PCS, energy storage system and charging method thereof

Abstract

According to the PCS, the energy storage system and the electricity supplementing method of the PCS, the four bridge arms which are connected in parallel are arranged in the PCS, the midpoints of the four bridge arms are connected with the four alternating current ports after being connected with the inductors in series, and the four alternating current ports are used for being connected with one phase line or one neutral line of a power grid. Therefore, when two of the four alternating current ports are connected with the power grid, the PCS can be controlled to work to supplement power to the energy storage system by controlling the bridge arms connected with the two alternating current ports connected with the power grid to work. Moreover, when three alternating current ports in the four alternating current ports are connected with three phase lines of a three-phase power grid, and the four alternating current ports are connected with three phase lines and a neutral line of a three-phase four-line system (or a three-phase five-line system), the PCS can also work to supplement power to the energy storage system. Therefore, when the energy storage system is connected with the power grid of any system, the energy storage system can be charged, so that the adaptability of charging of the energy storage system can be improved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly to a PCS, an energy storage system and a charging method thereof. Background Art

[0002] With the increasing market share of energy storage systems, the installation areas of energy storage systems are getting farther away, and the transportation and storage times of energy storage systems are getting longer. In order to avoid over-discharge of the battery during the transportation and storage of the energy storage system, when the state of charge (SOC) of the battery in the energy storage system is lower than a certain threshold, the energy storage system needs to be charged during the gap period of storage or transportation to ensure the reliability of the battery.

[0003] Currently, a common charging solution in the industry is to charge each battery pack in the energy storage system using a charging machine. Since the container or battery cabinet serving as the energy storage system contains a battery cluster composed of multiple parallel-connected battery packs, the charging efficiency of a single battery pack is low, and at the same time, a dedicated charging machine needs to be configured. Another common charging solution in the industry is to charge the entire battery cluster in the container or battery cabinet through a power conversion system (PCS) in the energy storage system. Since the current PCS requires a three-phase power grid system to operate, the charging power grid environment requirements for the energy storage system are high. Summary of the Invention

[0004] A PCS, an energy storage system and a charging method thereof provided by the present application are used to improve the versatility of charging the energy storage system.

[0005] In a first aspect, the present application provides a PCS including: four parallel-connected bridge arms, four AC ports and a controller. Both ends of each bridge arm are used to connect to the DC bus of the energy storage system. The midpoint of each bridge arm is connected to one of the four AC ports after being connected in series with an inductor. The four AC ports are used to connect to the power grid. The controller is configured to: when it is detected that two of the four AC ports are connected to the power grid, control the switching tubes included in the bridge arms connected to the other two AC ports to turn off, that is, the bridge arms connected to the other two AC ports are turned off, and the other two AC ports are the two AC ports among the four AC ports that are not connected to the power grid. The controller is further configured to: control the switching tubes included in the bridge arms connected to the two AC ports connected to the power grid to turn on or off, that is, the bridge arms connected to the two AC ports connected to the power grid operate, so that the energy storage system forms a current loop with the power grid through the conducting bridge arms to charge the energy storage system.

[0006] In this application, when the controller connects to the power grid at two AC ports, it can control the operation of the arms connected to the two AC ports connected to the power grid, that is, control the PCS to operate to charge the energy storage system. Moreover, when three of the four AC ports are connected to the three phase lines of the three-phase power grid, and when the four AC ports are connected to the three phase lines and the neutral line of a three-phase four-wire system (or a three-phase five-wire system), the PCS can also operate to charge the energy storage system, enabling the energy storage system to be charged when connected to any type of power grid, thus improving the adaptability of the energy storage system charging.

[0007] In this application, when the power grid is connected to the AC port of the PCS, the PCS detects the phase of the connected power grid and, according to the set power, controls the on or off of the switching tubes included in the arms connected to the two AC ports connected to the power grid through a phase-locked loop. Specifically, each arm of the PCS includes an upper arm and a lower arm connected in series, and both the upper arm and the lower arm include switching tubes. When the detected phase of the connected power grid is 0 - 180°, the controller can control the switching tubes of the upper arm in the arms connected to the two AC ports connected to the power grid to conduct. When the phase of the connected power grid is 180° - 360°, the controller can control the switching tubes of the lower arm in the arms connected to the two AC ports connected to the power grid to conduct, so as to charge the energy storage system through the conducting switching tubes.

[0008] In some embodiments of this application, when the circuit topology of a single arm of the PCS specifically adopts a T-type three-level topology, the PCS further includes two capacitors connected in series, and the two capacitors connected in series are arranged in parallel with the arm. Each arm further includes a cross arm, one end of the cross arm is connected to the series connection point of the upper arm and the lower arm, and the other end of the cross arm is connected to the series connection point of the two capacitors; the cross arm includes two switching tubes connected in series. The controller can also control the two switching tubes connected in series in the cross arm of the arms connected to the two AC ports connected to the power grid to conduct alternately, so as to charge the energy storage system through the conducting switching tubes.

[0009] In some other embodiments of this application, when the circuit topology of a single arm of the PCS specifically adopts a diode-type three-level topology, the PCS further includes two capacitors connected in series, and the two capacitors connected in series are arranged in parallel with the arm. The upper arm of each arm includes two switching tubes connected in series, and the lower arm of each arm includes two switching tubes connected in series. Each arm further includes two diodes, one diode is connected between the series connection point of the two capacitors and the midpoint of the upper arm, and the other diode is connected between the series connection point of the two capacitors and the midpoint of the lower arm.

[0010] In some other embodiments of the present application, when the circuit topology of a single arm of the PCS specifically adopts an active three-level topology, the PCS further includes two capacitors connected in series, and the two capacitors connected in series are arranged in parallel with the arm. The upper arm of each arm includes two switching tubes connected in series, and the lower arm of each arm includes two switching tubes connected in series. Each arm further includes two clamping switching tubes, one of the clamping switching tubes is connected between the series connection point of the two capacitors and the midpoint of the upper arm, and the other clamping switching tube is connected between the series connection point of the two capacitors and the midpoint of the lower arm. The controller can also control the two clamping switching tubes in the arms connected to the two AC ports connected to the power grid to conduct alternately, so as to charge the energy storage system through the conducting switching tubes.

[0011] In some embodiments of the present application, the two AC ports of the PCS can be connected to the L-phase line and the neutral line of a single-phase power grid. Or, when the three-phase power grid includes a neutral line, the two AC ports of the PCS can also be connected to any one phase line and the neutral line in the three-phase power grid, that is, the two AC ports of the PCS are connected to the AN line or the BN line or the CN line. Or, the two AC ports of the PCS can also be connected to any two phase lines in the three-phase power grid, that is, the AB phase line or the BC phase line or the CA phase line. Therefore, the PCS in the energy storage system provided by the present application works without being restricted by the power grid system requirements, which can improve the adaptability of the energy storage system for charging.

[0012] In a second aspect, the present application provides an energy storage system, including: a battery pack, a DC bus, and the PCS provided in the first aspect. Each battery pack is composed of one or more battery cells connected in series, and multiple battery packs are connected in series to form a battery cluster. One or more parallel battery clusters can be included in the energy storage system. Multiple battery packs are connected in series to the DC bus, and the DC port of the PCS is connected to the DC bus. The PCS is used to charge the energy storage system when the two AC ports are connected to the power grid. Moreover, when three of the four AC ports are connected to the three phase lines of a three-phase power grid, and when the four AC ports are connected to the three phase lines and the neutral line of a three-phase four-wire system (or a three-phase five-wire system), the PCS can also work to charge the energy storage system, which can improve the generality of charging. And the PCS charges multiple battery packs as a whole, which can improve the charging efficiency.

[0013] In some other embodiments of the present application, a DC converter can also be provided between the DC port of the PCS and the DC bus, and the DC converter is used to perform voltage conversion on the direct current of the DC bus.

[0014] In a third aspect, the present application provides a method for charging a energy storage system, including: when it is detected that two of the four AC ports of the PCS are connected to the power grid, controlling the switching tubes included in the bridge arms connected to the other two AC ports to turn off, that is, turning off the bridge arms connected to the other two AC ports, and the other two AC ports are the two AC ports among the four AC ports that are not connected to the power grid. And controlling the switching tubes included in the bridge arms connected to the two AC ports connected to the power grid to turn on or off, that is, the bridge arms connected to the two AC ports connected to the power grid operate, so that the energy storage system forms a current loop with the power grid through the conducting bridge arms to charge the energy storage system.

[0015] In the charging method of the present application, when two AC ports are connected to the power grid, the bridge arms connected to the two AC ports connected to the power grid can be controlled to operate, that is, controlling the PCS to operate to charge the energy storage system. Moreover, when three of the four AC ports are connected to the three phase lines of the three-phase power grid, and when the four AC ports are connected to the three phase lines and the neutral line of a three-phase four-wire system (or three-phase five-wire system), the PCS can also operate to charge the energy storage system, so that the energy storage system can be charged when connected to any type of power grid, thus improving the adaptability of the energy storage system charging.

[0016] In the present application, the energy storage system includes: a battery pack, a DC bus, and a PCS, and the battery pack is connected to the DC bus. The PCS includes: four parallel bridge arms and four AC ports. Both ends of each bridge arm are connected to the DC bus, and the midpoint of each bridge arm is connected to one of the four AC ports in series with an inductor, and the four AC ports are used to connect to the power grid.

[0017] In the present application, when the power grid is connected to the AC port of the PCS, the PCS detects the phase of the connected power grid, and according to the set power, controls the switching tubes included in the bridge arms connected to the two AC ports connected to the power grid to turn on or off through a phase-locked loop. Specifically, when it is detected that the phase of the connected power grid is 0 - 180°, the switching tubes of the upper bridge arm of the bridge arms connected to the two AC ports connected to the power grid can be controlled to turn on, and when the phase of the connected power grid is 180° - 360°, the switching tubes of the lower bridge arm of the bridge arms connected to the two AC ports connected to the power grid can be controlled to turn on, so as to charge the energy storage system through the conducting switching tubes.

[0018] In some embodiments of the present application, when the circuit topology of a single bridge arm of the PCS specifically adopts a T-type three-level topology, the two switching tubes of the cross bridge arm of the bridge arms connected to the two AC ports connected to the power grid can also be controlled to alternately turn on, so as to charge the energy storage system through the conducting switching tubes.

[0019] In some embodiments of the present application, when the circuit topology of a single leg of the PCS specifically adopts an active three-level topology, it is also possible to control the two clamping switch tubes in the legs connected to the two AC ports of the power grid to conduct alternately, so as to charge the energy storage system through the conducting switch tubes.

[0020] For the technical effects that can be achieved by any possible design in the second aspect and the third aspect, please refer to the technical effects that can be achieved by any possible design in the first aspect above, and will not be repeated here. These aspects or other aspects of the present application will be more clearly understood in the following description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Structural schematic diagram of a charging scheme in the prior art;

[0022] Figure 2 Structural schematic diagram of another charging scheme in the prior art;

[0023] Figure 3 Structural schematic diagram of an energy storage system provided by an embodiment of the present application;

[0024] Figure 4 Structural schematic diagram of a PCS provided by an embodiment of the present application;

[0025] Figure 5 Structural schematic diagram of a charging structure of an energy storage system provided by an embodiment of the present application;

[0026] Figure 6 Structural schematic diagram of another charging structure of an energy storage system provided by an embodiment of the present application;

[0027] Figure 7 Structural schematic diagram of another PCS provided by an embodiment of the present application;

[0028] Figure 8 Structural schematic diagram of another PCS provided by an embodiment of the present application;

[0029] Figure 9 Structural schematic diagram of an energy storage system provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings. However, the exemplary embodiments can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; on the contrary, these embodiments are provided so that the present application will be more complete and comprehensive, and the concept of the exemplary embodiments will be fully conveyed to those skilled in the art.

[0031] Refer to Figure 1, currently, a common charging scheme in the industry is to use a charging motor to charge each battery pack in the energy storage system. Since the container or battery cabinet serving as the energy storage system contains battery clusters composed of multiple battery packs connected in parallel, the charging efficiency of a single battery pack is low, and a dedicated charging motor needs to be configured.

[0032] Referring to Figure 2 , another common charging scheme in the industry is to charge the battery clusters in the container or battery cabinet as a whole through a power conversion system (PCS) in the energy storage system. Since the current PCS requires a three-phase power grid system to operate, the charging power grid environment requirements for the energy storage system are high.

[0033] In view of this, the embodiments of the present application provide a PCS, an energy storage system, and a charging method thereof. A three-phase four-wire PCS is set in the energy storage system, and the PCS controls the corresponding bridge arm to work according to the power grid system connected. It can charge the battery without following the power grid system requirements, improving the versatility of the energy storage system charging.

[0034] Referring to Figure 3 , an energy storage system provided by the embodiments of the present application includes: battery packs, a DC bus (BUS), and a PCS. Each battery pack is composed of one or more battery cells connected in series, and multiple battery packs are connected in series to form a battery cluster. One or more parallel battery clusters can be included in the energy storage system. Multiple battery packs are connected in series and then connected to the DC bus (BUS), and the DC port of the PCS is connected to the DC bus (BUS). The PCS is used to charge the energy storage system when two AC ports are connected to the power grid. Moreover, when three phase lines of a three-phase power grid are connected to three of the four AC ports, and when three phase lines and the neutral line of a three-phase four-wire system (or three-phase five-wire system) are connected to the four AC ports, the PCS can also work to charge the energy storage system, which can improve the charging versatility, and the PCS charges multiple battery packs as a whole, which can improve the charging efficiency.

[0035] Referring to Figure 4, the PCS provided by this application includes: four parallel bridge arms LA, LB, LC, LN, four AC ports A, B, C, N, and a controller (not shown in the figure). Each bridge arm LA, LB, LC, LN of the PCS includes a series-connected upper bridge arm and a lower bridge arm. Both the upper bridge arm and the lower bridge arm include at least one switching tube. The connection points of the upper bridge arm and the lower bridge arm serve as the midpoints M1, M2, M3, M4 of the bridge arms LA, LB, LC, and LN. Both ends of each bridge arm LA, LB, LC, LN are used to connect to the DC bus. Specifically, generally, the upper bridge arm is connected to the positive bus BUS+, and the lower bridge arm is connected to the negative bus BUS-. The midpoints M1, M2, M3, M4 of each bridge arm LA, LB, LC, LN are respectively connected to an AC port A, B, C, or N after being connected in series with inductors L1, L2, L3, L4. The four AC ports A, B, C, N are used to connect to the power grid. Specifically, the four AC ports are used to connect to one of the phase lines of the power grid (such as the A phase line, B phase line, C phase line in a three-phase power grid, or the L phase line in a single-phase power grid) or the neutral line N. The power grid can specifically be a three-phase power grid. The three-phase power grid can be a three-phase three-wire power grid (only including the A phase line, B phase line, C phase line), or a three-phase four-wire power grid (including the A phase line, B phase line, C phase line, and the neutral line), or a three-phase five-wire power grid (including the A phase line, B phase line, C phase line, neutral line N, and the ground wire). The power grid can also be a single-phase power grid (including the L phase line and the neutral line). The controller is used to: when detecting that two of the four AC ports A, B, C, N are connected to the power grid, control the switching tubes included in the bridge arms connected to the other two AC ports to turn off, that is, the bridge arms connected to the other two AC ports are turned off, and the other two AC ports are the two AC ports among the four AC ports that are not connected to the power grid. The controller is also used to: control the switching tubes included in the bridge arms connected to the two AC ports connected to the power grid to turn on or off, that is, the bridge arms connected to the two AC ports connected to the power grid work, so that the energy storage system forms a current loop with the power grid through the conducting bridge arms to charge the energy storage system.

[0036] In this application, when two AC ports are connected to the power grid, the controller can control the bridge arms connected to the two AC ports connected to the power grid to work, that is, control the PCS to work to charge the energy storage system. Moreover, when three of the four AC ports are connected to the three phase lines of a three-phase power grid, and when the four AC ports are connected to the three phase lines and the neutral line of a three-phase four-wire (or three-phase five-wire) power grid, the PCS can also work to charge the energy storage system, enabling the energy storage system to be charged when connected to any type of power grid, thus improving the adaptability of the energy storage system for charging. Specifically, referring to Figure 5 , two AC ports of the PCS can be connected to the L phase line and the neutral line of a single-phase power grid. Or, referring to Figure 6, when the three-phase power grid includes a neutral line, the two AC ports of the PCS can also be connected to any one phase line and the neutral line in the three-phase power grid, that is, the two AC ports of the PCS are connected to the AN line or the BN line or the CN line. Alternatively, the two AC ports of the PCS can also be connected to any two phase lines in the three-phase power grid, that is, the AB phase line or the BC phase line or the CA phase line. Therefore, the operation of the PCS in the energy storage system provided by this application is not subject to the requirements of the power grid system, which can improve the adaptability of the energy storage system for supplementary power supply.

[0037] In this application, for the convenience of drive control, the circuit topologies of the four arms included in the PCS are generally the same. The circuit topology of a single arm can adopt a neutral point clamped (NPC) three-level topology, that is, the PCS also includes two capacitors C1 and C2 connected in series. The two capacitors C1 and C2 connected in series are arranged in parallel with the arm. The two capacitors C1 and C2 are used for voltage division on the DC side, and the series connection point of the two capacitors C1 and C2 is used as the neutral N point, and the voltage is clamped.

[0038] Referring to Figure 4 , in some embodiments of this application, the circuit topology of a single arm of the PCS can specifically adopt a T-type three-level topology. Specifically, the upper arm of each arm of the PCS can include a switching tube, and the lower arm can include a switching tube. The series connection point of the upper arm and the lower arm, that is, the midpoint of the arm, is connected to an AC port in series with an inductor. And each arm can also include a cross arm. One end of the cross arm is connected to the series connection point of the upper arm and the lower arm, that is, the midpoint of the arm, and the other end of the cross arm is connected to the series connection point of the two capacitors C1 and C2. The cross arm includes two switching tubes connected in series. Specifically, the cross arm generally includes two switching tubes with opposite freewheeling directions, and the two switching tubes with opposite freewheeling directions form a bidirectional switch.

[0039] Exemplarily, the upper arm of arm LA includes switching tube SA1, the lower arm includes switching tube SA2, the cross arm includes switching tubes SA3 and SA4 with opposite freewheeling directions, and an inductor L1 is connected in series between the series connection point M1 of switching tubes SA1 and SA2 and AC port A; the upper arm of arm LB includes switching tube SB1, the lower arm includes switching tube SB2, the cross arm includes switching tubes SB3 and SB4 with opposite freewheeling directions, and an inductor L2 is connected in series between the series connection point M2 of switching tubes SB1 and SB2 and AC port B; the upper arm of arm LC includes switching tube SC1, the lower arm includes switching tube SC2, the cross arm includes switching tubes SC3 and SC4 with opposite freewheeling directions, and an inductor L3 is connected in series between the series connection point M3 of switching tubes SC1 and SC2 and AC port C; the upper arm of arm LN includes switching tube SN1, the lower arm includes switching tube SN2, the cross arm includes switching tubes SN3 and SN4 with opposite freewheeling directions, and an inductor L4 is connected in series between the series connection point M4 of switching tubes SN1 and SN2 and AC port N.

[0040] Referring to Figure 7 , in some other embodiments of the present application, the circuit topology of a single arm of the PCS may specifically adopt a diode-type three-level topology. Specifically, the upper arm of each arm of the PCS may include two switching tubes connected in series, and the lower arm may include two switching tubes connected in series. The series connection point of the upper arm and the lower arm, that is, the midpoint of the arm, is connected to an AC port after being connected in series with an inductor. Moreover, each arm may further include two diodes. One diode is connected between the series connection point of the two capacitors C1 and C2 and the series connection point of the two switching tubes of the upper arm, that is, the midpoint of the upper arm, and the other diode is connected between the series connection point of the two capacitors C1 and C2 and the series connection point of the two switching tubes of the lower arm, that is, the midpoint of the lower arm.

[0041] Exemplarily, the upper arm of arm LA includes switching tubes SA1 and SA2 connected in series, the lower arm includes switching tubes SA3 and SA4 connected in series. An inductor L1 is connected in series between the series connection point M1 of switching tubes SA2 and SA3 and the AC port A. A diode DA1 is connected in series between the series connection point of switching tubes SA1 and SA2 and the series connection point of the two capacitors C1 and C2. A diode DA2 is connected in series between the series connection point of switching tubes SA3 and SA4 and the series connection point of the two capacitors C1 and C2; the upper arm of arm LB includes switching tubes SB1 and SB2 connected in series, the lower arm includes switching tubes SB3 and SB4 connected in series. An inductor L2 is connected in series between the series connection point M2 of switching tubes SB2 and SB3 and the AC port B. A diode DB1 is connected in series between the series connection point of switching tubes SB1 and SB2 and the series connection point of the two capacitors C1 and C2. A diode DB2 is connected in series between the series connection point of switching tubes SB3 and SB4 and the series connection point of the two capacitors C1 and C2; the upper arm of arm LC includes switching tubes SC1 and SC2 connected in series, the lower arm includes switching tubes SC3 and SC4 connected in series. An inductor L3 is connected in series between the series connection point M3 of switching tubes SC2 and SC3 and the AC port C. A diode DC1 is connected in series between the series connection point of switching tubes SC1 and SC2 and the series connection point of the two capacitors C1 and C2. A diode DC2 is connected in series between the series connection point of switching tubes SC3 and SC4 and the series connection point of the two capacitors C1 and C2; the upper arm of arm LN includes switching tubes SN1 and SN2 connected in series, the lower arm includes switching tubes SN3 and SN4 connected in series. An inductor L4 is connected in series between the series connection point M3 of switching tubes SN2 and SN3 and the AC port N. A diode DN1 is connected in series between the series connection point of switching tubes SN1 and SN2 and the series connection point of the two capacitors C1 and C2. A diode DN2 is connected in series between the series connection point of switching tubes SN3 and SN4 and the series connection point of the two capacitors C1 and C2.

[0042] Referring to Figure 8, in some other embodiments of the present application, the circuit topology of a single arm of the PCS may specifically adopt an active three-level topology. Specifically, the upper arm of each arm of the PCS may include two series-connected switching tubes, and the lower arm may include two series-connected switching tubes. The series connection point of the upper arm and the lower arm, i.e., the midpoint of the arm, is connected to an AC port after being series-connected with an inductor. Moreover, each arm may further include two clamping switching tubes for clamping the midpoint. One clamping switching tube is connected between the series connection point of two capacitors C1 and C2 and the series connection point of the two switching tubes of the upper arm, i.e., the midpoint of the upper arm, and the other clamping switching tube is connected between the series connection point of two capacitors C1 and C2 and the series connection point of the two switching tubes of the lower arm, i.e., the midpoint of the lower arm.

[0043] Exemplarily, the upper arm of arm LA includes series-connected switching tubes SA1 and SA2, the lower arm includes series-connected switching tubes SA3 and SA4. An inductor L1 is series-connected between the series connection point M1 of switching tubes SA2 and SA3 and the AC port A. A clamping switching tube SA5 is series-connected between the series connection point of switching tubes SA1 and SA2 and the series connection point of two capacitors C1 and C2. A clamping switching tube SA6 is series-connected between the series connection point of switching tubes SA3 and SA4 and the series connection point of two capacitors C1 and C2; the upper arm of arm LB includes series-connected switching tubes SB1 and SB2, the lower arm includes series-connected switching tubes SB3 and SB4. An inductor L2 is series-connected between the series connection point M2 of switching tubes SB2 and SB3 and the AC port B. A clamping switching tube SB5 is series-connected between the series connection point of switching tubes SB1 and SB2 and the series connection point of two capacitors C1 and C2. A clamping switching tube SB6 is series-connected between the series connection point of switching tubes SB3 and SB4 and the series connection point of two capacitors C1 and C2; the upper arm of arm LC includes series-connected switching tubes SC1 and SC2, the lower arm includes series-connected switching tubes SC3 and SC4. An inductor L3 is series-connected between the series connection point M3 of switching tubes SC2 and SC3 and the AC port C. A clamping switching tube SC5 is series-connected between the series connection point of switching tubes SC1 and SC2 and the series connection point of two capacitors C1 and C2. A clamping switching tube SC6 is series-connected between the series connection point of switching tubes SC3 and SC4 and the series connection point of two capacitors C1 and C2; the upper arm of arm LN includes series-connected switching tubes SN1 and SN2, the lower arm includes series-connected switching tubes SN3 and SN4. An inductor L4 is series-connected between the series connection point M3 of switching tubes SN2 and SN3 and the AC port N. A clamping switching tube SN5 is series-connected between the series connection point of switching tubes SN1 and SN2 and the series connection point of two capacitors C1 and C2. A clamping switching tube SN6 is series-connected between the series connection point of switching tubes SN3 and SN4 and the series connection point of two capacitors C1 and C2.

[0044] In this application, the switching tubes included in the PCS may specifically be metal-oxide-semiconductor field-effect transistors (MOSFETs), or insulated gate bipolar transistors (IGBTs), or gallium nitride (GaN) high electron mobility transistors (HEMTs), etc.

[0045] In this application, when the power grid is connected to the AC port of the PCS, the PCS detects the phase of the connected power grid and controls the conduction or cut-off of the switching tubes included in the bridge arms connected to the two AC ports of the connected power grid according to the set power through a phase-locked loop. Exemplarily, when the detected phase of the connected power grid is 0 - 180°, the controller may control the switching tubes of the upper bridge arm of the bridge arms connected to the two AC ports of the connected power grid to conduct. When the phase of the connected power grid is 180° - 360°, the controller may control the switching tubes of the lower bridge arm of the bridge arms connected to the two AC ports of the connected power grid to conduct, so as to charge the energy storage system through the conducting switching tubes.

[0046] In some embodiments of this application, when the circuit topology of a single bridge arm of the PCS specifically adopts a T-type three-level topology, the controller may also control the two switching tubes of the cross bridge arm of the bridge arms connected to the two AC ports of the connected power grid to conduct alternately, so as to charge the energy storage system through the conducting switching tubes.

[0047] In some embodiments of this application, when the circuit topology of a single bridge arm of the PCS specifically adopts an active three-level topology, the controller may also control the two clamping switching tubes of the bridge arms connected to the two AC ports of the connected power grid to conduct alternately, so as to charge the energy storage system through the conducting switching tubes.

[0048] Exemplarily, referring to Figure 5 , when a single-phase power grid is connected to the AC ports A and N of the PCS, the PCS detects the phase of the L-phase line of the power grid and locks the phase of the power grid. When the detected phase of the L-phase line is 0 - 180°, the switching tube SA1 in the bridge arm LA of the controller conducts, and SA3 and SA4 conduct alternately. The switching tube SN1 in the bridge arm LN conducts, and SN3 and SN4 conduct alternately. When the phase of the connected L-phase line is 180° - 360°, the switching tube SA2 in the bridge arm LA of the controller conducts, and SA3 and SA4 conduct alternately. The switching tube SN2 in the bridge arm LN conducts, and SN3 and SN4 conduct alternately, so as to charge the energy storage system through the conducting switching tubes. And all the switching tubes in the bridge arm LB and the bridge arm LC are in the cut-off state.

[0049] Exemplarily, referring to Figure 6 , when the AB phase lines of a three-phase power grid are respectively connected to the AC ports A and B of the PCS, the PCS detects the phases of the A-phase line and the B-phase line of the power grid. When the phase difference between the A-phase line and the B-phase line is detected to be 0 - 180°, the switch SA1 in the controller arm LA is turned on and SA3 and SA4 are alternately turned on, and the switch SB1 in the controller arm LB is turned on and SB3 and SB4 are alternately turned on; when the phase difference between the A-phase line and the B-phase line is detected to be 180° - 360°, the switch SA2 in the controller arm LA is turned on and SA3 and SA4 are alternately turned on, and the switch SB2 in the controller arm LB is turned on and SB3 and SB4 are alternately turned on, so as to charge the energy storage system through the turned-on switches. And all the switches in the controller arm LC and the controller arm LN are in the off state.

[0050] Referring to Figure 9 , in some other embodiments of the present application, the energy storage system may further include a DC converter DCDC disposed between the DC port of the PCS and the DC bus, and the DCDC is used to perform voltage conversion on the direct current of the DC bus.

[0051] Based on the same inventive concept, an embodiment of the present application further provides a method for charging an energy storage system, including the following steps:

[0052] When it is detected that two of the four AC ports of the PCS are connected to the power grid, control the switches included in the arms connected to the other two AC ports to be turned off, that is, the arms connected to the other two AC ports are turned off, and the other two AC ports are the two AC ports among the four AC ports that are not connected to the power grid. And control the switches included in the arms connected to the two AC ports connected to the power grid to be turned on or off, that is, the arms connected to the two AC ports connected to the power grid work, so that the energy storage system forms a current loop with the power grid through the turned-on arms to charge the energy storage system. Wherein, the energy storage system includes: a battery pack, a DC bus, and a PCS, and the battery pack is connected to the DC bus. The PCS includes: four parallel arms and four AC ports, both ends of each arm are connected to the DC bus, the midpoint of each arm is connected in series with an inductor and then respectively connected to one of the four AC ports, and the four AC ports are used to connect to the power grid.

[0053] In the power replenishment method of the present application, when two AC ports are connected to the power grid, the bridge arms connected to the two AC ports connected to the power grid can be controlled to operate, that is, the PCS is controlled to operate to replenish the energy storage system. Moreover, when three phase lines of a three-phase power grid are connected to three of the four AC ports, and when three phase lines and the neutral line of a three-phase four-wire system (or three-phase five-wire system) are connected to the four AC ports, the PCS can also operate to replenish the energy storage system, enabling the energy storage system to be replenished when connected to a power grid of any system. Therefore, the adaptability of power replenishment of the energy storage system can be improved. Specifically, the two AC ports of the PCS can be connected to the L phase line and the neutral line of a single-phase power grid. When the three-phase power grid includes a neutral line, the two AC ports of the PCS can also be connected to any one phase line and the neutral line in the three-phase power grid, that is, the two AC ports of the PCS are connected to the AN line or the BN line or the CN line. Alternatively, the two AC ports of the PCS can also be connected to any two phase lines in the three-phase power grid, that is, the AB phase line or the BC phase line or the CA phase line. Therefore, in the power replenishment method provided by the present application, the operation of the PCS is not subject to the requirements of the power grid system, and the adaptability of power replenishment of the energy storage system can be improved.

[0054] In the present application, when the power grid is connected to the AC port of the PCS, the PCS detects the phase of the connected power grid and controls the on or off of the switching tubes included in the bridge arms connected to the two AC ports connected to the power grid according to the set power through a phase-locked loop. Exemplarily, when the detected phase of the connected power grid is 0-180°, the switching tubes of the upper bridge arm of the bridge arms connected to the two AC ports connected to the power grid can be controlled to conduct, and when the phase of the connected power grid is 180°-360°, the switching tubes of the lower bridge arm of the bridge arms connected to the two AC ports connected to the power grid can be controlled to conduct, so as to replenish the energy storage system through the conducting switching tubes.

[0055] In some embodiments of the present application, when the circuit topology of a single bridge arm of the PCS specifically adopts a T-type three-level topology, the two switching tubes of the cross bridge arm of the bridge arms connected to the two AC ports connected to the power grid can also be controlled to conduct alternately, so as to replenish the energy storage system through the conducting switching tubes.

[0056] In some embodiments of the present application, when the circuit topology of a single bridge arm of the PCS specifically adopts an active three-level topology, the controller can also control the two clamping switching tubes of the bridge arms connected to the two AC ports connected to the power grid to conduct alternately, so as to replenish the energy storage system through the conducting switching tubes.

[0057] In the above-mentioned PCS, energy storage system and its power replenishment method provided by the present application, four parallel-connected bridge arms are arranged in the PCS. The midpoints of the four bridge arms are respectively connected in series with inductors and then to four AC ports, and the four AC ports are used to connect to the power grid. In this way, when two of the four AC ports are connected to the power grid, by controlling the operation of the bridge arms connected to the two AC ports connected to the power grid, the operation of the PCS can be controlled to replenish power to the energy storage system. Moreover, when three of the four AC ports are connected to three phase lines of a three-phase power grid, and when the four AC ports are connected to three phase lines and the neutral line of a three-phase four-wire system (or three-phase five-wire system), the PCS can also operate to replenish power to the energy storage system, enabling the energy storage system to replenish power when connected to any type of power grid, thus improving the adaptability of the energy storage system for power replenishment.

[0058] As described above, the above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A power conversion system (PCS) for energy storage, characterized in that, Comprising: Four parallel bridge arms, four AC ports, and a controller. Both ends of each of the bridge arms are used to connect to the DC bus of the energy storage system. The midpoint of each of the bridge arms is connected to one of the four AC ports after being serially connected with an inductor. The four AC ports are used to connect to the power grid. The controller is configured to: when detecting that two of the four AC ports are connected to the power grid, control the switching tubes included in the bridge arms connected to the two AC ports connected to the power grid to conduct or turn off, and control the switching tubes included in the other two bridge arms connected to the AC ports to turn off, so as to charge the energy storage system. The other two AC ports are the two AC ports among the four AC ports that are not connected to the power grid.

2. The PCS according to claim 1, wherein Each of the bridge arms includes an upper bridge arm and a lower bridge arm connected in series. Both the upper bridge arm and the lower bridge arm include switching tubes. The controller is further configured to: when the phase of the connected power grid is 0 - 180°, control the switching tube of the upper bridge arm in the bridge arm connected to the two AC ports connected to the power grid to conduct, and the switching tube of the lower bridge arm to turn off; when the phase of the connected power grid is 180° - 360°, control the switching tube of the lower bridge arm in the bridge arm connected to the two AC ports connected to the power grid to conduct, and the switching tube of the upper bridge arm to turn off.

3. The PCS according to claim 2, wherein The PCS further includes two capacitors connected in series, and the two capacitors connected in series are arranged in parallel with the bridge arms. Each of the bridge arms further includes a cross bridge arm. One end of the cross bridge arm is connected to the series connection point of the upper bridge arm and the lower bridge arm, and the other end of the cross bridge arm is connected to the series connection point of the two capacitors. The cross bridge arm includes two switching tubes connected in series. The controller is further configured to: control the two switching tubes connected in series in the cross bridge arm of the bridge arm connected to the two AC ports connected to the power grid to conduct alternately.

4. The PCS according to claim 2, wherein, The PCS further includes two capacitors connected in series, and the two capacitors connected in series are arranged in parallel with the bridge arms. The upper bridge arm of each of the bridge arms includes two switching tubes connected in series, and the lower bridge arm of each of the bridge arms includes two switching tubes connected in series. Each of the bridge arms further includes two diodes. One diode is connected between the series connection point of the two capacitors and the midpoint of the upper bridge arm, and the other diode is connected between the series connection point of the two capacitors and the midpoint of the lower bridge arm.

5. The PCS according to claim 2, wherein The PCS further includes two capacitors connected in series, and the two capacitors connected in series are arranged in parallel with the bridge arms. The upper bridge arm of each of the bridge arms includes two switching tubes connected in series, and the lower bridge arm of each of the bridge arms includes two switching tubes connected in series. Each of the bridge arms further includes two clamping switching tubes. One clamping switching tube is connected between the series connection point of the two capacitors and the midpoint of the upper bridge arm, and the other clamping switching tube is connected between the series connection point of the two capacitors and the midpoint of the lower bridge arm. The controller is further configured to: control the two clamping switching tubes in the bridge arm connected to the two AC ports connected to the power grid to conduct alternately.

6. The PCS according to any one of claims 1-5, characterized in that, Two of the four AC ports are connected to the phase line and neutral line of a single-phase power grid, or connected to any one phase line and the neutral line in a three-phase power grid, or connected to any two phase lines in a three-phase power grid.

7. A energy storage system, characterized in that, Comprising: A battery pack, a DC bus, and a PCS as described in any one of claims 1-6, the DC port of the PCS is connected to the DC bus, the battery pack is connected to the DC bus, and the PCS is used to charge the battery pack when the two AC ports are connected to the power grid.

8. The energy storage system according to claim 7, wherein, Further comprising: A DC converter, the DC converter is connected between the DC bus and the DC port of the PCS.

9. A method for charging a energy storage system, characterized in that Comprising: When it is detected that two of the four AC ports of the PCS are connected to the power grid, control the switching tubes included in the arm connected to the two AC ports connected to the power grid to turn on or off, and control the switching tubes included in the arm connected to the other two AC ports to turn off, so as to charge the energy storage system.

10. The supplementary power supply method according to claim 9, characterized in that, The energy storage system includes: a battery pack, a DC bus, and the PCS, the battery pack is connected to the DC bus; The PCS includes: four parallel arms and the four AC ports, both ends of each arm are connected to the DC bus, the midpoint of each arm is connected to one of the four AC ports respectively after being serially connected with an inductor, and the four AC ports are used to connect to the power grid.

11. The supplementary power supply method according to claim 9 or 10, characterized in that, Further comprising: When the phase of the connected power grid is 0-180°, control the switching tube of the upper arm of the arm connected to the two AC ports connected to the power grid to turn on, and the switching tube of the lower arm to turn off; When the phase of the connected power grid is 180°-360°, control the switching tube of the lower arm of the arm connected to the two AC ports connected to the power grid to turn on, and the switching tube of the upper arm to turn off.

12. The supplementary power method according to claim 11, wherein, Further comprising: Control the two serially connected switching tubes of the cross arm of the arm connected to the two AC ports connected to the power grid to alternately turn on, wherein one end of the cross arm is connected to the series connection point of the upper arm and the lower arm, the other end of the cross arm is connected to the series connection point of the two capacitors, and the two capacitors are arranged in parallel with the arm.

13. The supplementary power method according to claim 11, wherein Further comprising: Control the two clamping switching tubes of the arm connected to the two AC ports connected to the power grid to alternately turn on, one clamping switching tube is connected between the series connection point of the two capacitors and the midpoint of the upper arm, and the other clamping switching tube is connected between the series connection point of the two capacitors and the midpoint of the lower arm, and the two capacitors are arranged in parallel with the arm.

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