Battery cluster voltage balancing method and energy storage system

Abstract

The invention discloses a voltage balancing method between battery clusters and an energy storage system, and the method comprises the steps: obtaining a first voltage difference value between different battery clusters in a standby state, and carrying out the first-stage voltage balancing adjustment of the battery clusters if the first voltage difference value between at least one pair of battery clusters is greater than a preset first voltage difference threshold value; calculating a voltage average value of all the battery clusters after the first-stage voltage balance adjustment; and obtaining a second voltage difference value between the voltage of each battery cluster in the operation state and the voltage average value, and carrying out second-stage voltage balance adjustment on the battery clusters of which the second voltage difference values are greater than a preset second voltage difference threshold value. According to the voltage balancing method between the battery clusters and the energy storage system, the voltage of the battery clusters can be dynamically balanced, the voltage difference between the battery clusters is corrected in real time when the energy storage system runs, and the situation that the battery clusters are used in an overload mode is avoided.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage systems, and in particular to a method for voltage balancing between battery clusters and an energy storage system. Background Art

[0002] The use of multiple battery clusters in parallel is a common method of use in the current energy storage market. However, the parallel connection of battery clusters will cause inconsistent voltages in the battery clusters due to factors such as the individual capacity of the cells in the cluster, the internal resistance of the battery cluster, and the temperature of the working environment. When the voltages of the battery clusters are inconsistent, the discharge capacity of the battery clusters will also be unbalanced, which will cause some battery clusters to be overloaded, seriously affecting the stability and safety of the entire energy storage system, as well as the service life and usage capacity of the battery clusters.

[0003] To address this problem, in the prior art, a DC / DC module or a DC / AC module is usually provided in the power transmission branch of each battery cluster, and the DC / DC module is used to perform voltage conversion and then parallel operation on the DC side, or the DC / AC module is used to perform voltage conversion and then parallel operation on the AC side. Although this method of managing the battery cluster as a single cluster through the DC / DC module or the DC / AC module can make the voltages of each battery cluster basically reach a consistent state before parallel operation, the use of a large number of DC / DC modules or DC / AC modules will result in large secondary power consumption, greatly increase the overall cost of the energy storage system, and generate resonance due to excessive parallel connection, which is not conducive to the stable operation of the system.

[0004] Therefore, it is necessary to provide an improved technical solution to overcome the above technical problems existing in the prior art. Summary of the invention

[0005] In view of the above problems, the purpose of this application is to provide a method for voltage balancing between battery clusters and an energy storage system, which can dynamically balance the voltage of the battery cluster and correct the voltage difference between the battery clusters in real time when the energy storage system is running, so as to avoid overloading the battery cluster.

[0006] The present application provides a method for voltage balancing between battery clusters, comprising: Acquire a first voltage difference between different battery clusters in a standby state, and if the first voltage difference between at least one pair of battery clusters is greater than a preset first voltage difference threshold, perform a first stage of voltage balancing adjustment on the battery clusters; Calculate the average voltage of all battery clusters after voltage balancing adjustment in the first stage; Acquire a second voltage difference between the voltage of each battery cluster in the operating state and the voltage average value, and perform a second-stage voltage balancing adjustment on the battery clusters whose second voltage difference is greater than a preset second voltage difference threshold; The first stage of voltage balancing adjustment of the battery cluster includes: sorting the first voltage differences between different battery clusters in order of magnitude; Determine the two battery clusters corresponding to the sorted first voltage difference values ​​as the first target balancing battery cluster group in order from largest to smallest; Closing the balancing switch modules connected to the two battery clusters in the first target balancing battery cluster group, performing power transfer balancing between the two battery clusters in the first target balancing battery cluster group, so that the first voltage difference between different battery clusters is less than or equal to the first voltage difference threshold; The step of performing a second-stage voltage balancing adjustment on the battery cluster whose second voltage difference is greater than a preset second voltage difference threshold comprises: Determine a battery cluster whose second voltage difference value is greater than the second voltage difference threshold as a second target balancing battery cluster; When the voltages of the second target balanced battery clusters are all higher than the voltage average, the electricity in the second target balanced battery clusters is transferred to the battery storage; When the voltages of the second target balanced battery clusters are all lower than the voltage average value, the second target balanced battery clusters are charged with electricity through a storage battery and / or an AC power source.

[0007] Furthermore, the voltage balancing adjustment of the battery cluster in the first stage further includes: Obtaining the voltage value of each battery cluster in the standby state, and sorting the battery clusters according to the magnitude of the voltage values; Add the sorted battery clusters to the first target balanced battery cluster group in order from small to large; The balancing switch module connected to the battery cluster in the first target balancing battery cluster group is closed to transfer and balance the power between the multiple battery clusters that have been added to the first target balancing battery cluster group, so that the first voltage difference between different battery clusters is less than or equal to the first voltage difference threshold.

[0008] Furthermore, in the operating state, the balancing switch modules connected to each battery cluster are in a closed state.

[0009] Furthermore, the method further includes: when the second target balanced battery cluster includes both battery clusters with voltages higher than the voltage average and battery clusters with voltages lower than the voltage average, controlling the transfer of power between the second target balanced battery clusters to perform voltage balancing adjustment so that the second voltage difference of the second target balanced battery clusters is less than or equal to the second voltage difference threshold.

[0010] Furthermore, the method further includes: when the second voltage difference of each second target balanced battery cluster cannot be made less than or equal to the second voltage difference threshold by controlling the power transfer between each second target balanced battery cluster, storing or replenishing power by using the storage battery and / or AC power supply.

[0011] The present application also provides an energy storage system, comprising a plurality of battery clusters, balancing switch modules and balancing converter modules corresponding one to the plurality of battery clusters, a first DC busbar electrically connected to the plurality of balancing switch modules, a second DC busbar electrically connected to the plurality of balancing converter modules, an energy storage converter electrically connected to the first DC busbar, and a control module communicatively connected to the plurality of battery clusters, the plurality of balancing switch modules, and the plurality of balancing converter modules, respectively; wherein the balancing switch module is used to perform a first stage of voltage balancing regulation on the battery cluster under the control of the control module in a standby state; and the balancing converter module is used to perform a second stage of voltage balancing regulation on the battery cluster under the control of the control module.

[0012] Furthermore, the energy storage system also includes a first converter conversion module and a battery module, the first converter conversion module is electrically connected to the battery module, the first DC bus and the second DC bus respectively, and the battery module is used to store or replenish electricity during the voltage balancing regulation process.

[0013] Furthermore, the energy storage system also includes a second converter conversion module and an AC power supply module, the second converter conversion module is electrically connected to the AC power supply module and the second DC busbar respectively, and the AC power supply module is used to replenish the battery cluster or the battery module during the voltage balancing adjustment process.

[0014] As described above, the battery cluster voltage balancing method and energy storage system provided by the present application perform the first stage of voltage balancing adjustment on the battery clusters in the standby state, so that the voltages of the battery clusters reach a basically balanced state before the system enters the operating state. After the system enters the operating state, the voltage values ​​of the battery clusters in the operating state are monitored in real time, and the voltage difference between the battery clusters is corrected in time through the second stage of voltage balancing adjustment, thereby avoiding the situation of overloading the battery clusters. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 A schematic diagram of the circuit structure of an energy storage system provided in one embodiment of the present application.

[0017] Figure 2 A schematic diagram of a flow chart of a method for voltage balancing between battery clusters provided in an embodiment of the present application.

[0018] Figure 3 A schematic diagram of a flow chart of voltage balancing adjustment in the first stage provided in an embodiment of the present application.

[0019] Figure 4 A schematic diagram of a flow chart of voltage balancing adjustment in the first stage provided by another embodiment of the present application.

[0020] Figure 5 A schematic diagram of a flow chart of voltage balancing adjustment in the second stage provided in an embodiment of the present application. DETAILED DESCRIPTION

[0021] The aforementioned and other technical contents, features and effects of the present application will be clearly presented in the following detailed description of the preferred embodiments with reference to the drawings. Through the description of the specific implementation methods, the technical means and effects adopted by the present application to achieve the intended purpose can be more deeply and specifically understood. However, the attached drawings are only for reference and illustration, not for limiting the present application, and some well-known parts may not be shown. In each of the drawings, the same elements are represented by similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.

[0022] Figure 1 A schematic diagram of the circuit structure of an energy storage system provided in one embodiment of the present application; Figure 1As shown, an energy storage system provided by an embodiment of the present application includes a plurality of battery clusters Rack1-Rackn, balancing switch modules 111-11n and balancing converter modules 121-12n corresponding to the plurality of battery clusters Rack1-Rackn, a first DC busbar DC BUS-1 electrically connected to the plurality of balancing switch modules 111-11n, a second DC busbar DC BUS-2 electrically connected to the plurality of balancing converter modules 121-12n, and a first DC busbar DC BUS-1 electrically connected to the plurality of balancing switch modules 111-11n. The energy storage inverter 130 electrically connected to BUS-1 and the control module 140 which is respectively communicatively connected to multiple battery clusters Rack1~Rackn, multiple balancing switch modules 111~11n, and multiple balancing inverter modules 121~12n; wherein the balancing switch module 11n is used to perform the first stage voltage balancing adjustment on the battery cluster Rackn under the control of the control module 140 in the standby state; the balancing inverter module 12n is used to perform the second stage voltage balancing adjustment on the battery cluster Rackn under the control of the control module 140.

[0023] Specifically, Figure 1 As shown, in this embodiment, the balancing switch module 11n specifically includes a balancing positive relay KM1, a balancing negative relay KM2, a pre-charging relay KM3 and a pre-charging resistor R; wherein, one end of the balancing positive relay KM1 is electrically connected to the positive output port of the corresponding battery cluster, and the other end of the balancing positive relay KM1 is electrically connected to the positive bus DC+ of the first DC bus DCBUS-1; one end of the balancing negative relay KM2 is electrically connected to the negative output port of the corresponding battery cluster, and the other end of the balancing negative relay KM2 is electrically connected to the negative bus DC- of the first DC bus DC BUS-1; the pre-charging relay KM3 is connected in series with the pre-charging resistor R and then connected in parallel with the balancing positive relay KM1. The balancing converter modules 121-12n are respectively connected in parallel between the positive bus and the negative bus of the second DC bus DC BUS-2 and the positive output port and the negative output port of the corresponding battery cluster, and are used to realize the power transfer between the battery clusters through the second DC bus DC BUS-2 under the control of the control module 140. The balancing converter modules 121-12n can be composed of one or more bidirectional converters, which can control the voltage, current and power input or output of the battery cluster. The energy storage converter (PCS, Power Conversion Systerm) is electrically connected to the positive bus DC+ of the first DC bus DC BUS-1 and the negative bus DC- of the first DC bus DC BUS-1 through the main positive relay KM4 and the main negative relay KM5, respectively, and is used to control the charging and discharging process of the energy storage system and perform AC-DC conversion.

[0024] In this embodiment, the energy storage system also includes a first inverter conversion module 150 and a battery module 160. The first inverter conversion module 150 is electrically connected to the battery module 160, the first DC busbar DC BUS-1 and the second DC busbar DC BUS-2, respectively, and includes one or more inverter modules for converting the electric energy flowing between the battery module 160, the first DC busbar DC BUS-1 and the second DC busbar DC BUS-2; the battery module 160 is used to store or replenish electricity during the voltage balancing adjustment process.

[0025] In this embodiment, the energy storage system further includes a second converter conversion module 170 and an AC power supply module 180. The second converter conversion module 170 is electrically connected to the AC power supply module 180 and a second DC busbar DC BUS-2, respectively, and is used to convert the electric energy output by the AC power supply module 180, so that the AC power supply module 180 can replenish the battery cluster Rackn or the battery module 160 with electric energy through the second DC busbar DC BUS-2 during the voltage balancing adjustment process.

[0026] In this embodiment, the control module 140 is also electrically connected to the first inverter conversion module 150, the battery module 160, the second inverter conversion module 170 and the AC power supply module 180, and is used to control the corresponding balancing switch module, balancing inverter module, first inverter conversion module, battery module, second inverter conversion module and AC power supply module to perform voltage balancing adjustment according to the charge state of each battery cluster. The control module 140 can be a separate control unit or an electronic device integrated with other units with data processing capabilities such as a battery management system (BMS, Battery Management System), and the present application does not impose any restrictions on this.

[0027] The voltage balancing control method provided in the present application is described in detail below in conjunction with the energy storage system provided in the above embodiments.

[0028] Figure 2 A schematic diagram of a flow chart of a method for voltage balancing between battery clusters provided in an embodiment of the present application; Figure 2 As shown, the method for voltage balancing between battery clusters provided in the present application specifically includes the following steps: Step S100: obtaining a first voltage difference between different battery clusters in a standby state, and if the first voltage difference between at least one pair of battery clusters is greater than a preset first voltage difference threshold, performing a first stage of voltage balancing adjustment on the battery clusters.

[0029] Specifically, when the energy storage system is not started and is in a standby state, that is, when the relays KM1 to KM5 in the energy storage system of the above embodiment are all in an unclosed state, the control module can read the voltage value of each battery cluster through communication methods such as CAN, RS485, LAN, etc., and calculate the first voltage difference between the battery clusters, and determine whether there is one or more pairs of battery clusters whose first voltage difference is greater than a preset first voltage difference threshold △U1 based on the calculated first voltage difference.

[0030] Figure 3 A schematic diagram of a flow chart of voltage balancing adjustment in the first stage provided by an embodiment of the present application; Figure 3 As shown, in one embodiment of the present application, the voltage balancing adjustment of the battery cluster in the first stage specifically includes: Step S111: sorting the first voltage differences between different battery clusters in order of magnitude.

[0031] Step S112: determining the two battery clusters corresponding to the sorted first voltage differences in order from large to small as a first target balancing battery cluster group.

[0032] Step S113: closing the balancing switch modules connected to the two battery clusters in the first target balancing battery cluster group, performing power transfer balancing between the two battery clusters in the first target balancing battery cluster group, so that the first voltage difference between different battery clusters is less than or equal to the first voltage difference threshold.

[0033] Exemplarily, assuming that the battery clusters in the above energy storage system are Rack1~Rack5, the voltages of the battery clusters detected by the control module are: Rack1 is 745Vdc, Rack2 is 747Vdc, Rack3 is 755Vdc, Rack4 is 754Vdc, and Rack5 is 750Vdc; the preset first voltage difference threshold △U1=3V.

[0034] According to the first voltage difference between different battery clusters, the two battery clusters corresponding to the first group with the largest first voltage difference and greater than △U1 are Rack1 and Rack3, and the first voltage difference is 10Vdc. First, Rack1 and Rack3 are determined as the first target balanced battery cluster group; at the same time, the balanced negative relay KM2 and the pre-charge relay KM3 in the balanced switch module connected to Rack1 and Rack3 are closed, and the pre-charge resistor R is used as the loop resistor to realize the energy transfer and voltage balance between the battery clusters Rack1 and Rack3. Assuming that after balancing, the voltage of the battery cluster Rack1 becomes 750Vdc, and the voltage of the battery cluster Rack3 becomes 751Vdc, the first voltage difference is 1Vdc, which is less than the first voltage difference threshold △U1, then the balanced negative relay KM2 and the pre-charge relay KM3 connected to Rack1 and Rack3 are disconnected.

[0035] At this time, the voltages of battery clusters Rack1 to Rack5 are respectively Rack1: 750Vdc, Rack2: 747Vdc, Rack3: 751Vdc, Rack4: 754Vdc, and Rack5: 750Vdc; it can be obtained that the two battery clusters corresponding to the second group with the largest first voltage difference and greater than △U1 are Rack2 and Rack4, and the first voltage difference is 7Vdc. At this time, Rack2 and Rack4 are determined as the first target balanced battery cluster group; at the same time, the balanced negative relay KM2 and the pre-charge relay KM3 in the balanced switch module connected to Rack2 and Rack4 are closed to balance the power transfer between battery clusters Rack2 and Rack4. Assuming that after balancing, the voltage of battery cluster Rack2 becomes 749Vdc, and the voltage of battery cluster Rack4 becomes 751Vdc, the first voltage difference is 2Vdc, which is less than the first voltage difference threshold △U1, then the balanced negative relay KM2 and the pre-charge relay KM3 connected to Rack2 and Rack4 are disconnected. At this time, the voltages of battery clusters Rack1 to Rack5 are respectively Rack1: 750Vdc, Rack2: 749Vdc, Rack3: 751Vdc, Rack4: 751Vdc, and Rack5: 750Vdc; at this time, the first voltage difference between all battery clusters is less than or equal to the first voltage difference threshold △U1, and the first stage of voltage balancing adjustment can be ended.

[0036] In this embodiment, when there are one or more pairs of battery clusters whose first voltage difference is greater than the preset first voltage difference threshold, voltage balancing is performed between the battery clusters whose first voltage difference is greater than the preset first voltage difference threshold in order from large to small, until the first voltage difference between all battery clusters is less than or equal to the preset first voltage difference threshold, then the first stage of voltage balancing adjustment is terminated.

[0037] Figure 4 A schematic diagram of a flow chart of voltage balancing adjustment in the first stage provided by another embodiment of the present application; Figure 4 As shown, in another embodiment of the present application, the voltage balancing adjustment of the battery cluster in the first stage may further include: Step S121: obtaining the voltage value of each battery cluster in the standby state, and sorting the battery clusters according to the voltage values.

[0038] Step S122: adding the sorted battery clusters in order from small to large to the first target balancing battery cluster group.

[0039] Step S123: closing the balancing switch module connected to the battery clusters in the first target balancing battery cluster group, and performing power transfer balancing between multiple battery clusters that have been added to the first target balancing battery cluster group, so that the first voltage difference between different battery clusters is less than or equal to the first voltage difference threshold.

[0040] For example, in this embodiment, the voltages of the battery clusters are: Rack1 is 745Vdc, Rack2 is 747Vdc, Rack3 is 755Vdc, Rack4 is 754Vdc, Rack5 is 750Vdc, and the first voltage difference threshold △U1=3V is preset as an example to introduce in detail the voltage balancing adjustment method of the first stage in another embodiment of the present application.

[0041] After sorting the battery clusters according to the magnitudes of the above battery cluster voltage values, we get: Rack1 < Rack2 < Rack5 < Rack4 < Rack3; First, add battery clusters Rack1 and Rack2 to the first target balanced battery cluster group. At the same time, close the equalizing negative relay KM2 and the precharge relay KM3 in the equalizing switch module connected to battery clusters Rack1 and Rack2, and connect battery clusters Rack1 and Rack2 to the first DC busbar DC BUS-1 to achieve energy transfer and voltage balance between battery clusters Rack1 and Rac2. Assume that after equalization, the voltage of battery cluster Rack1 becomes 745.8 Vdc, and the voltage of battery cluster Rack2 becomes 746 Vdc. The first voltage difference is 0.2 Vdc, which is less than the first voltage difference threshold △U1. Then, keep the equalizing negative relay KM2 and the precharge relay KM3 connected to battery clusters Rack1 and Rack2 closed, and continue to add battery cluster Rack5 to the first target balanced battery cluster group. Close the equalizing negative relay KM2 and the precharge relay KM3 in the equalizing switch module connected to battery cluster Rack5, and connect battery cluster Rack5 to the first DC busbar DC BUS-1 to achieve charge transfer balance among battery clusters Rack1, Rack2, and Rack5 until the first voltage difference among battery clusters Rack1, Rack2, and Rack5 is also less than or equal to the first voltage difference threshold △U1. Keep the equalizing negative relay KM2 and the precharge relay KM3 connected to battery clusters Rack1, Rack2, and Rack5 closed, and continue to add battery cluster Rack4 to the first target balanced battery cluster group. By closing the equalizing negative relay KM2 and the precharge relay KM3 in the equalizing switch module connected to Rack4, connect battery cluster Rack4 to the first DC busbar DC BUS-1 for charge transfer balance... and so on until all battery clusters in the energy storage system are connected to the first DC busbar DC BUS-1 for charge transfer balance, making the first voltage differences among all battery clusters less than or equal to the first voltage difference threshold △U1, thus completing the voltage balance adjustment in the first stage.

[0042] In this embodiment, when there are battery clusters with a first voltage difference greater than the preset first voltage difference threshold, according to the magnitudes of the battery cluster voltage values, starting from the one with the lower voltage value, add the battery clusters to the first DC busbar one by one for voltage balance until all battery clusters are connected to the first DC busbar, making the first voltage differences among all battery clusters less than or equal to the preset first voltage difference threshold, then the voltage balance adjustment in the first stage is completed.

[0043] It should be noted that, in the above embodiment, after the voltage balancing adjustment of the first stage is completed, if the energy storage system does not need to be operated at this time, the relays in the above embodiment are disconnected to keep the system in a standby state.

[0044] Step S200: calculating the average voltage of all battery clusters after the voltage balancing adjustment in the first stage.

[0045] Step S300: obtaining a second voltage difference between the voltage of each battery cluster and the voltage average value in the running state, and performing a second stage of voltage balancing adjustment on the battery clusters whose second voltage difference is greater than a preset second voltage difference threshold.

[0046] It should be noted that when the energy storage system is in operation, the balancing switch modules connected to each battery cluster are all in a closed state. Specifically, when the energy storage system is started, the above-mentioned balancing negative relay KM2, pre-charge relay KM3, main positive relay KM4 and main negative relay KM5 are all in a closed state. When the voltage difference across the pre-charge resistor R is less than the preset value, the pre-charge relay KM3 is disconnected and the balancing positive relay KM1 is closed, so that the energy storage system is in a powered-on state.

[0047] In the embodiments of the present application, when the energy storage system is in operation, most of the battery clusters are generally in a voltage balance state. At this time, the control module will collect the status of each battery cluster in real time, including the voltage, current, power and other parameters of each battery cluster. When the voltage of any battery cluster deviates, the control module will start the voltage balance adjustment function. It should be noted that the voltage deviation will be reflected in the magnitude of the current. The battery cluster with a high voltage has a large output current, and the battery cluster with a low voltage has a small output current. Therefore, in some embodiments of the present application, the control module can also adjust the output current of the battery cluster in real time so that the output current of each battery cluster reaches a basically balanced state, thereby achieving dynamic balance of the voltage of each battery cluster and avoiding deviations in battery characteristics due to over-output or under-output of the battery cluster.

[0048] Figure 5 A schematic diagram of a flow chart of voltage balancing adjustment in the second stage provided in an embodiment of the present application; Figure 5 As shown, the second stage of voltage balancing adjustment for the battery cluster whose second voltage difference is greater than the preset second voltage difference threshold specifically includes: Step S311: determining a battery cluster whose second voltage difference is greater than a second voltage difference threshold as a second target balancing battery cluster.

[0049] Step S312: when the voltages of the second target balanced battery cluster are all higher than the voltage average, the electricity in the second target balanced battery cluster is transferred to the battery for storage.

[0050] For example, it is assumed that after the voltage balancing adjustment in the first stage, the voltages of the battery clusters are: Rack1 is 750Vdc, Rack2 is 751Vdc, Rack3 is 750Vdc, Rack4 is 750Vdc, and Rack5 is 750Vdc, and the second voltage difference threshold △U2=0.5V is preset. Therefore, after calculating the voltage average value Uave=750.2Vdc of the battery cluster, only the second voltage difference between the voltage of the battery cluster Rack2 and the voltage average value Uave is greater than the second voltage difference threshold △U2, and the voltage of the battery cluster Rack2 is higher than the voltage average value Uave. At this time, the battery cluster Rack2 is determined as the second target balancing battery cluster, and the control module controls the balancing converter module 122 and the first converter conversion module 150 to transfer the electric energy of the battery cluster Rack2 to the storage battery module 160 for storage, until the second voltage difference of the battery cluster Rack2 is less than or equal to the second voltage difference threshold △U2.

[0051] Step S313: when the voltages of the second target balanced battery cluster are all lower than the voltage average, the second target balanced battery cluster is charged with electricity through the storage battery and / or the AC power supply.

[0052] Exemplarily, assuming that after the first stage of voltage balancing adjustment, the voltages of the battery clusters are: Rack1 is 750Vdc, Rack2 is 749Vdc, Rack3 is 750Vdc, Rack4 is 750Vdc, Rack5 is 750Vdc, and the second voltage difference threshold △U2 is preset to be 0.5V. After calculating the average voltage value Uave of the battery cluster = 749.8Vdc, at this time, the second voltage difference between the voltage of the battery cluster Rack2 and the voltage average value Uave is 0.8V, which is greater than the second voltage difference threshold value △U2, and the voltage of the battery cluster Rack2 is lower than the voltage average value Uave. Therefore, after the battery cluster Rack2 is determined as the second target balanced battery cluster, the control module 140 controls the balanced converter module 122 and the first converter conversion module 150 to supplement the electric energy in the battery module 160 to the battery cluster Rack2 until the second voltage difference value of the battery cluster Rack2 is less than or equal to the second voltage difference threshold value △U2; if the battery module 160 is insufficient in power, the second converter conversion module 170 is controlled to supplement the electric energy in the AC power supply module 180 to the battery cluster Rack2.

[0053] In the embodiment of the present application, when the second target balanced battery cluster includes both battery clusters with voltages higher than the voltage average and battery clusters with voltages lower than the voltage average, the second target balanced battery clusters are controlled to transfer electricity to perform voltage balancing adjustment so that the second voltage difference of each second target balanced battery cluster is less than or equal to the second voltage difference threshold. When the second voltage difference of each second target balanced battery cluster cannot be made less than or equal to the second voltage difference threshold by controlling the electricity transfer between each second target balanced battery cluster, electricity is stored or supplemented by the storage battery and / or AC power supply.

[0054] Exemplarily, assuming that after the first stage of voltage balancing adjustment, the voltages of the battery clusters are: Rack1 is 750Vdc, Rack2 is 749Vdc, Rack3 is 751Vdc, Rack4 is 751Vdc, Rack5 is 750Vdc, and the second voltage difference threshold △U2 is preset to be 0.5V. After calculating the average voltage Uave of the battery cluster = 750.2Vdc, at this time, the second voltage difference between the voltage of the battery clusters Rack2, Rack3, Rack4 and the voltage average Uave is greater than the second voltage difference threshold △U2, and the voltage of the battery cluster Rack2 is lower than the voltage average Uave, and the voltage of the battery clusters Rack3 and Rack4 is higher than the voltage average Uave. At this time, the battery clusters Rack2, Rack3, Rack4 are all determined as the second target balanced battery clusters, and the control module 140 controls the balanced converter module 123 and the balanced converter module 124 (not shown in the figure) to release electric energy to the second DC bus DC BUS-2, and controls the balanced converter module 122 to obtain electric energy from the second DC bus DC BUS-2 for replenishment until the second voltage difference of the battery clusters Rack2, Rack3, Rack4 is less than or equal to the second voltage difference threshold △U2. In the second stage of voltage balancing and adjustment, if the power between battery clusters Rack2, Rack3, and Rack4 cannot meet the balancing requirement, the battery module 160 provides or stores energy to achieve balancing. If the amount of energy required to be supplemented is too large, the AC power module 180 can also provide additional energy.

[0055] In summary, the method for voltage balancing between battery clusters and the energy storage system provided in the embodiments of the present application perform the first stage of voltage balancing adjustment on the battery clusters in the standby state, so that the voltages of the battery clusters reach a basically balanced state before the system enters the operating state. After the system enters the operating state, the voltage values ​​of the battery clusters in the operating state are monitored in real time, and the voltage difference between the battery clusters is corrected in time through the second stage of voltage balancing adjustment, thereby avoiding the overload of the battery cluster, improving the stability and safety of the entire energy storage system, and further ensuring the service life and usage capacity of the battery cluster.

[0056] In the description of this application, unless otherwise clearly specified and limited, the terms "first", "second", etc. are only used to distinguish elements with similar properties, rather than indicating or implying relative importance or a specific order. The terms "include", "comprises", or any other variants thereof are intended to cover non-exclusive inclusion, and may include other elements not explicitly listed in addition to those listed elements.

[0057] The units in the device of the embodiment of the present application can be merged, divided and deleted according to actual needs. The technical features of the technical solution of the present application can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the present application.

[0058] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for voltage balancing between battery clusters, characterized in that: include: Acquire a first voltage difference between different battery clusters in a standby state, and if the first voltage difference between at least one pair of battery clusters is greater than a preset first voltage difference threshold, perform a first stage of voltage balancing adjustment on the battery clusters; Calculate the average voltage of all battery clusters after voltage balancing adjustment in the first stage; Acquire a second voltage difference between the voltage of each battery cluster in the operating state and the voltage average value, and perform a second-stage voltage balancing adjustment on the battery clusters whose second voltage difference is greater than a preset second voltage difference threshold; The first stage of voltage balancing adjustment of the battery cluster includes: sorting the first voltage differences between different battery clusters in order of magnitude; Determine the two battery clusters corresponding to the sorted first voltage difference values ​​as the first target balancing battery cluster group in order from largest to smallest; Closing the balancing switch modules connected to the two battery clusters in the first target balancing battery cluster group, performing power transfer balancing between the two battery clusters in the first target balancing battery cluster group, so that the first voltage difference between different battery clusters is less than or equal to the first voltage difference threshold; The step of performing a second-stage voltage balancing adjustment on the battery cluster whose second voltage difference is greater than a preset second voltage difference threshold comprises: Determine a battery cluster whose second voltage difference value is greater than the second voltage difference threshold as a second target balancing battery cluster; When the voltages of the second target balanced battery clusters are all higher than the voltage average, the electricity in the second target balanced battery clusters is transferred to the battery storage; When the voltages of the second target balanced battery clusters are all lower than the voltage average value, the second target balanced battery clusters are charged with electricity through a storage battery and / or an AC power source.

2. The method for voltage balancing between battery clusters according to claim 1, characterized in that: The first stage of voltage balancing adjustment of the battery cluster further includes: Obtaining the voltage value of each battery cluster in the standby state, and sorting the battery clusters according to the magnitude of the voltage values; Add the sorted battery clusters to the first target balanced battery cluster group in order from small to large; The balancing switch module connected to the battery cluster in the first target balancing battery cluster group is closed to transfer and balance the power between the multiple battery clusters that have been added to the first target balancing battery cluster group, so that the first voltage difference between different battery clusters is less than or equal to the first voltage difference threshold.

3. The method for voltage balancing between battery clusters according to claim 1, characterized in that: In the operating state, the balancing switch modules connected to each battery cluster are all in a closed state.

4. The method for voltage balancing between battery clusters according to claim 1, characterized in that: The method further comprises: When the second target balanced battery cluster includes both battery clusters with voltages higher than the voltage average and battery clusters with voltages lower than the voltage average, the second target balanced battery clusters are controlled to transfer electricity to perform voltage balancing adjustment so that the second voltage difference of each second target balanced battery cluster is less than or equal to the second voltage difference threshold.

5. The method for voltage balancing between battery clusters according to claim 4, characterized in that: The method further comprises: When the second voltage difference of each second target balancing battery cluster cannot be made less than or equal to the second voltage difference threshold by controlling the power transfer between each second target balancing battery cluster, power is stored or supplemented by the storage battery and / or AC power supply.

6. An energy storage system, characterized in that: The invention comprises a plurality of battery clusters, a balancing switch module and a balancing converter module corresponding to the plurality of battery clusters one by one, a first DC busbar electrically connected to the plurality of balancing switch modules, a second DC busbar electrically connected to the plurality of balancing converter modules, an energy storage converter electrically connected to the first DC busbar, and a control module respectively connected to the plurality of battery clusters, the plurality of balancing switch modules, and the plurality of balancing converter modules for communication; wherein, The balancing switch module is used to perform a first-stage voltage balancing adjustment on the battery cluster under the control of the control module in a standby state; The balancing converter module is used to perform a second-stage voltage balancing adjustment on the battery cluster under the control of the control module.

7. The energy storage system according to claim 6, characterized in that: It also includes a first inverter conversion module and a battery module. The first inverter conversion module is electrically connected to the battery module, the first DC busbar and the second DC busbar respectively. The battery module is used to store or replenish electricity during the voltage balancing adjustment process.

8. The energy storage system according to claim 7, characterized in that: It also includes a second inverter conversion module and an AC power supply module, wherein the second inverter conversion module is electrically connected to the AC power supply module and the second DC busbar respectively, and the AC power supply module is used to replenish the battery cluster or the battery module during voltage balancing regulation.

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