CN100433525C - Soft switch back exciting converter used for solar energy photovoltaic generation incorporate in power network - Google Patents

Abstract

A soft-switching flyback inverter for solar photovoltaic grid-connected power generation, which belongs to the technical field of solar photovoltaic grid-connected power generation, and solves the problem that existing inverters for solar photovoltaic grid-connected power generation cannot improve switching losses at the same time and power decoupling issues. The DC voltage (v _s ) input by the photovoltaic array (PV) of the solar panel is applied to both ends of the input capacitor (C1), and one end of the input capacitor (C1) is connected to one end of the second inductor (L1), and the second inductor (L1) The other end of the first capacitor (C2) is connected to the collector of the fourth controllable switch (S1) and the first capacitor (C2), and the other end of the first capacitor (C2) is connected to the positive terminal of the third diode (D1) and the third The emitter and other terminals of the controllable switch tube (S2). The inverter of the invention can realize soft switching operation of all switches, thereby reducing switching loss and improving system efficiency; it can significantly reduce the volume and capacity of decoupling capacitors, thereby improving power decoupling.

Description

A soft-switching flyback inverter for solar photovoltaic grid-connected power generation

technical field

The invention belongs to the technical field of solar photovoltaic grid-connected power generation, and specifically relates to a soft-switching flyback inverter that can be used for solar photovoltaic (Photovoltaic, PV) grid-connected power generation.

Background technique

With the growth of traditional energy consumption, the deteriorating ecological environment and the requirement of sustainable human development, all countries in the world are actively developing non-polluting and renewable new energy. Solar energy resources are abundant, widely distributed, renewable, and do not pollute the environment, making solar photovoltaic power generation the mainstream of new energy development. The photovoltaic inverter is the core part of the photovoltaic power generation system, and its efficiency and reliability will directly affect the performance and investment of the entire photovoltaic system. In a traditional photovoltaic power generation system, multiple groups of photoelectric modules form a PV array to obtain a high enough direct current (DC) bus voltage, and then generate an alternating current (AC) voltage through an inverter and incorporate it into the grid. However, due to the change of solar radiation intensity and the shading of obstacles such as nearby buildings and trees, the total output power of the PV array will change significantly. In order to make the photovoltaic system always work at the maximum power point, the concept of AC module is proposed. In this AC module system, each group of photovoltaic modules is equipped with an inverter to form an AC module, and the outputs of these AC modules are connected in parallel and then connected to the grid. This kind of AC module inverter completes functions such as boosting voltage, maximum power point tracking (MPPT) and inverter for each photovoltaic module. Many inverter topologies and corresponding control strategies for photovoltaic grid-connected power generation have been reported, among which Buck-Boost inverter and flyback inverter are typical and have been greatly developed. The Buck-Boost inverter uses four or five switches to achieve boost and inversion, and the flyback inverter uses three switches. Although they can achieve inversion and electrical isolation, both structures use high-frequency switches In this way, a large amount of switching loss is generated, which reduces the system efficiency. For example, as shown in Figure 1, the traditional flyback inverter only uses three switches, and uses a three-winding transformer as energy storage and isolation components. The waveform of the output current is controlled by the switch _S1 , and the switches _S2 and _S3 To control the polarity of the output current, the disadvantage of this inverter is that S ₁ is hard switched at high frequency, and the loss is very large, which limits its practical application, and a large electrolytic capacitor is connected in parallel on the DC input side, which increases the volume of the entire device , shortening the service life of the system. As shown in Figure 2, it is a flyback grid-connected inverter suitable for AC modules. It adds a smoothing circuit to the circuit of the traditional flyback inverter to transfer the power ripple to the small-capacity inverter. On the non-electrolytic capacitor C, and the capacity of the smoothing capacitor on the DC side is greatly reduced, which prolongs the life of the system. Although the addition of the smoothing circuit improves the power decoupling, the two high-frequency switches on the input side are hard turned off. Its switching loss is larger than that of the traditional flyback inverter, and the efficiency of the system is also greatly reduced. As shown in Figure 3, a soft-switching inverter topology based on a high-frequency flyback converter has lower system losses and higher efficiency; but its structure cannot improve power decoupling, and the DC side still needs to be connected in parallel Large-capacity electrolytic capacitors limit their service life. In summary, so far there is no topology that achieves both soft switching and improved power decoupling, two functions that are clearly crucial for single-phase PV inverters. Therefore, there is an urgent need for a new type of inverter that, in addition to realizing inversion and electrical isolation, should also have the following two functions: reducing switching losses and improving power decoupling.

Contents of the invention

In order to solve the problem that the existing inverters for solar photovoltaic grid-connected power generation cannot simultaneously improve switching loss and power decoupling, the present invention provides a soft-switching flyback inverter for solar photovoltaic grid-connected power generation.

The soft-switching flyback inverter of the present invention includes a switch tube drive circuit 1, a solar panel photovoltaic array PV, a flyback transformer T, a first controllable switch tube S3, a second controllable switch tube S4, and a third controllable switch tube. Tube S2, the first diode D3, the second diode D4, the output capacitor C3 and the first inductance L _f , the photovoltaic array PV of the solar panel is located on the same side of the primary winding L2 of the flyback transformer T, and the flyback transformer The non-identical terminal of the first winding L3 on the secondary side of T is connected to the collector of the first controllable switching transistor S3, and the emitter of the first controllable switching transistor S3 is connected to the positive terminal of the first diode D3, and the first diode The negative end of D3 is connected to one end of the first inductor _Lf , one end of the output capacitor C3 and the positive end of the second diode D4, and the negative end of the second diode D4 is connected to the collector of the second controllable switch transistor S4, The emitter of the second controllable switch tube S4 is connected to the same-named end of the secondary winding L4 of the flyback transformer T, and the non-identical end of the secondary winding L4 of the flyback transformer T is connected to the second secondary winding L4 of the flyback transformer T. The terminal with the same name of a winding L3 and the other terminal of the output capacitor C3; the soft-switching flyback inverter also includes an input capacitor C1, a second inductor L1, a first capacitor C2, a second capacitor C _s1 , and a third capacitor C _s2 , the fourth controllable switch tube S1, the third diode D1 and the fourth diode D2, the DC voltage V _s input by the photovoltaic array PV of the solar panel is applied to both ends of the input capacitor C1, and one end of the input capacitor C1 is connected to One end of the second inductor L1, the other end of the second inductor L1 is connected to the collector of the fourth controllable switch S1 and one end of the first capacitor C2, and the other end of the first capacitor C2 is connected to the positive end of the third diode D1 , the emitter of the third controllable switch tube S2, one end of the second capacitor C _s1 and one end of the third capacitor C _s2 , the collector of the third controllable switch tube S2 is connected to the negative end of the fourth diode D2 and the first The other end of the third capacitor C _s2 , the positive end of the fourth diode D2 is connected to the non-identical end of the primary winding L2 of the flyback transformer T and the other end of the second capacitor C _s1 , and the primary winding L2 of the flyback transformer T The end with the same name of the third diode D1 is connected to the negative end of the third diode D1, the emitter of the fourth controllable switch tube S1 and the other end of the input capacitor C1, and the output terminals of the four drive signals of the switch tube drive circuit 1 are respectively connected to the first The gates of the first controllable switch tube S3, the second controllable switch tube S4, the third controllable switch tube S2, and the fourth controllable switch tube S1, the output capacitor C3 and the other end of the first inductor L _f output an AC voltage v _oIntegrated into the grid. The first controllable switch tube S3, the second controllable switch tube S4, the third controllable switch tube S2, and the fourth controllable switch tube S1 adopt IGBT switch tubes, and the fourth controllable switch tube S1 and the third controllable switch tube S1 The switching tube S2 is a high-frequency switching tube, the switching frequency is in the range of 10K to 100KHZ, and switching tubes with reversed diodes can be used; the first controllable switching tube S3 and the second controllable switching tube S4 are power frequency switching tubes. The input capacitor C1 , the first capacitor C2 , one end of the second capacitor C _s1 and the third capacitor C _s2 are non-polar capacitors with a small capacity.

As shown in Fig. 4, the present invention organically combines a Sepic converter and a traditional flyback inverter to obtain a novel PV inverter with two functions of soft switching and improved power decoupling. As shown in Table 1 below and Figures 5 to 10, according to the operating status of the four switching tubes (S1, S2, S3, S4) and the positive and negative conditions of the output current, the circuit has the following six effective working modes.

Table 1 Comparison of six working modes

Way S1 S2 S3 S4 i_L2 i_L3 i_L4 i_C2 i₂ i_o 1 1 1 0 0 x 0 0 i_L2 0 x 2 1 0 1 0 0 x 0 0 i_L3 + 3 1 0 0 1 0 0 × 0 i_L4 - 4 0 0 1 0 0 x 0 i_L2 i_L3 + 5 0 0 0 1 0 0 x i_L1 i_L4 - 6 0 0 0 0 0 0 0 i_L1 0 x

(In the above table, "1" means conduction, "0" means the switch tube is turned off or the current is zero, "×" means invalid, "+" means the current is greater than zero, and "-" means the current is less than zero.)

Mode 1: As shown in Figure 5, in this mode, the fourth controllable switch tube S1 and the third controllable switch tube S2 are turned on, and the first controllable switch tube S3 and the second controllable switch tube S4 are turned off. Due to the input voltage v _s Directly added to the second inductor L1, the input current i ₁ increases linearly, and the voltage v _C2 on the first capacitor C2 also charges the primary winding L2 of the flyback transformer T, so that the current i L1 flowing through _L2 also increases linearly.

Mode 2: As shown in Figure 6, S1 and S3 are turned on, and S2 and S4 are turned off. Since S1 is still turned on, the input current i ₁ still increases linearly, and S2 is turned off, so that the currents i C2 and i L2 flowing through _C2 and _L2 is 0. In this process, S3 is turned on and S4 is turned off, so the output current i _o is greater than 0.

Mode 3: As shown in Figure 7, S1 and S4 are turned on, and S2 and S3 are turned off. This process is similar to Mode 2. The difference is that the output current i _o is less than 0.

Mode 4: As shown in Figure 8, S1, S2 and S4 are all off, only S3 is on, the input voltage and inductance L1 are charging the capacitor C2, and the output current i _o is greater than 0 because the switch S3 is on.

Mode 5: As shown in Figure 9, the switches S1, S2, and S3 are all turned off, and only S4 is turned on. The input voltage v _s and L1 both charge C2. At the same time, because S4 is turned on, the output current i _o is less than 0.

Mode 6: As shown in Figure 10, all four switches are turned off. Same as Mode 4 and Mode 5, the input voltage V _s and L1 both charge C2, and the output capacitor C3 supplies current to the grid.

For the single-phase inverter proposed by the present invention, when working at unity power factor, its AC side voltage and current can be expressed as follows:

v _o ＝V _o sinω _o t (1)

i _o ＝I _o sinω _o t (2)

Therefore, there are a large number of power ripples in the circuit as:

P _o ＝V _o I _o (1-cos2ω _o t)(3)

In the above formula, ω _o is the frequency of the AC voltage, V _o is the amplitude of the AC side voltage, and I _o is the amplitude of the AC side current.

In order to make the output current sinusoidal, the peak current envelope flowing through L2 must be a sinusoidal waveform. It can be known from the above formula that in the inverter of the present invention, the power contains low-frequency (double frequency) components, and this fluctuating component is transferred to the first capacitor C2, so that the voltage on the DC input capacitor C1 remains unchanged, and Can make the capacity of C1 a very small value. Since the voltage on C2 fluctuates at a frequency twice the power frequency at a certain DC bias, this makes the duty cycle of the PWM signal driving the third controllable switch S2 have a nonlinear relationship with the current flowing through L2 , so the present invention uses a peak current control method to control S2. The peak current control method refers to: as shown in Figure 12, the current i L2 flowing through _L2 is detected by the current sensor, when S2 is turned on, i _L2 increases, and when the current i _L2 increases to a sinusoidal reference value, the output is low The level driving signal makes S2 turn off, so that it can ensure that the current peak value of i _L2 always accurately tracks the sinusoidal reference value, thereby controlling the output current i _o to be a standard sinusoidal waveform. Of course, the present invention can also use other control schemes to control S2, such as by detecting the voltage on C2, obtaining the duty cycle of each switching cycle through calculation, and outputting drive pulses to complete the control of S2, but the realization is different from the peak value The current control scheme is relatively complex. The fourth controllable switch tube S1 controls the magnitude of the input current i _o , thereby determining the magnitude of the input energy. In order to track the maximum power of the PV cell, it is necessary to ensure a constant energy input, which requires S1 to work with a fixed duty cycle. Considering the effective working state of the circuit, S1 and S2 should be turned on at the same time, and the duty cycle of the S2 conduction signal must be smaller than the duty cycle of the S1 conduction signal. The first controllable switch tube S3 and the second controllable switch tube S4 control the polarity of the output current i _o , and the two are turned on and off alternately in the positive and negative half cycles of the power frequency, so as to obtain the output current in both positive and negative directions i _o .

In the structure of the present invention, the soft switching operation of the high-frequency switches S1 and S2 depends on the parasitic capacitance on the third controllable switch tube S2 and the fourth diode D2 and the introduced second capacitance C _s1 and the third capacitance C _s2 to achieve (as shown in Figure 4). As shown in Figure 11, the voltage and current waveforms on S1 and S2 are given. S1 and S2 are turned on at the same time, and the current on them increases linearly from 0, so both switches are soft-on with zero current (ZCS). When S2 is turned off, the current on L2 does not immediately flow to the secondary side, but first flows through C _s1 and C _s2 until there is current on the secondary side, thus realizing zero-voltage (ZVS) shutdown of S2 . And when S1 is turned off, the input current does not flow through diode D1 immediately, but discharges C _s1 first until D1 is turned on, so that the zero-voltage turn-off of S1 is realized. In addition, the switch tubes S3 and S4 work at power frequency, and the turn-on and turn-off processes of these two switches are also the same as the traditional flyback inverter, working in the soft switching state.

In summary, the improved power decoupling of the present invention is realized by the circuit structure itself, and it is precisely because the Sepic circuit transfers the power pulsation to the voltage on the capacitor C2 that the capacities of both capacitors C1 and C2 can be reduced; The soft switching characteristic of the present invention is because the second capacitor C _s1 and the third capacitor C _s2 are introduced into the circuit, so as to ensure that the two high-frequency switches can also realize soft switching when they are turned off. The peak current control scheme proposed by the present invention is applied to the circuit of the present invention in order to provide high-quality output current to the grid. With a suitable control scheme, better power decoupling and soft switching characteristics can be achieved. .

The inverter of the present invention has the following advantages: (1) its circuit structure is simple, and only four power switching devices are used; (2) it can realize the soft switching operation of all switches, thereby reducing switching losses and improving system efficiency ; (3) It can significantly reduce the volume and capacity of the decoupling capacitor by converting the power pulsation into the voltage pulsation on the capacitor C2, thereby improving the power decoupling; (4) The switch S1 works at a fixed duty cycle, Switch S2 adopts a peak current control scheme, switches S3 and S4 operate at power frequency, which is easy to control and realize; (5) It can realize electrical isolation of input and output through a flyback transformer; (6) It can provide unit power to the grid and Low harmonic output current; (7) Harmonic suppression and reactive power compensation functions can be realized through appropriate control according to needs.

Description of drawings

Figure 1 is a traditional flyback inverter.

Fig. 2 is a flyback grid-connected inverter suitable for AC modules in the prior art.

FIG. 3 is a topological structure of a soft-switching inverter based on a high-frequency flyback converter in the prior art.

Fig. 4 is a structural schematic diagram of the PV soft-switching flyback inverter of the present invention.

Fig. 5 to Fig. 10 are the simple structure schematic diagrams of six effective working modes of the inverter of the present invention in turn, in the figure, i ₁ is the input current, i _L1 is the current flowing through the second inductance L1, and i _C2 is the current flowing through the second inductance L1 The current of a capacitor C2, v _c2 is the voltage on the first capacitor C2, i _L2 is the current flowing through the primary winding L2 of the flyback transformer T, and i _L3 is the current flowing through the secondary winding L3 of the flyback transformer T i _L4 is the current flowing through the second secondary winding L4 of the flyback transformer T, i ₂ is the secondary winding current of the flyback transformer T, and i _o is the output current.

Fig. 11 is a schematic diagram of conduction signal waveforms, voltage waveforms and current waveforms on the fourth controllable switch tube S1 and the third controllable switch tube S2. In the figure, v _S1 represents the voltage on the fourth controllable switch tube S1, i _S1 represents the current on the fourth controllable switch tube S1, v _S2 represents the voltage on the third controllable switch tube S2, v _cs1 represents the voltage across the second capacitor C _s1 , v _cs2 represents the voltage across the third capacitor C _s2 The voltage, i _S2 represents the current on the third controllable switch tube S2.

Fig. 12 is the working waveform of the inverter of the present invention.

Detailed ways

Referring to Fig. 4, the soft-switching flyback inverter in this specific embodiment consists of a switching tube drive circuit 1, a solar panel photovoltaic array PV, a flyback transformer T, a first controllable switching tube S3, and a second controllable switch Tube S4, third controllable switch tube S2, first diode D3, second diode D4, output capacitor C3, first inductance L _f , input capacitor C1, second inductance L1, first capacitor C2, second The second capacitor C _s1 , the third capacitor C _s2 , the fourth controllable switch tube S1, the third diode D1 and the fourth diode D2 are composed. The photovoltaic array PV of the solar panel is located in the primary winding L2 of the flyback transformer T On the same side of the flyback transformer T, the non-identical end of the first secondary winding L3 of the flyback transformer T is connected to the collector of the first controllable switch S3, and the emitter of the first controllable switch S3 is connected to the positive electrode of the first diode D3. terminal, the negative terminal of the first diode D3 is connected to one terminal of the first inductance L _f , one terminal of the output capacitor C3 and the positive terminal of the second diode D4, and the negative terminal of the second diode D4 is connected to the second controllable The collector of the switching tube S4 and the emitter of the second controllable switching tube S4 are connected to the terminal with the same name of the second secondary winding L4 of the flyback transformer T, and the non-identical terminal of the second secondary winding L4 of the flyback transformer T is connected to the reverse The terminal with the same name of the first winding L3 on the secondary side of the excitation transformer T and the other terminal of the output capacitor C3; the DC voltage V _s input by the photovoltaic array PV of the solar panel is applied to both ends of the input capacitor C1, and one end of the input capacitor C1 is connected to the second One end of the inductor L1, the other end of the second inductor L1 is connected to the collector of the fourth controllable switch transistor S1 and one end of the first capacitor C2, and the other end of the first capacitor C2 is connected to the positive end of the third diode D1, the second The emitter of three controllable switch tubes S2, one end of the second capacitor C _s1 and one end of the third capacitor C _s2 , the collector of the third controllable switch tube S2 is connected to the negative terminal of the fourth diode D2 and the third capacitor The other end of C _s2 , the positive end of the fourth diode D2 is connected to the non-identical end of the primary winding L2 of the flyback transformer T and the other end of the second capacitor C _s1 , the same name of the primary winding L2 of the flyback transformer T connected to the negative end of the third diode D1, the emitter of the fourth controllable switch tube S1 and the other end of the input capacitor C1, and the output terminals of the four drive signals of the switch tube drive circuit 1 are connected to the first controllable switch tube S1 respectively. The gates of the controllable switch tube S3, the second controllable switch tube S4, the third controllable switch tube S2, and the fourth controllable switch tube S1, the output capacitor C3 and the other end of the first inductor Lf output an AC voltage v _o into the power grid. The fourth controllable switch tube S1 and the third controllable switch tube S2 are high-frequency IGBT switch tubes, and the switching frequency is in the range of 10K to 100KHZ; the first controllable switch tube S3 and the second controllable switch tube S4 are power frequency IGBT turning tube. The input capacitor C1 and the first capacitor C2 are non-polar capacitors. The transformation ratio of the flyback transformer T is 1:n:n (n>1).

The drive signal waveforms of the four switches (S1, S2, S3, S4) shown in Figure 12, the first controllable switch tube S3 and the second controllable switch tube S4 complement each other in the positive and negative half cycles of power frequency; The turn-off of the control switch tube S2 is controlled by the peak current control method based on the current sine wave envelope flowing through the primary winding L2 of the flyback transformer T; the fourth controllable switch tube S1 operates at a high frequency with a fixed duty cycle , the duty cycle of the conduction signal of the fourth controllable switch S1 is always greater than the duty cycle of the conduction signal of the third controllable switch S2, and the fourth controllable switch S1 and the third controllable switch S2 are simultaneously turned on .

Claims (6)

1. A soft-switching flyback inverter for solar photovoltaic grid-connected power generation. The soft-switching flyback inverter includes a switching tube drive circuit (1), a solar panel photovoltaic array (PV), and a flyback transformer (T), the first controllable switch tube (S3), the second controllable switch tube (S4), the third controllable switch tube (S2), the first diode (D3), the second diode (D4 ), the output capacitor (C3) and the first inductor (L _f ), the solar panel photovoltaic array (PV) is located on the same side of the primary winding (L2) of the flyback transformer (T), and the secondary winding (L2) of the flyback transformer (T) The non-identical end of the first winding (L3) is connected to the collector of the first controllable switch (S3), and the emitter of the first controllable switch (S3) is connected to the positive terminal of the first diode (D3), The negative terminal of the first diode (D3) is connected to one terminal of the first inductor (L _f ), one terminal of the output capacitor (C3) and the positive terminal of the second diode (D4), and the second diode (D4) The negative terminal of the second controllable switch tube (S4) is connected to the collector of the second controllable switch tube (S4), and the emitter of the second controllable switch tube (S4) is connected to the terminal with the same name of the secondary winding (L4) of the flyback transformer (T). The non-identical end of the secondary winding (L4) of the excitation transformer (T) is connected to the end of the same name of the secondary winding (L3) of the flyback transformer (T) and the other end of the output capacitor (C3); it is characterized in that The soft-switching flyback inverter further includes an input capacitor (C1), a second inductor (L1), a first capacitor (C2), a second capacitor (C _s1 ), a third capacitor (C _s2 ), a fourth optional Control the switch (S1), the third diode (D1) and the fourth diode (D2), the DC voltage (v _s ) input by the photovoltaic array (PV) of the solar panel is applied to the two sides of the input capacitor (C1) One end of the input capacitor (C1) is connected to one end of the second inductor (L1), and the other end of the second inductor (L1) is connected to the collector of the fourth controllable switch (S1) and one end of the first capacitor (C2) , the other end of the first capacitor (C2) is connected to the positive end of the third diode (D1), the emitter of the third controllable switch (S2), one end of the second capacitor (C _s1 ) and the third capacitor ( One end of C _s2 ), the collector of the third controllable switch (S2) is connected to the negative end of the fourth diode (D2) and the other end of the third capacitor (C _s2 ), the fourth diode (D2) The positive terminal of the flyback transformer (T) is connected to the non-identical terminal of the primary winding (L2) of the flyback transformer (T) and the other terminal of the second capacitor (C _s1 ), and the terminal of the same name of the primary winding (L2) of the flyback transformer (T) is connected to The negative terminal of the third diode (D1), the emitter of the fourth controllable switch tube (S1) and the other end of the input capacitor (C1), the output terminals of the four drive signals of the switch tube drive circuit (1) are respectively Connect the gates of the first controllable switch tube (S3), the second controllable switch tube (S4), the third controllable switch tube (S2), and the fourth controllable switch tube (S1), the output capacitor (C3 ) and the other end of the first inductance (L _f ) output an AC voltage (v _o ) into the power grid. 2. A soft-switching flyback inverter for solar photovoltaic grid-connected power generation according to claim 1, characterized in that the fourth controllable switching tube (S1) and the third controllable switching tube (S2) are High-frequency switching tube, the switching frequency is in the range of 10K to 100KHZ. 3. A soft-switching flyback inverter for solar photovoltaic grid-connected power generation according to claim 1, characterized in that the first controllable switch tube (S3) and the second controllable switch tube (S4) are Power frequency switching tube. 4. A soft-switching flyback inverter for solar photovoltaic grid-connected power generation according to claim 1, characterized in that the input capacitor (C1) and the first capacitor (C2) are non-polar capacitors. 5. A soft-switching flyback inverter for solar photovoltaic grid-connected power generation according to claim 1, 2, 3 or 4, characterized in that the first controllable switching tube (S3) and the second controllable The switching tube (S4) works complementary to the positive and negative half cycles of the power frequency; the third controllable switching tube (S2) is turned off according to the current sine wave envelope that flows through the primary winding (L2) of the flyback transformer (T) The peak current control method is used for control; the fourth controllable switch tube (S1) operates at a high frequency with a fixed duty cycle, and the duty cycle of the turn-on signal of the fourth controllable switch tube (S1) is always greater than that of the third controllable switch tube The duty cycle of the conduction signal of the tube (S2), and the fourth controllable switch tube (S1) and the third controllable switch tube (S2) are simultaneously turned on. 6. A soft-switching flyback inverter for solar photovoltaic grid-connected power generation according to claim 5, characterized in that the first controllable switching tube (S3), the second controllable switching tube (S4 ), the third controllable switch tube (S2), and the fourth controllable switch tube (S1) adopt IGBT switch tubes.

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