Bus capacitance activation circuit, reactive power compensation circuit and photovoltaic inverter

Abstract

The utility model provides a bus capacitor activation circuit, wattless compensation circuit and photovoltaic inverter. Bus capacitor activation circuit includes first resistance, second resistance, third resistance, fourth resistance, first relay, second relay, third relay, fourth relay and rectifier circuit. First relay and third relay are used for closing in the first activation stage of bus capacitor, to activate bus capacitor through first circuit, and first circuit is composed of first resistance, second resistance, third resistance, fourth resistance and rectifier circuit; Second relay and fourth relay are used for closing in the second activation stage of bus capacitor, to activate bus capacitor through second circuit, and second circuit is composed of second resistance, fourth resistance and rectifier circuit, and first relay and third relay still are in the closed state in second activation stage. The utility model discloses the technical scheme can controllable step by step activation bus capacitor, realizes cost and control difficulty is lower.

Description

Technical Field

[0001] This utility model relates to the field of power electronics technology, and in particular to a bus capacitor activation circuit, a reactive power compensation circuit, and a photovoltaic inverter. Background Technology

[0002] When a photovoltaic (PV) inverter remains idle for an extended period due to reasons such as inventory buildup or power plant inactivity, the DC bus capacitors within the inverter remain unenergized. Directly energizing these DC bus capacitors under these conditions can lead to increased leakage current and voltage imbalance between the positive and negative bus terminals. In severe cases, this can cause the DC bus capacitors to explode, threatening the safe operation of the PV inverter. Therefore, it is necessary to activate DC bus capacitors that have been idle for a long time.

[0003] Currently, the need to activate the DC bus capacitor is usually determined based on the duration of no power supply. If activation is required, the DC bus capacitor is activated through an external circuit.

[0004] However, the above solutions will increase the operating costs of photovoltaic inverters. Utility Model Content

[0005] This invention provides a bus capacitor activation circuit, a reactive power compensation circuit, and a photovoltaic inverter to achieve controllable and gradual activation of the bus capacitor, thereby reducing implementation costs and control difficulty.

[0006] In a first aspect, this utility model provides a bus capacitor activation circuit, which can be applied in a photovoltaic inverter. The bus capacitor activation circuit may include: a first resistor, a second resistor, a third resistor, a fourth resistor, a first relay, a second relay, a third relay, a fourth relay, and a rectifier circuit. One end of the first resistor is connected to the grid side of the photovoltaic inverter, and the other end of the first resistor is connected to the first input terminal of the rectifier circuit through the second resistor and the first relay. The second relay is connected in parallel with the first resistor. One end of the third resistor is connected to the grid side, and the other end of the third resistor is connected to the second input terminal of the rectifier circuit through the fourth resistor and the third relay. The fourth relay is connected in parallel with the third resistor. The output terminal of the rectifier circuit is connected to the bus capacitor. The first relay and the third relay are used to close during the first activation phase of the bus capacitor to activate the bus capacitor through a first circuit, which consists of a first resistor, a second resistor, a third resistor, a fourth resistor, and a rectifier circuit. The second relay and the fourth relay are used to close during the second activation phase of the bus capacitor to activate the bus capacitor through the second circuit, which consists of the second resistor, the fourth resistor and the rectifier circuit. During the second activation phase, the first relay and the third relay are still in the closed state.

[0007] In conjunction with the first aspect, in one possible implementation, the sum of the impedances of the first resistor and the second resistor is equal to the sum of the impedances of the third resistor and the fourth resistor; The impedance of the second resistor is equal to the impedance of the fourth resistor.

[0008] In conjunction with the first aspect, in one possible implementation, during the first activation phase, the voltage across the bus capacitor is less than a first threshold.

[0009] In conjunction with the first aspect, in one possible implementation, the bus capacitor activation circuit further includes: a detection circuit connected to the bus capacitor; The detection circuit is used to detect the voltage across the bus capacitor.

[0010] In conjunction with the first aspect, in one possible implementation, the rectifier circuit includes: a first diode, a second diode, a third diode, and a fourth diode; The positive terminal of the first diode is connected to the negative terminal of the third diode and the first relay, the negative terminal of the first diode is connected to the negative terminal of the second diode and one end of the bus capacitor, the positive terminal of the second diode is connected to the negative terminal of the fourth diode and the third relay, and the positive terminal of the third diode is connected to the positive terminal of the fourth diode and the other end of the bus capacitor.

[0011] Secondly, this utility model provides a reactive power compensation circuit that can be applied in a photovoltaic inverter. The reactive power compensation circuit may include a bus capacitor activation circuit as described in the first aspect or any possible implementation thereof.

[0012] In conjunction with the second aspect, in one possible implementation, the reactive power compensation circuit further includes: an inverter circuit; The inverter circuit is connected in parallel with the bus capacitor activation circuit; The inverter circuit is used to send reactive power to the grid side of the photovoltaic inverter.

[0013] In conjunction with the second aspect, in one possible implementation, the inverter circuit includes: a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch; The first terminal of the first switch is connected to one end of the bus capacitor, the first terminal of the second switch, and the first terminal of the third switch. The second terminal of the first switch is connected to the first terminal of the fourth switch and the first phase of the power grid. The second terminal of the second switch is connected to the first terminal of the fifth switch and the second phase of the power grid. The second terminal of the third switch is connected to the first terminal of the sixth switch and the third phase of the power grid. The second terminal of the fourth switch is connected to the other end of the bus capacitor, the second terminal of the fifth switch, and the second terminal of the sixth switch.

[0014] In conjunction with the second aspect, in one possible implementation, the first to the sixth switching transistors are of the same type, which is any one of the following: insulated gate bipolar transistor, NMOS, or PMOS.

[0015] Thirdly, this utility model provides a photovoltaic inverter, which may include a bus capacitor activation circuit as in the first aspect or any possible implementation of the first aspect, or may include a reactive power compensation circuit as in the second aspect or any possible implementation of the second aspect.

[0016] This invention provides a bus capacitor activation circuit, a reactive power compensation circuit, and a photovoltaic inverter. In the technical solution provided by this invention, the grid side of the photovoltaic inverter is used as the activation energy source for the bus capacitor. The impedance of the activation circuit is adjusted by controlling the on / off state of a relay, thereby regulating the charging current of the bus capacitor and achieving controllable, gradual activation of the bus capacitor. This effectively reduces implementation costs and control difficulty. Attached Figure Description

[0017] Figure 1 A schematic structural diagram of a bus capacitor activation circuit provided by this utility model; Figure 2 This is a schematic structural diagram of a reactive power compensation circuit provided by this utility model. Detailed Implementation

[0018] The technical solution of this utility model will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0019] When a photovoltaic (PV) inverter remains idle for an extended period due to reasons such as inventory buildup or power plant inactivity, the DC bus capacitors within the inverter remain unenergized. Directly energizing these DC bus capacitors under these conditions can lead to increased leakage current and voltage imbalance between the positive and negative bus terminals. In severe cases, this can cause the DC bus capacitors to explode, threatening the safe operation of the PV inverter. Therefore, it is necessary to activate DC bus capacitors that have been idle for a long time.

[0020] Currently, the need for activation of the DC bus capacitor is typically determined based on the length of time it has been unpowered. If activation is required, it is done via an external circuit. However, this external circuit increases the operating cost of the photovoltaic inverter.

[0021] In one possible implementation, the activation voltage can be directly output from the DC-DC converter circuit of the photovoltaic inverter to activate the DC bus capacitor. However, this approach requires activating the DC-DC converter circuit of the photovoltaic inverter, increasing control complexity and risk. Furthermore, the DC-DC converter circuit requires photovoltaic modules as an energy source, making the activation effect susceptible to environmental influences. For example, activation of the DC bus capacitor may fail at night or in poor weather conditions.

[0022] Therefore, how to activate the bus capacitor without using an external circuit and using the grid side of the photovoltaic inverter as an energy source has become the technical problem that this utility model needs to solve.

[0023] In view of this, the present invention provides a bus capacitor activation circuit, a reactive power compensation circuit, and a photovoltaic inverter. In the technical solution provided by the present invention, the grid side of the photovoltaic inverter is used as the activation energy source for the bus capacitor. The impedance of the activation circuit is adjusted by controlling the on / off state of the relay, thereby regulating the charging current of the bus capacitor and activating it. The technical solution provided in this application uses the grid-side voltage as the energy source, which is highly operable and reduces the difficulty of implementation and application risks. Furthermore, the activation circuit provided in this application can also pre-charge the activated bus capacitor, providing a prerequisite for subsequent reactive power compensation on the grid side of the photovoltaic inverter, realizing the reuse of the activation circuit, and further reducing the implementation cost of the photovoltaic inverter. It should be understood that the technical solution provided by the present invention can be applied to scenarios in photovoltaic inverters where the DC bus capacitor needs to be activated due to long-term lack of power.

[0024] The following is combined Figure 1 and Figure 2 The technical solution provided by this utility model will be described in detail below.

[0025] Figure 1 A schematic structural diagram of a bus capacitor activation circuit provided by this utility model. Figure 1The bus capacitor activation circuit shown can be applied to photovoltaic inverters to activate the bus capacitors within the inverter. It should be understood that the photovoltaic inverter includes the grid side.

[0026] like Figure 1 As shown, the bus capacitor activation circuit 100 may include: a first resistor 110, a second resistor 120, a third resistor 130, a fourth resistor 140, a first relay 150, a second relay 160, a third relay 170, a fourth relay 180, and a rectifier circuit 190.

[0027] One end of the first resistor 110 is connected to the grid side of the photovoltaic inverter. The other end of the first resistor 110 is connected to the first input terminal of the rectifier circuit 190 through the second resistor 120 and the first relay 150. The second relay 160 is connected in parallel with the first resistor 110. One end of the third resistor 130 is connected to the grid side of the photovoltaic inverter. The other end of the third resistor 130 is connected to the second input terminal of the rectifier circuit 190 through the fourth resistor 140 and the third relay 170. The fourth relay 180 is connected in parallel with the third resistor 130. The output terminal of the rectifier circuit 190 is connected to the bus capacitor. It should be noted that one end of the bus capacitor is connected to the positive terminal of the DC bus (BUS) of the photovoltaic inverter, and the other end of the bus capacitor is connected to the negative terminal of the DC bus of the photovoltaic inverter.

[0028] In this invention, the first resistor 110, the second resistor 120, the third resistor 130, and the fourth resistor 140 are used to divide the AC voltage output from the grid side.

[0029] The first relay 150 is used to transmit AC voltage from the grid side to the rectifier circuit 190 through the first resistor 110 and the second resistor 120 when closed; correspondingly, the third relay 170 is used to transmit AC voltage from the grid side to the rectifier circuit 190 through the third resistor 130 and the fourth resistor 140 when closed; the rectifier circuit 190 is used to convert AC voltage into DC voltage and charge the bus capacitor, thereby activating the bus capacitor.

[0030] The second relay 160 is used to short-circuit the first resistor 110 when closed, so as to increase the charging current of the bus capacitor.

[0031] The fourth relay 180 is used to short-circuit the third resistor 130 when closed, so as to increase the charging current of the bus capacitor.

[0032] In this invention, the activation of the bus capacitor includes a first activation stage and a second activation stage. In the first activation stage, the first relay 150 and the third relay 170 are closed to activate the bus capacitor through a first circuit. The first circuit consists of a first resistor 110, a second resistor 120, a third resistor 130, a fourth resistor 140, and a rectifier circuit 190. In other words, the AC voltage from the grid side charges the bus capacitor through the first resistor 110, the second resistor 120, the third resistor 130, the fourth resistor 140, and the rectifier circuit 190. In the second activation stage, the second relay 160 and the fourth relay 180 remain closed to short-circuit the first resistor 110 and the third resistor 130, respectively, to activate the bus capacitor through the second circuit. The second circuit consists of a second resistor 120, a fourth resistor 140, and a rectifier circuit 190. In other words, the AC voltage from the grid side charges the bus capacitor through the second resistor 120, the fourth resistor 140, and the rectifier circuit 190. It should be understood that in the second activation stage, the first relay 150 and the third relay 170 remain closed. The charging current of the bus capacitor in the first activation stage is less than the charging current of the bus capacitor in the second activation stage.

[0033] In this invention, the bus capacitor is slowly charged with a small current in the first activation stage to improve activation safety. In the second activation stage, the second and fourth relays are closed to short-circuit the first and third resistors respectively, thereby reducing the impedance of the activation circuit, increasing the charging current of the bus capacitor, and thus improving the activation efficiency. This invention uses a stepped current charging method to activate the bus capacitor, balancing activation safety and efficiency, and extending the service life of the bus capacitor.

[0034] It should be noted that the first to fourth resistors can be understood as equivalent resistances, meaning that one or more of the first to fourth resistors can include at least one resistor.

[0035] Optionally, after the bus capacitor is activated, the first relay 150 to the fourth relay 180 can be disconnected.

[0036] In one possible implementation, the sum of the impedances of the first resistor 110 and the second resistor 120 can be equal to the sum of the impedances of the third resistor 130 and the fourth resistor 140 to improve the voltage stability of the activation circuit in the first activation stage. Correspondingly, the impedance of the second resistor 120 can be equal to the impedance of the fourth resistor 140 to improve the voltage stability of the activation circuit in the second activation stage.

[0037] In one possible implementation, the first activation phase can be stopped and the second activation phase can be started when the voltage across the bus capacitor reaches a first threshold; the second activation phase can be stopped when the voltage across the bus capacitor reaches a second threshold. That is, during the first activation phase, the voltage across the bus capacitor is less than the first threshold; during the second activation phase, the voltage across the bus capacitor is greater than or equal to the first threshold and less than the second threshold. When the voltage across the bus capacitor equals the second threshold, the bus capacitor can be considered fully charged.

[0038] In this implementation, the first threshold and the second threshold can be set according to actual conditions, and this application does not impose any restrictions on them. For example, the second threshold can be the rated voltage of the bus capacitor.

[0039] In one possible implementation, the bus capacitor activation circuit 100 may further include a detection circuit (not shown in the figure). The detection circuit may be connected to the bus capacitor.

[0040] The detection circuit is used to detect the voltage across the bus capacitor in order to switch the activation phase of the bus capacitor.

[0041] In one possible implementation, the rectifier circuit 190 may include: a first diode, a second diode, a third diode, and a fourth diode. The first diode is as follows: Figure 1 In the D1, the second diode is as follows Figure 1 In the D2, the third diode is as follows Figure 1 In the D3, the fourth diode is as follows Figure 1 D4 in the middle.

[0042] The anode of the first diode is connected to the cathode of the third diode and the first relay 150, the cathode of the first diode is connected to the cathode of the second diode and one end of the bus capacitor, the anode of the second diode is connected to the cathode of the fourth diode and the third relay 170, and the anode of the third diode is connected to the anode of the fourth diode and the other end of the bus capacitor.

[0043] Figure 2 This is a schematic structural diagram of a reactive power compensation circuit provided by this utility model. Figure 2 The reactive power compensation circuit shown may include Figure 1 The bus capacitor activation circuit 100 is described.

[0044] In some implementations, the bus capacitor activation circuit 100 can not only activate bus capacitors that have not been energized for a long time, but also precharge activated bus capacitors to facilitate reactive power compensation on the grid side of the photovoltaic inverter.

[0045] It should be noted that, compared to the activation process of the bus capacitor, the pre-charging process of the bus capacitor does not require a stepped current charging method; instead, a fixed current can be used to pre-charge the bus capacitor. This fixed current can be the current of the first activation stage or the current of the second activation stage, and can be set according to actual needs. No specific restrictions are imposed here.

[0046] like Figure 2 As shown, the reactive power compensation circuit may also include an inverter circuit. The inverter circuit can be connected in parallel with the bus capacitor activation circuit.

[0047] In this invention, after the bus capacitor has completed pre-charging, reactive power can be sent to the grid side of the photovoltaic inverter through the inverter circuit to achieve reactive power compensation on the grid side.

[0048] like Figure 2 As shown, the inverter circuit may include: a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch. The first switch is Q1 as shown in the figure, the second switch is Q2 as shown in the figure, the third switch is Q3 as shown in the figure, the fourth switch is Q4 as shown in the figure, the fifth switch is Q5 as shown in the figure, and the sixth switch is Q6 as shown in the figure.

[0049] The first terminal of the first switch is connected to one end of the bus capacitor, the first terminal of the second switch, and the first terminal of the third switch, respectively. The second terminal of the first switch is connected to the first terminal of the fourth switch and the first phase of the power grid, respectively. The second terminal of the second switch is connected to the first terminal of the fifth switch and the second phase of the power grid, respectively. The second terminal of the third switch is connected to the first terminal of the sixth switch and the third phase of the power grid, respectively. The second terminal of the fourth switch is connected to the other end of the bus capacitor, the second terminal of the fifth switch, and the second terminal of the sixth switch, respectively.

[0050] In this invention, the first phase can be a C-phase, the second phase can be a B-phase, and the third phase can be an A-phase, such as... Figure 2 As shown. In some implementations, the first phase can be phase A, the second phase can be phase B, and the third phase can be phase C; this application does not impose any restrictions on this.

[0051] In this invention, the voltage output from the power grid side to the activation circuit can be a line voltage. This invention does not limit the specific type of line voltage, such as... Figure 2 The neutral voltage is the voltage of line BC.

[0052] In this invention, the first to sixth switching transistors can be of the same type. For example, they can be any of the following: insulated gate bipolar transistor (IGBT), NMOS, or PMOS, without specific limitations.

[0053] The bus capacitor activation circuit provided by this utility model can not only activate the bus capacitor, but also be used for the pre-charging process of the bus capacitor during reactive power compensation. This enables circuit reuse, reduces implementation and maintenance costs, simplifies the inverter system structure, and improves system reliability.

[0054] This application also provides an inverter, including the bus capacitor activation circuit described in the foregoing embodiments, or including the reactive power compensation circuit described in the foregoing embodiments. Optionally, the inverter can be a photovoltaic inverter.

[0055] In one possible implementation, the inverter may further include a controller to control the switching on and off of the first to fourth relays and the first to sixth switching transistors in the foregoing embodiments.

[0056] The term "multiple" in this document refers to two or more. The character " / " generally indicates an "or" relationship between related objects; in formulas, " / " indicates a "division" relationship between related objects. Furthermore, it should be understood that in the description of this application, terms such as "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or order.

[0057] It is understood that, in the embodiments of this application, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0058] It should be emphasized that the above are merely preferred embodiments of the present utility model and are not intended to limit the present utility model in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present utility model shall still fall within the scope of the technical solution of the present utility model.

Claims

1. A bus capacitor activation circuit, applied in a photovoltaic inverter, characterized in that, include: The circuit consists of a first resistor, a second resistor, a third resistor, a fourth resistor, a first relay, a second relay, a third relay, a fourth relay, and a rectifier circuit. One end of the first resistor is connected to the grid side of the photovoltaic inverter, and the other end of the first resistor is connected to the first input terminal of the rectifier circuit through the second resistor and the first relay. The second relay is connected in parallel with the first resistor. One end of the third resistor is connected to the grid side, and the other end of the third resistor is connected to the second input terminal of the rectifier circuit through the fourth resistor and the third relay. The fourth relay is connected in parallel with the third resistor. The output terminal of the rectifier circuit is connected to the bus capacitor. The first relay and the third relay are used to close during the first activation phase of the bus capacitor to activate the bus capacitor through a first circuit, which consists of a first resistor, a second resistor, a third resistor, a fourth resistor, and a rectifier circuit. The second relay and the fourth relay are used to close during the second activation phase of the bus capacitor to activate the bus capacitor through the second circuit, which consists of the second resistor, the fourth resistor and the rectifier circuit. During the second activation phase, the first relay and the third relay are still in the closed state.

2. The bus capacitor activation circuit according to claim 1, characterized in that, The sum of the impedances of the first resistor and the second resistor is equal to the sum of the impedances of the third resistor and the fourth resistor; The impedance of the second resistor is equal to the impedance of the fourth resistor.

3. The bus capacitor activation circuit according to claim 1, characterized in that, During the first activation phase, the voltage across the bus capacitor is less than a first threshold.

4. The bus capacitor activation circuit according to claim 3, characterized in that, Also includes: The detection circuit is connected to the bus capacitor; The detection circuit is used to detect the voltage across the bus capacitor.

5. The bus capacitor activation circuit according to claim 1, characterized in that, The rectifier circuit includes: a first diode, a second diode, a third diode, and a fourth diode; The positive terminal of the first diode is connected to the negative terminal of the third diode and the first relay, the negative terminal of the first diode is connected to the negative terminal of the second diode and one end of the bus capacitor, the positive terminal of the second diode is connected to the negative terminal of the fourth diode and the third relay, and the positive terminal of the third diode is connected to the positive terminal of the fourth diode and the other end of the bus capacitor.

6. A reactive power compensation circuit, applied in a photovoltaic inverter, characterized in that, Includes the bus capacitor activation circuit as described in any one of claims 1 to 5.

7. The reactive power compensation circuit according to claim 6, characterized in that, Also includes: Inverter circuit; The inverter circuit is connected in parallel with the bus capacitor activation circuit; The inverter circuit is used to send reactive power to the grid side of the photovoltaic inverter.

8. The reactive power compensation circuit according to claim 7, characterized in that, The inverter circuit includes: a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch; The first terminal of the first switch is connected to one end of the bus capacitor, the first terminal of the second switch, and the first terminal of the third switch. The second terminal of the first switch is connected to the first terminal of the fourth switch and the first phase of the power grid. The second terminal of the second switch is connected to the first terminal of the fifth switch and the second phase of the power grid. The second terminal of the third switch is connected to the first terminal of the sixth switch and the third phase of the power grid. The second terminal of the fourth switch is connected to the other end of the bus capacitor, the second terminal of the fifth switch, and the second terminal of the sixth switch.

9. The reactive power compensation circuit according to claim 8, characterized in that, The first to the sixth switching transistors are of the same type, which is any one of the following: insulated gate bipolar transistor, NMOS or PMOS.

10. A photovoltaic inverter, characterized in that, It includes a bus capacitor activation circuit as described in any one of claims 1 to 5, or a reactive power compensation circuit as described in any one of claims 6 to 9.

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