CN110611451A - A photovoltaic inverter based on gallium nitride device and its control method - Google Patents

Abstract

The invention discloses a photovoltaic inverter based on gallium nitride devices and a control method thereof, including a first-stage converter for converting low-voltage direct current generated by photovoltaic cells into high-voltage direct current, and for converting the high-voltage direct current The second-stage converter converted into a sine wave; including an anti-reverse diode, a low-voltage DC filter capacitor, a low-voltage full-bridge inverter circuit, a resonant circuit, a high-frequency transformer, a voltage doubler rectifier circuit, a high-voltage DC filter capacitor, and a high-voltage full-bridge inverter Transformer circuit and output filter; each part of the whole machine has the advantages of high voltage gain, low loss and high power density after optimized design.

Description

A photovoltaic inverter based on gallium nitride device and its control method

technical field

The invention relates to the technical field of photovoltaic power generation, in particular to a photovoltaic inverter based on gallium nitride devices and a control method thereof.

Background technique

Photovoltaic power generation technology is a new energy technology that converts light energy into electrical energy. The photovoltaic inverter converts the direct current output from the photovoltaic panel into alternating current and sends the electric energy into the alternating current grid. According to the capacity, photovoltaic inverters can be divided into centralized photovoltaic inverters, string photovoltaic inverters, and micro photovoltaic inverters. Among them, microinverters have attracted much attention because of their advantages in maximum power tracking efficiency, flexibility, and reliability. The research and development of micro grid-connected photovoltaic inverters with high efficiency and high power density has huge market value and good development prospects. Due to the increase of circuit operating frequency, technicians can use smaller inductors, transformers and other components in power electronic converters, thereby reducing the size of the whole machine and improving power density; therefore, the use of faster semiconductor switching devices has become a trend.

At present, micro photovoltaic inverters mainly use silicon-based semiconductor devices. However, the performance of silicon-based semiconductor devices is gradually approaching the theoretical limit of silicon materials, and the speed of replacement continues to slow down, making it difficult to further improve the performance of the inverter. How to provide an inverter to improve the performance of the whole machine, optimize circuit topology, improve efficiency and reduce cost.

The basic requirement of photovoltaic inverters is long-term stable grid-connected operation. Generally, the service life of micro photovoltaic inverters is required to reach 20 to 25 years. The electrolytic capacitor in the main circuit is the bottleneck of the life of all power electronic converters. The long-life design must reduce or avoid the use of electrolytic capacitors. Therefore, it is necessary to research and develop power conversion technologies without electrolytic capacitors.

Contents of the invention

The object of the present invention is to provide a photovoltaic inverter based on gallium nitride devices and its control method, so as to solve the above-mentioned defects or one of the defects in the prior art.

In order to achieve the above object, the present invention is achieved by adopting the following technical solutions:

A photovoltaic inverter based on gallium nitride devices, including a first-stage converter for converting low-voltage direct current generated by photovoltaic cells into high-voltage direct current, and a second stage for converting the high-voltage direct current into a sine wave converter;

The first-stage converter includes a low-voltage DC filter capacitor C ₁ , a low-voltage full-bridge inverter circuit, a resonant circuit, a high-frequency transformer T ₁ and a voltage doubler rectifier circuit, and the low-voltage DC filter capacitor C ₁ is connected to two terminals of the photovoltaic cell end; the DC side of the low-voltage full-bridge inverter circuit is connected to the low-voltage DC filter capacitor, and its AC side is connected to the resonant circuit and the primary winding of the high _- frequency transformer T1, and the secondary side _of the high-frequency transformer T1 The winding combination is connected to the input end of the voltage doubler rectifier circuit;

The second-stage converter includes a high-voltage filter capacitor _C4 and a high-voltage full-bridge inverter circuit, and the output terminal of the voltage doubler rectifier circuit is connected to the high-voltage DC filter capacitor _C4 and the DC side of the high-voltage full-bridge inverter circuit, so The AC side of the high-voltage full-bridge inverter circuit is connected to the power grid.

Further, an anti-reverse diode is also included, the anode of the anti-reverse diode is connected to the positive terminal of the photovoltaic cell, and its cathode and the negative terminal of the photovoltaic cell are respectively connected to both ends of the low-voltage DC filter capacitor _C1 .

Further, the resonant circuit includes a resonant capacitor C _r and a resonant inductance L _r .

Further, an output filter is also connected between the AC side of the full-bridge inverter circuit and the power grid.

Further, the high-frequency transformer T1 is _a step-up transformer.

Further, the low-voltage full-bridge inverter circuit includes four gallium nitride switches.

Further, the high-voltage filter capacitor _C4 is a film capacitor.

Further, the full-bridge inverter circuit includes a low-frequency bridge arm and a high-frequency bridge arm, the low-frequency bridge arm includes two silicon switches, and the high-frequency bridge arm includes two gallium nitride switches.

The present invention also provides a method for controlling a photovoltaic inverter based on gallium nitride devices, the method comprising:

Obtain the predicted value of the high-voltage DC bus voltage in the next cycle according to the instantaneous value of the high-voltage DC bus voltage collected in the current period;

Obtain the voltage gain ratio K of the first-stage converter in the next cycle according to the predicted value of the high-voltage DC bus in the next cycle;

Obtain the equivalent load resistance R of the first-stage converter;

According to the voltage gain ratio K and the equivalent load resistance R of the next cycle, obtain the switching frequency f ₁ of the first stage converter in the next cycle;

According to the switching frequency f ₁ , a driving signal of a switch of the low-voltage full-bridge inverter circuit is obtained.

Further, the method also includes:

Obtain the reference value U _dcref of the instantaneous value of the low-voltage DC bus voltage;

Obtain the amplitude I _{acref of the reference value of the output current of the photovoltaic inverter according to the reference value U dcref ;}

Obtain the phase factor sinθ of the grid voltage according to the instantaneous value u _ac of the grid voltage;

According to the phase factor sinθ of the grid voltage and the amplitude I _acref of the reference value of the output current of the photovoltaic inverter, the reference value i _acref of the output current of the photovoltaic inverter is obtained;

Obtain the modulation ratio d of the output voltage of the photovoltaic inverter according to the reference value i _acref of the output current;

According to the modulation ratio d, the driving signals of two switches in the high-voltage full-bridge inverter circuit are obtained;

According to the instantaneous value u _ac of the grid voltage, the drive signals of the other two switches of the high-voltage full-bridge inverter circuit are obtained.

According to the above technical solution, embodiments of the present invention at least have the following effects:

1. The present invention designs the LLC resonant soft switching circuit usually used in the step-down circuit as a boost mode, and combines it with a voltage doubler rectifier circuit to achieve the effect of further improving the boost ratio, especially suitable for photovoltaic cells in micro photovoltaic inverters Applications where the terminal voltage is low and the grid-connected inverter requires a high DC bus voltage; at the same time, due to the use of new GaN switching devices, the circuit can work at high frequencies, and the LLC resonance realizes zero-voltage turn-on (ZVS), making the circuit response Fast, the ripple of voltage and current is reduced, so the volume of the main components of the circuit such as inductors, capacitors, and transformers can be reduced, thereby greatly improving power density and reducing losses.

2. The present invention uses a silicon switch controlled by power frequency and a gallium nitride switch modulated by high frequency in the two bridge arms of the full-bridge inverter circuit, and fully utilizes the advantages of the two switching devices, which not only meets the quality requirements of the grid-connected current waveform, Loss and cost are reduced as much as possible.

3. The power decoupling control method using power feedforward and voltage feedback control proposed by the present invention predicts the fluctuation of the high-voltage DC bus voltage by introducing power feedforward, and adjusts the operating frequency to control the first The voltage gain K of the first-stage DC-DC converter fluctuates with the AC power; since the output voltage of the first-stage DC-DC converter actively adapts to the voltage fluctuation caused by power fluctuations on the high-voltage DC bus, the voltage of the low-voltage DC bus can maintain a basic Stablize. As a result, on the one hand, due to the small voltage ripple of the low-voltage DC bus, it is beneficial for the photovoltaic cell to maintain the maximum power generation, and at the same time reduce the capacity of the low-voltage filter capacitor _C1 ; on the other hand, this control method allows the high-voltage DC bus There is no need to use a high-voltage electrolytic capacitor with a large capacity but a short life to control the voltage ripple, so a small-capacity high-reliability film capacitor can be used to greatly extend the life of the whole machine.

Description of drawings

Fig. 1 is the circuit structure diagram of the inverter of the specific embodiment of the present invention;

Fig. 2 is a schematic diagram of analysis of power and voltage fluctuations in various parts of the inverter according to the specific embodiment of the present invention;

3 is a flowchart of a first-stage DC-DC circuit control method in a specific embodiment of the present invention;

4 is a block diagram of a second-stage DC-AC circuit control method in a specific embodiment of the present invention;

Fig. 5 is the flowchart of the perturbation observation method that adopts in the specific embodiment of the present invention;

Fig. 6 is a schematic diagram of the relationship curve of KF _x in a specific embodiment of the present invention.

Detailed ways

In order to make the technical means, creative features, goals and effects achieved by the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

A high-efficiency, high-power-density, high-reliability two-stage soft-switching micro-photovoltaic inverter composed of gallium nitride devices; The first-stage soft-switching DC-DC converter with switching frequency reduces the size and improves the efficiency of the whole machine. In the second-stage DC-AC converter, a single-phase full-bridge inverter circuit with a mixture of low-frequency bridge arms and high-frequency bridge arms is used. The low-frequency bridge arms use conventional silicon-based semiconductor switching devices, while the high-frequency bridge arms use nitrided Gallium switching devices, which reduce costs while meeting performance indicators; finally realize efficient power conversion from photovoltaic panels to single-phase AC grids.

As shown in Figure 1, a photovoltaic inverter based on gallium nitride devices provided by the present invention includes an anti-reverse diode, a low-voltage DC filter capacitor C ₁ , a low-voltage full-bridge inverter circuit, a resonant circuit, and a high-frequency transformer T _1. Voltage doubler rectifier circuit, high-voltage DC filter capacitor C ₄ , high-voltage full-bridge inverter circuit and output filter; the anode of the anti-reverse diode is connected to the positive terminal of the photovoltaic cell, and its cathode and the negative terminal of the photovoltaic cell are respectively connected to The two ends of the low-voltage DC filter capacitor C ₁ ; the four switches of the low-voltage full-bridge inverter circuit use gallium nitride switches Q ₁ ~ Q ₄ , the DC side of which is connected to the low-voltage DC filter capacitor C ₁ , and the AC side is connected to the resonant circuit and The primary windings of the high _- frequency transformer T1 are connected; the resonant circuit includes a resonant capacitor C _r and a resonant inductance L _r ; the two terminals _of the secondary winding of the high-frequency transformer T1 are respectively connected to two rectifier diodes D of the voltage doubler rectifier circuit ₁ , between D ₂ and between two capacitors C ₂ and C ₃ ; the output terminal of the voltage doubler rectifier circuit is connected to the high-voltage DC filter capacitor C ₄ and the DC side of the high-voltage full-bridge inverter circuit; the output filter includes an inductor L _f , capacitor C _f , and inductance L _f are connected in series between the AC side of the high-voltage full-bridge inverter circuit and the grid, while capacitor C _{f is} connected in parallel to the two terminals of the single-phase grid.

The first-stage soft-switching DC-DC converter in the photovoltaic inverter of the present invention is composed of a low-voltage DC filter capacitor C ₁ , a low-voltage full-bridge inverter circuit, a resonant circuit, a high-frequency transformer T ₁ and a voltage doubler rectifier circuit. Convert the low-voltage direct current output by the photovoltaic cell into high-voltage direct current, and make the input and output of the whole machine electrically isolated. The voltage and current stress of the low-voltage full-bridge inverter circuit is small, and the low-voltage gallium nitride switch is used, and Q ₁ , Q ₄ and Q ₂ , Q ₃ are divided into two groups, and two circuits with opposite phases and appropriate dead time are applied respectively. High-frequency square-wave control signal; the zero-voltage turn-on (ZVS) of Q ₁ ~ Q ₄ is realized through the resonant circuit, which effectively reduces the switching loss. Through magnetic integration technology, the leakage inductance of the primary side of the high-frequency transformer T ₁ is used to replace the resonant inductance L _r to reduce the volume of the whole machine; the ratio of primary and secondary turns of the high-frequency transformer T ₁ is 1:n, due to The circuit can double the rectified DC voltage, so the number of turns _of the secondary side of the transformer T1 can be appropriately reduced, which is conducive to the use of a smaller transformer core.

The second-stage soft-switching DC-AC converter in the photovoltaic inverter of the present invention is composed of a high-voltage DC filter capacitor C ₄ , a high-voltage full-bridge inverter circuit and an output filter. The high-voltage direct current output by the first-stage soft-switching DC-DC converter is converted into a sine wave through SPWM modulation control and output to the single-phase AC power grid. Since the current of the high-voltage DC bus is small, the required capacitor capacity is small, so the high-voltage DC filter capacitor C ₄ adopts a small-capacity film capacitor, and combined with appropriate control technology, it can absorb the double frequency caused by the single-phase inverter Power fluctuations prevent such fluctuations from being transmitted to the low-voltage DC bus of the first-stage DC-DC converter, thereby avoiding the use of large-capacity electrolytic capacitors (usually thousands to tens of thousands of uF) on the low-voltage side, effectively improving the life of the whole machine. The high-voltage full-bridge inverter circuit adopts switches with high withstand voltage, and the two switches Q ₅ and Q ₆ of the left bridge arm are silicon switches, which adopt power frequency control to reduce the switching loss of the inverter circuit. The two switches Q ₇ and Q ₈ of the bridge arm are GaN switches, which adopt high-frequency modulation to increase the equivalent switching frequency, thereby reducing the volume of the output filter.

Specifically, the terminal voltage of the photovoltaic cell connected to the common micro photovoltaic inverter is about 30-45V, so the terminal voltage of the low-voltage DC capacitor _C1 is very low, and the four switches of the low-voltage full-bridge inverter circuit can use 100V nitrogen Gallium Fe MOSFET switch, and Q ₁ , Q ₄ and Q ₂ , Q ₃ are divided into two groups, respectively apply two high-frequency square wave control signals with opposite phases and dead time of 0.1 to 0.2 microseconds, and the frequency of the control signals can reach Above 1MHz, much higher than the switching frequency of silicon switches; the zero voltage turn-on (ZVS) of Q ₁ ~ Q ₄ is realized through the resonant circuit, which effectively reduces the switching loss; through the magnetic integration technology, the primary leakage of the high-frequency transformer T ₁ is used Inductance replaces the resonant inductance L _r , reducing the volume of the whole machine.

If the rated voltage of the single-phase power grid connected to the micro photovoltaic inverter is 220V, the high-voltage DC bus voltage needs to reach 320-380V. Since the single-phase inverter causes large fluctuations in the high-voltage DC voltage, the high-voltage DC filter capacitor C ₄ can be selected as a high-voltage film capacitor with a withstand voltage of 650V. The high-voltage full-bridge inverter circuit adopts a switch with a withstand voltage of 600V or 650V. The two switches Q ₅ and Q ₆ on the left bridge arm are silicon MOSFET switches, which are controlled by power frequency to reduce the switching loss of the inverter circuit. The two switches Q ₇ and Q ₈ on the right bridge arm are GaN material MOSFET switches, which adopt high-frequency SPWM modulation with a carrier frequency of several thousand Hz, which can increase the equivalent switching frequency and reduce the size of the output filter .

Due to the large DC voltage difference between the low-voltage side and the high-voltage side, the high-frequency transformer T ₁ is designed as a step-up transformer, and the turns ratio of the primary side and the secondary side is 1:n. For further optimization, a voltage doubler rectifier circuit capable of doubling the voltage is used at the output end of the transformer, so the number of turns _of the secondary side of the transformer T1 can be appropriately reduced, which is conducive to the use of a smaller transformer core. The high-frequency transformer T1 also plays _a role in realizing the electrical isolation of the input/output of the whole machine.

When the power is constant, since the current of the high-voltage DC bus is small, the required capacitance is small, so the high-voltage DC filter capacitor _C4 adopts a small-capacity film capacitor, and then combines the power feedforward and voltage feedback control of the present invention. The power decoupling control method can absorb double-frequency power fluctuations caused by single-phase inverters on the high-voltage side, and prevent such fluctuations from being transmitted to the low-voltage DC bus, thereby avoiding the use of large-capacity electrolytic capacitors (usually thousands to Tens of thousands of uF), effectively improving the life of the whole machine.

The invention also discloses a control method of a photovoltaic inverter based on a gallium nitride device, which adopts a power decoupling control method of power feedforward and voltage feedback control, including generating a low-voltage full-bridge inverter in the first-stage DC-DC circuit The driving signal of the switch of the inverter circuit; and the driving signal of the switch of the high-voltage full-bridge inverter circuit in the second-stage DC-AC circuit is generated.

The first-stage DC-DC circuit control algorithm flow is shown in Figure 3, with the following steps:

Step 1: Collect the instantaneous value u _ac of the grid voltage and the instantaneous value i _ac of the output current of the photovoltaic inverter, and calculate the instantaneous AC output power of the photovoltaic inverter p _ac = u _ac × i _ac . Collect the instantaneous value of low-voltage DC bus voltage u _dc1 and the instantaneous value of photovoltaic cell output current i _dc1 , and calculate the average values U _dc1 and I _dc1 of the two at a period of 10 ms, and calculate the output power of photovoltaic cell P _pv = U _dc1 × I _dc1 . Collect the instantaneous value u _dc2 of the high-voltage DC bus voltage, and calculate the variation Δu _dc2 of u _dc2 in the next switching cycle according to the following formula, where T ₀ is the current switching cycle of the first-stage DC-DC converter:

Add the obtained u _dc2 and Δu _dc2 to obtain the predicted value of the high-voltage DC bus voltage in the next switching cycle u′ _dc2 =u _dc2 +Δu _dc2 , and then calculate the voltage of the first-stage DC-DC converter in the next switching cycle according to the following formula Gain ratio K:

Among them, n is the transformation ratio of the high-frequency transformer.

Step 2: Collect the instantaneous value of the input current i _dc2 of the DC side of the high-voltage full-bridge inverter circuit, and calculate the average value U _dc2 and I _dc2 of u _dc2 and i _dc2 obtained in step 1 with a cycle of 10ms, and calculate the first level according to the following formula The equivalent load resistance R of the DC-DC converter:

Make quality factor Inductance ratio parameter LLC resonant frequency Normalized switching frequency Among them, L _r is the resonant inductance of LLC, C _r is the resonant capacitance of LLC, L _m is the primary excitation inductance of high frequency transformer T ₁ , f ₁ is the next cycle of the first stage DC-DC converter to be obtained On-off level. According to the principle of LLC soft switching resonant converter, there will be the following formula:

Figure 6 is an example of a KF _x relationship curve. According to the KF _x relationship curve calculated offline, look up the table to find the solution of F _x that satisfies the following conditions:

Then, according to the relationship between F _x and f ₁ , f ₁ =F _x ×f _r is obtained as the switching frequency of the low-voltage full-bridge inverter circuit in the next cycle; and t ₁ in the next cycle = 1/f ₁ .

Step 3: Convert the switching frequency obtained in step 2 to a square wave signal with a duty ratio of 50% through voltage-frequency conversion, and add a suitable dead time after inversion, as the two groups of switches Q ₁ , Q ₄ and Q ₂ , Q ₃ drive signal.

The second stage DC-AC circuit control has the following steps:

Step 1: Calculate the reference value U _dcref of u _dc1 according to the instantaneous value of low-voltage DC bus voltage u _dc1 and the instantaneous value of photovoltaic cell output current i _dc1 with a cycle of 100 ms, using the disturbance and observation method as the algorithm for maximum power tracking of photovoltaic cells. The block diagram of the algorithm is shown in Figure 5.

Step 2: Calculate the error between the reference value U _dcref obtained in step 1 and the instantaneous value u _dc1 , and use a proportional-integral controller (PI) to obtain the amplitude I _acref of the reference value of the output current of the photovoltaic inverter; by the first stage DC- The DC circuit control step 1 obtains the instantaneous value of grid voltage u _ac , and obtains the phase factor sinθ of the grid voltage through the phase-locked loop module, and then obtains the reference value i _acref of the output current = I _acref × sinθ; calculates the reference value i _acref of the output current and The first-stage DC-DC circuit controls the error of the instantaneous value _iac obtained in step 1, and uses a proportional controller (P) to obtain the modulation ratio d of the output voltage of the photovoltaic inverter; the modulation ratio d and the power frequency square with an amplitude of 1 Wave subtraction, the obtained result is SPWM modulated with the high-frequency triangular carrier wave, and the switching signals of the two switches Q ₇ and Q ₈ of the right bridge arm of the high-voltage full-bridge inverter circuit are obtained, while the two switches Q ₅ of the left bridge arm , The switching signal of Q ₆ is a power frequency square wave with a duty ratio of 50%. The block diagram of the algorithm is shown in Figure 4.

It can be known from common technical knowledge that the present invention can be realized through other embodiments without departing from its spirit or essential features. Accordingly, the above-disclosed embodiments are, in all respects, illustrative and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are embraced by the present invention.

Claims (10)

1. A photovoltaic inverter based on a gallium nitride device, characterized in that it includes a first-stage converter for converting the low-voltage direct current generated by the photovoltaic cell into a high-voltage direct current, and for converting the high-voltage direct current into Second stage converter for sine wave; The first-stage converter includes a low-voltage DC filter capacitor C ₁ , a low-voltage full-bridge inverter circuit, a resonant circuit, a high-frequency transformer T ₁ and a voltage doubler rectifier circuit, and the low-voltage DC filter capacitor C ₁ is connected to two terminals of the photovoltaic cell end; the DC side of the low-voltage full-bridge inverter circuit is connected to the low-voltage DC filter capacitor, and its AC side is connected to the resonant circuit and the primary winding of the high _- frequency transformer T1, and the secondary side _of the high-frequency transformer T1 The winding combination is connected to the input end of the voltage doubler rectifier circuit; The second-stage converter includes a high-voltage filter capacitor _C4 and a high-voltage full-bridge inverter circuit, and the output terminal of the voltage doubler rectifier circuit is connected to the high-voltage DC filter capacitor _C4 and the DC side of the high-voltage full-bridge inverter circuit, so The AC side of the high-voltage full-bridge inverter circuit is connected to the power grid. 2. The photovoltaic inverter according to claim 1, further comprising an anti-reverse diode, the anode of the anti-reverse diode is connected to the positive end of the photovoltaic cell, and its cathode and the negative end of the photovoltaic cell are respectively connected To both ends of the low voltage DC filter capacitor _C1 . 3 . The photovoltaic inverter according to claim 1 , wherein the resonant circuit comprises a resonant capacitor C _r and a resonant inductance L _r . 4. The photovoltaic inverter according to claim 1, wherein an output filter is connected between the AC side of the full-bridge inverter circuit and the power grid. 5. The photovoltaic inverter according to claim 1, characterized in that, the high-frequency transformer T1 is _a step-up transformer. 6. The photovoltaic inverter according to claim 1, wherein the low-voltage full-bridge inverter circuit comprises four gallium nitride switches. 7. The photovoltaic inverter according to claim 1, wherein the high-voltage filter capacitor _C4 is a film capacitor. 8. The photovoltaic inverter according to claim 1, wherein the full-bridge inverter circuit includes a low-frequency bridge arm and a high-frequency bridge arm, the low-frequency bridge arm includes two silicon switches, and the high-frequency bridge arm The bridge arms consist of two GaN switches. 9. The method for controlling a photovoltaic inverter according to any one of claims 1-8, wherein the method comprises: Obtain the predicted value of the high-voltage DC bus voltage in the next cycle according to the instantaneous value of the high-voltage DC bus voltage collected in the current period; Obtain the voltage gain ratio K of the first-stage converter in the next cycle according to the predicted value of the high-voltage DC bus in the next cycle; obtain the equivalent load resistance R of the first-stage converter; According to the voltage gain ratio K and the equivalent load resistance R of the next cycle, obtain the switching frequency f ₁ of the first stage converter in the next cycle; According to the switching frequency f ₁ , a driving signal of a switch of the low-voltage full-bridge inverter circuit is obtained. 10. The control method of a photovoltaic inverter according to claim 9, wherein the method further comprises: Obtain the reference value U _dcref of the instantaneous value of the low-voltage DC bus voltage; Obtain the amplitude I _{acref of the reference value of the output current of the photovoltaic inverter according to the reference value U dcref ;} Obtain the phase factor sinθ of the grid voltage according to the instantaneous value u _ac of the grid voltage; According to the phase factor sinθ of the grid voltage and the amplitude I _acref of the reference value of the output current of the photovoltaic inverter, the reference value i _acref of the output current of the photovoltaic inverter is obtained; Obtain the modulation ratio d of the output voltage of the photovoltaic inverter according to the reference value i _acref of the output current; According to the modulation ratio d, the driving signals of two switches in the high-voltage full-bridge inverter circuit are obtained; According to the instantaneous value u _ac of the grid voltage, the drive signals of the other two switches of the high-voltage full-bridge inverter circuit are obtained.