Inverter and photovoltaic energy storage system

Abstract

The utility model provides an inverter and a photovoltaic energy storage system. The inverter comprises a positive direct-current bus, a negative direct-current bus, a capacitor unit, an inverter circuit, a first inverter switch unit, a second inverter switch unit and a pre-charging circuit, the capacitor unit is connected to the direct-current bus, and the inverter circuit is connected with the direct-current bus and the capacitor unit. The first inversion switch unit and the second inversion switch unit are connected in series between the inversion circuit and a power grid; the pre-charging circuit comprises a rectification unit, a current limiting unit and a pre-charging switch unit; the rectification unit is connected between the first inversion switch unit and the second inversion switch unit, the rectification unit is further connected with the current limiting unit, and the current limiting unit and the pre-charging switch unit are connected in series and then connected to a direct current bus; the pre-charging switch unit and the first inversion switch unit are both used for being in a closed state when the power grid voltage exists so as to allow the power grid to charge the capacitor unit. The energy storage inverter and the photovoltaic energy storage system provided by the utility model have relatively high safety and stability.

Description

Technical Field

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

[0002] The inverter, also known as a photovoltaic inverter or energy storage inverter, is a key component of a photovoltaic energy storage system. It converts the DC power generated by the photovoltaic array into AC power for integration into the grid or supply to households. At night, when the photovoltaic array is idle and the energy storage battery is depleted, the inverter shuts down. At this point, the grid is required to supply the auxiliary power supply in the inverter to maintain the inverter's standby mode, after which the energy storage battery is activated to charge.

[0003] To maintain the inverter's standby mode, the current practice is to close the grid relay and inverter relay after the grid is input to the inverter. The grid directly charges the DC bus capacitors, and the DC bus then supplies power to the auxiliary power supply to maintain the inverter's standby mode. However, this approach results in a high surge current when the inverter is shut down, as the initial DC bus voltage is low and the voltage difference between the grid and DC bus voltages is significant. Closing the grid relay and inverter relay instantly creates a large inrush current. If this inrush current exceeds the maximum current rating of the relays, it can damage various components in the inverter. Utility Model Content

[0004] In view of the above, it is necessary to provide an inverter and a photovoltaic energy storage system with high safety and stability.

[0005] In a first aspect, the present application provides an inverter, which includes a positive DC bus, a negative DC bus, a capacitor unit, an inverter circuit, a first inverter switch unit, a second inverter switch unit, and a pre-charging circuit. The capacitor unit is connected to the positive DC bus and the negative DC bus, the inverter circuit is connected to the positive DC bus, the negative DC bus, and the capacitor unit, the first inverter switch unit and the second inverter switch unit are connected in series between the inverter circuit and the power grid, and the pre-charging circuit includes: a rectifier unit, a current limiting unit, and a pre-charging switch unit; the input end of the rectifier unit is connected between the first inverter switch unit and the second inverter switch unit, the output end of the rectifier unit is connected to the current limiting unit, and the current limiting unit and the pre-charging switch unit are connected in series to the positive DC bus and the negative DC bus; wherein, the pre-charging switch unit and the first inverter switch unit are both used to be in a closed state when there is a power grid voltage to allow the power grid to charge the capacitor unit.

[0006] In some embodiments, the pre-charge switch unit is also used to be in an open state when the capacitor unit is charged to a preset voltage; the second inverter switch unit is also used to be in a closed state after the pre-charge switch unit is disconnected for a preset time to allow the inverter circuit to be electrically connected to the power grid.

[0007] In some embodiments, the preset voltage is a value where the difference between the voltage between the positive DC bus and the negative DC bus and the peak voltage of the power grid is less than a predetermined value.

[0008] In some embodiments, the inverter further includes a controller, which is connected to the first inverter switch unit, the second inverter switch unit and the pre-charge switch unit, and is used to: when there is a grid voltage, control the pre-charge switch unit and the first inverter switch unit to be in a closed state at the same time; and when the capacitor unit is charged to a preset voltage, control the pre-charge switch unit to be in a disconnected state, and control the second inverter switch unit to be in a closed state after the pre-charge switch unit is disconnected for a preset time.

[0009] In some embodiments, a grid switch unit is provided between the first inverter switch unit and the grid, and the grid switch unit is configured to be in a closed state before the pre-charging switch unit and the first inverter switch unit are simultaneously closed.

[0010] In some embodiments, the controller is connected to the grid switch unit, and the controller is further configured to control the grid switch unit to be in a closed state before the pre-charging switch unit and the first inverter switch unit are simultaneously in a closed state.

[0011] In some embodiments, the rectifier unit includes a first rectifier tube, a second rectifier tube, a third rectifier tube and a fourth rectifier tube. The first rectifier tube and the third rectifier tube are connected in series to form a first bridge arm, the second rectifier tube and the fourth rectifier tube are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are connected in parallel; the midpoint of the first bridge arm and the midpoint of the second bridge arm are both electrically connected to the output end of the inverter circuit; the midpoint of the first bridge arm and the midpoint of the second bridge arm constitute the input end of the rectifier unit, and the two ends of the first bridge arm and the two ends of the second bridge arm constitute the output end of the rectifier unit.

[0012] In some embodiments, the inverter circuit includes a first inverter bridge arm, a second inverter bridge arm, and a third inverter bridge arm; each inverter bridge arm of the inverter circuit includes at least one inductor element and multiple inverter elements, and the input end of each inverter bridge arm is connected to the positive DC bus, the negative DC bus and the capacitor unit, and the output end of each inverter bridge arm is connected to the power grid.

[0013] In some embodiments, the inverter further includes: an auxiliary power supply connected to the power grid and used to supply power to the controller.

[0014] The second aspect of the present application provides a photovoltaic energy storage system, including: photovoltaic power generation equipment, energy storage batteries and inverters; the photovoltaic power generation equipment is connected to the inverter, used to generate electricity using solar energy and connect the electric energy to the power grid or energy storage battery through the inverter; the energy storage battery is connected to the inverter, used to obtain electric energy from the photovoltaic power generation equipment or the power grid through the inverter; the inverter includes: a positive DC bus, a negative DC bus, a capacitor unit, an inverter circuit, a first inverter switch unit and a second inverter switch unit, multiple electrolytic capacitors in the capacitor unit are connected to the positive DC bus and the negative DC bus, the inverter circuit is connected to the positive DC bus, the negative DC bus and the capacitor unit, the first inverter switch unit and the second inverter switch unit are connected in series between the inverter circuit and the power grid; the inverter also includes a pre-charge circuit and a controller, pre- The charging circuit includes: a rectifier unit, a current limiting unit, and a pre-charging switch unit; the input of the rectifier unit is connected between the first inverter switch unit and the second inverter switch unit, the first end of the current limiting unit and the pre-charging switch unit connected in series is connected to the output end of the rectifier unit, and the second end of the current limiting unit and the pre-charging switch unit connected in series is connected to the positive DC bus and the negative DC bus; the controller is connected to the first inverter switch unit and the pre-charging switch unit, and is used to: when the presence of grid voltage is detected, control the pre-charging switch unit and the first inverter switch unit to be closed at the same time, so as to allow the grid to pre-charge the capacitor unit through the pre-charging circuit; when the capacitor unit is charged to a preset voltage, control the pre-charging switch unit to be disconnected, and control the second inverter switch to be closed after the pre-charging switch unit is disconnected for a preset time, so as to allow the rectifier unit to be connected to the grid.

[0015] Compared with the prior art, this application has at least the following advantages:

[0016] 1. In the inverter and photovoltaic energy storage system of the present application, the rectifier unit of the pre-charging circuit is connected between the first inverter switch unit and the second inverter switch unit, and the current limiting unit and the pre-charging switch unit of the pre-charging circuit are connected in series and then connected to the rectifier unit, the positive DC bus, and the negative DC bus. Thus, by controlling the opening and closing of the first inverter switch unit, the second inverter switch unit, and the pre-charging switch unit, the electric energy of the power grid can be pre-inputted into the capacitor unit of the inverter to complete the pre-charging of the positive DC bus and the negative DC bus, which can reduce the problem of inrush current generated when the capacitor unit is directly charged through the power grid.

[0017] 2. In the inverter and photovoltaic energy storage system of the present application, a current limiting unit is added to the pre-charging circuit to limit the current of the electric energy input from the pre-charging circuit to the capacitor unit, thereby playing a role in safety and stability.

[0018] 3. In the inverter and photovoltaic energy storage system of the present application, the pre-charge switch unit can be controlled to disconnect when the capacitor unit is charged to a preset voltage, and the second inverter switch unit can be controlled to close after a preset time, that is, the second inverter switch unit is controlled to be a soft switching operation, thereby reducing the situation where the pre-charge circuit, the capacitor unit, and the inverter circuit form a loop, resulting in abnormal operation of the inverter circuit, and at the same time, it can also reduce the situation where the voltage of the positive DC bus and the negative DC bus drops too much. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural diagram of the energy storage inverter of the first embodiment of the present application.

[0020] Figure 2 It is a structural diagram of the energy storage inverter of the second embodiment of the present application.

[0021] Figure 3 It is a structural diagram of the energy storage inverter of the third embodiment of the present application.

[0022] Figure 4 This application Figure 3 A circuit diagram principle of a partial structure of an energy storage inverter of an embodiment.

[0023] Figure 5 1 is an equivalent circuit diagram of a loop consisting of an auxiliary power supply, a pre-charging circuit and a capacitor unit in an embodiment of the present application.

[0024] Figure 6 It is a structural diagram of the photovoltaic energy storage system of an embodiment of the present application.

[0025] Description of main component symbols:

[0026] Photovoltaic energy storage system 1

[0027] Inverter 11

[0028] Photovoltaic power generation equipment12

[0029] Energy storage battery 13

[0030] Grid 2

[0031] Capacitor unit 111

[0032] Inverter circuit 112

[0033] The first inverter switch unit 113

[0034] The second inverter switch unit 114

[0035] Grid switch unit 21

[0036] Precharge circuit 115

[0037] Controller 116

[0038] Auxiliary power supply 117

[0039] Precharge switch unit 1151

[0040] Current limiting unit 1152

[0041] Rectification unit 1153

[0042] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0043] In the description of the embodiments of this application, words such as "exemplary," "or," and "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary," "or," and "for example" is intended to present the relevant concepts in a concrete manner.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be understood that, unless otherwise specified in this application, " / " means or. For example, A / B can mean A or B. "And / or" in this application is merely a way to describe the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. "At least one" means one or more. "Multiple" means two or more than two. For example, at least one of a, b or c can mean: a, b, c, a and b, a and c, b and c, a, b and c.

[0045] It should also be noted that the terms "first" and "second" in the description, claims and drawings of this application are used to distinguish similar objects, rather than to describe a specific order or sequence.

[0046] In recent years, global demand for renewable energy has been growing, and photovoltaic power generation, as a clean, renewable energy source, has become increasingly widely used. A photovoltaic energy storage system typically consists of a photovoltaic array (also known as a photovoltaic power generation device), an inverter (also known as a photovoltaic inverter or energy storage inverter), and an energy storage battery. The inverter is a key component, responsible for converting the DC power generated by the photovoltaic array into AC power for integration into the grid or supply to households. When the photovoltaic array's energy is sufficient to meet demand, excess energy is stored in the energy storage battery through the inverter, making it available when solar power is unavailable. At night, when the photovoltaic array has no power output and the energy storage battery is depleted, the inverter shuts down. At this point, the inverter requires the grid to supply an auxiliary power supply to maintain the inverter's standby mode, after which the energy storage battery is activated to recharge.

[0047] One method of maintaining the inverter in standby mode is to close the grid relay and inverter relay after the grid is input to the inverter, and the grid directly provides charging energy to the DC bus capacitor. After that, the DC bus supplies power to the auxiliary power supply to maintain the inverter in standby mode. However, when the inverter is shut down, the initial voltage of the DC bus is low, and the voltage difference between the grid and DC bus voltage is huge. The grid voltage is about 230V, and the peak voltage can reach When the grid relay and the inverter relay are closed, a very large surge current is likely to occur when a path is formed between the DC bus and the grid, especially at the peak of the grid voltage. When the surge current exceeds the maximum current specification of the relay, it will damage various components in the inverter.

[0048] Another approach is to incorporate a DC bus pre-charging circuit (also called a BUS pre-charging circuit or pre-charging circuit) into the inverter. This circuit pre-charges the DC bus to a predetermined state before the grid is fed into the inverter. Existing pre-charging circuits either have a simple structure but lack safety and stability, or offer high safety and stability but complex structure. This can increase the cost and size of PV energy storage systems, posing a challenge for space-constrained PV energy storage systems.

[0049] In addition, if the current limiting resistor is incorrectly selected and the resistor is overloaded for a long time, it will also cause the resistor to be damaged, causing the circuit to fail and affecting the function of the inverter.

[0050] To this end, the present application provides an inverter and a photovoltaic energy storage system. Some embodiments are described below with reference to the accompanying drawings. The following embodiments and features thereof may be combined with one another unless they conflict.

[0051] Figure 1This is a schematic diagram of the structure of the inverter 11 of the first embodiment of the present application. The present application first provides an inverter 11, please refer to Figure 1 The inverter 11 may include a DC bus, a capacitor unit 111 , an inverter circuit 112 , a first inverter switch unit 113 , a second inverter switch unit 114 , a pre-charging circuit 115 and a controller 116 .

[0052] The DC bus may include a positive DC bus (BUS+) and a negative DC bus (BUS-).

[0053] The capacitor unit 111 is connected to the positive DC bus and the negative DC bus, and is used to obtain charging energy through the pre-charging circuit 115 to increase the voltage of the DC bus.

[0054] The capacitor unit 111 may be connected to a positive DC bus and a negative DC bus.

[0055] In some embodiments, capacitor unit 111 may include multiple electrolytic capacitors, and multiple electrolytic capacitors in capacitor unit 111 are connected to the positive DC bus and the negative DC bus, and multiple electrolytic capacitors in capacitor unit 111 are connected in series and parallel. Inverter circuit 112 is connected to the positive DC bus, the negative DC bus, and capacitor unit 111, and is used to convert the current of the DC bus to the current of grid 2, for example, converting the AC power of grid 2 to DC power and inputting it to the DC bus, or converting the DC power of the DC bus to AC power and inputting it to grid 2.

[0056] In some embodiments, the inverter circuit 112 may include multiple inverter bridge arms, and each inverter bridge arm may be provided with multiple thyristors and multiple inductors.

[0057] In some embodiments, the inverter circuit 112 has three inverter bridge arms, and the three inverter bridge arms can form a three-phase inverter bridge.

[0058] The first inverter switch unit 113 and the second inverter switch unit 114 are connected in series between the inverter circuit 112 and the grid 2 , and are used to connect or disconnect the inverter circuit 112 from the grid 2 .

[0059] In the embodiment of the present application, by providing the first inverter switch unit 113 and the second inverter switch unit 114, it is possible to facilitate the pre-charging circuit 115 to pre-charge the capacitor unit 111 to raise the voltage of the DC bus before connecting the inverter circuit 112 to the power grid 2. This can reduce the problem of inrush current generated when the capacitor unit 111 is directly charged through the power grid 2.

[0060] See also Figure 1 The pre-charging circuit 115 may include: a rectifying unit 1153 , a current limiting unit 1152 , and a pre-charging switch unit 1151 .

[0061] The input of the rectifier unit 1153 is connected between the first inverter switch unit 113 and the second inverter switch unit 114, and is used to convert the AC power of the grid 2 into DC power and then input it into the DC bus, so that the capacitor unit 111 can obtain electrical energy for pre-charging.

[0062] The current limiting unit 1152 and the pre-charge switch unit 1151 are connected between the output end of the rectifier unit 1153 and the DC bus. Specifically, the first end of the current limiting unit 1152 and the pre-charge switch unit 1151 connected in series is connected to the output end of the rectifier unit 1153, and the second end of the current limiting unit 1152 and the pre-charge switch unit 1151 connected in series is connected to the positive DC bus and the negative DC bus.

[0063] In an embodiment of the present application, the controller 116 is connected to the first inverter switch unit 113 and the pre-charging switch unit 1151, and is used to control the pre-charging switch unit 1151 and the first inverter switch unit 113 to be closed at the same time when the presence of the grid 2 voltage is detected, so as to allow the grid 2 to pre-charge the capacitor unit 111 through the pre-charging circuit 115.

[0064] In some embodiments, the controller 116 is also connected to the second inverter switch unit 114, which is used to control the pre-charge switch unit 1151 to disconnect when the capacitor unit 111 is charged to a preset voltage, and control the second inverter switch to close after a preset time to allow the rectifier unit 1153 to be connected to the power grid 2.

[0065] In some embodiments, the first inverter switch unit 113 may include a plurality of switches, which may be arranged in a line connected to the grid 2 .

[0066] In some embodiments, the second inverter switch unit 114 may include a plurality of switches, which may be arranged in a line connected to the grid 2 .

[0067] In some embodiments, the pre-charging switch unit 1151 may include a plurality of switches, which may be disposed between the DC bus and the pre-charging circuit 115 .

[0068] In some embodiments, the preset voltage may be that the difference between the voltage of the DC bus and the peak voltage of the grid 2 is less than a predetermined value, that is, the difference between the voltage between the positive DC bus and the negative DC bus and the peak voltage of the grid 2 is less than a predetermined value.

[0069] In some embodiments, the predetermined value may be, for example, 20V.

[0070] In some embodiments, the controller 116 may be a control element such as an MCU (Microcontroller Unit).

[0071] Figure 2This is a schematic diagram of the structure of the inverter 11 according to the second embodiment of the present application. Figure 2 In other embodiments, a grid switch unit 21 may be provided between the first inverter switch unit 113 and the grid 2. In this embodiment, the controller 116 may also be configured to control the grid switch unit 21 to close before the pre-charging switch unit 1151 and the first inverter switch unit 113 are simultaneously closed. Providing the grid switch unit 21 can improve safety and meet the safety regulations of the grid 2.

[0072] In some embodiments, the grid switch unit 21 may include multiple switches. Multiple switches may be provided in the lines connecting the grid 2, that is, between the first inverter switch unit 113 and the grid 2. For example, switches are provided in each of the three live wires and one neutral wire connecting the grid 2, that is, the grid switch unit 21 includes four switches.

[0073] In other embodiments, to meet higher safety standards for the power grid 2, the power grid switch units 21 may be provided in two groups, and the two groups of power grid switch units 21 may be connected in series between the first inverter switch unit 113 and the power grid 2. For example, two switches are provided for each of the three live wires and one neutral wire connected to the power grid 2, that is, the power grid switch units 21 include eight switches.

[0074] Figure 3 This is a schematic diagram of the structure of the inverter 11 according to the third embodiment of the present application. Figure 3 In other embodiments, the inverter 11 may further include an auxiliary power supply 117 , which is connected to the grid 2 and used to supply power to the controller 116 .

[0075] In some embodiments, the output voltage of the auxiliary power supply 117 may include multiple values, such as 12V and 15V.

[0076] In the embodiment of the present application, after the grid 2 supplies power, the auxiliary power supply 117 starts to work and obtains electric energy from the grid 2. The auxiliary power supply 117 can output voltages of 12V and 15V to the controller 116. The controller 116 can control the grid switch unit 21 to close, and then control the first inverter switch unit 113 and the pre-charge switch unit 1151 to close at the same time, so that the pre-charge circuit 115 obtains electric energy from the grid 2 and outputs it to the DC bus after conversion. At this time, the capacitor unit 111 starts to pre-charge. When the capacitor unit 111 is pre-charged to the point where the difference between the bus voltage and the peak voltage of the grid 2 is less than a predetermined value, such as 20V, the controller 116 controls the pre-charge switch unit 1151 to disconnect, and controls the second inverter switch unit 114 to close after a preset time, such as 10ms, thereby connecting the rectifier unit 1153 to the grid 2.

[0077] Figure 4 This application Figure 3A circuit diagram showing a partial structure of the inverter 11 of the embodiment is shown in FIG.

[0078] In some embodiments, see Figure 4 The rectifier unit 1153 can be connected to the positive DC bus and the negative DC bus to form a three-phase inverter bridge. Each inverter bridge arm of the three-phase inverter bridge includes at least one inductive element and multiple inverter elements, the inductive element includes an inductor, and the inverter element includes a thyristor. For example, the first inverter bridge arm includes three thyristors (Q1, Q2, Q7, and Q8) and an inductor La, the second inverter bridge arm includes three thyristors (Q3, Q4, Q9, and Q10) and an inductor Lb, and the third inverter bridge arm includes three thyristors (Q5, Q6, Q11, and Q12) and an inductor Lc.

[0079] In some embodiments, see Figure 4 The multiple electrolytic capacitors (capacitors C1, C2, C3, and C4) of capacitor unit 111 are connected in series and parallel between the positive DC bus and the negative DC bus. For example, capacitors C1 and C2 are connected in series, capacitors C3 and C4 are connected in series, capacitors C1 and C3 are connected in parallel, and capacitors C2 and C4 are connected in parallel.

[0080] In some embodiments, the switch in the first inverter switch unit 113 may be a relay. Figure 4 The first inverter switch unit 113 may include four relays. One relay is provided for each of the three live wires (L1, L2, L3) and one neutral wire (N) of the power grid 2. For ease of description, three of the relays are referred to as relay group RLY5, and the remaining relays are referred to as relay group RLY6.

[0081] In some embodiments, the switch in the second inverter switch unit 114 may be a relay. Figure 4 The second inverter switch unit 114 may include four relays. One relay is provided for each of the three live wires (L1, L2, L3) and one neutral wire (N) of the power grid 2. For ease of description, three of the relays are referred to as relay group RLY7, and the remaining relays are referred to as relay group RLY8.

[0082] In some embodiments, the switch in the grid switch unit 21 may be a relay. Figure 4 The grid switch unit 21 may include eight relays, two of which are provided for each of the three live wires (L1, L2, L3) and one neutral wire (N) of the grid 2. For ease of description, three of the relays are referred to as relay group RLY1, three of the relays are referred to as relay group RLY3, and the remaining relays are referred to as relay groups RLY3 and RLY4.

[0083] In some other embodiments, the grid switch unit 21 may include four relays, wherein one relay is provided for each of the three live wires (L1, L2, L3) and one neutral wire (N) of the grid 2.

[0084] In other embodiments, the number of relays of the grid switch unit 21 can be set to 4n, where n is a natural number 1, 2, 3..., and n relays are provided in the three live wires (L1, L2, L3) and one neutral wire (N) of the grid 2.

[0085] In some embodiments, the rectifier unit 1153 may include multiple rectifier tubes, such as diodes. The multiple rectifier tubes may form a rectifier bridge to convert the AC power of the grid 2 into DC power. Figure 4 Rectifier unit 1153 includes a first rectifier tube D1, a second rectifier tube D2, a third rectifier tube D3, and a fourth rectifier tube D4. The first rectifier tube D1 and the third rectifier tube D3 are connected in series to form a first bridge arm, and the second rectifier tube D2 and the fourth rectifier tube D4 are connected in series to form a second bridge arm. The first bridge arm and the second bridge arm are connected in parallel, and the midpoint of the first bridge arm and the midpoint of the second bridge arm are both electrically connected to the output end of inverter circuit 112. The midpoint of the first bridge arm and the midpoint of the second bridge arm constitute the input end of rectifier unit 1153, and the two ends of the first bridge arm and the two ends of the second bridge arm constitute the output end of rectifier unit 1153.

[0086] In some embodiments, see Figure 4 The current limiting unit 1152 may include multiple current limiting resistors, such as resistors R1 and R2. The multiple current limiting resistors can divide the voltage of the electric energy converted by the rectifier unit 1153 to reduce the damage of the electrolytic capacitor in the capacitor unit 111 caused by overcurrent.

[0087] In some embodiments, the switch in the pre-charge switch unit 1151 may be a relay. Figure 4 The pre-charge switch unit 1151 may include four relays. Two relays are connected in series between the resistor R1 and the DC bus, and two relays are connected in series between the resistor R2 and the DC bus. For ease of description, two of the relays are referred to as relay group RLY9, and the other two relays are referred to as relay group RLY10. This further improves the safety of the pre-charge circuit 115 being connected to the positive DC bus and the negative DC bus.

[0088] In some other embodiments, the pre-charge switch unit 1151 may include two relays, wherein one relay is connected in series between the resistor R1 and the DC bus, and the other relay is connected in series between the resistor R2 and the DC bus.

[0089] In other embodiments, the pre-charge switch unit 1151 may include 2n relays, where n is a natural number 1, 2, 3, ..., n relays are connected in series between the resistor R1 and the DC bus, and another n relays are connected in series between the resistor R2 and the DC bus.

[0090] In some embodiments, please refer to Figure 4 Auxiliary power supply 117 includes an AC auxiliary power supply 117a and a DC auxiliary power supply 117b. The input of AC auxiliary power supply 117 is connected to grid 2, and the output is connected to the positive and negative DC buses. Thus, AC auxiliary power supply 117 can obtain AC power from grid 2 and convert it into DC power for operating controller 116, thereby maintaining controller 116 in a standby state, such as when the DC bus is deenergized.

[0091] In some embodiments, please refer to Figure 4 The input end of the DC auxiliary power supply 117 is connected to the positive DC bus and the negative DC bus, and the output end of the DC auxiliary power supply 117 is connected to the controller 116. Thus, the DC auxiliary power supply 117 can obtain DC power from the DC bus and convert it into DC power for operating the controller 116, thereby maintaining the normal operation of the controller 116.

[0092] In some embodiments, the positive output terminal of the AC auxiliary power supply 117 is connected to the positive DC bus, and the negative output terminal of the AC auxiliary power supply 117 is connected to the negative DC bus.

[0093] In some embodiments, a diode is provided between the positive output terminal of the AC auxiliary power supply 117 and the positive DC bus.

[0094] In an embodiment of the present application, after the grid 2 is powered, the auxiliary power supply 117 starts to work and obtains power from the grid 2. The auxiliary power supply 117 can output voltages of 12V and 15V to the controller 116. The controller 116 can control the relay groups RLY1, RLY2, RLY3, and RLY4 to close, and then control the relay groups RLY5, RLY6 and the relay groups RLY9 and RLY10 to close simultaneously. In this way, the pre-charging circuit 115 obtains power from the grid 2 and outputs it to the DC bus after conversion. At this time, the electrolytic capacitors C1, C2, C3, and C4 begin to pre-charge. When the difference between the bus voltage and the peak voltage of the grid 2 is less than a predetermined value, such as 20V, the controller 116 controls the relay groups RLY9 and RLY10 to open, and controls the relay groups RLY7 and RLY8 to close after a preset time, such as 10ms, thereby connecting the rectifier unit 1153 to the grid 2.

[0095] Figure 5This is an equivalent circuit diagram of the loop formed by the auxiliary power supply 117, the pre-charge circuit 115, and the capacitor unit 111 in the embodiment of the present application. As mentioned above, if the current limiting resistor specifications are incorrectly selected and the current limiting resistor is overloaded for a long time, it will also cause the current limiting resistor to be damaged, thereby causing the circuit to fail and affecting the function of the inverter 11. To solve this problem, this application also provides the following technical content on the selection of current limiting resistors:

[0096] In the examples of this application, please refer to Figure 5 , the auxiliary power supply 117, the pre-charge circuit 115 and the capacitor unit 111 can be equivalent to a loop, wherein the auxiliary power supply 117 and the capacitor unit 111 can be equivalent to being connected in parallel at both ends of the pre-charge circuit 115. The total capacitance Cbus of the capacitors C1, C2, C3 and C4 is Cbus = (C1 + C2) / / (C3 + C4), the maximum inrush current of the current limiting unit 1152 is: Ir = (Uac_rms*√2) / (R1 + R2), where Uac_rms is the equivalent voltage of the grid 2 ( Figure 5 (As shown in the figure, AC is used as an example). R is the sum of R1 and R2, and Ro is the equivalent load of the auxiliary power supply 117.

[0097] The voltage of the resistor changing with time is: UR(t)=C*(dUc(t)) / dt*R, the voltage of the capacitor changing with time is: Uc(t), the equivalent circuit diagram can be obtained according to KVL: UR(t)+Uc(t)=Uac_rms,

[0098]

[0099] Simplification can obtain a first-order linear non-homogeneous differential equation, and the general solution can be obtained as:

[0100] Uc(t)=Uac_rms*(1-e^(-t / (R*C)))

[0101] This expression is the change of capacitor voltage over time. According to KVL, the resistor voltage is:

[0102]

[0103] Assuming that the capacitor voltage is fully charged in about 5 time constants, the energy consumed by the resistor in this process is:

[0104]

[0105] The average power is: Pr = WR / (5 * R * C). Assuming that after the electrolytic capacitor is successfully precharged, the auxiliary power supply 117 load Ro continues to carry the load (assuming that the relay of the precharge circuit 115 is damaged and cannot be disconnected, resulting in the DC bus loss energy being provided by the grid 2 through the precharge circuit 115), the load power at this time is:

[0106]

[0107] The capacitor voltage can be obtained as follows:

[0108]

[0109] In summary, in the present application, the minimum startup voltage of the auxiliary power supply 117 can be designed as: Ux < Uc * 0.9. At this time, the power specification of the resistor selected by the current limiting unit 1152 can be: P > Pr and P > Uc^2 / Ro. The withstand voltage of the current limiting resistor can be: Ur > Uac_rms * √2 * 1.5, where 0.9 is the margin coefficient, that is, a certain margin needs to be reserved for the capacitor voltage, and the minimum startup voltage should be less than 0.9 times the capacitor voltage; 1.5 is the margin coefficient, that is, the withstand voltage of the current limiting resistor needs to be greater than 1.5 times the peak value of the grid voltage (Uac_rms * √2 is the peak value of the grid voltage).

[0110] Figure 6 is a schematic structural diagram of the photovoltaic energy storage system 1 according to an embodiment of the present application. Please refer to Figure 6 , the present application also provides a photovoltaic energy storage system 1, and the photovoltaic energy storage system 1 may include: a photovoltaic power generation device 12, a storage battery 13, and an inverter 11.

[0111] The photovoltaic power generation device 12 is connected to the inverter 11 and is used for generating electricity by using solar energy and accessing the electric energy into the power grid 2 or the storage battery 13 through the inverter 11.

[0112] The storage battery 13 is connected to the inverter 11 and is used for obtaining electric energy from the photovoltaic power generation device 12 or the power grid 2 through the inverter 11. The inverter 11 may include a DC bus, a capacitor unit 111, an inverter circuit 112, a first inverter switch unit 113, a second inverter switch unit 114, a pre-charge circuit 115, and a controller 116.

[0113] In some embodiments, the DC bus may include a positive DC bus and a negative DC bus.

[0114] The capacitor unit 111 is connected between the positive DC bus and the negative DC bus and is used for obtaining charging electric energy through the pre-charge circuit 115 to increase the voltage of the DC bus.

[0115] In some embodiments, the capacitor unit 111 may include a plurality of electrolytic capacitors. The plurality of electrolytic capacitors in the capacitor unit 111 are connected between the positive DC bus and the negative DC bus, and the plurality of electrolytic capacitors in the capacitor unit 111 are connected in a series-parallel manner.

[0116] The inverter circuit 112 is connected to the positive DC bus, the negative DC bus and the capacitor unit 111, and is used to convert the current of the DC bus and the current of the grid 2 into each other, for example, converting the AC power of the grid 2 into DC power and inputting it into the DC bus, or converting the DC power of the DC bus into AC power and inputting it into the grid 2.

[0117] The pre-charging circuit 115 includes a rectifier unit 1153, a current limiting unit 1152, and a pre-charging switch unit 1151. The input of the rectifier unit 1153 is connected between the first inverter switch unit 113 and the second inverter switch unit 114. The first end of the series connection of the current limiting unit 1152 and the pre-charging switch unit 1151 is connected to the output end of the rectifier unit 1153. The second end of the series connection of the current limiting unit 1152 and the pre-charging switch unit 1151 is connected to the positive DC bus and the negative DC bus.

[0118] The controller 116 is connected to the first inverter switch unit 113 and the pre-charge switch unit 1151, and is used to control the pre-charge switch unit 1151 and the first inverter switch unit 113 to be closed at the same time when the presence of the grid 2 voltage is detected, so as to allow the grid 2 to pre-charge the capacitor unit 111 through the pre-charge circuit 115; or, when the capacitor unit 111 is charged to a preset voltage, control the pre-charge switch unit 1151 to be disconnected, and control the second inverter switch to be closed after a preset time, so as to allow the rectifier unit 1153 to be connected to the grid 2.

[0119] In some embodiments, the photovoltaic power generation device 12 and the energy storage battery 13 can be connected to the DC bus through an intermediate circuit (not shown), for example, the intermediate circuit is a power conversion circuit, including a boost circuit or a DC-DC conversion circuit.

[0120] In addition, other embodiments of the inverter 11 in the photovoltaic energy storage system 1 of the present application may be the same as any of the inverters 11 described above, and will not be described in detail here.

[0121] In the inverter 11 and photovoltaic energy storage system 1 of the present application, the rectifier unit 1153 of the pre-charging circuit 115 is connected between the first inverter switch unit 113 and the second inverter switch unit 114. The current limiting unit 1152 and the pre-charging switch unit 1151 of the pre-charging circuit 115 are connected in series and then connected to the rectifier unit 1153, the positive DC bus and the negative DC bus. Thus, by controlling the opening and closing of the first inverter switch unit 113, the second inverter switch unit 114 and the pre-charging switch unit 1151, the electric energy of the grid 2 can be pre-inputted into the capacitor unit 111 of the inverter 11 to complete the pre-charging of the positive DC bus and the negative DC bus, which can reduce the problem of inrush current generated when the capacitor unit 111 is directly charged by the grid 2.

[0122] In addition, in the inverter 11 and photovoltaic energy storage system 1 of the present application, the pre-charging circuit 115 is added with a current limiting unit 1152, which can limit the current of the electric energy input from the pre-charging circuit 115 to the capacitor unit 111, thereby playing a role in safety and stability.

[0123] In addition, in the inverter 11 and photovoltaic energy storage system 1 of the present application, the controller 116 can control the pre-charging switch unit 1151 to disconnect when the capacitor unit 111 is charged to a preset voltage, and control the second inverter switch unit 114 to close after a preset time, that is, control the second inverter switch unit 114 to perform a soft switching operation, thereby reducing the situation where the pre-charging circuit 115 forms a loop with the capacitor unit 111 and the inverter circuit 112, resulting in abnormal operation of the inverter circuit 112, and at the same time, it can also reduce the situation where the voltage of the positive DC bus and the negative DC bus drops too much.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. An inverter, characterized in that: The inverter includes a positive DC bus, a negative DC bus, a capacitor unit, an inverter circuit, a first inverter switch unit, a second inverter switch unit, and a pre-charging circuit, wherein the capacitor unit is connected to the positive DC bus and the negative DC bus, the inverter circuit is connected to the positive DC bus, the negative DC bus, and the capacitor unit, the first inverter switch unit and the second inverter switch unit are connected in series between the inverter circuit and the power grid, and the pre-charging circuit includes: a rectifier unit, a current limiting unit, and a pre-charging switch unit; The input end of the rectifier unit is connected between the first inverter switch unit and the second inverter switch unit, the output end of the rectifier unit is connected to the current limiting unit, and the current limiting unit and the pre-charge switch unit are connected in series and then connected to the positive DC bus and the negative DC bus; The pre-charging switch unit and the first inverter switch unit are both configured to be in a closed state when a grid voltage is present, so as to allow the grid to charge the capacitor unit.

2. The inverter according to claim 1, characterized in that The pre-charge switch unit is further configured to be in a disconnected state when the capacitor unit is charged to a preset voltage; The second inverter switch unit is further configured to be in a closed state after the pre-charging switch unit is disconnected for a preset time, so as to allow the inverter circuit to be electrically connected to the power grid.

3. The inverter according to claim 2, characterized in that: The preset voltage is a value where the difference between the voltage between the positive DC bus and the negative DC bus and the peak voltage of the power grid is less than a predetermined value.

4. The inverter according to claim 2, characterized in that: The inverter further includes a controller connected to the first inverter switch unit, the second inverter switch unit, and the pre-charge switch unit, and configured to: When the grid voltage exists, controlling the pre-charging switch unit and the first inverter switch unit to be in a closed state at the same time; and When the capacitor unit is charged to the preset voltage, the pre-charge switch unit is controlled to be in an open state, and after the pre-charge switch unit is opened for the preset time, the second inverter switch unit is controlled to be in a closed state.

5. The inverter according to claim 4, characterized in that: A grid switch unit is provided between the first inverter switch unit and the grid, and the grid switch unit is configured to be in a closed state before the pre-charging switch unit and the first inverter switch unit are simultaneously closed.

6. The inverter according to claim 5, characterized in that The controller is connected to the grid switch unit, and is further configured to control the grid switch unit to be in a closed state before the pre-charging switch unit and the first inverter switch unit are simultaneously in a closed state.

7. The inverter according to claim 1, characterized in that The rectifier unit includes a first rectifier tube, a second rectifier tube, a third rectifier tube, and a fourth rectifier tube, the first rectifier tube and the third rectifier tube are connected in series to form a first bridge arm, the second rectifier tube and the fourth rectifier tube are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are connected in parallel; The midpoint of the first bridge arm and the midpoint of the second bridge arm are both electrically connected to the output end of the inverter circuit; The midpoint of the first bridge arm and the midpoint of the second bridge arm constitute the input end of the rectifier unit, and the two ends of the first bridge arm and the two ends of the second bridge arm constitute the output end of the rectifier unit.

8. The inverter according to claim 1, characterized in that The inverter circuit includes a first inverter bridge arm, a second inverter bridge arm and a third inverter bridge arm; Each inverter bridge arm of the inverter circuit includes at least one inductive element and multiple inverter elements, and the input end of each inverter bridge arm is connected to the positive DC bus, the negative DC bus and the capacitor unit, and the output end of each inverter bridge arm is connected to the power grid.

9. The inverter according to claim 4 or 6, characterized in that: The inverter further includes an auxiliary power supply connected to a power grid and used to supply power to the controller.

10. A photovoltaic energy storage system, characterized in that: include: Photovoltaic power generation equipment, energy storage battery and inverter; the photovoltaic power generation equipment is connected to the inverter to generate electricity using solar energy and connect the electricity to the power grid or the energy storage battery through the inverter; The energy storage battery is connected to the inverter and is used to obtain electrical energy from the photovoltaic power generation equipment or the power grid through the inverter; The inverter includes: a positive DC bus, a negative DC bus, a capacitor unit, an inverter circuit, a first inverter switch unit, and a second inverter switch unit. A plurality of electrolytic capacitors in the capacitor unit are connected to the positive DC bus and the negative DC bus. The inverter circuit is connected to the positive DC bus, the negative DC bus, and the capacitor unit. The first inverter switch unit and the second inverter switch unit are connected in series between the inverter circuit and the power grid. The inverter further includes a pre-charging circuit and a controller, wherein the pre-charging circuit includes: a rectifier unit, a current limiting unit, and a pre-charging switch unit; The input of the rectifier unit is connected between the first inverter switch unit and the second inverter switch unit, a first end of the current limiting unit and the pre-charge switch unit connected in series is connected to the output end of the rectifier unit, and a second end of the current limiting unit and the pre-charge switch unit connected in series is connected to the positive DC bus and the negative DC bus; The controller is connected to the first inverter switch unit and the pre-charge switch unit, and is configured to: When the presence of a grid voltage is detected, controlling the pre-charging switch unit and the first inverter switch unit to be closed simultaneously, so as to allow the grid to pre-charge the capacitor unit through the pre-charging circuit; When the capacitor unit is charged to a preset voltage, the pre-charge switch unit is controlled to be disconnected, and after the pre-charge switch unit is disconnected for a preset time, the second inverter switch is controlled to be closed to allow the rectifier unit to be connected to the power grid.

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