Household energy storage system and charging and discharging control method thereof

Abstract

The invention provides a household energy storage system and a charging and discharging control method thereof, and belongs to the field of energy storage, the household energy storage system comprises a battery system and an energy storage converter PCS, the battery system comprises a battery cluster, a heating film and a battery management system BMS, the battery cluster is connected to a power grid through the energy storage converter PCS, and the energy storage converter PCS is used for controlling the charging and discharging process of the battery cluster. The heating film is located on the periphery of the battery cluster and connected to the direct current side of the PCS, and the BMS is in communication connection with the PCS and used for managing and controlling the battery cluster; a heating film is arranged in the battery system, the heating film is located on the periphery of the battery cluster and connected to the direct current side of the PCS, when the energy storage system is in a grid-connected charging mode, the PCS operates in an SVG mode and is connected with the heating film, the battery cell is heated at the low temperature, and the low-temperature charging problem of the energy storage system is solved; and a heating source is not from the outside of the system and is not from a battery system, so that the heating flexibility, reliability and working efficiency of the household energy storage system are improved.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, and in particular to a household energy storage system and a charging and discharging control method thereof. Background Art

[0002] With the vigorous promotion of renewable energy, the continuous implementation of encouraging policies, the continuous increase in the installed capacity of household photovoltaic systems, as well as factors such as rising energy prices, high residential electricity prices and increasing differences in peak and valley electricity prices, household energy storage system products have ushered in an explosion worldwide; household energy storage systems are mainly composed of energy storage inverter management systems, energy storage battery systems and other electrical equipment. Among them, the energy storage inverter management system includes the energy storage inverter PCS (Power Conversion System) and the energy management system EMS (Energy Storage System), and the energy storage battery system includes battery modules (cells) and the battery management system BMS (Battery Management System). Battery modules usually use lithium batteries. Due to the poor low-temperature performance of lithium batteries and the wide ambient temperature range of household energy storage systems, a heating device is required to heat the battery modules to ensure that they operate within the adaptive temperature range. The existing heating devices of household energy storage systems are mostly heating films, PTC heaters, air conditioning heating, etc. The heating sources are mostly external power supply or battery system power supply. The battery system power supply consumes battery energy, which will reduce the efficiency of the energy storage system. When the power is externally powered, the heating source is independent of the energy storage system, and the heating of the battery cell is not flexible enough. Therefore, how to achieve heating of the battery cell in the energy storage battery system at low temperature, where the heating source does not come from the outside of the system and does not come from the battery system, has become a problem that needs to be solved urgently.

[0003] In the prior art, in the Chinese invention patent application entitled "An Energy Storage System and Its Battery Heating Method" with publication number CN114400388A, when the temperature of the battery cell is lower than a preset temperature, the corresponding DC / DC conversion circuit is controlled to discharge the electric energy of the battery cell to the DC bus at a preset frequency to achieve heating of the battery cell itself. Since the heat comes from inside the battery cell, there is a problem of consuming battery energy and thus reducing the efficiency of the energy storage system. Summary of the invention

[0004] The technical problem to be solved by the present invention is how to achieve heating of the battery cells in the energy storage battery system at low temperatures, wherein the heating source does not come from outside the system and does not come from the battery system.

[0005] The present invention solves the above technical problems through the following technical solutions: a household energy storage system, including a battery system and an energy storage inverter PCS, wherein the battery system includes a battery cluster, a heating film and a battery management system BMS, the battery cluster is connected to a power grid through the energy storage inverter PCS, the energy storage inverter PCS is used to control the charging and discharging process of the battery cluster, the heating film is located outside the battery cluster and connected to the DC side of the energy storage inverter PCS, and the battery management system BMS is communicatively connected to the energy storage inverter PCS for managing and controlling the battery cluster.

[0006] Beneficial effect: A heating film is provided in the battery system of the present invention. The heating film is located on the periphery of the battery cluster and connected to the DC side of the energy storage inverter PCS. When the energy storage system is in the grid-connected charging mode, the energy storage inverter PCS can operate in the SVG mode and connect the heating film to achieve heating of the battery cells in the energy storage battery system at low temperatures, thereby solving the problem of low-temperature charging of the energy storage system. The heating source comes from the DC side of the energy storage inverter PCS, not from the outside of the system and not from the battery system, thereby improving the flexibility, reliability and work efficiency of heating the household energy storage system.

[0007] Preferably, the household energy storage system also includes relays KM1-KM4, relay KM7, capacitor C, a first pre-charging circuit and a second pre-charging circuit, one end of the battery cluster is connected to one end of the relay KM1, the other end of the battery cluster is connected to one end of the relay KM2, the other end of the relay KM1 is connected to one end of the relay KM3 and one end of the first pre-charging circuit, the other end of the relay KM3 is connected to the other end of the first pre-charging circuit and then connected to one end of the DC side of the energy storage inverter PCS and one end of the capacitor C, the other end of the relay KM2 is connected to one end of the relay KM4 and one end of the second pre-charging circuit, the other end of the relay KM4 is connected to the other end of the second pre-charging circuit and then connected to the other end of the DC side of the energy storage inverter PCS and the other end of the capacitor C, one end of the heating film is connected to one end of the relay KM7, the other end of the relay KM7 is connected to the other end of the relay KM1, the other end of the heating film is connected to one end of the relay KM2, and the AC side of the energy storage inverter PCS is connected to the power grid.

[0008] Beneficial effect: By setting a pre-charging circuit, when the energy storage converter PCS detects that the battery side voltage is within the starting voltage range of the energy storage converter PCS, the pre-charging circuit is closed, and the energy storage converter PCS bus is pre-charged first, which can ensure that the voltage difference between the output side voltage of the battery system and the DC side voltage of the energy storage converter PCS is within a safe range.

[0009] Preferably, the first pre-charging circuit includes a resistor R1 and a relay KM5, the resistor R1 and the relay KM5 are connected in series and then connected in parallel at both ends of the relay KM3, and the second pre-charging circuit includes a resistor R2 and a relay KM6, the resistor R2 and the relay KM6 are connected in series and then connected in parallel at both ends of the relay KM4.

[0010] Preferably, the household energy storage system also includes fuse FUSE1, fuse FUSE2, and circuit breaker QF1. One end of the battery cluster is connected to one end of the relay KM1 through fuse FUSE1, and the other end of the battery cluster is connected to one end of the relay KM2 through fuse FUSE2. The AC side of the energy storage inverter PCS is connected to the power grid through circuit breaker QF1.

[0011] Preferably, the battery management system BMS is connected to the energy storage converter PCS via CAN or RS485 communication.

[0012] The present invention also provides a charge and discharge control method for a household energy storage system. Based on the household energy storage system, the method includes: when the operation mode of the energy storage system is a grid-connected charging mode, the battery management system BMS determines whether the current minimum battery cell temperature T1 is less than or equal to the battery cell minimum heating temperature setting value T0. If so, the battery management system BMS sends a heating request to the energy storage converter PCS, the energy storage converter PCS enters the SVG operation mode, and the DC side of the energy storage converter PCS is connected to a heating film to heat the battery cluster. During the heating process, the battery management system BMS cyclically detects the current minimum battery cell temperature T1. If the current minimum battery cell temperature T1 ≥ the battery cell minimum heating temperature setting value T0 + ΔT3, ΔT3 is the hysteresis temperature, the heating is stopped, and the battery cluster is connected after a set delay time. The energy storage system is in a grid-connected charging mode, and the battery management system BMS cyclically detects the current minimum battery cell temperature T1. When it is detected that the current minimum battery cell temperature T1 has a decreasing trend, the DC side of the energy storage converter PCS is connected to a heating film to heat the battery cluster; if not, the energy storage system operates according to the issued operation mode and power.

[0013] Beneficial effect: The battery management system BMS of the present invention determines whether the operation mode of the energy storage system is the grid-connected charging mode. If and only if the operation mode of the energy storage system is the grid-connected charging mode, the battery management system BMS further reads the current lowest temperature T1 of the battery cell in the battery cluster and decides whether the battery cluster needs to be heated. Compared with the method of directly heating the battery without distinguishing the operation mode of the energy storage system, the present invention can reduce the operation risks and costs caused by frequent heating according to the operation mode of the energy storage system, and ensure the safety of heating the battery cells.

[0014] Preferably, when the energy storage inverter PCS enters the SVG operation mode, the battery management system BMS controls relay KM1 to disconnect, and relay KM2 and relay KM7 to close. After the energy storage inverter PCS receives the heating request from the battery management system BMS, the energy storage inverter PCS controls relay KM3 and relay KM4 to close, and heats the heating film according to the voltage and power requested by the battery management system BMS.

[0015] Beneficial effect: When heating starts, the battery cluster is not connected and the energy storage inverter PCS is in SVG operation mode. At this time, the DC side of the energy storage inverter PCS connects the heating film to heat the battery cluster, and the battery system is electrically isolated from the heating circuit to ensure the safety of the battery system.

[0016] Preferably, when the current minimum temperature of the battery cell T1 ≥ the minimum heating temperature setting value of the battery cell T0 + ΔT3, the battery management system BMS sends a stop heating request to the energy storage inverter PCS, and the battery management system BMS controls relay KM2 and relay KM7 to disconnect. After receiving the stop heating request from the battery management system BMS, the energy storage inverter PCS shuts down and controls relay KM3 and relay KM4 to disconnect. After a set delay time, the battery management system BMS controls relay KM1 and relay KM2 to close. When the energy storage inverter PCS detects that the battery side voltage is within the starting voltage range of the energy storage inverter PCS, it controls relay KM5 and relay KM6 to close, and pre-charges the energy storage inverter PCS bus. After the pre-charging is completed, the energy storage inverter PCS controls relay KM3 and relay KM4 to close, and controls relay KM5 and relay KM6 to disconnect. At this time, the energy storage system operates according to the charging power sent by the upper computer.

[0017] Beneficial effect: When the energy storage converter PCS detects that the battery side voltage is within the starting voltage range of the energy storage converter PCS, relays KM5 and KM6 are closed, and the energy storage converter PCS bus is pre-charged first to ensure that the voltage difference between the battery system output side voltage and the energy storage converter PCS DC side voltage is within a safe range.

[0018] Preferably, the energy storage system is in the grid-connected charging mode, and the battery management system BMS cyclically detects the current minimum battery cell temperature T1, and determines whether the current minimum battery cell temperature T1 is greater than the battery cell minimum heating temperature setting value T0+ΔT4, ΔT4 is the hysteresis temperature, and ΔT4 is less than ΔT3. If not, the battery management system BMS sends a heating request to the energy storage inverter PCS, the energy storage inverter PCS adjusts the output power, and the DC side of the energy storage inverter PCS connects to the heating film to heat the battery cluster until the current minimum battery cell temperature T1 ≥ the battery cell minimum heating temperature setting value T0+ΔT3, and stops heating. If so, the energy storage system operates at the original charging power.

[0019] Beneficial effect: When the energy storage system is in grid-connected charging mode, the battery management system BMS cyclically detects the current minimum temperature T1 of the battery cell. When it is detected that the battery cell temperature has a decreasing trend, the output power of the energy storage inverter PCS is adjusted to meet the normal operation of the energy storage system.

[0020] Preferably, when the current cell minimum temperature T1 ≤ the cell minimum heating temperature setting value T0 + ΔT4, the battery management system BMS controls the relay KM7 to close and sends a heating request to the energy storage converter PCS, together with the heating power. After receiving the heating request, the energy storage converter PCS adjusts the output power P 总 Until the current minimum cell temperature T1 ≥ the minimum cell heating temperature setting value T0 + ΔT3, the battery management system BMS sends a stop heating request to the energy storage converter PCS and controls the relay KM7 to disconnect. After receiving the stop heating request from the battery management system BMS, the energy storage converter PCS adjusts the output power. At this time, the output power of the energy storage converter PCS is the power sent by the host computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of a household energy storage system provided by an embodiment of the present invention;

[0022] Figure 2 A flow chart of a charge and discharge control method for a household energy storage system provided by an embodiment of the present invention;

[0023] Figure 3 Another flow chart of the charge and discharge control method of the household energy storage system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the technical solution of the present invention is clearly and completely described below in combination with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] like Figure 1As shown, this embodiment provides a household energy storage system, including a battery system, an energy storage converter PCS, relays KM1-KM4, relay KM7, capacitor C, a first pre-charging circuit and a second pre-charging circuit. The battery system includes a battery cluster, a heating film and a battery management system BMS. One end of the battery cluster is connected to one end of the relay KM1, and the other end of the battery cluster is connected to one end of the relay KM2. The other end of the relay KM1 is connected to one end of the relay KM3 and one end of the first pre-charging circuit. The other end of the relay KM3 is connected to the other end of the first pre-charging circuit and then connected to one end of the DC side of the energy storage converter PCS and one end of the capacitor C. The relay The other end of KM2 is connected to one end of relay KM4 and one end of the second pre-charging circuit. The other end of relay KM4 is connected to the other end of the second pre-charging circuit and then connected to the other end of the DC side of the energy storage inverter PCS and the other end of the capacitor C. One end of the heating film is connected to one end of relay KM7. The other end of relay KM7 is connected to the other end of relay KM1. The other end of the heating film is connected to one end of relay KM2. The AC side of the energy storage inverter PCS is connected to the power grid. The energy storage inverter PCS is used to control the charging and discharging process of the battery cluster. The battery management system BMS is communicated with the energy storage inverter PCS for managing and controlling the battery cluster.

[0026] The battery system of the present invention is provided with a heating film, which is located at the periphery of the battery cluster and connected to the DC side of the energy storage inverter PCS. When the energy storage system is in the grid-connected charging mode, the energy storage inverter PCS can operate in the SVG mode and turn on the heating film to achieve heating of the battery cells in the energy storage battery system at low temperatures, thereby solving the low-temperature charging problem of the energy storage system. The heating source does not come from outside the system and does not come from the battery system, thereby improving the flexibility, reliability and working efficiency of heating the household energy storage system.

[0027] The SVG operation mode in the present invention means that when there is no DC voltage access on the DC side of the energy storage converter PCS, and the grid side voltage is within a certain voltage range, it can be rectified to generate a DC voltage, and the DC side of the energy storage converter PCS can provide stable voltage and power to the load.

[0028] The first pre-charging circuit includes a resistor R1 and a relay KM5. The resistor R1 and the relay KM5 are connected in series and then connected in parallel to both ends of the relay KM3. Figure 1 As shown, one end of the resistor R1 is connected to one end of the relay KM3, the other end of the resistor R1 is connected to one end of the relay KM5, and the other end of the relay KM5 is connected to the other end of the relay KM3. The second pre-charging circuit includes a resistor R2 and a relay KM6. The resistor R2 and the relay KM6 are connected in series and then connected in parallel to the two ends of the relay KM4. Figure 1As shown, one end of the resistor R2 is connected to one end of the relay KM4, the other end of the resistor R2 is connected to one end of the relay KM6, and the other end of the relay KM6 is connected to the other end of the relay KM4.

[0029] By setting up a pre-charging circuit, when the energy storage converter PCS detects that the battery side voltage is within the starting voltage range of the energy storage converter PCS, relays KM5 and KM6 are closed, and the energy storage converter PCS bus is pre-charged first, which can ensure that the voltage difference between the battery system output side voltage and the energy storage converter PCS DC side voltage is within a safe range.

[0030] It also includes fuse FUSE1, fuse FUSE2, and circuit breaker QF1. One end of the battery cluster is connected to one end of the relay KM1 through fuse FUSE1, and the other end of the battery cluster is connected to one end of the relay KM2 through fuse FUSE2. The AC side of the energy storage converter PCS is connected to the power grid through circuit breaker QF1. The battery cluster includes a number of battery packs connected in series or in parallel.

[0031] The battery management system BMS is connected to the energy storage converter PCS via CAN or RS485 communication.

[0032] The battery system is located in a high-voltage box, which has two power lines, namely the positive output side HV+ and the negative output side HV-. The positive pole BAT+ of the battery cluster is connected to the positive output side HV+, the negative pole BAT- of the battery cluster is connected to the negative output side HV-, the positive pole of the DC side of the energy storage inverter PCS is connected to the positive output side HV+, and the negative pole of the DC side of the energy storage inverter PCS is connected to the negative output side HV-.

[0033] like Figure 2 and 3 As shown, this embodiment provides a charging and discharging control method for a household energy storage system, including:

[0034] Step 1: The energy storage converter PCS reads the energy storage system operation mode and sends the energy storage system operation mode to the battery management system BMS;

[0035] Step 2: The battery management system BMS determines whether the energy storage system operation mode is the grid-connected charging mode. If so, the battery management system BMS reads the current minimum temperature T1 of the battery cell in the battery cluster and proceeds to step 3. If not, the energy storage system operates according to the issued operation mode and power.

[0036] Step 3: The battery management system BMS determines whether the current minimum battery cell temperature T1 is less than or equal to the battery cell minimum heating temperature setting value T0. If so, the battery management system BMS sends a heating request to the energy storage converter PCS, and the energy storage converter PCS enters the SVG operation mode. The DC side of the energy storage converter PCS connects to the heating film to heat the battery cluster. During the heating process, the battery management system BMS cyclically detects the current minimum battery cell temperature T1. If the current minimum battery cell temperature T1 ≥ the battery cell minimum heating temperature setting value T0 + ΔT3, the heating is stopped, and the battery cluster is connected after a delay of the set time, and the energy storage system is in the grid-connected charging mode; if not, the energy storage system operates according to the issued operation mode and power;

[0037] In step three, when the current minimum temperature of the battery cell T1 ≤ the minimum heating temperature setting value T0 of the battery cell, the battery cluster needs to be heated first so that the battery system can work normally in the grid-connected charging mode. The battery management system BMS sends a heating request message to the energy storage inverter PCS, together with the heating voltage and heating power. The battery management system BMS controls relay KM1 to disconnect, and relay KM2 and relay KM7 to close. After the energy storage inverter PCS receives the heating request from the battery management system BMS, the energy storage inverter PCS controls relay KM3 and relay KM4 to close, and heats the heating film according to the voltage and power requested by the battery management system BMS to provide energy.

[0038] When the current minimum cell temperature T1 ≥ the minimum cell heating temperature setting value T0 + ΔT3, the battery management system BMS sends a stop heating request to the energy storage converter PCS. The battery management system BMS controls relays KM2 and KM7 to disconnect and stop heating. After receiving the stop heating request from the battery management system BMS, the energy storage converter PCS shuts down and controls relays KM3 and KM4 to disconnect. After the set delay time, the battery management system BMS controls relays KM1 and KM2 to close. When the energy storage converter PCS detects that the battery side voltage is within the starting voltage range of the energy storage converter PCS, it controls relays KM5 and KM6 to close and pre-charges the busbar of the energy storage converter PCS. After the pre-charging is completed, the energy storage converter PCS controls relays KM3 and KM4 to close and controls relays KM5 and KM6 to disconnect. At this time, the energy storage system operates according to the charging power sent by the host computer.

[0039] Step 4: When the energy storage system is in the grid-connected charging mode, the battery management system BMS cyclically detects the current minimum battery cell temperature T1 and determines whether the current minimum battery cell temperature T1 is greater than the battery cell minimum heating temperature setting value T0+ΔT4, ΔT3 and ΔT4 are both hysteresis temperatures, and ΔT4 is less than ΔT3. If not, the battery management system BMS sends a heating request to the energy storage inverter PCS, the energy storage inverter PCS adjusts the output power, and the DC side of the energy storage inverter PCS connects to the heating film to heat the battery cluster until the current minimum battery cell temperature T1 ≥ the battery cell minimum heating temperature setting value T0+ΔT3, then stops heating. If so, the energy storage system operates at the original charging power.

[0040] In step 4, when the battery management system BMS determines that the current minimum cell temperature T1 ≤ the minimum cell heating temperature setting value T0 + ΔT4, that is, the battery management system BMS detects that the current minimum cell temperature T1 has a decreasing trend, the battery management system BMS controls the relay KM7 to close, and sends a heating request to the energy storage converter PCS, along with the heating power. After receiving the heating request, the energy storage converter PCS adjusts the output power P 总 Until the current minimum cell temperature T1 ≥ the minimum cell heating temperature setting value T0 + ΔT3, the battery management system BMS sends a stop heating request to the energy storage converter PCS and controls the relay KM7 to disconnect. After receiving the stop heating request from the battery management system BMS, the energy storage converter PCS adjusts the output power. At this time, the output power of the energy storage converter PCS is the power sent by the host computer. Output power P 总 =P 充 +P 加 , where P 充 Charging power for the battery system, P 加 is the heating film power.

[0041] The operation modes of the energy storage system of the present invention include an off-grid mode and a grid-connected mode. The grid-connected mode includes a grid-connected charging mode and a grid-connected discharging mode. When the grid side of the energy storage system does not detect the grid voltage, the energy storage system can operate in the off-grid mode to supply power to important loads, or it can seamlessly switch from the grid-connected mode to the off-grid mode to supply power to important loads. When the energy storage system is operated in an off-grid mode, the cells in the battery cluster can only discharge externally, and the discharge temperature range of the cells is relatively wide, so there is no need to heat the cells. When the energy storage system is operated in a grid-connected discharge mode, the cells in the battery cluster discharge externally, and the temperature range of the cells during discharge is relatively wide, so there is no need to heat the cells. When the energy storage system is operated in a grid-connected charging mode, the temperature range of the cells in the battery cluster is relatively narrow, so the battery cluster needs to be heated. When the energy storage system is switched from a non-grid-connected mode to a grid-connected mode, the battery management system BMS of the present invention determines whether the operation mode of the energy storage system is a grid-connected charging mode. When and only when it is detected that the operation mode of the energy storage system is a grid-connected charging mode, the battery management system BMS further reads the current lowest temperature T1 of the cells in the battery cluster, and determines whether the battery cluster needs to be heated. Compared with a method of directly heating the battery without distinguishing the operation mode of the energy storage system, the present invention can reduce the operation risk and cost caused by frequent heating according to the operation mode of the energy storage system, and ensure the safety of heating the cells.

[0042] At the beginning of heating, the battery cluster is not connected, and the energy storage converter PCS is in SVG operation mode. At this time, the DC side of the energy storage converter PCS connects the heating film to heat the battery cluster. The battery system is electrically isolated from the heating circuit to ensure the safety of the battery system. During the heating process, the battery management system BMS cyclically detects the current minimum temperature T1 of the battery cell. If the current minimum temperature T1 of the battery cell is ≥ the minimum heating temperature setting value T0+ΔT3 of the battery cell, the heating is stopped, and the battery cluster is connected after a delay of the set time. The energy storage system is in grid-connected charging mode. In the grid-connected charging mode, the battery management system BMS cyclically detects the current minimum temperature T1 of the battery cell. When it is detected that the battery cell temperature has a downward trend, the output power of the energy storage converter PCS is adjusted to meet the normal operation of the energy storage system.

[0043] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A household energy storage system, characterized in that: It includes a battery system and an energy storage inverter PCS. The battery system includes a battery cluster, a heating film and a battery management system BMS. The battery cluster is connected to the power grid through the energy storage inverter PCS. The energy storage inverter PCS is used to control the charging and discharging process of the battery cluster. The heating film is located outside the battery cluster and connected to the DC side of the energy storage inverter PCS. The battery management system BMS is communicated with the energy storage inverter PCS for managing and controlling the battery cluster.

2. The household energy storage system according to claim 1, characterized in that: The household energy storage system also includes relays KM1-KM4, relay KM7, capacitor C, a first pre-charging circuit and a second pre-charging circuit. One end of the battery cluster is connected to one end of the relay KM1, and the other end of the battery cluster is connected to one end of the relay KM2. The other end of the relay KM1 is connected to one end of the relay KM3 and one end of the first pre-charging circuit. The other end of the relay KM3 is connected to the other end of the first pre-charging circuit and then connected to one end of the DC side of the energy storage inverter PCS and one end of the capacitor C. The other end of the relay KM2 is connected to one end of the relay KM4 and one end of the second pre-charging circuit. The other end of the relay KM4 is connected to the other end of the second pre-charging circuit and then connected to the other end of the DC side of the energy storage inverter PCS and the other end of the capacitor C. One end of the heating film is connected to one end of the relay KM7, and the other end of the relay KM7 is connected to the other end of the relay KM1. The other end of the heating film is connected to one end of the relay KM2. The AC side of the energy storage inverter PCS is connected to the power grid.

3. The household energy storage system according to claim 2, characterized in that: The first pre-charging circuit includes a resistor R1 and a relay KM5. The resistor R1 and the relay KM5 are connected in series and then connected in parallel at both ends of the relay KM3. The second pre-charging circuit includes a resistor R2 and a relay KM6. The resistor R2 and the relay KM6 are connected in series and then connected in parallel at both ends of the relay KM4.

4. The household energy storage system according to claim 2, characterized in that: The household energy storage system also includes fuse FUSE1, fuse FUSE2, and circuit breaker QF1. One end of the battery cluster is connected to one end of the relay KM1 through fuse FUSE1, and the other end of the battery cluster is connected to one end of the relay KM2 through fuse FUSE2. The AC side of the energy storage converter PCS is connected to the power grid through circuit breaker QF1.

5. The household energy storage system according to claim 1, characterized in that: The battery management system BMS is connected to the energy storage converter PCS via CAN or RS485 communication.

6. A charge and discharge control method for a household energy storage system, based on the household energy storage system according to any one of claims 1 to 5, characterized in that: The method includes: when the operation mode of the energy storage system is the grid-connected charging mode, the battery management system BMS determines whether the current lowest battery cell temperature T1 is less than or equal to the battery cell lowest heating temperature setting value T0. If so, the battery management system BMS sends a heating request to the energy storage converter PCS, the energy storage converter PCS enters the SVG operation mode, the DC side of the energy storage converter PCS connects the heating film to heat the battery cluster, and during the heating process, the battery management system BMS cyclically detects the current lowest battery cell temperature T1. If the current lowest battery cell temperature T1 is greater than or equal to the battery cell lowest heating temperature setting value T0+ΔT3, ΔT3 is the hysteresis temperature, the heating is stopped, and the battery cluster is connected after a set delay time. The energy storage system is in the grid-connected charging mode, and the battery management system BMS cyclically detects the current lowest battery cell temperature T1. When it is detected that the current lowest battery cell temperature T1 has a decreasing trend, the DC side of the energy storage converter PCS connects the heating film to heat the battery cluster; if not, the energy storage system operates according to the issued operation mode and power.

7. The charge and discharge control method of the household energy storage system according to claim 6, characterized in that: When the energy storage inverter PCS enters the SVG operation mode, the battery management system BMS controls relay KM1 to be disconnected, and relays KM2 and KM7 to be closed. After the energy storage inverter PCS receives the heating request from the battery management system BMS, the energy storage inverter PCS controls relays KM3 and KM4 to be closed, and heats the heating film according to the voltage and power requested by the battery management system BMS.

8. The charge and discharge control method of the household energy storage system according to claim 6, characterized in that: When the current minimum cell temperature T1 ≥ the cell minimum heating temperature setting value T0 + ΔT3, the battery management system BMS sends a heating stop request to the energy storage converter PCS, and the battery management system BMS controls relays KM2 and KM7 to disconnect. After receiving the heating stop request from the battery management system BMS, the energy storage converter PCS shuts down and controls relays KM3 and KM4 to disconnect. After the set delay time, the battery management system BMS controls relays KM1 and KM2 to close. When the energy storage converter PCS detects that the battery side voltage is within the starting voltage range of the energy storage converter PCS, it controls relays KM5 and KM6 to close and pre-charges the PCS busbar. After the pre-charging is completed, the energy storage converter PCS controls relays KM3 and KM4 to close, and controls relays KM5 and KM6 to disconnect. At this time, the energy storage system operates according to the charging power sent by the host computer.

9. The charge and discharge control method of the household energy storage system according to claim 6, characterized in that: When the energy storage system is in the grid-connected charging mode, the battery management system BMS cyclically detects the current minimum battery cell temperature T1 and determines whether the current minimum battery cell temperature T1 is greater than the battery cell minimum heating temperature setting value T0+ΔT4, ΔT4 is the hysteresis temperature, and ΔT4 is less than ΔT3. If not, the battery management system BMS sends a heating request to the energy storage inverter PCS, the energy storage inverter PCS adjusts the output power, and the DC side of the energy storage inverter PCS connects to the heating film to heat the battery cluster until the current minimum battery cell temperature T1 ≥ the battery cell minimum heating temperature setting value T0+ΔT3, then stops heating. If so, the energy storage system operates at the original charging power.

10. The charge and discharge control method of the household energy storage system according to claim 9, characterized in that: When the current minimum cell temperature T1 ≤ the minimum cell heating temperature setting value T0 + ΔT4, the battery management system BMS controls the relay KM7 to close and sends a heating request to the energy storage converter PCS, along with the heating power. After receiving the heating request, the energy storage converter PCS adjusts the output power P 总 Until the current minimum cell temperature T1 ≥ the minimum cell heating temperature setting value T0 + ΔT3, the battery management system BMS sends a stop heating request to the energy storage converter PCS and controls the relay KM7 to disconnect. After receiving the stop heating request from the battery management system BMS, the energy storage converter PCS adjusts the output power. At this time, the output power of the energy storage converter PCS is the power sent by the host computer.

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