimizer in the multi-stage power optimizer.

15. The photovoltaic power generation system with the power optimizer of claim 6, wherein the first and second circuit breaking modules are further configured to be controlled by a second controller to be in a switch-on state when the inverter controls the multistage power optimizer to start up, so as to use an energy storage capacitor as a voltage source of the multistage power optimizer; and

the first controller of each stage of the power optimizer is used for detecting whether the power optimizer of the stage of the power optimizer receives the voltage and/or the current transmitted by the inverter or not, and if so, the first controller of each stage of the power optimizer controls the plurality of sets of BUCK circuits to start to perform the voltage conversion function.

16. The photovoltaic power generation system with the power optimizer of claim 1, wherein the power optimizer at any stage further comprises a detection module for extracting communication carriers emitted by other power optimizers from the current flowing on the transmission line of the power optimizers connected in series so as to realize mutual communication among different power optimizers.

17. The photovoltaic power generation system with the power optimizer is characterized by comprising an inverter, a multi-stage photovoltaic cell string and a multi-stage power optimizer, wherein each stage of the power optimizer comprises a multi-stage BUCK circuit;

in each stage of the power optimizer: any one stage of BUCK circuit performs voltage reduction conversion on the voltage generated by the corresponding one stage of photovoltaic cell string and outputs the voltage on one output capacitor, and the output capacitors of the multiple stages of BUCK circuits in each stage of power optimizer are connected in series, so that the voltage superposed on the output capacitors connected in series provides the output voltage of each stage of power optimizer;

the multiple stages of the power optimizers are connected in series with each other, so that the respective output voltages of all the power optimizers are superposed together to form the total output voltage of the multiple stages of the power optimizers, and the total output voltage belonging to direct current is converted into alternating current by the inverter and is output;

each stage of BUCK circuit is connected in series, and then the output capacitors connected in series are connected with the communication circuit in parallel;

in each stage of the power optimizer:

the communication circuit comprises a first switch and a bypass capacitor which are connected in series, the first switch and the bypass capacitor are connected in series and then connected in parallel with output capacitors which are connected in series in each stage of BUCK circuit, and a bypass resistor is connected in parallel at two ends of the bypass capacitor; or

The communication circuit comprises a resistor, a first switch and a bypass capacitor which are connected in series, the resistor, the first switch and the bypass capacitor are connected in series and then connected in parallel with output capacitors which are connected in series in each stage of BUCK circuit, and a bypass resistor is connected in parallel at two ends of the bypass capacitor;

the power optimizer at each stage also comprises a second switch arranged in any one stage or multi-stage BUCK circuit of the power optimizer, and an output capacitor of the one-stage BUCK circuit with the second switch is correspondingly connected with one second switch in series; therefore, any one-stage BUCK circuit with the second switch can step down and convert the voltage generated by the corresponding one-stage photovoltaic cell string and output the voltage to one output capacitor of the one-stage BUCK circuit connected with the second switch in series;

the second switch is used for being controlled to be in an off state by the first controller at the stage that each power optimizer sends the communication information, and the second switch is controlled to be in an on state by the first controller after the power optimizer finishes sending the communication information.

18. The photovoltaic power generation system with the power optimizer of claim 17, wherein the inverter further comprises a command unit connected between a set of first and second input nodes of the inverter for receiving the total output voltage;

the instruction unit comprises a third switch and a first resistor which are connected in series, or the instruction unit comprises a third switch and a first resistor and a second resistor which are connected in series.

19. The photovoltaic power generation system with power optimizer of claim 18 wherein a capacitor is connected in parallel across the first resistor.