SVG circuit applied to photovoltaic inverter and photovoltaic inverter

Abstract

This utility model discloses an SVG circuit and a photovoltaic inverter for use in photovoltaic inverters. The SVG circuit includes: a rectifier module, with its input end connected to a three-phase AC power grid and its output end connected to the AC auxiliary power source of the photovoltaic inverter, used to convert the AC power from the three-phase AC power grid into DC power to charge the AC auxiliary power source of the photovoltaic inverter; a switch module, connected to the output end of the rectifier module and the DC bus of the photovoltaic inverter, used to switch the electrical connection between the output end of the rectifier module and the DC bus of the photovoltaic inverter; and a control module, connected to the switch module, used to control the switch module to conduct the electrical connection between the output end of the rectifier module and the DC bus of the photovoltaic inverter during nighttime, so that the DC power output by the rectifier module is input to the DC bus of the photovoltaic inverter. The SVG circuit of this application, by sharing a rectifier module with the AC auxiliary power source of the photovoltaic inverter, has a simpler overall structure and can effectively reduce the cost of the entire system.

Description

Technical Field

[0001] This utility model relates to the field of photovoltaic inverter technology, and in particular to an SVG circuit and a photovoltaic inverter used in photovoltaic inverters. Background Technology

[0002] As the nation begins to build a power system primarily based on new energy sources, the proportion of new energy power generation (wind power / solar power) in the power grid is increasing, placing increasingly higher demands on the power quality of the grid. Currently, photovoltaic inverters already possess nighttime SVG (Static Var Generator) functionality. The SVG generates electricity during the day, and at night, it compensates for reactive power through the SVG circuit, regulating the power quality of the grid. Current SVG solutions for photovoltaic inverters draw power from the three-phase AC grid side and charge the inverter's bus voltage through an independent AC-DC rectifier circuit. Once the bus voltage reaches a level sufficient for the DC auxiliary power source to operate, this independent AC-DC rectifier circuit is disconnected, allowing the photovoltaic inverter to operate even at night. However, the photovoltaic inverter itself already has an AC-DC rectifier circuit for charging the AC auxiliary power source. Having two independent AC-DC rectifier circuits increases the number of circuit components and the complexity of the circuit structure, increasing the overall system cost. Utility Model Content

[0003] This utility model provides an SVG circuit and a photovoltaic inverter for use in photovoltaic inverters, which solves the problems of complex system circuit structure and high system cost of existing photovoltaic inverters.

[0004] In a first aspect, this utility model provides an SVG circuit for a photovoltaic inverter, comprising: a rectifier module, with its input end connected to a three-phase AC power grid and its output end connected to an AC auxiliary power source of the photovoltaic inverter, for converting AC power from the three-phase AC power grid into DC power to charge the AC auxiliary power source of the photovoltaic inverter; a switch module, connected to the output end of the rectifier module and the DC bus of the photovoltaic inverter, for switching the electrical connection between the output end of the rectifier module and the DC bus of the photovoltaic inverter; and a control module, connected to the switch module, for controlling the switch module to conduct the electrical connection between the output end of the rectifier module and the DC bus of the photovoltaic inverter during nighttime, so that the DC power output by the rectifier module is input to the DC bus of the photovoltaic inverter.

[0005] In the SVG circuit provided in this embodiment of the present invention, the rectifier module includes a rectifier bridge, the switch module includes at least one switch device, the input terminal of the rectifier bridge is used to connect to a three-phase AC power grid, the output terminal of the rectifier bridge is connected to the input side of the AC auxiliary power source of the photovoltaic inverter, the switch device is connected to the output terminal of the rectifier bridge and the DC bus of the photovoltaic inverter, and the control module is connected to the switch device, wherein the control module controls the switch module to be turned on during the nighttime period.

[0006] In the SVG circuit provided in this embodiment of the present invention, the rectifier bridge includes a first diode, a second diode, a third diode, and a fourth diode. The anodes of the first diode and the second diode are respectively connected to the cathodes of the third diode and the fourth diode. The cathodes of the first diode and the second diode are connected to one input terminal of the AC auxiliary power source of the photovoltaic inverter. The anodes of the third diode and the fourth diode are connected to the other input terminal of the AC auxiliary power source of the photovoltaic inverter. The switching device is connected to the cathodes of the first diode and the second diode and / or the anodes of the third diode and the fourth diode. The anodes of the first diode and the second diode are respectively used to connect to any two phases of the three-phase AC power grid.

[0007] In the SVG circuit provided in this embodiment of the present invention, the rectifier bridge further includes a fifth diode and a sixth diode. The anodes of the fifth diode and the sixth diode are connected to the anodes of the third diode and the fourth diode, and the cathodes of the fifth diode and the sixth diode are connected to the cathodes of the first diode and the second diode. The anode of the fifth diode is used to connect to the remaining phase of the three-phase AC power grid.

[0008] In the SVG circuit provided in this embodiment of the present invention, the rectifier module further includes a first resistor and a second resistor. One end of the first resistor and the second resistor are respectively connected to the anode of the first diode and the anode of the second diode. The other ends of the first resistor and the second resistor are respectively used to connect to any two phases of the three-phase AC power grid.

[0009] In the SVG circuit provided in this embodiment of the present invention, the rectifier module further includes a third resistor, one end of which is connected to the anode of the fifth diode, and the other end of which is used to connect to the remaining phase of the three-phase AC power grid.

[0010] In the SVG circuit provided in this embodiment of the present invention, two switching devices are provided, one of which is connected to the positive output terminal of the rectifier bridge and the positive DC bus of the photovoltaic inverter, and the other switching device is connected to the negative output terminal of the rectifier bridge and the negative DC bus of the photovoltaic inverter.

[0011] In the SVG circuit provided in this embodiment of the present invention, the switching device is a relay.

[0012] In the SVG circuit provided in this embodiment of the present invention, the switching device is a DC contactor.

[0013] Secondly, this utility model provides a photovoltaic inverter that includes the SVG circuit described in the first aspect.

[0014] This utility model provides an SVG circuit and a photovoltaic inverter for use in photovoltaic inverters. The SVG circuit includes: a rectifier module, with its input end connected to a three-phase AC power grid and its output end connected to the AC auxiliary power source of the photovoltaic inverter, used to convert the AC power from the three-phase AC power grid into DC power to charge the AC auxiliary power source of the photovoltaic inverter; a switch module, connected to the output end of the rectifier module and the DC bus of the photovoltaic inverter, used to switch the electrical connection between the output end of the rectifier module and the DC bus of the photovoltaic inverter; and a control module, connected to the switch module, used to control the switch module to conduct the electrical connection between the output end of the rectifier module and the DC bus of the photovoltaic inverter during nighttime, so that the DC power output by the rectifier module is input to the DC bus of the photovoltaic inverter. The SVG circuit of this application shares a rectifier module with the AC auxiliary power source of the photovoltaic inverter, resulting in fewer components and a simpler overall structure, which can effectively reduce the cost of the entire system. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A simplified structural diagram of the SVG circuit provided in this embodiment of the utility model;

[0017] Figure 2 A circuit diagram of the SVG circuit provided in this embodiment of the utility model;

[0018] Figure 3 Another circuit diagram of the SVG circuit provided in this embodiment of the utility model;

[0019] Figure 4 This is an application scenario diagram of the photovoltaic inverter provided in an embodiment of the present utility model.

[0020] The labels for the attached figures are as follows:

[0021] 10. Photovoltaic inverter; 11. AC auxiliary power supply; 12. Inverter circuit; 13. DC auxiliary power supply; 14. MPPT circuit; 2. Rectifier module; 21. Rectifier bridge; 3. Switching module; 4. Control module; 20. Three-phase AC power grid; 30. Photovoltaic power generation module. Detailed Implementation

[0022] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present utility model.

[0023] The directional terms used in this invention, such as "up," "down," "front," "back," "left," "right," "inner," "outer," and "side," are merely for reference to the accompanying drawings. Therefore, the directional terms used are for explanation and understanding of this invention, and not for limiting it. Furthermore, in the accompanying drawings, structures that are similar or identical are indicated by the same reference numerals.

[0024] To facilitate understanding of this utility model, the SVG circuit applied to the photovoltaic inverter 10 provided in the embodiment of this utility model will be described first. (Refer to...) Figures 1 to 3 See reference for details. Figure 1 The SVG circuit includes: an AC auxiliary power source 11 for supplying power to the photovoltaic inverter 10; a rectifier module 2 connected to the input terminal of the AC auxiliary power source 11 of the photovoltaic inverter 10, for connecting to the three-phase AC power grid 20 to convert AC power into DC power for use by the AC auxiliary power source 11 of the photovoltaic inverter 10; a switch module 3 connected to the output terminal of the rectifier module 2 and the DC bus of the photovoltaic inverter 10, for switching the electrical connection between the output terminal of the rectifier module 2 and the DC bus of the photovoltaic inverter 10; and a control module 4 connected to the switch module 3, for controlling the switch module 3 to conduct the electrical connection between the output terminal of the rectifier module 2 and the DC bus of the photovoltaic inverter 10 during nighttime, so that the DC power output by the rectifier module 2 is input to the DC bus of the photovoltaic inverter 10.

[0025] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0026] Currently, in photovoltaic power supply systems, photovoltaic inverters 10 typically integrate SVG (Static Var Generator) circuits. During the daytime, the photovoltaic inverter 10 operates normally to generate electricity for the grid. To improve power quality, at night, the photovoltaic inverter 10 operates the SVG function through the SVG circuit to compensate for reactive power in the grid. The SVG has two independent AC-DC rectifier circuits: one for operating the SVG function and another to charge the AC auxiliary power source 11 of the photovoltaic inverter 10. These two circuits operate independently. During the daytime, the AC-DC rectifier circuit connected to the AC auxiliary power source 11 charges the AC auxiliary power source 11, which then supplies power to the photovoltaic inverter 10. At night, the other independent AC-DC rectifier circuit charges the electrolytic capacitors on the DC bus of the photovoltaic inverter 10, enabling the DC auxiliary power source 13 within the photovoltaic inverter 10 to operate, thus achieving reactive power compensation for the grid. This approach obviously results in the photovoltaic inverter 10 having two sets of ACDC rectifier circuits, making the system circuitry too complex and increasing the system's circuit cost.

[0027] To address the aforementioned problems, this utility model provides an SVG circuit for a photovoltaic inverter 10, the specific concept of which is as follows:

[0028] The SVG circuit of this application includes a rectifier module 2, a switch module 3, and a control module 4. The input terminal of the rectifier module 2 is connected to a three-phase AC power grid 20, and the output terminal is connected to the AC auxiliary power source 11 of the photovoltaic inverter 10. It is used to convert the AC power of the three-phase AC power grid 20 into DC power to charge the AC auxiliary power source 11 of the photovoltaic inverter 10. The switch module 3 is connected to the output terminal of the rectifier module 2 and the DC bus of the photovoltaic inverter 10. It is used to switch the electrical connection between the output terminal of the rectifier module 2 and the DC bus of the photovoltaic inverter 10. The control module 4 is connected to the switch module 3. It is used to control the switch module 3 to conduct the electrical connection between the output terminal of the rectifier module 2 and the DC bus of the photovoltaic inverter 10 during the nighttime period, so that the DC power output by the rectifier module 2 is input to the DC bus of the photovoltaic inverter 10.

[0029] In specific implementation, the input terminal of rectifier module 2 is connected to the three-phase AC power grid 20, drawing power from it. The output terminal of rectifier module 2 is connected to the input side of AC auxiliary power source 11. Rectifier module 2 is used to convert the DC power from the three-phase AC power grid 20 into DC power to charge AC auxiliary power source 11. The AC auxiliary power source 11 of photovoltaic inverter 10 is mainly a DC isolated step-down power supply, which supplies power to photovoltaic inverter 10, providing auxiliary power to ensure the normal operation of photovoltaic inverter 10. Switch module 3 is connected to the output terminal of rectifier module 2 and to the DC bus of photovoltaic inverter 10. Switch module 3 adopts an electronically controlled switch design. Switch module 3 is used to connect and disconnect the electrical connection between the output terminal of rectifier module 2 and the DC bus of photovoltaic inverter 10. When switch module 3 is on, an electrical connection is established between the output terminal of rectifier module 2 and the DC bus of photovoltaic inverter 10. When switch module 3 is off, the electrical connection between the output terminal of rectifier module 2 and the DC bus of photovoltaic inverter 10 is disconnected. Control module 4 is connected to switch module 3. Control module 4 is an IC with logic control function, such as a microcontroller. Control module 4 is used to control switch module 3 to conduct the electrical connection between the output terminal of rectifier module 2 and the DC bus of photovoltaic inverter 10 during the nighttime period. In actual application, according to the control logic of SVG function, during the nighttime period, control module 4 controls switch module 3 to disconnect the electrical connection between the output terminal of rectifier module 2 and the DC bus of photovoltaic inverter 10, so that the DC power output of rectifier module 2 is input to the DC bus of photovoltaic inverter 10 to charge the capacitor on the DC bus of photovoltaic inverter 10, so that the bus voltage of photovoltaic inverter 10 rises to the voltage at which DC auxiliary power source 13 can work, so that DC auxiliary power source 13 can work normally, and the entire photovoltaic inverter 10 can start working and start reactive power compensation. Then rectifier module 2 can be disconnected, thereby achieving the purpose of photovoltaic inverter 10 working during the nighttime period. During the daytime, the photovoltaic inverter 10 does not need to operate the SVG function. The control module 4 controls the switch module 3 to disconnect the electrical connection between the output of the rectifier module 2 and the DC bus of the photovoltaic inverter 10. The specific times for daytime and nighttime can be defined in the control system. Overall, the SVG function and the AC auxiliary power source 11 of the photovoltaic inverter 10 share the same rectifier module 2, which simplifies the structure and reduces the system cost.

[0030] In one embodiment, reference is made to Figures 1 to 3The rectifier module 2 includes a rectifier bridge 21, and the switch module 3 includes at least one switch device S. The input terminal of the rectifier bridge 21 is connected to a three-phase AC power grid 20, and the output terminal of the rectifier bridge 21 is connected to the input side of the AC auxiliary power source 11 of the photovoltaic inverter 10. The switch device S is connected to the output terminal of the rectifier bridge 21 and the DC bus of the photovoltaic inverter 10. The control module 4 is connected to the switch device S, wherein the control module 4 controls the switch module 3 to be turned on during nighttime. In specific implementations, the rectifier module 2 is mainly composed of a rectifier bridge 21, which can be a single-phase rectifier bridge 21 or a three-phase rectifier bridge 21. The input terminal of the rectifier bridge 21 is connected to the three-phase AC power grid 20, and the output terminal of the rectifier bridge 21 is connected to the input side of the AC auxiliary power source 11 of the photovoltaic inverter 10. The switching module 3 consists of at least one switching device S, which is connected to the output terminal of the rectifier bridge 21 and the DC bus of the photovoltaic inverter 10. The number of switching devices S can be one or two. With one switching device S, it can be connected to either the positive or negative output terminal of the rectifier bridge 21, corresponding to the positive or negative DC bus of the photovoltaic inverter 10. With two switching devices S, one is connected to either the positive or negative output terminal of the rectifier bridge 21, and each device is connected to the positive or negative DC bus of the photovoltaic inverter 10. The control module 4 is connected to the switching devices S and can control their conduction state. In practical applications, the rectifier bridge 21 draws power from the three-phase AC power grid 20 and converts the AC power from the three-phase AC power grid 20 into DC power through rectification. This DC power is then output to the input side of the AC auxiliary power source 11 of the photovoltaic inverter 10, constantly charging the AC auxiliary power source 11 to ensure its functionality. Meanwhile, the control module 4 controls the conduction state of the switching device S according to the control logic of the system's SVG function. That is, the control module 4 controls the switching device S to conduct during the night and to disconnect during the day. Thus, during the night, the DC power output from the rectifier bridge is input to the DC bus of the photovoltaic inverter 10, supplying power to the DC bus of the photovoltaic inverter 10, charging the capacitors in the circuit, and enabling the DC auxiliary power source 13 to work, achieving reactive power compensation. During the day, the SVG function is not activated.

[0031] Furthermore, referring to Figure 2The rectifier bridge 21 includes a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4. The anodes of the first diode D1 and the second diode D2 are connected to the cathodes of the third diode D3 and the fourth diode D4, respectively. The cathodes of the first diode D1 and the second diode D2 are connected to one input terminal of the AC auxiliary power source 11 of the photovoltaic inverter 10, and the anodes of the third diode D3 and the fourth diode D4 are connected to the other input terminal of the AC auxiliary power source 11 of the photovoltaic inverter 10. The switching device S is connected to the cathodes of the first diode D1 and the second diode D2 and / or the anodes of the third diode D3 and the fourth diode D4. The anodes of the first diode D1 and the second diode D2 are respectively used to connect to any two phases of the three-phase AC power grid 20. In specific implementation, the rectifier bridge 21 is composed of a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4. The four diodes form a single-phase rectifier bridge 21, with each diode serving as a bridge arm. The anodes of the first diode D1 and the second diode D2 are connected to the cathodes of the third diode D3 and the fourth diode D4, respectively. The cathodes of the first diode D1 and the second diode D2 are connected to one input terminal of the AC auxiliary power source 11 of the photovoltaic inverter 10, specifically the positive input terminal. The anodes of the third diode D3 and the fourth diode D4 are connected to the other input terminal of the AC auxiliary power source 11 of the photovoltaic inverter 10, specifically the negative input terminal. The switching device S is connected to the cathodes of the first diode D1 and the second diode D2 and / or the anodes of the third diode D3 and the fourth diode D4. Specifically, when there is only one switching device S, it can be connected to either the positive or negative side of the rectifier bridge 21 output. When connected to the positive side of the rectifier bridge 21 output, it is connected to the cathodes of the first diode D1 and the second diode D2; when connected to the negative side of the rectifier bridge 21 output, it is connected to the anodes of the third diode D3 and the fourth diode D4. When there are two switching devices S, one is connected to the cathodes of the first diode D1 and the second diode D2, and the other is connected to the anodes of the third diode D3 and the fourth diode D4. The anodes of the first diode D1 and the second diode D2 are used to connect to any two phases of the three-phase AC power grid 20, respectively, drawing power from any two phases of the three-phase AC power grid 20, resulting in lower power extraction costs.

[0032] Furthermore, referring to Figure 3The rectifier bridge 21 further includes a fifth diode D5 and a sixth diode D6. The anodes of the fifth diode D5 and the sixth diode D6 are connected to the anodes of the third diode D3 and the fourth diode D4, and the cathodes of the fifth diode D5 and the sixth diode D6 are connected to the cathodes of the first diode D1 and the second diode D2. The anode of the fifth diode D5 is used to connect to the remaining phase of the three-phase AC power grid 20. In specific implementation, the rectifier bridge 21 is also composed of a fifth diode D5 and a sixth diode D6. The anodes of the fifth diode D5 and the sixth diode D6 are connected to the anodes of the third diode D3 and the fourth diode D4, and the cathodes of the fifth diode D5 and the sixth diode D6 are connected to the cathodes of the first diode D1 and the second diode D2. Overall, the fifth diode D5 and the sixth diode D6 together with the first diode D1 to the fourth diode D4 form a three-phase rectifier bridge 21. The anode of the fifth diode D5 is used to connect to the remaining phase of the three-phase AC power grid 20. Overall, the anodes of the first diode D1, the second diode D2, and the fifth diode D5 are respectively connected to the three phases of the three-phase AC power grid 20, so as to draw power from the three phases of the three-phase AC power grid 20 and meet the three-phase power demand.

[0033] Furthermore, referring to Figure 2 The rectifier module 2 further includes a first resistor R1 and a second resistor R2. One end of the first resistor R1 and the second resistor R2 are respectively connected to the anode of the first diode D1 and the anode of the second diode D2. The other ends of the first resistor R1 and the second resistor R2 are respectively used to connect to any two phases of the three-phase AC power grid 20. In a specific implementation, the rectifier module 2 further includes a first resistor R1 and a second resistor R2. One end of the first resistor R1 and the second resistor R2 are respectively connected to the anode of the first diode D1 and the anode of the second diode D2. The other ends of the first resistor R1 and the second resistor R2 are respectively used to connect to any two phases of the three-phase AC power grid 20. Overall, the first resistor R1 and the second resistor R2 are connected in series between the input side of the rectifier bridge 21 and the AC power grid. The first resistor R1 and the second resistor R2 can play a current-limiting role to prevent overcurrent from damaging the rectifier bridge 21 and other components.

[0034] Furthermore, referring to Figure 3The rectifier module 2 further includes a third resistor R3. One end of the third resistor R3 is connected to the anode of the fifth diode D5, and the other end of the third resistor R3 is used to connect to the remaining phase of the three-phase AC power grid 20. In a specific implementation, the rectifier module 2 further includes a third resistor R3. One end of the third resistor R3 is connected to the anode of the fifth diode D5. Two phases of the three-phase AC power grid 20 are respectively connected to the first resistor R1 and the second resistor R2. One end of the third resistor R3 is used to connect to the remaining phase of the three-phase AC power grid 20. The third resistor R3 serves to limit current and prevent overcurrent from damaging the rectifier bridge 21 and other components.

[0035] In one embodiment, reference is made to Figures 1 to 3 The system includes two switching devices S. One switching device S is connected to the positive output terminal of the rectifier bridge 21 and the positive DC bus of the photovoltaic inverter 10, while the other switching device S is connected to the negative output terminal of the rectifier bridge 21 and the negative DC bus of the photovoltaic inverter 10. Specifically, two switching devices S are used, connected to the positive and negative terminals of the DC bus of the photovoltaic inverter 10, respectively. One switching device S is connected to the positive output terminal of the rectifier bridge 21 and the positive DC bus of the photovoltaic inverter 10, while the other switching device S is connected to the negative output terminal of the rectifier bridge 21 and the negative DC bus of the photovoltaic inverter 10. The control module 4 is connected to both switching devices S and controls them simultaneously. In practical applications, the two switching devices S form a two-way switching function, which can improve the safety and reliability of the input. The control module 4 controls the two switches to be turned on simultaneously during the nighttime period so that the DC power output of the rectifier bridge 21 is input to the DC bus of the photovoltaic inverter 10, thereby charging the capacitor on the DC bus of the photovoltaic inverter 10. The DC auxiliary power source 13 realizes reactive power compensation.

[0036] In one embodiment, the switching device S is a relay. Specifically, the switching device S uses a relay, with corresponding contacts connected to the output terminal of the rectifier bridge 21 and the DC bus of the photovoltaic inverter 10. The relay coil is energized or de-energized by the control module 4, thereby achieving the connection and disconnection between the contacts and realizing the on / off control between the output terminal of the rectifier bridge 21 and the DC bus of the photovoltaic inverter 10. Since the relay achieves circuit switching through electromagnetic induction control of a mechanical switch, it has high reliability and durability.

[0037] In one embodiment, the switching device S is a DC contactor. Specifically, the switching device S uses a DC contactor, with its corresponding terminals connected to the output terminal of the rectifier bridge 21 and the DC bus of the photovoltaic inverter 10. The control module 4 outputs signals to control the connection and disconnection between the DC contactor terminals, thereby achieving the connection and disconnection between the contacts and realizing the on / off control between the output terminal of the rectifier bridge 21 and the DC bus of the photovoltaic inverter 10. The DC contactor has a strong overall current carrying capacity and better reliability of on / off control.

[0038] The SVG circuit provided in this application embodiment shares a set of rectifier modules with the AC auxiliary power source of the photovoltaic inverter, which reduces the number of components in the system and simplifies the overall structure, thus effectively reducing the cost of the entire system.

[0039] like Figure 4As shown, this utility model also provides a photovoltaic inverter 10. The photovoltaic inverter 10 includes the SVG circuit of the above embodiment. In addition, the photovoltaic inverter 10 may also include an inverter circuit 12, an AC auxiliary power supply circuit 11, a DC auxiliary power supply circuit 13, an MPPT (Maximum PowerPoint Tracking) circuit, etc. The MPPT circuit 14 is connected between the output side of the photovoltaic power generation module 30 and the DC bus of the photovoltaic inverter 10 to ensure that the photovoltaic system can output maximum power under various environmental conditions. The inverter circuit 12 is connected between the DC circuit side of the photovoltaic inverter 10 and the power grid on the user side, mainly used to convert DC power into AC power for input to the power grid for user use. The AC auxiliary power supply circuit 11 and the DC auxiliary power supply circuit 13 are both used to supply power for the operation of the photovoltaic inverter 10. The SVG circuit is integrated into the photovoltaic inverter 10 system to enable the photovoltaic inverter 10 to perform nighttime SVG function. The input terminal of the rectifier module 2 of the SVG circuit is connected to the three-phase AC power grid 20, and the output terminal is connected to the input side of the AC auxiliary power source 11 circuit of the photovoltaic inverter 10. The switching module 3 of the SVG circuit is connected to the output terminal of the rectifier module 2 and the DC bus of the photovoltaic inverter 10. The control module 4 of the SVG circuit can be integrated with the core control module 4 of the photovoltaic inverter 10 as a single module. In practical applications, during the daytime, the photovoltaic inverter 10 does not need to operate the SVG function. The switching module 3 of the SVG circuit disconnects the output terminal of the rectifier module 2 from the DC bus of the photovoltaic inverter 10. During the nighttime, the SVG circuit operates, and the switching module 3 connects the output terminal of the rectifier module 2 to the DC bus of the photovoltaic inverter 10, allowing the DC power output from the rectifier module 2 to be input to the DC bus. This charges the capacitors on the DC bus of the photovoltaic inverter 10, increases the bus voltage, and activates the DC auxiliary power source 13 circuit, enabling the entire photovoltaic inverter 10 to operate, achieving reactive power compensation for the power grid and improving the power supply quality of the grid. Since the previous instruction manual has already provided a detailed description of the specific structure and working principle of the SVG circuit, it will not be repeated here for the sake of brevity.

[0040] The photovoltaic inverter in this embodiment uses the SVG circuit described in the previous embodiment, resulting in a simpler overall circuit structure and lower system operating costs.

[0041] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this utility model, and these modifications or substitutions should all be covered within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the scope of the claims.

Claims

1. An SVG circuit for use in photovoltaic inverters, characterized in that, The SVG circuit includes: The rectifier module has its input end connected to the three-phase AC power grid and its output end connected to the AC auxiliary power source of the photovoltaic inverter. It is used to convert the AC power from the three-phase AC power grid into DC power to charge the AC auxiliary power source of the photovoltaic inverter. A switching module connects the output terminal of the rectifier module and the DC bus of the photovoltaic inverter, and is used to switch the electrical connection between the output terminal of the rectifier module and the DC bus of the photovoltaic inverter. The control module, connected to the switch module, is used to control the switch module to conduct the electrical connection between the output terminal of the rectifier module and the DC bus of the photovoltaic inverter during the nighttime period, so that the DC power output by the rectifier module is input into the DC bus of the photovoltaic inverter.

2. The SVG circuit according to claim 1, characterized in that, The rectifier module includes a rectifier bridge, and the switching module includes at least one switching device. The input terminal of the rectifier bridge is used to connect to a three-phase AC power grid, and the output terminal of the rectifier bridge is connected to the input side of the AC auxiliary power source of the photovoltaic inverter. The switching device is connected to the output terminal of the rectifier bridge and the DC bus of the photovoltaic inverter. The control module is connected to the switching device, wherein the control module controls the switching module to be turned on during nighttime.

3. The SVG circuit according to claim 2, characterized in that, The rectifier bridge includes a first diode, a second diode, a third diode, and a fourth diode. The anodes of the first diode and the second diode are connected to the cathodes of the third diode and the fourth diode, respectively. The cathodes of the first diode and the second diode are connected to one input terminal of the AC auxiliary power source of the photovoltaic inverter. The anodes of the third diode and the fourth diode are connected to the other input terminal of the AC auxiliary power source of the photovoltaic inverter. The switching device is connected to the cathodes of the first diode and the second diode and / or the anodes of the third diode and the fourth diode. The anodes of the first diode and the second diode are respectively used to connect to any two phases of the three-phase AC power grid.

4. The SVG circuit according to claim 3, characterized in that, The rectifier bridge also includes a fifth diode and a sixth diode. The anodes of the fifth diode and the sixth diode are connected to the anodes of the third diode and the fourth diode, and the cathodes of the fifth diode and the sixth diode are connected to the cathodes of the first diode and the second diode. The anode of the fifth diode is used to connect to the remaining phase of the three-phase AC power grid.

5. The SVG circuit according to claim 4, characterized in that, The rectifier module further includes a first resistor and a second resistor. One end of the first resistor and the second resistor are respectively connected to the anode of the first diode and the anode of the second diode. The other end of the first resistor and the second resistor are respectively used to connect to any two phases of the three-phase AC power grid.

6. The SVG circuit according to claim 5, characterized in that, The rectifier module also includes a third resistor, one end of which is connected to the anode of the fifth diode, and the other end of which is used to connect to the remaining phase of the three-phase AC power grid.

7. The SVG circuit according to any one of claims 2-6, characterized in that, The switching device is provided in two parts. One of the switching devices is connected to the positive output terminal of the rectifier bridge and the positive DC bus of the photovoltaic inverter, and the other switching device is connected to the negative output terminal of the rectifier bridge and the negative DC bus of the photovoltaic inverter.

8. The SVG circuit according to any one of claims 2-6, characterized in that, The switching device is a relay.

9. The SVG circuit according to any one of claims 2-6, characterized in that, The switching device is a DC contactor.

10. A photovoltaic inverter, characterized in that, Includes the SVG circuit as described in any one of claims 1-9.

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