Battery energy storage system equalization device and equalization method based on reconfigurable converter

Abstract

The invention discloses a battery energy storage system equalization device and equalization method based on a reconfigurable converter, and belongs to the technical field of battery management. The device comprises a battery pack formed by connecting N single batteries in series, a switch array, a reconfigurable converter, a current monitoring circuit, an SOC monitoring circuit and a control circuit, N is larger than or equal to 1, each single battery is connected with the input end of the SOC monitoring circuit, the switch array comprises 2N gating switches, and the control circuit is connected with the input end of the SOC monitoring circuit. The two ends of each single battery are respectively provided with a gating switch and are connected with the primary side of the reconfigurable converter and the input end of the current monitoring circuit through the gating switches arranged at the two ends, and the secondary side of the reconfigurable converter is connected with the two ends of the battery pack; the control circuit is connected with the reconfigurable converter, the reconfigurable converter is provided with at least two circuit structures, and the two circuit structures correspond to different gains respectively; the control circuit is further connected with the output end of the SOC monitoring circuit, the output end of the current monitoring circuit and the switch array.

Description

Technical Field

[0001] The present invention belongs to the field of battery management technology, and in particular, relates to a battery energy storage system long series battery group balancing device and balancing method, more specifically, to a battery energy storage system balancing device and balancing method based on a reconfigurable converter. Background Art

[0002] In high-power application scenarios such as battery energy storage systems and electric vehicles, single cells are often built into battery packs in a long series manner to participate in energy storage and transmission. However, due to the differences in characteristics between battery cells and the unbalanced performance during the charging and discharging process, long-series battery packs are prone to power imbalance problems, and this problem will be further aggravated as the battery energy storage system continues to age. This imbalance will not only significantly affect the overall performance and service life of the battery pack, reduce the charging and discharging efficiency of the energy storage system, but may even bring serious safety hazards, leading to fires, explosions, etc. For this reason, it is particularly important to use battery balancing technology to balance the battery pack.

[0003] At present, it is more common to use an active balancing circuit composed of a DC / DC converter and a switch array to perform balancing operations on a long series battery pack. The switch array is responsible for selecting the balanced single battery. According to the designed balancing algorithm, different single batteries are selected to connect to the DC / DC converter; the primary side of the DC / DC converter is connected to the switch array, and the secondary side is connected to the two ends of the series battery pack, which is responsible for balancing the power of each single battery. In the above scheme, the structure of the DC / DC converter is fixed, which leads to its fixed gain, and it is therefore not suitable for balancing different numbers of single batteries. This leads to large losses, low balancing efficiency, and slow balancing speed in the existing balancing system. Summary of the invention

[0004] The present application provides a battery energy storage system balancing device and balancing method based on a reconfigurable converter. A reconfigurable converter is added to the balancing device, and the circuit structure of the reconfigurable converter can be switched according to the number of single cells to be balanced, so as to be suitable for balancing different numbers of single cells, and suitable conversion circuits are matched for different numbers of single cells, thereby improving the system balancing efficiency.

[0005] The technical solutions adopted in this application are as follows: A first aspect of the present application provides a battery energy storage system balancing device based on a reconfigurable converter, the balancing device comprising a battery pack, a switch array, a reconfigurable converter, a current monitoring circuit, a SOC monitoring circuit and a control circuit, wherein: The battery pack is formed by N single cells connected in series, N≥1, each single cell is connected to the input end of the SOC monitoring circuit, the switch array includes 2N selection switches, and each single cell is respectively configured with one selection switch at both ends and connected to the primary side of the reconfigurable converter and the input end of the current monitoring circuit through the selection switches configured at both ends, and the secondary side of the reconfigurable converter is connected to both ends of the battery pack; the control circuit is connected to the reconfigurable converter, and the reconfigurable converter has at least two circuit structures, and the two circuit structures correspond to different gains respectively; The control circuit is also connected to the output end of the SOC monitoring circuit, the output end of the current monitoring circuit and the switch array, and the control circuit first determines the single cell to be balanced according to the output signal of the SOC monitoring circuit, and then drives the switch array to connect the corresponding single cell to the primary side of the reconfigurable converter and the input end of the current monitoring circuit, and drives the reconfigurable converter to switch to a circuit structure corresponding to the number of connected single cells.

[0006] In some examples, the control circuit includes a microcontroller and a drive circuit connected to the microcontroller, and the drive circuit is connected to the reconfigurable converter, and the drive circuit can drive the reconfigurable converter to switch between at least two circuit structures with different gains based on instructions from the microcontroller; The microcontroller is connected to the output end of the SOC monitoring circuit, the output end of the current monitoring circuit and the switch array, and the microcontroller first determines the single cell to be balanced according to the output signal of the SOC monitoring circuit, and then drives the switch array to connect the corresponding single cell to the primary side of the reconfigurable converter and the input end of the current monitoring circuit, and drives the reconfigurable converter to switch to a circuit structure corresponding to the number of connected single cells.

[0007] In some examples, the reconfigurable converter includes: Cascade transformer; A primary full-bridge circuit, comprising a first primary half-bridge circuit consisting of a first primary switch tube, a fifth primary switch tube, and a second primary switch tube connected in series, and a second primary half-bridge circuit consisting of a third primary switch tube and a fourth primary switch tube connected in series in sequence, wherein the first primary half-bridge circuit and the second primary half-bridge circuit are connected in parallel with a first capacitor, the first primary switch tube and the fifth primary switch tube, and the fifth primary switch tube and the second primary switch tube are connected to two ends of a low-voltage side of a cascade transformer through a second capacitor and a third capacitor respectively, and the third primary switch tube and the fourth primary switch tube are connected to a primary center tap of the cascade transformer; and, A secondary full-bridge circuit includes a first secondary half-bridge circuit formed by a first secondary switch tube and a second secondary switch tube connected in series, and a second secondary half-bridge circuit formed by a third secondary switch tube and a fourth secondary switch tube connected in series, and the first secondary half-bridge circuit and the second secondary half-bridge circuit are connected in parallel with a fourth capacitor and a fifth capacitor connected in series, the first secondary switch tube and the second secondary switch tube are connected to the same-name end on the high-voltage side of the cascade transformer through a first inductor, the third secondary switch tube and the fourth secondary switch tube are connected to the non-same-name end on the high-voltage side of the cascade transformer through a second inductor, and the fourth capacitor and the fifth capacitor are connected to the secondary center tap of the cascade transformer.

[0008] In some examples, the cascade transformer is formed by cascading two transformers, and the turns ratio of the two transformers is 1:n.

[0009] In some examples, the first inductor and the second inductor are AC clamping inductors, and are both formed by the leakage inductance of the cascade transformer and an external inductor connected in series.

[0010] A second aspect of the present application provides a battery energy storage system balancing method based on a reconfigurable converter. The balancing method is based on the above battery energy storage system balancing device. The balancing method comprises the following steps: Determining the state of the single cell to be balanced and each single cell in the battery pack according to the output signal of the SOC monitoring circuit; Controlling the switch array to connect the single cells to be balanced in the same state to the primary side of the reconfigurable converter and the input end of the current monitoring circuit; Switching the circuit structure of the reconfigurable converter according to the number of connected single cells, and determining a balanced working mode according to the state of the connected single cells, wherein the balanced working mode includes a charging balanced mode and a discharging balanced mode; and, Perform battery balancing in the corresponding balancing working mode.

[0011] In some examples, the step of determining the single cells to be balanced in the battery pack and the states of each single cell according to the output signal of the SOC monitoring circuit includes: Using the SOC monitoring circuit to monitor the SOC parameters of each single battery in the battery pack in real time; Calculating an average value of the SOC parameters of all the single cells in the battery pack; Calculating the difference between the SOC parameter of each single battery and the average value, and determining whether the difference exceeds a preset balancing threshold; If yes, the corresponding single cell is determined as the single cell to be balanced, and whether the difference between the SOC parameter of the corresponding single cell and the average value is positive; If yes, the state of the corresponding single battery is determined to be an overcharged state; If not, the state of the corresponding single battery is determined to be an undercharged state.

[0012] In some examples, the same state is an overcharge state or an undercharge state, and when the same state is an overcharge state, the balancing working mode determined according to the state of the connected single cell is a discharge balancing mode, and when the same state is an undercharge state, the balancing working mode determined according to the state of the connected single cell is a charge balancing mode.

[0013] In some examples, the reconfigurable converter has a first conversion circuit structure, a second conversion circuit structure, a third conversion circuit structure, and a fourth conversion circuit structure, and the gain of the fourth conversion circuit structure is greater than the gain of the third conversion circuit structure, and the gain of the third conversion circuit structure is greater than the gain of the second conversion circuit structure and the gain of the first conversion circuit structure.

[0014] In some examples, the battery pack is formed by N single cells connected in series, N≥1, and when the number of single cells to be balanced is less than 0.2N, the circuit structure of the reconfigurable converter is switched to the fourth conversion circuit structure; when the number of single cells to be balanced is greater than 0.8N, the circuit structure of the reconfigurable converter is switched to the gain of the second conversion circuit structure or the first conversion circuit structure; when the number of single cells to be balanced is between 0.2N and 0.8N, the circuit structure of the reconfigurable converter is switched to the third conversion circuit structure.

[0015] The reconfigurable converter involved in the present application has a switchable circuit structure, which can be switched to different gain modes according to the number of single cells required to be balanced each time. Therefore, when balancing different numbers of single cells, the voltage gain of the required balanced battery can be matched with the voltage of the battery pack, reducing transformer losses, improving the balancing efficiency, and shortening the balancing time. In addition, the reconfigurable converter greatly improves the reliability and efficiency of the overall system compared to the fixed structure, and is particularly suitable for the balancing management of long series battery packs in high-power scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of a battery energy storage system balancing device based on a reconfigurable converter provided in an embodiment of the present application; Figure 2 This is the first working circuit structure of the reconfigurable converter provided in the embodiment of the present application; Figure 3 This is the second working circuit structure of the reconfigurable converter provided in the embodiment of the present application; Figure 4This is the third working circuit structure of the reconfigurable converter provided in the embodiment of the present application; Figure 5 This is the fourth working circuit structure of the reconfigurable converter provided in the embodiment of the present application; Figure 6 It is a schematic diagram of implementing equalization for a single battery in an overcharged state provided by an embodiment of the present application; Figure 7 It is a schematic diagram of implementing equalization for a single battery in an undercharged state provided by an embodiment of the present application; Figure 8 It is a schematic diagram of implementing equalization for two batteries in an overcharged state provided by an embodiment of the present application; Fig. 9 is a schematic diagram of implementing balancing for two batteries in an undercharged state provided by an embodiment of the present application; Fig.10 It is a schematic diagram of implementing equalization for four batteries in an overcharged state provided by an embodiment of the present application; Fig.11 It is a schematic diagram of implementing equalization for four batteries in an undercharged state provided by an embodiment of the present application; Fig.12 It is a flow chart of a battery energy storage system balancing method based on a reconfigurable converter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0017] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, but should not be construed as limiting the present invention.

[0018] Figure 1 is a schematic diagram of a battery energy storage system balancing device based on a reconfigurable converter provided in an embodiment of the present application, Figures 2 to 5 are four different working circuit structures of the reconfigurable converter provided in the embodiments of the present application (see the black solid line). n Indicates single battery, S c11 , S c12 , S c21 , S c22 , ..., S cn1 , S cn2 represents the selection switch, C1, C2, C3, C4 represent capacitors, S p1 , S p2 , S p3 , S p4 , S p5 Represents the primary switch tube, S s1 , S s2 , S s3 , S s4Indicates the secondary switch tube, L s1 , L s2 represents inductance, T1 and T2 represent transformers, and 1:n is the transformer turns ratio. a, b, c, d, e, and f represent circuit nodes, V LV V is the low voltage side voltage of the converter, used to connect long series battery packs; HV is the high voltage side voltage of the converter Combination Figures 1 to 5 As shown, the present embodiment provides a battery energy storage system balancing device based on a reconfigurable converter, including a battery pack, a switch array, a reconfigurable converter, a current monitoring circuit, an SOC monitoring circuit and a control circuit, wherein the SOC monitoring circuit is used to monitor the SOC parameters (State of Charge) of each single cell in the battery pack, and the current monitoring circuit is used to monitor the current of the battery energy storage system balancing device during the balancing operation. The battery pack, switch array, reconfigurable converter and control circuit as described above are respectively introduced below, and their connection and functions with the SOC monitoring circuit and the control circuit.

[0019] Battery Pack The battery pack is formed by N single cells connected in series, N ≥ 1, such as Figure 1 Schematic diagram of single cell B1, single cell B2, ... single cell B n , single cell B1, single cell B2... single cell B n Each of them is connected to the input end of the SOC monitoring circuit, so that the SOC monitoring circuit can obtain the sampled value of the SOC parameter.

[0020] Switch Array The switch array includes 2N gate switches, such as Figure 1 Schematic diagram of the gate switch S c11 , select switch S c12 , the gate switch S c21 , select switch S c22 , ..., select switch S cn1 , select switch S cn2 , and each of the above-described single cells is respectively provided with a gate switch at both ends, and each single cell is connected to the primary side of the reconfigurable converter and the input end of the current monitoring circuit through the gate switches provided at both ends. For example, the single cell B1 is provided with a gate switch S at both ends. c11 and the strobe switch S c12 The single cell B2 is connected to the primary side of the reconfigurable converter and the input end of the current monitoring circuit. The single cell B2 is connected to the primary side of the reconfigurable converter and the input end of the current monitoring circuit. c21 and the strobe switch S c22Connected to the primary side of the reconfigurable converter and the input of the current monitoring circuit... single cell B n By configuring the gate switch S at both ends cn1 and the strobe switch S cn2 Connected to the primary side of the reconfigurable converter and the input of the current monitoring circuit.

[0021] Reconfigurable Converter The secondary side of the reconfigurable converter is connected to both ends of the battery pack as a whole. The reconfigurable converter has at least two working circuit structures, and the reconfigurable converter has different gains when the two working circuit structures perform balanced operation. For example, Figure 1 The schematic reconfigurable converter has Figure 2 , Figure 3 , Figure 4 , Figure 5 Four working circuit structures are shown, and the gains of the four working circuit structures are different.

[0022] Control Circuit The control circuit is connected to the reconfigurable converter, and is also connected to the output end of the SOC monitoring circuit, the output end of the current monitoring circuit and the switch array. The SOC monitoring circuit collects the SOC parameters of each single cell and transmits the collected SOC parameters to the control circuit. The current monitoring circuit monitors the working current of the equalization device. The switch array is controlled by the control circuit, and the control circuit first determines the single cell to be balanced according to the output signal of the SOC monitoring circuit, and then drives the switch array to make the corresponding selection switch on or off so as to connect the corresponding single cell to the primary side of the reconfigurable converter and the input end of the current monitoring circuit, and drives the reconfigurable converter to switch to the working circuit structure corresponding to the number of connected single cells, and the connected single cells are subjected to the equalization operation under the corresponding working circuit structure.

[0023] The fixed structure converters commonly used in existing balancing devices, such as flyback converters and Buck-Boost converters, cannot switch the working structure and can only work in a fixed gain mode, that is, they can only maintain high balancing efficiency and speed when balancing a specific number of single cells, and control the loss at a low level. With the use and aging of battery energy storage systems, the number of single cells that need to be balanced is not fixed, and the number of single cells to be balanced changes, so the balancing efficiency and speed of existing balancing devices become lower.

[0024] Compared with the existing balancing device, the reconfigurable converter used in this embodiment can switch the working circuit structure according to the number of single cells to be balanced to adapt to the needs of balancing operations of different numbers of single cells, thereby improving the balancing efficiency. For example, when the number of single cells to be balanced is smaller, the reconfigurable converter switches to a working circuit structure with a higher gain to complete the battery balancing efficiently. In addition, this embodiment can achieve simultaneous balancing of multiple single cells, greatly accelerating the balancing speed of the battery energy storage system.

[0025] In some examples, combined Figure 1 As shown, the control circuit as above includes a microcontroller and a driving circuit connected to the microcontroller, and the driving circuit is connected to the reconfigurable converter. The microcontroller is convenient for programming and design to execute the required instructions and algorithms, and can control the driving circuit to perform corresponding actions through the instructions generated by the microcontroller. Specifically, the driving circuit can drive the reconfigurable converter to switch between at least two working circuit structures with different gains based on the instructions of the microcontroller. In this way, the microcontroller can be used to easily switch the working circuit structure of the reconfigurable converter according to the number of single cells to be balanced; the microcontroller is connected to the output end of the SOC monitoring circuit, the output end of the current monitoring circuit and the switch array, and the microcontroller first determines the single cell to be balanced according to the output signal of the SOC monitoring circuit, and then drives the switch array to connect the corresponding single cell to the primary side of the reconfigurable converter and the input end of the current monitoring circuit, and drives the reconfigurable converter to switch to the circuit structure corresponding to the number of connected single cells.

[0026] Combination Figures 1 to 5 As shown, in some examples, the reconfigurable converter includes: Cascade transformer, exemplarily, the cascade transformer is formed by cascading a first transformer T1 and a second transformer T2, the turns ratio of the two transformers is 1:n, exemplarily, 1≤n≤5; The primary full-bridge circuit includes a first primary switch tube S p1 , the fifth primary switch tube S p5 , the second primary switch tube S p2 The first primary half-bridge circuit connected in series and the third primary switch tube S p3 , the fourth primary switch tube S p4 The second primary half-bridge circuit is connected in series, and the first primary half-bridge circuit and the second primary half-bridge circuit are connected in parallel with the first capacitor C1, and the first primary switch tube S p1 With the fifth primary switch tube S p5 Between (as shown in the figure at point a), the fifth primary switch tube S p5 With the second primary switch tube S p2 The two capacitors (point c in the figure) are connected to the low voltage side V of the cascade transformer through the second capacitor C2 and the third capacitor C3.LV The third primary switch tube S p3 , the fourth primary switch tube S p4 The center tap of the primary side of the cascade transformer is connected between (point b in the figure); and, The secondary full-bridge circuit includes a first secondary switch tube S s1 , the second secondary switch tube S s2 The first secondary half-bridge circuit is formed in series, and the third secondary switch tube S s3 , the fourth secondary switch tube S s4 The second secondary half-bridge circuit is formed in series, and the first secondary half-bridge circuit, the second secondary half-bridge circuit, the fourth capacitor C4 and the fifth capacitor C5 connected in series are connected in parallel, and the first secondary switch tube S s1 The second secondary switch tube S s2 The first inductor L s1 Connect to the high voltage side of the cascade transformer V HV The same-name end of the third secondary switch tube S s3 With the fourth secondary switch tube S s4 The second inductor L s2 Connect to the high voltage side of the cascade transformer V HV The non-same-name ends of the two fourth capacitors C4 (such as point e in the figure) are connected to the secondary center tap of the cascade transformer; Furthermore, the first primary switch tube S p1 , the second primary switch tube S p2 , the third primary switch tube S p3 , the fourth primary switch tube S p4 , the fifth primary switch tube S p5 And the first secondary switch tube S s1 , the second secondary switch tube S s2 , the third secondary switch tube S s3 , the fourth secondary switch tube S s4 They are all connected to the driving circuit and controlled by it to switch between the on and off states.

[0027] In this embodiment, the low-voltage side of the reconfigurable converter is formed by two half-bridge circuits connected in parallel, and the first bridge arm is composed of three power switches (the first secondary switch tube S p1 , the fifth secondary switch tube S p5 , and the second secondary switch tube S p2 ) are connected in series, and the midpoint of each two power switches is connected to the primary winding of the cascade transformer; the second bridge arm consists of two power switches (the third secondary switch tube S p3 , and the fourth secondary switch tube S p4) are connected in series, and the midpoint of the two power switches is connected to the center tap of the cascade transformer. The high-voltage side of the reconfigurable converter is composed of two half-bridge circuits in parallel, and the midpoint of each bridge arm is connected to the secondary winding of the cascade transformer. This embodiment is based on the fact that the reconfigurable converter can achieve multiple voltage gains while reducing the transformer turns ratio, which helps to reduce transformer losses. In this embodiment, the PWM signal generated by the microcontroller controls the conduction of each switch tube through the drive circuit, thereby realizing the switching of the working circuit structure of the reconfigurable converter. In some examples, the first inductor and the second inductor are AC clamping inductors, and are both formed by the leakage inductance of the cascade transformer and the external inductor in series.

[0028] Figures 6 to 11 The diagram shows the balancing when the number of single cells connected to the balancing circuit is 1, 2, and 4 respectively.

[0029] When the number of cells to be balanced is one, the reconfigurable converter switches to a high-gain operating circuit structure during balancing (corresponding to Figure 5 See Figure 6 As shown, at this time, the driving signal of the secondary side of the reconfigurable converter lags behind the driving signal of the primary side of the reconfigurable converter, releasing the energy of the overcharged battery in the battery pack to the entire long series battery pack (assuming that the single cell B1 is in an overcharged state), and the single cell B1 is switched on by switching on the switch S c11 , select switch S c12 Connected to the primary side of the reconfigurable converter, the SOC parameters of a single overcharged battery are balanced to the average value through the discharge of the reconfigurable converter. Figure 7 As shown, at this time, the driving signal of the secondary side of the reconfigurable converter is ahead of the driving signal of the primary side of the reconfigurable converter, and the energy of the battery pack is transferred to the undercharged battery (assuming that the single battery B1 is in an undercharged state). The single battery B1 is switched on by the switch S c11 , select switch S c12 Connected to the primary side of the reconfigurable converter, the SOC parameters of the single undercharged battery are balanced to the average value through the charging of the reconfigurable converter.

[0030] When the number of batteries to be balanced is two, the reconfigurable converter switches to a medium-gain working circuit structure during balancing operation. Figure 8 As shown, at this time, the driving signal of the secondary side of the reconfigurable converter lags behind the driving signal of the primary side of the reconfigurable converter, and the energy of the overcharged battery in the battery pack is released to the entire long series battery pack (assuming that the single battery B1 and the single battery B2 are both in an overcharged state). The single battery B1 and the single battery B2 are connected by the gate switch S c11 , select switch S c12 , select switch S c21 , select switch S c22Connected to the primary side of the reconfigurable converter, the SOC parameters of the two overcharged batteries are balanced to the average value through the discharge of the reconfigurable converter. Fig. 9 As shown, at this time, the driving signal of the secondary side of the reconfigurable converter is ahead of the driving signal of the primary side of the reconfigurable converter, and the energy of the battery pack is transmitted to the undercharged battery (assuming that the single battery B1 and the single battery B2 are both in an undercharged state). The single battery B1 and the single battery B2 are connected by the gate switch S c11 , select switch S c12 , select switch S c21 , select switch S c22 Connected to the primary side of the reconfigurable converter, the SOC parameters of the two under-charged batteries are balanced to the average value through the charging of the reconfigurable converter.

[0031] When the number of batteries to be balanced is four, the reconfigurable converter switches to a low-gain working circuit structure during balancing operation. Fig.10 and Fig.11 For details, refer to Fig.10 As shown, at this time, the driving signal of the secondary side of the reconfigurable converter lags behind the driving signal of the primary side of the reconfigurable converter, and the energy of the overcharged battery in the battery pack is released to the entire long series battery pack (assuming that the single battery B1, single battery B2, single battery B3, and single battery B4 are in an overcharged state). The single battery B1, single battery B2, single battery B3, and single battery B4 are connected to the battery pack through the gate switch S c11 , select switch S c12 , select switch S c21 , select switch S c22 , select switch S c31 , select switch S c32 , select switch S c41 , select switch S c42 Connected to the primary side of the reconfigurable converter, the SOC parameters of the four overcharged batteries are balanced to the average value through the discharge of the reconfigurable converter. Fig.11 As shown, at this time, the driving signal of the secondary side of the reconfigurable converter is ahead of the driving signal of the primary side of the reconfigurable converter, and the energy of the battery pack is transmitted to the undercharged battery (assuming that the single battery B1, single battery B2, single battery B3, and single battery B4 are in an undercharged state). The single battery B1, single battery B2, single battery B3, and single battery B4 are connected to the undercharged battery through the gate switch S c11 , select switch S c12 , select switch S c21 , select switch S c22 , select switch S c31 , select switch S c32 , select switch S c41 , select switch S c42Connected to the primary side of the reconfigurable converter, the SOC parameters of the four under-charged batteries are balanced to the average value through the charging of the reconfigurable converter.

[0032] Fig.12 It is a flow chart of a battery energy storage system balancing method based on a reconfigurable converter provided in an embodiment of the present application.

[0033] Reference Fig.12 As shown, combined with Figures 1 to 11 The embodiment of the present application further provides a battery energy storage system balancing method based on a reconfigurable converter. The balancing method is based on the above battery energy storage system balancing device. The balancing method includes the following steps S10 to S40, wherein: Step S10, determining the single cell to be balanced and the state of each single cell in the battery pack according to the output signal of the SOC monitoring circuit; Step S20, controlling the switch array to connect the single cells to be balanced in the same state to the primary side of the reconfigurable converter and the input end of the current monitoring circuit; Step S30, switching the working circuit structure of the reconfigurable converter according to the number of connected single cells, and determining a balanced working mode according to the state of the connected single cells, the balanced working mode including a charging balanced mode and a discharging balanced mode; and, Step S40: Perform battery balancing in a corresponding balancing working mode.

[0034] The method of this embodiment can switch the working circuit structure of the reconfigurable converter according to the number of batteries to be balanced connected to the balancing circuit, so that the reconfigurable converter is always in a high-efficiency operating state, which greatly improves the stability and efficiency of the battery energy storage system balancing device. Specifically, the method of this embodiment uses a reconfigurable converter with a switchable working circuit structure to enable the reconfigurable converter to switch different gain modes according to the number of single cells that need to be balanced each time, and the fewer the number of single cells that need to be balanced, the higher the gain mode the converter operates in, while ensuring that the transformer turns are relatively low, significantly reducing transformer losses, improving balancing efficiency, and shortening balancing time. In addition, compared with fixed-structure converters, reconfigurable converters greatly improve the reliability and efficiency of the system, and are particularly suitable for balancing management of long series battery packs in high-power scenarios.

[0035] In some examples, the step of determining the single cells to be balanced in the battery pack and the states of each single cell according to the output signal of the SOC monitoring circuit as described in the above embodiment includes: Using the SOC monitoring circuit to monitor the SOC parameters of each single cell in the battery pack in real time, for example, sampling the SOC parameters of each single cell to achieve real-time monitoring; Calculate the average value of the SOC parameters of all the single cells in the battery pack using the received sampled values; Calculate the difference between the SOC parameter of each single battery and the average value, and determine whether the difference exceeds a preset balancing threshold; If yes, the corresponding single cell is determined as the single cell to be balanced, and the difference between the SOC parameter of the corresponding single cell and the average value is determined to be positive, and it can also be determined whether the SOC parameter of the corresponding single cell is greater than the average value; If yes, the state of the corresponding single battery is determined to be an overcharged state; If not, the state of the corresponding single battery is determined to be an undercharged state.

[0036] In this example, the SOC parameters of each single cell in the battery energy storage system are monitored in real time, and the single cells and their states to be balanced are determined based on this, and the number of single cells to be balanced can be calculated, so that the reconfigurable converter can be switched to the corresponding working circuit structure during balancing, and the balancing mode can be determined according to the states of the single cells to be balanced, thereby performing real-time battery balancing under the corresponding balancing mode.

[0037] In some examples, the same state is an overcharge state or an undercharge state, and when the same state is an overcharge state, the balancing working mode determined according to the state of the connected single cell is a discharge balancing mode, so that the energy of the single cell in the overcharge state is released to the long-series battery group to achieve the discharge of the single cell, and the SOC parameters of the single cell in the overcharge state are balanced to the average value through the discharge process; and when the same state is an undercharge state, the balancing working mode determined according to the state of the connected single cell is a charge balancing mode, so that the energy of the long-series battery group is transmitted to the single cell in the undercharge state to achieve the charging of the single cell, and the SOC parameters of the single cell in the undercharge state are balanced to the average value through the charging process.

[0038] In some examples, the reconfigurable converter has a first conversion circuit structure, a second conversion circuit structure, a third conversion circuit structure, and a fourth conversion circuit structure, and the gain of the fourth conversion circuit structure is greater than the gain of the third conversion circuit structure, and the gain of the third conversion circuit structure is greater than the gain of the second conversion circuit structure and the gain of the first conversion circuit structure.

[0039] In some examples, the battery pack is formed by N single cells connected in series, N≥1, and when the number of single cells to be balanced is less than 0.2N, the circuit structure of the reconfigurable converter is switched to the fourth conversion circuit structure, when the number of single cells to be balanced is greater than 0.8N, the circuit structure of the reconfigurable converter is switched to the gain of the second conversion circuit structure or the first conversion circuit structure, when the number of single cells to be balanced is between 0.2N and 0.8N, the circuit structure of the reconfigurable converter is switched to the third conversion circuit structure. N can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10..., for example, N can be 10.

[0040] The reconfigurable converter involved in the present application has a switchable circuit structure, which can be switched to different gain modes according to the number of single cells required to be balanced each time. Therefore, high voltage gain can be achieved when balancing different numbers of single cells, reducing transformer losses, improving balancing efficiency, and shortening balancing time. In addition, the reconfigurable converter greatly improves the reliability and efficiency of the overall system compared to the fixed structure, and is particularly suitable for the balancing management of long series battery packs in high-power scenarios.

[0041] The above describes in detail the structure, features and effects of the present invention based on the embodiments shown in the drawings. The above is only a preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown in the drawings. Any changes made according to the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which still do not exceed the spirit covered by the description and drawings, should be within the protection scope of the present invention.

Claims

1. A battery energy storage system balancing device based on a reconfigurable converter, characterized in that: It includes a battery pack, a switch array, a reconfigurable converter, a current monitoring circuit, a SOC monitoring circuit and a control circuit, wherein: The battery pack is formed by N single cells connected in series, N≥1, each single cell is connected to the input end of the SOC monitoring circuit, the switch array includes 2N selection switches, and each single cell is respectively configured with one selection switch at both ends and connected to the primary side of the reconfigurable converter and the input end of the current monitoring circuit through the selection switches configured at both ends, and the secondary side of the reconfigurable converter is connected to both ends of the battery pack; the control circuit is connected to the reconfigurable converter, and the reconfigurable converter has at least two circuit structures, and the two circuit structures correspond to different gains respectively; The control circuit is also connected to the output end of the SOC monitoring circuit, the output end of the current monitoring circuit and the switch array, and the control circuit first determines the single cell to be balanced according to the output signal of the SOC monitoring circuit, and then drives the switch array to connect the corresponding single cell to the primary side of the reconfigurable converter and the input end of the current monitoring circuit, and drives the reconfigurable converter to switch to a circuit structure corresponding to the number of connected single cells.

2. The battery energy storage system balancing device according to claim 1, characterized in that: The control circuit includes a microcontroller and a driving circuit connected to the microcontroller, and the driving circuit is connected to the reconfigurable converter, and the driving circuit can drive the reconfigurable converter to switch between at least two circuit structures with different gains based on instructions from the microcontroller; The microcontroller is connected to the output end of the SOC monitoring circuit, the output end of the current monitoring circuit and the switch array, and the microcontroller first determines the single cell to be balanced according to the output signal of the SOC monitoring circuit, and then drives the switch array to connect the corresponding single cell to the primary side of the reconfigurable converter and the input end of the current monitoring circuit, and drives the reconfigurable converter to switch to a circuit structure corresponding to the number of connected single cells.

3. The battery energy storage system balancing device according to claim 1, characterized in that: The reconfigurable converter comprises: Cascade transformer; A primary full-bridge circuit, comprising a first primary half-bridge circuit consisting of a first primary switch tube, a fifth primary switch tube, and a second primary switch tube connected in series, and a second primary half-bridge circuit consisting of a third primary switch tube and a fourth primary switch tube connected in series in sequence, wherein the first primary half-bridge circuit and the second primary half-bridge circuit are connected in parallel with a first capacitor, the first primary switch tube and the fifth primary switch tube, and the fifth primary switch tube and the second primary switch tube are connected to two ends of a low-voltage side of a cascade transformer through a second capacitor and a third capacitor respectively, and the third primary switch tube and the fourth primary switch tube are connected to a primary center tap of the cascade transformer; and, A secondary full-bridge circuit includes a first secondary half-bridge circuit formed by a first secondary switch tube and a second secondary switch tube connected in series, and a second secondary half-bridge circuit formed by a third secondary switch tube and a fourth secondary switch tube connected in series, and the first secondary half-bridge circuit and the second secondary half-bridge circuit are connected in parallel with a fourth capacitor and a fifth capacitor connected in series, the first secondary switch tube and the second secondary switch tube are connected to the same-name end on the high-voltage side of the cascade transformer through a first inductor, the third secondary switch tube and the fourth secondary switch tube are connected to the non-same-name end on the high-voltage side of the cascade transformer through a second inductor, and the fourth capacitor and the fifth capacitor are connected to the secondary center tap of the cascade transformer.

4. The battery energy storage system balancing device according to claim 3, characterized in that: The cascade transformer is formed by cascading two transformers, and the turns ratio of the two transformers is 1:n.

5. The battery energy storage system balancing device according to claim 3, characterized in that: The first inductor and the second inductor are AC clamping inductors, and are both formed by the leakage inductance of the cascade transformer and an external inductor connected in series.

6. A battery energy storage system balancing method based on a reconfigurable converter, the balancing method being based on the battery energy storage system balancing device according to claim 1, characterized in that: The following steps are involved: Determining the state of the single cell to be balanced and each single cell in the battery pack according to the output signal of the SOC monitoring circuit; Controlling the switch array to connect the single cells to be balanced in the same state to the primary side of the reconfigurable converter and the input end of the current monitoring circuit; Switching the circuit structure of the reconfigurable converter according to the number of connected single cells, and determining a balancing operation mode according to the state of the connected single cells, wherein the balancing operation mode includes a charging balancing mode and a discharging balancing mode; and, Perform battery balancing in the corresponding balancing working mode.

7. The battery energy storage system balancing method according to claim 6, characterized in that: The step of determining the single battery to be balanced and the state of each single battery in the battery pack according to the output signal of the SOC monitoring circuit comprises: Using the SOC monitoring circuit to monitor the SOC parameters of each single battery in the battery pack in real time; Calculating an average value of the SOC parameters of all the single cells in the battery pack; Calculating the difference between the SOC parameter of each single battery and the average value, and determining whether the difference exceeds a preset balancing threshold; If yes, the corresponding single cell is determined as the single cell to be balanced, and it is determined whether the difference between the SOC parameter of the corresponding single cell and the average value is positive; If yes, the state of the corresponding single battery is determined to be an overcharged state; If not, the state of the corresponding single battery is determined to be an undercharged state.

8. The battery energy storage system balancing method according to claim 7, characterized in that: The same state is an overcharge state or an undercharge state, and when the same state is an overcharge state, the balancing working mode determined according to the state of the connected single battery is a discharge balancing mode, and when the same state is an undercharge state, the balancing working mode determined according to the state of the connected single battery is a charge balancing mode.

9. The battery energy storage system balancing method according to claim 7, characterized in that: The reconfigurable converter has a first conversion circuit structure, a second conversion circuit structure, a third conversion circuit structure, and a fourth conversion circuit structure, and the gain of the fourth conversion circuit structure is greater than the gain of the third conversion circuit structure, and the gain of the third conversion circuit structure is greater than the gain of the second conversion circuit structure and the gain of the first conversion circuit structure.

10. The battery energy storage system balancing method according to claim 9, characterized in that: The battery pack is formed by N single cells connected in series, N≥1, and when the number of single cells to be balanced is less than 0.2N, the circuit structure of the reconfigurable converter is switched to the fourth conversion circuit structure; when the number of single cells to be balanced is greater than 0.8N, the circuit structure of the reconfigurable converter is switched to the gain of the second conversion circuit structure or the first conversion circuit structure; when the number of single cells to be balanced is between 0.2N and 0.8N, the circuit structure of the reconfigurable converter is switched to the third conversion circuit structure.

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