CN110176782B - A change of current and network-connected device and system for being incorporated into power networks photovoltaic power generation station - Google Patents
A change of current and network-connected device and system for being incorporated into power networks photovoltaic power generation station Download PDFInfo
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Abstract
The invention relates to the technical field of solar power generation control, in particular to a current conversion grid-connected device for a grid-connected photovoltaic power station, which comprises a current conversion unit, wherein the current conversion unit comprises an overvoltage protector, a capacitor, an inductor and a bridge circuit, the positive electrode and the negative electrode of the input end of the current conversion unit are respectively grounded through the overvoltage protector, and the capacitor is connected in series between the positive electrode and the negative electrode of the input end of the current conversion unit; the positive pole and the negative pole of the input end of the current transformation unit form the positive pole and the negative pole of the input end of the bridge circuit, and the output end of the bridge circuit is connected in series through an inductor; a system comprised of the apparatus is also disclosed. The device simplifies the original system, reduces the construction cost, improves the working reliability, can realize many additional functions such as power flow control and electric energy quality control on the basis of realizing the original basic function, enables the power grid to obtain higher stability, realizes a more flexible power transmission mode, and provides a more effective control means for the intelligent power grid.
Description
Technical Field
The invention relates to the technical field of solar power generation control, in particular to a current conversion grid-connected device and system for a grid-connected photovoltaic power station.
Background
High-efficiency, clean and renewable energy power generation technologies represented by wind energy, solar energy and the like are highly valued by countries all over the world, and how to safely connect the power supplies into a system needs to solve the problems of high-power, high-efficiency and high-quality energy conversion and control. The solar photovoltaic power generation has important significance for optimizing an energy structure, promoting energy conservation and emission reduction and realizing economic sustainable development. The domestic photovoltaic installed capacity reaches 174.63GW by the end of 2018. Undoubtedly, the improvement of the safe and economic operation level of the photovoltaic power station has great practical significance. As shown in fig. 3, an inverter must be configured in a conventional large and medium-sized photovoltaic power station to convert direct current generated by a solar photovoltaic cell into alternating current, a transformer and a reactive power compensation device required by a power grid need to be configured for grid-connected remote transmission, and the structure needs to be configured with a plurality of parts, and is complex and complicated, high in construction cost and unreliable in operation.
Disclosure of Invention
The invention aims to provide a conversion grid-connected device for a grid-connected photovoltaic power station, which can realize high-efficiency and high-quality energy conversion and control.
In order to realize the purpose, the invention adopts the technical scheme that: a current conversion grid-connected device for grid-connected photovoltaic power stations comprises N current conversion units, wherein each current conversion unit comprises an overvoltage protector Ri1、Ri2And a capacitor Ci1、Ci2、Ci3、Ci4And an inductance Li1、Li2And N bridge circuits, where the subscript i ∈ [1, N ]](ii) a The positive and negative poles of the input end of the ith converter unit pass through an overvoltage protector R respectivelyi1、Ri2Ground, capacitor Ci1、Ci2The current transformer is connected between the positive electrode and the negative electrode of the input end of the ith current transforming unit in series; the positive and negative poles of the input end of the ith current converting unit form the positive and negative poles of the input end of the ith bridge circuit, and the positive pole of the output end of the 1 st bridge circuit passes through an inductor L11The positive electrode of the output end of the device is connected, and the negative electrode of the output end of the Nth bridge circuit passes through an inductor LN2An inductor L is connected in series between the negative electrode of the output end of the device, the negative electrode of the output end of the ith bridge circuit and the positive electrode of the output end of the (i + 1) th bridge circuiti2And L(i+1)1(ii) a Capacitor C13、C14、…、CN3、CN4The anode and the cathode are connected in series between the output end of the device; capacitor Ci1、Ci2And a capacitance Ci3、Ci4Are short-circuited by a lead.
Compared with the prior art, the invention has the following technical effects: the device can realize inversion and phase modulation of direct current to alternating current and frequency conversion and voltage transformation of an alternating current system, namely, the high-power electronic device can run in four quadrants of a PQ plane, and further, the high-efficiency power grid power conversion and the power quality control can be realized; the device simplifies the original system, reduces the engineering cost and improves the working reliability, and can realize many additional functions such as power flow control, power quality control and the like on the basis of realizing basic functions such as electric energy direct current/alternating current form conversion, voltage grade conversion, electric isolation, energy transfer, reactive compensation and the like of the conventional power inverter, power transformer and reactive compensation device, so that the power grid obtains higher stability, a more flexible power transmission mode is realized, and a more effective control means is provided for the intelligent power grid.
The invention also aims to provide a conversion grid-connected system for a grid-connected photovoltaic power station, which ensures safe, stable and economic operation of a power grid.
In order to realize the purpose, the invention adopts the technical scheme that: a current conversion grid-connected system for a grid-connected photovoltaic power station comprises a photovoltaic component, a current transformer and a control unit, wherein the current transformer comprises N current transformation units, and each current transformation unit comprises an overvoltage protector Ri1、Ri2And a capacitor Ci1、Ci2、Ci3、Ci4And an inductance Li1、Li2And N bridge circuits, where the subscript i ∈ [1, N ]](ii) a The positive and negative poles of the input end of the ith converter unit pass through an overvoltage protector R respectivelyi1、Ri2Ground, capacitor Ci1、Ci2The current transformer is connected between the positive electrode and the negative electrode of the input end of the ith current transforming unit in series; the positive and negative poles of the input end of the ith current converting unit form the positive and negative poles of the input end of the ith bridge circuit, and the positive pole of the output end of the 1 st bridge circuit passes through an inductor L11The anode of the power grid is connected, and the cathode of the output end of the Nth bridge circuit passes through an inductor LN2An inductor L is connected in series between the negative electrode of the output end of the ith bridge circuit and the positive electrode of the output end of the (i + 1) th bridge circuiti2And L(i+1)1(ii) a Capacitor C13、C14、…、CN3、CN4The current transformer is connected in series between the positive electrode and the negative electrode of the output end of the current transformer; capacitor Ci1、Ci2And a capacitance Ci3、Ci4Are short-circuited through a lead; the ith photovoltaic module is connected with the positive electrode and the negative electrode of the input end of the ith converter unit, and the control unit acquires and processes the current and the voltage of the input end of the converter and the current and the voltage of the output end of the converter and outputs a PWM control signal to the converter.
Compared with the prior art, the invention has the following technical effects: the system greatly simplifies the traditional inversion grid-connected system of the photovoltaic power station at present, and is beneficial to the safe, stable and economic operation of a power grid; the one-time investment of the photovoltaic power station with high manufacturing cost is reduced, the operation loss of the power station is reduced, and the popularization of the technology has great social benefit and considerable economic benefit.
Drawings
Fig. 1 is a circuit diagram of a grid-connected device in the present invention;
FIG. 2 is a schematic block diagram of a grid tie system of the present invention;
fig. 3 is a schematic block diagram of a grid-connected system in the prior art.
Detailed Description
The present invention will be described in further detail with reference to fig. 1 to 2.
Referring to fig. 1, a current conversion grid-connected device for grid-connected photovoltaic power station comprises N current conversion units, wherein each current conversion unit comprises an overvoltage protector Ri1、Ri2And a capacitor Ci1、Ci2、Ci3、Ci4And an inductance Li1、Li2And N bridge circuits, where the subscript i ∈ [1, N ]](ii) a The positive and negative poles of the input end of the ith converter unit pass through an overvoltage protector R respectivelyi1、Ri2Ground, capacitor Ci1、Ci2The current transformer is connected between the positive electrode and the negative electrode of the input end of the ith current transforming unit in series; the positive and negative poles of the input end of the ith current converting unit form the positive and negative poles of the input end of the ith bridge circuit, and the positive pole of the output end of the 1 st bridge circuit passes through an inductor L11The positive electrode of the output end of the device is connected, and the negative electrode of the output end of the Nth bridge circuit passes through an inductor LN2An inductor L is connected in series between the negative electrode of the output end of the device, the negative electrode of the output end of the ith bridge circuit and the positive electrode of the output end of the (i + 1) th bridge circuiti2And L(i+1)1(ii) a Capacitor C13、C14、…、CN3、CN4The anode and the cathode are connected in series between the output end of the device; capacitor Ci1、Ci2And a capacitance Ci3、Ci4Are short-circuited by a lead. The device can realize inversion and phase modulation of direct current to alternating current and frequency conversion and voltage transformation of an alternating current system, namely, the high-power electronic device can run in four quadrants of a PQ plane, and further, the high-efficiency power grid power conversion and the power quality control can be realized; the device does not need to be provided with a traditional inverter, a transformer, a reactive power compensation device (SVG) and the like, simplifies the original system, reduces the engineering cost, improves the working reliability, and realizes the inverse of the conventional powerOn the basis of basic functions of electric energy direct current/alternating current form conversion, voltage grade conversion, electrical isolation, energy transfer, reactive compensation and the like of the transformer, the power transformer and the reactive compensation device, a plurality of additional functions such as power flow control, electric energy quality control and the like can be realized, so that the power grid obtains higher stability, a more flexible power transmission mode is realized, and a more effective control means is provided for the smart power grid.
The converter adopting PWM control has the advantages that: firstly, the variation range of the output voltage can be enlarged; secondly, the output voltage and current can be controlled more accurately, and voltage waveforms with high quality and low harmonic content are output; thirdly, the voltage and current stress of the components can be reduced, and low-voltage power switches and capacitor devices with low cost are used; fourthly, the output direct current side can easily realize the power supply of the independent direct current unit.
Specifically, the bridge circuit includes a first IGBT module, a second IGBT module, a third IGBT module, and a fourth IGBT module, collectors of the first IGBT module and the second IGBT module are connected to the positive electrode of the input end of the current transforming unit, emitters of the third IGBT module and the fourth IGBT module are connected to the negative electrode of the input end of the current transforming unit, and the emitter of the first IGBT module, the collector of the third IGBT module, and the inductor Li1The emitter of the second IGBT module is connected with the collector of the fourth IGBT module and the inductor Li2And the gates of the four IGBT modules receive the PWM control signal. The four IGBT modules are respectively composed of an insulated gate bipolar transistor and a diode, the diode is connected between a collector electrode and an emitter electrode of the insulated gate bipolar transistor in series, and the anode electrode of the diode is connected with the emitter electrode of the insulated gate bipolar transistor. The high-power electronic device is an insulated gate bipolar transistor IGBT full-control device and is very practical.
Referring to fig. 1 and 2, a commutation grid-connected system for a grid-connected photovoltaic power station includes a photovoltaic module, a converter and a control unit, where the converter includes a plurality of commutation units, where the number of the commutation units is generally 3N, and one phase of the commutation grid-connected system is described in detail below: the current transformation unit comprises an overvoltage protector Ri1、Ri2And a capacitor Ci1、Ci2、Ci3、Ci4And an inductance Li1、Li2And N bridge circuits, where the subscript i ∈ [1, N ]](ii) a The positive and negative poles of the input end of the ith converter unit pass through an overvoltage protector R respectivelyi1、Ri2Ground, capacitor Ci1、Ci2The current transformer is connected between the positive electrode and the negative electrode of the input end of the ith current transforming unit in series; the positive and negative poles of the input end of the ith current converting unit form the positive and negative poles of the input end of the ith bridge circuit, and the positive pole of the output end of the 1 st bridge circuit passes through an inductor L11Connecting phase lines, wherein the phase lines can be any one of the phases A, B or C, and the A, B, C three phases are arranged in the above connection mode, in other words: that is, the positive and negative terminals of the output terminal in fig. 2 are L1 and N, respectively, and then 2 sets of the same circuits are continuously provided according to the circuit of fig. 2, and the positive and negative terminals of the output terminals of the other 2 sets of circuits are L2 and N and L3 and N, respectively. The negative electrode of the output end of the Nth bridge circuit passes through an inductor LN2An inductor L is connected in series between the negative electrode of the output end of the ith bridge circuit and the positive electrode of the output end of the (i + 1) th bridge circuiti2And L(i+1)1(ii) a Capacitor C13、C14、…、CN3、CN4The current transformer is connected in series between the positive electrode and the negative electrode of the output end of the current transformer; capacitor Ci1、Ci2And a capacitance Ci3、Ci4Are short-circuited through a lead; the ith photovoltaic module is connected with the positive electrode and the negative electrode of the input end of the ith converter unit, and the control unit acquires and processes the current and the voltage of the input end of the converter and the current and the voltage of the output end of the converter and outputs a PWM control signal to the converter. The system greatly simplifies the traditional inversion grid-connected system of the photovoltaic power station at present, and is beneficial to the safe, stable and economic operation of a power grid; the one-time investment of the photovoltaic power station with high manufacturing cost is reduced, the operation loss of the power station is reduced, and the popularization of the technology has great social benefit and considerable economic benefit. The specific structure of the bridge circuit can refer to the description in the previous section, and is not described herein again.
The converter for converting direct current into alternating current can realize four-quadrant operation under PQ coordinates in principle, can provide capacitive reactive power for a power grid, can absorb inductive reactive power of the power grid, and has active power which is reversible in two directions. In detail, the control unit may adjust the flow direction of the reactive power and the active power according to the following steps: (S1) when the reactive power flow direction needs to be adjusted, the control unit outputs a PWM control signal to control the power angle between the output current of the converter and the voltage of the power grid; (S2) when the flowing direction of the active power needs to be adjusted, the control unit outputs a PWM control signal to control the amplitude of the converter output current. Namely, the control of the active power and the reactive power output by the converter can be realized by controlling the output current vector of the converter. This is easily achieved in PWM circuits, for example, where the control unit controls the converter using a direct power control strategy based on voltage orientation (V-DPC) or a direct power control strategy based on virtual flux orientation (VF-DPC) according to instantaneous power theory. After the converter is connected to the power grid, the power supply requirement of constant voltage, constant reactive power or constant power factors can be met, and the power supply quality is improved.
Preferably, the power supply system comprises an energy storage unit, alternating current on a power grid is converted into direct current through a converter and then directly supplies power to the control unit or charges the energy storage unit, and the energy storage unit provides a standby power supply for the control unit. The working power supply of the control unit is taken from a direct current bus, the control unit can be operated remotely or locally to realize the starting or the shutting of the converter, a high-voltage switch is not needed, and only an isolation switch or a safety device is needed to be arranged on the high-voltage side. The converter can realize bidirectional flow of active power, namely AC/DC conversion when necessary, so that the energy storage unit can be directly charged without being matched with a PCS unit, and the economy is improved.
Furthermore, the control unit comprises an overvoltage and overcurrent protection circuit, an under-frequency and over-frequency protection circuit and a communication circuit, the overvoltage and overcurrent protection circuit is used for providing overvoltage and overcurrent protection for the control unit, the under-frequency and over-frequency protection circuit provides under-frequency and over-frequency protection for the control unit, and the control unit is connected with the power grid dispatching center through the communication circuit to realize bidirectional data communication, so that remote four-remote (remote measurement, remote signaling, remote control and remote regulation) functions of the power grid dispatching side are realized.
Claims (4)
1. A change of current grid-connected system for being incorporated into power networks photovoltaic power generation station which characterized in that: the photovoltaic module comprises a photovoltaic module, a converter and a control unit, wherein the converter comprises a plurality of converter units, and each converter unit comprises an overvoltage protector Ri1、Ri2And a capacitor Ci1、Ci2、Ci3、Ci4And an inductance Li1、Li2And N bridge circuits, where the subscript i ∈ [1, N ]](ii) a The positive and negative poles of the input end of the ith converter unit pass through an overvoltage protector R respectivelyi1、Ri2Ground, capacitor Ci1、Ci2The current transformer is connected between the positive electrode and the negative electrode of the input end of the ith current transforming unit in series; the positive and negative poles of the input end of the ith current converting unit form the positive and negative poles of the input end of the ith bridge circuit, and the positive pole of the output end of the 1 st bridge circuit passes through an inductor L11A phase line is connected, and the negative electrode of the output end of the Nth bridge circuit passes through an inductor LN2An inductor L is connected in series between the negative electrode of the output end of the ith bridge circuit and the positive electrode of the output end of the (i + 1) th bridge circuiti2And L(i+1)1(ii) a Capacitor C13、C14、…、CN3、CN4The current transformer is connected in series between the positive electrode and the negative electrode of the output end of the current transformer; capacitor Ci1、Ci2And a capacitance Ci3、Ci4Are short-circuited through a lead; the control unit acquires and processes the current and voltage at the input end of the converter and the current and voltage at the output end of the converter and outputs a PWM control signal to the converter;
the control unit controls the converter by adopting a direct power control strategy based on voltage orientation according to an instantaneous power theory or a direct power control strategy based on virtual flux linkage orientation;
the control unit adjusts the flow direction of the reactive power and the active power according to the following steps: (S1) when the reactive power flow direction needs to be adjusted, the control unit outputs a PWM control signal to control the power angle between the output current of the converter and the voltage of the power grid; (S2) when the flowing direction of the active power needs to be adjusted, the control unit outputs a PWM control signal to control the amplitude of the output current of the converter;
the power supply system comprises an energy storage unit, alternating current on a power grid is converted into direct current through a converter and then directly supplies power to a control unit or charges the energy storage unit, and the energy storage unit provides a standby power supply for the control unit.
2. The inversion grid-connection system for grid-connected photovoltaic power plants of claim 1, characterized in that: the bridge circuit comprises a first IGBT module, a second IGBT module, a third IGBT module and a fourth IGBT module, collectors of the first IGBT module and the second IGBT module are connected with the positive electrode of the input end of the current converting unit, emitters of the third IGBT module and the fourth IGBT module are connected with the negative electrode of the input end of the current converting unit, and the emitter of the first IGBT module, the collector of the third IGBT module and the inductor L are connectedi1The emitter of the second IGBT module is connected with the collector of the fourth IGBT module and the inductor Li2And the gates of the four IGBT modules receive the PWM control signal output by the control unit.
3. The inversion grid-connection system for grid-connected photovoltaic power plants of claim 2, characterized in that: the four IGBT modules are all composed of insulated gate bipolar transistors and diodes, the diodes are connected in series between collectors and emitters of the insulated gate bipolar transistors, and anodes of the diodes are connected with the emitters of the insulated gate bipolar transistors.
4. The inversion grid-connection system for grid-connected photovoltaic power plants of claim 3, characterized in that: the control unit comprises an overvoltage and overcurrent protection circuit, an under-frequency and over-frequency protection circuit and a communication circuit, the overvoltage and overcurrent protection circuit is used for providing overvoltage and overcurrent protection for the control unit, the under-frequency and over-frequency protection circuit provides under-frequency and over-frequency protection for the control unit, and the control unit is connected with a power grid dispatching center through the communication circuit to achieve bidirectional data communication.
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| US7463500B2 (en) * | 2003-02-21 | 2008-12-09 | Xantrex Technology, Inc. | Monopolar DC to bipolar DC to AC converter |
| CN103312147A (en) * | 2012-03-17 | 2013-09-18 | 丰郅(上海)新能源科技有限公司 | Inverter common-mode interference suppression circuit |
| CN204168220U (en) * | 2014-09-16 | 2015-02-18 | 阳光电源股份有限公司 | A kind of earthing device of photovoltaic module and protection system |
| CN104638676B (en) * | 2015-02-17 | 2016-11-30 | 河海大学 | A kind of AC series photovoltaic power generation grid-connecting system and control system thereof and method |
| CN106033939A (en) * | 2015-03-13 | 2016-10-19 | 南京航空航天大学 | LCL non-isolation type grid-connected inverter system |
| CN209675953U (en) * | 2019-05-29 | 2019-11-22 | 王阳 | Change of current grid-connecting apparatus and system for grid-connected photovoltaic power generation station |
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