Reconfigurable layered equalization method based on retired battery energy storage module

Abstract

The invention provides a reconfigurable layered equalization method based on a retired battery energy storage module, and the method achieves the dynamic energy redistribution between a battery monomer and the module through the cooperative work of an inner-layer reconfigurable battery pack and an outer-layer DC / DC converter. According to the method, high-precision SOC estimation and a multi-objective optimization strategy are combined, the equalization speed and the energy utilization rate are remarkably improved, and the method is suitable for a large-scale retired battery energy storage system and has good economical efficiency and reliability.

Description

Technical Field

[0001] This invention belongs to the field of battery recycling technology, and in particular relates to a reconfigurable hierarchical balancing method based on retired battery energy storage modules. Background Technology

[0002] As power batteries enter a phase of large-scale retirement, the lack of an effective recycling and cascade utilization system not only affects resource utilization efficiency but may also lead to environmental pollution and safety hazards. Although retired batteries cannot meet the high-performance requirements of electric vehicles, they have a high remaining capacity and can be used to form power storage modules as a regulation resource for the power system. However, manufacturing processes, operating conditions, and other factors cause inconsistencies between battery cells, manifested as deviations in capacity, internal resistance, self-discharge rate, state of charge (SOC), and operating voltage, affecting the energy utilization rate, lifespan, and safety of the energy storage system. Therefore, it is necessary to construct an efficient balancing strategy to reduce differences between cells and ensure the stable operation of retired batteries in high-proportion renewable energy systems.

[0003] Currently, balancing is mainly divided into active balancing and passive balancing based on different balancing devices. Active balancing has advantages such as fast balancing speed, low energy dissipation, and wide application scenarios, and has become the mainstream method of balancing technology. For example, single inductors are combined with multiple inductors to form inductive balancing circuits, inductive elements are combined with Cuk chopper circuits to form novel two-layer balancing topologies, and Cuk circuits are combined with flyback transformers to form two-layer hybrid balancing structures. Although the above research all revolves around multi-layer balancing architectures to meet the balancing needs of large-scale energy storage systems, most of them still focus on active balancing topologies such as capacitor and inductive balancing.

[0004] Therefore, a reconfigurable hierarchical balancing method based on retired battery energy storage modules is needed to solve the above problems. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a reconfigurable hierarchical balancing method based on retired battery energy storage modules. The innermost layer uses a reconfigurable battery pack, and the battery cells with the highest inconsistency or faulty battery cells are isolated by control switches, and the connection relationship between batteries is changed to achieve balancing within the pack. The outer layer uses a reconfigurable battery pack as the smallest balancing unit, and the energy is transferred between the battery modules through a DC / DC converter to achieve balancing between the packs. It is mainly applied to large-scale power storage modules composed of retired batteries.

[0006] To achieve the above-mentioned technical effects, the technical solution adopted by the present invention is as follows: A reconfigurable hierarchical equalization method based on retired battery energy storage modules includes the following steps: Construct a hierarchical equalization topology, including an inner layer of reconfigurable battery packs and an outer layer of DC / DC converter equalization units; The inner layer dynamically reconstructs the battery connection relationship through a switch matrix to achieve the isolation and access of individual battery cells within the group; The outer layer uses a Buck-Boost converter to achieve graded energy transfer between battery modules; A state of charge (SOC) estimation method based on extended Kalman filtering is adopted to obtain the state of charge of each battery cell in real time. Based on the SOC estimation results, the inner layer switching state and the outer layer converter operating mode are dynamically controlled to achieve coordinated balancing within and between battery packs.

[0007] Preferably, the inner layer circuit is n A reconfigurable battery pack composed of connected series of batteries uses individual cells as the balancing element; the balancing circuit consists of individual cells. Control switch Composition: Each individual battery cell is connected in series with a switch, using... This indicates that the switch controls the connection of a single battery cell, and is then connected in parallel with another switch for... This indicates that the switch controls the isolation of individual battery cells.

[0008] Preferably, the outer layer circuit uses the inner layer reconfigurable battery pack as the outer layer equalization target, represented as follows: Two MOSFET switches and an inductor, the main components of the energy storage element, perform energy transfer between the two battery packs to achieve inter-pack balancing; this constitutes the smallest balancing unit for the outer layer. The outermost layer is balanced in pairs, forming the first layer of inter-group balancing. After the first layer of inter-group balancing is completed, the upper layer balancing unit becomes one of the battery modules in the second layer of inter-group balancing, and then performs pairwise balancing again; and so on. n Each battery pack passes k Layered DC / DC conversion completes overall equalization .

[0009] Preferably, the equalization method within the outer circuit groups of the two battery packs is as follows: With T as one switching cycle, the total resistance of the circuit through the switching transistor during conduction is set to... The total circuit voltage when turned off is When the switching transistor is turned on, the inductor The voltage on is When the switching transistor is turned off, The voltage on is ; assumed When the SOC difference between modules reaches a specified threshold, the first stage of the first-level component equalization begins; switching transistors M 11 Conductive, BP 1. L 11 ,M 11 Forming a pathway, battery pack BP 1. Inductor L 11 Charge, L 11 The current increases during this stage; inductance L 11 The Vi relationships are as follows: ; when At that time, there were: .

[0010] Preferably, when the inductor The current on reaches its maximum value i m hour, M 11 It was shut down. BP 2. L 11 With switch M 12 The freewheeling diode forms a path; in the previous stage L 11 Stored energy transferred to BP 2; Inductance L 11 The current in the inductor gradually decreases, and the energy transfer is complete; L 11 The currents in each stage are: ; ; Since the entire equalization process is performed in discontinuous current conduction mode, the duty cycle alpha of the corresponding equalization converter must meet the following conditions: ; ; In the formula, D is the duty cycle, which directly affects the equalization speed; the PWM signal controls the switching transistor to turn on and off; it is calculated that the duty cycle is at its maximum when the ratio of the inductor charging voltage to the discharging voltage is at its minimum.

[0011] Preferably, the method for equalizing inner-layer circuit groups is as follows: Inner circuit is n A reconfigurable battery pack consisting of 100 cells connected in series is denoted as _____. B i ( i =1,2,……, n When the battery B i Disconnect the switch when charging or discharging needs to be stopped.S n,2 Close the switch S n,1 ,Battery B i That is, the circuit is isolated when B i Disconnect the switch when the battery pack needs to be discharged or when discharging. S n,1 Close the switch S n,2 That is, battery B i Participating in the charging and discharging of the battery pack; n - After one isolation switch, the battery pack completes inter-pack balancing.

[0012] Preferably, the equalization method within the inner layer circuit group is as follows: During the charging process, the SOC value of each battery cell is first obtained using the extended Kalman filter method, and the battery cell with the highest SOC value is denoted as... B max The cell with the lowest SOC value is denoted as B min By controlling a switch, the battery cell with the highest SOC value is isolated from the circuit, denoted as... B i ,the remaining n -1 battery continues to charge; when B min Charge to SOC value and B i Align the battery cells with the highest SOC value in the battery pack at this time. B j To isolate, and B i It is connected to the circuit to participate in charging; During the discharge process, the SOC value of each individual cell is first obtained, and the cell with the lowest SOC is selected. B i Isolation, the rest n -1 battery is providing normal power; when B max Discharge to SOC value and B i Align the battery cells with the lowest SOC value in the battery pack at this time. B j To isolate, and B i The circuit is connected to participate in the discharge; the isolated batteries are continuously switched until equalization is completed.

[0013] Preferably, the SOC estimation uses a second-order RC equivalent battery model combined with an extended Kalman filter algorithm.

[0014] Preferably, it also includes a fault protection mechanism, which automatically triggers a bypass switch when a switch failure is detected through a switch redundancy control strategy to ensure continuous system operation.

[0015] Preferably, the balancing objective is to maximize the energy utilization rate of the battery pack, and a multi-objective optimization function based on SOC is established to guide the execution of the balancing strategy.

[0016] The beneficial effects of this invention are as follows: 1. The layered equalization method proposed in this invention is superior to the traditional single-layer equalization circuit in terms of equalization speed and energy transfer efficiency. It significantly improves the problem of energy transfer times in the traditional equalization circuit, thereby effectively reducing energy loss.

[0017] 2. This hierarchical equalization topology is suitable for power storage modules and can meet the application requirements of large-scale battery energy storage equipment. Users can flexibly set the number of module units according to actual needs. As the number of units increases, due to the core mechanism of the reconfigurable circuit, the voltage fluctuation caused by the battery units during isolation and connection will be smaller, which is conducive to improving system stability.

[0018] 3. This invention combines reconfigurable equalization circuits with Buck-Boost converter equalization to propose a hierarchical equalization method for retired batteries, realizing energy transfer between individual cells and between modules, and significantly improving their energy utilization rate, providing an efficient and feasible technical solution for the cascade utilization of retired batteries. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall working principle of the present invention; Figure 2 This is the inner layer balancing path diagram in an embodiment of the present invention; Figure 3 This is the outer layer equalization path diagram in an embodiment of the present invention; Figure 4 This is a flowchart of the inner layer equalization control in an embodiment of the present invention; Figure 5 This is a flowchart of the outer layer equalization control in an embodiment of the present invention; Figure 6 This is a diagram of the overall balanced SOC curve in an embodiment of the present invention.

[0020] Figure 7 This is a traditional equilibrium SOC curve diagram in an embodiment of the present invention. Detailed Implementation

[0021] Example 1: like Figure 1 As shown, a reconfigurable hierarchical balancing method based on retired battery energy storage modules includes the following steps: Construct a hierarchical equalization topology, including an inner layer of reconfigurable battery packs and an outer layer of DC / DC converter equalization units; The inner layer dynamically reconstructs the battery connection relationship through a switch matrix to achieve the isolation and access of individual battery cells within the group; The outer layer uses a Buck-Boost converter to achieve graded energy transfer between battery modules; A state of charge (SOC) estimation method based on extended Kalman filtering is adopted to obtain the state of charge of each battery cell in real time. Based on the SOC estimation results, the inner layer switching state and the outer layer converter operating mode are dynamically controlled to achieve coordinated balancing within and between battery packs.

[0022] Preferably, the inner layer circuit is n A reconfigurable battery pack composed of connected series of batteries uses individual cells as the balancing element; the balancing circuit consists of individual cells. Control switch Composition: Each individual battery cell is connected in series with a switch, using... This indicates that the switch controls the connection of a single battery cell, and is then connected in parallel with another switch for... This indicates that the switch controls the isolation of individual battery cells.

[0023] Preferably, the outer layer circuit uses the inner layer reconfigurable battery pack as the outer layer equalization target, represented as follows: Two MOSFET switches and an inductor, the main components of the energy storage element, perform energy transfer between the two battery packs to achieve inter-pack balancing; this constitutes the smallest balancing unit for the outer layer. The outermost layer is balanced in pairs, forming the first layer of inter-group balancing. After the first layer of inter-group balancing is completed, the upper layer balancing unit becomes one of the battery modules in the second layer of inter-group balancing, and then performs pairwise balancing again; and so on. n Each battery pack passes k Layered DC / DC conversion completes overall equalization .

[0024] like Figure 3 As shown, preferably, the equalization method within the outer circuit groups of the two battery packs is as follows: With T as one switching cycle, the total resistance of the circuit through the switching transistor during conduction is set to... The total circuit voltage when turned off is When the switching transistor is turned on, the inductor The voltage on is When the switching transistor is turned off, The voltage on is ; assumed When the SOC difference between modules reaches a specified threshold, the first stage of the first-level component equalization begins; switching transistors M11 Conductive, BP 1. L 11 , M 11 Forming a pathway, battery pack BP 1. Inductor L 11 Charge, L 11 The current on increases, such as Figure 3 As shown in (a); in this stage, the inductor L 11 The Vi relationships are as follows: ; when At that time, there were: .

[0025] Preferably, when the inductor The current on reaches its maximum value i m hour, M 11 It was shut down. BP 2. L 11 With switch M 12 The freewheeling diode forms a path, such as Figure 3 As shown in (b); previous stage L 11 Stored energy transferred to BP 2; Inductance L 11 The current in the inductor gradually decreases, and the energy transfer is complete; L 11 The currents in each stage are: ; ; Since the entire equalization process is performed in discontinuous current conduction mode, the duty cycle alpha of the corresponding equalization converter must meet the following conditions: ; ; In the formula, D is the duty cycle, which directly affects the equalization speed; the PWM signal controls the switching transistor to turn on and off; it is calculated that the duty cycle is at its maximum when the ratio of the inductor charging voltage to the discharging voltage is at its minimum.

[0026] like Figure 2 As shown, preferably, the inter-group equalization method for inner-layer circuits is as follows: Inner circuit is n A reconfigurable battery pack consisting of 100 cells connected in series is denoted as _____.B i ( i =1,2,……, n The initial state of the battery is as follows: Figure 2 (a); when the battery B i Disconnect the switch when charging or discharging needs to be stopped. S n,2 Close the switch S n,1 ,Battery B i That is, the isolated circuit, such as Figure 2 As shown in (b), when B i Disconnect the switch when the battery pack needs to be discharged or when discharging. S n,1 Close the switch S n,2 That is, battery B i Participating in the charging and discharging of the battery pack; n - After one isolation switch, the battery pack completes inter-pack equalization, such as Figure 2 As shown in (c)-(e).

[0027] Preferably, the equalization method within the inner layer circuit group is as follows: During the charging process, the SOC value of each battery cell is first obtained using the extended Kalman filter method, and the battery cell with the highest SOC value is denoted as... B max The cell with the lowest SOC value is denoted as B min By controlling a switch, the battery cell with the highest SOC value is isolated from the circuit, denoted as... B i ,the remaining n -1 battery continues to charge; when B min Charge to SOC value and B i Align the battery cells with the highest SOC value in the battery pack at this time. B j To isolate, and B i It is connected to the circuit to participate in charging; During the discharge process, the SOC value of each individual cell is first obtained, and the cell with the lowest SOC is selected. B i Isolation, the rest n -1 battery is providing normal power; when B max Discharge to SOC value and B iAlign the battery cells with the lowest SOC value in the battery pack at this time. B j To isolate, and B i The circuit is connected to participate in the discharge; the isolated batteries are continuously switched until equalization is completed.

[0028] Calculations show that the battery pack's balance improves with each switch of the isolated battery. This applies to a battery pack consisting of N batteries. n The load balancing process can be completed with a single isolation switch.

[0029] Preferably, the SOC estimation uses a second-order RC equivalent battery model combined with an extended Kalman filter algorithm.

[0030] Preferably, it also includes a fault protection mechanism, which automatically triggers a bypass switch when a switch failure is detected through a switch redundancy control strategy to ensure continuous system operation.

[0031] Preferably, the balancing objective is to maximize the energy utilization rate of the battery pack, and a multi-objective optimization function based on SOC is established to guide the execution of the balancing strategy.

[0032] Example 2: like Figures 4-7 As shown in Table 1, two battery modules with eight cells connected in series were used for discharge balancing simulation. The initial SOC and capacity settings of the batteries are shown in Table 1. The SOC range is above 85%, and the capacity range is 3.6%. The output voltage is set to 30V, and the load is an adjustable resistor. The overall balancing curve is shown in Table 1. Figure 7 As shown in the figure; the experimental results are shown in Table 1 below: Table 1: Experimental Results;

[0033] From Table 1 and Figure 7 The initial average SOC of the battery pack is 91.51%, and the equalization time is 128.7 s. Under the same initial values ​​for individual cells, the equalization time under the traditional equalization mode is 149.9 s. The equalization method proposed in this paper improves the equalization speed by 16.54%. Based on the initial SOC value and the average SOC value after equalization, the hierarchical equalization method in this paper improves energy utilization by 2.78% compared to the traditional equalization method. This method proposes a hierarchical equalization topology and strategy integrating a reconfigurable equalization circuit for power storage modules composed of large-scale retired batteries, and systematically elaborates on its working principle and equalization mechanism. The simulation results are then analyzed.

Claims

1. A reconfigurable hierarchical equalization method based on retired battery energy storage modules, characterized in that, Includes the following steps: Construct a hierarchical equalization topology, including an inner layer of reconfigurable battery packs and an outer layer of DC / DC converter equalization units; The inner layer dynamically reconstructs the battery connection relationship through a switch matrix to achieve the isolation and access of individual battery cells within the group; The outer layer uses a Buck-Boost converter to achieve graded energy transfer between battery modules; A state of charge (SOC) estimation method based on extended Kalman filtering is adopted to obtain the state of charge of each battery cell in real time. Based on the SOC estimation results, the inner layer switching state and the outer layer converter operating mode are dynamically controlled to achieve coordinated balancing within and between battery packs.

2. The reconfigurable hierarchical equalization method based on retired battery energy storage modules according to claim 1, characterized in that, Inner circuit is n A reconfigurable battery pack composed of connected cells uses individual cells as the balancing object; The equalization circuit consists of individual cells. Control switch Composition: Each individual battery cell is connected in series with a switch, using... This indicates that the switch controls the connection of a single battery cell, and is then connected in parallel with another switch for... This indicates that the switch controls the isolation of individual battery cells.

3. The reconfigurable hierarchical equalization method based on retired battery energy storage modules according to claim 1, characterized in that, The outer layer circuit uses the inner layer reconfigurable battery pack as the outer layer equalization object, represented as follows: Two MOSFET switches and an inductor, the main components of the energy storage element, perform energy transfer between the two battery packs to achieve inter-pack balancing; this constitutes the smallest balancing unit for the outer layer. Perform inter-group balancing of the outer first layer in pairs; After the first layer of inter-group balancing is completed, the upper-layer balancing unit, as one of the battery modules in the second layer of inter-group balancing, performs pairwise balancing; and so on. n Each battery pack passes k Layered DC / DC conversion completes overall equalization .

4. The reconfigurable hierarchical equalization method based on retired battery energy storage modules according to claim 3, characterized in that, The equalization method within the outer circuitry of the two battery packs is as follows: With T as one switching cycle, the total resistance of the circuit through the switching transistor during conduction is set to... The total circuit voltage when turned off is When the switching transistor is turned on, the inductor The voltage on is When the switching transistor is turned off, The voltage on is ; assumed When the SOC difference between modules reaches a specified threshold, the first stage of the first-level component equalization begins; switching transistors M 11 Conductive, BP 1. L 11 , M 11 Forming a pathway, battery pack BP 1. Inductor L 11 Charge, L 11 The current increases during this stage; inductance L 11 The Vi relationships are as follows: ； when At that time, there were: 。 5. The reconfigurable hierarchical equalization method based on retired battery energy storage modules according to claim 4, characterized in that, When the inductor The current on reaches its maximum value i m hour, M 11 It was shut down. BP 2. L 11 With switch M 12 The freewheeling diode forms a path; the previous one stage L 11 Stored energy transferred to BP 2; Inductance L 11 The current in the inductor gradually decreases, and the energy transfer is complete; L 11 The currents in each stage are: ； ； Since the entire equalization process is performed in discontinuous current conduction mode, the duty cycle alpha of the corresponding equalization converter must meet the following conditions: ； ； In the formula, D is the duty cycle, which directly affects the balancing speed; PWM signal controls the switching transistor to turn on and off; Calculations show that the duty cycle is at its maximum when the ratio of the inductor charging voltage to the discharging voltage is at its minimum.

6. The reconfigurable hierarchical equalization method based on retired battery energy storage modules according to claim 2, characterized in that, The method for equalizing inner-layer circuit groups is as follows: Inner circuit is n A reconfigurable battery pack consisting of 100 cells connected in series is denoted as _____. B i ( i =1,2,……, n When the battery B i Disconnect the switch when charging or discharging needs to be stopped. S n,2 Close the switch S n,1 ,Battery B i That is, the circuit is isolated when B i Disconnect the switch when the battery pack needs to be discharged or when discharging. S n,1 Close the switch S n,2 That is, battery B i Participating in the charging and discharging of the battery pack; n - After one isolation switch, the battery pack completes inter-pack balancing.

7. The reconfigurable hierarchical equalization method based on retired battery energy storage modules according to claim 6, characterized in that, The equalization method within the inner layer circuit group is as follows: During the charging process, the SOC value of each battery cell is first obtained using the extended Kalman filter method, and the battery cell with the highest SOC value is denoted as... B max The cell with the lowest SOC value is denoted as B min By controlling a switch, the battery cell with the highest SOC value is isolated from the circuit, denoted as... B i ,the remaining n -1 battery continues to charge; when B min Charge to SOC value and B i Align the battery cells with the highest SOC value in the battery pack at this time. B j To isolate, and B i It is connected to the circuit to participate in charging; During the discharge process, the SOC value of each individual cell is first obtained, and the cell with the lowest SOC is selected. B i Isolation, the rest n -1 battery is providing power normally; when B max Discharge to SOC value and B i Align the battery cells with the lowest SOC value in the battery pack at this time. B j To isolate, and B i The circuit is connected to participate in the discharge; the isolated batteries are continuously switched until equalization is completed.

8. The reconfigurable hierarchical equalization method based on retired battery energy storage modules according to claim 1, characterized in that, The SOC estimation uses a second-order RC equivalent battery model combined with an extended Kalman filter algorithm.

9. The reconfigurable hierarchical equalization method based on retired battery energy storage modules according to claim 1, characterized in that, It also includes a fault protection mechanism, which automatically triggers a bypass switch when a switch failure is detected through a switch redundancy control strategy, ensuring continuous system operation.

10. The reconfigurable hierarchical equalization method based on retired battery energy storage modules according to claim 1, characterized in that, The balancing objective is to maximize the energy utilization rate of the battery pack, and a multi-objective optimization function based on SOC is established to guide the execution of the balancing strategy.

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