An energy storage system

Abstract

The application discloses a kind of energy storage systems, comprising: controller, DC / AC conversion circuit, at least one battery unit and corresponding first transmission branch, battery heating circuit and first switch, each battery unit is sequentially connected DC bus of DC / AC conversion circuit by corresponding first switch and first transmission branch respectively, the power supply end of battery heating circuit is connected between first switch and corresponding first transmission branch, when the temperature of at least one battery unit is lower than preset temperature value, corresponding first transmission branch is controlled according to the high and low of DC bus voltage to DC bus voltage boost or buck to corresponding battery heating circuit power supply, to corresponding battery unit is heated.The power supply voltage of battery heating circuit in the application is DC bus voltage, so there is no phase voltage and line voltage connection wrong situation, thereby prolong the service life of battery heating circuit, facilitate the selection of electrical element.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically, to an energy storage system. Background Technology

[0002] The storage and conversion of clean energy is of great significance to solving global warming. Lithium-ion batteries have received extensive research and attention due to their advantages such as high power, high energy density, low self-discharge rate, no memory effect, long cycle life and environmental friendliness.

[0003] However, the external characteristics of lithium-ion power batteries are easily affected by ambient temperature, especially in low-temperature environments, where their capacity decreases. Charging at low temperatures not only fails to fully charge the battery but also damages it, reducing its lifespan and effective capacity. Therefore, in low-temperature environments, batteries need to be preheated before use to bring the battery core to its normal operating temperature range.

[0004] Traditional battery preheating methods typically draw power from the AC mains to power the battery heating circuit, which then uses logic to control the circuit and heat the battery. However, the power supply voltage from the AC mains is uncontrolled. In practice, users often connect the battery heating circuit from the AC phase voltage to the line voltage, causing a sharp increase in the heating power consumption. For example, if the phase voltage is 230V and the line voltage is 400V, and the heating resistor in the battery heating circuit is 200Ω, the heating power consumption will be 264.5W at the phase voltage setting and 800W at the line voltage setting—a difference of nearly three times. This not only easily damages the battery heating circuit but also makes the selection of electrical components in the circuit more difficult. Summary of the Invention

[0005] In view of this, the present invention discloses an energy storage system to achieve controllable power supply voltage for the battery heating circuit, eliminating the possibility of incorrect phase voltage and line voltage connection, thereby not only extending the service life of the battery heating circuit, but also facilitating the selection of electrical components in the battery heating circuit.

[0006] An energy storage system includes: a controller, a DC / AC conversion circuit, at least one battery cell and a corresponding first transmission branch, a battery heating circuit, and a number of first switches equal to the number of battery cells;

[0007] Each of the battery cells is connected to the DC bus of the DC / AC conversion circuit in sequence through the corresponding first switch and the first transmission branch;

[0008] The AC side of the DC / AC conversion circuit is connected to the power grid and / or the load;

[0009] The power supply end of the battery heating circuit is connected between the first switch and the corresponding first transmission branch;

[0010] The controller is configured to control the first switches, the first transmission branches, and the DC / AC conversion circuit to work, so that the battery cells achieve power conversion and transmission with the power grid or the load; and the controller is further configured to, when the temperature of at least one battery cell is lower than a preset temperature value, control the corresponding first transmission branch to boost or buck the DC bus voltage to supply power to the corresponding battery heating circuit, so as to heat the corresponding battery cell.

[0011] Optionally, the first transmission branch comprises a first DC / DC conversion circuit.

[0012] The controller is configured to, when controlling the corresponding first transmission branch to boost or buck the DC bus voltage to supply power to the corresponding battery heating circuit, so as to heat the corresponding battery cell according to the high or low of the DC bus voltage, specifically configured to:

[0013] When the energy of the DC bus is higher than an energy threshold value, the first switch corresponding to the target battery cell with a temperature lower than the preset temperature value is controlled to be turned off.

[0014] When the DC bus voltage is lower than a minimum voltage limit value, the first DC / DC conversion circuit is controlled to boost the DC bus voltage to supply power to the corresponding battery heating circuit, so as to heat the corresponding battery cell.

[0015] Optionally, the controller is configured to, when controlling the corresponding first transmission branch to boost or buck the DC bus voltage to supply power to the corresponding battery heating circuit, so as to heat the corresponding battery cell according to the high or low of the DC bus voltage, specifically configured to:

[0016] When the energy of the DC bus is higher than an energy threshold value, the first switch corresponding to the battery cell with a temperature lower than the preset temperature value is controlled to be turned off.

[0017] When the DC bus voltage is higher than a maximum voltage limit value, the first DC / DC conversion circuit is controlled to buck the DC bus voltage to supply power to the corresponding battery heating circuit, so as to heat the corresponding battery cell.

[0018] Optionally, the method further comprises: at least one photovoltaic string and a corresponding second transmission branch;

[0019] Each photovoltaic string is connected to the DC bus through the corresponding second transmission branch.

[0020] The controller is configured to control the second transmission branches and the DC / AC conversion circuit to work, so that each photovoltaic string realizes power conversion and transmission between the power grid and / or the load.

[0021] Optionally, the second transmission branch comprises a second DC / DC conversion circuit.

[0022] When the AC side of the DC / AC conversion circuit is connected to the power grid, the DC bus voltage comprises the voltage converted by the power grid to the DC bus through the DC / AC conversion circuit and the voltage converted by at least one photovoltaic string to the DC bus through the corresponding second DC / DC conversion circuit.

[0023] Optionally, the method further comprises:

[0024] When the AC side of the DC / AC conversion circuit is connected to the load, the DC bus voltage comprises the voltage converted by at least one photovoltaic string to the DC bus through the corresponding second DC / DC conversion circuit.

[0025] Optionally, the controller is configured to control the corresponding first transmission branch to step up or step down according to the high or low of the DC bus voltage to supply power to the battery heating circuit to heat the corresponding battery cell, and specifically configured to:

[0026] When the energy of the DC bus is lower than the energy threshold value, the first switch corresponding to the target battery cell with a temperature lower than the preset temperature value is controlled to be turned on, and the battery heating circuit is supplied with power by the energy of the DC bus and the energy of the target battery cell to heat the corresponding battery cell.

[0027] Optionally, the battery heating circuit comprises a heating resistor and a second switch.

[0028] The heating resistor and the heating second switch are connected in series.

[0029] Optionally, the heating resistor is a heating sheet, and the heating sheet is attached to the surface of the corresponding battery cell to heat the corresponding battery cell.

[0030] Optionally, the first switch is a circuit breaker or a relay.

[0031] From the above technical solutions can be known, the application discloses a kind of energy storage systems, comprising: controller, DC / AC conversion circuit, at least one battery unit and corresponding first transmission branch, battery heating circuit and with the first switch of battery unit, each battery unit is sequentially connected DC bus of DC / AC conversion circuit by corresponding first switch and first transmission branch respectively, the power supply end of battery heating circuit is connected between first switch and corresponding first transmission branch, controller is used to control each first switch, each first transmission branch and DC / AC conversion circuit work, and when the temperature of at least one battery unit is lower than preset temperature value, corresponding first transmission branch is controlled according to the high and low of DC bus voltage to DC bus voltage boost or buck to corresponding battery heating circuit power supply, to corresponding battery unit is heated.The power supply voltage of battery heating circuit in the application is DC bus voltage, which is obtained from the port of first transmission branch close to battery unit side, therefore, the power supply voltage of battery heating circuit is controllable, there is no phase voltage and line voltage connection wrong condition, thereby not only prolong the service life of battery heating circuit, facilitate the selection of electrical element in battery heating circuit. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by the disclosed drawings without creative labor for those skilled in the art.

[0033] Figure 1 The structural schematic diagram of the energy storage system disclosed by the embodiment of the present application is shown in the figure.

[0034] Figure 2 The structural schematic diagram of another energy storage system disclosed by the embodiment of the present application is shown in the figure.

[0035] Figure 3 The structural schematic diagram of another energy storage system disclosed by the embodiment of the present application is shown in the figure.

[0036] Figure 4 The structural schematic diagram of another energy storage system disclosed by the embodiment of the present application is shown in the figure.

[0037] Figure 5 The structural schematic diagram of another energy storage system disclosed by the embodiment of the present application is shown in the figure.

[0038] Figure 6 The circuit diagram of battery heating circuit in the energy storage system disclosed by the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0039] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of the present application.

[0040] The embodiment of the present application discloses a kind of energy storage systems, comprising: controller, DC / AC conversion circuit, at least one battery unit and corresponding first transmission branch, battery heating circuit and with battery unit equal number of first switch, each battery unit is sequentially connected DC bus of DC / AC conversion circuit by corresponding first switch and first transmission branch respectively, the power supply end of battery heating circuit is connected between first switch and corresponding first transmission branch, controller is used to control each first switch, each first transmission branch and DC / AC conversion circuit work, and when the temperature of at least one battery unit is lower than preset temperature value, corresponding first transmission branch is controlled according to the height of DC bus voltage to DC bus voltage boost or buck to corresponding battery heating circuit power supply, to corresponding battery unit is heated.The power supply voltage of battery heating circuit in the present application is DC bus voltage, it is obtained from the port of first transmission branch close to battery unit side, therefore, the power supply voltage of battery heating circuit is controllable, there is no phase voltage and line voltage connection wrong case, to not only prolong the service life of battery heating circuit, the selection of electrical element in battery heating circuit is also facilitated.

[0041] Referring to Figure 1 The embodiment of the present application discloses a kind of energy storage systems structure diagram, the energy storage system includes: controller ( Figure 1 Not shown in the embodiment of the present application), DC / AC conversion circuit 101, at least one battery unit 102 and corresponding first transmission branch 103, battery heating circuit 104 and with battery unit 102 equal number of first switch K1.

[0042] Wherein:

[0043] Each battery unit 102 is sequentially connected DC bus of DC / AC conversion circuit 101 by corresponding first switch K1 and first transmission branch 103 respectively, each first transmission branch 103 is used to realize the power transmission between corresponding battery power supply 102 and DC bus.That is to say, one end of first switch K1 connects the battery port of corresponding battery unit 102, the other end of first switch K1 connects the interface of first transmission branch 103, and first switch K1 is used to control the conduction and shutdown of the passage between battery unit 102 and corresponding first transmission branch 103 according to the conduction and shutdown signals sent by controller.

[0044] It should be noted that the first switch K1 can be a switch configured on the battery side, or it can be a switch configured internally in the first transmission branch 103. This article does not impose any restrictions. Figure 1 This is merely a schematic diagram illustrating that the connection between battery cell 102 and the first transmission branch 103 can be controlled to disconnect.

[0045] A bus capacitor is provided between the positive and negative terminals of the DC bus, which includes C1 (with voltage VbusP) and C2 (with voltage VbusN). The AC side of the DC / AC conversion circuit 101 is connected to the power grid and / or the load.

[0046] The battery unit 102 can refer to a battery cluster or a battery pack, etc. This energy storage system can be applied to a photovoltaic power generation system. In this case, to match the voltage of the photovoltaic strings in the photovoltaic power generation system, the battery unit 102 is preferably a battery cluster. The choice depends on the specific application environment and is within the scope of protection of this application.

[0047] The power supply terminal of the battery heating circuit 104 ( Figure 1 The A and B ends of the circuit are connected between the first switch K1 and the corresponding first transmission branch 103. The power supply voltage of the battery heating circuit 104 is mainly obtained by converting the DC bus voltage through the first transmission branch 103.

[0048] The number of battery heating circuits 104 and the number of battery cells 102 may be the same or different, depending on the actual needs. This invention does not limit the specific number of battery heating circuits 104.

[0049] In practical applications, the battery heating circuit 104 is set at a preset heating position of the corresponding battery cell 102, such as the side or bottom of the battery cell 102. The specific preset heating position depends on actual needs, and this invention does not limit it.

[0050] Under normal circumstances, the controller controls the operation of each of the first switches K1, each of the first transmission branches 103, and the DC / AC conversion circuit 101, enabling each of the battery units 102 to perform electrical energy conversion and transmission with the power grid or the load. For example, it controls each battery unit 102 to output electrical energy, which is then sequentially transmitted through the corresponding transmission branch 103 and the DC / AC conversion circuit 101 to supply power to the power grid and / or the load; or, it controls each battery unit 102 to receive electrical energy from the power grid for charging, sequentially transmitted through the corresponding transmission branch 103 and the DC / AC conversion circuit 101.

[0051] In addition, the controller is configured to control the first transmission branch 103 to boost or buck the DC bus voltage to supply power to the battery heating circuit 104 to heat the battery cell 102 when the temperature of the battery cell 102 is lower than a preset temperature value. This is because the battery heating circuit 104 has a certain internal resistance, and thus, by adjusting the supply voltage of the battery heating circuit 104 (i.e., the voltage between points A and B), the heating power of the battery heating circuit 104 can be changed to generate Joule heat on the battery heating circuit 104, which is used to heat the battery cell 102.

[0052] In the embodiment, the DC bus voltage refers to the voltage of the DC bus of the DC / AC conversion circuit 101. When the AC side of the DC / AC conversion circuit 101 is connected to the power grid, the DC bus voltage is provided by the power grid, and in this case, the DC bus voltage is the voltage converted from the AC voltage of the power grid to the DC bus voltage by the DC / AC conversion circuit 101. When the AC side of the DC / AC conversion circuit 101 is connected to the load only and not connected to the power grid, the DC bus voltage is provided by a power supply other than the power grid, such as at least one photovoltaic string when the energy storage system is applied to a photovoltaic power generation system. When at least one photovoltaic string is connected to the DC bus and the AC side of the DC / AC conversion circuit 101 is connected to the power grid, the DC bus voltage is provided by the power grid and at least one photovoltaic string.

[0053] It should be noted that the lower the temperature, the more likely the battery cell 102 will be overcharged (exceeding the maximum value Vmax) or undercharged (lower than the minimum value Vmin) due to charging or discharging. Therefore, in actual applications, the temperature (e.g., Temp1 in FIG. 2) and the voltage (e.g., Vrack1 in FIG. 2) of each battery cell 102 can be sampled. Figure 1 Figure 1 When the controller heats the corresponding battery cell 102, the temperature of the battery cell 102 can also be monitored in real time to prevent abnormality. If the temperature of the battery cell 102 is lower than the preset temperature value, the supply voltage of the corresponding battery heating circuit 104 can be increased to heat the corresponding battery cell 102, so that the voltage of the battery cell 102 is within the range [Vmin, Vmax].

[0054] The process of heating the corresponding battery cell 102 by the controller can be performed before the energy storage system is in normal operation, or can be performed while the energy storage system is in normal operation. The specific application environment can be determined accordingly, which is within the protection scope of the present application.

[0055] ​The application discloses a kind of energy storage systems, comprising: controller, DC / AC conversion circuit 101, at least one battery unit 102 and corresponding first transmission branch 103, battery heating circuit 104 and with battery unit 102 equal number of first switch K1, each battery unit 102 is sequentially connected DC / AC conversion circuit 101's DC bus by corresponding first switch K1 and first transmission branch 103, the power supply end of battery heating circuit 104 is connected between first switch K1 and corresponding first transmission branch 103, controller is used to control each first switch K1, each first transmission branch 103 and DC / AC conversion circuit 101 work, and when the temperature of at least one battery unit 102 is lower than preset temperature value, corresponding first transmission branch 103 is controlled according to the height of DC bus voltage to DC bus voltage boost or buck to corresponding battery heating circuit 104 power supply, to corresponding battery unit 102 is heated.The power supply voltage of battery heating circuit 104 in the application is DC bus voltage, which is obtained from the port of first transmission branch 103 close to battery unit 102 side, therefore, the power supply voltage of battery heating circuit 104 is controllable, there is no phase voltage and line voltage connection wrong case, so as to not only prolong the service life of battery heating circuit, but also facilitate the selection of electrical elements in battery heating circuit 104.

[0056] In order to further optimize the above-mentioned embodiments, referring to Figure 2 The application discloses another structure diagram of energy storage system, in Figure 1 The first transmission branch 103 comprises a first DC / DC conversion circuit (see DC / DC1 in Figure 2 ).

[0057] When the controller is used to control corresponding first transmission branch 103 to boost or buck to supply corresponding battery heating circuit 104 with power to heat corresponding battery unit 102 according to the height of DC bus voltage, it is specifically used for:

[0058] When the energy of DC bus is higher than energy threshold value, the first switch K1 corresponding to target battery unit with temperature lower than preset temperature value is turned off;

[0059] When the DC bus voltage is lower than the minimum voltage limit, the first DC / DC conversion circuit is controlled to boost the DC bus voltage to supply corresponding battery heating circuit 104 with power to heat corresponding battery unit 102.

[0060] To further optimize the above embodiment, the controller is configured to control the corresponding first transmission branch 103 to step up or step down the voltage of the DC bus according to the voltage of the DC bus to supply power to the corresponding battery heating circuit 104 to heat the corresponding battery cell 102, and specifically further configured to:

[0061] When the energy of the DC bus is higher than the energy threshold, the first switch K1 corresponding to the battery cell with a temperature lower than the preset temperature value is controlled to be turned off.

[0062] When the voltage of the DC bus is higher than the maximum voltage limit, the first DC / DC conversion circuit is controlled to step down the voltage of the DC bus to supply power to the corresponding battery heating circuit 104 to heat the corresponding battery cell 102.

[0063] In this embodiment, when the energy of the DC bus is higher than the energy threshold, the first switch K1 corresponding to the target battery cell with a temperature lower than the preset temperature value is controlled to be turned off, so that the supply voltage of the corresponding battery heating circuit 104 comes from the port (AB) of the first DC / DC conversion circuit, and the port voltage is obtained by converting the voltage of the DC bus through the first DC / DC conversion circuit. Figure 2

[0064] In actual application, when the voltage of the DC bus is lower than the minimum voltage limit, the controller controls the first DC / DC conversion circuit to step up the voltage of the DC bus to supply power to the corresponding battery heating circuit 104 to heat the corresponding battery cell 102. When the voltage of the DC bus is higher than the maximum voltage limit, the controller controls the first DC / DC conversion circuit to step down the voltage of the DC bus to supply power to the corresponding battery heating circuit 104 to heat the corresponding battery cell 102. Therefore, the supply voltage of the battery heating circuit 104 is adjusted by controlling the first DC / DC conversion circuit, and the heating power of the battery heating circuit 104 is adjusted, so that Joule heat can be generated on the battery heating circuit 104, and the Joule heat is used to heat the corresponding battery cell 102.

[0065] In addition, the power supply end of the battery heating circuit 104 is connected between the battery port and the first DC / DC conversion circuit, which is equivalent to that the battery heating circuit 104 is wired from the battery port to heat the battery cell 102, and the wiring process is simple and convenient, which reduces the cost to a certain extent.

[0066] It should be noted that the values of the energy threshold, the minimum voltage limit and the maximum voltage limit in this embodiment are determined according to actual needs, and the present application does not limit them.

[0067] ​When the energy storage system is applied in the photovoltaic power generation system, each battery unit 102 can share the DC / AC conversion circuit 101 with each photovoltaic string, that is, at least one photovoltaic string can also be connected to the DC bus.

[0068] Therefore, to further optimize the above-mentioned embodiments, referring to Figure 3 , the embodiment of the present application discloses another structural diagram of an energy storage system, in which Figure 1 On the basis of the embodiment shown, the energy storage system can further include at least one photovoltaic string 105 and a corresponding second transmission branch 106.

[0069] Each photovoltaic string 105 is connected to the DC bus through the corresponding second transmission branch 106;

[0070] The controller is configured to control the operation of each second transmission branch 106 and the DC / AC conversion circuit 101, so that each photovoltaic string 105 realizes the conversion and transmission of electric energy between the power grid and / or the load.

[0071] Therefore, the DC bus voltage in the embodiment can be provided by the power grid and / or the photovoltaic string 105, in which the voltage provided by the photovoltaic string 105 for the DC bus can be determined by monitoring the voltage (Vpv) of the photovoltaic string 105 in real time. Figure 3

[0072] Therefore, the supply voltage of the battery heating circuit 104, that is, the AB two-point voltage, can be converted by the power grid through the DC / AC conversion circuit 101 and the first transmission branch 103. Alternatively, the AB two-point voltage is obtained by summing the first voltage and the second voltage, the first voltage being the voltage converted by the power grid through the DC / AC conversion circuit 101 and the first transmission branch 103, and the second voltage being the voltage converted by at least one photovoltaic string 105 through the second transmission branch 106 and the first transmission branch 103.

[0073] In actual applications, the DC / AC conversion circuit 101 can be a circuit structure inside the energy storage system or a circuit structure in the photovoltaic power generation system inverter; it can be determined according to the specific application environment, and it is within the protection scope of the present application.

[0074] To further optimize the above-mentioned embodiments, referring to Figure 4 , the embodiment of the present application discloses another structural diagram of an energy storage system, in which the first transmission branch 103 includes a first DC / DC conversion circuit (see DC / DC1 in Figure 4 ), and the second transmission branch 106 includes a second DC / DC conversion circuit (see DC / DCm in Figure 4 );

[0075] ​When the AC side of the DC / AC conversion circuit 101 is connected to at least the power grid, that is, the AC side of the DC / AC conversion circuit 101 is connected to only the power grid, or the AC side of the DC / AC conversion circuit 101 is connected to both the load and the power grid.

[0076] At this time, the DC bus voltage includes the voltage converted by the power grid to the DC bus through the DC / AC conversion circuit 101, and the voltage converted by at least one photovoltaic string 105 to the DC bus through the corresponding second DC / DC conversion circuit.

[0077] When the AC side of the DC / AC conversion circuit is connected to only the load, the load cannot provide voltage for the DC bus, and at this time, the DC bus voltage includes the voltage converted by at least one photovoltaic string 105 to the DC bus through the corresponding second DC / DC conversion circuit.

[0078] It should be noted that in order to realize the basic function of each battery unit 102, each DC / DC conversion circuit (including the first DC / DC conversion circuit and the second DC / DC conversion circuit) in the present application is a bidirectional DC / DC conversion circuit.

[0079] It should be particularly pointed out that the above-mentioned embodiments are aimed at the case that the energy of the DC bus is not lower than the energy threshold (that is, the energy of the DC bus is sufficient) and the first switch K1 is off, at this time, each battery power supply 102 is in a low-temperature heating state and is not connected to the energy storage system.

[0080] When the energy of the DC bus is lower than the energy threshold, that is, the energy of the DC bus is insufficient, the present application can control the first switch K1 to be on, so that the energy of the DC bus and the energy of the battery unit 102 are used to heat the battery heating circuit 104 at the same time.

[0081] Therefore, the controller is used to control the corresponding first transmission branch 103 to step up or step down to supply power to the corresponding battery heating circuit 104 to heat the corresponding battery unit 102, and is further used to:

[0082] When the energy of the DC bus is lower than the energy threshold, the controller controls the first switch K1 corresponding to the target battery unit whose temperature is lower than the preset temperature value to be on, and the energy of the DC bus and the energy of the target battery unit are used to supply power to the battery heating circuit 104 at the same time to heat the corresponding battery unit 102.

[0083] Preferably, the first switch K1 can be a circuit breaker, a relay, etc., and the control end of the first switch K1 is connected to the controller and is controlled by the controller to be on and off. In actual application, the first switch K1 includes but is not limited toFigures 1 to 4 The first switch K1 can also be connected in other ways in the energy storage system, such as Figure 5 In the energy storage system shown, the first switch K1 only controls the passage between the positive electrode of the battery unit 102 and the first transmission branch 103. Therefore, the present application does not limit the connection mode of the first switch K1 in the energy storage system, as long as the first switch K1 can control the on-off of the passage between the corresponding battery unit 102 and the corresponding first transmission branch 103.

[0084] To further optimize the above embodiment, refer to Figure 6 The battery heating circuit disclosed in the embodiment of the present application comprises a heating resistor R1 and a second switch K2.

[0085] The heating resistor R1 and the heating second switch K2 are connected in series.

[0086] The controller controls the second switch K2 to turn on and off according to a preset on-off period, so as to control the impedance of the battery heating circuit 104.

[0087] It should be noted that Figure 6 The heating resistor R1 shown in the above embodiment is an equivalent heating circuit. In actual application, the heating resistor R1 can be obtained by connecting multiple resistors in series, in parallel, or in series-parallel.

[0088] When the heating resistor R1 is a heating sheet, the heating sheet is attached to the surface of the corresponding battery unit 102 to heat the battery unit 102.

[0089] Finally, it should be noted that in this document, relational terms such as first and second and the like can only be used to distinguish one entity or action from another entity or action, without necessarily requiring or implying that there is any such actual relationship or order between these entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof are intended to cover non-exclusive inclusions, so that a process, method, article, or apparatus that includes a list of elements does not only include those elements, but also includes other elements not explicitly listed, or other elements inherent to such a process, method, article, or apparatus. Without more limitations, an element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0090] The various embodiments in the present specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between various embodiments can be mutually referred to.

[0091] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and, while certain modifications are discussed, it is desired to be protected in accordance with the spirit and scope of the application. Therefore, the application is not limited to the specific embodiments shown and described, but only by the scope of the appended claims, unless otherwise specified.

Claims

1. An energy storage system, characterized by, The application relates to a battery energy storage system, which comprises a controller, a DC / AC conversion circuit, at least one battery unit and a corresponding first transmission branch, a battery heating circuit and a first switch corresponding to the battery unit. Each battery unit is connected to the DC bus of the DC / AC conversion circuit through the corresponding first switch and the first transmission branch in sequence. The AC side of the DC / AC conversion circuit is connected to a power grid and / or a load. The power supply end of the battery heating circuit is connected between the first switch and the corresponding first transmission branch. The controller is used for controlling the first switch, the first transmission branch and the DC / AC conversion circuit to work, so that the battery unit realizes energy conversion and transmission between the power grid or the load. When the temperature of at least one battery unit is lower than a preset temperature value, the controller controls the corresponding first transmission branch to boost or buck the DC bus voltage to supply power to the corresponding battery heating circuit to heat the corresponding battery unit. The first transmission branch comprises a first DC / DC conversion circuit.

2. The energy storage system of claim 1, wherein, When the controller controls the corresponding first transmission branch to boost or buck the DC bus voltage to supply power to the corresponding battery heating circuit to heat the corresponding battery unit, the controller is specifically used for: When the DC bus voltage is lower than a minimum voltage limit, the controller controls the first DC / DC conversion circuit to boost the DC bus voltage to supply power to the corresponding battery heating circuit to heat the corresponding battery unit. When the controller controls the corresponding first transmission branch to boost or buck the DC bus voltage to supply power to the corresponding battery heating circuit to heat the corresponding battery unit, the controller is specifically used for:

3. The energy storage system of claim 2, wherein, When the DC bus voltage is higher than a maximum voltage limit, the controller controls the first DC / DC conversion circuit to buck the DC bus voltage to supply power to the corresponding battery heating circuit to heat the corresponding battery unit. The application further comprises at least one photovoltaic group string and a corresponding second transmission branch.

4. The energy storage system of claim 1, wherein, Each photovoltaic group string is connected to the DC bus through the corresponding second transmission branch. The controller is used for controlling the second transmission branch and the DC / AC conversion circuit to work, so that the photovoltaic group string realizes energy conversion and transmission between the power grid and / or the load. The second transmission branch comprises a second DC / DC conversion circuit.

5. The energy storage system of claim 4, wherein, When the AC side of the DC / AC conversion circuit is connected to the power grid, the DC bus voltage comprises the voltage of the power grid converted to the DC bus through the DC / AC conversion circuit and the voltage of at least one photovoltaic group string converted to the DC bus through the corresponding second DC / DC conversion circuit. The application further comprises 6. The energy storage system of claim 5, wherein, ​ In a case that the load is connected to an alternating current side of the DC / AC conversion circuit only, the DC bus voltage comprises at least one voltage of the photovoltaic string converted to the DC bus by the corresponding second DC / DC conversion circuit.

7. The energy storage system of claim 1, wherein, The controller is configured to control the corresponding first transmission branch to boost or step down according to the high or low of the DC bus voltage to supply power to the battery heating circuit to heat the corresponding battery cell, and specifically configured to: In a case that the energy of the DC bus is lower than the energy threshold, the controller controls the first switch corresponding to the target battery cell with a temperature lower than the preset temperature value to be turned on, and the battery heating circuit is supplied with power by the energy of the DC bus and the energy of the target battery cell to heat the corresponding battery cell.

8. The energy storage system of claim 1, wherein, The battery heating circuit comprises a heating resistor and a second switch. The heating resistor and the second switch are connected in series.

9. The energy storage system of claim 8, wherein, The heating resistor is a heating sheet, and the heating sheet is attached to a surface of the corresponding battery cell to heat the corresponding battery cell.

10. The energy storage system of claim 1, wherein, The first switch is a circuit breaker or a relay.

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