Power converter

Abstract

The application provides a power converter, and belongs to the technical field of power electronics. The power converter comprises a discharge gap in parallel with an inductor. When the input end of a DC / DC conversion circuit suffers a differential mode lightning strike, due to the existence of the inductor, most of the lightning current charges a first capacitor, causing the voltage difference across the inductor to rise. When the voltage difference across the inductor rises to the breakdown voltage of the discharge gap, the two metal electrodes in the discharge gap are turned on and bypass the inductor. At this time, the lightning current can charge a second capacitor through the two turned-on metal electrodes, thereby discharging the lightning energy on the first capacitor to the second capacitor, so as to avoid the voltage of a direct current bus being too high to cause the switch tube in the DC / DC conversion circuit to fail due to voltage overstress. Moreover, the discharge gap is formed by metal electrodes on a circuit board, and has the advantages of simple structure and low cost.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a power converter. Background Technology

[0002] Power converters are core equipment in new energy power generation systems. Taking photovoltaic power generation systems as an example, the power converter used in photovoltaic power generation systems is a photovoltaic inverter, which is used to convert the direct current (DC) power from photovoltaic modules into alternating current (AC) power.

[0003] A photovoltaic (PV) inverter typically includes cascaded DC / DC converter circuits and DC / AC converter circuits. The input of the DC / DC converter circuit is connected to the PV modules, and its output is connected to the DC terminal of the DC / AC converter circuit via a DC bus. The AC terminal of the DC / AC converter circuit is used to connect to the power grid and the load. The DC / DC converter circuit performs voltage conversion (e.g., boost) on the DC output from the PV modules, while the DC / AC converter circuit converts the DC output from the DC / DC converter circuit into AC output.

[0004] Typically, photovoltaic inverters have surge protection circuits installed at the input terminals of the DC / DC conversion circuit and the AC terminals of the DC / AC conversion circuit. These surge protection circuits can provide protection against lightning strikes in common-mode lightning scenarios. However, these surge protection circuits cannot protect against differential-mode lightning strikes, resulting in lower safety and reliability of the photovoltaic inverter. Utility Model Content

[0005] This application provides a power converter that can solve the technical problem that the lightning protection circuit in the power converter cannot cope with differential mode lightning strikes, resulting in low safety and reliability of the power converter.

[0006] In a first aspect, a power converter is provided, comprising: a circuit board, a DC / DC conversion circuit, a DC bus, a DC / AC conversion circuit, a first capacitor, a second capacitor, an inductor, and a discharge gap. The input terminal of the DC / DC conversion circuit is connected to a DC source, and the DC bus is connected between the output terminal of the DC / DC conversion circuit and the DC terminal of the DC / AC conversion circuit. The first capacitor is connected between the positive and negative buses of the DC bus, and the second capacitor is connected in series with the inductor and then in parallel with the first capacitor. The discharge gap comprises: a first metal electrode and a second metal electrode located on the circuit board. One end of the first metal electrode is connected to one end of the inductor, and one end of the second metal electrode is connected to the other end of the inductor. The other ends of the first and second metal electrodes are opposite each other and separated by a gap. That is, there is a gap between the two metal electrodes in the discharge gap. The medium in the gap between the two metal electrodes is air, and this discharge gap is also called a gas discharge gap.

[0007] In the solution provided in this application, when the input terminal of the DC / DC converter circuit is struck by differential-mode lightning, the lightning current flows into the first capacitor through the DC / DC converter circuit. Due to the presence of the inductor, most of the lightning current charges the first capacitor, thereby increasing the voltage difference across the inductor. When the voltage difference across the inductor rises to the breakdown voltage of the discharge gap, the gas between the first and second metal electrodes in the discharge gap is broken down, and the first and second metal electrodes become conductive, thus bypassing the inductor. At this time, the lightning current can then charge the second capacitor through the conductive discharge gap, thereby discharging the lightning energy from the first capacitor to the second capacitor. Since both the first and second capacitors can absorb lightning energy after the discharge gap is conductive, excessively high DC bus voltage can be avoided, thus effectively preventing the switching transistors in the DC / DC converter circuit from failing due to voltage overstress. Based on the above analysis, it can be seen that the discharge gap in the power converter provided in this application can effectively protect the devices in the power converter under differential-mode lightning strike scenarios, thereby effectively improving the safety and reliability of the power converter. Furthermore, since the discharge gap is formed by metal electrodes on the circuit board, the structure of the discharge gap is simple and the cost is low.

[0008] Optionally, the circuit board is a printed circuit board (PCB), and both the first and second metal electrodes are copper foil traces on the PCB. That is, the discharge gap can be directly formed from the PCB copper foil. This significantly reduces the structural complexity and cost of the discharge gap.

[0009] Optionally, the capacitance of the second capacitor is greater than that of the first capacitor, that is, the capacitance of the second capacitor is greater than that of the first capacitor.

[0010] During the operation of the power converter, the first capacitor absorbs high-frequency ripple, and the second capacitor absorbs power frequency ripple. Since the energy of power frequency ripple is relatively large, the capacitance of the second capacitor is designed to be larger to ensure better absorption of power frequency ripple. Furthermore, in differential-mode lightning strike scenarios, when the discharge gap is closed and the lightning energy on the first capacitor is discharged to the second capacitor, the larger capacitance of the second capacitor results in a smaller voltage difference for the same lightning energy. This effectively avoids the risk of excessive voltage stress on the switching transistors caused by excessively high DC bus voltage.

[0011] Optionally, the first capacitor is a film capacitor, and the second capacitor is an electrolytic capacitor. Since the first capacitor is primarily used to absorb high-frequency ripple, and film capacitors have better high-frequency characteristics, a film capacitor is chosen for the first capacitor. Because the second capacitor needs a larger capacitance, and large-capacity electrolytic capacitors are less expensive, an electrolytic capacitor can be used for the second capacitor.

[0012] Optionally, the power converter includes two inductors and two discharge gaps corresponding to the two inductors. The two inductors are connected in series across the second capacitor, and each discharge gap is connected in parallel with its corresponding inductor. Furthermore, each discharge gap can bypass its corresponding inductor when the voltage difference across the inductor exceeds the breakdown voltage, thereby allowing the lightning strike energy to be discharged to the second capacitor in a timely and effective manner.

[0013] Optionally, the power converter also includes a third capacitor and a fourth capacitor. The first and third capacitors are connected in series between the positive and negative buses, and the second and fourth capacitors are connected in series between the positive and negative buses. Furthermore, one end of the inductor is connected to the series connection point between the first and third capacitors, and the other end of the inductor is connected to the series connection point between the second and fourth capacitors. That is, the fourth capacitor is connected in series with the inductor and then in parallel with the third capacitor.

[0014] Since the first and third capacitors are connected in series between the positive and negative busbars, and the second and fourth capacitors are also connected in series between the positive and negative busbars, an inductor can be placed between the two series nodes to achieve capacitor decoupling. Correspondingly, connecting a discharge gap in parallel with this inductor ensures effective dissipation of lightning energy in differential-mode lightning strike scenarios.

[0015] Secondly, a power converter is provided, comprising: a DC / DC conversion circuit, a DC bus, a DC / AC conversion circuit, a first capacitor, a second capacitor, an inductor, a switching circuit, and a control circuit. The input terminal of the DC / DC conversion circuit is connected to a DC source, and the DC bus is connected between the output terminal of the DC / DC conversion circuit and the DC terminal of the DC / AC conversion circuit. The first capacitor is connected between the positive and negative buses of the DC bus, and the second capacitor is connected in series with the inductor and then in parallel with the first capacitor. The switching circuit is connected in parallel with the inductor. The control circuit is used to control the switching circuit to conduct when the voltage difference across the inductor is detected to be greater than a voltage threshold, or when the current flowing into the inductor is detected to be greater than a current threshold.

[0016] In the solution provided in this application, when the input terminal of the DC / DC converter circuit is struck by differential-mode lightning, the lightning current flows into the first capacitor through the DC / DC converter circuit. Due to the presence of the inductor, most of the lightning current charges the first capacitor, thereby increasing the voltage difference across the inductor and increasing the current flowing into the inductor. When the voltage difference across the inductor exceeds the voltage threshold, or the current flowing into the inductor exceeds the current threshold, the control circuit can control the switching circuit to conduct, thereby bypassing the inductor. At this time, the lightning current can then charge the second capacitor through the conducting switching circuit, thereby dissipating the lightning energy on the first capacitor to the second capacitor. Since both the first and second capacitors can be used to absorb lightning energy, excessively high DC bus voltage can be avoided, thus effectively preventing the switching transistors in the DC / DC converter circuit from failing due to voltage overstress.

[0017] Optionally, the switching circuit is a switching transistor. This switching transistor can be, for example, an insulated-gate bipolar transistor (IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET). Because switching transistors have a fast response speed, using them as the switching circuit enables rapid discharge of lightning strike energy.

[0018] Optionally, the control circuit includes a detection unit and a driving unit. The detection unit detects the voltage difference across the inductor and the current flowing into the inductor. The driving unit controls the switching circuit's on / off state.

[0019] In power converters with large bus capacitors (i.e., large values ​​for the first and second capacitors), the inrush current generated by differential-mode lightning strikes is substantial. In this case, the voltage difference across the inductor changes more significantly, and the current flowing into the inductor also changes more noticeably. Correspondingly, the detection unit can more sensitively and quickly detect when the voltage difference exceeds a voltage threshold or the current exceeds a threshold. The drive unit can then promptly control the switching circuit to conduct, thereby enabling timely and rapid discharge of the lightning current.

[0020] Optionally, the capacitance of the second capacitor is greater than that of the first capacitor. The first capacitor is a film capacitor, and the second capacitor is an electrolytic capacitor.

[0021] Thirdly, a photovoltaic power generation system is provided, comprising: a plurality of power converters as provided in the first or second aspect above. The input terminals of the DC / DC conversion circuits in the plurality of power converters are used to connect to photovoltaic panels, and the AC terminals of the DC / AC conversion circuits in the plurality of power converters are connected in parallel, with the parallel AC terminals used to connect to the power grid.

[0022] In summary, this application provides a power converter. In the power converter provided by this application, a first capacitor is connected between the positive and negative DC bus, and a second capacitor is connected in series with an inductor and then in parallel with the first capacitor. Furthermore, the power converter also includes a discharge gap connected in parallel with the inductor. When the input terminal of the DC / DC converter circuit is struck by differential-mode lightning, the lightning current flows into the first capacitor through the DC / DC converter circuit. Due to the presence of the inductor, most of the lightning current charges the first capacitor, thereby increasing the voltage difference across the inductor. When the voltage difference across the inductor rises to the breakdown voltage of the discharge gap, the connection between the first and second metal electrodes in the discharge gap breaks down, and the first and second metal electrodes become conductive, thus bypassing the inductor. At this time, the lightning current can charge the second capacitor through the conductive discharge gap, thereby discharging the lightning energy from the first capacitor to the second capacitor. Since both the first and second capacitors can absorb lightning strike energy after the discharge gap is turned on, excessively high DC bus voltage can be avoided, thus effectively preventing the switching transistors in the DC / DC converter circuit from failing due to voltage overstress. This provides effective protection for the devices in the power converter, thereby significantly improving its safety and reliability. Furthermore, in the solution provided in this application, the discharge gap is formed by metal electrodes on the circuit board, resulting in a simpler structure and lower cost, effectively avoiding increasing the structural complexity and cost of the power converter. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a photovoltaic power generation system provided in an embodiment of this application;

[0024] Figure 2 This is a schematic diagram of the structure of a photovoltaic inverter provided in an embodiment of this application;

[0025] Figure 3 This is a schematic diagram of the structure of a power converter provided in an embodiment of this application;

[0026] Figure 4 This is a schematic diagram of another power converter provided in an embodiment of this application;

[0027] Figure 5 This is a schematic diagram of another power converter provided in the embodiments of this application;

[0028] Figure 6 This is a schematic diagram of another power converter provided in the embodiments of this application;

[0029] Figure 7 This is a schematic diagram of another power converter provided in the embodiments of this application. Detailed Implementation

[0030] The power converter provided in the embodiments of this application is described in detail below with reference to the accompanying drawings. First, the key terms involved in the embodiments of this application are introduced.

[0031] Photovoltaic (PV) panels: also known as photovoltaic modules, are devices used to convert solar energy into direct current (DC) electricity.

[0032] Power converter: A device used to convert power by switching power devices (i.e., switching transistors). Power converters include inverters used to implement DC / AC conversion. For example, an inverter can be a photovoltaic inverter or a power conversion system (PCS), etc.

[0033] Differential-mode lightning strike: This refers to the lightning voltage (also known as surge voltage) generated by a lightning strike appearing in a circuit as a differential-mode signal. For example, the surge voltage generated by a lightning strike is applied between the positive and negative terminals of the DC input of a power converter.

[0034] Common-mode lightning strike: This refers to the lightning voltage (also known as surge voltage) generated by a lightning strike appearing in a circuit as a common-mode signal. For example, the surge voltage generated by a lightning strike is applied between the positive terminal and ground, and between the negative terminal and ground, of the DC input of a power converter.

[0035] The power converter provided in this application embodiment can be a photovoltaic inverter in a photovoltaic power generation system. Taking a photovoltaic inverter as an example, the application scenario of this power converter (i.e., a photovoltaic power generation system) will be introduced. Figure 1 This is a schematic diagram of the structure of a photovoltaic power generation system provided in an embodiment of this application. Figure 1 As shown, the photovoltaic power generation system may include at least one (i.e., one or more) photovoltaic inverters. The DC terminal of each photovoltaic inverter is used to connect to the photovoltaic panels, and the AC terminal can be connected to one end of a transformer. For example, see reference... Figure 1 Multiple photovoltaic (PV) inverters can have their AC terminals connected in parallel to an AC bus, which is then connected to one end of a transformer. The other end of the transformer is used to connect to the power grid. Each PV inverter converts the direct current (DC) from the photovoltaic panels into alternating current (AC) before transmitting it to the transformer. The transformer then steps up the AC output from these multiple PV inverters before outputting it to the power grid. It is understandable that... Figure 1 The architecture of the photovoltaic power generation system shown is only an illustration. Other architectures can also be used for the photovoltaic power generation system, and this application does not limit them.

[0036] Figure 2 and Figure 3 This is a schematic diagram of the power converter provided in an embodiment of this application, and it is illustrated using a photovoltaic inverter as an example. Figure 2 and Figure 3 As shown, the photovoltaic inverter may include two cascaded power conversion circuits. The first stage power conversion circuit is a DC / DC converter 10, and the second stage power conversion circuit is a DC / AC converter 20. The input terminal of the DC / DC converter 10 is connected to the photovoltaic panel, and the output terminal is connected to a DC bus, which is connected to the DC terminal of the DC / AC converter 20. The DC / DC converter 10 can be used to convert the DC power provided by the photovoltaic panel and output it to the subsequent DC / AC converter 20. For example, the DC / DC converter 10 can be a boost circuit, which can boost the DC power provided by the photovoltaic panel and output it to the DC / AC converter 20. The AC terminal of the DC / AC converter 10 is connected to the power grid, for example, the AC terminal is connected to the power grid through a transformer. The DC / AC converter 20 is used to convert the DC power output from the DC / DC converter 10 into AC power and output it to the power grid. Optionally, refer to... Figure 2 The photovoltaic inverter may include multiple DC / DC conversion circuits 10, the outputs of which are connected in parallel to a DC bus. This DC bus is connected to the DC terminal of a DC / AC conversion circuit 20.

[0037] In the embodiments of this application, such as Figure 3As shown, the power converter also includes a first capacitor C1, a second capacitor C2, and a decoupling unit disposed between the two stages of power conversion circuits. The first capacitor C1 and the second capacitor C2 are also called bus capacitors, with the first capacitor C1 connected between the positive bus BUS+ and the negative bus BUS- of the DC bus. The second capacitor C2 is connected in series with the decoupling unit and then in parallel with the first capacitor C1. The first capacitor C1 is generally a small-capacity film capacitor used to absorb high-frequency ripple. The second capacitor C2 is generally a large-capacity electrolytic capacitor used to absorb power frequency ripple. The decoupling unit may include an inductor, or may also include a resistor connected in series and / or in parallel with the inductor. The decoupling unit is used to decouple (also called decoupling) the first capacitor C1 and the second capacitor C2 to prevent high-frequency ripple from flowing into the second capacitor C2.

[0038] Continue to refer to Figure 3 The input terminal of the DC / DC converter circuit 10 (i.e., the input terminal of the power converter) is usually equipped with an input surge protection circuit, and the AC output terminal of the DC / AC converter circuit 20 (i.e., the output terminal of the power converter) is usually equipped with an output surge protection circuit. These surge protection circuits can effectively protect the power converter from common-mode lightning strikes. However, in photovoltaic power generation systems, photovoltaic panels are generally arranged in an array, and the corresponding wiring (i.e., the wiring between the photovoltaic panels and the power converter) has loops at the top and bottom. The area of ​​the inductive loop formed by the wiring is large, making the DC side (i.e., the input terminal of the DC / DC converter circuit 10) susceptible to large differential-mode lightning strikes.

[0039] For differential-mode lightning strikes, the aforementioned lightning protection circuit is ineffective. Furthermore, the lightning current generated by this strike will flow from the loop formed by the inductor and diode in the DC / DC converter circuit 10 into the DC bus, charging the first capacitor C1. Due to the presence of the decoupling unit, the lightning current cannot enter the second capacitor C2, meaning the second capacitor C2 does not absorb the charge. This leads to an increase in the voltage across the first capacitor C1, which in turn increases the voltage across the DC bus, potentially causing overstress (e.g., voltage overstress) failure of the switching transistors in the DC / DC converter circuit 10.

[0040] This application provides a power converter that can effectively and promptly dissipate the lightning energy of a differential-mode lightning strike when subjected to such a strike, preventing the switching transistors in the power converter from failing due to overstress. Figure 4 and Figure 5As shown, the power converter provided in this embodiment includes: a circuit board 00, a DC / DC conversion circuit 10, a DC / AC conversion circuit 20, a DC bus (BUS+, BUS-), a first capacitor C1, a second capacitor C2, an inductor L, and a discharge gap 30. The input terminal of the DC / DC conversion circuit 10 is used to connect to a DC source. The DC bus is connected between the output terminal of the DC / DC conversion circuit 10 and the DC terminal of the DC / AC conversion circuit 20; that is, the output terminal of the DC / DC conversion circuit 10 is connected to the DC terminal of the DC / AC conversion circuit 20 through the DC bus. This DC bus includes a positive bus BUS+ and a negative bus BUS-.

[0041] In this embodiment, the power converter can be a photovoltaic inverter, and correspondingly, the DC source can be a photovoltaic panel. Alternatively, the power converter can be an energy storage converter, and correspondingly, the DC source can be an energy storage battery. The DC / DC converter circuit 10 is used to perform voltage conversion on the DC power supplied by the DC source, such as boost conversion. The DC / AC converter circuit 20 is used to convert the DC power output from the DC / DC converter circuit 10 into AC power and output it to the power grid or load. In the scenario where the power converter is an energy storage converter, the DC / AC converter circuit 20 is also used to convert the AC power from the power grid into DC power, and the DC / DC converter circuit 10 is also used to perform voltage conversion (such as step-down) on the DC power output from the DC / AC converter circuit 20 to charge the energy storage battery.

[0042] Continue to refer to Figure 4 In the power converter, the first capacitor C1 is connected between the positive bus BUS+ and the negative bus BUS-. The second capacitor C2 is connected in series with the inductor L and then in parallel with the first capacitor C1. (Reference) Figure 3 and Figure 4 The inductor L can be used as a decoupling unit to achieve decoupling between the first capacitor C1 and the second capacitor C2.

[0043] The discharge gap 30 includes a first metal electrode 31 and a second metal electrode 32 located on the circuit board 00. One end of the first metal electrode 31 is connected to one end of the inductor L, and one end of the second metal electrode 32 is connected to the other end of the inductor L. That is, the discharge gap 30 is connected in parallel with the inductor L. Furthermore, from... Figure 4 It can be seen that the other end of the first metal electrode 31 is opposite to the other end of the second metal electrode 32 and there is a certain distance between them. Alternatively, it can be understood that the other end of the first metal electrode 31 is opposite to the other end of the second metal electrode 32, and there is a gas medium between them. Accordingly, this discharge gap 30 can also be called a gas discharge gap, or simply a gas discharge gap.

[0044] In this embodiment, when the input terminal of the DC / DC converter circuit 10 is struck by differential-mode lightning, the lightning current flows into the DC bus through the DC / DC converter circuit 10. Due to the presence of the inductor L (also called the decoupling inductor), most of the lightning current charges the first capacitor C1, thereby increasing the voltage difference across the inductor L. When the voltage difference across the inductor L increases to the breakdown voltage of the discharge gap 30, the gas between the first metal electrode 31 and the second metal electrode 32 in the discharge gap 30 is broken down, and the first metal electrode 31 and the second metal electrode 32 become conductive, thus bypassing the inductor L. At this time, the lightning current can then charge the second capacitor C2 through the conductive discharge gap 30, thereby discharging the lightning energy on the first capacitor C1 to the second capacitor C2. Since both the first capacitor C1 and the second capacitor C2 can be used to absorb lightning energy (also known as absorbing lightning charge), the bus voltage of the DC bus (i.e., the voltage difference between the positive bus BUS+ and the negative bus BUS-) can be avoided from being too high, thereby effectively preventing the switching transistors in the DC / DC converter circuit 10 from failing due to voltage overstress.

[0045] Furthermore, in the solution provided in this application embodiment, the discharge gap 30 is formed by metal electrodes on the circuit board 00, which has a relatively simple structure and low cost, thereby effectively avoiding increasing the structural complexity and cost of the power converter.

[0046] It is understandable that the breakdown voltage of the discharge gap 30 refers to the minimum voltage value that can cause the discharge gap 30 to break down. This breakdown voltage is greater than the voltage difference across the inductor L during normal operation of the power converter, in order to prevent the discharge gap 30 from malfunctioning and affecting the normal operation of the power converter. For example, the range of voltage difference across the inductor L under different operating conditions of the power converter can be tested in advance. When designing the discharge gap 30, it is necessary to ensure that the breakdown voltage of the discharge gap 30 is greater than the upper limit of the tested voltage difference range.

[0047] It is also understandable that when lightning current (also known as surge current) enters the DC bus, inductor L and the first capacitor C1 will resonate and generate greater energy. The stress generated by the resonant energy may damage components such as switching transistors in the DC / DC converter circuit 10 and the DC / AC converter circuit 20. The solution provided in this application provides a discharge gap 30 connected in parallel with inductor L. When instantaneous energy rushes into inductor L, the discharge gap 30 bypasses inductor L, thereby effectively preventing damage to components in the power conversion circuit caused by resonance of inductor L due to the residual voltage of lightning surge.

[0048] Optionally, the circuit board 00 can be a PCB. The first metal electrode 31 and the second metal electrode 32 are both copper foil traces on the PCB. That is, the discharge gap 30 can be formed by copper foil on the PCB, thereby ensuring that the structure of the discharge gap 30 is relatively simple and the cost is low.

[0049] Optionally, the circuit board 00 in the power converter may include one or more PCBs. The DC / DC conversion circuit 10, the DC / AC conversion circuit 20, the DC bus, the first capacitor C1, the second capacitor C2, the inductor L, and the discharge gap 30 may be located on the same PCB or on different PCBs. For example, the DC / DC conversion circuit 10 may be located on one PCB, the DC / AC conversion circuit 20 may be located on one PCB, and the first capacitor C1, the second capacitor C2, the inductor L, and the discharge gap 30 may be located on one PCB.

[0050] Optionally, the capacitance value of the second capacitor C2 in the power converter is greater than that of the first capacitor C1. Since the second capacitor C2 is mainly used to absorb power frequency ripple, and the energy of power frequency ripple is relatively large, designing the capacitance value of the second capacitor C2 to be larger can ensure that its absorption effect (also known as suppression effect) of power frequency ripple is better.

[0051] In this embodiment, when the input terminal of the DC / DC converter circuit 10 is struck by differential-mode lightning, causing the discharge gap 30 to break down, the lightning energy on the first capacitor C1 can be quickly discharged to the second capacitor C2. Alternatively, it can be understood that the discharge gap 30 can discharge the voltage across the inductor L to the second capacitor C2. Because the capacitance of the second capacitor C2 is larger, i.e., its capacity is greater, the voltage difference generated by the same lightning energy on the second capacitor C2 is smaller, thus effectively avoiding the risk of excessive voltage on the DC bus causing voltage overstress in the switching transistor.

[0052] Optionally, the first capacitor C1 is a film capacitor, and the second capacitor C2 is an electrolytic capacitor. Since the first capacitor C1 is mainly used to absorb high-frequency ripple, and film capacitors have better high-frequency characteristics, a film capacitor is used for the first capacitor C1. Since the capacitance value of the second capacitor C2 needs to be large, and large-capacity electrolytic capacitors are cheaper, an electrolytic capacitor is used for the second capacitor C2.

[0053] As one possible implementation, such as Figure 4 As shown, the power converter includes two inductors L, which are connected in series across the two ends of the second capacitor C2. That is, one end of the second capacitor C2 is connected in series with one inductor L and then connected to one end of the first capacitor C1, for example, to the positive bus BUS+. The other end of the second capacitor C2 is connected in series with the other inductor L and then connected to the other end of the first capacitor C1, for example, to the negative bus BUS-.

[0054] In this implementation, refer to Figure 4 The power converter includes two discharge gaps 30 corresponding to the two inductors L, with each discharge gap 30 connected in parallel with one of the corresponding inductors L. Furthermore, each discharge gap 30 can bypass the corresponding inductor L when the voltage difference across it exceeds the breakdown voltage, thereby discharging the lightning strike energy to the second capacitor C2.

[0055] As another possible implementation, such as Figure 5 As shown, the power converter also includes a third capacitor C3 and a fourth capacitor C4. The first capacitor C1 and the third capacitor C3 are connected in series between the positive bus BUS+ and the negative bus BUS-, and the second capacitor C2 and the fourth capacitor C4 are connected in series between the positive bus BUS+ and the negative bus BUS-. Furthermore, in this implementation, one end of the inductor L is connected to the series connection point between the first capacitor C1 and the third capacitor C3, and the other end of the inductor L is connected to the series connection point between the second capacitor C2 and the fourth capacitor C4. That is, the fourth capacitor C4 is connected in series with the inductor L and then in parallel with the third capacitor C3.

[0056] In this implementation, since the first capacitor C1 and the third capacitor C3 are connected in series between the positive bus BUS+ and the negative bus BUS-, and the second capacitor C2 and the fourth capacitor C4 are connected in series between the positive bus BUS+ and the negative bus BUS-, a decoupling effect can be achieved by setting an inductor L between the two series nodes. Correspondingly, a discharge gap 30 is connected in parallel with this inductor L to ensure effective discharge of lightning energy in differential mode lightning strike scenarios.

[0057] In this implementation, the capacitance of the fourth capacitor C4 is greater than that of the third capacitor C3. Furthermore, the third capacitor C3 can be a film capacitor, and the fourth capacitor C4 can be an electrolytic capacitor.

[0058] In scenarios where the power converter also includes a third capacitor C3 and a fourth capacitor C4, the power converter can also include two inductors L. Furthermore, the second capacitor C2 is connected in series with one inductor L and then connected to the positive bus BUS+, and the fourth capacitor C4 is connected in series with the other inductor L and then connected to BUS-. The series connection point between the first capacitor C1 and the third capacitor C3 is directly connected to the series connection point between the second capacitor C2 and the fourth capacitor C4.

[0059] In summary, this application provides a power converter that includes a discharge gap connected in parallel with an inductor. When the input terminal of the DC / DC converter circuit is struck by differential-mode lightning, the lightning current flows through the DC / DC converter circuit into the first capacitor, increasing the voltage difference across the inductor. When this voltage difference reaches the breakdown voltage of the discharge gap, the gas between the first and second metal electrodes in the discharge gap is broken down, bypassing the inductor. At this time, the lightning current can charge the second capacitor through the conducting discharge gap, thereby discharging the lightning energy from the first capacitor to the second capacitor. Since both the first and second capacitors can absorb lightning energy after the discharge gap is conducting, excessively high DC bus voltage can be avoided, effectively preventing the switching transistors in the DC / DC converter circuit from failing due to voltage overstress.

[0060] This application provides another power converter, such as... Figure 6 As shown, the power converter includes: a DC / DC converter circuit 10, a DC bus, a DC / AC converter circuit 20, a first capacitor C1, a second capacitor C2, an inductor L, a switching circuit 40, and a control circuit 50. The input terminal of the DC / DC converter circuit 10 is connected to a DC source. The DC bus is connected between the output terminal of the DC / DC converter circuit 10 and the DC terminal of the DC / AC converter circuit 20; that is, the output terminal of the DC / DC converter circuit 10 is connected to the DC terminal of the DC / AC converter circuit 20 via the DC bus. The DC bus includes a positive bus BUS+ and a negative bus BUS-.

[0061] The first capacitor C1 is connected between the positive busbar BUS+ and the negative busbar BUS-. The second capacitor C2 is connected in series with the inductor L and then in parallel with the first capacitor C1. The switching circuit 40 is connected in parallel with the inductor L. The control circuit 50 is used to control the switching circuit 40 to conduct when the voltage difference across the inductor L is detected to be greater than a voltage threshold, or when the current flowing into the inductor L is detected to be greater than a current threshold.

[0062] In this embodiment, when the input terminal of the DC / DC converter circuit 10 is struck by differential-mode lightning, the lightning current flows into the DC bus through the DC / DC converter circuit 10. Due to the presence of the inductor L (also called the decoupling inductor), most of the lightning current charges the first capacitor C1, thereby increasing the voltage difference across the inductor L and increasing the current flowing into the inductor L. When the voltage difference across the inductor L exceeds the voltage threshold, or the current flowing into the inductor L exceeds the current threshold, the control circuit 50 can control the switching circuit 40 to conduct, thereby bypassing the inductor L. That is, the control circuit 50 can bypass the inductor L by actively controlling the switching circuit 40 to short-circuit. At this time, the lightning current can charge the second capacitor C2 through the conducting switching circuit 40, thereby discharging the lightning energy on the first capacitor C1 to the second capacitor C2. Since both the first capacitor C1 and the second capacitor C2 can be used to absorb lightning energy (also known as absorbing lightning charge), the bus voltage of the DC bus (i.e., the voltage difference between the positive bus BUS+ and the negative bus BUS-) can be avoided from being too high, thereby effectively preventing the switching transistors in the DC / DC converter circuit 10 from failing due to voltage overstress.

[0063] Understandably, the aforementioned voltage thresholds are greater than the voltage difference across inductor L during normal operation of the power converter, and the aforementioned current thresholds are greater than the current flowing into inductor L during normal operation of the power converter, in order to prevent the switching circuit 40 from malfunctioning and affecting the normal operation of the power converter. For example, the range of the voltage difference across inductor L and the range of the current flowing into inductor L under different operating conditions of the power converter can be tested in advance. When designing the aforementioned voltage and current thresholds, it must be ensured that the voltage threshold is greater than the upper limit of the tested voltage difference range, and the current threshold is greater than the upper limit of the tested current difference range.

[0064] It is also understandable that when lightning current (also known as surge current) enters the DC bus, inductor L and the first capacitor C1 will resonate and generate greater energy. The stress generated by the resonant energy may damage components such as the switching transistors in the DC / DC converter circuit 10 and the DC / AC converter circuit 20. The solution provided in this application provides a parallel switching circuit 40 to inductor L. When instantaneous energy surges into inductor L, the switching circuit 40 bypasses inductor L, thereby effectively preventing damage to components in the power conversion circuit caused by the residual voltage of the lightning surge due to resonance in inductor L.

[0065] For power converters with larger bus capacitors (i.e., larger values ​​for the first capacitor C1 and the second capacitor C2), the inrush current generated by differential-mode lightning strikes is larger. In this case, the voltage difference across inductor L changes more significantly, and the current flowing into inductor L changes more noticeably. Correspondingly, the control circuit 50 can more sensitively and quickly detect when the voltage difference exceeds a voltage threshold or the current exceeds a threshold, and promptly control the switching circuit 40 to conduct, thereby enabling timely discharge of the lightning current.

[0066] Optionally, the switching circuit 40 is a switching transistor. This switching transistor can be, for example, an IGBT or a MOSFET. Because of the fast response speed of the switching transistor, rapid discharge of lightning strike energy can be achieved. Furthermore, because the switching transistor is small in size, the size of the power converter can be avoided. Of course, besides a switching transistor, the switching circuit 40 can also be implemented using other devices; for example, the switching transistor circuit 40 can also be a controllable switching device such as a relay or contactor.

[0067] Optionally, such as Figure 6 and Figure 7 As shown, the control circuit 50 includes a detection unit 51 and a drive unit 52. The detection unit 51 detects the voltage difference across the inductor L and the current flowing into the inductor L. The drive unit 52 (also called a driver) controls the switching circuit 40. For example, the detection unit 51 may include a voltage detection unit for detecting the voltage difference across the inductor L, a current detection unit for detecting the current, and a control unit for detecting whether the voltage and current exceed corresponding thresholds and generating a control signal. This control unit may be, for example, a microcontroller unit (MCU). When the control unit detects that the voltage or current exceeds the corresponding threshold, it can generate a control signal and output it to the drive unit 52. The drive unit 52 can then output a drive signal to the switching circuit 40 to drive the switching transistor circuit 40 to conduct.

[0068] As one possible implementation, such as Figure 6 As shown, the power converter includes two inductors L, which are connected in series across the two ends of the second capacitor C2. That is, one end of the second capacitor C2 is connected in series with one inductor L and then connected to one end of the first capacitor C1, for example, to the positive bus BUS+. The other end of the second capacitor C2 is connected in series with the other inductor L and then connected to the other end of the first capacitor C1, for example, to the negative bus BUS-.

[0069] In this implementation, refer to Figure 6The power converter includes two switching circuits 40 and two control circuits 50 corresponding to two inductors L. Each switching circuit 40 is connected in parallel with its corresponding inductor L. Each control circuit 50 can turn on its switching circuit 40 when the voltage difference across its corresponding inductor L exceeds a voltage threshold, or when the current flowing into its corresponding inductor L exceeds a current threshold, thereby discharging the lightning strike energy to the second capacitor C2.

[0070] As another possible implementation, such as Figure 7 As shown, the power converter also includes a third capacitor C3 and a fourth capacitor C4. The first capacitor C1 and the third capacitor C3 are connected in series between the positive bus BUS+ and the negative bus BUS-, and the second capacitor C2 and the fourth capacitor C4 are connected in series between the positive bus BUS+ and the negative bus BUS-. Furthermore, in this implementation, one end of the inductor L is connected to the series connection point between the first capacitor C1 and the third capacitor C3, and the other end of the inductor L is connected to the series connection point between the second capacitor C2 and the fourth capacitor C4. That is, the fourth capacitor C4 is connected in series with the inductor L and then in parallel with the third capacitor C3.

[0071] In this implementation, since the first capacitor C1 and the third capacitor C3 are connected in series between the positive bus BUS+ and the negative bus BUS-, and the second capacitor C2 and the fourth capacitor C4 are connected in series between the positive bus BUS+ and the negative bus BUS-, decoupling can be achieved by setting an inductor L between the two series nodes. Correspondingly, connecting a switching circuit 40 in parallel with this inductor L ensures effective discharge of lightning energy in differential mode lightning strike scenarios.

[0072] Optionally, the capacitance of the second capacitor C2 is greater than that of the first capacitor C1. The first capacitor C1 can be a film capacitor, and the second capacitor C2 can be an electrolytic capacitor. For details regarding the first capacitor C1 and the second capacitor C2, please refer to the relevant descriptions in the above embodiments, which will not be repeated here. In scenarios where the power converter also includes a third capacitor C3 and a fourth capacitor C4, the capacitance of the fourth capacitor C4 is greater than that of the third capacitor C3. Furthermore, the third capacitor C3 can be a film capacitor, and the fourth capacitor C4 can be an electrolytic capacitor.

[0073] like Figure 3 As shown in the illustration, the power converter provided in this application embodiment further includes an input surge protection circuit 60 and an output surge protection circuit 70, which are also called surge protectors. The input surge protection circuit 60 is connected to the input terminal of the power converter (i.e., the input terminal of the DC / DC conversion circuit 10), and the output surge protection circuit 70 is connected to the output terminal of the power converter (i.e., the AC terminal of the DC / AC conversion circuit 20). The aforementioned input surge protection circuit 60 and output surge protection circuit 70 can effectively protect the power converter when it suffers a common-mode lightning strike.

[0074] In summary, this application provides a power converter that includes a switching circuit connected in parallel with an inductor. When the input terminal of the DC / DC converter circuit is struck by differential-mode lightning, the lightning current flows through the DC / DC converter circuit into the first capacitor, increasing the voltage difference across the inductor and the current flowing into the inductor. When the voltage difference across the inductor exceeds a voltage threshold, or the current flowing into the inductor exceeds a current threshold, the control circuit can actively control the switching circuit to conduct, thereby bypassing the inductor. At this time, the lightning current can charge the second capacitor through the conducting switching circuit, thereby dissipating the lightning energy on the first capacitor to the second capacitor. Since both the first and second capacitors can absorb lightning energy, excessively high DC bus voltage can be avoided, thus effectively preventing the switching transistors in the DC / DC converter circuit from failing due to voltage overstress.

[0075] refer to Figure 3 It can be seen that the inductance between the first capacitor C1 and the second capacitor C2 can serve as a decoupling unit to achieve decoupling between the capacitors. Furthermore, this decoupling unit may include not only the inductor but also a resistor connected in series and / or in parallel with the inductor. Figure 4 and Figure 5 The discharge gap 30 in the illustrated embodiment, or, Figure 6 and Figure 7 The switching circuit 40 and control circuit 50 in the illustrated embodiment can serve as a discharge unit connected in parallel with the decoupling unit. For example... Figure 3 As shown, the decoupling unit and its parallel discharge unit can be referred to as a decoupling circuit. Based on the above functional descriptions of the discharge gap 30, the switching circuit 40, and the control circuit 50, it can be seen that the decoupling circuit in this embodiment of the application simultaneously possesses decoupling capability and lightning surge protection capability.

[0076] The power converter provided in this application embodiment includes a decoupling circuit between two power conversion circuits, which simultaneously provides decoupling and lightning surge protection. When the power converter suffers a common-mode lightning strike, the input surge protection circuit 60 or the output surge protection circuit 70 directly activates to achieve lightning protection. When the power converter suffers a differential-mode lightning strike, the energy of the differential-mode lightning strike directly charges the first capacitor C1 (e.g., a film capacitor) through the loop of the first-stage power conversion circuit. Because the decoupling unit cannot quickly transfer the energy of the differential-mode lightning strike to the second capacitor C2 (e.g., an electrolytic capacitor) for absorption, a voltage difference will be generated across the decoupling unit. Figure 3As shown, a bleeder unit is connected in parallel with the decoupling unit. This bleeder unit bypasses the decoupling unit, allowing the voltage across the decoupling unit to be discharged to the second capacitor C2 (e.g., an electrolytic capacitor). Because the second capacitor C2 has a larger capacitance, the same lightning strike energy will produce a smaller voltage difference across it, effectively preventing a higher voltage difference on the DC bus that could damage the components in the power conversion circuit. Furthermore, by bypassing the decoupling unit, the bleeder unit also effectively prevents resonance between the decoupling unit and the first capacitor C1 after a lightning strike current flows into C1, thus avoiding the larger energy generated by resonance that could damage the components in the power conversion circuit.

[0077] In this embodiment, the topology of the capacitors and decoupling circuits between the DC / DC conversion circuit 10 and the DC / AC conversion circuit 20 can be flexibly adjusted according to the requirements of the application scenario. For example, only one inductor L can be connected in series between the second capacitor C2 and the first capacitor C1. Alternatively, the number of capacitors connected in series with each of the first capacitor C1 and the second capacitor C2 can be flexibly adjusted, and the position and number of the decoupling units set between the first capacitor C1 and the second capacitor C2 can also be flexibly adjusted. Correspondingly, the number of bleeder units in the power converter can be flexibly adjusted according to the number of decoupling units, as long as it is ensured that the bleeder units and decoupling units are set in parallel in pairs.

[0078] For example, a first capacitor branch and a second capacitor branch are provided between the positive bus BUS+ and the negative bus BUS-. The first capacitor branch includes a first capacitor C1 and N capacitors connected in series with the first capacitor C1. The second capacitor branch includes a second capacitor C2 and N capacitors connected in series with the second capacitor C2. Furthermore, the power converter may include N decoupling units and N discharge units connected in parallel with each of the N decoupling units. N is an integer greater than or equal to 1. A decoupling unit is connected between each series node between any two adjacent capacitors in the first capacitor branch and the corresponding series node between two capacitors in the second capacitor branch.

[0079] This application also provides a photovoltaic power generation system, see reference. Figure 1 The photovoltaic power generation system includes multiple power converters as provided in the above embodiments. The input terminal of the DC / DC conversion circuit of the multiple power converters is used to connect to the photovoltaic panel, and the AC terminal of the DC / AC conversion circuit of the multiple power converters can be connected in parallel to one end of a transformer, and the other end of the transformer is connected to the power grid.

[0080] It is understood that the photovoltaic power generation system has essentially the same technical effect as the power converter provided in the aforementioned embodiments. Therefore, for the sake of brevity, the technical effect of the photovoltaic power generation system will not be described again here.

[0081] In the embodiments of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "at least one" refers to one or more, and "multiple" refers to two or more.

[0082] The above description is merely an optional implementation of this application, but the scope of protection of this application 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 application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A power converter, characterized in that, The power converter includes: a circuit board, a DC / DC / DC conversion circuit, a DC bus, a DC / AC conversion circuit, a first capacitor, a second capacitor, an inductor, and a discharge gap; The input terminal of the DC / DC converter circuit is used to connect to a DC source, and the DC bus is connected between the output terminal of the DC / DC converter circuit and the DC terminal of the DC / AC converter circuit. The first capacitor is connected between the positive and negative busbars of the DC busbar, and the second capacitor is connected in series with the inductor and then in parallel with the first capacitor. The discharge gap includes a first metal electrode and a second metal electrode located on the circuit board. One end of the first metal electrode is connected to one end of the inductor, and one end of the second metal electrode is connected to the other end of the inductor. The other ends of the first metal electrode and the other ends of the second metal electrode are opposite to each other and are spaced apart.

2. The power converter according to claim 1, characterized in that, The circuit board is a printed circuit board (PCB), and the first metal electrode and the second metal electrode are both copper foil traces on the PCB.

3. The power converter according to claim 1 or 2, characterized in that, The capacitance value of the second capacitor is greater than the capacitance value of the first capacitor.

4. The power converter according to any one of claims 1 to 3, characterized in that, The first capacitor is a film capacitor, and the second capacitor is an electrolytic capacitor.

5. The power converter according to any one of claims 1 to 4, characterized in that, The power converter includes two inductors, which are connected in series across the two ends of the second capacitor. The power converter includes two discharge gaps corresponding to the two inductors, and each discharge gap is connected in parallel with one of the corresponding inductors.

6. The power converter according to any one of claims 1 to 4, characterized in that, The power converter also includes a third capacitor and a fourth capacitor; The first capacitor and the third capacitor are connected in series between the positive bus and the negative bus, and the second capacitor and the fourth capacitor are connected in series between the positive bus and the negative bus; One end of the inductor is connected to the series node between the first capacitor and the third capacitor, and the other end of the inductor is connected to the series node between the second capacitor and the fourth capacitor.

7. A power converter, characterized in that, The power converter includes: a DC / DC conversion circuit, a DC bus, a DC / AC conversion circuit, a first capacitor, a second capacitor, an inductor, a switching circuit, and a control circuit; The input terminal of the DC / DC converter circuit is used to connect to a DC source, and the DC bus is connected between the output terminal of the DC / DC converter circuit and the DC terminal of the DC / AC converter circuit. The first capacitor is connected between the positive and negative busbars of the DC busbar, and the second capacitor is connected in series with the inductor and then in parallel with the first capacitor. The switching circuit is connected in parallel with the inductor; The control circuit is used to control the switching circuit to turn on when it detects that the voltage difference across the inductor is greater than a voltage threshold, or when it detects that the current flowing into the inductor is greater than a current threshold.

8. The power converter according to claim 7, characterized in that, The switching circuit is a switching transistor.

9. The power converter according to claim 7 or 8, characterized in that, The control circuit includes a detection unit and a drive unit; The detection unit is used to detect the voltage difference across the inductor and the current flowing into the inductor; The driving unit is used to control the on / off state of the switching circuit.

10. The power converter according to any one of claims 7 to 9, characterized in that, The capacitance value of the second capacitor is greater than the capacitance value of the first capacitor.

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