A six-switch power decoupling circuit and control method thereof

Abstract

The present invention discloses a six-switch power decoupling circuit and a control method thereof, comprising: six switch tubes S1-S6, six diodes D1-D6, two capacitors C d1 , C d2 And inductance L d ; S1-S6 are connected in reverse parallel with D1-D6 respectively, the emitter of S1 is connected with the emitter of S2 to form the first branch, the emitter of S3 is connected with the emitter of S4 and connected in series with C d1 The second branch is formed, the emitter of S5 is connected to the emitter of S6 and connected in series with C d2 The third branch is formed, and the three branches are connected in parallel at the same time; the inductance L d The collector of S1 is connected to the AC output side of the micro-inverter. The present invention connects the power decoupling circuit to the AC output side of the micro-inverter, undertakes energy buffering, greatly reduces the coupling capacitance value, reduces the secondary disturbance power, and improves the performance and life of the micro-inverter. In addition, the present invention uses pulse modulation technology PEM to control the six-switch power coupling circuit, which has the characteristics of simple structure and convenient control.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-inverter, and in particular to a six-switch power decoupling circuit and a control method thereof. Background Art

[0002] Microinverters have many advantages, such as high power generation, easy expansion, low cost, hot plug and modular design, which make them gradually become the mainstream of distributed power generation systems. However, in distributed power generation systems, under the control of Maximum Power Point Tracking (MPPT), the input power generated by photovoltaic modules is constant, but the power entering the grid is twice the power pulsation of the power frequency, and the instantaneous values ​​of the two are inconsistent. Therefore, in traditional microinverters, electrolytic capacitors are relied on to balance the instantaneous input and output power, but this also causes the life of electrolytic capacitors to be much shorter than other components in the circuit. Therefore, studying microinverters without electrolytic capacitors has become a way to improve the performance and life of microinverters, and scholars at home and abroad have successively carried out research.

[0003] Electrolytic capacitor-free micro-inverter technology achieves energy buffering by connecting a power decoupling circuit in parallel in the micro-inverter. The power decoupling circuit is composed of a power switch and passive components. There are three types of power decoupling circuits classified by access point: DC input side type, DC-link (DC support capacitor) intermediate side type, and AC output side type.

[0004] Among them, the DC input side power coupling circuit is usually suitable for single-stage grid-connected microinverters. Professor Shimizu et al. of Tokyo Metropolitan University in Japan proposed a flyback single-stage microinverter. After adopting the power decoupling circuit, a 100W microinverter only needs a 40uF film capacitor, but the conversion efficiency is very low, only 70%. Professor BJPierquet et al. of the University of Washington in the United States proposed a two-stage microinverter structure, in which the power decoupling circuit is connected in series between the photovoltaic array and the microinverter to control energy storage and voltage fluctuations respectively, avoid the use of electrolytic capacitors, and maintain the reactive transmission of the microinverter. However, although the circuit structure of this type is simple, the power decoupling control of the system is relatively complex, and the MPPT and island detection operations are also relatively difficult, which reduces the system efficiency, the system boost ratio is low, the photovoltaic DC output voltage is high, and the decoupling capacitor value is still large.

[0005] In multi-level micro-inverters, due to the high voltage on the intermediate DC side, the power decoupling technology of the DC-link intermediate side type is adopted. GAJA Maratunga et al. from the University of Cambridge, UK, proposed a three-level micro photovoltaic grid-connected micro-inverter. The micro-inverter consists of a phase-shifted full-bridge circuit, a Buck circuit and a full-bridge micro-inverter. The phase-shifted full-bridge circuit realizes the boost and MPPT functions, the Buck circuit generates a sinusoidal half-wave current, and the last stage circuit generates a sinusoidal injection current. At this time, in order to reduce the decoupling capacitor value, the DC side voltage fluctuates greatly and still generates considerable secondary power disturbances.

[0006] It can be seen that the existing electrolytic capacitor-free micro-inverter technology generally has problems such as complex structure, inconvenient control, large decoupling capacitance value, and large secondary power disturbance. Summary of the invention

[0007] The purpose of the present invention is to provide a six-switch power decoupling circuit and a control method thereof to solve the common problems of the existing electrolytic capacitor-free micro-inverter technology, such as complex structure, inconvenient control, large decoupling capacitance value, and large secondary power disturbance.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] A six-switch power decoupling circuit includes: a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, a fifth switch tube S5, a sixth switch tube S6, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, a first capacitor C d1 , the second capacitor C d2 And the inductor L d ;

[0010] The collector of the first switch tube S1, the collector of the third switch tube S3 and the collector of the fifth switch tube S5 are all connected to one end of the AC output side of the micro-inverter;

[0011] The emitter of the first switch tube S1 is connected to the emitter of the second switch tube S2; the first switch tube S1 is connected in reverse parallel to the first diode D1; the second switch tube S2 is connected in reverse parallel to the second diode D2;

[0012] The emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the collector of the fourth switch tube S4 is connected to the first capacitor C d1 The third switch tube S3 is connected to the third diode D3 in reverse parallel; the fourth switch tube S4 is connected to the fourth diode D4 in reverse parallel;

[0013] The emitter of the fifth switch tube S5 is connected to the emitter of the sixth switch tube; the collector of the sixth switch tube is connected to the second capacitor C d2 The fifth switch tube S5 is connected in reverse parallel to the fifth diode D5; the sixth switch tube S6 is connected in reverse parallel to the sixth diode D6;

[0014] The collector of the second switch tube S2 and the first capacitor C d1 The other end of the second capacitor C d2 The other end of the inductor L d One end of the inductor L d The other end is connected to the other end of the AC output side of the micro-inverter.

[0015] Optionally, the reverse parallel connection is that the emitter of the switch tube is connected to the positive electrode of the diode, and the collector of the switch tube is connected to the negative electrode of the diode.

[0016] Optionally, the inductor L d The other end is connected to the common ground end of the AC output side of the micro-inverter and the grid voltage.

[0017] Optionally, both the first capacitor Cd1 and the second capacitor Cd2 are decoupling capacitors.

[0018] A control method for a six-switch power decoupling circuit, the six-switch power decoupling circuit comprising: a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, a fifth switch tube S5, a sixth switch tube S6, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, a first capacitor C d1 , the second capacitor C d2 And the inductor L d The collector of the first switch tube S1, the collector of the third switch tube S3 and the collector of the fifth switch tube S5 are all connected to one end of the AC output side of the micro-inverter; the emitter of the first switch tube S1 is connected to the emitter of the second switch tube S2; the first switch tube S1 is connected in reverse parallel to the first diode D1; the second switch tube S2 is connected in reverse parallel to the second diode D2; the emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the collector of the fourth switch tube S4 is connected to the first capacitor C d1 The third switch tube S3 is connected to the third diode D3 in reverse parallel; the fourth switch tube S4 is connected to the fourth diode D4 in reverse parallel; the emitter of the fifth switch tube S5 is connected to the emitter of the sixth switch tube; the collector of the sixth switch tube is connected to the second capacitor C d2The fifth switch tube S5 is connected in reverse parallel to the fifth diode D5; the sixth switch tube S6 is connected in reverse parallel to the sixth diode D6; the collector of the second switch tube S2, the first capacitor C d1 The other end of the second capacitor C d2 The other end of the inductor L d One end of the inductor L d The other end of the micro-inverter is connected to the other end of the AC output side of the micro-inverter;

[0019] The control method comprises:

[0020] Obtaining an output voltage at an AC output side of the micro-inverter and a decoupling current of the six-switch power decoupling circuit;

[0021] Determine whether the output voltage of the AC output side of the micro-inverter is greater than 0, and obtain a first determination result;

[0022] If the first judgment result is that the output voltage at the AC output side of the micro-inverter is greater than 0, determining whether the decoupling current is in the same direction as the output voltage to obtain a second judgment result;

[0023] If the second judgment result is that the decoupling current and the output voltage are in the same direction, controlling the six-switch power decoupling circuit to operate in the first operating mode to absorb energy;

[0024] If the second judgment result is that the decoupling current is in opposite directions to the output voltage, controlling the six-switch power decoupling circuit to operate in a second operating mode to release energy;

[0025] If the first judgment result is that the output voltage at the AC output side of the micro-inverter is less than 0, judging whether the decoupling current is in the same direction as the output voltage, and obtaining a third judgment result;

[0026] If the third judgment result is that the decoupling current and the output voltage are in the same direction, controlling the six-switch power decoupling circuit to operate in a third operating mode to absorb energy;

[0027] If the third judgment result is that the decoupling current is in opposite directions to the output voltage, the six-switch power decoupling circuit is controlled to operate in a fourth operating mode to release energy.

[0028] Optionally, controlling the six-switch power decoupling circuit to operate in a first operating mode to absorb energy specifically includes:

[0029] The second switch tube S2, the fourth switch tube S4, the fifth switch tube S5 and the sixth switch tube S6 are all turned off, the third switch tube S3 is turned on, and the first switch tube S1 is used as a main control switch and is controlled by a pulse energy modulation PEM signal; at this time, the first capacitor C d1 Absorb energy.

[0030] Optionally, controlling the six-switch power decoupling circuit to operate in the second operating mode to absorb energy specifically includes:

[0031] The first switch tube S1, the third switch tube S3, the fifth switch tube S5 and the sixth switch tube S6 are all turned off, the second switch tube S2 is turned on, and the fourth switch tube S4 is used as a main control switch and is controlled by the PEM signal; at this time, the first capacitor C d1 Release energy.

[0032] Optionally, the six-switch power decoupling circuit is controlled to work in the third working mode to absorb energy, specifically including: the first switch tube S1, the third switch tube S3, the fourth switch tube S4 and the fifth switch tube S5 are all turned off, the sixth switch tube S6 is turned on, and the second switch tube S2 is used as a main control switch and is controlled by a PEM signal; at this time, the second capacitor C d2 Absorb energy.

[0033] Optionally, the controlling the six-switch power decoupling circuit to operate in the fourth operating mode to absorb energy specifically includes: the second switch tube S2, the third switch tube S3, the fourth switch tube S4 and the sixth switch tube S6 are all turned off, the first switch tube S1 is turned on, and the fifth switch tube S5 is used as a main control switch and is controlled by a PEM signal; at this time, the second capacitor C d2 Release energy.

[0034] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0035] The present invention discloses a six-switch power decoupling circuit and a control method thereof, comprising: six switch tubes S1-S6, six diodes D1-D6, two capacitors C d1 , C d2 And inductance L d ; S1-S6 are connected in reverse parallel with D1-D6 respectively, the emitter of S1 is connected with the emitter of S2 to form the first branch, the emitter of S3 is connected with the emitter of S4 and connected in series with C d1 The second branch is formed, the emitter of S5 is connected to the emitter of S6 and connected in series with C d2 The third branch is formed, and the three branches are connected in parallel at the same time; the inductance L dThe collector of S1 is connected to the AC output side of the micro-inverter. The present invention connects the power decoupling circuit to the AC output side of the micro-inverter, undertakes energy buffering, greatly reduces the coupling capacitance value, reduces the secondary disturbance power, and improves the performance and life of the micro-inverter. In addition, the present invention uses pulse modulation technology PEM to control the six-switch power coupling circuit, which has the characteristics of simple structure and convenient control. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0037] Figure 1 A schematic diagram of the topological structure of a six-switch power decoupling circuit provided by the present invention;

[0038] Figure 2 The structure of the electrolytic capacitor-free micro-inverter and the power relationship diagram of the six-switch power decoupling circuit provided by the present invention;

[0039] Figure 3 The input power (P I ), output power (P o ) and decoupling power (P c ) diagram of the relationship between them;

[0040] Figure 4 A schematic diagram of the working mode sequence of the coupling circuit within a power grid cycle provided by the present invention;

[0041] Figure 5 Schematic diagram of four working modes of the power decoupling circuit provided by the present invention; Figure 5 (A) is a schematic diagram of the first working mode of the power decoupling circuit, Figure 5 (B) is a schematic diagram of the second working mode of the power decoupling circuit; Figure 5 (C) is a schematic diagram of the third working mode of the power decoupling circuit, Figure 5 (D) is a schematic diagram of a fourth working mode of the power decoupling circuit;

[0042] Figure 6 A schematic diagram of a six-switch power decoupling circuit provided by the present invention operating in a first operating mode; Figure 6 (a) is a schematic diagram of the main switch disconnection control and current flow path. Figure 6 (b) is a schematic diagram of an equivalent circuit of the six-switch power decoupling circuit operating in the first operating mode;

[0043] Figure 7 A schematic diagram of a six-switch power decoupling circuit provided by the present invention operating in a second operating mode; Figure 7 (a) is a schematic diagram of the main switch disconnection control and current flow path. Figure 7 (b) is a schematic diagram of an equivalent circuit of the six-switch power decoupling circuit operating in the second operating mode;

[0044] Figure 8 A schematic diagram of the six-switch power decoupling circuit provided by the present invention working in the third working mode; Figure 8 (a) is a schematic diagram of the main switch disconnection control and current flow path. Figure 8 (b) is a schematic diagram of an equivalent circuit of the six-switch power decoupling circuit operating in the third operating mode;

[0045] Fig. 9 A schematic diagram of the six-switch power decoupling circuit provided by the present invention working in the fourth working mode; Fig. 9 (a) is a schematic diagram of the main switch disconnection control and current flow path. Fig. 9 (b) is a schematic diagram of an equivalent circuit of the six-switch power decoupling circuit operating in the fourth operating mode;

[0046] Fig.10 A schematic diagram of a MATLAB simulation model of a control circuit of six switch tubes provided by the present invention; wherein NOT is a negation gate, AND is an AND gate, OR is an OR gate, boolean is a Matlab function for converting a numerical value into a Boolean value, and T1-T6 are driving signals of six corresponding switch tubes;

[0047] Fig.11 A MATLAB simulation schematic diagram of a PEM signal generating circuit provided by the present invention;

[0048] Fig.12 A MATLAB simulation diagram of a power decoupling circuit composed of six switch tubes provided by the present invention;

[0049] Fig.13 A schematic diagram of a driving signal for a switch tube of a six-switch decoupling circuit provided by the present invention; Fig.13 (a) is the driving signal of the decoupling circuit S1S2, (b) is the driving signal of the decoupling circuit S3S4, and (c) is the driving signal of the decoupling circuit S5S6.

[0050] Fig.14 A schematic diagram of relevant waveforms when the micro-inverter provided by the present invention is not connected to a six-switch power decoupling circuit;

[0051] Fig.15 A schematic diagram of relevant waveforms when the micro-inverter provided by the present invention is connected to a six-switch power decoupling circuit; DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] The purpose of the present invention is to provide a six-switch power decoupling circuit and a control method thereof to solve the common problems of the existing electrolytic capacitor-free micro-inverter technology, such as complex structure, inconvenient control, large decoupling capacitance value, and large secondary power disturbance.

[0054] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] Figure 1 Schematic diagram of the topological structure of the six-switch power decoupling circuit provided by the present invention. Figure 1 As shown, the six-switch power decoupling circuit includes: a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, a fifth switch tube S5, a sixth switch tube S6, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, a first capacitor C d1 , the second capacitor C d2 And the inductor L d S1-S6 are connected in reverse parallel with D1-D6 respectively, the emitter of switch tube S1 is connected with the emitter of switch tube S2 to form the first branch, the emitter of switch tube S3 is connected with the emitter of switch tube S4 and connected in series C d1 The second branch is formed, the emitter of the switch tube S5 is connected to the emitter of the switch tube S6 and connected in series with C d2 The third branch is formed, and the three branches are connected in parallel. d One end of the inductor is connected to the common ground of the AC output side of the micro-inverter and the grid voltage. d The other end is connected to the collector of the switch tube S2, and the collector of the switch tube S1 is connected to one end of the AC output side of the micro inverter. Wherein, the reverse parallel connection is that the emitter of the switch tube is connected to the positive electrode of the corresponding diode, and the collector of the switch tube is connected to the negative electrode of the corresponding diode.

[0056] Specifically, Figure 1As shown, the collector of the first switch tube S1, the collector of the third switch tube S3 and the collector of the fifth switch tube S5 are all connected to one end of the AC output side of the micro-inverter; the emitter of the first switch tube S1 is connected to the emitter of the second switch tube S2; the first switch tube S1 is connected in reverse parallel to the first diode D1; the second switch tube S2 is connected in reverse parallel to the second diode D2; the emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the collector of the fourth switch tube S4 is connected to the first capacitor C d1 The third switch tube S3 is connected to the third diode D3 in reverse parallel; the fourth switch tube S4 is connected to the fourth diode D4 in reverse parallel; the emitter of the fifth switch tube S5 is connected to the emitter of the sixth switch tube; the collector of the sixth switch tube is connected to the second capacitor C d2 The fifth switch tube S5 is connected in reverse parallel to the fifth diode D5; the sixth switch tube S6 is connected in reverse parallel to the sixth diode D6; the collector of the second switch tube S2, the first capacitor C d1 The other end of the second capacitor C d2 The other end of the inductor L d One end of the inductor L d The other end is connected to the other end of the AC output side of the micro-inverter.

[0057] The inductance L d The other end is connected to the common ground end of the AC output side of the micro-inverter and the grid voltage.

[0058] The first capacitor Cd1 and the second capacitor Cd2 are both decoupling capacitors.

[0059] Only when the two switch tubes of the same branch are disconnected at the same time, the branch is completely disconnected. By controlling the on and off of the switch tube, the working mode of the circuit is changed to achieve energy buffering.

[0060] Figure 2 The structure and power relationship diagram of the six-switch power decoupling circuit (referred to as power decoupling circuit) micro-inverter provided by the present invention. Figure 2 As shown, the micro-inverter and the power decoupling circuit constitute the micro-inverter. The micro-inverter adopts a common structure. The power decoupling circuit part adopts the six-switch power decoupling circuit provided by the present invention. The AC output side of the micro-inverter is connected in parallel to the power decoupling circuit. The inductor L and the capacitor C constitute a filtering device. Among them, V dc is the DC side voltage, I dc is the DC side current, U inv is the AC output voltage of the micro-inverter, v grid is the grid voltage, i gridis the current injected by the micro-inverter into the grid, P I is the DC side input power, P o is the output power of the micro-inverter, P c is the decoupling power of the power decoupling circuit.

[0061] Since the DC side input power and the instantaneous output power of the micro-inverter are inconsistent, the traditional method uses electrolytic capacitors to balance the two, but this greatly reduces the life of the micro-inverter. Using the three-phase six-switch power decoupling circuit in the present invention instead of electrolytic capacitors can greatly improve the stability and life of the micro-inverter.

[0062] Figure 3 is the input power in the micro-inverter (P I ), output power (P o ) and decoupling power (P c ) Figure 3 As shown in Figure 2, in the micro-inverter, the power decoupling circuit balances the input power and the instantaneous output power. Specifically, when P I <P o When P c >0, the power decoupling circuit supplements the input power; when P I >P o When P c <0, the power decoupling circuit absorbs the excess input power. DC side input power P I , instantaneous output power P o .

[0063] like Figure 2 As shown, the micro-inverter output voltage U inv There are positive and negative, so the input voltage of the power decoupling circuit is also positive and negative, and the decoupling current is also positive and negative, so the power decoupling circuit has four working modes:

[0064] Mode 1 (i.e. the first working mode): When U inv When >0, the decoupling current and voltage are in the same direction, and the power decoupling circuit absorbs energy;

[0065] Mode 2 (i.e. the second working mode): When U inv When >0, the decoupling current and voltage are in opposite directions, and the power decoupling circuit releases energy;

[0066] Mode 3 (ie the third working mode): when U inv When <0, the decoupling current and voltage are in the same direction, and the power decoupling circuit absorbs energy;

[0067] Mode 4 (ie the fourth working mode): when U inv When <0, the decoupling current and voltage are in opposite directions, and the power decoupling circuit releases energy.

[0068] Figure 4 Figure 1 is a schematic diagram of the working mode sequence of the coupling circuit in a power grid cycle. Figure 4 As shown, mode 1 and mode 2 work in the positive half cycle of the grid voltage, and mode 3 and mode 4 work in the negative half cycle. A cycle can be divided into 6 parts, which are mode 1 → mode 2 → mode 1 → mode 3 → mode 4 → mode 3 in order. The absorption and release of the input power by the power decoupling circuit are absorption → release → absorption → absorption → release → absorption.

[0069] Figure 5 Figure 2 is a schematic diagram of the four working modes of the power decoupling circuit. Figure 5 As shown in the figure, the power decoupling circuit realizes the power decoupling function through inductance and capacitance. The inductance connects the voltage and current of the micro inverter and the power decoupling circuit, and the capacitor absorbs and releases energy. The polarity of the two ends of the decoupling capacitor is fixed. If the power decoupling circuit absorbs energy, the voltage and current are in the same direction, and the direction of the capacitor is also the same as the current direction; if the power decoupling circuit releases energy, the voltage and current are in opposite directions, and the direction of the capacitor is also opposite to the current direction. The positive direction of the voltage is assumed to be positive at the top and negative at the bottom, and the positive direction of the current is from left to right.

[0070] When U inv >0, the power decoupling circuit absorbs energy, the capacitor voltage increases, and the direction of voltage and current is determined. The power decoupling circuit can be equivalent to a Boost circuit. Figure 5 (A); when U inv >0, the power decoupling circuit releases energy, the capacitor voltage decreases, and the direction of voltage and current is determined. The power decoupling circuit can be equivalent to a Buck circuit. Figure 5 (B); when U inv <0, the power decoupling circuit absorbs energy, the capacitor voltage increases, and the direction of voltage and current is determined. The power decoupling circuit can be equivalent to a Boost circuit. Figure 5 (C); When U inv <0, the power decoupling circuit releases energy, the capacitor voltage decreases, and the direction of voltage and current is determined. The power decoupling circuit can be equivalent to a Buck circuit. Figure 5 (D).

[0071] Based on the six-switch power decoupling circuit provided by the present invention, the present invention also provides a control method for the six-switch power decoupling circuit, the control method comprising:

[0072] Obtaining an output voltage at an AC output side of the micro-inverter and a decoupling current of the six-switch power decoupling circuit;

[0073] Determine whether the output voltage of the AC output side of the micro-inverter is greater than 0, and obtain a first determination result;

[0074] If the first judgment result is that the output voltage at the AC output side of the micro-inverter is greater than 0, determining whether the decoupling current is in the same direction as the output voltage to obtain a second judgment result;

[0075] If the second judgment result is that the decoupling current and the output voltage are in the same direction, controlling the six-switch power decoupling circuit to operate in the first operating mode to absorb energy;

[0076] If the second judgment result is that the decoupling current is in opposite directions to the output voltage, controlling the six-switch power decoupling circuit to operate in a second operating mode to release energy;

[0077] If the first judgment result is that the output voltage at the AC output side of the micro-inverter is less than 0, judging whether the decoupling current is in the same direction as the output voltage, and obtaining a third judgment result;

[0078] If the third judgment result is that the decoupling current and the output voltage are in the same direction, controlling the six-switch power decoupling circuit to operate in a third operating mode to absorb energy;

[0079] If the third judgment result is that the decoupling current is in opposite directions to the output voltage, the six-switch power decoupling circuit is controlled to operate in a fourth operating mode to release energy.

[0080] The first working mode (Mode I) to the fourth working mode (Mode IV) are respectively as follows: Figure 6 to Figure 9 As shown, Figure 6 to Figure 9 Figure (a) is a schematic diagram of the main switch disconnection control and current flow path, and Figure (b) is a schematic diagram of the equivalent circuit. The output of the micro-inverter is used as the equivalent voltage source, and U inv Indicates that U inv+ is the positive pole of the equivalent voltage source, U inv- is the negative pole of the equivalent voltage source, where P pv is the DC input power of the micro-inverter, P ac is the output power of the AC side of the micro-inverter, C d1+ Represents the coupling capacitor C d1 The positive electrode, C d1- Represents the coupling capacitor C d1 of the negative electrode.

[0081] Specifically, Figure 6 This is a schematic diagram of the six-switch power decoupling circuit provided by the present invention working in the first working mode. Figure 6 As shown, in the first working mode, U inv >0, and P pv >P ac, S2, S4, S5 and S6 are disconnected, S3 is always on, and S1 is controlled by the PEM signal as the main control switch. At this time, the decoupling capacitor C d1 Absorbing energy, the voltage rises. When S1 is turned on, i d The flow path is U inv+ →S1→D2→L d →U inv- , when S1 is disconnected, i d The flow path is U inv+ →S3→D4→C d1 →L d →U inv- .

[0082] Figure 7 This is a schematic diagram of the six-switch power decoupling circuit provided by the present invention working in the second working mode. Figure 7 As shown, in this working mode, U inv >0, and P pv <P ac , S1, S3, S5 and S6 are disconnected, S2 is always on, and S4 is controlled by the PEM signal as the main control switch. At this time, the decoupling capacitor C d1 Energy is released and the voltage drops. When S4 is turned on, i d The flow path is C d1+ →S4→D3→U inv →L d →C d1- , when S4 is disconnected, i d The flow path is U inv- →L d →S2→D1→U inv+ . Among them, C d1+ Represents the coupling capacitor C d1 The positive electrode, C d1- Represents the coupling capacitor C d1 of the negative electrode.

[0083] Figure 8 FIG. 1 is a schematic diagram of a six-switch power decoupling circuit operating in the third operating mode. Figure 8 As shown, this circuit is a buck-boost circuit and works in Boost mode. inv <0, and P pv >P ac , S1, S3, S4 and S5 are disconnected, S6 is always on, and S2 is controlled by the PEM signal as the main control switch. At this time, the decoupling capacitor C d2 Absorbing energy, the voltage rises. When S2 is turned on, i d The flow path is U inv+ →L d →S2→D1→U inv- , when S2 is disconnected, id The flow path is C d2- →S6→D5→U inv →L d →C d2+ . Among them, C d2+ Represents the coupling capacitor C d2 The positive electrode, C d2- Represents the coupling capacitor C d2 of the negative electrode.

[0084] Fig. 9 This is a schematic diagram of the six-switch power decoupling circuit provided by the present invention working in the fourth working mode. Fig. 9 As shown, this circuit is a step-up / step-down circuit and works in Buck mode. inv <0, and P pv <P ac , S2, S3, S4 and S6 are disconnected, S1 is always on, and S5 is controlled by the PEM signal as the main control switch. At this time, the decoupling capacitor C d2 Energy is released and the voltage rises. When S5 is turned on, i d The flow path is C d2+ →L d →U inv →S5→D6→C d2- , when S5 is disconnected, i d The flow path is U inv- →S1→D2→L d →U inv+ .

[0085] In each working mode, only one switch is in the On / Off state, which is the main switch. Its driving signal is generated by PEM, and the states of the other switches are fixed. The main switches S1, S2, S4, S5 and S6 are controlled by R1, R2 and PEM, and their logical relationship is shown in formula (1):

[0086]

[0087] In the formula, R1 represents the sign of the grid voltage. In the positive half cycle, R1 = 0, and in the negative half cycle, R1 = 1. R1 = sgn (-u o ) represents; R2 represents the sign of the micro-inverter decoupling power. When the decoupling power is positive, R2 = 1; when the decoupling power is negative, R2 = 0. R2 = sgn[-P pv cos(2ωt)], where sgn is the sign function and ω is the angular frequency.

[0088] The embodiment of the present invention establishes a control circuit for controlling six switch tubes as follows: Fig.10 As shown, the MATLAB simulation diagram of the PEM signal generation circuit is as follows Fig.11As shown in the figure, the MATLAB simulation diagram of the power decoupling circuit composed of six switch tubes is as follows Fig.12 shown. Fig.13 The driving signal shown is the driving signal of the six-switch power decoupling circuit used in the embodiment of the present invention. The experiment was conducted based on simulation. The main circuit of the experiment was a two-stage micro-inverter, and the power supply was a 1500W regulated DC power supply. The voltage-stabilizing large electrolytic capacitor of the front-stage Boost circuit in the two-stage micro-inverter replaced the 10μF film capacitor. When the decoupling capacitor is not connected, the experimental waveform can be obtained as shown below. Fig.14 As shown in the figure, the input voltage of the Boost in this experiment is 30V. When the decoupling circuit is not connected, it can be seen that there is a secondary ripple with obvious jitter at both ends of the film capacitor of the output measurement of the Boost circuit, and the pulsation amplitude of the secondary ripple is about 20V. It can be seen that the waveform has obvious distortion on the output side of the H bridge. When the decoupling circuit is connected, the experimental effect that can be achieved is as follows Fig.15 As shown in the figure, it can be seen that there is a secondary ripple with obvious jitter at both ends of the film capacitor of the output measurement of the Boost circuit, and the pulsation amplitude of the secondary ripple is about 15V. It can be seen that the waveform has been significantly improved on the output side of the H bridge. The decoupling circuit obviously plays a role in reducing the capacitance of the Boost side capacitor.

[0089] The present invention discloses a novel electrolytic capacitor-free micro-inverter technology, the innovation of which is reflected in the topological structure of the power coupling circuit. The inverter part adopts the traditional voltage source topology, and the power coupling circuit is connected in parallel to the AC output end of the micro-inverter, replacing the electrolytic capacitor to realize the power coupling function and improve the efficiency of the micro-inverter. Since the input power on the DC side is constant, and the AC output power is sinusoidally changed, there is an inconsistency between the instantaneous values ​​of the two. The power coupling circuit plays the role of energy buffering. Therefore, the micro-inverter circuit of the present invention has the following advantages and innovations:

[0090] 1. A power decoupling circuit is connected to the AC output side of the micro-inverter to perform energy buffering, greatly reduce the coupling capacitance value, improve the performance and life of the micro-inverter, and realize an electrolytic capacitor-free micro-inverter.

[0091] 2. Closed-loop control of the entire system is performed by adjusting the bus voltage U dc and bus current I dc The measurement time controls the switch duty cycle of the previous Boost circuit, and the grid voltage U ac , micro-inverter AC side output voltage U inv and the decoupling capacitor voltage U d The duty cycle of the four-switch H-bridge is controlled at the measurement time to control the grid voltage waveform and reduce the secondary disturbance power.

[0092] 3. A six-switch power decoupling circuit is connected in parallel on the AC output side of the micro-inverter, which is equivalent to an active power filter to balance the pulsating energy, thereby suppressing the secondary disturbance power in the micro-inverter and greatly reducing the coupling capacitance value by using the high voltage on the AC side.

[0093] 4. Pulse modulation technology PEM is used to control the six-switch power coupling circuit in DCM mode, with simple structure and convenient control.

[0094] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0095] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A six-switch power decoupling circuit, characterized in that: include: A first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, a fifth switch tube S5, a sixth switch tube S6, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, a first capacitor C d1 , the second capacitor C d2 And the inductor L d ; The collector of the first switch tube S1, the collector of the third switch tube S3 and the collector of the fifth switch tube S5 are all connected to one end of the AC output side of the micro-inverter; The emitter of the first switch tube S1 is connected to the emitter of the second switch tube S2; the first switch tube S1 is connected in reverse parallel to the first diode D1; the second switch tube S2 is connected in reverse parallel to the second diode D2; The emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the collector of the fourth switch tube S4 is connected to the first capacitor C d1 The third switch tube S3 is connected to the third diode D3 in reverse parallel; the fourth switch tube S4 is connected to the fourth diode D4 in reverse parallel; The emitter of the fifth switch tube S5 is connected to the emitter of the sixth switch tube S6; the collector of the sixth switch tube S6 is connected to the second capacitor C d2 The fifth switch tube S5 is connected in reverse parallel to the fifth diode D5; the sixth switch tube S6 is connected in reverse parallel to the sixth diode D6; The collector of the second switch tube S2 and the first capacitor C d1 The other end of the second capacitor C d2 The other end of the inductor L d One end of the inductor L d The other end is connected to the other end of the AC output side of the micro-inverter.

2. The six-switch power decoupling circuit according to claim 1, characterized in that: The reverse parallel connection is that the emitter of the switch tube is connected to the positive electrode of the diode, and the collector of the switch tube is connected to the negative electrode of the diode.

3. The six-switch power decoupling circuit according to claim 1, characterized in that: The inductance L d The other end is connected to the common ground end of the AC output side of the micro-inverter and the grid voltage.

4. The six-switch power decoupling circuit according to claim 1, characterized in that: The first capacitor C d1 and the second capacitor C d2 Both are decoupling capacitors.

5. A control method for a six-switch power decoupling circuit, characterized in that: The six-switch power decoupling circuit includes: a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, a fifth switch tube S5, a sixth switch tube S6, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, a first capacitor C d1 , the second capacitor C d2 And the inductor L d The collector of the first switch tube S1, the collector of the third switch tube S3 and the collector of the fifth switch tube S5 are all connected to one end of the AC output side of the micro-inverter; the emitter of the first switch tube S1 is connected to the emitter of the second switch tube S2; the first switch tube S1 is connected in reverse parallel to the first diode D1; the second switch tube S2 is connected in reverse parallel to the second diode D2; the emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the collector of the fourth switch tube S4 is connected to the first capacitor C d1 The third switch tube S3 is connected to the third diode D3 in reverse parallel; the fourth switch tube S4 is connected to the fourth diode D4 in reverse parallel; the emitter of the fifth switch tube S5 is connected to the emitter of the sixth switch tube S6; the collector of the sixth switch tube S6 is connected to the second capacitor C d2 The fifth switch tube S5 is connected in reverse parallel to the fifth diode D5; the sixth switch tube S6 is connected in reverse parallel to the sixth diode D6; the collector of the second switch tube S2, the first capacitor C d1 The other end of the second capacitor C d2 The other end of the inductor L d One end of the inductor L d The other end of the micro-inverter is connected to the other end of the AC output side of the micro-inverter; The control method comprises: Obtaining an output voltage at an AC output side of the micro-inverter and a decoupling current of the six-switch power decoupling circuit; Determine whether the output voltage of the AC output side of the micro-inverter is greater than 0, and obtain a first determination result; If the first judgment result is that the output voltage at the AC output side of the micro-inverter is greater than 0, determining whether the decoupling current is in the same direction as the output voltage to obtain a second judgment result; If the second judgment result is that the decoupling current and the output voltage are in the same direction, controlling the six-switch power decoupling circuit to operate in the first operating mode to absorb energy; If the second judgment result is that the decoupling current is in opposite directions to the output voltage, controlling the six-switch power decoupling circuit to operate in a second operating mode to release energy; If the first judgment result is that the output voltage at the AC output side of the micro-inverter is less than 0, judging whether the decoupling current is in the same direction as the output voltage, and obtaining a third judgment result; If the third judgment result is that the decoupling current and the output voltage are in the same direction, controlling the six-switch power decoupling circuit to operate in a third operating mode to absorb energy; If the third judgment result is that the decoupling current is in opposite directions to the output voltage, the six-switch power decoupling circuit is controlled to operate in a fourth operating mode to release energy.

6. The control method of the six-switch power decoupling circuit according to claim 5, characterized in that: The controlling the six-switch power decoupling circuit to operate in the first operating mode to absorb energy specifically includes: The second switch tube S2, the fourth switch tube S4, the fifth switch tube S5 and the sixth switch tube S6 are all turned off, the third switch tube S3 is turned on, and the first switch tube S1 is used as a main control switch and is controlled by a pulse energy modulation PEM signal; at this time, the first capacitor C d1 Absorb energy.

7. The control method of the six-switch power decoupling circuit according to claim 5, characterized in that: Controlling the six-switch power decoupling circuit to operate in the second operating mode to release energy specifically includes: The first switch tube S1, the third switch tube S3, the fifth switch tube S5 and the sixth switch tube S6 are all turned off, the second switch tube S2 is turned on, and the fourth switch tube S4 is used as a main control switch and is controlled by the PEM signal; at this time, the first capacitor C d1 Release energy.

8. The control method of the six-switch power decoupling circuit according to claim 5, characterized in that: The control of the six-switch power decoupling circuit to work in the third working mode to absorb energy specifically includes: the first switch tube S1, the third switch tube S3, the fourth switch tube S4 and the fifth switch tube S5 are all turned off, the sixth switch tube S6 is turned on, and the second switch tube S2 is used as a main control switch and is controlled by the PEM signal; at this time, the second capacitor C d2 Absorb energy.

9. The control method of the six-switch power decoupling circuit according to claim 5, characterized in that: The control of the six-switch power decoupling circuit to work in the fourth working mode to release energy specifically includes: the second switch tube S2, the third switch tube S3, the fourth switch tube S4 and the sixth switch tube S6 are all turned off, the first switch tube S1 is turned on, and the fifth switch tube S5 is used as a main control switch and is controlled by the PEM signal; at this time, the second capacitor C d2 Release energy.

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