Inverter, energy storage system and soft start method

Abstract

The present application relates to the field of power electronics technology, and in particular to an inverter, an energy storage system, and a soft start method. The inverter includes an inverter circuit, a pre-charging circuit, and a control circuit. The inverter circuit includes a bus capacitor, a plurality of inverter bridge arms, and a plurality of first relays. The inverter bridge arms are respectively connected to an AC power grid through the first relays. The pre-charging circuit is connected between the AC power grid and the bus capacitor. When the voltage of the bus capacitor is less than a target threshold, the pre-charging circuit is turned on to allow the AC power grid to charge the bus capacitor. When the voltage of the bus capacitor is greater than or equal to the target threshold, the pre-charging circuit is disconnected and the first relay is closed. The bus capacitor is powered by the AC power grid to complete the soft start of the bus capacitor and wake up the DC power supply. The present application completes the charging of the DC bus capacitor of the inverter by the AC power grid through the pre-charging circuit, simplifies the circuit structure, reduces the circuit cost, and improves the reliability of the DC bus soft start.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to an inverter, an energy storage system, and a soft start method. Background Art

[0002] In an energy storage inverter system, the inverter is typically connected between a DC power source and an AC grid, responsible for bidirectional power transmission. In certain application scenarios, the DC power source may stop supplying power to the power converter, for example, if the energy storage battery is depleted and unable to provide sufficient power. In this case, when the system reconnects to the grid, the DC side of the inverter needs to be charged from the grid, performing a DC bus soft-start operation to protect the inverter's internal components from damage caused by excessive current surges.

[0003] In order to achieve soft starting of the inverter DC bus, existing energy storage inverter systems generally require an independent auxiliary power supply to be configured at each main power supply port, and an additional main circuit soft starting circuit is added. This results in a complex overall circuit structure of the system, reduced reliability, and increased circuit layout costs. Summary of the Invention

[0004] In view of this, the embodiments of the present application provide an inverter, an energy storage system and a soft start method, which aim to solve the technical problem that an additional soft start circuit needs to be set up when soft-starting the DC bus in the inverter system, resulting in a complex circuit structure and increased costs. The inverter provided in the embodiments of the present application can simplify the circuit structure, reduce circuit costs, and improve the reliability of the DC bus soft start.

[0005] A first aspect of an embodiment of the present application provides an inverter, which is arranged between a DC power supply and an AC power grid. The inverter includes an inverter circuit, a pre-charging circuit and a control circuit. The inverter circuit includes a bus capacitor, a plurality of inverter bridge arms and a plurality of first relays, and the inverter bridge arms are respectively connected to the AC power grid through the first relays; the pre-charging circuit is connected between the AC power grid and the bus capacitor; the control circuit is used to: when the voltage of the bus capacitor is less than a target threshold, turn on the pre-charging circuit so that the AC power grid charges the bus capacitor through the pre-charging circuit; when the voltage of the bus capacitor is greater than or equal to the target threshold, disconnect the pre-charging circuit and close the first relay to supply power to the bus capacitor through the AC power grid to complete the soft start of the bus capacitor and wake up the DC power supply.

[0006] In one embodiment, the inverter circuit further includes a balancing circuit, which is connected to the bus capacitor, and the bus capacitor includes a first bus capacitor and a second bus capacitor. The control circuit is further used to: when the voltage of the first bus capacitor is less than a preset threshold, turn on the pre-charging circuit so that the AC power grid charges the first bus capacitor through the pre-charging circuit; when the voltage of the first bus capacitor is greater than or equal to the preset threshold, drive the balancing circuit to charge the second bus capacitor; when the sum of the voltages of the first bus capacitor and the second bus capacitor is greater than or equal to the target threshold, disconnect the pre-charging circuit and close the first relay.

[0007] In one embodiment, the balancing circuit includes a balancing bridge arm and a balancing inductor. The first bus capacitor and the second bus capacitor are connected in series and then connected in parallel with the inverter bridge arm. The balancing bridge arm is connected in parallel with the inverter bridge arm. One end of the balancing inductor is connected to the midpoint of the balancing bridge arm, and the other end of the balancing inductor is connected to the series node of the first bus capacitor and the second bus capacitor. One end of the first bus capacitor is connected to the ground point. In one embodiment, the preset threshold Calculated by the following formula: When the AC power grid is a split-phase power grid, the target threshold is calculated by the following formula: When the AC power grid is a three-phase power grid, the target threshold is calculated by the following formula: ;in, is the phase voltage of the AC grid.

[0008] In one embodiment, the pre-charging circuit includes a second relay and a current-limiting resistor connected in series; the pre-charging circuit is connected between a non-zero phase line of the AC power grid and the grounding point, or multiple pre-charging circuits are respectively connected between the non-zero phase line of the AC power grid and the grounding point.

[0009] In one embodiment, the pre-charging circuit is further connected in series with a protection diode, the anode of which is connected to the grounding point; and the pre-charging circuit is provided with a plurality of second relays connected in series with each other.

[0010] In one embodiment, the inverter further includes an auxiliary power supply circuit and a DC conversion circuit; the auxiliary power supply is connected to the AC power grid and is used to draw power from the AC power grid to provide system power for the soft start of the bus capacitor; the DC conversion circuit is arranged between the DC power supply and the inverter circuit, and is used to convert the DC voltage output by the inverter circuit into a wake-up voltage and then provide it to the DC power supply.

[0011] In one embodiment, a plurality of the inverter bridge arms are used to form an inverter topology, and the inverter topology is one of an H4-type two-level topology, a T-type three-level topology, and an I-type three-level topology.

[0012] A second aspect of the embodiments of the present application provides an energy storage system, including the inverter provided by the first aspect of the embodiments of the present application, wherein the DC power supply includes an energy storage battery.

[0013] A third aspect of an embodiment of the present application provides a soft start method, which is applicable to an inverter, wherein the inverter is arranged between a DC power supply and an AC power grid, and the inverter includes an inverter circuit, a pre-charging circuit and a control circuit. The inverter circuit includes a bus capacitor, a plurality of inverter bridge arms and a plurality of first relays, and the inverter bridge arms are respectively connected to the AC power grid through the first relays; the pre-charging circuit is connected between the AC power grid and the bus capacitor, and the soft start method includes: when the voltage of the bus capacitor is less than a target threshold, turning on the pre-charging circuit so that the AC power grid charges the bus capacitor through the pre-charging circuit; when the voltage of the bus capacitor is greater than or equal to the target threshold, disconnecting the pre-charging circuit and closing the first relay to supply power to the bus capacitor through the AC power grid, so as to complete the soft start of the bus capacitor and wake up the DC power supply.

[0014] The beneficial effect of the embodiment of the present application is that: only a pre-charging circuit needs to be set between the AC power grid and the bus capacitor of the inverter. When the DC power supply needs to be awakened, when the voltage of the bus capacitor is less than the target threshold, the pre-charging circuit is turned on so that the AC power grid charges the bus capacitor. When the voltage of the bus capacitor is greater than or equal to the target threshold, the pre-charging circuit is disconnected and the first relay is closed. At this time, the pre-charging circuit is disconnected, and the AC power grid continuously supplies power to the bus capacitor to complete the soft start of the bus capacitor, thereby realizing the awakening of the DC power supply, greatly simplifying the circuit structure, realizing the soft start of the inverter bus capacitor through the control circuit, and improving the stability and safety of the inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0016] Figure 1 A schematic diagram of the principle of an inverter provided in one embodiment of the present application;

[0017] Figure 2 A circuit diagram of an inverter provided in one embodiment of the present application;

[0018] Figure 3 A circuit schematic diagram of an inverter provided in another embodiment of the present application;

[0019] Figure 4 A circuit schematic diagram of an inverter applicable to a three-phase power grid provided in one embodiment of the present application;

[0020] Figure 5 A flowchart of a soft start method provided in one embodiment of the present application;

[0021] Figure 6 A flowchart of a soft start method provided in another embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0023] It should be noted that when an element is referred to as being “fixed on” or “disposed on” another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or indirectly connected to the other element.

[0024] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0025] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0026] See also Figure 1As shown, an embodiment of the present application provides an inverter, which is disposed between a DC power supply 300 and an AC power grid 400. One end of the inverter can be used to connect to the DC power supply 300, and the other end of the inverter can be used to connect to the AC power grid 400. In some embodiments, the inverter can convert the DC power provided by the DC power supply 300 into AC power and transmit it to the AC power grid 400. For example, the DC power supply 300 includes a storage battery, and the AC power grid 400 includes a power grid and an AC load. The inverter is used to convert the power stored in the energy storage battery into AC power and transmit it to the power grid or the AC load.

[0027] In some scenarios, when the AC grid 400 has sufficient power, the inverter can be used to store the power of the AC grid 400 in the energy storage battery. When the power of the AC grid 400 is insufficient or the power supply system is in an off-grid working state, the inverter can transmit the power of the DC power supply 300 to the AC grid or the local load. In some scenarios, when the power of the DC power supply 300 is exhausted, when the power supply system is reconnected to the grid or the DC end of the inverter is charged by the AC grid 400 to forcibly wake up the DC power supply 300, a soft start is required to prevent the components in the inverter from being damaged due to overcurrent shock.

[0028] See also Figure 1 The inverter provided in the embodiment of the present application includes an inverter circuit 100, a pre-charging circuit 200 and a control circuit (not shown in the figure). The inverter circuit 100 includes a bus capacitor, a plurality of inverter bridge arms and a plurality of first relays. The inverter bridge arms are respectively connected to the AC power grid 400 through corresponding first relays. Specifically, the bus capacitor includes a first bus capacitor C1 and a second bus capacitor C2. The first bus capacitor C1 is a negative half-DC bus capacitor, and the second bus capacitor C2 is a positive half-DC bus capacitor. The number of inverter bridge arms can be two or three. The midpoint of each inverter bridge arm is connected to the AC power grid 400 through a first relay. Taking the embodiment given in the present application as an example, the inverter provided in the present application can be applicable to split-phase power grids and three-phase power grids.

[0029] The pre-charging circuit 200 is connected between the AC power grid 400 and the bus capacitor. The control circuit is used to turn on the pre-charging circuit 200 when the voltage of the bus capacitor is less than the target threshold so that the AC power grid 400 charges the bus capacitor through the pre-charging circuit 200. When the voltage of the bus capacitor is greater than or equal to the target threshold, the pre-charging circuit 200 is disconnected and the first relay is closed to supply power to the bus capacitor through the AC power grid 400 to complete the soft start of the bus capacitor and wake up the DC power supply 300.

[0030] The inverter provided in the embodiment of the present application only needs to set up a pre-charging circuit 200 between the AC power grid 400 and the bus capacitor of the inverter. When the DC power supply 300 needs to be awakened, when the voltage of the bus capacitor is less than the target threshold, the pre-charging circuit 200 is turned on so that the AC power grid 400 pre-charges the bus capacitor. When the voltage of the bus capacitor is greater than or equal to the target threshold, the pre-charging circuit 200 is disconnected and the first relay is closed. At this time, the pre-charging circuit 200 is disconnected, and the AC power grid 400 continuously supplies power to the bus capacitor to complete the soft start of the bus capacitor, thereby realizing the awakening of the DC power supply 300. This greatly simplifies the circuit structure, realizes the soft start of the inverter bus capacitor through the control circuit, and improves the stability and safety of the inverter.

[0031] In one embodiment, see Figure 1 and Figure 2 As shown, the inverter circuit 100 further includes a balancing circuit 110, which is connected to the bus capacitors. The bus capacitors include a first bus capacitor C1, i.e., a negative half-DC bus capacitor, and a second bus capacitor C2, i.e., a positive half-DC bus capacitor. The control circuit is further configured to, when the voltage of the first bus capacitor C1 is less than a preset threshold, conduct the pre-charging circuit 200 so that the AC power grid 400 charges the first bus capacitor C1 through the pre-charging circuit 200; when the voltage of the first bus capacitor C1 is greater than or equal to the preset threshold, drive the balancing circuit 110 to charge the second bus capacitor C2; and when the sum of the voltages across the first bus capacitor C1 and the second bus capacitor C2 is greater than or equal to a target threshold, disconnect the pre-charging circuit 200 and close the first relay. At this time, the voltage across the bus capacitors is continuously maintained by the AC power grid 400, thereby completing the soft start. In existing solutions, it is generally necessary to set up multiple pre-charging circuits 200. This application only needs to set up a single pre-charging circuit 200. Through the control strategy of the control circuit, the first bus capacitor C1 is first charged through the pre-charging circuit 200, and then the second bus capacitor C2 is charged through the balancing circuit 110, saving the number of circuit components. By reusing the soft start pre-charging function of the balancing circuit 110, redundant bus capacitor pre-charging circuits are avoided and the circuit structure is simplified.

[0032] In one embodiment, see Figure 2 Each inverter bridge arm includes two switching tubes. Taking the AC power grid 400 as a split-phase power grid as an example, the inverter circuit 100 includes two inverter bridge arms, and the midpoints of the two inverter bridge arms are respectively connected to the first phase line L1 and the second phase line L2 of the power grid through a first relay.

[0033] In one embodiment, see Figure 1 and Figure 2As shown, the balancing circuit 110 includes a balancing bridge arm and a balancing inductor L30. The balancing bridge arm is composed of switching tubes Q5 and Q6. The first bus capacitor C1 and the second bus capacitor C2 are connected in series and then in parallel with the inverter bridge arm. The balancing bridge arm and the inverter bridge arm are connected in parallel. One end of the balancing inductor L30 is connected to the midpoint of the balancing bridge arm, and the other end of the balancing inductor L30 is connected to the series node of the first bus capacitor C1 and the second bus capacitor C2. One end of the first bus capacitor C1 is connected to ground. During the soft start phase, the balancing inductor L30 can transfer energy to charge the second bus capacitor C2 and is used for capacitor voltage balancing after the soft start is completed.

[0034] In one embodiment, see Figure 2 Each inverter bridge arm includes two switching tubes. Taking the AC power grid 400 as a split-phase power grid as an example, the split-phase power grid includes a first phase line L1, a second phase line L2, and a neutral line N. The inverter circuit 100 includes two inverter bridge arms. The midpoints of the two inverter bridge arms are respectively connected to the first phase line L1 and the second phase line L2 of the power grid via a first relay. The first relay includes relay S1, relay S2, and relay S3. The series node of the first bus capacitor C1 and the second bus capacitor C2 is connected to the neutral line N via relay S2. In some embodiments, please refer to Figure 2 The inverter circuit 100 also includes a filter circuit 120. Taking the AC power grid 400 as a split-phase power grid as an example, the inverter circuit 100 includes a filter capacitor C3, a filter capacitor C4, a filter inductor L10, and a filter inductor L20. Setting the filter circuit 120 between the inverter circuit 100 and the AC power grid 400 is a conventional setting and will not be repeated here.

[0035] In one embodiment, see Figure 4 Taking the AC power grid 400 as a three-phase four-wire power grid as an example, the inverter circuit 100 includes three inverter bridge arms, and the midpoints of the three inverter bridge arms are respectively connected to the first phase line L1, the second phase line L2 and the third phase line L3 of the power grid through a first relay. The first relay includes relay S1, relay S2, relay S3 and relay S5. The series node of the first bus capacitor C1 and the second bus capacitor C2 is connected to the neutral line N through relay S2. The inverter circuit 100 includes filter capacitors C3, filter capacitors C4, filter capacitors C5 and filter inductors L10, filter inductors L20 and filter inductors L40. Arranging the filter circuit 120 between the inverter circuit 100 and the AC power grid 400 is a conventional setting and will not be repeated here.

[0036] In one embodiment, see Figures 1 to 4 , the preset threshold value of the first bus capacitor C1 charging Calculated by the following formula: , when the AC grid 400 is a split-phase grid, refer to Figure 2 and Figure 3 , the target threshold value of the sum of the voltages of the first bus capacitor C1 and the second bus capacitor C2 is calculated by the following formula: , when the AC power grid is a three-phase power grid, refer to Figure 4 , the target threshold is calculated by the following formula: , where is the phase voltage of the AC grid. It can be understood that the preset threshold value represented by the above calculation formula is , target threshold The calculations are all calculated values ​​under ideal conditions. The above formula only represents the calculation method and does not limit the specific parameter values. In a specific embodiment, The value is 1.414, The value is 1.732.

[0037] In one embodiment, see Figure 2 、 Figure 3 and Figure 4 The pre-charging circuit 200 includes a second relay S4 and a current-limiting resistor R1 connected in series. The pre-charging circuit 200 is connected between a non-zero phase line of the AC power grid 400 and a grounding point, i.e., the ground terminal of the first bus capacitor C1. In some embodiments, multiple pre-charging circuits 200 may be provided, each of which is connected between each non-zero phase line of the AC power grid 400 and a grounding point. The second relay S4 is a normally open relay, and the current-limiting resistor R1 is used to provide current limiting protection when the second relay S4 is closed.

[0038] In one embodiment, see Figure 2 、 Figure 3 and Figure 4 Furthermore, the pre-charging circuit 200 is further connected in series with a protection diode D1, the anode of which is connected to the ground point. Furthermore, the pre-charging circuit 200 is provided with multiple second relays S4 connected in series. By providing multiple second relays S4, electrical isolation requirements can be met and electrical safety can be improved.

[0039] In one embodiment, see Figure 3 The inverter provided in the embodiment of the present application further includes an auxiliary power supply circuit 500 and a DC conversion circuit 600. The auxiliary power supply circuit 500 is connected to the AC power grid 400 and is used to draw power from the AC power grid 400 to provide the system power VCC for the soft start of the bus capacitor. The power drawn from the AC power grid 400 is rectified and then output as a DC regulated power supply as the system power VCC. The DC conversion circuit 600 is provided between the DC power supply 300 and the inverter circuit 100 and is used to convert the DC voltage output by the inverter circuit 100 into a wake-up voltage that matches the DC power supply 300 and then provide it to the DC power supply 300. In some embodiments, please refer to Figure 3, the auxiliary power supply circuit 500 includes four rectifier diodes D2 , D3 , D4 and D5 and resistors R2 and R3 .

[0040] In one embodiment, the inverter bridge arms of the inverter circuit 100 are used to form an inverter topology of an inverter, and the inverter topology is one of an H4 two-level topology, a T-type three-level topology, and an I-type three-level topology.

[0041] In order to better illustrate the working principle of the embodiment of the present application, Figures 1 to 4 The soft start process of the inverter in the embodiment of the present application is described. Taking the AC grid 400 as a split-phase grid as an example, refer to Figure 2 and Figure 3 During the negative half cycle of the second phase line L2 of the split-phase grid, the control circuit closes relay S2 and the second relay S4. It can be understood that in order to charge the first bus capacitor C1, relay S2 (neutral line relay) needs to be closed to form a loop. At this time, relay S1 and relay S3 (non-neutral line relay) are in the disconnected state, and the split-phase grid continues to charge the first bus capacitor C1. Assuming that the voltage of the first bus capacitor C1 after pre-charge is stable is , ignoring the diode voltage drop and all capacitance losses in the circuit, the preset threshold of the first bus capacitor C1 is , The control circuit detects the input voltage of the power grid and compares the calculated result with the voltage of the first bus capacitor C1. When it is greater than or equal to the preset threshold, When the voltage of the first bus capacitor C1 and the second bus capacitor C2 is greater than or equal to the target threshold, the control circuit drives the balancing circuit 110 to boost and charge the second bus capacitor C2. The boost circuit composed of the switch tube Q5, the switch tube Q6 and the balancing inductor L30 is intermittently driven to charge the second bus capacitor C2. When the target threshold , disconnect the second relay S4 of the pre-charging circuit 200 and close relay S1 and relay S2. At this time, the bus capacitor is powered by the split-phase grid to complete the soft start of the bus capacitor and wake up the DC power supply 300, thereby achieving the soft start purpose.

[0042] Take the AC grid 400 as a three-phase grid as an example, please refer to Figure 4 , during the negative half cycle of the third phase line L3 of the three-phase grid, the control circuit closes relay S2 and the second relay S4. It can be understood that in order to charge the first bus capacitor C1, it is necessary to close relay S2 (neutral line relay) to form a loop. At this time, relays S1, S3 and S5 (non-neutral line relays) are in the disconnected state, and the third phase line L3 of the three-phase grid continues to charge the first bus capacitor C1. Assuming that the voltage of the first bus capacitor C1 after pre-charge is stable is , ignoring the diode voltage drop and all capacitance losses in the circuit, the preset threshold of the first bus capacitor C1 is , The control circuit detects the input voltage of the power grid and compares the calculated result with the voltage of the first bus capacitor C1. When it is greater than or equal to the preset threshold, When the voltage of the first bus capacitor C1 and the second bus capacitor C2 is greater than or equal to the target threshold, the control circuit drives the balancing circuit 110 to boost and charge the second bus capacitor C2. The boost circuit composed of the switch tube Q5, the switch tube Q6 and the balancing inductor L30 is intermittently driven to charge the second bus capacitor C2. When the target threshold , disconnect the second relay S4 of the pre-charging circuit 200 and close relay S1, relay S2 and relay S3. At this time, the bus capacitor is powered by the three-phase power grid to complete the soft start of the bus capacitor and wake up the DC power supply 300, thereby achieving the soft start purpose.

[0043] The second aspect of the embodiment of the present application provides an energy storage system, including the inverter provided by the first aspect of the embodiment of the present application, wherein the DC power supply is an energy storage battery. Figures 1 to 4 See Figure 5 In a third aspect, an embodiment of the present application provides a soft start method. The soft start method is applicable to an inverter. The inverter includes an inverter circuit 100, a pre-charging circuit 200, and a control circuit. The inverter circuit 100 includes a bus capacitor, a plurality of inverter bridge arms, and a plurality of first relays. The inverter bridge arms are respectively connected to an AC power grid 400 via the first relays. The pre-charging circuit 200 is connected between the AC power grid 400 and the bus capacitor. The soft start method includes the following steps:

[0044] S100 : When the voltage of the bus capacitor is less than a target threshold, the pre-charging circuit is turned on to allow the AC power grid to charge the bus capacitor through the pre-charging circuit.

[0045] S200. When the voltage of the bus capacitor is greater than or equal to the target threshold, the pre-charging circuit is disconnected and the first relay is closed to supply power to the bus capacitor through the AC power grid to complete the soft start of the bus capacitor and wake up the DC power supply.

[0046] In one embodiment, please combine Figures 1 to 4 See Figure 6 The inverter circuit 100 further includes a balancing circuit 110, the balancing circuit 110 is connected to a bus capacitor, the bus capacitor includes a first bus capacitor C1 and a second bus capacitor C2, and the soft start method includes the following steps:

[0047] S110 : When the voltage of the first bus capacitor is less than a preset threshold, turn on the pre-charging circuit so that the AC power grid charges the first bus capacitor through the pre-charging circuit.

[0048] S120 : When the voltage of the first bus capacitor is greater than or equal to a preset threshold, drive the balancing circuit to charge the second bus capacitor.

[0049] S130: When the sum of the voltages of the first bus capacitor and the second bus capacitor is greater than or equal to a target threshold, disconnect the pre-charging circuit and close the first relay.

[0050] The inverter provided in the embodiment of the present application only needs to set up a pre-charging circuit 200 between the AC power grid 400 and the bus capacitor of the inverter. When the DC power supply 300 needs to be awakened, when the voltage of the bus capacitor is less than the target threshold, the pre-charging circuit 200 is turned on so that the AC power grid 400 pre-charges the bus capacitor. When the voltage of the bus capacitor is greater than or equal to the target threshold, the pre-charging circuit 200 is disconnected and the first relay is closed. At this time, the pre-charging circuit 200 is disconnected, and the AC power grid 400 continuously supplies power to the bus capacitor to complete the soft start of the bus capacitor, thereby realizing the awakening of the DC power supply 300. This greatly simplifies the circuit structure, realizes the soft start of the inverter bus capacitor through the control circuit, and improves the stability and safety of the inverter.

[0051] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. An inverter, which is arranged between a DC power supply and an AC power grid, characterized in that: The inverter includes an inverter circuit, a pre-charging circuit, and a control circuit. The inverter circuit includes a bus capacitor, a plurality of inverter bridge arms, and a plurality of first relays. The inverter bridge arms are respectively connected to the AC power grid via the first relays. The pre-charging circuit is connected between the AC power grid and the bus capacitor. The control circuit is configured to: When the voltage of the bus capacitor is less than a target threshold, turning on the pre-charging circuit so that the AC grid charges the bus capacitor through the pre-charging circuit; When the voltage of the bus capacitor is greater than or equal to a target threshold, disconnecting the pre-charging circuit and closing the first relay to supply power to the bus capacitor through the AC power grid to complete a soft start of the bus capacitor and wake up the DC power supply; The inverter circuit further includes a balancing circuit, the balancing circuit is connected to the bus capacitor, the bus capacitor includes a first bus capacitor and a second bus capacitor, and the control circuit is further configured to: When the voltage of the first bus capacitor is less than a preset threshold, turning on the pre-charging circuit so that the AC power grid charges the first bus capacitor through the pre-charging circuit; When the voltage of the first bus capacitor is greater than or equal to the preset threshold, driving the balancing circuit to charge the second bus capacitor; When the sum of the voltages of the first bus capacitor and the second bus capacitor is greater than or equal to the target threshold, the pre-charging circuit is opened and the first relay is closed.

2. The inverter according to claim 1, wherein: The balancing circuit includes a balancing bridge arm and a balancing inductor. The first bus capacitor and the second bus capacitor are connected in series and then connected in parallel with the inverter bridge arm. The balancing bridge arm is connected in parallel with the inverter bridge arm. One end of the balancing inductor is connected to the midpoint of the balancing bridge arm, and the other end of the balancing inductor is connected to the series node of the first bus capacitor and the second bus capacitor. One end of the first bus capacitor is connected to the ground point.

3. The inverter according to claim 1, wherein: The preset threshold Calculated by the following formula: ; When the AC power grid is a split-phase power grid, the target threshold is calculated by the following formula: ; When the AC power grid is a three-phase power grid, the target threshold is calculated by the following formula: ; in, is the phase voltage of the AC grid.

4. The inverter according to claim 2, wherein: The pre-charging circuit includes a second relay and a current-limiting resistor connected in series; The pre-charging circuit is connected between a non-zero phase line of the AC power grid and the grounding point, or a plurality of pre-charging circuits are respectively connected between the non-zero phase line of the AC power grid and the grounding point.

5. The inverter according to claim 4, characterized in that: The pre-charging circuit is further connected in series with a protection diode, and the anode of the protection diode is connected to the grounding point; The pre-charging circuit is provided with a plurality of second relays connected in series.

6. The inverter according to any one of claims 1 to 5, characterized in that: It also includes an auxiliary power supply circuit and a DC conversion circuit; The auxiliary power supply is connected to the AC power grid and is used to draw power from the AC power grid to provide system power for the soft start of the bus capacitor; The DC conversion circuit is arranged between the DC power supply and the inverter circuit, and is used to convert the DC voltage output by the inverter circuit into a wake-up voltage and then provide the wake-up voltage to the DC power supply.

7. The inverter according to any one of claims 1 to 5, characterized in that: The plurality of inverter bridge arms are used to form an inverter topology, and the inverter topology is one of an H4-type two-level topology, a T-type three-level topology, and an I-type three-level topology.

8. An energy storage system, characterized in that: The inverter comprises the inverter according to any one of claims 1 to 7, wherein the DC power supply comprises an energy storage battery.

9. A soft start method, characterized in that: Applicable to an inverter, the inverter is arranged between a DC power supply and an AC power grid, the inverter includes an inverter circuit, a pre-charging circuit and a control circuit, the inverter circuit includes a bus capacitor, a plurality of inverter bridge arms and a plurality of first relays, the inverter bridge arms are respectively connected to the AC power grid through the first relays; The pre-charging circuit is connected between the AC power grid and the bus capacitor, and the soft-start method includes: When the voltage of the bus capacitor is less than a target threshold, turning on the pre-charging circuit so that the AC grid charges the bus capacitor through the pre-charging circuit; When the voltage of the bus capacitor is greater than or equal to a target threshold, disconnecting the pre-charging circuit and closing the first relay to supply power to the bus capacitor through the AC power grid, thereby completing a soft start of the bus capacitor and waking up the DC power supply; The inverter circuit further includes a balancing circuit, the balancing circuit is connected to the bus capacitor, the bus capacitor includes a first bus capacitor and a second bus capacitor, and the soft start method further includes: When the voltage of the first bus capacitor is less than a preset threshold, turning on the pre-charging circuit so that the AC power grid charges the first bus capacitor through the pre-charging circuit; When the voltage of the first bus capacitor is greater than or equal to the preset threshold, driving the balancing circuit to charge the second bus capacitor; When the sum of the voltages of the first bus capacitor and the second bus capacitor is greater than or equal to the target threshold, the pre-charging circuit is opened and the first relay is closed.

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