Device for inhibiting potential-induced degradation and photovoltaic power generation system

Abstract

The utility model provides a device for suppressing potential-induced degradation and a photovoltaic power generation system. The input end of a rectifying circuit is connected with the alternating current end of an inverter, and the output end of the rectifying circuit is connected to the input end of a direct current conversion circuit through a positive direct current bus and a negative direct current bus; the output end of the DC conversion circuit is connected with the input end of the polarity switching circuit, the first output end of the polarity switching circuit is grounded, and the second output end of the polarity switching circuit is connected with the positive DC bus or the negative DC bus; the rectifying circuit converts alternating current into direct current; the direct current conversion circuit performs conversion processing on the direct current; the polarity switching circuit is configured to selectively output forward voltage or backward voltage based on the voltage output by the DC conversion circuit. According to the application, the direct current output by the rectifying circuit is converted through the direct current conversion circuit, and the forward voltage or the reverse voltage can be selectively output through the polarity switching circuit, so that the potential-induced degradation of the photovoltaic module is inhibited.

Description

Technical Field

[0001] This application relates to the field of photovoltaic technology, and in particular to a device for suppressing potential-induced degradation and a photovoltaic power generation system. Background Technology

[0002] Potential-induced degradation (PID) is a common degradation phenomenon in conventional framed crystalline silicon photovoltaic modules during operation.

[0003] For safety reasons, the frame of the photovoltaic module must be grounded, creating a potential difference between the photovoltaic cells and the module frame. The positive terminal of the cell string in the module is biased positively to the frame (ground), while the negative terminal is biased negatively. Near the ends, the bias voltage between the module cells and the frame is greater. Under this bias, the cations in the encapsulation material shift, resulting in a decrease in the cell's output power.

[0004] Therefore, solving the problem of performance degradation of photovoltaic modules caused by potential-induced degradation is a technical problem that needs to be solved by those skilled in the art. Utility Model Content

[0005] This application provides a device and a photovoltaic power generation system for suppressing potential-induced degradation, in order to solve the problem of performance degradation of photovoltaic modules caused by potential-induced degradation.

[0006] This application provides a device for suppressing potential-induced degradation, which is connected between the AC terminal of the inverter and the grid-connected transformer in a photovoltaic power generation system. The device includes a rectifier circuit, a positive DC bus, a negative DC bus, a DC-DC converter circuit, and a switching circuit, which includes a polarity switching circuit.

[0007] The input terminal of the rectifier circuit is connected to the AC terminal of the inverter. The output terminal of the rectifier circuit is connected to the input terminal of the DC-DC converter circuit through the positive DC bus and the negative DC bus. The output terminal of the DC-DC converter circuit is connected to the input terminal of the polarity switching circuit. The first output terminal of the polarity switching circuit is grounded. The second output terminal of the polarity switching circuit is connected to either the positive DC bus or the negative DC bus.

[0008] The rectifier circuit is used to convert alternating current into direct current; the DC-DC converter circuit is used to convert the direct current; the polarity switching circuit is configured to selectively output a positive voltage or a reverse voltage based on the voltage output by the DC-DC converter circuit, so as to suppress the potential-induced degradation of the photovoltaic modules in the photovoltaic power generation system.

[0009] This application also provides a photovoltaic power generation system, including the aforementioned device for suppressing potential-induced degradation, photovoltaic modules, inverters, and grid-connected transformers;

[0010] The photovoltaic module is connected to the DC terminal of the inverter, the AC terminal of the inverter is connected to the input terminal of the grid-connected transformer, and the output terminal of the grid-connected transformer is connected to the power grid or the load.

[0011] The device and photovoltaic power generation system for suppressing potential-induced degradation provided in this application convert the DC power output from the rectifier circuit through a DC-DC converter circuit, and selectively output positive or reverse voltage through a polarity switching circuit, thereby suppressing the potential-induced degradation of the photovoltaic module. Attached Figure Description

[0012] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0013] Figure 1 This is a schematic diagram of a photovoltaic power generation system provided in the embodiments of this application;

[0014] Figure 2 This is a schematic diagram of the rectifier circuit provided in the embodiments of this application;

[0015] Figure 3 This is a schematic diagram of another rectifier circuit provided in an embodiment of this application;

[0016] Figure 4 This is a schematic diagram of a DC-DC converter circuit provided in an embodiment of this application;

[0017] Figure 5 This is a schematic diagram of the switching circuit provided in the embodiments of this application. Detailed Implementation

[0018] To facilitate understanding of this application, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the application. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0019] This application provides a photovoltaic power generation system, including a photovoltaic module, an inverter, and a grid-connected transformer. The photovoltaic module is connected to the DC terminal of the inverter, the AC terminal of the inverter is connected to the input terminal of the grid-connected transformer, and the output terminal of the grid-connected transformer is connected to the power grid or a load.

[0020] The inverter can be one or at least two; when there are at least two inverters, the DC terminal of each inverter is connected to the corresponding photovoltaic module, and the AC terminals of all inverters are connected in parallel and then connected to the input terminal of the grid-connected transformer.

[0021] by Figure 1 For example, there are n inverters, as shown in the figure for inverters 1 to n. The topology of inverters 1 to n is not limited here and can be referenced from existing technologies. The DC terminal of inverter 1 is connected to the corresponding photovoltaic array 1... and the DC terminal of inverter n is connected to the corresponding photovoltaic array n. Photovoltaic arrays 1 to n consist of one or more photovoltaic modules (or one or more photovoltaic strings) assembled together mechanically and electrically in a certain way. The AC terminals of inverters 1 to n are connected in parallel and then connected to the input terminal of grid-connected transformer T1. The output terminal of grid-connected transformer T1 is connected to the power grid. The neutral point of the input terminal of grid-connected transformer T1 is not grounded.

[0022] Furthermore, the photovoltaic power generation system also includes a device for suppressing potential-induced degradation (such as a resistor) connected between the AC terminal of the inverter and the grid-connected transformer. Figure 1 (As shown in the dashed box). The device for suppressing potential-induced decay can be integrated inside the inverter cabinet or installed as a separate module on the low-voltage side (input side) of the grid-connected transformer T1.

[0023] In one example, the device for suppressing potential-induced decay includes a rectifier circuit, a positive DC bus BUS+, a negative DC bus BUS-, a DC-DC converter circuit, and a switching circuit, the switching circuit including a polarity switching circuit.

[0024] The input terminal of the rectifier circuit is connected to the AC terminal of the inverter. The output terminal of the rectifier circuit is connected to the input terminal of the DC-DC converter circuit through the positive DC bus BUS+ and the negative DC bus BUS-. The output terminal of the DC-DC converter circuit is connected to the input terminal of the polarity switching circuit. The first output terminal of the polarity switching circuit is grounded to PE. The second output terminal of the polarity switching circuit is connected to either the positive DC bus BUS+ or the negative DC bus BUS-.

[0025] The rectifier circuit converts alternating current (AC) to direct current (DC); the DC-DC converter circuit processes the DC-DC power; the polarity switching circuit is configured to selectively output a forward or reverse voltage based on the voltage output by the DC-DC converter circuit, thereby suppressing potential-induced degradation (PID) of the photovoltaic modules in the photovoltaic power generation system. Specifically, this achieves the compensation of the PV- potential to ground of P-type photovoltaic modules to be greater than or equal to 0, or the compensation of the PV+ potential to ground of N-type photovoltaic modules to be less than or equal to 0, thus suppressing the PID phenomenon of the photovoltaic modules.

[0026] Furthermore, the device for suppressing potential-induced decay also includes DC bus capacitors C1 and C2. DC bus capacitors C1 or C2 can be a series / parallel structure combining capacitors and resistors. One end of DC bus capacitor C1 is connected to the positive DC bus BUS+ (connection point: BUS+_PID), and the other end of DC bus capacitor C1 is connected to DC bus capacitor C2 (connection point: BUSN_PID). The other end of DC bus capacitor C2 is connected to the positive DC bus BUS- (connection point: BUS-_PID).

[0027] In one example, the rectifier circuit includes at least one of a three-phase two-level controllable rectifier circuit, a three-phase three-level controllable rectifier circuit, and a three-phase multi-level controllable rectifier circuit.

[0028] like Figure 2 As shown, switching transistors Q1 to Q6 constitute a three-phase two-level controlled rectifier circuit. This circuit converts three-phase AC power (phases A, B, and C in the diagram) into DC power, outputting a constant DC voltage. Specifically, the rectifier circuit also includes a rectifier controller, which adjusts the drive signals of switching transistors Q1 to Q6 to control the rectifier circuit to output a constant DC voltage.

[0029] Among them, the switching transistors Q1 to Q6 can be any combination of switching devices such as relays, bipolar junction transistors, insulated gate bipolar transistors, and metal-oxide-semiconductor field-effect transistors. Furthermore, a filter circuit is also provided between the rectifier circuit and the three phases, such as the filter inductors L1 to L3 in the figure.

[0030] like Figure 3 As shown, the device for suppressing potential-induced voltage decay also includes a power frequency transformer T2. The input terminal of the rectifier circuit is connected to the AC terminal of the inverter through the power frequency transformer T2. The power frequency transformer T2 enables step-up / step-down conversion of the grid voltage. The scheme with the power frequency transformer T2 allows for an additional stage of voltage regulation, increasing the voltage regulation range and facilitating the selection of switching devices in the rectifier circuit and DC-DC converter circuit.

[0031] In one example, the DC-DC converter circuit includes a buck isolation circuit that includes a DC / DC converter with an isolation transformer.

[0032] like Figure 4 As shown, the DC / DC converter with isolation transformer is a flyback converter topology, consisting of switch Q7, isolation transformer T3, diode D1, and capacitor C3. The DC-DC converter circuit can step down the constant DC voltage output from the rectifier circuit, and its output voltage is adjustable. Specifically, the step-down isolation power supply includes a power controller. Based on the voltage information on the DC side of the inverter, the power controller calculates a suitable output voltage reference value and controls the DC-DC converter circuit to output this voltage value, achieving positive and negative potential compensation on the DC side of the inverter. For P-type photovoltaic modules, the PV- to ground potential is compensated to be greater than or equal to 0; for N-type photovoltaic modules, the PV+ to ground potential is compensated to be less than or equal to 0.

[0033] The polarity switching circuit is a switching array composed of multiple switching transistors, which can invert the output voltage of the DC-DC converter circuit when needed, thereby increasing the voltage regulation range.

[0034] In one example, the polarity switching circuit includes a first switching circuit and a second switching circuit connected in parallel; the first switching circuit includes a first switching transistor and a second switching transistor connected in series, and the connection point between the first switching transistor and the second switching transistor is the second output terminal of the polarity switching circuit; the second switching circuit includes a third switching transistor and a fourth switching transistor connected in series, and the connection point between the third switching transistor and the fourth switching transistor is the first output terminal of the polarity switching circuit.

[0035] like Figure 5 As shown, the first switch K1 and the second switch K2, connected in series, constitute the first switching circuit. The third switch K3 and the fourth switch K4, also connected in series, constitute the second switching circuit. The first and second switching circuits are connected in parallel, specifically between the positive and negative input terminals of the polarity switching circuit. The connection point between the third switch K3 and the fourth switch K4 is the first output terminal of the polarity switching circuit, and the connection point between the first switch K1 and the second switch K2 is the second output terminal. When the first switch K1 and the fourth switch K4 are closed, and the second switch K2 and the third switch K3 are open, the polarity switching circuit outputs a positive voltage. When the first switch K1 and the fourth switch K4 are open, and the second switch K2 and the third switch K3 are closed, the polarity switching circuit outputs a reverse voltage.

[0036] The implementation methods of the first switch K1 to the fourth switch K4 can be referenced from the implementation methods of the switches Q1 to Q6.

[0037] The first output terminal of the polarity switching circuit is grounded through an inductor and / or a resistor, and can be an inductor, a resistor, or a combination of both (e.g., a series-parallel structure). The second output terminal of the polarity switching circuit is connected to the component selection circuit.

[0038] It should be noted that, in other examples, the polarity switching circuit can be located between the rectifier circuit and the DC-DC converter circuit.

[0039] In one example, the input terminal of the component selection circuit is connected to the second output terminal of the polarity switching circuit, the first output terminal of the component selection circuit is connected to the positive DC bus, and the second output terminal of the component selection circuit is connected to the negative DC bus.

[0040] The selection circuit is configured to selectively connect the second output terminal of the polarity switching circuit to the positive DC bus or connect the second output terminal of the polarity switching circuit to the negative DC bus.

[0041] like Figure 5 As shown, the component selection circuit includes a fifth switch K5 and a sixth switch K6. One end of the fifth switch K5 is connected to one end of the sixth switch K6 and serves as the input terminal of the component selection circuit. The other end of the fifth switch K5 is the first output terminal of the component selection circuit, and the other end of the sixth switch K6 is the second output terminal of the component selection circuit.

[0042] In practical implementation, the fifth switch K5 and the sixth switch K6 can be a single-pole double-throw switch or two independent switches. When the photovoltaic module is P-type, the module selection circuit is connected to the negative DC bus; when the photovoltaic module is N-type, the module selection circuit is connected to the positive DC bus. Alternatively, when the photovoltaic module is P-type, the module selection circuit is connected to the positive DC bus; when the photovoltaic module is N-type, the module selection circuit is connected to the negative DC bus.

[0043] It should be noted that while preferred embodiments of this application are provided in the specification and accompanying drawings, this application can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are not intended to impose additional limitations on the content of this application; their purpose is to provide a more thorough and comprehensive understanding of the disclosure of this application. Furthermore, the above-described technical features can be combined with each other to form various embodiments not listed above, all of which are considered to be within the scope of this application's specification. Moreover, those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A device for suppressing potential-induced degradation, said device being connected between the AC terminal of an inverter and a grid-connected transformer in a photovoltaic power generation system; characterized in that, The device includes a rectifier circuit, a positive DC bus, a negative DC bus, a DC-DC converter circuit, and a switching circuit, wherein the switching circuit includes a polarity switching circuit. The input terminal of the rectifier circuit is connected to the AC terminal of the inverter. The output terminal of the rectifier circuit is connected to the input terminal of the DC-DC converter circuit through the positive DC bus and the negative DC bus. The output terminal of the DC-DC converter circuit is connected to the input terminal of the polarity switching circuit. The first output terminal of the polarity switching circuit is grounded. The second output terminal of the polarity switching circuit is connected to either the positive DC bus or the negative DC bus. The rectifier circuit is used to convert alternating current into direct current; the DC-DC converter circuit is used to convert the direct current; the polarity switching circuit is configured to selectively output a positive voltage or a reverse voltage based on the voltage output by the DC-DC converter circuit, so as to suppress the potential-induced degradation of the photovoltaic modules in the photovoltaic power generation system.

2. The device for suppressing potential-induced decay according to claim 1, characterized in that, The polarity switching circuit includes a first switching circuit and a second switching circuit connected in parallel. The first switching circuit includes a first switching transistor and a second switching transistor connected in series, and the connection point between the first switching transistor and the second switching transistor is the second output terminal of the polarity switching circuit; the second switching circuit includes a third switching transistor and a fourth switching transistor connected in series, and the connection point between the third switching transistor and the fourth switching transistor is the first output terminal of the polarity switching circuit.

3. The device for suppressing potential-induced decay according to claim 1, characterized in that, The polarity switching circuit further includes a component selection circuit. The input terminal of the component selection circuit is connected to the second output terminal of the polarity switching circuit. The first output terminal of the component selection circuit is connected to the positive DC bus, and the second output terminal of the component selection circuit is connected to the negative DC bus. The selection circuit is configured to selectively connect the second output terminal of the polarity switching circuit to the positive DC bus or connect the second output terminal of the polarity switching circuit to the negative DC bus.

4. The device for suppressing potential-induced decay according to claim 3, characterized in that, The component selection circuit includes a fifth switch and a sixth switch. One end of the fifth switch and one end of the sixth switch are connected together and serve as the input terminal of the component selection circuit. The other end of the fifth switch is the first output terminal of the component selection circuit, and the other end of the sixth switch is the second output terminal of the component selection circuit.

5. The device for suppressing potential-induced decay according to claim 1, characterized in that, The first output terminal of the polarity switching circuit is grounded through an inductor and / or a resistor.

6. The device for suppressing potential-induced decay according to claim 1, characterized in that, The DC-DC conversion circuit includes a DC / DC converter with an isolation transformer.

7. The device for suppressing potential-induced decay according to claim 1, characterized in that, The rectifier circuit outputs a constant DC voltage, and the rectifier circuit includes at least one of a three-phase two-level controllable rectifier circuit, a three-phase three-level controllable rectifier circuit, and a three-phase multi-level controllable rectifier circuit.

8. The device for suppressing potential-induced decay according to claim 1, characterized in that, The device also includes a power frequency transformer, and the input terminal of the rectifier circuit is connected to the AC terminal of the inverter through the power frequency transformer.

9. A photovoltaic power generation system, characterized in that, Includes the device for suppressing potential-induced degradation, photovoltaic modules, inverters, and grid-connected transformers as described in any one of claims 1-8; The photovoltaic module is connected to the DC terminal of the inverter, the AC terminal of the inverter is connected to the input terminal of the grid-connected transformer, and the output terminal of the grid-connected transformer is connected to the power grid or the load.

10. The photovoltaic power generation system according to claim 9, characterized in that, The inverter is one or at least two; When there are at least two inverters, the DC terminal of each inverter is connected to the corresponding photovoltaic module, and the AC terminals of all inverters are connected in parallel and then connected to the input terminal of the grid-connected transformer.

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