Photovoltaic inverter and power supply control method

Abstract

The present application relates to the technical field of photovoltaics, and discloses a photovoltaic inverter and a power supply control method. The photovoltaic inverter comprises: a direct current-to-direct current converter connected to a photovoltaic module and a direct current bus, an alternating current-to-direct current converter connected to the direct current bus and connected to a power grid by means of a pre-charge circuit; a controller, configured for controlling the pre-charge circuit to be in a conducting state upon detecting that a voltage of the direct current bus is less than a first threshold and an input voltage of the direct current-to-direct current converter is less than zero, so that the alternating current-to-direct current converter draws electric power from the power grid to raise the voltage of the direct current bus to the first threshold, enabling a direct current auxiliary power supply to draw electric power from the direct current bus to supply power to switching transistors in the controller, the direct current-to-direct current converter, the alternating current-to-direct current converter, and the pre-charge circuit. In this way, when a photovoltaic module is connected with reverse polarity, a power grid can be controlled to supply reverse power to a direct current bus in a photovoltaic inverter, so as to raise a voltage of the direct current bus to a first threshold capable of ensuring normal operation of a direct current auxiliary power supply, thereby achieving reverse polarity protection for photovoltaic inverters.

Description

Photovoltaic inverters and power supply control methods

[0001] This application claims priority to Chinese patent application filed on March 19, 2025, with application number 202510329403.9 and entitled "Photovoltaic Inverter and Power Supply Control Method", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of photovoltaic technology, and in particular to a photovoltaic inverter and a power supply control method. Background Technology

[0003] Photovoltaic technology is a technology that uses the photoelectric effect of photovoltaic solar panels to convert the energy of sunlight into electrical energy. During the photovoltaic module power generation process, the photovoltaic inverter can convert the direct current generated by the photovoltaic module into alternating current that meets the grid frequency requirements or direct current that meets the external load voltage requirements. During the installation of a photovoltaic system, there may be instances where the positive and negative terminals of the photovoltaic module are reversed, or the terminals of the photovoltaic module and the photovoltaic inverter are connected in reverse. When the photovoltaic module is connected to the photovoltaic inverter in reverse, the positive and negative terminals of the photovoltaic module are short-circuited, which can easily damage the components inside the photovoltaic inverter connected to the photovoltaic module. Summary of the Invention

[0004] Embodiments of this application provide a photovoltaic inverter and a power supply control method for reversing protection of the photovoltaic inverter when the photovoltaic module is reverse-connected to the photovoltaic inverter.

[0005] In a first aspect, this application provides a photovoltaic inverter, which includes: a controller, an inverter circuit, a soft-start circuit, a DC auxiliary power supply, and an AC auxiliary power supply; the inverter circuit includes a DC bus, a DC-DC converter, and an AC-DC converter, the input terminal of the DC-DC converter is used to connect to photovoltaic modules, the soft-start circuit is used to connect between the AC terminal of the AC-DC converter and the power grid, and the output terminal of the DC-DC converter and the DC terminal of the AC-DC converter are both connected to the DC bus; the DC auxiliary power supply is used to obtain power from the DC bus when the voltage of the DC bus is greater than or equal to a first threshold. It can supply power to the controller, DC-DC converter, AC-DC converter, and the switching transistors in the soft-start circuit; the AC auxiliary power supply is used to obtain power from the grid to supply power to the controller and the soft-start circuit when the voltage of the DC bus is less than the first threshold; the controller is used to control the soft-start circuit to conduct when it detects that the voltage of the DC bus is less than the first threshold and the input voltage of the DC-DC converter is less than zero, so that the AC-DC converter obtains power from the grid to raise the voltage of the DC bus to the first threshold; after the voltage of the DC bus rises to the first threshold, the controller is used to control the switching transistors in the DC-DC converter to conduct.

[0006] In the photovoltaic inverter provided in this application embodiment, both DC auxiliary power supply and AC auxiliary power supply can power the switching transistors in functional modules such as the controller and soft-start circuit. Only the DC auxiliary power supply powers the DC-DC converter and AC-DC converter drive, avoiding the need for additional windings between the AC auxiliary power supply and the DC-DC converter, thus reducing the manufacturing cost and static energy consumption of the photovoltaic inverter. Simultaneously, since the DC auxiliary power supply operates normally when the DC bus voltage is greater than or equal to a first threshold, when the DC bus voltage is detected to be less than the first threshold and the DC-DC converter input voltage is less than zero (i.e., when the photovoltaic module is reverse-connected to the DC-DC converter), the AC auxiliary power supply can normally power the controller and soft-start circuit. The controller controls the soft-start circuit to conduct, allowing the grid to reverse-power the DC bus in the photovoltaic inverter, raising the DC bus voltage to the first threshold that ensures the normal operation of the DC auxiliary power supply.

[0007] Therefore, when photovoltaic (PV) modules are reverse-connected to a DC-DC converter, the DC bus obtains power from the grid to compensate for the DC power supply, ensuring that the auxiliary DC power supply can operate normally and drive the DC-DC converter even with the PV modules reverse-connected. When the PV modules are reverse-connected, a short-circuit current will occur in the DC-DC converter. When the switching transistors in the DC-DC converter are driven to conduct under the action of the auxiliary DC power supply, the voltage across the switching transistors is much lower than the voltage across the body diode of the switching transistors when they are conducting. This ensures that the switching transistors in the DC-DC converter will not overheat and be damaged due to excessive power when reverse-connected to the PV modules, thus achieving reverse connection protection for the PV inverter and improving the safety and reliability of the PV inverter operation.

[0008] In one embodiment, the photovoltaic inverter further includes a detector connected to a DC bus and a DC-DC converter; the detector is used to collect the voltage of the DC bus and the input voltage of the DC-DC converter.

[0009] In this embodiment, by setting a detector to collect the voltage of the DC bus and the input voltage of the DC-DC converter, the controller can obtain the voltage information fed back by the detector to monitor the working status of the photovoltaic inverter in real time, realize the early warning and rapid location of faults, and thus make reasonable adjustments to the operating status of each functional module of the photovoltaic inverter to ensure the safe and stable operation of the photovoltaic inverter.

[0010] In one embodiment, the aforementioned DC auxiliary power supply is further used to supply power to the detector when the voltage of the DC bus is greater than or equal to the first threshold; the AC auxiliary power supply is further used to supply power to the detector when the voltage of the DC bus is less than the first threshold.

[0011] In this embodiment, both the DC auxiliary power supply and the AC auxiliary power supply can power the detector, ensuring that the detector can operate normally under different working conditions of the photovoltaic module. The voltage of the DC bus and the input voltage of the DC-DC converter are detected in real time to diagnose the operating faults of the photovoltaic inverter and ensure the safety and reliability of the photovoltaic inverter operation.

[0012] In one embodiment, the aforementioned soft-start circuit includes a first switching device, a second switching device, a third switching device, and a first resistor; one end of the first switching device is connected to a connection terminal on the AC side of the inverter circuit, and the other end of the first switching device is used to connect to the power grid; one end of the second switching device is connected to another connection terminal on the AC side of the inverter circuit, and the other end of the second switching device is used to connect to the power grid; the third switching device is connected in series with the first resistor, and the series-connected third switching device and the first resistor are connected in parallel across the first switching device.

[0013] In this embodiment, the AC-DC converter is connected to the power grid through a soft-start circuit. When the power grid supplies power to the AC-DC converter at the moment of grid connection, the first resistor can reduce the peak inrush current when the AC-DC converter rectifies the AC power input from the power grid, so that the voltage rises more smoothly and protects the working safety of other components in the circuit.

[0014] In one embodiment, the controller is further configured to control the first switching device, the second switching device, and the third switching device to turn off when the voltage of the DC bus is detected to be greater than or equal to a first threshold and the input voltage of the DC-DC converter is greater than zero.

[0015] In this embodiment, when the voltage of the DC bus is detected to be greater than or equal to the first threshold and the input voltage of the DC-DC converter is greater than zero, the DC auxiliary power supply can start normally. The controller controls the soft-start circuit to shut down, so that the grid does not supply power to the AC-DC converter in reverse. Since the grid supplies power to the AC-DC converter in reverse under this operating condition, this part of the electrical energy may not only be unable to be effectively utilized, but will also generate additional losses in the circuit, such as resistor heating, resulting in energy waste. Therefore, the controller controls the soft-start circuit to shut down, which can reduce energy waste during the operation of the photovoltaic inverter.

[0016] In one embodiment, the controller is further configured to, when detecting that the voltage of the DC bus is less than a first threshold and the input voltage of the DC-DC converter is less than zero, control the first switching device to turn off, and control the second and third switching devices to turn on, so that the AC-DC converter can obtain power from the grid to supply power to the DC bus; the controller is further configured to, when detecting that the voltage of the DC bus rises to the first threshold and the input voltage of the DC-DC converter is less than zero, control the first and second switching devices to turn on, and control the third switching device to turn off, so that the AC-DC converter can obtain power from the grid to supply power to the DC bus.

[0017] In this embodiment, when the controller controls the soft-start circuit to conduct so that the power grid can compensate the DC bus for power, before raising the DC bus voltage to the first threshold, the circuit containing the first resistor is controlled to conduct. By utilizing the impedance of the first resistor, the peak inrush current when the AC-DC converter rectifies the AC input from the power grid can be reduced, making the voltage rise more smoothly. After raising the DC bus voltage to the first threshold and maintaining the DC bus voltage, the first resistor is controlled to no longer be connected to the circuit so as not to consume power. This can reduce the power consumption of the AC-DC converter when it obtains power from the power grid to supply power to the DC bus, thereby ensuring the safety of components while avoiding energy waste.

[0018] In one embodiment, the aforementioned soft-start circuit further includes a fourth switching device and a fifth switching device; the fourth switching device is connected in series between the other end of the first switching device and the power grid, the third switching device and the first resistor are connected in parallel across the first switching device, or the third switching device and the first resistor are connected in parallel across the first and fourth switching devices; the fifth switching device is connected in series between the other end of the second switching device and the power grid.

[0019] In this embodiment, the switching device in the soft-start circuit can be a single switching device or multiple switching devices connected in series. When a component fails during the turn-on and turn-off process of the soft-start circuit, the multiple switching devices connected in series can isolate the fault, thereby improving the reliability and stability of the soft-start circuit.

[0020] In one embodiment, the aforementioned DC auxiliary power supply includes a DC primary winding and a DC secondary winding; the DC primary winding is connected to a DC bus to obtain electrical energy from the DC bus; the DC secondary winding is used to connect to a controller, a DC-DC converter, an AC-DC converter, and a soft-start circuit to supply power to the controller, the DC-DC converter, the AC-DC converter, and the soft-start circuit.

[0021] In this embodiment, the DC auxiliary power supply obtains power from the DC bus through the DC primary winding, which can provide independent DC power to the controller, DC-DC converter, AC-DC converter and soft-start circuit. This ensures that each functional module is not affected by the fluctuations of other circuits during the operation of the photovoltaic inverter, and has a stable power supply, thus guaranteeing the stable operation of each functional module.

[0022] In one embodiment, the aforementioned DC auxiliary power supply further includes a first switching transistor, a first diode, a first capacitor, and a second resistor; the source of the first switching transistor is connected to the anode of the first diode, the drain of the first switching transistor is connected to the cathode of the DC bus, the gate of the first switching transistor is connected to a controller, the anode and drain of the body diode of the first switching transistor are connected, and the cathode and source of the body diode of the first switching transistor are connected; the first capacitor is connected in series between the cathode of the first diode and the cathode of the DC bus, and the second resistor is connected in parallel with the first capacitor; the DC primary winding is connected in parallel with the first diode and the first capacitor.

[0023] In this embodiment, the first capacitor and the second resistor are used to smooth the voltage peaks that occur when the first switch is turned on and off, thus smoothing the voltage waveform and ensuring the operational safety of the DC auxiliary power supply. The first diode acts as a freewheeling diode. When the controller turns off the first switch, the current in the DC primary winding cannot change abruptly. At this time, the first diode provides a path for releasing the electrical energy stored in the DC primary winding, allowing the current to continue flowing through the first diode to form a loop. The capacitor and resistor can release the electrical energy, thereby preventing excessively high reverse voltage from being generated across the DC primary winding and protecting the circuit components.

[0024] In one embodiment, the aforementioned AC auxiliary power supply includes a rectifier, an AC primary winding, and an AC secondary winding; the input terminal of the rectifier is used to connect to the power grid, and the output terminal of the rectifier is connected to the AC primary winding to obtain electrical energy from the power grid and supply power to the AC primary winding; the AC secondary winding is used to connect to the controller and the soft-start circuit to supply power to the controller and the soft-start circuit.

[0025] In this embodiment, in addition to setting a DC auxiliary power supply to power the switching transistors in each functional module, an AC auxiliary power supply is set to obtain power from the grid. This provides an independent DC power supply for the controller and the soft-start circuit, ensuring a stable power supply for the controller and the soft-start circuit even when the DC auxiliary power supply cannot maintain normal operation. This guarantees real-time monitoring and control of the photovoltaic inverter's operating status and improves the operational safety of the photovoltaic inverter.

[0026] In one embodiment, the AC auxiliary power supply further includes a second switching transistor, a second diode, a second capacitor, and a third resistor; the source of the second switching transistor is connected to the anode of the second diode, the drain of the second switching transistor is connected to one output terminal of the rectifier, the gate of the second switching transistor is connected to the controller, the anode and drain of the body diode of the second switching transistor are connected, and the cathode and source of the body diode of the second switching transistor are connected; the second capacitor is connected in series between the cathode of the second diode and the other output terminal of the rectifier, and the third resistor is connected in parallel with the second capacitor; the AC primary winding is connected in parallel with the second diode and the second capacitor.

[0027] In this embodiment, the second capacitor and the third resistor are used to smooth the voltage peaks that occur when the second switch is turned on and off, thus smoothing the voltage waveform and ensuring the operational safety of the AC auxiliary power supply. The second diode acts as a freewheeling diode. When the controller turns off the second switch, the current in the AC primary winding cannot change abruptly. At this time, the second diode provides a path for releasing the electrical energy stored in the AC primary winding, allowing the current to continue flowing through the second diode to form a loop. The capacitor and resistor can release the electrical energy, thereby preventing excessively high reverse voltage from being generated across the AC primary winding and protecting the circuit components.

[0028] In one embodiment, the DC-DC converter includes a first inductor, a third switching transistor, and a third diode; one end of the first inductor is connected to the positive terminal of the photovoltaic module, and the other end of the first inductor is connected to the positive terminal of the third diode; the source of the third switching transistor is connected to the positive terminal of the third diode, the drain of the third switching transistor is connected to the negative terminal of the photovoltaic module and the negative terminal of the DC bus, the gate of the third switching transistor is connected to a controller, the positive terminal of the body diode of the third switching transistor is connected to the drain, and the negative terminal of the body diode of the third switching transistor is connected to the source; the negative terminal of the third diode is connected to the negative terminal of the DC bus.

[0029] In this embodiment, the circuit structure of the DC-DC converter can realize the voltage boosting or bucking function, so that when the photovoltaic module inputs DC power to the DC-DC converter, the DC power can be converted into power, thereby providing DC power that meets the power requirements of the DC bus and / or external load.

[0030] In one embodiment, the AC-DC converter includes a first bridge arm and a second bridge arm connected in parallel with a DC bus; the first bridge arm includes a fourth switch and a fifth switch connected in series, and the series connection point of the fourth switch and the fifth switch is connected to a soft-start circuit; the second bridge arm includes a sixth switch and a seventh switch connected in series, and the series connection point of the sixth switch and the seventh switch is connected to a soft-start circuit.

[0031] In this embodiment, the circuit structure of the AC-DC converter can realize functions such as voltage boosting, voltage bucking, and AC-DC conversion. Thus, when the power grid inputs AC power to the AC-DC converter, it can convert AC power into DC power to supply the DC bus. Alternatively, when the DC bus outputs excess DC power to the AC-DC converter, it can convert DC power into AC power to supply the power grid.

[0032] Secondly, this application provides a power supply control method applied to the photovoltaic inverter provided in the above embodiments. The photovoltaic inverter includes a DC bus, a DC-DC converter, an AC-DC converter, a soft-start circuit, a DC auxiliary power supply, an AC auxiliary power supply, and a detector. The input terminal of the DC-DC converter is used to connect to the photovoltaic module. The soft-start circuit is used to connect between the AC terminal of the AC-DC converter and the power grid. The output terminal of the DC-DC converter and the DC terminal of the AC-DC converter are both connected to the DC bus. The detector is connected to the DC bus and the DC-DC converter. The power supply control method includes: obtaining the voltage of the DC bus and the input voltage of the DC-DC converter from the detector; when the input voltage of the DC-DC converter is detected to be less than zero, adjusting the conduction state of the soft-start circuit based on the voltage of the DC bus, so that the DC auxiliary power supply continuously obtains power from the DC bus to supply power to the switching transistor of the DC-DC converter.

[0033] In one embodiment, the above-mentioned adjustment of the conduction state of the DC bus voltage-based soft-start circuit when the input voltage of the DC-DC converter is detected to be less than zero includes: when the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is greater than or equal to a first threshold, controlling the soft-start circuit to turn off.

[0034] In one embodiment, the conduction state of the voltage adjustment soft-start circuit based on the DC bus when the input voltage of the DC-DC converter is detected to be less than zero includes: when the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is less than a first threshold, controlling the soft-start circuit to conduct, so that the AC-DC converter obtains power from the grid to raise the voltage of the DC bus to the first threshold.

[0035] In one embodiment, the aforementioned soft-start circuit includes a first switching device, a second switching device, a third switching device, and a first resistor. The first switching device is used to connect one terminal of the AC side of the inverter circuit to the power grid. The second switching device is used to connect the other terminal of the AC side of the inverter circuit to the power grid. The third switching device is connected in series with the first resistor, and the series-connected third switching device and the first resistor are connected in parallel across the first switching device. The method further includes: when the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is greater than or equal to a first threshold, controlling the first switching device, the second switching device, and the third switching device in the soft-start circuit to turn off, thereby turning off the soft-start circuit.

[0036] In one embodiment, the method further includes: when the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is less than a first threshold, controlling the first switching device in the soft-start circuit to turn off, and controlling the second and third switching devices to turn on, so that the soft-start circuit is turned on; when the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus rises to the first threshold, controlling the first and second switching devices to turn on, and controlling the third switching device to turn off, so that the soft-start circuit is turned on.

[0037] In this embodiment, the beneficial effects of the second aspect can be referred to the description of the first aspect and any of its implementations, and will not be repeated here. Attached Figure Description

[0038] Figure 1 is a structural schematic diagram of a photovoltaic inverter provided in an embodiment of this application;

[0039] Figure 2 is a schematic diagram of another photovoltaic inverter provided in an embodiment of this application;

[0040] Figure 3 is a structural schematic diagram of another photovoltaic inverter provided in an embodiment of this application;

[0041] Figure 4 is a structural schematic diagram of another photovoltaic inverter provided in an embodiment of this application;

[0042] Figure 5 shows a flowchart of a power supply control method provided in an embodiment of this application;

[0043] Figure 6 shows a current flow diagram of the photovoltaic inverter provided in Figure 4;

[0044] Figure 7 shows another current flow diagram of the photovoltaic inverter provided in Figure 4;

[0045] Figure 8 shows another current flow diagram of the photovoltaic inverter provided in Figure 4;

[0046] Figure 9 shows a flowchart of another power supply control method provided in an embodiment of this application;

[0047] Figure 10 is a schematic diagram of a soft-start circuit provided in an embodiment of this application;

[0048] Figure 11 is a schematic diagram of a DC auxiliary power supply provided in an embodiment of this application;

[0049] Figure 12 is a schematic diagram of an AC auxiliary power supply provided in an embodiment of this application;

[0050] Figure 13 is a schematic diagram of another AC auxiliary power supply provided in an embodiment of this application. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Please refer to Figure 1, which is a schematic diagram of the structure of a photovoltaic inverter 1 provided in an embodiment of this application. As shown in Figure 1, the photovoltaic inverter 1 provided in this embodiment of the application includes at least a controller (not shown in Figure 1), an inverter circuit 10, a soft-start circuit 20, a DC auxiliary power supply 30, and an AC auxiliary power supply 40.

[0053] In this embodiment, the inverter circuit 10 includes a DC bus 11, a DC-DC converter 12, and an AC-DC converter 13. The input terminal of the DC-DC converter 12 is connected to the photovoltaic module 2, and the AC terminal of the AC-DC converter 13 is used to connect to the power grid 3 through the soft start circuit 20. The output terminal of the DC-DC converter 12 and the DC terminal of the AC-DC converter 13 are both connected to the DC bus 11.

[0054] In this embodiment, the DC power generated by the photovoltaic module 2 is used to input the photovoltaic inverter 1 in real time. The photovoltaic inverter 1 is in a dynamic working scenario, that is, under the irradiation of sunlight, the semiconductor material in the photovoltaic module 2 absorbs photon energy and generates electron-hole pairs, thereby forming a DC power input to the DC-DC converter 12. The DC bus 11 obtains electrical energy from the photovoltaic module 2 through the DC-DC converter 12 to raise the voltage of the DC bus 11, thereby supplying power to the external load, and / or supplying power to the grid 3 through the AC-DC converter 13. The DC-DC converter 12 is used to boost or buck the DC power input from the photovoltaic module 2 to the photovoltaic inverter 1 to supply power to the DC bus 11. The AC-DC converter 13 is used to convert the DC power in the DC bus 11 into AC power when the DC bus 11 supplies power to the grid 3, and boost or buck the AC power to supply it to the grid 3. Alternatively, the AC-DC converter 13 is used to convert the AC power supplied by the grid 3 to the photovoltaic inverter 1 into DC power when the grid 3 supplies power to the DC bus 11, and boost or buck the DC power to supply it to the DC bus 11.

[0055] In one embodiment, the DC auxiliary power supply 30 is used to obtain electrical energy from the DC bus 11 when the voltage of the DC bus 11 is greater than or equal to a first threshold, and to perform power conversion on the electrical energy obtained from the DC bus 11 to power the switching transistors in the controller, DC-DC converter 12, AC-DC converter 13, and soft-start circuit 20. Specifically, after the DC bus 11 obtains electrical energy from the photovoltaic module 2 through the DC-DC converter 12, when the controller detects that the voltage of the DC bus 11 has risen to greater than or equal to the first threshold, since there is sufficient electrical energy available for distribution on the DC bus 11, the controller controls the DC auxiliary power supply 30 to obtain electrical energy from the DC bus 11 to power the switching transistors in the controller, DC-DC converter 12, AC-DC converter 13, and soft-start circuit 20, etc.

[0056] Furthermore, in the photovoltaic inverter 1, the circuits of the DC-DC converter 12 and the AC-DC converter 13 contain one or more switching transistors. The DC auxiliary power supply 30 is used to drive and supply power to the switching transistors of the DC-DC converter 12 and / or the AC-DC converter 13 when the photovoltaic inverter 1 is in a dynamic operating scenario. By providing a sufficiently large drive current to the control terminal of the switching transistor, the DC auxiliary power supply 30 can quickly drive the switching transistor from the off state to the on state, thereby reducing the loss of the switching transistor and improving the operating efficiency of the photovoltaic inverter 1. Specifically, the switching transistor in this application can be a metal-oxide-semiconductor field-effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), gallium nitride (GaN), a high electron mobility transistor (HEMT), etc., and this application does not limit it to any particular type.

[0057] In this embodiment, when the photovoltaic inverter 1 is in a static working scenario, that is, when there is no sunlight at night or the sunlight intensity is too weak, the photovoltaic module 2 cannot provide enough power to the DC bus 11 through the DC-DC converter 12 to meet the power supply needs of the external load and / or the power grid 3. Therefore, the photovoltaic inverter 1 does not supply power to the external load and the power grid 3.

[0058] In one embodiment, the AC auxiliary power supply 40 is used to obtain electrical energy from the power grid 3 when the voltage of the DC bus 11 is less than a first threshold, and to perform power conversion on the electrical energy obtained from the power grid 3 to power the switching transistors in the controller and the soft-start circuit 20. Specifically, when the controller detects that the voltage of the DC bus 11 is less than the first threshold, there is insufficient electrical energy available for distribution in the DC bus 11, and the DC auxiliary power supply 30 cannot normally power the controller, DC-DC converter 12, AC-DC converter 13, and soft-start circuit 20. To ensure the normal operation of each functional module in the photovoltaic inverter 1, the controller controls the AC auxiliary power supply 40 to obtain electrical energy from the power grid 3 when the voltage of the DC bus 11 is less than the first threshold, in order to power the switching transistors in the controller, soft-start circuit 20, and other functional modules.

[0059] In addition, when photovoltaic module 2 is connected to photovoltaic inverter 1, if photovoltaic module 2 is normally connected to DC-DC converter 12 in photovoltaic inverter 1, the DC power output by photovoltaic module 2 flows into DC-DC converter 12 according to the design path, and flows to DC bus 11 after being transformed by the input voltage of DC-DC converter 12. However, if photovoltaic module 2 is reverse-connected to DC-DC converter 12, that is, the positive terminal of photovoltaic module 2 is connected to the negative terminal of the input terminal of DC-DC converter 12, and the negative terminal of photovoltaic module 2 is connected to the positive terminal of the input terminal of DC-DC converter 12, the photovoltaic module 2 generates DC current under sunlight and inputs it to DC-DC converter 12. After the photovoltaic module 2 is reverse-connected, the direction of the DC current input to DC-DC converter 12 is reversed. The direction of the DC current input to DC-DC converter 12 by photovoltaic module 2 matches the forward conduction direction of the body diode of the switching transistor. The positive terminal of photovoltaic module 2 is directly connected to the negative terminal through the forward-conducting body diode of the switching transistor. At this time, the input voltage of DC-DC converter 12 is the supply voltage of DC-DC converter 12 when photovoltaic module 2 is reverse-connected to DC-DC converter 12, and a short-circuit current is formed in DC-DC converter 12.

[0060] When the photovoltaic module 2 is reverse-connected to the DC-DC converter 12, if the voltage of the DC bus 11 rises to a level greater than or equal to the first threshold, the DC auxiliary power supply 30 can obtain power from the DC bus 11 to provide a sufficiently large drive current to the control terminal of the switching transistor in the DC-DC converter 12, thereby quickly driving the switching transistor from the off state to the on state. At this time, the switching transistor exhibits a low resistance state, and the voltage drop across the switching transistor is much smaller than the forward conduction voltage drop of the body diode of the switching transistor. However, if the voltage of the DC bus 11 rises to a level less than the first threshold, neither the DC auxiliary power supply 30 nor the AC auxiliary power supply 40 can supply power to drive the switching transistor in the DC-DC converter 12. At this time, when the switching transistor is on, the voltage drop across it approaches the forward conduction voltage drop of the body diode of the switching transistor. According to the power formula P=UI, when the photovoltaic module 2 is reverse-connected to the DC-DC converter 12, the short-circuit current I flowing through the switching transistor remains unchanged. When the switching transistor is not driven and is conducting, the higher the voltage U across the switching transistor, the more heat the switching transistor generates under the action of the short-circuit current I, which may cause the temperature of the switching transistor to rise to exceed its limit temperature, resulting in damage to the switching transistor.

[0061] In related technologies, the DC auxiliary power supply 30 and AC auxiliary power supply 40 are configured to supply power to the switching transistors in functional modules such as the controller and the soft-start circuit 20, and are also used to drive the switching transistors in the DC-DC converter 12 and the AC-DC converter 13. This allows the AC auxiliary power supply 40 to be reverse-connected to the DC-DC converter 12 in the photovoltaic module 2, and at least one of the DC auxiliary power supply 30 and the AC auxiliary power supply 40 can drive the DC-DC converter 12 to ensure the safety and reliability of the operation of the DC-DC converter 12.

[0062] However, when the photovoltaic inverter 1 is in a static operating scenario, since it does not supply power to the external load or the power grid 3, the AC auxiliary power supply 40 only needs to ensure the normal operation of functional modules such as the controller and soft-start circuit 20, which are used to maintain the communication, self-test, and maintenance functions of the photovoltaic inverter 1. It does not need to supply power to the switching transistors in functional modules such as the DC-DC converter 12 and the AC-DC converter 13, which are used to convert power between the photovoltaic inverter 1 and the photovoltaic module 2, the external load, and the power grid 3. If both the DC auxiliary power supply 30 and the AC auxiliary power supply 40 are used to drive the switching transistors in the DC-DC converter 12 and the AC-DC converter 13, an additional winding needs to be added between the AC auxiliary power supply 40 and the DC-DC converter 12 and the AC-DC converter 13, which increases the manufacturing cost of the photovoltaic inverter 1 and greatly increases the energy consumption of the AC auxiliary power supply 40 during operation. This problem of excessive energy consumption is particularly prominent when the photovoltaic inverter 1 is in a static operating scenario.

[0063] Based on this, the photovoltaic inverter 1 provided in this application embodiment maintains low energy consumption and low cost, and in order to ensure the safe operation of the photovoltaic inverter 1 when the photovoltaic module 2 is reverse-connected to the photovoltaic inverter 1, a soft start circuit 20 is set between the AC-DC converter 13 and the power grid 3. The AC terminal of the AC-DC converter 13 is used to connect to the power grid 3 through the soft start circuit 20, and both the DC-DC converter 12 and the AC-DC converter 13 are used to supply power to the switching transistors in the soft start circuit 20.

[0064] In this embodiment, when the controller detects that the voltage of the DC bus 11 is less than the first threshold and the input voltage of the DC-DC converter 12 is less than zero, i.e., the photovoltaic module 2 is reverse-connected to the DC-DC converter 12 causing the input voltage of the DC-DC converter 12 to be less than zero, and there is not enough electrical energy in the DC bus 11 to be distributed to the DC auxiliary power supply 30, the DC auxiliary power supply 30 cannot supply power to the controller, DC-DC converter 12, AC-DC converter 13, and soft-start circuit 20 and other functional modules normally. The AC auxiliary power supply 40 obtains electrical energy from the grid 3 to supply power to the controller and the switching transistors in the soft-start circuit 20. The controller controls the soft-start circuit 20 to be turned on, so that the AC-DC converter 13 can obtain electrical energy from the grid 3 through the turned-on soft-start circuit 20. The grid 3 can supply power to the DC bus 11 in the photovoltaic inverter 1 in reverse to raise the voltage of the DC bus 11 to the first threshold.

[0065] Thus, without setting up AC auxiliary power supply 40 to drive AC-DC converter 12 and AC-DC converter 13, the controller can, when photovoltaic module 2 is reverse-connected, reverse power supply to DC bus 11 through grid 3 to raise the voltage of DC bus 11 to the first threshold, so that DC auxiliary power supply 30 can drive the switching transistor in DC-DC converter 12 with photovoltaic module 2 reverse-connected. At this time, the controller controls the switching transistor in DC-DC converter 12 to conduct, ensuring that the switching transistor in DC-DC converter 12 with photovoltaic module 2 reverse-connected will not overheat and be damaged when driven to conduct by DC-DC converter 12, thereby improving the safety and reliability of photovoltaic inverter 1 operation, and avoiding the need to add additional windings between AC auxiliary power supply 40 and DC-DC converter 12 and AC-DC converter 13, reducing the manufacturing cost and operating power consumption of photovoltaic inverter 1.

[0066] In one embodiment, when the controller detects that the input voltage of the DC-DC converter 12 is less than zero, the controller is also used to generate an alarm signal to alert the operation and maintenance personnel that an abnormal operating condition has occurred in the photovoltaic inverter 1 where the photovoltaic module 2 and the DC-DC converter 12 are reverse connected, prompting the operation and maintenance personnel to perform timely maintenance on the photovoltaic inverter 1 and the photovoltaic module 2 to ensure the safe operation of the photovoltaic inverter 1.

[0067] In this embodiment, when the controller detects that the voltage of the DC bus 11 is greater than the first threshold, that is, there is enough electrical energy in the DC bus 11 to be distributed to the DC auxiliary power supply 30. The DC auxiliary power supply 30 can supply power to the controller, DC-DC converter 12, AC-DC converter 13 and soft start circuit 20 and other functional modules normally. The controller controls the soft start circuit 20 to remain in the off state, and the power grid 3 does not supply power to the DC bus 11 in reverse.

[0068] In some implementations, one or more DC-DC converters 12 may be provided in the photovoltaic inverter 1. As shown in FIG2, when multiple DC-DC converters 12 are provided in the photovoltaic inverter 1, the input terminal of each DC-DC converter 12 is connected to the corresponding photovoltaic module 2, and the output terminal of each DC-DC converter 12 is connected to the DC bus 11.

[0069] For example, when the controller detects that the voltage of the DC bus 11 is greater than or equal to the first threshold, and the input voltage of each DC-DC converter 12 is greater than zero, that is, the DC-DC converter 12 and its corresponding photovoltaic module 2 are both positively connected, or when the input voltage of at least one DC-DC converter 12 is less than zero, that is, there is a DC-DC converter 12 and its corresponding photovoltaic module 2 reverse connected, since the DC auxiliary power supply 30 can obtain electrical energy from the DC bus 11 to power the controller, DC-DC converter 12, AC-DC converter 13 and the switching transistors in the soft-start circuit 20 when the voltage of the DC bus 11 is greater than or equal to the first threshold, the DC auxiliary power supply 30 can drive the switching transistors in the reverse-connected DC-DC converter 12 to power the controller, DC-DC converter 12, AC-DC converter 13 and the soft-start circuit 20. Since the controller controls the switching transistors to be turned on, the DC auxiliary power supply 30 can drive the switching transistors in the reverse-connected DC-DC converter 12 to power the switch transistors, ensuring that the switching transistors in the reverse-connected DC-DC converter 12 will not overheat and be damaged. Thus, even if the photovoltaic module 2 is reverse-connected to the DC-DC converter 12, since the other DC-DC converters 12 that are normally connected to the photovoltaic module 2 can raise the voltage of the DC bus 11 to the first threshold, the controller controls the soft start circuit 20 to remain off, and the grid 3 does not need to supply power to the DC bus 11 in reverse, so as to avoid the photovoltaic inverter 1 obtaining additional power from the grid 3 and increasing the energy cost.

[0070] Furthermore, when the controller detects that the voltage of the DC bus 11 is less than the first threshold and the input voltage of multiple DC-DC converters 12 is greater than or equal to zero, the photovoltaic inverter 1 may be in a static operating scenario at night or in a scenario with low light intensity. Since multiple DC-DC converters 12 are normally connected to the DC-DC converter 12, even if the DC auxiliary power supply 30 cannot supply power to the switching transistors in the DC-DC converter 12, the DC-DC converter 12 will not experience short-circuit current, and the switching transistors in the DC-DC converter 12 will not overheat and be damaged. Since the photovoltaic module 2 is set to provide the photovoltaic power generated by the external load to reduce the power that the external load needs to obtain from the grid 3 when it is working, thereby reducing the energy cost, the controller controls the soft start circuit 20 to remain off when the voltage of the DC bus 11 is less than the first threshold and the input voltage of multiple DC-DC converters 12 is greater than or equal to zero. The grid 3 does not supply power to the DC bus 11 in reverse to avoid the photovoltaic inverter 1 obtaining additional power from the grid 3 and increasing the energy cost.

[0071] In this embodiment, both the DC auxiliary power supply 30 and the AC auxiliary power supply 40 can supply power to the controller and the switching transistors in the soft-start circuit 20. When the photovoltaic module 2 is reverse-connected to the DC-DC converter 12, the controller controls the soft-start circuit 20 to conduct, and the power grid 3 can supply power to the DC bus 11 in the photovoltaic inverter 1 in reverse, raising the voltage of the DC bus 11 to a first threshold that ensures the normal operation of the DC auxiliary power supply 30. This ensures that the DC auxiliary power supply 30 can drive the switching transistors in the DC-DC converter 12 with the photovoltaic module 2 reverse-connected. Thus, when the switching transistors in the DC-DC converter 12 are driven to conduct under the action of the DC auxiliary power supply 30, the voltage across the switching transistors will be much lower than the voltage when the body diode of the switching transistors is conducting. Therefore, even if the reverse connection of the photovoltaic module 2 causes a short-circuit current in the DC-DC converter 12, it can be ensured that the switching transistors in the DC-DC converter 12 will not overheat and be damaged due to excessive power. This achieves reverse connection protection for the photovoltaic inverter 1 and improves the safety and reliability of the photovoltaic inverter 1 operation.

[0072] In some embodiments, please refer to Figure 3, which is a schematic diagram of another photovoltaic inverter 1 provided in an embodiment of this application. As shown in Figure 3, the photovoltaic inverter 1 includes at least a controller, an inverter circuit 10, a soft-start circuit 20, a DC auxiliary power supply 30, and an AC auxiliary power supply 40.

[0073] In this embodiment, the inverter circuit 10 includes a DC bus 11, a DC-DC converter 12, and an AC-DC converter 13. The input terminal of the DC-DC converter 12 is connected to the photovoltaic module 2, and the AC terminal of the AC-DC converter 13 is used to connect to the power grid 3 through the soft start circuit 20. The output terminal of the DC-DC converter 12 and the DC terminal of the AC-DC converter 13 are both connected to the DC bus 11.

[0074] The photovoltaic inverter 1 also includes a detector 50, which is connected to the DC bus 11 and the DC-DC converter 12. The detector 50 is used to collect the voltage of the DC bus 11 and the input voltage of the DC-DC converter 12, and send the collected voltage information to the controller. The DC auxiliary power supply 30 is used to draw power from the DC bus 11 to supply power to the controller, DC-DC converter 12, AC-DC converter 13, soft-start circuit 20, and detector 50 when the voltage of the DC bus 11 is greater than or equal to a first threshold. The AC auxiliary power supply 40 is used to draw power from the grid 3 to supply power to the controller, soft-start circuit 20, and detector 50 when the voltage of the DC bus 11 is less than the first threshold. The detector 50 includes, but is not limited to, Hall effect sensors, smart meters, etc.

[0075] In this embodiment, the photovoltaic module 2 is connected to the input terminal of the DC-DC converter 12. The controller analyzes whether there is a problem of reverse connection between the photovoltaic module 2 and the DC-DC converter 12 based on the input voltage of the DC-DC converter 12 obtained from the detector 50. When the controller detects that the input voltage of the DC-DC converter 12 is less than zero, it can determine that there is a problem of reverse connection between the photovoltaic module 2 and the DC-DC converter 12. The detector 50 can also determine whether there is a problem of reverse connection between the photovoltaic module 2 and the DC-DC converter 12 by detecting the current flowing through the DC-DC converter 12.

[0076] Furthermore, the controller is also used to obtain the voltage of the DC bus 11 from the detector 50. If the controller detects that the input voltage of the DC-DC converter 12 is less than zero and also detects that the voltage of the DC bus 11 is less than the first threshold, it determines that the DC auxiliary power supply 30 cannot obtain power from the DC bus 11. The controller controls the soft-start circuit 20 to be turned on, so that the AC-DC converter 13 can obtain power from the grid 3 through the turned-on soft-start circuit 20. The grid 3 can supply power to the DC bus 11 in the photovoltaic inverter 1 in reverse to raise the voltage of the DC bus 11 to the first threshold. In this way, the DC auxiliary power supply 30 can obtain power from the DC bus 11 to drive the switching transistor in the DC-DC converter 12 where the photovoltaic module 2 is reverse-connected, thereby ensuring that the switching transistor in the DC-DC converter 12 where the photovoltaic module 2 is reverse-connected will not overheat and be damaged, thus improving the safety and reliability of the operation of the photovoltaic inverter 1.

[0077] In this embodiment, by setting a detector 50 to collect the voltage of the DC bus 11 and the input voltage of the DC-DC converter 12, the controller can obtain the voltage information fed back by the detector 50 to monitor the working status of the photovoltaic inverter 1 in real time, realize early warning and rapid location of faults, and thus make reasonable adjustments to the operating status of each functional module of the photovoltaic inverter 1 to ensure the safe and stable operation of the photovoltaic inverter 1.

[0078] As shown in Figure 4, Figure 4 is a structural schematic diagram of another photovoltaic inverter provided in an embodiment of this application. The photovoltaic inverter provided in this embodiment includes at least a controller, an inverter circuit, a soft-start circuit 20, a DC auxiliary power supply 30, an AC auxiliary power supply 40, and a detector 50.

[0079] In this embodiment, the inverter circuit includes a DC bus 11, a DC-DC converter 12, and an AC-DC converter 13. The input terminal of the DC-DC converter 12 is connected to the photovoltaic module 2, and the AC terminal of the AC-DC converter 13 is used to connect to the power grid 3 through the soft start circuit 20. The output terminal of the DC-DC converter 12 and the DC terminal of the AC-DC converter 13 are both connected to the DC bus 11.

[0080] The inverter circuit also includes a bus capacitor C3, which is connected in parallel to the DC bus 11. The voltage of the DC bus 11 fluctuates due to factors such as fluctuations in the DC input of the DC-DC converter 12 or AC-DC converter 13, and changes in the external load. The bus capacitor C3 has the ability to store and release electrical energy. For example, when the voltage of the DC bus 11 increases, the DC bus 11 charges the bus capacitor C3, and the bus capacitor C3 absorbs excess electrical energy from the DC bus 11. When the voltage of the DC bus 11 decreases, the bus capacitor C3 discharges to the DC bus 11, replenishing the DC bus 11 with electrical energy, thereby stabilizing the voltage of the DC bus 11 and ensuring that the subsequent circuits can operate under a stable voltage.

[0081] In one embodiment, the DC-DC converter 12 includes a first inductor L1, a third switch Q3, and a third diode D3, used to boost or buck the DC power input to the photovoltaic module 2. One end of the first inductor L1 is connected to the positive terminal of the photovoltaic module 2, and the other end is connected to the positive terminal of the third diode D3. The source of the third switch Q3 is connected to the positive terminal of the third diode D3, the drain of the third switch Q3 is connected to the negative terminal of the photovoltaic module 2 and the negative terminal of the DC bus 11, the gate of the third switch Q3 is connected to the controller, the anode and drain of the body diode of the third switch Q3 are connected, and the cathode and source of the body diode of the third switch Q3 are connected. The cathode of the third diode D3 is connected to the negative terminal of the DC bus 11. The topology of the DC-DC converter 12 can be any other structure capable of boosting or bucking the voltage, such as a three-level boost topology, and is not limited here.

[0082] Please refer to Figure 5, which shows a schematic flowchart of a power supply control method provided in an embodiment of this application. This power supply control method is applied to the photovoltaic inverter shown in Figure 4. The power supply control method provided in this embodiment includes the following steps S410 to S450:

[0083] S410: Obtains the voltage of the DC bus and the input voltage of the DC-DC converter from the detector.

[0084] In this embodiment, when the voltage of the DC bus and the input voltage of the DC-DC converter in the photovoltaic inverter are collected in real time by the detector, in order to ensure the safe and stable operation of the photovoltaic inverter, the controller determines whether the photovoltaic inverter can currently guarantee normal operation by obtaining the voltage of the DC bus and the input voltage of the DC-DC converter from the detector.

[0085] S420: Determine whether the voltage of the DC bus is greater than or equal to the first threshold.

[0086] If yes, that is, the voltage of the DC bus is detected to be greater than or equal to the first threshold, then proceed to S430; if no, that is, the voltage of the DC bus is detected to be less than the first threshold, then proceed to S440.

[0087] S430: Controls the soft-start circuit to shut down.

[0088] In this embodiment, when the voltage of the DC bus is detected to be greater than or equal to the first threshold, the control soft-start circuit is turned off. That is, when the voltage of the DC bus is greater than or equal to the first threshold, the DC auxiliary power supply can obtain power from the DC bus to supply power to the controller, DC-DC converter, AC-DC converter and the switching transistor in the soft-start circuit.

[0089] At this time, even if the photovoltaic module and the DC-DC converter are reverse-connected, the DC auxiliary power supply can drive the switching transistor in the DC-DC converter that is reverse-connected to the photovoltaic module to provide power when the controller controls the switching transistor to conduct. This ensures that the switching transistor in the reverse-connected DC-DC converter will not overheat and be damaged. The controller can control the soft start circuit to shut down, and the DC bus does not need to obtain power from the grid for compensation.

[0090] S440: Determines whether the input voltage of the DC-DC converter is less than zero.

[0091] If yes, that is, if the input voltage of the DC-DC converter is detected to be less than zero, then proceed to S450; if no, that is, if the input voltage of the DC-DC converter is detected to be greater than or equal to zero, then proceed to S430. At this time, there is no reverse connection between the photovoltaic module and the DC-DC converter, and the DC bus does not need to obtain power from the grid to compensate for raising the voltage of the DC bus to the first threshold. The control soft start circuit is kept in the off state.

[0092] S450: Controls the soft-start circuit to turn on, enabling the AC-DC converter to draw power from the grid and raise the DC bus voltage to the first threshold.

[0093] In this embodiment, when the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is less than the first threshold, the control soft-start circuit is turned on. That is, when the DC auxiliary power supply cannot obtain power from the DC bus to drive the switching transistors in the reverse-connected DC-DC converter, in order to ensure that the switching transistors in the DC-DC converter reverse-connected to the photovoltaic module will not overheat and be damaged, the control soft-start circuit is turned on to enable the AC-DC converter to obtain power from the grid to raise the voltage of the DC bus to the first threshold, thereby enabling the DC auxiliary power supply to obtain power from the DC bus to drive the switching transistors in the reverse-connected DC-DC converter.

[0094] When the photovoltaic module 2 is positively connected to the DC-DC converter 12, as shown in Figure 6, Figure 6 is a current flow diagram of the photovoltaic inverter provided in Figure 4.

[0095] In this embodiment, during the process of photovoltaic module 2 outputting DC power, the DC power output from the positive terminal of photovoltaic module 2 flows to the positive terminal of the third diode D3 after passing through the first inductor L1 in the DC-DC converter 12. The third diode D3 is forward-biased. The DC power output from the positive terminal of photovoltaic module 2 flows to the positive terminal of DC bus 11 through the first inductor L1 and the conducting third diode D3. The negative terminal of photovoltaic module 2 is connected to the negative terminal of DC bus 11.

[0096] Under this operating condition, the photovoltaic module 2, the first inductor L1, the third diode D3, and the bus capacitor C3 form a conducting loop, allowing the DC-DC converter 12 to draw power from the photovoltaic module 2 to raise the voltage of the DC bus 11 to the first threshold. Furthermore, after the DC bus 11 draws power from the photovoltaic module 2 through the DC-DC converter 12, when the controller detects that the voltage of the DC bus 11 has risen to a level greater than or equal to the first threshold, since there is sufficient power available for distribution on the DC bus 11, the controller controls the DC auxiliary power supply 30 to draw power from the DC bus 11 to power the switching transistors in the controller, DC-DC converter 12, AC-DC converter 13, soft-start circuit 20, and detector 50.

[0097] When the photovoltaic module 2 is reverse-connected to the DC-DC converter 12, as shown in Figure 7, Figure 7 is another current flow diagram of the photovoltaic inverter provided in Figure 4.

[0098] In this embodiment, the positive terminal of the third diode D3 is connected to the negative terminal of the photovoltaic module 2 through the first inductor L1, and the negative terminal of the third diode D3 is connected to the negative terminal of the DC bus 11; the source of the third switch Q3 is connected to the positive terminal of the third diode D3, the drain of the third switch Q3 is connected to the positive terminal of the photovoltaic module 2 and the negative terminal of the DC bus 11, the gate of the third switch Q3 is connected to the controller, the positive terminal of the body diode of the third switch Q3 is connected to the drain, and the negative terminal of the body diode of the third switch Q3 is connected to the source.

[0099] In addition, during the process of the photovoltaic module 2 outputting DC power in reverse connection, the DC current output from the positive terminal of the photovoltaic module 2 flows to the drain of the third switch Q3 and the negative terminal of the DC bus 11. The negative terminal of the photovoltaic module 2 is connected to the positive terminal of the third diode D3 through the first inductor L1. Under this condition, the photovoltaic module 2, the first inductor L1 and the third switch Q3 form a conducting loop.

[0100] Understandably, when the voltage of DC bus 11 is less than the first threshold and the input voltage of DC-DC converter 12 is less than zero, before the controller controls the soft-start circuit 20 to turn on and enable AC-DC converter 13 to obtain power from grid 3, the DC power output from the positive terminal of photovoltaic module 2 flows to the first inductor L1 through the forward-conducting body diode in the third switch Q3. The positive terminal of photovoltaic module 2 is equivalent to being directly connected to the negative terminal of photovoltaic module 2 through the forward-conducting body diode in the third switch Q3, resulting in a short-circuit current in DC-DC converter 12. When the short-circuit current through the body diode in the third switch Q3 is large, a large amount of power will be consumed on the body diode, causing the third switch Q3 to heat up severely and easily damage the third switch Q3.

[0101] In this embodiment, when the controller detects that the voltage of the DC bus 11 is less than a first threshold and the input voltage of the DC-DC converter 12 is less than zero, since there is not enough power available for distribution to the DC bus 11, the controller controls the AC auxiliary power supply 40 to obtain power from the power grid 3 to power the switching transistors in the controller, the soft-start circuit 20, and the detector 50. Furthermore, when the AC auxiliary power supply 40 is supplying power to the switching transistors in the soft-start circuit 20, the controller also controls the soft-start circuit 20 to conduct, enabling the AC-DC converter 13 to obtain power from the power grid 3 to raise the voltage of the DC bus 11.

[0102] When the photovoltaic module 2 is reverse-connected to the DC-DC converter 12, if the controller controls the soft start circuit 20 to be turned on, the AC-DC converter 13 obtains power from the grid 3 and raises the voltage of the DC bus 11 to the first threshold, as shown in Figure 8. Figure 8 is another current flow diagram of the photovoltaic inverter provided in Figure 4.

[0103] In this embodiment, the soft-start circuit 20 is turned on, and the AC-DC converter 13 obtains power from the power grid 3 to raise the voltage of the DC bus 11 to the first threshold. Since the DC bus 11 has enough power available for distribution, the controller controls the DC auxiliary power supply 30 to obtain power from the DC bus 11 to supply power to the switching transistors in the functional modules such as the controller, DC-DC converter 12, AC-DC converter 13, soft-start circuit 20, and detector 50.

[0104] Under this operating condition, the DC auxiliary power supply 30 drives the third switch Q3 in the DC-DC converter 12 to turn on the third switch Q3. During the process of the reverse-connected photovoltaic module 2 outputting DC power, the DC current output from the positive terminal of the photovoltaic module 2 flows to the drain of the third switch Q3, and then flows through the third switch Q3 driven by the DC auxiliary power supply 30 to the first inductor L1. At this time, the positive terminal of photovoltaic module 2 is directly connected to the negative terminal of photovoltaic module 2 through the conducting third switch Q3. Therefore, when a short-circuit current occurs in DC-DC converter 12, the short-circuit current no longer flows mainly through the body diode in the third switch Q3, but is conducted through the conductive channel of the third switch Q3. Moreover, the on-resistance of the third switch Q3 is usually very small when it is in the conducting state. This greatly reduces the voltage drop across the third switch Q3 when photovoltaic module 2 and DC-DC converter 12 are reverse connected, avoiding the problem of overheating and damage to the third switch Q3 in DC-DC converter 12 when photovoltaic module 2 is reverse connected, and improving the safety and reliability of photovoltaic inverter operation.

[0105] In one embodiment, the AC-DC converter 13 includes a first bridge arm and a second bridge arm connected in parallel with the DC bus 11. The first bridge arm includes a fourth switch Q4 and a fifth switch Q5 connected in series, and the series connection point of the fourth switch Q4 and the fifth switch Q5 is connected to the soft-start circuit 20. The second bridge arm includes a sixth switch Q6 and a seventh switch Q7 connected in series, and the series connection point of the sixth switch Q6 and the seventh switch Q7 is connected to the soft-start circuit 20. The power grid 3 connected to the AC-DC converter 13 can be a single-phase power input, a two-phase power input, or a three-phase power input. The circuit topology of the AC-DC converter 13 can be a high-efficiency and reliable inverter concept topology (HERIC), a T-type three-level topology, or a flying capacitor three-level topology, etc., and is not limited thereto.

[0106] In some embodiments, the AC-DC converter 13 further includes a second inductor L2 and a filter capacitor C4. The series connection point of the fourth switch Q4 and the fifth switch Q5 is connected to the soft-start circuit 20 through the second inductor L2. The filter capacitor C4 is connected in parallel between the series connection point of the fourth switch Q4 and the fifth switch Q5 and the series connection point of the sixth switch Q6 and the seventh switch Q7. When the switches in the AC-DC converter 13 switch states, the current may fluctuate momentarily. The second inductor L2 and the filter capacitor C4 are used to mitigate the current fluctuations in the AC-DC converter 13, making the current smoother and thus protecting other components in the circuit. Furthermore, the second inductor L2 and the filter capacitor C4 are also used to store and release the electrical energy input from the power grid 3 to the AC-DC converter 13 to maintain the continuity of the current in the circuit, enabling the AC-DC converter 13 to stably output DC power to the DC bus 11.

[0107] In this embodiment, the soft-start circuit 20 includes a first switching device S1, a second switching device S2, a third switching device S3, and a first resistor R1. The controller controls the on / off state of the soft-start circuit 20 by switching the on / off states of the first switching device S1, the second switching device S2, and the third switching device S3. One end of the first switching device S1 is connected to one connection terminal on the AC side of the inverter circuit, and the other end of the first switching device S1 is used to connect to the power grid 3. One end of the second switching device S2 is connected to the other connection terminal on the AC side of the inverter circuit, and the other end of the second switching device S2 is used to connect to the power grid 3. The third switching device S3 is connected in series with the first resistor R1, and the series-connected third switching device S3 and the first resistor R1 are connected in parallel across the first switching device S1.

[0108] In the soft-start circuit 20, the first resistor R1 includes, but is not limited to, a series-connected large resistor string, a cement resistor, a negative temperature coefficient thermistor (NTC), and a positive temperature coefficient thermistor (PTC). When the soft-start circuit 20 is turned on and the power grid 3 supplies power to the AC-DC converter 13, at the instant the power grid 3 is connected, the first resistor R1, together with the second inductor L2 and the filter capacitor C4 in the AC-DC converter 13, forms a charging circuit. This reduces the peak inrush current when the AC-DC converter 13 rectifies the AC power input from the power grid 3, allowing the current to rise more smoothly and protecting the operational safety of other components in the circuit.

[0109] Please refer to Figure 9, which shows a flowchart of another power supply control method provided in an embodiment of this application. This power supply control method is applied to the photovoltaic inverter shown in Figure 4. The power supply control method provided in this embodiment includes the following steps S510 to S540:

[0110] S510: Obtains the voltage of the DC bus and the input voltage of the DC-DC converter from the detector.

[0111] In this embodiment, when the voltage of the DC bus and the input voltage of the DC-DC converter in the photovoltaic inverter are collected in real time by the detector, in order to ensure the safe and stable operation of the photovoltaic inverter, the controller determines whether the photovoltaic inverter can currently guarantee normal operation by obtaining the voltage of the DC bus and the input voltage of the DC-DC converter from the detector.

[0112] S520: When the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is greater than or equal to the first threshold, the first, second and third switching devices in the soft start circuit are controlled to turn off, so that the soft start circuit is turned off.

[0113] In this embodiment, when the input voltage is detected to be less than zero and the voltage of the DC bus is greater than or equal to the first threshold, although there is a reverse connection between the photovoltaic module and the DC-DC converter, the DC auxiliary power supply obtains power from the DC bus to drive the switching transistor in the DC-DC converter that is reverse-connected to the photovoltaic module when the controller controls the switching transistor to be turned on. This ensures that the switching transistor in the reverse-connected DC-DC converter will not overheat and be damaged. At this time, the controller can control the soft start circuit to be turned off (that is, control the first switching device, the second switching device and the third switching device in the soft start circuit to be turned off), and the DC bus does not need to obtain power from the grid for compensation.

[0114] S530: When the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is less than the first threshold, the first switching device in the soft start circuit is turned off, and the second and third switching devices are turned on, so that the soft start circuit is turned on.

[0115] In this embodiment, when the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is less than a first threshold, since the DC auxiliary power supply cannot obtain power from the DC bus to drive the switching transistors in the reverse-connected DC-DC converter, to ensure that the switching transistors in the DC-DC converter reverse-connected to the photovoltaic module do not overheat and be damaged, the soft-start circuit is controlled to turn on, allowing the AC-DC converter to obtain power from the grid to raise the voltage of the DC bus. Furthermore, by controlling the first switching device in the soft-start circuit to turn off and controlling the second and third switching devices to turn on to turn on the soft-start circuit, the first resistor in the soft-start circuit can be connected to the circuit, reducing the peak inrush current when the AC-DC converter rectifies the AC input from the grid, thus protecting the safe operation of the components.

[0116] S540: When the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus rises to the first threshold, the first and second switching devices are controlled to turn on, and the third switching device is controlled to turn off, so that the soft start circuit is turned on.

[0117] In this embodiment, when the voltage of the DC bus rises to the first threshold and the input voltage of the DC-DC converter is less than zero, the soft-start circuit needs to be kept on to maintain the voltage of the DC bus. However, in order to reduce the energy consumption of maintaining the voltage of the DC bus, the first and second switching devices are turned on, and the third switching device is turned off, so that the first resistor in the soft-start circuit is no longer connected to the circuit and no longer consumes power, thereby reducing the power consumption of the AC-DC converter when it obtains power from the grid to supply power to the DC bus.

[0118] As shown in Figure 6, when the photovoltaic module 2 is directly connected to the DC-DC converter 12, the controller detects that the voltage of the DC bus 11 is greater than or equal to the first threshold and the input voltage of the DC-DC converter 12 is greater than zero. This means that the DC bus 11 can obtain sufficient electrical energy from the photovoltaic module 2 for distribution through the DC-DC converter 12, and the DC auxiliary power supply 30 can start normally. The controller then controls the soft-start circuit 20 to shut down, specifically controlling the first switching device S1, the second switching device S2, and the third switching device S3 in the soft-start circuit 20 to turn off. At this time, the power grid 3 does not supply power to the AC-DC converter 13 in reverse. Because the electrical energy supplied by the power grid 3 in reverse under this condition may not only be inefficiently utilized but also generate additional losses in the circuit, such as resistor heating, resulting in energy waste, the controller controls the soft-start circuit 20 to shut down, which can reduce energy waste during the operation of the photovoltaic inverter.

[0119] When the photovoltaic module 2 and the DC-DC converter 12 are reverse-connected, as shown in Figure 7, when the controller detects that the voltage of the DC bus 11 is less than the first threshold and the input voltage of the DC-DC converter 12 is less than zero, that is, the DC bus 11 does not have enough power to distribute, and the DC auxiliary power supply 30 cannot start normally, the controller controls the soft-start circuit 20 to turn on, that is, controls the first switching device S1 in the soft-start circuit 20 to turn off, and controls the second switching device S2 and the third switching device S3 to turn on, so that the AC-DC converter 13 can obtain power from the grid 3 to supply power to the DC bus 11. Furthermore, at this time, the first resistor R1 in the soft-start circuit 20 is connected in the circuit, which can reduce the peak inrush current when the AC-DC converter 13 rectifies the AC power input to the grid 3, protecting the safe operation of the components.

[0120] When the photovoltaic module 2 and the DC-DC converter 12 are reverse-connected, as shown in Figure 8, after the controller controls the soft-start circuit 20 to be turned on, the AC-DC converter 13 obtains power from the grid 3 to raise the voltage of the DC bus 11 to the first threshold. Since the input voltage of the DC-DC converter 12 is less than zero at this time, but the DC bus 11 has enough power to be distributed, the DC auxiliary power supply 30 can start normally. The controller is used to control the soft-start circuit 20 to remain on so that the grid 3 continuously supplies power to the DC bus 11 through the AC-DC converter 13, keeping the voltage of the DC bus 11 greater than or equal to the first threshold. However, the controller is also used to control the first switching device S1 and the second switching device S2 to turn on and the third switching device S3 to turn off when the voltage of the DC bus 11 rises to the first threshold and the input voltage of the DC-DC converter 12 is less than zero. That is, when the soft-start circuit 20 remains on to maintain the voltage of the DC bus 11, the controller controls the first resistor R1 in the soft-start circuit 20 to no longer be connected in the circuit and no longer consume power, so as to reduce the power consumption of the AC-DC converter 13 when it obtains power from the grid 3 to supply power to the DC bus 11.

[0121] In some other embodiments, as shown in FIG10, the soft-start circuit includes not only the first switching device S1, the second switching device S2, the third switching device S3 and the first resistor R1, but also the fourth switching device S4 and the fifth switching device S5.

[0122] In this embodiment, the fourth switching device S4 is connected in series between the first switching device S1 and the power grid 3, and the fifth switching device S5 is connected in series between the other end of the second switching device S2 and the power grid 3. That is, the switching devices in the soft-start circuit can be a single switching device or multiple switching devices connected in series. The fact that the switching devices in the soft-start circuit can be a single switching device or multiple switching devices connected in series allows the multiple switching devices connected in series to isolate the fault when a component fails during the turn-on and turn-off process of the soft-start circuit, thus improving the reliability and stability of the soft-start circuit.

[0123] For example, as shown in Figure 10(a), the third switching device S3 connected in series and the first resistor R1 are connected in parallel across the first switching device S1. Alternatively, as shown in Figure 10(b), the third switching device S3 connected in series and the first resistor R1 are connected in parallel across the first switching device S1 and the fourth switching device S4 connected in series. That is, the third switching device S3 connected in series and the first resistor R1 can be connected across any one of the switching devices or across multiple switching devices connected in series, without any limitation.

[0124] In one embodiment, as shown in FIG11, the DC auxiliary power supply includes a DC primary winding 31 and a DC secondary winding 32.

[0125] In this embodiment, the DC primary winding 31 is connected to the DC bus 11 to obtain electrical energy from the DC bus 11. The DC auxiliary power supply may further include a first switching transistor Q1, a first diode D1, a first capacitor C1, and a second resistor R2. The source of the first switching transistor Q1 is connected to the anode of the first diode D1, the drain of the first switching transistor Q1 is connected to the cathode of the DC bus 11, the gate of the first switching transistor Q1 is connected to the controller, the anode and drain of the body diode of the first switching transistor Q1 are connected, and the cathode and source of the body diode of the first switching transistor Q1 are connected. The first capacitor C1 is connected in series between the cathode of the first diode D1 and the cathode of the DC bus 11, and the second resistor R2 is connected in parallel with the first capacitor C1. The DC primary winding 31 is connected in parallel with the first diode D1 and the first capacitor C1.

[0126] Specifically, when the controller detects that the voltage of the DC bus 11 is greater than or equal to the first voltage threshold, the controller outputs a drive signal to the gate of the first switch Q1 to drive and power the first switch Q1, causing the first switch Q1 to conduct. The DC current input to the positive terminal of the DC bus 11 flows through the DC primary winding 31 and the conducting first switch Q1 to the negative terminal of the DC bus 11, thereby forming a loop to power the DC primary winding 31.

[0127] The first capacitor C1 and the second resistor R2 are used to smooth the voltage peaks that occur when the first switch Q1 is turned on and off, thus smoothing the voltage waveform and ensuring the safe operation of the DC auxiliary power supply. The first diode D1 acts as a freewheeling diode. When the controller turns off the first switch Q1, the current in the DC primary winding 31 cannot change abruptly. At this time, the first diode D1 provides a path for releasing the electrical energy stored in the DC primary winding 31, allowing the current to continue flowing through the first diode D1 to form a loop. The capacitor and resistor can release the electrical energy, thereby avoiding excessive reverse voltage across the DC primary winding 31 and protecting the circuit components.

[0128] In this embodiment, the DC primary winding 31 obtains electrical energy from the DC bus 11 and supplies power to the DC secondary winding 32. The DC secondary winding 32 is used to connect to the controller, DC-DC converter 12, AC-DC converter 13, soft-start circuit and detector to supply power to the switching transistors in the controller, DC-DC converter 12, AC-DC converter 13, soft-start circuit and detector. The number of DC secondary windings 32 can be one or more, which is not limited here.

[0129] In some embodiments, the DC secondary winding 32 is further connected in series with a diode and in parallel with a capacitor. After the DC primary winding 31 supplies power to the DC secondary winding 32, the current in the DC secondary winding 32 flows unidirectionally due to the unidirectional conduction characteristic of the diode, providing DC power of appropriate direction to each functional module. The capacitor, as a filter element, can absorb or release electrical energy, thereby smoothing the DC power output from the DC secondary winding 32 and improving the power supply quality when the DC auxiliary power supply supplies power to the switching transistors in each functional module.

[0130] In one embodiment, as shown in FIG12, the AC auxiliary power supply includes a rectifier 41, an AC primary winding 42, and an AC secondary winding 43.

[0131] In this embodiment, the input terminal of rectifier 41 is connected to the power grid 3, and the output terminal of rectifier 41 is connected to the AC primary winding 42 to obtain electrical energy from the power grid 3 and supply power to the AC primary winding 42. The AC auxiliary power supply may further include a second switch Q2, a second diode D2, a second capacitor C2, and a third resistor R3. The source of the second switch Q2 is connected to the anode of the second diode D2, the drain of the second switch Q2 is connected to one output terminal of rectifier 41, the gate of the second switch Q2 is connected to the controller, the anode of the body diode of the second switch Q2 is connected to the drain, and the cathode of the body diode of the second switch Q2 is connected to the source. The second capacitor C2 is connected in series between the cathode of the second diode D2 and the other output terminal of rectifier 41, and the third resistor R3 is connected in parallel with the second capacitor C2. The AC primary winding 42 is connected in parallel with the second diode D2 and the second capacitor C2.

[0132] Specifically, when the controller detects that the voltage of the DC bus is less than the first voltage threshold, the controller outputs a drive signal to the gate of the second switch Q2 to drive and power the second switch Q2, causing the second switch Q2 to turn on. The AC power input from the power grid 3 is converted into DC power by the rectifier 41, and flows back to the rectifier 41 through the AC primary winding 42 and the turned-on second switch Q2, thus forming a loop to power the AC primary winding 42.

[0133] The roles of the second diode D2, the second capacitor C2, and the third resistor R3 in the AC auxiliary power supply are similar to those of the first diode D1, the first capacitor C1, and the second resistor R2 in the DC auxiliary power supply, and will not be repeated here.

[0134] In this embodiment, the AC primary winding 42 obtains electrical energy from the power grid 3 and supplies power to the AC secondary winding 43. The AC secondary winding 43 is used to connect to the controller, the soft start circuit, and the detector to supply power to the controller, the soft start circuit, and the detector. The number of AC secondary windings 43 can be one or more, and there is no limitation.

[0135] In some implementations, the AC secondary winding 43 is further connected in series with a diode and in parallel with a capacitor. After the AC primary winding 42 supplies power to the AC secondary winding 43, the current in the DC secondary winding 32 flows unidirectionally due to the unidirectional conduction characteristic of the diode, providing DC power of appropriate direction to each functional module. The capacitor, as a filter element, can absorb or release electrical energy, thereby smoothing the DC power output from the AC secondary winding 43 and improving the power supply quality when the AC auxiliary power supply supplies power to the switching transistors in each functional module.

[0136] In this embodiment, the power grid 3 connected to the AC auxiliary power supply can be a single-phase power input, a two-phase power input, or a three-phase power input, as shown in Figure 12. When the power grid 3 is a two-phase power input, the rectifier 41 in the AC auxiliary power supply includes two parallel-connected bridge arms, each bridge arm including two series-connected switching transistors or diodes. For example, when each bridge arm includes two series-connected diodes, the series connection point of the two diodes in each bridge arm is connected to the input terminal of the rectifier 41, and the input terminal of the rectifier 41 is used to connect to the power grid 3; the parallel connection point of the two-phase bridge arms is connected to the output terminal of the rectifier 41, and the output terminal of the rectifier 41 is connected to the AC primary winding 42.

[0137] As shown in Figure 13, when the power grid 3 is a three-phase power input, the rectifier 41 in the AC auxiliary power supply includes three-phase bridge arms connected in parallel. Each phase bridge arm includes two switching transistors or diodes connected in series. Compared to single-phase or two-phase power input, the three-phase power supply can provide greater power and more stable power supply to the AC auxiliary power supply. For example, when each phase bridge arm includes two diodes connected in series, the series connection point of the two diodes in each phase bridge arm is connected to the input terminal of the rectifier 41, and the input terminal of the rectifier 41 is used to connect to the power grid 3. The parallel connection point of the three-phase bridge arms is connected to the output terminal of the rectifier 41, and the output terminal of the rectifier 41 is connected to the AC primary winding 42.

[0138] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be included 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 photovoltaic inverter, characterized in that, The photovoltaic inverter includes a controller, an inverter circuit, a soft-start circuit, a DC auxiliary power supply, and an AC auxiliary power supply. The inverter circuit includes a DC bus, a DC-DC converter, and an AC-DC converter. The input terminal of the DC-DC converter is used to connect to the photovoltaic module. The soft-start circuit is used to connect the AC terminal of the AC-DC converter and the power grid. The output terminal of the DC-DC converter and the DC terminal of the AC-DC converter are both connected to the DC bus. The DC auxiliary power supply is used to obtain electrical energy from the DC bus to power the controller, the DC-DC converter, the AC-DC converter, and the switching transistors in the soft-start circuit when the voltage of the DC bus is greater than or equal to a first threshold. The AC auxiliary power supply is used to obtain electrical energy from the power grid to power the controller and the soft start circuit when the voltage of the DC bus is less than the first threshold. The controller is used to control the soft-start circuit to turn on when it detects that the voltage of the DC bus is less than the first threshold and the input voltage of the DC-DC converter is less than zero, so that the AC-DC converter can obtain power from the grid to raise the voltage of the DC bus to the first threshold. When the voltage of the DC bus rises to the first threshold, the controller is used to control the switching transistors in the DC-DC converter to turn on.

2. The photovoltaic inverter according to claim 1, characterized in that, The photovoltaic inverter also includes a detector, which is connected to the DC bus and the DC-DC converter. The detector is used to collect the voltage of the DC bus and the input voltage of the DC-DC converter.

3. The photovoltaic inverter according to claim 2, characterized in that, The DC auxiliary power supply is also used to supply power to the detector when the voltage of the DC bus is greater than or equal to the first threshold. The AC auxiliary power supply is also used to supply power to the detector when the voltage of the DC bus is less than the first threshold.

4. The photovoltaic inverter according to any one of claims 1 to 3, characterized in that, The soft-start circuit includes a first switching device, a second switching device, a third switching device, and a first resistor; One end of the first switching device is connected to a connection terminal on the AC side of the inverter circuit, and the other end of the first switching device is used to connect to the power grid; One end of the second switching device is connected to another connection terminal on the AC side of the inverter circuit, and the other end of the second switching device is used to connect to the power grid; The third switching device is connected in series with the first resistor, and the third switching device and the first resistor are connected in parallel across the first switching device.

5. The photovoltaic inverter according to claim 4, characterized in that, The controller is further configured to control the first switching device, the second switching device, and the third switching device to turn off when the voltage of the DC bus is detected to be greater than or equal to the first threshold and the input voltage of the DC-DC converter is greater than zero.

6. The photovoltaic inverter according to claim 4, characterized in that, The controller is also configured to, when it detects that the voltage of the DC bus is less than the first threshold and the input voltage of the DC-DC converter is less than zero, control the first switching device to turn off, control the second switching device and the third switching device to turn on, so that the AC-DC converter can obtain power from the power grid to supply power to the DC bus; The controller is further configured to, when it detects that the voltage of the DC bus rises to the first threshold and the input voltage of the DC-DC converter is less than zero, control the first switching device and the second switching device to turn on, and control the third switching device to turn off, so that the AC-DC converter can obtain power from the power grid to supply power to the DC bus.

7. The photovoltaic inverter according to any one of claims 4 to 6, characterized in that, The soft-start circuit also includes a fourth switching device and a fifth switching device; The fourth switching device is connected in series between the other end of the first switching device and the power grid, and the third switching device and the first resistor connected in series are connected in parallel across the first switching device, or the third switching device and the first resistor connected in series are connected in parallel across the first switching device and the fourth switching device connected in series. The fifth switching device is connected in series between the other end of the second switching device and the power grid.

8. The photovoltaic inverter according to any one of claims 1 to 7, characterized in that, The DC auxiliary power supply includes a DC primary winding and a DC secondary winding; The DC primary winding is connected to the DC bus to obtain electrical energy from the DC bus; The DC secondary winding is used to connect to the controller, the DC-DC converter, the AC-DC converter, and the soft-start circuit to supply power to the controller, the DC-DC converter, the AC-DC converter, and the soft-start circuit.

9. The photovoltaic inverter according to claim 8, characterized in that, The DC auxiliary power supply also includes a first switching transistor, a first diode, a first capacitor, and a second resistor; The source of the first switching transistor is connected to the anode of the first diode, the drain of the first switching transistor is connected to the cathode of the DC bus, the gate of the first switching transistor is connected to the controller, the anode of the body diode of the first switching transistor is connected to the drain, and the cathode of the body diode of the first switching transistor is connected to the source. The first capacitor is connected in series between the negative terminal of the first diode and the negative terminal of the DC bus, and the second resistor is connected in parallel with the first capacitor; The DC primary winding is connected in parallel with the first diode and the first capacitor.

10. The photovoltaic inverter according to any one of claims 1 to 7, characterized in that, The AC auxiliary power supply includes a rectifier, an AC primary winding, and an AC secondary winding; The input terminal of the rectifier is used to connect to the power grid, and the output terminal of the rectifier is connected to the AC primary winding to obtain electrical energy from the power grid and supply power to the AC primary winding. The AC secondary winding is used to connect to the controller and the soft-start circuit to supply power to the controller and the soft-start circuit.

11. The photovoltaic inverter according to claim 10, characterized in that, The AC auxiliary power supply also includes a second switching transistor, a second diode, a second capacitor, and a third resistor; The source of the second switching transistor is connected to the anode of the second diode, the drain of the second switching transistor is connected to one output terminal of the rectifier, the gate of the second switching transistor is connected to the controller, the anode of the body diode of the second switching transistor is connected to the drain, and the cathode of the body diode of the second switching transistor is connected to the source. The second capacitor is connected in series between the negative terminal of the second diode and the other output terminal of the rectifier, and the third resistor is connected in parallel with the second capacitor; The DC primary winding is connected in parallel with the second diode and the second capacitor.

12. The photovoltaic inverter according to any one of claims 1 to 11, characterized in that, The DC-DC converter includes a first inductor, a third switching transistor, and a third diode; One end of the first inductor is connected to the positive terminal of the photovoltaic module, and the other end of the first inductor is connected to the positive terminal of the third diode; The source of the third switch is connected to the anode of the third diode, the drain of the third switch is connected to the cathode of the photovoltaic module and the cathode of the DC bus, the gate of the third switch is connected to the controller, the anode and drain of the body diode of the third switch are connected, and the cathode and source of the body diode of the third switch are connected. The negative terminal of the third diode is connected to the negative terminal of the DC bus.

13. The photovoltaic inverter according to any one of claims 1 to 11, characterized in that, The AC-DC converter includes a first bridge arm and a second bridge arm connected in parallel with the DC bus; The first bridge arm includes a fourth switch and a fifth switch connected in series, and the series connection point of the fourth switch and the fifth switch is connected to the soft start circuit. The second bridge arm includes a sixth switch and a seventh switch connected in series, and the connection point of the sixth switch and the seventh switch is connected to the soft-start circuit.

14. A power supply control method, characterized in that, An application is made in a photovoltaic inverter, the photovoltaic inverter including a DC bus, a DC-DC converter, an AC-DC converter, a soft-start circuit, a DC auxiliary power supply, an AC auxiliary power supply, and a detector. The input terminal of the DC-DC converter is used to connect to photovoltaic modules. The soft-start circuit is used to connect the AC terminal of the AC-DC converter to the power grid. The output terminal of the DC-DC converter and the DC terminal of the AC-DC converter are both connected to the DC bus. The detector is connected to the DC bus and the DC-DC converter. The method includes: The voltage of the DC bus and the input voltage of the DC-DC converter are obtained from the detector; When the input voltage of the DC-DC converter is detected to be less than zero, the conduction state of the soft-start circuit is adjusted based on the voltage of the DC bus, so that the DC auxiliary power supply continuously draws power from the DC bus to supply power to the switching transistors of the DC-DC converter.

15. The power supply control method according to claim 14, characterized in that, The step of adjusting the conduction state of the soft-start circuit based on the DC bus voltage when the input voltage of the DC-DC converter is detected to be less than zero includes: When the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is greater than or equal to a first threshold, the soft-start circuit is controlled to turn off.

16. The power supply control method according to claim 14, characterized in that, The step of adjusting the conduction state of the soft-start circuit based on the DC bus voltage when the input voltage of the DC-DC converter is detected to be less than zero includes: When the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is less than the first threshold, the soft-start circuit is controlled to turn on, so that the AC-DC converter can obtain power from the grid to raise the voltage of the DC bus to the first threshold.

17. The power supply control method according to any one of claims 15 to 16, characterized in that, The soft-start circuit includes a first switching device, a second switching device, a third switching device, and a first resistor. The first switching device is used to connect one terminal of the AC side of the inverter circuit to the power grid. The second switching device is used to connect the other terminal of the AC side of the inverter circuit to the power grid. The third switching device is connected in series with the first resistor, and the series-connected third switching device and the first resistor are connected in parallel across the first switching device. The method further includes: When the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is greater than or equal to the first threshold, the first, second, and third switching devices in the soft-start circuit are controlled to turn off, thereby turning off the soft-start circuit.

18. The power supply control method according to claim 17, characterized in that, The method further includes: When the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus is less than the first threshold, the first switching device in the soft start circuit is controlled to turn off, and the second and third switching devices are controlled to turn on, so that the soft start circuit is turned on. When the input voltage of the DC-DC converter is detected to be less than zero and the voltage of the DC bus rises to the first threshold, the first and second switching devices are controlled to turn on, and the third switching device is controlled to turn off, so that the soft-start circuit is turned on.

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