Two-stage three-phase inverter with wide output voltage range applied to photovoltaic system

Abstract

The invention relates to the technical field of inverters, in particular to a three-phase voltage source inverter which comprises a direct-current voltage source module, an MOSFET control module 1, an MOSFET control module 2, a phase-shifted full-bridge ZVS direct-current conversion module, a three-phase Buck-Boost inversion module and a load based on the two-stage three-phase voltage source inverter. The phase-shifted full-bridge ZVS direct-current conversion module is adopted in the input stage part, fluctuation of output voltage of a photovoltaic panel is restrained, stable operation can be further achieved, meanwhile, a switching tube of the module can achieve the functions of zero-voltage switching-on and zero-voltage switching-off, and the phase-shifted full-bridge ZVS direct-current conversion module has wide application prospects in the field of photovoltaic new energy power generation-energy storage. Compared with the prior art, the high-frequency inverter circuit has the advantages that the switching tube loss of the MOSFET under the high-frequency working condition is reduced, and the Buck-Boost inverter circuit adopted by the high-frequency inverter circuit has a buck-boost function and a larger voltage output range, so that the high-frequency inverter circuit can flexibly adapt to the power supply requirement of a load end and has a wide prospect in the field of photovoltaic inversion.

Description

Technical Field

[0001] This invention relates to the field of inverter technology, and more specifically to a two-stage three-phase inverter with a wide output voltage range applicable to photovoltaic systems. Background Technology

[0002] The photovoltaic industry and new energy power generation sector are developing rapidly, and the market demand for high-efficiency and reliable inverters is increasing daily. Distribution networks also have stringent requirements for the power quality of connected distributed power sources. An inverter is a device that converts direct current (DC) to alternating current (AC) based on various power electronic components, primarily switching devices. Common single-phase inverters include single-phase half-bridge inverters, single-phase full-bridge inverters, and multi-level inverters. For photovoltaic (PV) system inverters, the output voltage of PV panels often fluctuates significantly due to factors such as uneven sunlight, temperature fluctuations, and dust obstruction. Therefore, to achieve stable operation under various conditions, the inverter should have a wide input voltage range to adapt to the operation of PV panels under different conditions, while ensuring a stable and clean output voltage to avoid damage to the load due to voltage quality issues. Traditional bridge inverters have advantages such as simple structure, simple switching control strategy, and stable operation under a single DC input. However, when faced with highly fluctuating DC inputs (such as those from photovoltaic and wind power, which are easily affected by environmental factors), it is difficult to guarantee the stability and smoothness of the output voltage waveform. To ensure the stability of the output voltage, the photovoltaic panels usually need to operate under ideal conditions, which makes it difficult to improve energy utilization and power conversion efficiency. To optimize the output voltage waveform, the filter capacitors and inductors in the circuit must be increased, which will greatly increase the size, cost, and losses of the inverter.

[0003] To address the aforementioned problems, this invention proposes a two-stage three-phase inverter with a wide input voltage range based on a Buck-Boost inverter circuit and a phase-shifted full-bridge ZVS DC-DC converter circuit. Summary of the Invention

[0004] The purpose of this invention is to provide a two-stage three-phase inverter with a wide output voltage range for use in photovoltaic systems, which solves the problem of unstable output voltage of traditional three-phase photovoltaic system inverters under abnormal operating conditions such as uneven illumination, dust obstruction, and temperature fluctuations.

[0005] The technical solution adopted in this invention is as follows: a three-phase inverter with a wide input voltage range based on a Buck-Boost inverter circuit and a phase-shifted full-bridge ZVS DC-DC converter circuit, comprising a DC voltage source module, a MOSFET control module 1, a MOSFET control module 2, a phase-shifted full-bridge ZVS DC-DC converter module, a three-phase Buck-Boost inverter module, and a load; characterized in that: the output of the DC voltage source is connected to the input of the phase-shifted full-bridge ZVS DC-DC converter module; the output of the MOSFET control module 1 is connected to the control pins of four MOSFET switches in the phase-shifted full-bridge ZVS DC-DC converter module; the output of the MOSFET control module 2 is connected to the control pins of twelve MOSFET switches in the three-phase Buck-Boost inverter module; and the output of the Buck-Boost inverter module is connected to a load configured in a three-phase star topology; the photovoltaic panel DC input module includes an input V... in The phase-shifted full-bridge ZVS DC-DC converter module includes transistors S1, S2, S3, and S4; diodes D1, D2, D3, and D4; capacitors C1, C2, C3, and C4; a resonant inductor Lm; a transformer T; rectifier diodes Dr and Dr2; an inductor Lr; and a capacitor Cr. The three-phase Buck-Boost inverter module includes transistors Ta1, Ta2, Ta3, Ta4, Tb1, Tb2, Tb3, and Tb4. Transistor Tc1, transistor Tc2, transistor Tc3, transistor Tc4, transistor Daa, transistor Dab, transistor Dba, transistor Dbb, transistor Dca, transistor Dcb, diode Da1, diode Da2, diode Da3, diode Da4, diode Db1, diode Db2, diode Db3, diode Db4, diode Dc1, diode Dc2, diode Dc3, diode Dc4, diode Daa, diode Dab, diode Dba, diode Dbb, diode Dca, diode Dcb, capacitor C1, capacitor C2, capacitor C3.

[0006] The positive output terminal of the DC voltage module is connected to the drain of crystal switch S1, the drain of crystal switch S3, the cathode of diode D1, the cathode of diode D3, the positive terminal of capacitor C1, and the positive terminal of capacitor C3. The negative output terminal is connected to the source of crystal switch S1, the source of crystal switch S3, the anode of diode D2, the anode of diode D4, the negative terminal of capacitor C2, and the negative terminal of capacitor C4.

[0007] The MOSFET control module 1 outputs 4 control signals, with output interfaces for crystal switches S2, S1, S4, and S3, respectively. The MOSFET control module 2 outputs 18 control signals, with output interfaces for crystal switches Tc3, Tc1, Tb3, Tb1, Ta3, Ta1, Tc4, Tc2, Tb4, Tb2, Ta4, Ta2, Taa, Tab, Tba, Tbb, Tca, and Tcb, respectively.

[0008] In the phase-shifted full-bridge ZVS DC-DC converter module, the gate of transistor S1 is connected to the S1 output interface of MOSFET control module 1, its drain is connected to the cathode of diode D1, the positive terminal of capacitor C1, and the drain of transistor S3, its source is connected to the positive terminal of resonant inductor Lr, the drain of transistor S2, the anode of diode D1, and the negative terminal of capacitor C1. The gate of transistor S3 is connected to the S3 output interface of MOSFET control module 1, its drain is connected to the cathode of diode D3, the positive terminal of capacitor C3, and the drain of transistor S1, its source is connected to the drain of transistor S4, the opposite terminal of the primary winding of the transformer, the anode of diode D3, and the negative terminal of capacitor C3. The gate of transistor S2 is connected to the S2 output interface of MOSFET control module 1, its drain is connected to the source of transistor S1, the source of transistor S4, the cathode of diode D2, and the positive terminal of capacitor C2. The gate of transistor S4 is connected to the MOSFET control module... The output interface of transistor S4 is connected to the transformer. The drain of the inductor is connected to the cathode of diode D4, the anode of capacitor C4 is connected to the source of transistor S3, the source of transistor S3 is connected to the anode of diode D4, and the cathode of capacitor C4 is connected to the source of transistor S2. The anode of the resonant inductor is connected to the source of transistor S1 and the drain of transistor S2. The cathode is connected to the same-name terminal of the primary winding of the transformer. The same-name terminal of part 1 of the secondary winding of the transformer is connected to the anode of rectifier diode Dr1, and the opposite-name terminal is connected to the rectifier diode Dr1. The cathodes of Dr2 are connected together. The cathodes of rectifier diode Dr1 and Lr are connected together. The cathodes of rectifier diode Dr2 and Lr are connected together. The cathode of Lr is connected together. The cathode of Cr is connected together. The cathode of Cr is connected together. The opposite terminal of part 1 of the transformer secondary winding is connected together. The same terminal of part 2 of the transformer secondary winding is connected together. The opposite terminal of part 1 of the transformer secondary winding is connected together. The opposite terminal of part 2 of the transformer secondary winding is connected together. The anode of rectifier diode Dr2 is connected together.

[0009] In the three-phase Buck-Boost inverter module, the gate of transistor Ta1 is connected to the Ta1 output interface of MOSFET control module 2, its drain is connected to the cathode of diode Da1, the drain of transistor Ta2, and the positive terminal of filter capacitor Cr, and its source is connected to the anode of diode Da1, the positive terminal of inductor L1, and the drain of transistor Ta3. The gate of transistor Ta2 is connected to the Ta2 output interface of MOSFET control module 2, its drain is connected to the drain of transistor Ta1 and the cathode of diode Da2, and its source is connected to the anode of diode Da2, the negative terminal of inductor L1, the drain of transistor Ta4, and the drain of transistor Taa. The gate of transistor Ta3 is connected to the Ta3 output interface of MOSFET control module 2, its drain is connected to the cathode of diode Da3, and the source of transistor Ta1. The anode of diode Da3, the cathode of filter capacitor Cr, and the source of crystal switch Ta4 are connected. The gate of crystal switch Ta4 is connected to the output interface of MOSFET control module 2. The drain of crystal switch Taa is connected to the cathode of diode Da4, the cathode of inductor L1, and the source of crystal switch Ta2. The source of crystal switch Taa is connected to the source of crystal switch Ta3 and the cathode of capacitor C1. The drain of crystal switch Taa is connected to the cathode of inductor L1 and the cathode of diode Daa. The gate of crystal switch Taa is connected to the output interface of MOSFET control module 2. The source of crystal switch Taa is connected to the anode of diode Daa and the source of crystal switch Tab. The gate of crystal switch Tab is connected to the output interface of MOSFET control module 2. The drain of crystal switch Taa is connected to the cathode of diode Dab and the positive terminal of capacitor C1. The source of crystal switch Taa is connected to the source of crystal switch Taa and the anode of diode Dab.The gate of transistor Tb1 is connected to the Tb1 output interface of MOSFET control module 2; its drain is connected to the cathode of diode Db1, the drain of transistor Tb2, and the positive terminal of filter capacitor Cr; its source is connected to the anode of diode Db1, the positive terminal of inductor L2, and the drain of transistor Tb3. The gate of transistor Tb2 is connected to the Tb2 output interface of MOSFET control module 2; its drain is connected to the drain of transistor Tb1 and the cathode of diode Db2; its source is connected to the anode of diode Db2, the negative terminal of inductor L2, the drain of transistor Tb4, and the drain of transistor Tba. The gate of transistor Tb3 is connected to the Tb3 output interface of MOSFET control module 2; its drain is connected to the cathode of diode Db3 and the source of transistor Tb1; and its source is connected to the anode of diode Db3. The negative terminal of the filter capacitor Cr is connected to the source of the crystal switch Tb4. The gate of the crystal switch Tb4 is connected to the output interface of the MOSFET control module 2. The drain is connected to the cathode of the diode Db4 and the negative terminal of the inductor L2 and the source of the crystal switch Tb2. The source is connected to the source of the crystal switch Tb3 and the negative terminal of the capacitor C2. The drain of the crystal switch Tba is connected to the negative terminal of the inductor L2 and the cathode of the diode Dba. The gate is connected to the output interface of the MOSFET control module 2. The source is connected to the anode of the diode Dba and the source of the crystal switch Tbb. The gate of the crystal switch Tbb is connected to the output interface of the MOSFET control module 2. The drain is connected to the cathode of the diode Dbb and the positive terminal of the capacitor C2. The source is connected to the source of the crystal switch Tba and the anode of the diode Dbb.The gate of transistor Tc1 is connected to the output interface of MOSFET control module 2; its drain is connected to the cathode of diode Dc1, the drain of transistor Tc2, and the positive terminal of filter capacitor Cr; its source is connected to the anode of diode Dc1, the positive terminal of inductor L3, and the drain of transistor Tc3. The gate of transistor Tc2 is connected to the output interface of MOSFET control module 2; its drain is connected to the drain of transistor Tc1 and the cathode of diode Dc2; its source is connected to the anode of diode Dc2, the negative terminal of inductor L3, the drain of transistor Tc4, and the drain of transistor Tca. The gate of transistor Tc3 is connected to the output interface of MOSFET control module 2; its drain is connected to the cathode of diode Dc3 and the source of transistor Tc1; and its source is connected to the anode of diode Dc3. The negative terminal of the filter capacitor Cr is connected to the source of the crystal switch Tc4. The gate of the crystal switch Tc4 is connected to the output interface of MOSFET control module 2. The drain of the crystal switch Tc4 is connected to the cathode of diode Dc4 and the negative terminal of inductor L3, which is connected to the source of crystal switch Tc2. The source of Tc4 is connected to the source of crystal switch Tc3 and the negative terminal of capacitor C3. The drain of crystal switch Tca is connected to the negative terminal of inductor L3 and the cathode of diode Dca. The gate of Tca is connected to the output interface of MOSFET control module 2. The source of Tca is connected to the anode of diode Dca and the source of crystal switch Tcb. The gate of crystal switch Tcb is connected to the output interface of MOSFET control module 2. The drain of Tcb is connected to the cathode of diode Dcb and the positive terminal of capacitor C3. The source of Tca is connected to the source of crystal switch Tca and the anode of diode Dcb.

[0010] In the three-phase load module, the three-phase load adopts a Y-connection method, and the input of the three-phase load is connected to the positive terminals of capacitor C1, capacitor C2, and capacitor C3, respectively.

[0011] The advantages of this invention's two-stage three-phase inverter with a wide output voltage range for photovoltaic systems are as follows: First, compared to traditional single-phase half-bridge inverter circuits, single-phase full-bridge inverter circuits, and multi-level inverter circuits, the adopted two-stage conversion strategy can improve energy utilization over a wider range while ensuring stable output voltage. The two-stage inverter design of this invention uses a phase-shifted full-bridge ZVS DC-DC converter module as the front stage of the inverter to achieve MPPT of the photovoltaic panels and obtain a relatively stable front-stage output voltage. The rear stage uses a Buck-Boost inverter circuit to invert the DC power output from the front stage into symmetrical three-phase power, while also having both boost and buck functions, allowing for flexible adjustment of the output voltage according to the load requirements. Compared to traditional single-phase half-bridge inverters, this two-stage three-phase inverter with a wide output voltage range for photovoltaic systems can accept input voltage fluctuations within a certain range and has a larger voltage output range, offering flexible voltage regulation and high power supply reliability.

[0012] To more clearly illustrate the two-stage three-phase inverter with a wide output voltage range applicable to photovoltaic systems proposed in this invention, the following detailed description and explanation of the invention are provided in conjunction with the accompanying drawings and specific embodiments. Attached Figure Description

[0013] To more clearly illustrate the two-stage three-phase inverter with a wide output voltage range applicable to photovoltaic systems proposed in this invention, the invention will be further described and explained in detail below with reference to the accompanying drawings and specific embodiments.

[0014] Figure 1 This is a circuit topology diagram of a two-stage three-phase inverter with a wide output voltage range applicable to photovoltaic systems according to the present invention.

[0015] Figure 2 This is a circuit diagram of the A-phase Buck-Boost inverter module in the inverter.

[0016] Figure 3 This describes the three operating states of the Buck-Boost inverter module in the inverter when the output voltage is negative.

[0017] Figure 4 This describes the operating states of the Buck-Boost inverter module in the inverter during three stages when the output voltage is positive.

[0018] Figure 5 This is a circuit diagram of the phase-shifted full-bridge ZVS DC-DC converter module in an inverter.

[0019] Figure 6 This is a schematic diagram showing the current flow of the phase-shifted full-bridge ZVS DC-DC converter module in the inverter during its six operating stages.

[0020] Figure 7 This refers to the switching transistor turn-on signal of the phase-shifted full-bridge ZVS DC-DC converter module in the inverter during its six operating stages. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It should be noted that the embodiments described herein are only some embodiments of the present invention, and not all practical ways of the present invention. The embodiments are only exemplary.

[0022] Figure 1 The diagram shows the circuit structure of a two-stage three-phase inverter with a wide output voltage range for photovoltaic systems according to the present invention. Its specific structure is as follows: it includes a DC voltage source module, MOSFET control module 1, MOSFET control module 2, a phase-shifted full-bridge ZVS DC-DC converter module, a three-phase Buck-Boost inverter module, and a load; its key features are: the output of the DC voltage source is connected to the input of the phase-shifted full-bridge ZVS DC-DC converter module; the output of MOSFET control module 1 is connected to the control pins of the four MOSFET switches in the phase-shifted full-bridge ZVS DC-DC converter module; the output of MOSFET control module 2 is connected to the control pins of the twelve MOSFET switches in the three-phase Buck-Boost inverter module; and the output of the Buck-Boost inverter module is connected to a load configured in a three-phase star topology; the photovoltaic panel DC input module includes an input V... inThe phase-shifted full-bridge ZVS DC-DC converter module includes transistors S1, S2, S3, and S4; diodes D1, D2, D3, and D4; capacitors C1, C2, C3, and C4; a resonant inductor Lm; a transformer T; rectifier diodes Dr and Dr2; an inductor Lr; and a capacitor Cr. The three-phase Buck-Boost inverter module includes transistors Ta1, Ta2, Ta3, Ta4, Tb1, Tb2, Tb3, and Tb4. Transistor Tc1, transistor Tc2, transistor Tc3, transistor Tc4, transistor Daa, transistor Dab, transistor Dba, transistor Dbb, transistor Dca, transistor Dcb, diode Da1, diode Da2, diode Da3, diode Da4, diode Db1, diode Db2, diode Db3, diode Db4, diode Dc1, diode Dc2, diode Dc3, diode Dc4, diode Daa, diode Dab, diode Dba, diode Dbb, diode Dca, diode Dcb, capacitor C1, capacitor C2, capacitor C3.

[0023] The photovoltaic panel DC input module is connected to the positive terminal of capacitor C1 and the anode of diode D1.

[0024] In the three-phase Buck-Boost inverter module, the gate of transistor Ta1 is connected to the Ta1 output interface of MOSFET control module 2, its drain is connected to the cathode of diode Da1, the drain of transistor Ta2, and the positive terminal of filter capacitor Cr, and its source is connected to the anode of diode Da1, the positive terminal of inductor L1, and the drain of transistor Ta3. The gate of transistor Ta2 is connected to the Ta2 output interface of MOSFET control module 2, its drain is connected to the drain of transistor Ta1 and the cathode of diode Da2, and its source is connected to the anode of diode Da2, the negative terminal of inductor L1, the drain of transistor Ta4, and the drain of transistor Taa. The gate of transistor Ta3 is connected to the Ta3 output interface of MOSFET control module 2, its drain is connected to the cathode of diode Da3, and the source of transistor Ta1. The anode of diode Da3, the cathode of filter capacitor Cr, and the source of crystal switch Ta4 are connected. The gate of crystal switch Ta4 is connected to the output interface of MOSFET control module 2. The drain of crystal switch Taa is connected to the cathode of diode Da4, the cathode of inductor L1, and the source of crystal switch Ta2. The source of crystal switch Taa is connected to the source of crystal switch Ta3 and the cathode of capacitor C1. The drain of crystal switch Taa is connected to the cathode of inductor L1 and the cathode of diode Daa. The gate of crystal switch Taa is connected to the output interface of MOSFET control module 2. The source of crystal switch Taa is connected to the anode of diode Daa and the source of crystal switch Tab. The gate of crystal switch Tab is connected to the output interface of MOSFET control module 2. The drain of crystal switch Taa is connected to the cathode of diode Dab and the positive terminal of capacitor C1. The source of crystal switch Taa is connected to the source of crystal switch Taa and the anode of diode Dab.The gate of transistor Tb1 is connected to the Tb1 output interface of MOSFET control module 2; its drain is connected to the cathode of diode Db1, the drain of transistor Tb2, and the positive terminal of filter capacitor Cr; its source is connected to the anode of diode Db1, the positive terminal of inductor L2, and the drain of transistor Tb3. The gate of transistor Tb2 is connected to the Tb2 output interface of MOSFET control module 2; its drain is connected to the drain of transistor Tb1 and the cathode of diode Db2; its source is connected to the anode of diode Db2, the negative terminal of inductor L2, the drain of transistor Tb4, and the drain of transistor Tba. The gate of transistor Tb3 is connected to the Tb3 output interface of MOSFET control module 2; its drain is connected to the cathode of diode Db3 and the source of transistor Tb1; and its source is connected to the anode of diode Db3. The negative terminal of the filter capacitor Cr is connected to the source of the crystal switch Tb4. The gate of the crystal switch Tb4 is connected to the output interface of the MOSFET control module 2. The drain is connected to the cathode of the diode Db4 and the negative terminal of the inductor L2 and the source of the crystal switch Tb2. The source is connected to the source of the crystal switch Tb3 and the negative terminal of the capacitor C2. The drain of the crystal switch Tba is connected to the negative terminal of the inductor L2 and the cathode of the diode Dba. The gate is connected to the output interface of the MOSFET control module 2. The source is connected to the anode of the diode Dba and the source of the crystal switch Tbb. The gate of the crystal switch Tbb is connected to the output interface of the MOSFET control module 2. The drain is connected to the cathode of the diode Dbb and the positive terminal of the capacitor C2. The source is connected to the source of the crystal switch Tba and the anode of the diode Dbb.The gate of transistor Tc1 is connected to the output interface of MOSFET control module 2; its drain is connected to the cathode of diode Dc1, the drain of transistor Tc2, and the positive terminal of filter capacitor Cr; its source is connected to the anode of diode Dc1, the positive terminal of inductor L3, and the drain of transistor Tc3. The gate of transistor Tc2 is connected to the output interface of MOSFET control module 2; its drain is connected to the drain of transistor Tc1 and the cathode of diode Dc2; its source is connected to the anode of diode Dc2, the negative terminal of inductor L3, the drain of transistor Tc4, and the drain of transistor Tca. The gate of transistor Tc3 is connected to the output interface of MOSFET control module 2; its drain is connected to the cathode of diode Dc3 and the source of transistor Tc1; and its source is connected to the anode of diode Dc3. The negative terminal of the filter capacitor Cr is connected to the source of the crystal switch Tc4. The gate of the crystal switch Tc4 is connected to the output interface of MOSFET control module 2. The drain of the crystal switch Tc4 is connected to the cathode of diode Dc4 and the negative terminal of inductor L3, which is connected to the source of crystal switch Tc2. The source of Tc4 is connected to the source of crystal switch Tc3 and the negative terminal of capacitor C3. The drain of crystal switch Tca is connected to the negative terminal of inductor L3 and the cathode of diode Dca. The gate of Tca is connected to the output interface of MOSFET control module 2. The source of Tca is connected to the anode of diode Dca and the source of crystal switch Tcb. The gate of crystal switch Tcb is connected to the output interface of MOSFET control module 2. The drain of Tcb is connected to the cathode of diode Dcb and the positive terminal of capacitor C3. The source of Tca is connected to the source of crystal switch Tca and the anode of diode Dcb.

[0025] The MOSFET control module 1 outputs 4 control signals, with output interfaces for crystal switches S2, S1, S4, and S3, respectively. The MOSFET control module 2 outputs 18 control signals, with output interfaces for crystal switches Tc3, Tc1, Tb3, Tb1, Ta3, Ta1, Tc4, Tc2, Tb4, Tb2, Ta4, Ta2, Taa, Tab, Tba, Tbb, Tca, and Tcb, respectively.

[0026] In the phase-shifted full-bridge ZVS DC-DC converter module, the gate of transistor S1 is connected to the S1 output interface of MOSFET control module 1, its drain is connected to the cathode of diode D1, the positive terminal of capacitor C1, and the drain of transistor S3, its source is connected to the positive terminal of resonant inductor Lr, the drain of transistor S2, the anode of diode D1, and the negative terminal of capacitor C1. The gate of transistor S3 is connected to the S3 output interface of MOSFET control module 1, its drain is connected to the cathode of diode D3, the positive terminal of capacitor C3, and the drain of transistor S1, its source is connected to the drain of transistor S4, the opposite terminal of the primary winding of the transformer, the anode of diode D3, and the negative terminal of capacitor C3. The gate of transistor S2 is connected to the S2 output interface of MOSFET control module 1, its drain is connected to the source of transistor S1, the source of transistor S4, the cathode of diode D2, and the positive terminal of capacitor C2. The gate of transistor S4 is connected to the MOSFET control module... The output interface of transistor S4 is connected to the transformer. The drain of the inductor is connected to the cathode of diode D4, the anode of capacitor C4 is connected to the source of transistor S3, the source of transistor S3 is connected to the anode of diode D4, and the cathode of capacitor C4 is connected to the source of transistor S2. The anode of the resonant inductor is connected to the source of transistor S1 and the drain of transistor S2. The cathode is connected to the same-name terminal of the primary winding of the transformer. The same-name terminal of part 1 of the secondary winding of the transformer is connected to the anode of rectifier diode Dr1, and the opposite-name terminal is connected to the rectifier diode Dr1. The cathodes of Dr2 are connected together. The cathodes of rectifier diode Dr1 are connected to the positive terminals of filter inductor Lr and rectifier diode Dr2. The negative terminal of filter inductor Lr is connected to the positive terminal of filter capacitor Cr. The negative terminal of filter capacitor Cr is connected to the opposite terminal of transformer secondary winding Lr1 and the cathode of rectifier diode Dr2. The same terminal of transformer secondary winding Lr2 is connected to the opposite terminal of transformer secondary winding Lr1. The opposite terminal of transformer secondary winding Lr2 is connected to the anode of rectifier diode Dr2.

[0027] In the three-phase load module, the three-phase load adopts a Y-connection method, and the input of the three-phase load is connected to the positive terminals of capacitor C1, capacitor C2, and capacitor C3, respectively.

[0028] Next, please refer to Figure 5 , Figure 6 , Figure 7 The inverter's front-end uses a phase-shifted full-bridge ZVS DC-DC converter module to transform the output voltage of the photovoltaic panels. (Reference) Figure 6 and Figure 7During the time interval t0-t1, switches S1 and S4 are turned on. At time t1, S1 is turned off, and capacitors C1 and C2 are directly connected in parallel across the power supply. Since the voltage across capacitor C2 is positive at the top and negative at the bottom, diode D2 is clamped and cannot conduct. The current flowing through the resonant inductor Lm charges capacitor C1 and discharges capacitor C2, creating the prerequisite for the turn-on of switch S2. At time t2, capacitor C2 is discharged until its voltage reaches 0, at which point diode D2 is ready to conduct, and the current flowing through the resonant inductor Lm... The transformer's primary winding, switch S4, and diode D2 connected in parallel with switch S2 are connected. During the time interval t2-t3, since diode D2 is already conducting, turning on S2 at this time allows for zero-voltage conduction, reducing switching losses. At time t3, switch S4 is turned off. During the time interval t3-t4, capacitors C3 and C4 are connected in parallel across the power supply. Because the voltage across capacitor C3 is positive at the top and negative at the bottom, diode D3 is clamped and cannot conduct. The current flowing through the resonant inductor Lm affects the voltage across the transformer. Capacitor C3 discharges, charging capacitor C4, creating the prerequisite for the turn-on of switch S3; at time t4, capacitor C3 is discharged to a voltage of 0, at which point diode D3 is ready to conduct, and the current of resonant inductor Lm flows through diode D3 (connected in parallel with switch S3), the primary winding of the transformer, and switch S2; during the time interval t4-t5, since diode D3 (connected in parallel with switch S3) is already conducting, turning on S3 at this time can achieve zero-voltage conduction, reducing switching losses; t3-t During time interval t5, the direction of the current flowing through the primary winding of the transformer changes. Since the inductor current cannot change abruptly, the secondary winding is effectively in a short-circuit state, and the converter output DC voltage is 0 during this time interval. After commutation during the above time intervals, during time intervals t5-t6, the direction of the current flowing through the secondary winding of the transformer changes, but after rectification, the converter still outputs DC voltage. At time t6, switch S2 is turned off, and under the action of capacitors C1 and C2, conditions are created for the zero-voltage turn-on of switch S1. The above describes the six operating modes of the phase-shifted full-bridge ZVS DC-DC converter module within one cycle. (Reference) Figure 7 By controlling the switching transistor S 1，2 and switching transistor S 4，3 By opening the phase difference, the output voltage can be controlled to suppress voltage fluctuations in the photovoltaic panel output voltage caused by uneven illumination, temperature fluctuations, and dust obstruction, thereby achieving maximum power point tracking of the photovoltaic panel and providing a more stable input voltage for the downstream inverter module.

[0029] After the aforementioned DC-DC conversion process, the front-stage DC-DC converter module outputs a stable DC voltage, which serves as the input voltage for the subsequent inverter module. The Buck-Boost full-bridge inverter module structure used in this invention differs from traditional bridge inverters in that it adds two switching transistors, Taa and Tab, along with their corresponding freewheeling diodes to facilitate control of the output voltage. Figure 3 The conduction state of each switch and the current flow in the circuit are given when the output voltage of the Buck-Boost full-bridge inverter module is in the negative half-cycle. Figure 3 In the first stage of the inverter module's output voltage negative half-cycle, when switching transistors Ta2 and Tab are turned on, the freewheeling diode Daa is reverse biased, and the power supply charges inductor L1. The current in inductor L1 increases linearly, and the load is powered by capacitor C1. The current flow path at this time is shown in the figure. Since no current flows through switching transistor Tab when it is turned on, the conduction of Tab can be regarded as zero-voltage conduction, reducing switching losses. In the second stage of the inverter module's output voltage negative half-cycle, switching transistor Ta2 is turned off. Since the current in the inductor cannot change abruptly, the freewheeling diode Daa is forward biased, providing a conduction path for the current in the inductor. At this time, the current in inductor L1 decreases linearly, and the inductor current flows through the capacitor and the load, supplying power to them. During the third stage of the negative half-cycle of the inverter module's output voltage, switch Taa is turned on, and inductor L1 continues to supply power to the capacitor and load. Since the load current flows through the diode connected in parallel with switch Taa before it turns on, the conduction of Taa can be considered zero-voltage conduction, reducing switching losses. By changing the on / off state of switch Ta2 and controlling the charging and discharging time of inductor L1 within one operating cycle—that is, controlling the duty cycle—the output voltage can be controlled. When the Buck-Boost three-phase inverter module's output voltage is in the positive half-cycle, switch Ta2 remains off, and switches Ta1 and Ta4 are closed, charging inductor L1. In this switching state, the inverter module's output voltage is positive. By changing the positive and negative half-cycles of the output voltage, the inversion function is achieved. When the inverter module's output voltage is positive, the current flow in the circuit is as follows: Figure 4 As shown. For the B-phase inverter module, the conduction angle of its switching transistor lags behind that of the A-phase module by 120 degrees, and for the C-phase inverter module, the conduction angle lags behind that of the A-phase module by 240 degrees. Thus, the Buck-Boost three-phase inverter module converts the output DC power into three symmetrical AC power phases, each phase differing by 120 degrees. By adjusting the duty cycle, in conjunction with the preceding DC-DC module, step-up and step-down voltage functions can be achieved to adapt to different voltage requirements at the load end.

[0030] The above description is only a preferred embodiment of the present invention, but it is not intended to limit the present invention. Various modifications and alterations can be made by those skilled in the art without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the claims.

Claims

1. A two-stage three-phase inverter with a wide output voltage range for use in photovoltaic systems, comprising a DC voltage source module, a MOSFET control module 1, a MOSFET control module 2, a phase-shifted full-bridge ZVS DC-DC converter module, a three-phase Buck-Boost inverter module, and a load; characterized in that: The DC voltage source output is connected to the input of the phase-shifted full-bridge ZVS DC-DC converter module. The output of MOSFET control module 1 is connected to the control pins of the four MOSFET switches in the phase-shifted full-bridge ZVS DC-DC converter module. The output of MOSFET control module 2 is connected to the control pins of the twelve MOSFET switches in the three-phase Buck-Boost inverter module. The output of the Buck-Boost inverter module is connected to a load configured in a three-phase star topology. The photovoltaic panel DC input module includes an input V... in The phase-shifted full-bridge ZVS DC-DC converter module includes transistors S1, S2, S3, and S4; diodes D1, D2, D3, and D4; capacitors C1, C2, C3, and C4; a resonant inductor Lm; a transformer T; rectifier diodes Dr and Dr2; an inductor Lr; and a capacitor Cr. The three-phase Buck-Boost inverter module includes transistors Ta1, Ta2, Ta3, Ta4, Tb1, Tb2, Tb3, and Tb4. Transistor Tc1, transistor Tc2, transistor Tc3, transistor Tc4, transistor Daa, transistor Dab, transistor Dba, transistor Dbb, transistor Dca, transistor Dcb, diode Da1, diode Da2, diode Da3, diode Da4, diode Db1, diode Db2, diode Db3, diode Db4, diode Dc1, diode Dc2, diode Dc3, diode Dc4, diode Daa, diode Dab, diode Dba, diode Dbb, diode Dca, diode Dcb, capacitor C1, capacitor C2, capacitor C3.

2. The two-stage three-phase inverter with a wide output voltage range for photovoltaic systems as described in claim 1, characterized in that: The positive output terminal of the DC voltage module is connected to the drain of crystal switch S1, the drain of crystal switch S3, the cathode of diode D1, the cathode of diode D3, the positive terminal of capacitor C1, and the positive terminal of capacitor C3. The negative output terminal is connected to the source of crystal switch S1, the source of crystal switch S3, the anode of diode D2, the anode of diode D4, the negative terminal of capacitor C2, and the negative terminal of capacitor C4.

3. The two-stage three-phase inverter with a wide output voltage range for photovoltaic systems as described in claim 1, characterized in that: The MOSFET control module 1 outputs four control signals, with output interfaces for transistors S2, S1, S4, and S3, respectively. The MOSFET control module 2 outputs eighteen control signals, with output interfaces for transistors Tc3, Tc1, Tb3, Tb1, Ta3, Ta1, Tc4, Tc2, Tb4, Tb2, Ta4, Ta2, Taa, Tab, Tba, Tbb, Tca, and Tcb, respectively.

4. The two-stage three-phase inverter with a wide output voltage range for photovoltaic systems as described in claim 1, characterized in that: In the phase-shifted full-bridge ZVS DC-DC converter module, the gate of transistor S1 is connected to the S1 output interface of MOSFET control module 1, its drain is connected to the cathode of diode D1, the positive terminal of capacitor C1, and the drain of transistor S3, its source is connected to the positive terminal of resonant inductor Lr, the drain of transistor S2, the anode of diode D1, and the negative terminal of capacitor C1. The gate of transistor S3 is connected to the S3 output interface of MOSFET control module 1, its drain is connected to the cathode of diode D3, the positive terminal of capacitor C3, and the drain of transistor S1, its source is connected to the drain of transistor S4, the opposite terminal of the primary winding of the transformer, the anode of diode D3, and the negative terminal of capacitor C3. The gate of transistor S2 is connected to the S2 output interface of MOSFET control module 1, its drain is connected to the source of transistor S1, the source of transistor S4, the cathode of diode D2, and the positive terminal of capacitor C2. The gate of transistor S4 is connected to the MOSFET control module... The output interface of transistor S4 is connected to the transformer. The drain of the inductor is connected to the cathode of diode D4, the anode of capacitor C4 is connected to the source of transistor S3, the source of transistor S3 is connected to the anode of diode D4, and the cathode of capacitor C4 is connected to the source of transistor S2. The anode of the resonant inductor is connected to the source of transistor S1 and the drain of transistor S2. The cathode is connected to the same-name terminal of the primary winding of the transformer. The same-name terminal of part 1 of the secondary winding of the transformer is connected to the anode of rectifier diode Dr1, and the opposite-name terminal is connected to the rectifier diode Dr1. The cathodes of Dr2 are connected together. The cathodes of rectifier diode Dr1 and Lr are connected together. The cathodes of rectifier diode Dr2 and Lr are connected together. The cathode of Lr is connected together. The cathode of Cr is connected together. The cathode of Cr is connected together. The opposite terminal of part 1 of the transformer secondary winding is connected together. The same terminal of part 2 of the transformer secondary winding is connected together. The opposite terminal of part 1 of the transformer secondary winding is connected together. The opposite terminal of part 2 of the transformer secondary winding is connected together. The anode of rectifier diode Dr2 is connected together.

5. A two-stage three-phase inverter with a wide output voltage range for photovoltaic systems as described in claim 1, characterized in that: In the three-phase Buck-Boost inverter module, the gate of transistor Ta1 is connected to the Ta1 output interface of MOSFET control module 2, its drain is connected to the cathode of diode Da1, the drain of transistor Ta2, and the positive terminal of filter capacitor Cr, and its source is connected to the anode of diode Da1, the positive terminal of inductor L1, and the drain of transistor Ta3. The gate of transistor Ta2 is connected to the Ta2 output interface of MOSFET control module 2, its drain is connected to the drain of transistor Ta1 and the cathode of diode Da2, and its source is connected to the anode of diode Da2, the negative terminal of inductor L1, the drain of transistor Ta4, and the drain of transistor Taa. The gate of transistor Ta3 is connected to the Ta3 output interface of MOSFET control module 2, its drain is connected to the cathode of diode Da3, and the source of transistor Ta1. The anode of diode Da3, the cathode of filter capacitor Cr, and the source of crystal switch Ta4 are connected. The gate of crystal switch Ta4 is connected to the output interface of MOSFET control module 2. The drain of crystal switch Taa is connected to the cathode of diode Da4, the cathode of inductor L1, and the source of crystal switch Ta2. The source of crystal switch Taa is connected to the source of crystal switch Ta3 and the cathode of capacitor C1. The drain of crystal switch Taa is connected to the cathode of inductor L1 and the cathode of diode Daa. The gate of crystal switch Taa is connected to the output interface of MOSFET control module 2. The source of crystal switch Taa is connected to the anode of diode Daa and the source of crystal switch Tab. The gate of crystal switch Tab is connected to the output interface of MOSFET control module 2. The drain of crystal switch Taa is connected to the cathode of diode Dab and the positive terminal of capacitor C1. The source of crystal switch Taa is connected to the source of crystal switch Taa and the anode of diode Dab.The gate of transistor Tb1 is connected to the Tb1 output interface of MOSFET control module 2; its drain is connected to the cathode of diode Db1, the drain of transistor Tb2, and the positive terminal of filter capacitor Cr; its source is connected to the anode of diode Db1, the positive terminal of inductor L2, and the drain of transistor Tb3. The gate of transistor Tb2 is connected to the Tb2 output interface of MOSFET control module 2; its drain is connected to the drain of transistor Tb1 and the cathode of diode Db2; its source is connected to the anode of diode Db2, the negative terminal of inductor L2, the drain of transistor Tb4, and the drain of transistor Tba. The gate of transistor Tb3 is connected to the Tb3 output interface of MOSFET control module 2; its drain is connected to the cathode of diode Db3 and the source of transistor Tb1; and its source is connected to the anode of diode Db3. The negative terminal of the filter capacitor Cr is connected to the source of the crystal switch Tb4. The gate of the crystal switch Tb4 is connected to the output interface of the MOSFET control module 2. The drain is connected to the cathode of the diode Db4 and the negative terminal of the inductor L2 and the source of the crystal switch Tb2. The source is connected to the source of the crystal switch Tb3 and the negative terminal of the capacitor C2. The drain of the crystal switch Tba is connected to the negative terminal of the inductor L2 and the cathode of the diode Dba. The gate is connected to the output interface of the MOSFET control module 2. The source is connected to the anode of the diode Dba and the source of the crystal switch Tbb. The gate of the crystal switch Tbb is connected to the output interface of the MOSFET control module 2. The drain is connected to the cathode of the diode Dbb and the positive terminal of the capacitor C2. The source is connected to the source of the crystal switch Tba and the anode of the diode Dbb.The gate of transistor Tc1 is connected to the output interface of MOSFET control module 2; its drain is connected to the cathode of diode Dc1, the drain of transistor Tc2, and the positive terminal of filter capacitor Cr; its source is connected to the anode of diode Dc1, the positive terminal of inductor L3, and the drain of transistor Tc3. The gate of transistor Tc2 is connected to the output interface of MOSFET control module 2; its drain is connected to the drain of transistor Tc1 and the cathode of diode Dc2; its source is connected to the anode of diode Dc2, the negative terminal of inductor L3, the drain of transistor Tc4, and the drain of transistor Tca. The gate of transistor Tc3 is connected to the output interface of MOSFET control module 2; its drain is connected to the cathode of diode Dc3 and the source of transistor Tc1; and its source is connected to the anode of diode Dc3. The negative terminal of the filter capacitor Cr is connected to the source of the crystal switch Tc4. The gate of the crystal switch Tc4 is connected to the output interface of MOSFET control module 2. The drain of the crystal switch Tc4 is connected to the cathode of diode Dc4 and the negative terminal of inductor L3, which is connected to the source of crystal switch Tc2. The source of Tc4 is connected to the source of crystal switch Tc3 and the negative terminal of capacitor C3. The drain of crystal switch Tca is connected to the negative terminal of inductor L3 and the cathode of diode Dca. The gate of Tca is connected to the output interface of MOSFET control module 2. The source of Tca is connected to the anode of diode Dca and the source of crystal switch Tcb. The gate of crystal switch Tcb is connected to the output interface of MOSFET control module 2. The drain of Tcb is connected to the cathode of diode Dcb and the positive terminal of capacitor C3. The source of Tca is connected to the source of crystal switch Tca and the anode of diode Dcb.

6. A two-stage three-phase inverter with a wide output voltage range for photovoltaic systems as described in claim 1, characterized in that: The three-phase load adopts a Y-connection method, and the input of the three-phase load is connected to the positive terminals of capacitor C1, capacitor C2, and capacitor C3 respectively.

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