Power conversion system and method of starting

Abstract

The application discloses a power conversion system and a starting method. The power conversion system comprises a direct-current transmission device, an inverter and a control module. The control module is configured to: during starting of the inverter, control a direct-current auxiliary power supply of the inverter to be in a shutdown state; control a slow start switch to be closed, and control the direct-current transmission device to charge a bus capacitor of the inverter through a current limiting resistor; during the charging of the bus capacitor of the inverter, if a voltage difference across the main switch is detected to be less than a preset voltage threshold, the main switch is controlled to be closed; after the main switch is closed, a starting signal is sent to the direct-current auxiliary power supply, the direct-current auxiliary power supply is controlled to start, and after the starting of the direct-current auxiliary power supply is completed, the inverter is controlled to perform a starting operation. Based on the above technical scheme, the starting efficiency of the inverter can be effectively improved, and the starting success rate of the inverter can also be improved.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a power conversion system and a start-up method. Background Technology

[0002] With the rapid development of photovoltaic power generation technology, large-capacity photovoltaic power plants generally adopt a system architecture that cascades front-end DC transmission equipment with back-end inverters to achieve efficient energy management and power conversion of the photovoltaic array. During the startup process of the power conversion system, the front-end DC transmission equipment pre-charges the bus capacitor of the back-end inverter through a soft-start circuit. The DC power board of the back-end inverter typically draws power from the bus capacitor. When the bus voltage exceeds the power board's startup threshold, the power board begins to supply power to the internal circuitry of the inverter.

[0003] However, the DC power supply board consumes the energy stored in the bus capacitor after startup, resulting in a prolonged pre-charge time. In severe cases, the bus voltage may drop below the startup threshold due to rapid energy release, causing the inverter to fail to start. Summary of the Invention

[0004] This application provides a power conversion system and a startup method that can effectively improve the startup efficiency of the inverter and also increase the startup success rate of the inverter.

[0005] In a first aspect, embodiments of this application provide a power conversion system, including a DC transmission device, an inverter, and a control module; wherein, the output side of the DC transmission device is connected to the DC side of the inverter via a main switch, and a soft-start circuit is connected in parallel across the two ends of the main switch; the soft-start circuit includes a soft-start switch and a current-limiting resistor connected in series; The control module is configured as follows: During the startup process of the inverter, the DC auxiliary power supply of the inverter is kept in the off state. The soft-start switch is closed to control the DC transmission device to charge the inverter's bus capacitor through the current-limiting resistor. During the charging process of the inverter's bus capacitor, if the voltage difference across the main switch is detected to be less than a preset voltage threshold, the main switch is controlled to close. After the main switch is closed, a power-on signal is sent to the DC auxiliary power supply to control the DC auxiliary power supply to start up. After the DC auxiliary power supply is started up, the inverter is controlled to perform a startup operation.

[0006] In some embodiments, the control module is configured to: After the DC transmission equipment is started and the soft-start switch is closed, the DC auxiliary power supply is controlled to be in the off state; or, Before the DC transmission equipment is started and the soft-start switch is closed, the DC auxiliary power supply is controlled to be in the off state; or, Before the DC transmission equipment is started, the DC auxiliary power supply is controlled to be in the off state; or, During the startup process of the inverter, and before the inverter meets the startup conditions, the DC auxiliary power supply is controlled to be in the shutdown state.

[0007] In some embodiments, the inverter includes an overcurrent protection circuit connected to the DC auxiliary power supply, and the control module is configured to: A first level signal is sent to the overcurrent protection circuit, and the first level signal is used to trigger the overcurrent protection circuit; The overcurrent protection circuit is used to respond to the first level signal and control the overcurrent protection circuit to be in a triggered state so that the DC auxiliary power supply is in the shutdown state.

[0008] In some embodiments, the inverter includes a start-stop trigger circuit connected to the control module, the control module being configured to: Generate a shutdown control signal and send the shutdown control signal to the start / stop trigger circuit; The start / stop trigger circuit is used to respond to the shutdown control signal, generate the first level signal, and send the first level signal to the overcurrent protection circuit.

[0009] In some embodiments, the control module is configured to: Send a second-level signal to the overcurrent protection circuit; The overcurrent protection circuit is used to release the trigger state in response to the second level signal, wherein the second level signal is the power-on signal, and the first level signal is different from the second level signal.

[0010] In some embodiments, the control module is configured to: Generate a power-on control signal and send the power-on control signal to the start / stop trigger circuit; The start / stop trigger circuit is used to respond to the power-on control signal, generate the second level signal, and send the second level signal to the overcurrent protection circuit.

[0011] In some embodiments, the start / stop trigger circuit includes an isolation drive circuit and a trigger circuit, wherein the input terminal of the isolation drive circuit is connected to the control module, the output terminal of the isolation drive circuit is connected to the input terminal of the trigger circuit, and the output terminal of the trigger circuit is connected to the overcurrent protection circuit.

[0012] In some embodiments, the first level signal is a low level signal and the second level signal is a high level signal.

[0013] In some embodiments, the overcurrent protection circuit is configured to receive an overcurrent feedback signal when the start / stop trigger circuit is in an open state, and adjust the current state of the overcurrent protection circuit according to the overcurrent feedback signal.

[0014] Secondly, embodiments of this application also provide a startup method for a power conversion system. The power conversion system includes a DC transmission device and an inverter. The output side of the DC transmission device is connected to the DC side of the inverter via a main switch. A soft-start circuit is connected in parallel across the two ends of the main switch. The soft-start circuit includes a soft-start switch and a current-limiting resistor connected in series. The method includes: During the startup process of the inverter, the DC auxiliary power supply of the inverter is kept in the off state. The soft-start switch is closed to control the DC transmission device to charge the inverter's bus capacitor through the current-limiting resistor. During the charging process of the inverter's bus capacitor, if the voltage difference across the main switch is detected to be less than a preset voltage threshold, the main switch is controlled to close. After the main switch is closed, a power-on signal is sent to the DC auxiliary power supply to control the DC auxiliary power supply to start up. After the DC auxiliary power supply is started up, the inverter is controlled to perform a startup operation.

[0015] In some embodiments, controlling the DC auxiliary power supply of the inverter to be in a powered-off state during the startup process of the inverter includes: After the DC transmission equipment is started and the soft-start switch is closed, the DC auxiliary power supply is controlled to be in the off state; or, Before the DC transmission equipment is started and the soft-start switch is closed, the DC auxiliary power supply is controlled to be in the off state; or, Before the DC transmission equipment is started, the DC auxiliary power supply is controlled to be in the off state; or, During the startup process of the inverter, and before the inverter meets the startup conditions, the DC auxiliary power supply is controlled to be in the shutdown state.

[0016] In some embodiments, the inverter includes an overcurrent protection circuit connected to the DC auxiliary power supply, and the control of the DC auxiliary power supply of the inverter to be in a powered-off state includes: A first level signal is sent to the overcurrent protection circuit, and the first level signal is used to trigger the overcurrent protection circuit; The overcurrent protection circuit is controlled to respond to the first level signal, so that the overcurrent protection circuit is in the triggered state, and the DC auxiliary power supply is controlled to be in the shutdown state.

[0017] In some embodiments, the inverter includes a control module and a start / stop trigger circuit connected to the control module, wherein sending a start-up signal to the DC auxiliary power supply includes: The control module generates a shutdown control signal and sends the shutdown control signal to the start / stop trigger circuit. The start / stop trigger circuit responds to the shutdown control signal, generates the first level signal, and sends the first level signal to the overcurrent protection circuit.

[0018] In some embodiments, sending a power-on signal to the DC auxiliary power supply includes: A second level signal is sent to the overcurrent protection circuit to deactivate the trigger state of the overcurrent protection circuit, wherein the second level signal is the power-on signal, and the first level signal is different from the second level signal.

[0019] In some embodiments, sending a second-level signal to the overcurrent protection circuit includes: The control module generates a power-on control signal and sends the power-on control signal to the start / stop trigger circuit. The start / stop trigger circuit responds to the power-on control signal, generates the second level signal, and sends the second level signal to the overcurrent protection circuit.

[0020] The power conversion system provided in this application embodiment controls the DC auxiliary power supply of the inverter to be in a shutdown state during the inverter startup process; controls the soft-start switch to close, and controls the DC transmission equipment to charge the inverter's bus capacitor through the current-limiting resistor; during the charging process of the inverter's bus capacitor, if the voltage difference across the main switch is detected to be less than a preset voltage threshold, the main switch is controlled to close; after the main switch closes, a startup signal is sent to the DC auxiliary power supply to control the DC auxiliary power supply to start; after the DC auxiliary power supply is started, the inverter is controlled to perform a startup operation. Based on the above technical solution, by actively controlling the DC auxiliary power supply to remain in a shutdown state during the pre-charging phase of inverter startup, the premature start-up of the DC auxiliary power supply and its energy consumption of the bus capacitor are avoided, ensuring that the bus capacitor voltage can rise steadily to the preset threshold, so that the voltage difference across the main switch meets the closing condition, thereby improving the inverter's startup efficiency and startup success rate. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0023] Figure 1 This is a schematic diagram of the structure of a power conversion system provided in an exemplary embodiment of the present disclosure; Figure 2 This is a schematic diagram of the connection between the control module and the DC auxiliary power supply provided in an exemplary embodiment of the present disclosure; Figure 3 A flowchart illustrating the startup method of a power conversion system provided in an exemplary embodiment of this disclosure; Figure 4 A flowchart illustrating the first startup logic of an inverter provided as an exemplary embodiment of this disclosure; Figure 5 A flowchart illustrating the second startup logic of an inverter provided as an exemplary embodiment of this disclosure; Figure 6 A flowchart illustrating the third startup logic of an inverter provided as an exemplary embodiment of this disclosure; Figure 7 This is a flowchart illustrating the fourth startup logic of an inverter provided in an exemplary embodiment of this disclosure.

[0024] Explanation of reference numerals in the attached figures: 10. DC transmission equipment; 20. Inverter; 21. DC auxiliary power supply; 22. Bus capacitor; 23. Control module; 24. Isolation drive circuit; 25. Trigger circuit; 26. Overcurrent protection circuit; 30. Photovoltaic string; 41. Soft start switch; 42. Main switch; 43. Current limiting resistor; 50. Power grid. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0026] In the embodiments of this application, "at least one" refers to one or more; "multiple" refers to two or more. In the description of this application, the terms "first," "second," etc., are used only for the purpose of distinguishing descriptions and should not be construed as indicating or implying relative importance, nor should they be construed as indicating or implying order.

[0027] References such as “one embodiment” or “some embodiments” as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the terms “comprising,” “including,” “having,” and variations thereof, as used in this specification, mean “including, but not limited to,” unless otherwise specifically emphasized.

[0028] It should be noted that in the embodiments of this application, "and / or" describes the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. In addition, the character " / ", unless otherwise specified, generally indicates that the associated objects before and after it are in an "or" relationship.

[0029] It should be noted that in the embodiments of this application, "connection" can be understood as electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0030] See Figure 1 This application provides a power conversion system, which includes a DC transmission device 10 and an inverter 20. The input side of the DC transmission device 10 is used to connect to a photovoltaic string 30, and the output side of the DC transmission device 10 is connected to the DC side of the inverter 20 through a main switch 42. A soft-start circuit is connected in parallel across the two ends of the main switch 42. The soft-start circuit includes a soft-start switch 41 and a current-limiting resistor 43 connected in series. The AC side of the inverter 20 is used to connect to the power grid 50.

[0031] In some embodiments, the soft-start switch 41 is connected in series with the current-limiting resistor 43 to form a soft-start pre-charge branch, which is used to limit the charging current during the startup phase; the main switch 42 is used to carry the normal operating current of the system after the pre-charge is completed.

[0032] In some embodiments, inverter 20 includes inverter circuitry.

[0033] In some embodiments, the inverter 20 includes a DC auxiliary power supply 21 and a bus capacitor 22, wherein the bus capacitor 22 is disposed on the DC bus of the inverter 20 and is used to stabilize the DC bus voltage. The input terminal of the DC auxiliary power supply 21 is connected to the bus capacitor 22, and the output terminal of the DC auxiliary power supply 21 is used to supply power to the electrical components inside the inverter 20 (such as sampling circuits, drive circuits, signal processing circuits, etc.).

[0034] In some embodiments, the DC auxiliary power supply 21 may be any of a DC power supply board, a switching power supply module, etc.

[0035] In some embodiments, the DC auxiliary power supply 21 needs to draw power from the bus capacitor. Therefore, during the startup process of the inverter 20, when neither the soft-start switch 41 nor the main switch 42 is closed, the DC auxiliary power supply cannot supply power to some functional units inside the inverter 20.

[0036] In some embodiments, during the bus pre-charging phase, when the voltage of the bus capacitor 22 exceeds the start-up threshold of the DC auxiliary power supply 21, the DC auxiliary power supply 21 will automatically start, consuming the energy stored in the bus capacitor 22. Since the energy stored in the bus capacitor 22 during the pre-charging phase is limited, the start-up of the DC auxiliary power supply 21 will lead to a prolonged pre-charging time and even a drop in the bus voltage, making it impossible for the voltage difference across the main switch 42 to drop below the closing threshold, resulting in the main switch 42 failing to close and ultimately causing the inverter 20 to fail to start up.

[0037] In some embodiments, the power conversion system further includes a control module, which can be located in the inverter 20, the DC transmission device 10, or other devices independent of the inverter 20 and the DC transmission device 10. This control module is connected to the soft-start switch 41, the main switch 42, and the DC auxiliary power supply 21, respectively. It is used to control the DC auxiliary power supply 21 to remain off during the startup process of the inverter 20, and then control the DC auxiliary power supply 21 to start up only after the main switch 42 has reliably closed. Thus, the above technical solution enables the linkage control between the startup and shutdown of the DC auxiliary power supply 21 and the startup state of the inverter. Without increasing system hardware costs, it effectively avoids the problems of bus voltage drop and main switch 42 failure to close due to premature startup of the DC auxiliary power supply 21.

[0038] In some embodiments, the inverter 20 may further include an AC auxiliary power supply (not shown in the figure). The input terminal of the AC auxiliary power supply is connected to the AC side (i.e., the grid side) of the inverter 20 to draw power from the grid and to supply power to at least some of the functional units inside the inverter 20.

[0039] Taking inverter 20, including the control module, as an example, Figure 2As shown, the inverter 20 includes a control module 23 and an overcurrent protection circuit 26 connected to the DC auxiliary power supply 21. At this time, a first level signal can be sent to the overcurrent protection circuit 26, which is used to trigger the overcurrent protection circuit 26. The overcurrent protection circuit 26 is used to respond to the first level signal and control the overcurrent protection circuit 26 to be in the triggered state so that the DC auxiliary power supply 21 is in the off state.

[0040] In some embodiments, the inverter 20 may further include a start-stop trigger circuit connected between the control module and the overcurrent protection circuit 26. During the start-up process of the inverter 20, the control module 23 pre-generates a shutdown control signal and sends it to the start-stop trigger circuit. The start-stop trigger circuit responds to the shutdown control signal by generating a first-level signal and sending it to the overcurrent protection circuit 26. Additionally, the control module 23 may generate a power-on control signal and send it to the start-stop trigger circuit. In this case, the start-stop trigger circuit also responds to the power-on control signal by generating a second-level signal and sending it to the overcurrent protection circuit 26. The overcurrent protection circuit 26 responds to the second-level signal, deactivates the trigger state, and then controls the DC auxiliary power supply 21 to start. After the DC auxiliary power supply 21 starts, it controls the inverter 20 to perform a start-up operation.

[0041] In some embodiments, the start / stop trigger circuit includes an isolation drive circuit 24 and a trigger circuit 25. The input terminal of the isolation drive circuit 24 is connected to the control module 23, the output terminal of the isolation drive circuit 24 is connected to the input terminal of the trigger circuit 25, and the output terminal of the trigger circuit 25 is connected to the overcurrent protection circuit 26. This allows the shutdown control signal sent by the control module 23 to be transmitted to the overcurrent protection circuit 26 through the start / stop trigger circuit, thereby triggering the overcurrent protection circuit 26.

[0042] In some embodiments, the isolation drive circuit 24 can be any of an optocoupler drive circuit, a magnetic isolation circuit, and a capacitive isolation circuit. Furthermore, the trigger circuit 25 can be any of a relay, an analog switch chip (such as a CMOS bidirectional analog switch), a transmission gate, a switching transistor, an optocoupler, a metal-oxide-semiconductor field-effect transistor (MOSFET) switch, a transistor switching circuit, and a radio frequency switch.

[0043] Specifically, during the process of the control module 23 outputting the shutdown control signal to the DC auxiliary power supply 21, the shutdown control signal is first output to the isolation drive circuit 24. After isolation by the isolation drive circuit 24, it is input to the trigger circuit 25. The trigger circuit 25 responds to the shutdown control signal and outputs a first-level signal. The first-level signal is then wired-ANDed with the overcurrent protection signal and input to the overcurrent protection circuit 26. Taking a low-level shutdown control signal as an example, when the control module 23 outputs a low-level signal, the low-level signal also outputs a low-level signal after passing through the isolation drive circuit 24 and the trigger circuit 25. After receiving the low-level signal, the overcurrent protection circuit 26 will remain in the triggered state, keeping the DC auxiliary power supply 21 in an overcurrent protection state and preventing it from starting.

[0044] In some embodiments, when the inverter 20 is in the power-on state, if the overcurrent protection circuit 26 receives a real overcurrent feedback signal (e.g., detects that the output current exceeds a safety threshold), the overcurrent protection circuit 26 triggers a protection action in response to the overcurrent feedback signal, shutting down the DC auxiliary power supply to protect the DC auxiliary power supply 21 and downstream loads from overcurrent damage. In the power-on state, the output of the start-stop trigger circuit is in a high-impedance state, equivalent to being disconnected from the trigger terminal of the overcurrent protection circuit 26. Therefore, the overcurrent protection circuit 26 fully restores its original protection function, responding only to real overcurrent feedback signals without being interfered with by the start-stop trigger circuit.

[0045] Using the technical solution of this embodiment, the start / stop trigger circuit can control the DC auxiliary power supply to a shutdown state or a start state according to the level of the control signal output by the control module 23, without the need for additional complex circuits. Under the premise of low cost, it realizes the controllable start / stop of the DC auxiliary power supply and the compatibility and reuse of the original protection functions.

[0046] Based on the above power conversion system, this application provides a power conversion system startup method, such as... Figure 3 As shown, it includes steps S301-S304, wherein, Step S301: During the startup process of the inverter, the DC auxiliary power supply of the inverter is kept in the off state.

[0047] In some embodiments, the above steps S301-S304 are executed by the control module of the power conversion system. The following example shows the control module being located in the inverter.

[0048] In some embodiments, during the inverter's startup process, the inverter is in standby mode. At this time, the inverter's control module draws power from the grid, putting the control module into operation. Thus, after the power conversion system receives a startup command or meets the startup conditions, it can output a control signal through the control module to keep the DC auxiliary power supply in a shutdown state, preventing it from automatically starting and consuming energy in the bus capacitor during subsequent pre-charging.

[0049] In some embodiments, the inverter includes an overcurrent protection circuit connected to a DC auxiliary power supply. In this case, a first level signal can be sent to the overcurrent protection circuit to trigger the overcurrent protection circuit. The overcurrent protection circuit is controlled to respond to the first level signal so that it is in a triggered state and the DC auxiliary power supply is controlled to be in a shutdown state.

[0050] In some embodiments, the inverter includes a start-stop trigger circuit connected between the control module and the overcurrent protection circuit. Thus, during the start-up process of the inverter, a shutdown control signal is first generated by the control module and then sent to the start-stop trigger circuit; and the start-stop trigger circuit responds to the shutdown control signal, generates a first level signal, and sends the first level signal to the overcurrent protection circuit.

[0051] Taking a user-input start command as an example, after the control module receives the start command, it generates a shutdown control signal based on the start command. The shutdown control signal can be a low-level signal or a high-level signal. Then, it sends the shutdown control signal to the start / stop trigger circuit. After receiving the shutdown control signal, the start / stop trigger circuit generates a first-level signal and sends it to the overcurrent protection circuit. The overcurrent protection circuit receives and responds to the first-level signal, controlling the overcurrent protection circuit to be in the triggered state. This allows the DC auxiliary power supply to be controlled in the overcurrent protection state. When the DC auxiliary power supply is in the overcurrent protection state, it is forced to shut down and cannot start.

[0052] In some embodiments, the first level signal may be the same as or a different level signal from the power-off control signal; this application does not impose specific limitations.

[0053] In some embodiments, when the start / stop trigger circuit is in the off state, the overcurrent protection circuit can receive an overcurrent feedback signal and adjust the current state of the overcurrent protection circuit according to the overcurrent feedback signal.

[0054] In some embodiments, the overcurrent protection circuit of the DC auxiliary power supply is a built-in protection circuit. It is used to trigger a protection action when the output current or internal current exceeds a safety threshold during normal operation of the DC auxiliary power supply, locking the DC auxiliary power supply in a protected state to prevent damage to components due to overcurrent. During the inverter startup process, a first-level signal (e.g., a low-level signal) can be sent to the overcurrent protection circuit through the start-stop trigger circuit to forcibly trigger the overcurrent protection circuit, keeping the DC auxiliary power supply in a shutdown state. This forced trigger signal and the original overcurrent feedback signal of the overcurrent protection circuit jointly control the trigger terminal of the overcurrent protection circuit through "wired-AND logic." That is, the trigger terminal of the overcurrent protection circuit is simultaneously controlled by two signals: one is the actual overcurrent feedback signal, and the other is the forced trigger signal output by the start-stop trigger circuit.

[0055] In some embodiments, when the control module outputs a power-on control signal (e.g., a high-level signal), the start-stop trigger circuit is in an open state. This is equivalent to disconnecting from the trigger terminal of the overcurrent protection circuit, and it no longer outputs any forced trigger signal. At this time, the trigger terminal of the overcurrent protection circuit is only controlled by the actual overcurrent feedback signal. Furthermore, when the start-stop trigger circuit is in an open state (i.e., a high-impedance state), the overcurrent protection circuit receives an overcurrent feedback signal through its trigger terminal. This overcurrent feedback signal originates from the current detection circuit inside the DC auxiliary power supply (e.g., a signal generated by amplifying the voltage drop across the sampling resistor, or a detection signal output by a current transformer). This signal reflects the magnitude of the current output current or internal operating current of the DC auxiliary power supply.

[0056] Specifically, if the overcurrent feedback signal indicates that the current is below the preset safety threshold (i.e., the current is normal), the overcurrent protection circuit maintains its current non-triggered state, and the DC auxiliary power supply continues to operate normally, supplying power to the various functional units inside the inverter. If the overcurrent feedback signal indicates that the current exceeds the preset safety threshold (i.e., an overcurrent has occurred), the overcurrent protection circuit responds to the overcurrent feedback signal and switches from the non-triggered state to the triggered state. When the overcurrent protection circuit is in the triggered state, it latches the overcurrent fault state and outputs a protection action signal (e.g., pulling down the voltage) to stop the DC auxiliary power supply from operating, thereby protecting the DC auxiliary power supply and downstream loads from overcurrent damage.

[0057] Furthermore, if it is necessary to restore the operation of the DC auxiliary power supply after the overcurrent protection circuit is triggered due to a real overcurrent, a reset signal can be output by the control module (e.g., first outputting a low level and then a high level) to reset the overcurrent protection circuit from the latched state and allow it to re-enter the working state. This reset process can be executed automatically by the control module or manually triggered by maintenance personnel through a host computer or local operation interface.

[0058] In some embodiments, the overcurrent feedback signal is an analog voltage signal or a digital signal. When an analog voltage signal is used, the overcurrent protection circuit compares the analog voltage signal with a preset reference voltage through a comparator. If the analog voltage signal is higher than the reference voltage, it is determined to be an overcurrent. When a digital signal is used, the overcurrent protection circuit directly makes a judgment based on the logic level of the digital signal.

[0059] In some embodiments, the overcurrent feedback signal also includes a temperature feedback signal. That is, when the internal temperature of the DC auxiliary power supply exceeds a preset temperature threshold, the overcurrent protection circuit is also triggered, causing the DC auxiliary power supply to stop working, thereby achieving over-temperature protection. In this case, the overcurrent protection circuit is essentially an "overcurrent and over-temperature protection circuit," and the feedback signals it receives include both current feedback signals and temperature feedback signals. When either one exceeds the corresponding preset threshold, the protection action is triggered.

[0060] Although the above embodiments are illustrated using current overcurrent as an example, those skilled in the art should understand that the technical solutions of this application are also applicable to other types of fault protection such as overvoltage and overtemperature. It is only necessary to input the corresponding fault detection signal as a feedback signal to the protection circuit.

[0061] In this way, by connecting the start / stop trigger circuit and the overcurrent protection circuit via a wired-AND logic, the trigger terminal of the overcurrent protection circuit can receive both the forced trigger signal from the start / stop trigger circuit (for shutdown control) and the real overcurrent feedback signal (for fault protection). This allows the two signals to share the same trigger terminal without interfering with each other, eliminating the need for additional protection circuits or control logic for start / stop control. Controllable start / stop of the DC auxiliary power supply is achieved without increasing hardware costs.

[0062] In some embodiments, when controlling the DC auxiliary power supply to be in a shutdown state, the DC transmission equipment can be started and the soft-start switch closed before controlling the DC auxiliary power supply to be in a shutdown state.

[0063] In some embodiments, when controlling the DC auxiliary power supply to be in a shutdown state, the DC auxiliary power supply can also be controlled to be in a shutdown state before the DC transmission equipment is started and the soft start switch is closed.

[0064] In some embodiments, when controlling the DC auxiliary power supply to be in a powered-off state, the DC auxiliary power supply can also be controlled to be in a powered-off state before the DC transmission equipment is started.

[0065] In some embodiments, when controlling the DC auxiliary power supply to be in a shutdown state, the DC auxiliary power supply can also be controlled to be in a shutdown state during the inverter startup process, before the inverter meets the startup conditions.

[0066] Step S302: Control the soft start switch to close, and control the DC transmission equipment to charge the inverter's bus capacitor through the current-limiting resistor.

[0067] In some embodiments, in step S301, the control module sends a first closing command to the drive circuit of the soft-start switch before or after controlling the DC auxiliary power supply to remain in the off state. The drive circuit of the soft-start switch (e.g., a relay drive circuit or an IGBT drive circuit) responds to this first closing command and drives the main contacts of the soft-start switch to close. After the soft-start switch closes, the DC power output by the DC transmission device flows to the inverter through the branch containing the soft-start switch. Since the soft-start switch is connected in series with a current-limiting resistor, which is connected in series between the output terminal of the DC transmission device and the bus capacitor of the inverter, the current output by the DC transmission device first flows through the current-limiting resistor and then enters the bus capacitor.

[0068] Specifically, the current-limiting resistor has a preset resistance value, which is set according to actual needs. At the initial moment of the soft-start switch closing, the voltage across the bus capacitor is zero or close to zero. Furthermore, during the pre-charging process of the inverter's bus capacitor, the voltage across the bus capacitor gradually increases from the initial voltage.

[0069] In some embodiments, the soft-start switch can be a normally open switch, which remains open when not energized and only closes upon receiving a first closing command from the control module and energizing the circuit. In some embodiments, the soft-start switch can be a DC contactor. The current-limiting resistor can be any of a power resistor, a thermistor, etc.

[0070] In some embodiments, during the closing of the soft-start switch, the main switch is in the open state, and the DC power of the DC transmission equipment charges the bus capacitor only through the current-limiting resistor, without directly connecting the DC transmission equipment to the main power circuit of the inverter. This soft-start pre-charging method ensures that the bus capacitor gradually builds up voltage under low current conditions, creating safe conditions for the subsequent closing of the main switch.

[0071] Step S303: During the charging process of the inverter's bus capacitor, if the voltage difference across the main switch is detected to be less than a preset voltage threshold, the main switch is controlled to close.

[0072] In some embodiments, after the soft-start switch is closed, the control module continuously monitors the voltage difference across the main switch. The two ends of the main switch are connected to the output side of the DC transmission equipment (i.e., the input terminal of the soft-start switch) and the DC bus of the inverter (i.e., the positive terminal of the bus capacitor), respectively. Therefore, the voltage difference across the main switch is equal to the difference between the output voltage of the DC transmission equipment and the voltage across the bus capacitor.

[0073] Specifically, the control module can acquire the voltage difference across the main switch via a voltage detection circuit. In some embodiments, the voltage detection circuit includes a voltage divider resistor network and an operational amplifier connected across the main switch. As the pre-charging process continues, the voltage across the bus capacitor gradually increases, causing the voltage difference across the main switch to gradually decrease. When the control module detects that the voltage difference across the main switch is less than a preset voltage threshold, it determines that the pre-charging is complete.

[0074] In some embodiments, the preset voltage threshold can be set according to implementation requirements, wherein the preset voltage threshold can be determined based on the electrical parameters of the main switch. For example, the voltage threshold can be determined based on the maximum allowable closing voltage difference of the main switch. If the maximum allowable closing voltage difference of the main switch is 50V, the voltage threshold can be set to 30V to 40V to allow for a certain safety margin. In some embodiments, the voltage threshold can also be set comprehensively based on the capacitance value of the bus capacitor and the system's requirements for precharge time.

[0075] In some embodiments, after detecting that the voltage difference across the main switch is less than a preset voltage threshold, the control module sends a second closing command to the drive circuit of the main switch. In response to this second closing command, the drive circuit of the main switch drives the main contacts of the main switch to close. Furthermore, after the main switch closes, the DC transmission device and the DC bus of the inverter are directly connected through the branch where the main switch is located. The DC power output by the DC transmission device no longer passes through the current-limiting resistor but is directly transmitted to the DC bus of the inverter via the main switch, providing energy for the subsequent grid-connected operation of the inverter.

[0076] In some embodiments, at the instant the main switch is closed, since the voltage difference has been controlled within a preset voltage threshold, the closing inrush current is limited to the range allowed by the main switch, thereby reducing the probability of damage to the contacts of the main switch and the probability of current surge to the DC bus and bus capacitor.

[0077] In some embodiments, the main switch is a normally open contactor that remains open when not energized and closes only when a second closing command is received from the control module and energized.

[0078] In this way, by continuously monitoring the voltage difference across the main switch and controlling the main switch to close when the voltage difference is less than a preset threshold, the voltage difference across the main switch is ensured to be within a safe range at the moment of closure. This effectively avoids the problem of damage to the main switch contacts caused by the closing inrush current due to excessive voltage difference, and improves the service life and reliability of the main switch.

[0079] Step S304: After the main switch is closed, a start-up signal is sent to the DC auxiliary power supply to control the DC auxiliary power supply to start up. After the DC auxiliary power supply is started up, the inverter is controlled to perform the start-up operation.

[0080] In some embodiments, after the main switch is closed, a second level signal can be sent to the overcurrent protection circuit to deactivate the overcurrent protection circuit. The second level signal is a power-on signal, and the first level signal is different from the second level signal.

[0081] Specifically, a power-on control signal can be generated by the control module and sent to the start / stop trigger circuit; then, the start / stop trigger circuit responds to the power-on control signal, generates a second-level signal, and sends the second-level signal to the overcurrent protection circuit.

[0082] In some embodiments, if the first level signal is a low level signal, then the second level signal is a high level signal; if the first level signal is a high level signal, then the second level signal is a low level signal.

[0083] like Figure 4 As shown, the first startup logic of the inverter includes steps S401-S407, wherein: first, step S401 is executed to start the DC transmission equipment; then step S402 is executed to close the soft start switch for pre-charging; after the soft start switch is closed, step S403 is executed to shut down the DC power supply board; and after the DC power supply board is shut down, step S404 is executed to detect whether the voltage difference across the main switch is less than the voltage threshold; if the voltage difference is not less than the voltage threshold, step S404 is continued; if the voltage difference is less than the voltage threshold, step S405 is executed to close the main switch; after the main switch is closed, step S406 is executed to start the DC power supply board; and after step S406 is executed, step S407 is executed to start the inverter.

[0084] Since the DC power board is not yet powered off during the initial stage of the soft-start switch closure, the bus capacitors need to charge themselves and supply power to the DC power board simultaneously during the initial pre-charge phase. Therefore, the pre-charge speed is relatively slow, and the startup time is relatively long. However, on the other hand, the brief operation of the DC power board during the initial pre-charge phase allows some functional units inside the inverter to receive power in advance. This is beneficial for preliminary monitoring and diagnosis of the system status during the pre-charge phase, making the first startup logic applicable to scenarios where startup speed requirements are not high but monitoring of the pre-charge process is necessary.

[0085] like Figure 5As shown, the second startup logic of the inverter includes steps S501-S507, wherein: first, step S501 is executed to start the DC transmission equipment; then step S502 is executed to shut down the DC power supply board; after the DC power supply board is shut down, step S503 is executed to close the soft-start switch for pre-charging; and after the soft-start switch is closed, step S504 is executed to detect whether the voltage difference across the main switch is less than the voltage threshold; if the voltage difference is not less than the voltage threshold, step S504 is continued; if the voltage difference is less than the voltage threshold, step S505 is executed to close the main switch; after the main switch is closed, step S506 is executed to start the DC power supply board; and after step S506 is executed, step S507 is executed to start the inverter.

[0086] In the second startup logic described above, the DC power board's shutdown action is performed after the combiner box is started but before the soft-start switch is closed. Compared to the first startup logic, the second startup logic completes the DC power board's shutdown control before the soft-start switch closes, ensuring that the energy stored in the bus capacitors during the entire pre-charging process is not consumed by the DC power board, allowing the bus voltage to rise to the target value more quickly. By immediately cutting off the DC power board's startup possibility after the combiner box is started, it ensures that all bus energy during the pre-charging stage is used to charge the bus capacitors, effectively shortening the pre-charging time and improving startup efficiency. This makes the second startup logic suitable for scenarios with certain startup speed requirements and where there is no need to power the inverter's internal functional units during the pre-charging stage.

[0087] like Figure 6 As shown, the third startup logic of the inverter includes steps S601-S607. First, step S601 is executed to shut down the DC power supply board; then step S602 is executed to start the DC transmission equipment; after the combiner box is started, step S603 is executed to close the soft-start switch for pre-charging; and after the soft-start switch is closed, step S604 is executed to check whether the voltage difference across the main switch is less than the voltage threshold; if the voltage difference is not less than the voltage threshold, step S604 is continued; if the voltage difference is less than the voltage threshold, step S605 is executed to close the main switch; after the main switch is closed, step S606 is executed to start the DC power supply board; and after step S606 is executed, step S607 is executed to start the inverter.

[0088] In the third startup logic described above, the shutdown action of the DC power board is executed before the combiner box is started. This ensures that reliable control of the DC power board is established in the earliest stage of inverter startup, allowing the bus voltage to be established at the fastest speed, with the shortest pre-charge time and the highest startup efficiency. This makes the third startup logic suitable for scenarios with high requirements for startup speed (such as situations requiring rapid power restoration).

[0089] like Figure 7As shown, the fourth startup logic of the inverter includes steps S701-S704. First, step S701 is executed to shut down the DC power supply board; then step S702 is executed to determine whether the inverter startup conditions are met; if the inverter startup conditions are not met, step S702 is executed continuously; if the inverter startup conditions are met, step S703 is executed to start the DC power supply board; and after executing step S703, step S704 is executed to start the inverter.

[0090] In the fourth startup logic described above, the DC power supply board remains in a shutdown state throughout the entire inverter startup process until the inverter meets the startup conditions. When the inverter already meets the startup conditions (e.g., the DC bus has voltage, the power grid is normal, etc.), there is no need to perform a pre-charging process. The DC power supply board can start directly and run under load, enabling the fastest startup of the inverter. This allows the fourth startup logic to be applicable to scenarios where the inverter quickly recovers from standby or hibernation to the operating state.

[0091] Thus, by using the four startup logics mentioned above to correspond to different startup speeds, different startup logics can be selected according to actual needs to improve the startup flexibility of the inverter.

[0092] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0093] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Although this application has disclosed preferred embodiments as above, it is not intended to limit this application. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the technical solution of this application. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A power conversion system, characterized in that, This includes DC transmission equipment, inverters, and control modules; among which, The output side of the DC transmission device is connected to the DC side of the inverter via a main switch, and a soft-start circuit is connected in parallel across the two ends of the main switch; the soft-start circuit includes a soft-start switch and a current-limiting resistor connected in series. The control module is configured as follows: During the startup process of the inverter, the DC auxiliary power supply of the inverter is kept in the off state. The soft-start switch is closed to control the DC transmission device to charge the inverter's bus capacitor through the current-limiting resistor. During the charging process of the inverter's bus capacitor, if the voltage difference across the main switch is detected to be less than a preset voltage threshold, the main switch is controlled to close. After the main switch is closed, a power-on signal is sent to the DC auxiliary power supply to control the DC auxiliary power supply to start up. After the DC auxiliary power supply is started up, the inverter is controlled to perform a startup operation.

2. The power conversion system according to claim 1, characterized in that, The control module is configured as follows: After the DC transmission equipment is started and the soft-start switch is closed, the DC auxiliary power supply is controlled to be in the off state; or, Before the DC transmission equipment is started and the soft start switch is closed, the DC auxiliary power supply is controlled to be in the shutdown state. or, Before the DC transmission equipment is started, the DC auxiliary power supply is controlled to be in the off state; or, During the startup process of the inverter, and before the inverter meets the startup conditions, the DC auxiliary power supply is controlled to be in the shutdown state.

3. The power conversion system according to claim 1, characterized in that, The inverter includes an overcurrent protection circuit connected to the DC auxiliary power supply, and the control module is configured to: A first level signal is sent to the overcurrent protection circuit, and the first level signal is used to trigger the overcurrent protection circuit; The overcurrent protection circuit is used to respond to the first level signal and control the overcurrent protection circuit to be in a triggered state so that the DC auxiliary power supply is in the shutdown state.

4. The power conversion system according to claim 3, characterized in that, The inverter includes a start / stop trigger circuit connected to the control module, and the control module is configured to: Generate a shutdown control signal and send the shutdown control signal to the start / stop trigger circuit; The start / stop trigger circuit is used to respond to the shutdown control signal, generate the first level signal, and send the first level signal to the overcurrent protection circuit.

5. The power conversion system according to claim 4, characterized in that, The control module is configured as follows: Send a second-level signal to the overcurrent protection circuit; The overcurrent protection circuit is used to release the trigger state in response to the second level signal, wherein the second level signal is the power-on signal, and the first level signal is different from the second level signal.

6. The power conversion system according to claim 5, characterized in that, The control module is configured as follows: Generate a power-on control signal and send the power-on control signal to the start / stop trigger circuit; The start / stop trigger circuit is used to respond to the power-on control signal, generate the second level signal, and send the second level signal to the overcurrent protection circuit.

7. The power conversion system according to claim 6, characterized in that, The start / stop trigger circuit includes an isolation drive circuit and a trigger circuit. The input terminal of the isolation drive circuit is connected to the control module, the output terminal of the isolation drive circuit is connected to the input terminal of the trigger circuit, and the output terminal of the trigger circuit is connected to the overcurrent protection circuit.

8. The power conversion system according to claim 5, characterized in that, The first level signal is a low level signal, and the second level signal is a high level signal.

9. The power conversion system according to claim 5, characterized in that, The overcurrent protection circuit is used to receive an overcurrent feedback signal when the start / stop trigger circuit is in the off state, and to adjust the current state of the overcurrent protection circuit according to the overcurrent feedback signal.

10. A startup method for a power conversion system, characterized in that, The power conversion system includes a DC transmission device and an inverter. The output side of the DC transmission device is connected to the DC side of the inverter via a main switch. A soft-start circuit is connected in parallel across the two ends of the main switch. The soft-start circuit includes a soft-start switch and a current-limiting resistor connected in series. The method includes: During the startup process of the inverter, the DC auxiliary power supply of the inverter is kept in the off state. The soft-start switch is closed to control the DC transmission device to charge the inverter's bus capacitor through the current-limiting resistor. During the charging process of the inverter's bus capacitor, if the voltage difference across the main switch is detected to be less than a preset voltage threshold, the main switch is controlled to close. After the main switch is closed, a power-on signal is sent to the DC auxiliary power supply to control the DC auxiliary power supply to start up. After the DC auxiliary power supply is started up, the inverter is controlled to perform a startup operation.

11. The power conversion system startup method according to claim 10, characterized in that, During the startup process of the inverter, controlling the DC auxiliary power supply of the inverter to be in a shutdown state includes: After the DC transmission equipment is started and the soft-start switch is closed, the DC auxiliary power supply is controlled to be in the off state; or, Before the DC transmission equipment is started and the soft-start switch is closed, the DC auxiliary power supply is controlled to be in the off state; or, Before the DC transmission equipment is started, the DC auxiliary power supply is controlled to be in the off state; or, During the startup process of the inverter, and before the inverter meets the startup conditions, the DC auxiliary power supply is controlled to be in the shutdown state.

12. The power conversion system startup method according to claim 10, characterized in that, The inverter includes an overcurrent protection circuit connected to the DC auxiliary power supply. The control of the DC auxiliary power supply to be in a powered-off state includes: A first level signal is sent to the overcurrent protection circuit, and the first level signal is used to trigger the overcurrent protection circuit; The overcurrent protection circuit is controlled to respond to the first level signal, so that the overcurrent protection circuit is in the triggered state, and the DC auxiliary power supply is controlled to be in the shutdown state.

13. The power conversion system startup method according to claim 12, characterized in that, The inverter includes a control module and a start / stop trigger circuit connected to the control module. Sending a start-up signal to the DC auxiliary power supply includes: The control module generates a shutdown control signal and sends the shutdown control signal to the start / stop trigger circuit. The start / stop trigger circuit responds to the shutdown control signal, generates the first level signal, and sends the first level signal to the overcurrent protection circuit.

14. The power conversion system startup method according to claim 13, characterized in that, Sending a power-on signal to the DC auxiliary power supply includes: A second level signal is sent to the overcurrent protection circuit to deactivate the trigger state of the overcurrent protection circuit, wherein the second level signal is the power-on signal, and the first level signal is different from the second level signal.

15. The power conversion system startup method according to claim 14, characterized in that, Sending a second-level signal to the overcurrent protection circuit includes: The control module generates a power-on control signal and sends the power-on control signal to the start / stop trigger circuit. The start / stop trigger circuit responds to the power-on control signal, generates the second level signal, and sends the second level signal to the overcurrent protection circuit.

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