A method for charge equalization control of a transformer-based reconfigurable battery system

Abstract

The application discloses a charge equalization control method of a reconfigurable battery system based on a converter, designs a battery system structure of a reconfigurable power unit topology, and proposes a charge equalization control strategy for the structure, so that the battery system can switch the series-parallel connection mode of each power unit in the system for different types of loads, more effectively meet the needs of various complex loads, and has fault tolerance control under different connection modes. Meanwhile, the application also adjusts the duty cycle of each power unit converter to separately control the charging and discharging of each battery, realizes the charge equalization between the batteries under any connection mode, and avoids the problem of frequent operation of reconfiguration switches.

Description

Technical Field

[0001] The present invention relates to the technical field of battery balancing, and in particular to a charge balancing control method for a converter-based reconfigurable battery system. Background Art

[0002] Traditional battery systems typically use a fixed configuration based on hardwired connections, which limits system flexibility, fault tolerance, and battery imbalance. This fixed configuration is designed for specific applications and lacks flexibility. If requirements change, the system may need to be reassembled. The fixed configuration also affects the system's fault tolerance, and when a single battery fails, it may cause the entire system to shut down. In addition, state of charge (SOC) imbalance is a significant issue in battery systems. Due to manufacturing and aging reasons, inconsistencies can occur between battery cells, ultimately leading to overcharging or overdischarging, affecting the performance of the entire battery system. In traditional battery systems, additional balancers are used to alleviate the SOC imbalance problem.

[0003] To address the challenges of traditional battery systems, reconfigurable battery systems (RBSS) have garnered widespread attention in recent years as a promising solution. Reconfigurable battery systems utilize power electronic switches to flexibly change system topology configurations, such as series, parallel, or series-parallel, depending on load demand. Furthermore, some reconfigurable battery systems can utilize switches to remove faulty batteries online without interrupting system operation.

[0004] For example, in the paper "Haoyong Cui, Zhongbao Wei, Hongwen He, et al. Novel reconfigurable topology-enabled hierarchical equalization of lithium-ion battery for maximum capacity utilization," IEEE Transactions on Industrial Electronics, vol. 70, no. 1, pp. 396–406, Jan. 2023, a novel reconfigurable battery system and balancing control method based on a four-switch architecture are proposed. In this battery system, each battery is connected to four reconfiguration switches, enabling three different configurations: series, parallel, and parallel-first-then-series, along with corresponding fault-tolerance schemes. For battery balancing, the paper proposes a split-and-recombine control strategy. During discharge, for parallel modules with a high SOC in the battery system, the reconfiguration switches are operated to first split the module into multiple submodules connected in series. This increases the discharge rate of the parallel module and accelerates the SOC drop, thereby achieving SOC balance. Once SOC balance is achieved, the reconfiguration switches are operated again to recombine the submodules back into their original parallel modules.

[0005] Furthermore, Reference 2, "Huang Huizhen, Amer MYMGhias, Acuna Pablo, et al., A fast battery balance method for a modular-reconfigurable battery energy storage system, Applied Energy, vol. 356, pp. 122470, 2024," proposes a three-switch reconfigurable battery system architecture and a corresponding fast balancing method. In this architecture, each battery is connected to only three reconfiguration switches, enabling series, parallel, and series-first-then-parallel configurations, as well as fault-tolerant control of these configurations. To achieve battery balancing, the proposed control method involves first selecting a battery with a high SOC to charge a capacitor through a converter within a switching cycle. Subsequently, the switch selects a battery with a low SOC, allowing the capacitor to discharge through the converter, thereby achieving convergence between the battery SOCs. Before achieving battery balancing, the reconfiguration switch must be operated multiple times to select the battery and capacitor for charging and discharging.

[0006] Because of the flexible switch configuration of the RBSS, battery-level power switch control is achieved, allowing the RBSS to actively control at the battery level, thereby scheduling the charging and discharging of each battery. Therefore, the RBSS can alleviate the problem of battery imbalance without additional balancing circuits. However, there is a potential risk. Frequent operation of the reconfiguration switch changes the configuration structure of the system, which may conflict with the design requirements of the system. For example, the control strategy adopted in document 1 increases the voltage across the two ends of the battery string when the module is split, and a larger current will flow through the battery split from parallel to series. The control strategy adopted in document 2 requires direct interruption of the power supply of the system to be idle. In addition, documents 1 and 2 can implement three configuration structures, but cannot implement any series-parallel connection structure. Therefore, a more flexible RBSS and a battery balancing control method that does not affect the normal operation of the system need to be designed. SUMMARY

[0007] (I) Technical problems to be solved

[0008] Therefore, the present application provides a charge equalization control method for a reconfigurable battery system based on a converter to solve the problems of not being able to implement any series-parallel structure, poor fault-tolerant control, the need for frequent operation of the reconfiguration switch, and the impact of reconfiguration on the normal operation of the battery system.

[0009] (II) Technical solutions

[0010] In order to achieve the above-mentioned purpose, the present application provides a charge equalization control method for a reconfigurable battery system based on a converter, each battery being connected to a power converter to form a power unit, the reconfigurable battery system comprising n power units and 4n-5 reconfiguration switches, the reconfiguration switches comprising K 1-i , K 2-i , K 3-i and K 4-i , wherein K 1-i , K 2-i , K 3-i i has a value of 1-n-1, and K 4-i i has a value of 2-n-1; in the first-n power units, the positive output terminal of the first power unit is connected to the positive terminal of the load / charger, and the negative output terminal of the n-th power unit is connected to the negative terminal of the load / charger; one end of K 1-i is connected to the positive output terminal of the i-th power unit, wherein i has an odd value between 1 and n-1; one end of K 1-i is connected to the other end of K 3-i , wherein i has an even value between 1 and n-1; the other end of K 1-i is connected to one end of K 1-(i+1) , and K1-(n-1) The other end is connected to the positive output terminal of the nth power unit, where i ranges from 1 to n-2; K 2-i One end of K is connected to the negative output terminal of the i-th power unit, and the other end is connected to the positive output terminal of the i+1-th power unit, where i ranges from 1 to n-1; 3-1 One end of K 4-2 One end is connected to the negative output terminal of the second power unit, and the other end is connected to the negative output terminal of the first power unit and K 2-1 One end of K 3-i One end of K 4-(i-1) The other end and K 4-i One end is connected to the negative terminal of the output terminal of the i-th power unit and the K 2-i One end of the connection, where i is an odd number between 2 and n-1; K 3-i One end is connected to the positive output terminal of the i-th power unit, and the other end is connected to the positive output terminal of K 1-(i-1) The other end of the connection; K 4-i One end of the output terminal of the i-th power unit is connected to the negative electrode, and the other end is connected to the negative electrode of the output terminal of the K 3-(i+1) One end of the K is connected, where i is an even number between 1 and n-1; 4-i One end and K 3-i One end of the resistor is connected to the negative terminal of the output terminal of the i+1th power unit, and the other end is connected to the negative terminal of the output terminal of the i+1th power unit, where the value of i is an odd number between 2 and n-1;

[0011] The reconfigurable battery system includes the following four structural configurations (a) to (d): (a) series; (b) parallel; (c) series first then parallel; (d) parallel first then series; (a) and (d) are overall series structures, and (b) and (c) are overall parallel structures; and each structural configuration has fault tolerance control;

[0012] When the reconfigurable battery system with n power units is operated, it is an overall series / parallel structure consisting of M series / parallel modules, where the i-th module consists of N i When the power units are connected in parallel or series, the duty cycle control strategy of the jth power unit in the i-th module includes the voltage loop, the inter-module SOC balance loop and the intra-module SOC balance loop;

[0013] For the overall series structure, in the voltage loop, the output voltage V of the entire battery system bus is specified and used to derive the output voltage reference value of each power unit as follows:

[0014]

[0015] wherein V refi_j represents the output voltage reference value of the jth power unit in the ith module, θ i_j is the pre-voltage division coefficient, and

[0016]

[0017] a i is the SOC coefficient of the ith module, from the inter-module SOC balancing loop;

[0018] The output voltage reference value V refi_j of each power unit is obtained refi_j The difference between V i_j and the output voltage measurement value V vol of the power unit is passed through the voltage compensator G refi_j (s) to obtain the duty cycle reference value D refi_j , as follows:

[0019] D refi_j = (V i_j -V vol )G i_j (s)

[0020] wherein V refi_j represents the output voltage measurement value of the jth power unit in the ith module;

[0021] The duty cycle reference value D i_j is multiplied by the SOC coefficient b i_j in the power unit to finally obtain the duty cycle D i_j of the converter of the power unit, as follows:

[0022] D refi_j = D i_j b

[0023] wherein D i_j represents the duty cycle of the converter of the jth power unit in the ith module, i.e., the output duty cycle; and b i_j represents the SOC coefficient of the jth power unit in the ith module, from the intra-module SOC balancing loop.

[0024] Preferably, the fault-tolerant scheme of series-parallel configuration needs to disconnect all the fault battery strings, i.e., disconnect all the batteries in series with the fault battery, in order to avoid forming a circulating current between the parallel batteries.

[0025] Preferably, when n = 4, the positive electrode of the output end of the first power unit is connected to the positive electrode of the load / charger, and the negative electrode of the output end of the fourth power unit is connected to the negative electrode of the load / charger; K 1-1one end of which is connected to the positive pole of the output terminal of the first power unit, K 1-3 one end of which is connected to the positive pole of the output terminal of the third power unit; K 1-2 one end of which is connected to K 3-2 the other end of which is connected to K 1-1 the other end of which is connected to K 1-2 one end of which is connected to K 1-2 the other end of which is connected to K 1-3 one end of which is connected to K 1-3 the other end of which is connected to the positive pole of the output terminal of the fourth power unit; K 2-1 one end of which is connected to the negative pole of the output terminal of the first power unit, K 2-2 one end of which is connected to the negative pole of the output terminal of the second power unit, K 2-3 one end of which is connected to the negative pole of the output terminal of the third power unit; K 2-1 the other end of which is connected to the positive pole of the output terminal of the second power unit, K 2-2 the other end of which is connected to the positive pole of the output terminal of the third power unit, K 2-3 the other end of which is connected to the positive pole of the output terminal of the fourth power unit; K 3-1 one end of which is connected to K 4-2 one end of which is connected to the negative pole of the output terminal of the second power unit and the other end of which is connected to the negative pole of the output terminal of the first power unit and K 2-1 one end of which is connected; K 3-3 one end of which is connected to K 4-2 the other end of which is connected to K 4-3 one end of which is connected and the other end of which is connected to the negative pole of the output terminal of the third power unit and K 2-3 one end of which is connected; K 3-2 one end of which is connected to the positive pole of the output terminal of the second power unit; K 3-2 the other end of which is connected to K 1-1 the other end of which is connected; K 4-2 one end of which is connected to the negative pole of the output terminal of the second power unit; K 4-2 the other end of which is connected to K 3-3 one end of which is connected; K 4-3 one end of which is connected to K 3-3 one end of which is connected, K 4-3 the other end of which is connected to the negative pole of the output terminal of the fourth power unit;

[0026] when the structure of the system is in series configuration, i.e., the first to fourth power units are connected in series, switches K 2-1 , K 2-2 , K 2-3 are all closed, switches K 1-1 , K 1-2 , K 1-3 , K 3-1 , K 3-2 , K3-3 , K 4-2 , K 4-3 are all open; if the 2nd power unit fails, the fault-tolerant control scheme is to open K 2-1 , close K 3-1 , and the rest of the switches remain unchanged;

[0027] When the structure of the system is in parallel configuration, i.e. the 1st-4th power units are in parallel, switches K 1-1 , K 1-2 , K 1-3 , K 3-1 , K 3-2 , K 3-3 , K 4-2 , K 4-3 are all closed, and switches K 2-1 , K 2-2 , K 2-3 are all open; if the 2nd power unit fails, the fault-tolerant control scheme is to open K 3-2 , and the rest of the switches remain unchanged;

[0028] When the structure of the system is in series-parallel configuration, i.e. the branch of the 1st power unit and the 2nd power unit in series is in parallel with the branch of the 3rd power unit and the 4th power unit in series, switches K 1-1 , K 1-2 , K 2-1 , K 2-3 , K 4-2 , K 4-3 are all closed, and switches K 1-3 , K 2-2 , K 3-1 , K 3-2 , K 3-3 are all open; if the 2nd power unit fails, the fault-tolerant control scheme is to open K 2-1 , K 4-2 , K 4-3 , and the rest of the switches remain unchanged;

[0029] When the structure of the system is in parallel-series configuration, i.e. the branch of the 1st power unit and the 2nd power unit in parallel is in series with the branch of the 3rd power unit and the 4th power unit in parallel, switches K 1-1 , K 1-3 , K 2-2 , K 3-1 , K 3-2 , K 3-3 , K 4-3 are all closed, and switches K 1-2 , K 2-1 , K 2-3 , K 4-2If the second power unit fails, the fault-tolerant control scheme is to disconnect K 1-1 , the other switches remain in their original states.

[0030] Preferably, the power converter is a Boost converter, and the battery parameters in the 1st to nth power units are the same.

[0031] Preferably, for the overall parallel structure, in the voltage loop, the output voltage V of the entire battery system is bus is specified and used to derive the output voltage reference value of each power unit as follows:

[0032]

[0033] Among them, V refi_j represents the output voltage reference value of the jth power unit in the i-th module, θ i_j is the pre-voltage divider coefficient, and

[0034]

[0035] b i_j It represents the SOC coefficient of the jth power unit of the i-th module, which comes from the SOC balance loop within the module;

[0036] Get the output voltage reference value V of each power unit refi_j After that, V refi_j The output voltage measurement value of the power unit V i_j The difference is passed through the voltage compensator G vol (s), and obtain the duty cycle reference value D refi_j , as shown below:

[0037] D refi_j =(V refi_j -V i_j )G vol (s)

[0038] Among them, V i_j represents the output voltage measurement value of the jth power unit in the i-th module;

[0039] The duty cycle reference value D refi_j Multiply by the SOC coefficient a of the i-th module i , and finally obtain the duty cycle D of the converter of the power unit i_j , as shown below:

[0040] D i_j =D refi_j a i

[0041] Among them, D i_jDuty cycle of the converter of the jth power unit of the ith module, i.e., output duty cycle; a i is the SOC coefficient of the ith module, from the inter-module SOC balancing loop.

[0042] Preferably, in the inter-module SOC balancing control loop, the SOC average value SOC ref of the battery system is compensated by the inter-module SOC compensator G

[0043]

[0044] wherein SOC i_j represents the SOC value of the jth power unit of the ith module.

[0045] The SOC average value SOC i of the ith module is compensated by the intra-module SOC compensator G

[0046]

[0047] The difference between SOC ref and SOC i is compensated by the inter-module SOC compensator G inter (s), and finally the SOC coefficient a i of the ith module is obtained, as shown below:

[0048] a i = 1-(SOC ref -SOC i )G inter (s).

[0049] Preferably, in the intra-module SOC balancing control loop, the difference between the SOC average value SOC i of the ith module and the SOC value SOC i_j of the jth power unit of the ith module is compensated by the intra-module SOC compensator G intra (s), and the SOC coefficient b i_j of the power unit is obtained, as shown below:

[0050] b i_j = 1-(SOC i -SOC i_j )G intra (s).

[0051] (Three) beneficial effects

[0052] From the above technical solution, the present application proposes a charge balancing control method for a reconfigurable battery system based on a converter, which has the following beneficial effects:

[0053] 1. The battery system can be configured with any series-parallel connection structure by reconfiguring the switch array, realizing topology reconstruction, adapting to different working conditions and improving system flexibility.

[0054] 2. The battery system can isolate faulty units and reconfigure the topology to ensure continued normal operation of the system.

[0055] 3. Each power unit is equipped with an independent converter. By adjusting the converter's duty cycle, the battery's charge and discharge power is individually controlled to achieve precise SOC balancing. Moreover, during the battery SOC balancing process, there is no need to operate the reconfiguration switch for charging and discharging, avoiding the problem of frequent reconfiguration switch operation in the battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0057] Figure 1 Schematic diagram of the structure of the reconfigurable battery system of the present invention;

[0058] Figure 2 Figure 1 is a simplified schematic diagram of different configurations of the reconfigurable battery system of the present invention, wherein (a) shows a four-battery full series connection and fault-tolerant configuration; (b) shows a four-battery full parallel connection and fault-tolerant configuration; (c) shows a four-battery series-first, then parallel connection and fault-tolerant configuration; (d) shows a four-battery parallel-first, then series connection and fault-tolerant configuration;

[0059] Figure 3 The schematic diagram of the structure of the converter-based reconfigurable battery system of the present invention is a reconfigurable battery system structure based on the Boost converter;

[0060] Figure 4 Schematic diagram of the charge balancing control strategy of the converter-based reconfigurable battery system of the present invention. DETAILED DESCRIPTION

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0062] The structure of the reconfigurable battery system of the present invention is as follows Figure 1As shown, this structure includes n batteries and 4n-5 reconfiguration switches. Based on this reconfiguration switch array, the battery system can be configured in any series-parallel connection structure (including series, parallel, series first then parallel, and parallel first then series). All configurations have fault tolerance control, which means that faulty batteries are isolated without affecting the normal operation of the system.

[0063] Figure 2 Taking a four-battery reconfigurable system as an example, different series-parallel connection structures (i.e., configurations) of the reconfigurable battery system are demonstrated, along with the fault-tolerant control schemes for each structure. The connection between the batteries and the reconfiguration switch in the four-battery reconfigurable system is as follows:

[0064] The batteries are numbered from left to right as B#1 to B#4 (the same below). The positive terminal of battery B#1 is connected to the positive terminal of the load, and the negative terminal of battery B#4 is connected to the negative terminal of the load; K 1-1 One end of the battery is connected to the positive terminal of battery B#1, K 1-3 One end of K is connected to the positive terminal of battery B#3; 1-2 One end and K 3-2 The other end of the connection; K 1-1 The other end of K 1-2 One end of the connection, K 1-2 The other end of K 1-3 One end of K 1-3 The other end of K is connected to the positive terminal of battery B#4; 2-1 One end of the battery is connected to the negative terminal of battery B#1, K 2-2 One end of the battery is connected to the negative terminal of battery B#2, K 2-3 One end of K is connected to the negative terminal of battery B#3; 2-1 The other end is connected to the positive terminal of battery B#2, K 2-2 The other end is connected to the positive terminal of battery B#3, K 2-3 The other end of K is connected to the positive terminal of battery B#4; 3-1 One end of K 4-2 One end is connected to the negative terminal of battery B#2, and the other end is connected to the negative terminal of battery B#1 and K 2-1 One end of the connection; K 3-3 One end of K 4-2 The other end and K 4-3 One end is connected to the negative terminal of battery B#3 and the other end is connected to the negative terminal of battery B#3 and K 2-3 One end of the connection; K 3-2 One end of K is connected to the positive terminal of battery B#2; 3-2 The other end of K 1-1 The other end of the connection; K 4-2 One end of K is connected to the negative terminal of battery B#2; 4-2 The other end and K 3-3One end of the connection; K 4-3 One end and K 3-3 One end of K 4-3 The other end is connected to the negative terminal of battery B#4.

[0065] Figure 2 (a) shows the series configuration of batteries and their fault-tolerant control, where the left figure shows the series configuration, switch K 2-1 , K 2-2 , K 2-3 Fully closed, switch K 1-1 , K 1-2 , K 1-3 , K 3-1 , K 3-2 , K 3-3 , K 4-2 , K 4-3 The right figure shows the fault-tolerant control scheme of the series configuration. Assuming that battery B#2 fails, based on the connection method in the left figure, disconnect K 2-1 , closed K 3-1 ; Figure 2 (b) shows the parallel configuration of batteries and their fault-tolerant control, where the left figure shows the parallel configuration, switch K 1-1 , K 1-2 , K 1-3 , K 3-1 , K 3-2 , K 3-3 , K 4-2 , K 4-3 Fully closed, switch K 2-1 , K 2-2 , K 2-3 The right figure shows the fault-tolerant control scheme of parallel configuration. Assume that battery B#2 fails (similarly, there are fault-tolerant control schemes for other battery failures, the same below). Based on the connection method in the left figure, disconnect K 3-2 ; Figure 2 (c) shows the battery configuration of series first and then parallel and its fault-tolerant control. The left figure shows the battery configuration of series first and then parallel. The switch K 1-1 , K 1-2 , K 2-1 , K 2-3 , K 4-2 , K 4-3 Fully closed, switch K 1-3 , K 2-2 , K 3-1 , K 3-2 , K 3-3 The right figure shows the fault-tolerant control scheme of series-first and parallel-later configuration. Assuming that battery B#2 fails, based on the connection method in the left figure, disconnect K 2-1 , K 4-2 , K4-3 ; Figure 2 (d) shows the battery first parallel and then series configuration and its fault-tolerant control. The left figure shows the first parallel and then series configuration. Switch K 1-1 , K 1-3 , K 2-2 , K 3-1 , K 3-2 , K 3-3 , K 4-3 Fully closed, switch K 1-2 , K 2-1 , K 2-3 , K 4-2 The right figure shows the fault-tolerant control scheme of series-first and parallel-later configuration. Assuming that battery B#2 fails, based on the connection method in the left figure, disconnect K 1-1 The reconfigurable system structure can flexibly switch different configuration schemes according to different load or power requirements. Figure 2 (c) The fault-tolerant solution of connecting batteries in series first and then in parallel as shown in the right figure requires that the faulty battery string (including the faulty battery and all batteries connected in series with the faulty battery) be completely disconnected to avoid circulating current between the parallel-connected batteries.

[0066] Integrating the power converter into the reconfigurable battery system has formed Figure 3 The converter-based reconfigurable battery system shown in Figure 1. In this structure, each battery is connected to a converter to form a power unit. The proposed control strategy achieves output voltage modulation and charge balancing control of the battery system by controlling the duty cycle of the converter in the power unit.

[0067] The converter in each power unit can be a Boost circuit. In order to reduce power consumption, you can choose Figure 3 The synchronous type Boost circuit shown in the figure is different from the traditional Boost circuit in that the diode is replaced by a MOS tube S H1 This MOS tube is controlled by the logic inside the synchronous chip, which is connected to the main control signal S L1 The signal complements the chip. When the chip is not working, the MOS tube S H1 By turning off the output, diode leakage issues are eliminated. Furthermore, the MOS transistor has a low conduction voltage drop and low power loss, making it more efficient to replace the diode. Of course, the converter of the present invention can also be other DC-DC converters, and the converter type does not affect the charge balancing control method of the reconfigurable battery system.

[0068] by Figure 3 Take the first power unit in the example, Cell1 represents battery No. 1, and its connected capacitor C1, inductor L1 and MOS switch S H1 and S L1The Boost converter of battery No. 1 is composed of Cell1 and the Boost converter, which together form the first power unit. B1 Represents the current flowing through the battery Cell1, V1 represents the output voltage of the first power unit, I1 represents the output current of the first power unit, and D1 represents the duty cycle of the PWM signal of the Boost converter in the first power unit. The entire reconfigurable battery system can be freely provided with n such power units (i.e., containing n batteries), which are interconnected through 4n-5 reconfiguration switches. The reconfiguration switches include K 1-i , K 2-i , K 3-i (i ranges from 1 to n-1) and K 4-i (The value of i ranges from 2 to n-1).

[0069] To achieve any series-parallel structure, the connection method of each reconfiguration switch in the 1st to nth power units is as follows:

[0070] The positive pole of the output end of the first power unit is connected to the positive pole of the load / charger, and the negative pole of the output end of the nth power unit is connected to the negative pole of the load / charger; K 1-i One end of the K (i is an odd number between 1 and n-1) is connected to the positive output terminal of the i-th power unit; 1-i (i is an even number between 1 and n-1) and K 3-i The other end of the connection; K 1-i (i ranges from 1 to n-2) and the other end of K 1-(i+1) One end of K 1-(n-1) The other end is connected to the positive output terminal of the nth power unit; K 2-i One end of K (the value of i ranges from 1 to n-1) is connected to the negative output terminal of the i-th power unit, and the other end is connected to the positive output terminal of the i+1-th power unit; 3-1 One end of K 4-2 One end is connected to the negative output terminal of the second power unit, and the other end is connected to the negative output terminal of the first power unit and K 2-1 One end of K 3-i (i is an odd number between 2 and n-1) and K 4-(i-1) The other end and K 4-i One end is connected to the negative terminal of the output terminal of the i-th power unit and the K 2-i One end of the connection; K 3-i One end of the positive terminal of the output terminal of the i-th power unit is connected to the positive terminal of the output terminal of the K 1-(i-1) The other end of the connection; K 4-iOne end of the output terminal of the i-th power unit is connected to the negative electrode, and the other end is connected to the negative electrode of the output terminal of the K 3-(i+1) One end of the connection; K 4-i (i is an odd number between 2 and n-1) and K 3-i One end is connected to , and the other end is connected to the negative output terminal of the (i+1)th power unit.

[0071] The output voltage of the entire reconfigurable battery system is V bus , that is, the load voltage, the output current is I bus , that is, the load current.

[0072] Under the action of the reconfigurable switch array, the battery system has good flexibility and fault tolerance.

[0073] For another important problem faced by the battery system, the charge balancing problem, the present invention proposes a charge balancing control method for a reconfigurable battery system structure based on a converter. For the reconfigurable battery system, the structure is divided into overall series and overall parallel, which are composed of multiple series modules and parallel modules respectively. For a reconfigurable system with n batteries (including n power units), it is assumed that it is an overall series / parallel structure composed of M series / parallel modules, where the i-th module consists of N i If the power units are connected in parallel or series, the duty cycle control strategy of the jth power unit in the i-th module is given by Figure 4 It is given, including the voltage loop, the inter-module SOC balance loop and the intra-module SOC balance loop.

[0074] For the overall series structure (i.e. series configuration or parallel-first then series configuration), in the voltage loop, the output voltage V bus is specified and used to derive the output voltage reference value of each power unit as follows:

[0075]

[0076] Among them, V refi_j represents the output voltage reference value of the jth power unit in the i-th module, θ i_j is the pre-voltage divider coefficient, and

[0077]

[0078] a i is the SOC coefficient of the i-th module, which comes from the inter-module SOC balancing loop.

[0079] In the inter-module SOC balance control loop, the average SOC value of the battery system SOC ref The calculation formula is as follows:

[0080]

[0081] Among them, SOC i_j Indicates the SOC value of the jth power unit of the i-th module.

[0082] The average SOC value of the i-th module is SOC i The calculation formula is as follows:

[0083]

[0084] SOC ref and SOC i The difference between the modules passes through the SOC compensator G inter (s), and finally the SOC coefficient a of the i-th module is obtained i , as shown below:

[0085] a i =1-(SOC ref -SOC i )G inter (s) (5)

[0086] Get the output voltage reference value V of each power unit refi_j After that, V refi_j The output voltage measurement value of the power unit V i_j The difference is passed through the voltage compensator G vol (s), and obtain the duty cycle reference value D refi_j , as shown below:

[0087] D refi_j =(V refi_j -V i_j )G vol (s) (6)

[0088] Among them, V i_j Represents the output voltage measurement value of the jth power unit in the i-th module.

[0089] The duty cycle reference value D refi_j Multiply by the SOC coefficient b in the power unit i_j , and finally obtain the duty cycle D of the converter of the power unit i_j , as shown below:

[0090] D i_j =D refi_j b i_j (7)

[0091] Among them, D i_j represents the duty cycle (i.e., output duty cycle) of the converter of the jth power unit of the i-th module; bi_j SOC coefficient of the jth power unit of the ith module, from the intra-module SOC balancing loop.

[0092] In the intra-module SOC balancing control loop of the ith module, the average value of the SOC of the ith module SOC i is compared with the SOC value of the jth power unit of the ith module SOC i_j , and the difference is input into the intra-module SOC compensator G intra (s) to obtain the SOC coefficient b i_j of the power unit, as shown below:

[0093] b i_j = 1-(SOC i -SOC i_j )G intra (s) (8)

[0094] The charge equalization control method of the overall parallel structure (i.e. parallel configuration or series-parallel configuration) is the same as that of the overall series structure, and also passes through three control loops (i.e. voltage loop, inter-module SOC balancing loop and intra-module SOC balancing loop). The difference is that, since the output voltage of the parallel module is the output voltage V bus of the system, the formula of the pre-voltage division coefficient is different from that of the overall series structure, and the formula of the pre-voltage division coefficient of the overall parallel structure is shown as follows:

[0095]

[0096] In addition, in the charge equalization control method of the overall parallel structure, the intra-module SOC balancing loop is prior to the inter-module SOC balancing loop, and the output voltage reference value and output duty cycle of each power unit are shown as follows:

[0097]

[0098] D i_j = D refi_j a i (11)

[0099] In the embodiment of the present application, the SOC value of the battery is calculated by using the ampere-hour integration method, and the calculation formula is shown as follows:

[0100]

[0101] wherein, SOC i_j represents the SOC value of the battery in the jth power unit of the ith module; SOC0 represents the initial SOC value of the battery, which can be obtained by measuring the open circuit voltage OCV of the battery and then looking up the OCV-SOC table of the battery; t sta and tend are the initial time and end time of SOC calculation respectively; I i_j and Q i_j is the discharge current and capacity of the battery.

[0102] In summary, although the order of action of the inter-module SOC balance loop and the intra-module SOC balance loop is different in the charge balance control algorithm of the overall series and overall parallel structures, the feedback effect is the same. i and b i_j They are positively correlated with the SOC value, and the duty cycle D of the converter i_j and a i or b i_j The correlation is also positive. Therefore, the greater the battery SOC value, the greater the duty cycle of the converter of the corresponding power unit under the action of the reconstruction balancing controller. As a result, the battery will discharge at a faster rate, so that the SOC of the entire battery system converges with each other (that is, batteries with large SOC discharge quickly and their SOC decreases quickly; batteries with small SOC discharge slowly and their SOC decreases slowly; thus, the SOC values ​​of the batteries gradually become equal, and the SOC curves converge and overlap), achieving battery balance.

[0103] The compensators designed in the present invention (including the inter-module SOC compensator, the intra-module SOC compensator and the voltage compensator) are all PI controllers.

[0104] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be covered by the scope of protection of the present invention.

Claims

1. A charge balancing control method for a converter-based reconfigurable battery system, characterized in that: Each battery is connected to a power converter to form a power unit. The reconfigurable battery system includes n power units, 4n-5 reconfiguration switches, and the reconfiguration switches include K 1-i , K 2-i , K 3-i and K 4-i , where K 1-i , K 2-i , K 3-i The value of i is 1 to n-1, K 4-i The value of i is 2 to n-1; in the 1st to nth power units, the positive output terminal of the 1st power unit is connected to the positive terminal of the load / charger, and the negative output terminal of the nth power unit is connected to the negative terminal of the load / charger; K 1-i One end of K is connected to the positive output terminal of the i-th power unit, where i is an odd number between 1 and n-1; 1-i One end and K 3-i The other end of the K is connected, where i is an even number between 1 and n-1; 1-i The other end of K 1-(i+1) One end is connected, where i ranges from 1 to n-2, K 1-(n-1) The other end is connected to the positive output terminal of the nth power unit; K 2-i One end of K is connected to the negative output terminal of the i-th power unit, and the other end is connected to the positive output terminal of the i+1-th power unit, where i ranges from 1 to n-1; 3-1 One end of K 4-2 One end is connected to the negative output terminal of the second power unit, and the other end is connected to the negative output terminal of the first power unit and K 2-1 One end of K 3-i One end of K 4-(i-1) The other end and K 4-i One end is connected to the negative terminal of the output terminal of the i-th power unit and the K 2-i One end of the connection, where i is an odd number between 2 and n-1; K 3-i One end is connected to the positive output terminal of the i-th power unit, and the other end is connected to the positive output terminal of K 1-(i-1) The other end of the K is connected, where i is an even number between 1 and n-1; 4-i One end is connected to the negative output terminal of the i-th power unit, and the other end is connected to the K 3-(i+1) One end of the K is connected, where i is an even number between 1 and n-1; 4-i One end and K 3-i One end of the resistor is connected to the negative terminal of the output terminal of the i+1th power unit, and the other end is connected to the negative terminal of the output terminal of the i+1th power unit, where the value of i is an odd number between 2 and n-1; The reconfigurable battery system includes the following four structural configurations (a) to (d): (a) series; (b) parallel; (c) series first then parallel; (d) parallel first then series; (a) and (d) are overall series structures, and (b) and (c) are overall parallel structures; and each structural configuration has fault tolerance control; When the reconfigurable battery system with n power units is operated, it is an overall series / parallel structure consisting of M series / parallel modules, where the i-th module consists of N i When the power units are connected in parallel or series, the duty cycle control strategy of the jth power unit in the i-th module includes the voltage loop, the inter-module SOC balance loop and the intra-module SOC balance loop; For the overall series structure, in the voltage loop, the output voltage V of the entire battery system bus is specified and used to derive the output voltage reference value of each power unit as follows: Among them, V refi_j represents the output voltage reference value of the jth power unit in the i-th module, θ i_j is the pre-voltage divider coefficient, and a i is the SOC coefficient of the i-th module, which comes from the inter-module SOC balancing loop; Get the output voltage reference value V of each power unit refi_j Then, V refi_j The output voltage measurement value of the power unit V i_j The difference is passed through the voltage compensator G vol (s), and obtain the duty cycle reference value D refi_j , as shown below: D refi_j =(V refi_j -V i_j )G vol (s) Among them, V i_j represents the output voltage measurement value of the jth power unit in the i-th module; The duty cycle reference value D refi_j Multiply by the SOC coefficient b in the power unit i_j , and finally obtain the duty cycle D of the converter of the power unit i_j , as shown below: D i_j =D refi_j b i_j Among them, D i_j represents the duty cycle of the converter of the jth power unit of the i-th module, that is, the output duty cycle; b i_j Represents the SOC coefficient of the jth power unit in the i-th module, which comes from the SOC balance loop within the module.

2. The method according to claim 1, characterized in that To prevent loop currents between parallel-connected batteries, the faulty battery string must be completely disconnected. This means that the faulty battery and all batteries connected in series with it must be disconnected.

3. The method according to claim 1, characterized in that When n=4, the positive electrode of the output end of the first power unit is connected to the positive electrode of the load / charger, and the negative electrode of the output end of the fourth power unit is connected to the negative electrode of the load / charger; K 1-1 One end of K is connected to the positive terminal of the output terminal of the first power unit, 1-3 One end of K is connected to the positive electrode of the output end of the third power unit; 1-2 One end and K 3-2 The other end of the connection; K 1-1 The other end of K 1-2 One end of K 1-2 The other end of K 1-3 One end of K 1-3 The other end of K is connected to the positive electrode of the output end of the fourth power unit; 2-1 One end of K is connected to the negative pole of the output terminal of the first power unit, 2-2 One end of K is connected to the negative pole of the output terminal of the second power unit, 2-3 One end of K is connected to the negative pole of the output end of the third power unit of the battery; 2-1 The other end is connected to the positive electrode of the output terminal of the second power unit, K 2-2 The other end is connected to the positive terminal of the output terminal of the third power unit, K 2-3 The other end of K is connected to the positive electrode of the output end of the fourth power unit; 3-1 One end of K 4-2 One end is connected to the negative output terminal of the second power unit, and the other end is connected to the negative output terminal of the first power unit and K 2-1 One end of the connection; K 3-3 One end of K 4-2 The other end and K 4-3 One end is connected to the negative pole of the output terminal of the third power unit and K 2-3 One end of the connection; K 3-2 One end of K is connected to the positive electrode of the output end of the second power unit; 3-2 The other end of K 1-1 The other end of the connection; K 4-2 One end of K is connected to the negative pole of the output end of the second power unit; 4-2 The other end and K 3-3 One end of the connection; K 4-3 One end and K 3-3 One end of K 4-3 The other end is connected to the negative pole of the output end of the fourth power unit; When the system is in series configuration, that is, the 1st to 4th power units are connected in series, switch K 2-1 , K 2-2 , K 2-3 Fully closed, switch K 1-1 , K 1-2 , K 1-3 , K 3-1 , K 3-2 , K 3-3 , K 4-2 , K 4-3 If the second power unit fails, the fault-tolerant control scheme is to disconnect K 2-1 , closed K 3-1 , the other switches remain in their original states; When the system is in parallel configuration, that is, the 1st to 4th power units are connected in parallel, switch K 1-1 , K 1-2 , K 1-3 , K 3-1 , K 3-2 , K 3-3 , K 4-2 , K 4-3 Fully closed, switch K 2-1 , K 2-2 , K 2-3 If the second power unit fails, the fault-tolerant control scheme is to disconnect K 3-2 , the other switches remain in their original states; When the system structure is a series-first and then parallel configuration, that is, the branch formed by the series connection of the first power unit and the second power unit is connected in parallel with the branch formed by the series connection of the third power unit and the fourth power unit, the switch K 1-1 , K 1-2 , K 2-1 , K 2-3 , K 4-2 , K 4-3 Fully closed, switch K 1-3 , K 2-2 , K 3-1 , K 3-2 , K 3-3 If the second power unit fails, the fault-tolerant control scheme is to disconnect K 2-1 , K 4-2 , K 4-3 , the other switches remain in their original states; When the system structure is parallel first and then series, that is, the branch after the first power unit and the second power unit are connected in parallel is connected in series with the branch after the third power unit and the fourth power unit are connected in parallel, the switch K 1-1 , K 1-3 , K 2-2 , K 3-1 , K 3-2 , K 3-3 , K 4-3 Fully closed, switch K 1-2 , K 2-1 , K 2-3 , K 4-2 If the second power unit fails, the fault-tolerant control scheme is to disconnect K 1-1 , the other switches remain in their original states.

4. The method according to claim 1, wherein The power converter is specifically a Boost converter, and the battery parameters in the 1st to nth power units are the same.

5. The method according to claim 1, wherein For the overall parallel structure, in the voltage loop, the output voltage V of the entire battery system bus is specified and used to derive the output voltage reference value of each power unit as follows: Among them, V refi_j represents the output voltage reference value of the jth power unit in the i-th module, θ i_j is the pre-voltage divider coefficient, and b i_j It represents the SOC coefficient of the jth power unit of the i-th module, which comes from the SOC balance loop within the module; Get the output voltage reference value V of each power unit refi_j Then, V refi_j The output voltage measurement value of the power unit V i_j The difference is passed through the voltage compensator G vol (s), and obtain the duty cycle reference value D refi_j , as shown below: D refi_j =(V refi_j -V i_j )G vol (s) Among them, V i_j represents the output voltage measurement value of the jth power unit in the i-th module; The duty cycle reference value D refi_j Multiply by the SOC coefficient a of the i-th module i , and finally obtain the duty cycle D of the converter of the power unit i_j , as shown below: D i_j =D refi_j a i Among them, D i_j represents the duty cycle of the converter of the jth power unit of the i-th module, that is, the output duty cycle; a i is the SOC coefficient of the i-th module, which comes from the inter-module SOC balancing loop.

6. The method according to claim 1 or 5, characterized in that In the inter-module SOC balance control loop, the average SOC value of the battery system is SOC ref The calculation formula is as follows: Among them, SOC i_j Indicates the SOC value of the jth power unit of the i-th module; The average SOC value of the i-th module is SOC i The calculation formula is as follows: SOC ref and SOC i The difference between the modules passes through the SOC compensator G inter (s), and finally the SOC coefficient a of the i-th module is obtained i , as shown below: a i =1-(SOC ref -SOC i )G inter (s)。 7. The method according to claim 1 or 5, characterized in that In the SOC balance control loop within the i-th module, the SOC average value SOC of the i-th module is i , and the SOC value SOC of the jth power unit of the i-th module i_j The difference is passed through the SOC compensator G in the module intra (s), and the SOC coefficient b of the power unit is obtained i_j , as shown below: b i_j =1-(SOC i -SOC i_j )G intra (s)。

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