CN109450239B - Six-switch micro-inverter alternating-current side power coupling circuit - Google Patents
Six-switch micro-inverter alternating-current side power coupling circuit Download PDFInfo
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- 239000003990 capacitor Substances 0.000 claims abstract description 94
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
- H02M1/34—Snubber circuits
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
- H02M1/34—Snubber circuits
- H02M1/344—Active dissipative snubbers
Abstract
A six-switch micro-inverter AC side power coupling circuit is composed of six switching tubes (T1-T6), six diodes (D1-D6), two coupling capacitors (Cd 1, cd 2) and an inductor (L). According to the polarity of the output voltage of the inverter and the energy absorption/release of the coupling circuit, the power coupling circuit can be divided into four working modes, namely working mode 1: the output voltage of the inverter is positive, and the coupling circuit absorbs energy; working mode 2: the output voltage of the inverter is positive, and the coupling circuit releases energy; working mode 3: the output voltage of the inverter is negative, and the coupling circuit absorbs energy; working mode 4: the inverter output voltage is negative and the coupling circuit releases energy. The power decoupling circuit is connected in parallel to the alternating current output side of the inverter, the circuit structure of the inverter is simple, and the decoupling circuit and the inverter circuit can be independently controlled; the power coupling circuit provided by the invention realizes power balance, can realize no electrolytic capacitor and prolongs the service life of the inverter.
Description
Technical Field
The invention relates to a six-switch micro-inverter alternating-current side power coupling circuit, and belongs to the technical field of micro-inverters.
Background
The micro-inverter gradually becomes a trend of future distributed photovoltaic inverters due to the advantages of multiple power generation, easy expansion, low cost, hot plug and modularized design. However, in a distributed power generation system, the photovoltaic module generates constant input power due to MPPT control, while the power transmitted to the grid contains power pulses of twice the power frequency, and the instantaneous values of the two are inconsistent. Therefore, the traditional micro-inverter adopts electrolytic capacitors to realize the balance of the instantaneous input and output power of the inverter. Thus, the lifetime of the electrolytic capacitor is less than 1 ten thousand hours, which is a key to limit the stability and the service life of the micro-inverter, compared to the semiconductor device and the passive element having the lifetime of 5-10 ten thousand hours. Therefore, the research of the micro-inverter technology without the electrolytic capacitor becomes a preferable technical scheme for improving the performance and the service life of the micro-inverter, and is one of important research directions of a plurality of scholars.
The technology of the micro-inverter without the electrolytic capacitor is that a power electronic power coupling circuit consisting of a power switch and a passive device is adopted to replace the traditional electrolytic capacitor to realize the energy buffering function. The power coupling circuit is divided into four types of direct current input side type, DC-link middle side type, alternating current output side type and three-port decoupling type according to the different access points of the power coupling circuit.
The direct current input side power coupling technique is generally applicable to single stage grid-connected micro-inverters. Professor Shimizu, university of kyoto, japan, et al, propose a flyback grid-connected inverter with a power coupling circuit, wherein when the input power of the inverter is greater than the output power, the decoupling capacitor is charged through the primary side excitation inductance of the transformer, and when the input power of the inverter is less than the output power, the decoupling capacitor is discharged to supplement energy to the excitation inductance. The professor b.j.pierque et al, university of washington, in the united states, proposes a two-stage micro-inverter structure formed by connecting a power coupling circuit in series between a photovoltaic array and a micro-inverter, thus facilitating independent control of energy storage voltage and ripple, avoiding the use of electrolytic capacitors, and maintaining the reactive power transfer function of the micro-inverter. However, although the single-stage micro-inverter has a single-stage structure, MPPT, island detection and power coupling control of the system are complex, the boosting ratio of the system is low, the photovoltaic direct-current output voltage is high, and the coupling capacitance value is still large.
In the multistage micro-inverter, since the intermediate DC side voltage contains a relatively high voltage, a DC-link intermediate side power coupling technique is generally employed, and in this case, in order to reduce the coupling capacitance value, the DC side voltage is allowed to fluctuate relatively much. G.A.J.Amaraatunga et al, university of Cambridge, UK, propose a three-level structured micro-grid-connected photovoltaic inverter consisting of a phase-shifted full-bridge circuit, a Buck circuit and a full-bridge inverter. The phase-shifting full-bridge circuit realizes the functions of boosting and MPPT, the Buck circuit generates sine half-wave current, and the final stage circuit generates sine injection current. The topological structure synchronously controls different circuits in front of and behind the direct current bus to ensure energy conservation and stable bus voltage, thereby realizing balance of input power and output power.
The coupling technology of the alternating current side is to connect the coupling capacitor in parallel with the alternating current side, and the decoupling capacitor can be effectively reduced because the voltage is larger and is the alternating current voltage. The B.S. Wang et al of the state university of Arizona in America propose a bidirectional AC-AC frequency conversion type micro-inverter topology, a three-phase current source type converter consisting of six bidirectional switches realizes AC-side grid connection, wherein two phases are connected with a power grid, and the other phase is connected with the power grid through a coupling capacitor, so that bidirectional flow of power and energy buffering are realized, and the coupling capacitor can be greatly reduced.
For the three-port power coupling technology, one port of the three-port converter is used for realizing maximum power point tracking, the other port realizes power decoupling, and the third port realizes grid connection. The professor Hu Haibing of Nanjing aviation aerospace university and the like researches a three-port flyback type single-stage photovoltaic micro inverter with a power decoupling function, and on a traditional flyback circuit, the 3 rd port formed by a switch and a group of primary windings is added to realize power decoupling, and a power decoupling capacitor is simultaneously used as a power storage element and a leakage inductance energy absorption buffer circuit, so that the power loss can be reduced, and the efficiency is improved. A three-port flyback single-stage photovoltaic micro-inverter with an active power coupling circuit is also provided, and the design of a control system of an alternating current grid-connected port is greatly simplified by adding a power decoupling port formed by a group of negative side windings and a four-quadrant running bridge type converter. The Krein, P.T teachings of the university of illinois, usa, et al, propose an ac-connected three-port micro-inverter configuration in which a set of windings and bridge converters are added to the ac side port of the transformer to form a power coupling circuit. The three-port photovoltaic micro-inverter utilizes the transformer winding to greatly improve the capacitance voltage and the voltage ripple, and can greatly reduce the coupling capacitance value.
Disclosure of Invention
The invention aims to provide a six-switch micro-inverter alternating-current side power coupling circuit for realizing the power coupling function of a micro-inverter instead of an electrolytic capacitor.
The technical scheme of the invention is that the power coupling circuit of the alternating current side of the six-switch micro-inverter consists of six switching tubes T1-T6, six diodes D1-D6, two coupling capacitors Cd1 and an inductor L. The first switching tube T1 and the first diode D1, the second switching tube T2 and the second diode D2, the third switching tube T3 and the third diode D3, the fourth switching tube T4 and the fourth diode D4, the fifth switching tube T5 and the fifth diode D5 and the sixth switching tube T6 and the sixth diode D6 are connected in anti-parallel; the first switching tube T1 is connected with the collector electrode of the second switching tube T2, the third switching tube T3 is connected with the emitter electrode of the fourth switching tube T4 to form two series branches, and the two branches are connected in parallel and then are respectively connected with a second capacitor Cd2 between the emitter electrode of the first switching tube T1 and the collector electrode of the third switching tube T3; the emitter of the first switching tube T1 is connected with the negative end of the second capacitor Cd2, and the collector of the third switching tube T3 is connected with the positive end of the second capacitor Cd2; the emitter of the second switching tube T2 is connected with the collector of the fourth switching tube T4 together and is connected with the upper end of the inductor L; the lower end of the inductor L is connected with the output side of the inverter; the fifth switching tube T5 and the sixth switching tube T6 are connected in parallel in the same direction; the collectors of the fifth switching tube T5 and the sixth switching tube T6 are respectively connected with the upper end and the lower end of the inductor; an emitter of the fifth switching tube T5 is connected with a negative end of the first capacitor Cd1, and an emitter of the sixth switching tube T6 is connected with a positive end of the first capacitor Cd 1;
according to the polarity of the output voltage of the inverter and the energy absorption/release of the coupling circuit, the power coupling circuit can be divided into four working modes, namely working mode 1: the output voltage of the inverter is positive, and the coupling circuit absorbs energy; working mode 2: the output voltage of the inverter is positive, and the coupling circuit releases energy; working mode 3: the output voltage of the inverter is negative, and the coupling circuit absorbs energy; working mode 4: the inverter output voltage is negative and the coupling circuit releases energy.
In the working mode 1, when the power coupling circuit is in the working mode 1, the input voltage is positive, the coupling circuit absorbs energy, and the voltage of the first capacitor Cd1 is increased;
the first diode D1 and the fifth diode D5 are turned on, the first switching tube T1 and the fifth switching tube T5 are turned off, the fourth switching tube T4 and the third switching tube T3 are turned off, the sixth switching tube T6 is turned on, and the second switching tube T2 is a main control switch; the duty ratio of the driving signal of the second switching tube T2 is adjusted to be adjustableThe energy absorbed by the section coupling circuit is increased, and the voltage of the first capacitor Cd1 is increased; when the second switching tube T2 is turned on, the current i d The circulation path is the power supply positive-the first diode D1-the second switching tube T2-the inductance L-the power supply negative; when the second switching tube T2 is turned off, the current i d The flow path is the inductance L-the sixth switching tube T6-the first capacitor Cd 1-the fifth diode D5-the inductance L.
In the working mode 2, when the power coupling circuit is in the working mode 2, the input voltage is positive, the coupling circuit releases energy, and the voltage of the first capacitor Cd1 is reduced;
the second diode D2 and the sixth diode D6 are turned on, the second switching tube T2 and the sixth switching tube T6 are turned off, the fourth switching tube T4 and the third switching tube T3 are turned off, the first switching tube T1 is turned on, and the fifth switching tube T5 is a main control switch; the energy released by the coupling circuit can be adjusted by adjusting the duty ratio of the driving signal of the fifth switching tube T5, and the voltage of the first capacitor Cd1 is reduced at the moment; when the fifth switching tube T5 is on, the current i d The circulation path is that the first capacitor Cd1 is positive, the sixth diode D6 is connected with the inductor L, the fifth switching tube T5 is connected with the first capacitor Cd1 in a negative mode; when the second switching tube T2 is turned off, the current i d The flow path is the inductance L-the second diode D2-the first switching tube T1-the power supply positive-the power supply negative-the inductance L.
In the working mode 3, when the power coupling circuit is in the working mode 3, the input voltage is negative, the coupling circuit absorbs energy, and the voltage of the second capacitor Cd2 is increased;
the second diode D2 and the third diode D3 are turned on, the second switching tube T2 and the third switching tube T3 are turned off, the fifth switching tube T5 and the sixth switching tube T6 are turned off, the first switching tube T1 is turned on, and the fourth switching tube T4 is a main control switch; the driving signal of the fourth switching tube T4 is regulated, the duty ratio can regulate the energy absorbed by the coupling circuit, at the moment, the voltage of the second capacitor Cd2 is increased, the polarity is consistent with the input voltage, and when the fourth switching tube T4 is turned on, the current i is obtained d The circulation path is positive of the first capacitor Cd1, the sixth diode D6, the inductor L, the fourth switching tube T4 and negative of the capacitor Cd 1; when the fourth switching tube T4 is opened, the current i d The flow path is the inductance L-the second diode D2-the first switching tube T1-the power supply positive-the power supply negative-the inductance L.
In the working mode 4, when the power coupling circuit is in the working mode 4, the input voltage is negative, the coupling circuit releases energy, and the voltage of the second capacitor Cd2 is reduced;
the first diode D1 and the fourth diode D4 are conducted, the first switching tube T1 and the fourth switching tube T4 are turned off, the fifth switching tube T5 and the sixth switching tube T6 are turned off, the second switching tube T2 is conducted, and the third switching tube T3 is a main control switch; the energy released by the coupling circuit can be adjusted by adjusting the duty ratio of the driving signal of the third switching tube T3, the voltage of the second capacitor Cd2 is reduced at the moment, the polarity is consistent with the input voltage, and when the third switching tube T3 is turned on, the current i is obtained d The circulation path is positive of the second capacitor Cd2, the third switching tube T3, the fourth diode D4, the inductor L, the second capacitor Cd2 and negative, when the third switching tube T3 is disconnected, the current i d The circulation path is inductance L-power negative-power positive-first diode D1-second switch tube T2-inductance L.
The power coupling circuit is connected in parallel to the alternating current output end of the inverter to replace the electrolytic capacitor to realize the power coupling function.
The power decoupling circuit is connected in parallel to the alternating current output side of the inverter, the circuit structure of the inverter is simple, and the decoupling circuit and the inverter circuit can be controlled independently; the power coupling circuit provided by the invention realizes power balance, can realize no electrolytic capacitor and prolongs the service life of the inverter.
In the invention, the total of the inversion unit and the decoupling unit only needs 10 switching tubes, and compared with the prior alternating-current side power decoupling scheme, the power decoupling unit and the inversion unit are integrated together, and the total of the inversion unit and the decoupling unit needs 6 bidirectional switching tubes, namely 12 unidirectional switches.
The main circuit is designed into a common two-stage voltage source type topology, and the decoupling unit is independent of the main circuit, so that the circuit structure of the inverter is not required to be modified.
Drawings
FIG. 1 is a six-switch power decoupling circuit;
FIG. 2 is a diagram of a six-switch power decoupling circuit based electrolytic capacitor-less micro-inverter architecture and power relationship;
FIG. 3 is a schematic diagram of the power coupling circuit absorbing energy in mode 1 of operation;
FIG. 4 is a schematic diagram of the power coupling circuit releasing energy in mode 2 of operation;
FIG. 5 is a schematic diagram of the power coupling circuit absorbing energy in mode 3 of operation;
FIG. 6 is a schematic diagram of the power coupling circuit releasing energy in mode 4 of operation;
FIG. 7 is a schematic diagram of matlab simulation results for each switching pulse control;
FIG. 8 shows a bus capacitor voltage U dc And input current I dc Simulating waveforms;
FIG. 8 (a) shows the bus capacitor voltage U when the decoupling circuit is not in operation dc And input current I dc The waveform is simulated and the waveform is simulated,
FIG. 8 (b) shows the bus capacitor voltage U when the decoupling circuit is in operation dc And input current I dc Simulating waveforms;
fig. 9 shows the grid voltage v g Current i g Simulating waveforms;
wherein: FIG. 9 (a) shows the grid voltage v when the decoupling circuit is not operating g Current i g The waveform is simulated and the waveform is simulated,
fig. 9 (b) shows the grid voltage v when the decoupling circuit is operating g Current i g Simulating waveforms;
figure 10 is a grid side current harmonic analysis,
wherein: figure 10 (a) is a schematic diagram of a network side current harmonic analysis when the decoupling circuit is not operating,
FIG. 10 (b) is a schematic diagram illustrating harmonic analysis of the network side current during operation of the decoupling circuit;
FIG. 11 is a schematic diagram of a decoupling circuit key waveform;
wherein: FIG. 11 (a) shows the decoupling capacitance voltage U d1 And U d2 Simulating waveforms;
FIG. 11 (b) shows the decoupling inductor current i d A waveform;
FIG. 12 is a diagram of decoupling current and inverter bridge drive pulses;
in the figure, T1 is a first switching tube;t2 is a second switching tube; t3 is a third switching tube; t4 is a fourth switching tube; t5 is a fifth switching tube; t6 is a sixth switching tube; d1 is a first diode; d2 is a second diode; d3 is a third diode; d4 is a fourth diode; d5 is a fifth diode; d6 sixth diode; l is inductance; cd1 is the first capacitance; cd1 is a second capacitor; p (P) o Is the output power of the micro inverter; p (P) I The power is input to the direct current side; p (P) c The coupling power of the power coupling circuit; u (U) dc Is the DC side voltage of the inverter; i dc The direct-current side current of the inverter; v o The voltage is the AC output side voltage of the inverter; v g Is the grid voltage; i.e g And injecting current into the power grid for micro-inversion.
Detailed Description
An embodiment of the present invention is shown in fig. 1.
The power coupling circuit of the alternating current side of the six-switch micro-inverter is composed of six switching tubes T1-T6, six diodes D1-D6, two coupling capacitors Cd1 and an inductor L. The first switching tube T1 and the first diode D1, the second switching tube T2 and the second diode D2, the third switching tube T3 and the third diode D3, the fourth switching tube T4 and the fourth diode D4, the fifth switching tube T5 and the fifth diode D5 and the sixth switching tube T6 and the sixth diode D6 are connected in anti-parallel; the first switching tube T1 is connected with the collector electrode of the second switching tube T2, the third switching tube T3 is connected with the emitter electrode of the fourth switching tube T4 to form two series branches, and the two branches are connected in parallel and then are respectively connected with a second capacitor Cd2 between the emitter electrode of the first switching tube T1 and the collector electrode of the third switching tube T3; the emitter of the first switching tube T1 is connected with the negative end of the second capacitor Cd2, and the collector of the third switching tube T3 is connected with the positive end of the second capacitor Cd2; the emitter of the second switching tube T2 is connected with the collector of the fourth switching tube T4 together and is connected with the upper end of the inductor L; the lower end of the inductor L is connected with the output side of the inverter; the fifth switching tube T5 and the sixth switching tube T6 are connected in parallel in the same direction; the collectors of the fifth switching tube T5 and the sixth switching tube T6 are respectively connected with the upper end and the lower end of the inductor; an emitter of the fifth switching tube T5 is connected with a negative end of the first capacitor Cd1, and an emitter of the sixth switching tube T6 is connected with a positive end of the first capacitor Cd 1. The series branch is completely disconnected only if both switching tubes in the series are switched off. The charging route of the inductor L to the capacitor can be adjusted through controlling the two serial branches, so that the equivalent circuit of the power coupling circuit is changed, and energy buffering is realized.
The structure and the power relation of the micro-inverter without electrolytic capacitor based on the six-switch power decoupling circuit are shown in fig. 2, wherein the micro-inverter mainly comprises an inverter and a power coupling circuit. The inverter adopts a common voltage source inverter structure, the power decoupling circuit adopts the circuit structure of the invention, the power decoupling circuit is connected with the alternating current output side of the inverter in parallel, and the inductance L and the capacitance C are filter inductance and capacitance. U in the figure dc For the DC side voltage of the inverter, I dc V is the DC side current of the inverter o V is the voltage of the AC output side of the inverter g For the grid voltage, i g And injecting current into the power grid for micro-inversion. P (P) I The input power is constant for the direct current side; p (P) o Is the output power of the micro-inverter, the average value of the output power is equal to P I The output instantaneous power is sinusoidal and the frequency is 2 times of the frequency of the power grid; p (P) c Is the coupling power of the power coupling circuit. Therefore, the instantaneous values of the input power at the direct current side and the output power of the inverter are unbalanced, and the power coupling circuit provided by the invention is adopted to realize power balance, so that no electrolytic capacitor can be realized, and the service life of the inverter is prolonged.
According to the polarity of the output voltage of the inverter and the energy absorption/release of the coupling circuit, the power coupling circuit can be divided into four working modes, namely working mode 1: the output voltage of the inverter is positive, and the coupling circuit absorbs energy; working mode 2: the output voltage of the inverter is positive, and the coupling circuit releases energy; working mode 3: the output voltage of the inverter is negative, and the coupling circuit absorbs energy; working mode 4: the inverter output voltage is negative and the coupling circuit releases energy.
In the working mode 1, when the power coupling circuit is in the working mode 1, the input voltage is positive, the coupling circuit absorbs energy, the voltage of the first capacitor Cd1 rises, and the equivalent circuit and the current flowing path are shown in fig. 3.
As shown in fig. 3, the first diode D1 and the fifth diode D5 are turned on, the first switching tube T1 and the fifth switching tube T5 are turned off, the fourth switching tube T4 and the third switching tube T3 are turned off, the sixth switching tube T6 is turned on, and the second switching tube T2 is a master switch; the energy absorbed by the coupling circuit can be adjusted by adjusting the duty ratio of the driving signal of the second switching tube T2, and the voltage of the first capacitor Cd1 rises at the moment; when the second switching tube T2 is turned on, the current i d The circulation path is the power supply positive-the first diode D1-the second switching tube T2-the inductance L-the power supply negative; when the second switching tube T2 is turned off, the current i d The flow path is the inductance L-the sixth switching tube T6-the first capacitor Cd 1-the fifth diode D5-the inductance L. Because the input and output voltages are opposite in direction, the equivalent working circuit is a buck-boost circuit.
In the working mode 2, when the power coupling circuit is in the working mode 2, the input voltage is positive, the coupling circuit releases energy, the voltage of the first capacitor Cd1 is reduced, and the equivalent circuit and the current flowing path are shown in fig. 4.
As shown in fig. 4, the second diode D2 and the sixth diode D6 are turned on, the second switching tube T2 and the sixth switching tube T6 are turned off, the fourth switching tube T4 and the third switching tube T3 are turned off, the first switching tube T1 is turned on, and the fifth switching tube T5 is a master switch; the energy released by the coupling circuit can be adjusted by adjusting the duty ratio of the driving signal of the fifth switching tube T5, and the voltage of the first capacitor Cd1 is reduced at the moment; when the fifth switching tube T5 is on, the current i d The circulation path is that the first capacitor Cd1 is positive, the sixth diode D6 is connected with the inductor L, the fifth switching tube T5 is connected with the first capacitor Cd1 in a negative mode; when the second switching tube T2 is turned off, the current i d The flow path is the inductance L-the second diode D2-the first switching tube T1-the power supply positive-the power supply negative-the inductance L. Because the input and output voltages are opposite in direction, the equivalent working circuit is also a buck-boost circuit.
In the working mode 3, when the power coupling circuit is in the working mode 3, the input voltage is negative, the coupling circuit absorbs energy, the voltage of the second capacitor Cd2 rises, and the equivalent circuit and the current flowing path are shown in fig. 5.
As shown in fig. 5, a second diodeThe third diode D3 is conducted, the second switching tube T2 and the third switching tube T3 are turned off, the fifth switching tube T5 and the sixth switching tube T6 are turned off, the first switching tube T1 is conducted, and the fourth switching tube T4 is a main control switch; and the driving signal of the fourth switching tube T4 is regulated, the duty ratio can regulate the energy absorbed by the coupling circuit, the voltage of the second capacitor Cd2 is increased at the moment, the polarity is consistent with the input voltage, and the equivalent of the voltage is a Boost circuit. When the fourth switching tube T4 is on, the current i d The circulation path is positive of the first capacitor Cd1, the sixth diode D6, the inductor L, the fourth switching tube T4 and negative of the capacitor Cd 1; when the fourth switching tube T4 is opened, the current i d The flow path is the inductance L-the second diode D2-the first switching tube T1-the power supply positive-the power supply negative-the inductance L.
In the working mode 4, when the power coupling circuit is in the working mode 4, the input voltage is negative, the coupling circuit releases energy, the voltage of the second capacitor Cd2 is reduced, and the equivalent circuit and the current flowing path are shown in fig. 6.
As shown in fig. 6, the first diode D1 and the fourth diode D4 are turned on, the first switching tube T1 and the fourth switching tube T4 are turned off, the fifth switching tube T5 and the sixth switching tube T6 are turned off, the second switching tube T2 is turned on, and the third switching tube T3 is a master switch; the energy released by the coupling circuit can be adjusted by adjusting the duty ratio of the driving signal of the third switching tube T3, the voltage of the second capacitor Cd2 is reduced at the moment, the polarity is consistent with the input voltage, and the coupling circuit is equivalent to a Buck circuit. When the third switching tube T3 is on, the current i d The circulation path is positive of the second capacitor Cd2, the third switching tube T3, the fourth diode D4, the inductor L, the second capacitor Cd2 and negative, when the third switching tube T3 is disconnected, the current i d The circulation path is inductance L-power negative-power positive-first diode D1-second switch tube T2-inductance L.
In summary, the states of the switches in each mode of operation are shown in table 1.
Table 1 on-off state table for each mode of operation
| T1 | T2 | T3 | T4 | T5 | T6 | |
| Mode 1 | 0 | 1/0 | 0 | 0 | 0 | 1 |
| Mode 2 | 1 | 0 | 0 | 0 | 1/0 | 0 |
| Mode 3 | 1/0 | 0 | 0 | 1 | 0 | 0 |
| Mode 4 | 0 | 1 | 1/0 | 0 | 0 | 0 |
In each of the modes of operation, only one switch is shown in a controllable state, and the remaining switches remain in a fixed state. Each switch state is related to the grid voltage polarity, the decoupling circuit absorbing or releasing energy.
Fig. 7 shows waveforms of control signals of the first switching tube T1 to the sixth switching tube T6 in one grid period.
For example, in the working mode 1, when working in the Boost mode, T2 is used as a master control switch to control the decoupling circuit to absorb energy, and at the moment, T1, T3, T4 and T5 are in an off state, and T6 is in an on state. From the simulation results of each switching pulse control in fig. 11, it can be seen that the switching logic formula in formula (1) meets the requirement of the operation mode a. The simulation result is compared with the switching states of the working modes 2, 3 and 4 of the circuit topology step by step, so that the switching tube working in each working mode is consistent with theoretical analysis.
In order to verify the theoretical analysis, MATLAB software is used for carrying out simulation verification on the working principle of a circuit on a 500W system, the rated output power is designed to be 500W, the direct current input voltage is designed to be 360V, the average voltage of a decoupling capacitor is 485V, the amplitude is 200V, and the required capacitor can be calculated to be 16uF according to the formula (1)
In the formula (1), omega represents the angular frequency of a power grid, and U av Represents the average value of the decoupling capacitance voltage, Δu=u H -U L Representing the magnitude of the decoupling capacitance voltage ripple. Other simulation parameters are shown in table 2.
Table 2 simulation parameters
| Circuit parameters | (symbol) | Reference value | Circuit parameters | (symbol) | Reference value | |
| Rated power | P n | 500W | Decoupling capacitance 2 | C d2 | 16uF | |
| Input voltage | U in | 100V | Filtering inductance | L f | 20mF | |
| Bus voltage | U dc | 360V | Output frequency | f | 50Hz | |
| Bus capacitor | C b | 70uF | Boost switching frequency | f b | 50KHz | |
| Decoupling circuit inductance | L d | 100uH | H-bridge switching frequency | f H | 20KHz | |
| Decoupling capacitor 1 | C d1 | 16uF | Decoupling circuit switching frequency | f d | 20KHz |
FIG. 8 (a) shows the voltage U of the bus capacitor of the inverter when the decoupling circuit is not in operation dc And input current I dc The voltage secondary ripple is up to 130V, and the input current secondary ripple is about 3A; fig. 8 (b) shows the bus capacitor voltage and the input current when the decoupling circuit is in operation, the voltage secondary ripple is only 20V, and the input current secondary ripple is about 1.2A. The decoupling circuit has obvious secondary ripple suppression effect, stable input current is favorable for improving the tracking performance of MPPT, the photovoltaic utilization rate is improved, and stable bus current is favorable for reducing grid-connected current THD.
Fig. 9 shows the network side voltage v when the decoupling circuit is not operating and is operating, respectively g And current waveform i g In both figures, the grid-connected current and the grid voltage are kept in phase. The grid-tie current is slightly distorted when the decoupling circuit in fig. 9 (a) is not operating; when the decoupling circuit in fig. 9 (b) is in operation, the grid-connected current waveform is good.
FIG. 10 is the THD of the grid-tie current, which is 9.86% when the decoupling circuit of FIG. 10 (a) is not operating; in fig. 10 (b), the grid-connected current THD is 4.04%, less than 5%, and meets the grid-connected standard.
FIG. 11 (a) is a decoupling capacitance voltage U d1 ，U d2 Is a simulation waveform of the decoupling capacitor C d1 ，C d2 Working for half a power frequency period; FIG. 11 (b) is a decoupling inductor current i d Black envelope represents the peak given value I of the decoupling inductor current dref The inductor current reaches I basically right in the rest time except the vicinity of the zero crossing point moment (t=0.01K, K=0, 1,2 …) of the grid voltage dref And then the voltage drops, because the pulse width of the inverter bridge driving pulse changes according to sine according to the SPWM modulation characteristic, the conducting time of the inverter bridge in each switching period is determined by the pulse width, and the pulse width of the inverter bridge driving pulse near the voltage zero crossing point is
t pulse ＝m a T s sin(0.01ωK+τ) (2)
In the formula (2), m a Is the degree of modulation of the light source,T s the switching frequency of the inverter bridge is that tau represents the time difference from the zero crossing point to any time nearby, and tau is extremely small, so that t is nearby the zero crossing point pulse The decoupling circuit may not be able to buffer enough energy during this time, but from the effect of fig. 8,9, the effect on the decoupling circuit performance is very small. Fig. 12 shows the relationship between the decoupling inductor current and the inverter driving pulse, when the decoupling circuit achieves complete decoupling, the decoupling inductor current drops to zero before the driving pulse of the inverter bridge is completed.
Claims (1)
1. The power coupling circuit is characterized by comprising six switching tubes, six diodes, two coupling capacitors and an inductor; the first switching tube and the first diode, the second switching tube and the second diode, the third switching tube and the third diode, the fourth switching tube and the fourth diode, the fifth switching tube and the fifth diode and the sixth switching tube and the sixth diode are connected in anti-parallel; the first switching tube is connected with the collector electrode of the second switching tube, the third switching tube is connected with the emitter electrode of the fourth switching tube to form two series branches, and the two branches are connected in parallel and then are respectively connected with a second capacitor between the emitter electrode of the first switching tube and the collector electrode of the third switching tube; the emitter of the first switching tube is connected with the negative end of the second capacitor, and the collector of the third switching tube is connected with the positive end of the second capacitor; the emitter of the second switching tube is connected with the collector of the fourth switching tube and is connected with the upper end of the inductor; the lower end of the inductor is connected with the output side of the inverter; the fifth switching tube and the sixth switching tube are connected in parallel in the same direction; the collector electrodes of the fifth switching tube and the sixth switching tube are respectively connected with the upper end and the lower end of the inductor; an emitter of the fifth switching tube is connected with a negative end of the first capacitor, and an emitter of the sixth switching tube is connected with a positive end of the first coupling capacitor;
according to the polarity of the output voltage of the inverter and the energy absorption/release of the coupling circuit, the power coupling circuit is divided into four working modes: the working modes are respectively a working mode 1, a working mode 2, a working mode 3 and a working mode 4;
in the working mode 1, when the power coupling circuit is in the working mode 1, the input voltage is positive, the coupling circuit absorbs energy, and the voltage of the first coupling capacitor is increased;
the first diode and the fifth diode are conducted, the first switching tube and the fifth switching tube are turned off, the fourth switching tube and the third switching tube are turned off, the sixth switching tube is conducted, and the second switching tube is a main control switch; the energy absorbed by the coupling circuit can be adjusted by adjusting the duty ratio of the driving signal of the second switching tube, and the voltage of the first coupling capacitor is increased at the moment; when the second switching tube is turned on, the current flow path is power supply positive, the first diode, the second switching tube, the inductor and the power supply negative; when the second switching tube is disconnected, the current flow path is an inductor, a sixth switching tube, a first coupling capacitor, a fifth diode and an inductor;
in the working mode 2, when the power coupling circuit is in the working mode 2, the input voltage is positive, the coupling circuit releases energy, and the voltage of the first coupling capacitor is reduced;
the second diode and the sixth diode are conducted, the second switching tube and the sixth switching tube are turned off, the fourth switching tube and the third switching tube are turned off, the first switching tube is conducted, and the fifth switching tube is a main control switch; the energy released by the coupling circuit can be adjusted by adjusting the duty ratio of the driving signal of the fifth switching tube, and the voltage of the first coupling capacitor is reduced at the moment; when the fifth switching tube is turned on, the current flow path is positive of the first coupling capacitor, the sixth diode, the inductor, the fifth switching tube and the first coupling capacitor; when the second switching tube is disconnected, the current flow path is an inductor, a second diode, a first switching tube, a power supply positive power supply negative power supply inductor;
in the working mode 3, when the power coupling circuit is in the working mode 3, the input voltage is negative, the coupling circuit absorbs energy, and the voltage of the second coupling capacitor is increased;
the second diode and the third diode are conducted, the second switching tube and the third switching tube are turned off, the fifth switching tube and the sixth switching tube are turned off, the first switching tube is conducted, and the fourth switching tube is a main control switch; the driving signal of the fourth switching tube is regulated, the duty ratio can regulate the energy absorbed by the coupling circuit, at the moment, the voltage of the second coupling capacitor is increased, the polarity is consistent with the input voltage, and when the fourth switching tube is opened, the current flow path is positive of the first coupling capacitor, negative of the sixth diode, negative of the inductance, and negative of the fourth switching tube; when the fourth switching tube is disconnected, the current flow path is an inductor, a second diode, a first switching tube, a power supply positive power supply negative power supply inductor;
in the working mode 4, when the power coupling circuit is in the working mode 4, the input voltage is negative, the coupling circuit releases energy, and the voltage of the second coupling capacitor is reduced;
the first diode and the fourth diode are conducted, the first switching tube and the fourth switching tube are turned off, the fifth switching tube and the sixth switching tube are turned off, the second switching tube is conducted, and the third switching tube is a main control switch; the driving signal duty ratio of the third switching tube is adjusted to adjust the energy released by the coupling circuit, at the moment, the voltage of the second coupling capacitor is reduced, the polarity is consistent with the input voltage, when the third switching tube is turned on, the current flow path is the second coupling capacitor positive-the third switching tube-the fourth diode-the inductor-the second coupling capacitor negative, and when the third switching tube is turned off, the current flow path is the inductor-the power supply negative-the power supply positive-the first diode-the second switching tube-the inductor.
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| CN206564546U (en) * | 2017-03-10 | 2017-10-17 | 华东交通大学 | A kind of micro- inverter ac side power coupling circuit of six switches |
| CN107508479A (en) * | 2017-08-01 | 2017-12-22 | 华东交通大学 | A kind of four switch AC side power decoupling circuits and decoupling control method |
| CN208797827U (en) * | 2018-10-24 | 2019-04-26 | 华东交通大学 | A kind of micro- inverter ac side power coupling circuit of six switches |
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| CA2502798C (en) * | 2004-03-31 | 2011-06-14 | University Of New Brunswick | Single-stage buck-boost inverter |
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| CN104201927A (en) * | 2014-09-23 | 2014-12-10 | 青岛理工大学 | Single-stage coupling inductance ZETA reactance source inverter |
| CN104682762A (en) * | 2015-02-10 | 2015-06-03 | 华中科技大学 | Low-leakage-current grid-connected inverter |
| CN106961226A (en) * | 2017-03-10 | 2017-07-18 | 华东交通大学 | A kind of micro- inverter ac side power coupling circuit of six switches |
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