Charge equalization control method of reconfigurable battery system based on converter

Abstract

The invention discloses a charge balance control method for a reconfigurable battery system based on a converter, and provides a charge balance control strategy for a battery system structure of a reconfigurable power unit topology. The series-parallel connection mode of each power unit in the system can be conveniently switched when the battery system aims at different types of loads, the requirements of various complex loads are more effectively met, and fault tolerance control is achieved under different connection modes. Meanwhile, by adjusting the duty ratio of each power unit converter, independent charge and discharge control is carried out on each battery, charge balance between the batteries in any connection mode is achieved, and the problem of frequent operation and switch reconstruction is avoided.

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 has limitations in system flexibility, fault tolerance, and battery imbalance. This fixed configuration is designed for a specific application and lacks flexibility. If the requirements change, the system may need to be reassembled. The fixed configuration also affects the fault tolerance of the system, 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 will occur between battery cells, which will eventually lead to overcharging or over-discharging, affecting the performance of the entire battery system. In traditional battery systems, additional equalizers are used to alleviate the SOC imbalance problem.

[0003] In order to deal with the problems of traditional battery systems, reconfigurable battery systems (RBSS) have received widespread attention in recent years as a candidate promising solution. Reconfigurable battery systems use power electronic switches to flexibly change system topology configurations, such as series, parallel, or series-parallel, according to load requirements. In addition, some reconfigurable battery systems can use switches to remove faulty batteries online without interrupting system operation.

[0004] For example, in the literature 1, “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 based on a four-switch structure and a balancing control method are proposed. In the battery system structure, each battery is connected to four reconfiguration switches to achieve three different configuration structures of series connection, parallel connection, and first parallel connection and then series connection, as well as corresponding fault tolerance schemes. For battery balancing, the paper proposes a split-recombination control idea. During the discharge process, for a battery parallel module with a large SOC in the battery system, the module is first split into multiple sub-modules in series by operating the reconfiguration switch, so that the discharge rate of the parallel module is increased and the SOC decreases faster, thereby achieving the purpose of SOC balancing. When the SOC is balanced, the reconfiguration switch is operated to reorganize the sub-modules into the original parallel modules.

[0005] In addition, document 2 "Huang Huizhen, Amer MYMGhias, Acuna Pablo, et al, Afastbattery balance method for a modular-reconfigurable battery energy storage system, Applied Energy, vol. 356, pp. 122470, 2024." proposes a reconfigurable battery system structure based on three switches and a corresponding fast balancing method. In this structure, each battery is connected to only three reconfiguration switches, which can realize series, parallel and series-first-then-parallel configuration structures, as well as fault-tolerant control of these configuration structures. In order to achieve battery balancing, the control method proposed in this article first selects a battery with a large SOC to charge the capacitor through a converter within a switching cycle, and then operates the switch to select a battery with a low SOC, allowing the capacitor to discharge it through the converter, thereby achieving mutual convergence between the battery SOCs. Before achieving battery balancing, it is necessary to operate the reconfiguration switch multiple times to select the battery and capacitor for charging and discharging operations.

[0006] Due to the flexible switch configuration of RBSS, battery-level power switch control is realized, allowing RBSS to actively control at the battery level, thereby scheduling the charging and discharging of each battery. Therefore, RBSS can alleviate the battery imbalance problem without the need for additional balancing circuits. However, there is a potential hidden danger. Frequent operation of the reconstruction switch will change 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 will increase the voltage at both ends of the battery string when the module is split, and the battery split from parallel to series will flow through a larger current. The control strategy adopted in Document 2 requires direct interruption of the system power supply and can only be performed when idle. In addition, Documents 1 and 2 can both realize three configuration structures, but cannot realize arbitrary series-parallel connection structures. Therefore, it is necessary to design a more flexible RBSS and a battery balancing control method that does not affect the normal operation of the system. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] Based on this, the present invention provides a charge balancing control method for a converter-based reconfigurable battery system to solve the problems mentioned in the background technology, such as the inability to realize arbitrary series-parallel structure, poor fault tolerance control, the need for frequent operation of the reconstruction switch, and the impact of reconstruction on the normal operation of the battery system.

[0009] (II) Technical solution

[0010] In order to achieve the above object, the present invention provides a charge balancing control method for a reconfigurable battery system based on a converter, wherein each battery is connected to a power converter to form a power unit, and 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 (i ranges from 1 to n-1) and K 4-i (i ranges from 2 to n-1); in the 1st to nth power units, the positive electrode of the output end of the 1st power unit is connected to the positive electrode of the load / charger, and the negative electrode of the output end of the nth power unit is connected to the negative electrode of the load / charger; K 1-i One end of 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 is connected to K 1-(i+1) One end of K 1-(n-1) The other end of K is connected to the positive output terminal of the nth power unit; 2-iOne end of K (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 electrode of the output terminal of the second power unit, and the other end is connected to the negative electrode of the 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 electrode of the output terminal of the i-th power unit and 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-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 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 of the power cell is connected to the negative electrode of the output terminal of the i+1th power cell; and the other end of the power cell is connected to the negative electrode of the output terminal of the i+1th power cell;

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

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

[0013] Preferably, in order to avoid loop current between parallel-connected batteries, the fault-tolerant scheme of the series-first-then-parallel configuration requires disconnecting all faulty battery strings, that is, disconnecting the faulty battery and all batteries connected in series with the faulty battery.

[0014] 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 1-1 One end of is connected to the positive electrode of the output end of the first power unit, K1-3 One end of K is connected to the positive electrode of the output end of the third power unit; 1-2 One end of 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 is connected to the negative pole of the output end of the first power unit, K 2-2 One end of is connected to the negative pole of the output end of the second power unit, K 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 end of the second power unit, K 2-2 The other end is connected to the positive electrode of the output end 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 electrode of the output terminal of the second power unit, and the other end is connected to the negative electrode of the 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 end of the third power unit and K 2-3 One end of the connection; K 3-2 One end of is connected to the positive pole of the output end of the second power unit; K 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 of 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;

[0015] When the system structure is a series configuration, that is, the 1st to 4th power units are connected in series, the 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 , K4-3 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;

[0016] 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;

[0017] When the system structure is a series-first and then parallel configuration, that is, the branch after the first power unit and the second power unit are connected in series is connected in parallel with the branch after the third power unit and the fourth power unit are connected in series, 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;

[0018] 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.

[0019] Preferably, the power converter is a Boost converter, and the battery parameters in the 1st to nth power units are the same.

[0020] Preferably, for the overall series 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 for each power unit as follows:

[0021]

[0022] 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

[0023]

[0024] a i is the SOC coefficient of the i-th module, which comes from the inter-module SOC balancing loop;

[0025] Get the output voltage reference value V of each power unit refi_j After that, V refi_j The output voltage measurement value 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:

[0026] D refi_j =(V refi_j -V i_j )G vol (s)

[0027] Among them, V i_j represents the output voltage measurement value of the jth power unit in the i-th module;

[0028] The duty cycle reference value D refi_j Multiply by the SOC factor 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:

[0029] D i_j =D refi_j b i_j

[0030] 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; b i_jRepresents the SOC coefficient of the jth power unit of the ith module, which comes from the SOC balance loop within the module.

[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 for 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 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_j represents the duty cycle (i.e., output duty cycle) of the converter of the jth power unit of the i-th module; a i is the SOC coefficient of the ith module, which comes from the inter-module SOC balancing loop.

[0042] Preferably, in the inter-module SOC balancing control loop, the average SOC value of the battery system SOC ref The calculation formula is as follows:

[0043]

[0044] Among them, SOC i_j represents the SOC value of the jth power unit of the i-th module;

[0045] The average SOC value of the i-th module is SOC i The calculation formula is as follows:

[0046]

[0047] The 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:

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

[0049] Preferably, in the SOC balance control loop within the i-th module, the SOC average value SOC i , and the SOC value SOC of the jth power unit of the i-th module i_j The difference passes 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:

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

[0051] (III) Beneficial effects

[0052] It can be seen from the above technical solution that the charge balancing control method of a converter-based reconfigurable battery system proposed by the present invention has the following beneficial effects:

[0053] 1. The battery system can configure any series-parallel connection structure by reconstructing 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 reconstruct the topology to ensure the system continues to operate normally.

[0055] 3. Each power unit is equipped with an independent converter. By adjusting the duty cycle of the converter, the charge and discharge power of the battery is individually controlled to achieve precise SOC balancing. Moreover, in the process of achieving battery SOC balancing, there is no need to operate the reconstruction switch for charging and discharging operations, avoiding the problem of frequent operation of the reconstruction switch of 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 It is a structural schematic diagram of the reconfigurable battery system of the present invention;

[0058] Figure 2 The figure is a simplified schematic diagram of different configuration schemes of the reconfigurable battery system of the present invention, wherein (a) shows four batteries fully connected in series and in a fault-tolerant configuration; (b) shows four batteries fully connected in parallel and in a fault-tolerant configuration; (c) shows four batteries connected in series first and then in parallel and in a fault-tolerant configuration; (d) shows four batteries connected in parallel first and then in series and in a fault-tolerant configuration;

[0059] Figure 3 The structure diagram of the converter-based reconfigurable battery system of the present invention is a reconfigurable battery system structure based on a 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] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are 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 1 As shown, in this structure, there are n batteries and 4n-5 reconstruction switches. Based on the reconstruction switch array, the battery system can be configured with any series-parallel connection structure (including series, parallel, series first then parallel, and parallel first then series), and different structures have fault tolerance control, that is, isolating faulty batteries 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 and the fault-tolerant control schemes of their respective structures are demonstrated. The connection between the battery and the reconfiguration switch in the four-battery reconfigurable system is as follows:

[0064] Number the batteries from left to right as B#1 to B#4 (the same below), the positive electrode of battery B#1 is connected to the positive electrode of the load, and the negative electrode of battery B#4 is connected to the negative electrode of the load; K 1-1 One end of K is connected to the positive terminal of battery B#1. 1-3 One end of K is connected to the positive terminal of battery B#3; 1-2 One end of 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 terminal of battery B#4; 2-1 One end of K is connected to the negative terminal of battery B#1. 2-2 One end of K is connected to the negative terminal of battery B#2. 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 electrode of battery B#2, and the other end is connected to the negative electrode 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 electrode of battery B#3 and the other end is connected to the negative electrode 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 electrode 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 electrode of battery B#2; 4-2 The other end and K 3-3 One end of the connection; K 4-3 One end of K 3-3 One end of K 4-3 The other end is connected to the negative electrode 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. The left figure shows the parallel configuration. The 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. Assuming that battery B#2 fails (similarly, there are also 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 , K 4-3 ; Figure 2 (d) shows the battery configuration of first parallel and then series connection and its fault-tolerant control. The left figure shows the battery configuration of first parallel and then series connection. 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 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 all faulty battery strings (including the faulty battery and all batteries connected in series with the faulty battery) be disconnected in order to avoid circulating currents between the batteries connected in parallel.

[0066] Integrating the power converter into the reconfigurable battery system has formed Figure 3 The converter-based reconfigurable battery system shown in FIG. 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 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 signals of the MOS tube are complementary. When the chip is not working, the MOS tube S H1 The output is turned off, so there will be no leakage problem of the diode, and the MOS tube has a small conduction voltage drop and a small power loss, so it is more efficient to use it 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 as an example, Cell 1 Represents battery No. 1, and the capacitor C connected to it 1 , inductance L 1 and MOS switch S H1 and S L1 The boost converter that makes up the No. 1 battery, Cell 1 Together with the Boost converter, it forms the first power unit. B1 Indicates that the current flows through the battery Cell1 The current, V 1 Indicates the output voltage of the first power unit, I 1 represents the output current of the first power unit, D 1 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, including 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] In order to realize any series-parallel structure, in the 1st to nth power units, the connection method of each reconfiguration switch is as follows:

[0070] The positive pole of the output terminal of the first power unit is connected to the positive pole of the load / charger, and the negative pole of the output terminal of the nth power unit is connected to the negative pole of the load / charger; K 1-i One end of 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 is connected to K 1-(i+1) One end of K 1-(n-1) The other end of K is connected to the positive output terminal of the nth power unit; 2-i One end of K (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 electrode of the output terminal of the second power unit, and the other end is connected to the negative electrode of the 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 electrode of the output terminal of the i-th power unit and 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 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 the negative electrode of the output end of the i+1th power unit, and the other end is connected to the negative electrode of the output end of the i+1th 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] With the help of the reconfigurable switch array, the battery system has good flexibility and fault tolerance.

[0073] Regarding 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 running (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 of the entire battery system bus is specified and used to derive the output voltage reference value for 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 ith 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] The 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 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 factor 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 Represents the SOC coefficient of the jth power unit of the ith module, which comes from the SOC balance loop within the module.

[0092] In the SOC balance control loop within the i-th module, the SOC average value SOC i , and the SOC value SOC of the jth power unit of the i-th module i_j The difference passes 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:

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

[0094] The charge balancing control method of the overall parallel structure (i.e., parallel configuration or series-first-parallel configuration) is the same as the charge balancing control method of the overall series structure, and also goes 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 modules is the system output voltage V bus Therefore, the formula of the pre-voltage divider coefficient is different from that of the overall series structure. The formula of the pre-voltage divider coefficient of the overall parallel structure is as follows:

[0095]

[0096] In addition, in the charge balancing control method of the overall parallel structure, the SOC balancing loop within the module is before the SOC balancing loop between modules, and the output voltage reference value and output duty cycle of each power unit are as follows:

[0097]

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

[0099] In the embodiment of the present invention, the ampere-hour integration method is used to calculate the SOC value of the battery, and the calculation formula is as follows:

[0100]

[0101] Among them, SOC i_j Indicates the SOC value of the battery in the jth power unit of the i-th module; SOC 0 Indicates 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 staand t end 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 inter-module SOC balancing loop and the intra-module SOC balancing loop have different action orders in the charge balancing control algorithms of the overall series and overall parallel structures, the feedback effects are the same. i and b i_j Both are positively correlated with the SOC value. The duty cycle D i_j and a i or b i_j Therefore, the larger the SOC value of the battery, the larger the duty cycle of the converter of the corresponding power unit under the action of the reconstruction balance controller, so that the battery will discharge at a faster rate, so that the SOC of the entire battery system converges with each other (that is, the battery with a large SOC discharges quickly and the SOC decreases quickly; the battery with a small SOC discharges slowly and the SOC decreases slowly; so that the SOC values ​​between 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 implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope 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 (i ranges from 1 to n-1) and K 4-i (i ranges from 2 to n-1); in the 1st to nth power units, the positive electrode of the output end of the 1st power unit is connected to the positive electrode of the load / charger, and the negative electrode of the output end of the nth power unit is connected to the negative electrode of the load / charger; K 1-i One end of 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 is connected to K 1-(i+1) One end of K 1-(n-1) The other end of K is connected to the positive output terminal of the nth power unit; 2-i One end of K (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 electrode of the output terminal of the second power unit, and the other end is connected to the negative electrode of the 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 electrode of the output terminal of the i-th power unit and 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-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 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 of the power cell is connected to the negative electrode of the output terminal of the i+1th power cell; and the other end of the power cell is connected to the negative electrode of the output terminal of the i+1th power cell; The reconfigurable battery system includes the following four structural configurations (a) to (d): (a) series connection; (b) parallel connection; (c) series connection first and then parallel connection; (d) parallel connection first and then series connection; (a) and (d) are overall series connection structures, and (b) and (c) are overall parallel connection structures; and different structural configurations all have fault tolerance control; Assume that the reconfigurable battery system with n power units is an overall series / parallel structure consisting of M series / parallel modules, where the i-th module consists of N i If the power units are connected in parallel / series, the duty cycle control strategy of the jth power unit in the ith module includes a voltage loop, an inter-module SOC balance loop, and an intra-module SOC balance loop.

2. The method according to claim 1, characterized in that In order to avoid loop current between parallel-connected batteries, the fault-tolerant scheme of the series-first-then-parallel configuration requires disconnecting all faulty battery strings, that is, disconnecting the faulty battery and all batteries connected in series with the faulty battery.

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 is connected to the positive electrode of the output end of the first power unit, K 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 of 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 is connected to the negative pole of the output end of the first power unit, K 2-2 One end of is connected to the negative pole of the output end of the second power unit, K 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 end of the second power unit, K 2-2 The other end is connected to the positive electrode of the output end 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 electrode of the output terminal of the second power unit, and the other end is connected to the negative electrode of the 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 end of the third power unit and K 2-3 One end of the connection; K 3-2 One end of is connected to the positive pole of the output end of the second power unit; K 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 of 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 structure is a series configuration, that is, the 1st to 4th power units are connected in series, the 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 after the first power unit and the second power unit are connected in series is connected in parallel with the branch after the third power unit and the fourth power unit are connected in series, 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, characterized in that: 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, characterized in that 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 for 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 After that, V refi_j The output voltage measurement value 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 factor 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 (i.e., output duty cycle) of the converter of the jth power unit of the i-th module; b i_j Represents the SOC coefficient of the jth power unit of the ith module, which comes from the SOC balance loop within the module.

6. The method according to claim 1, characterized in that 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 for 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 After that, V refi_j The output voltage measurement value 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 (i.e., output duty cycle) of the converter of the jth power unit of the i-th module; a i is the SOC coefficient of the i-th module, which comes from the inter-module SOC balancing loop.

7. The method according to claim 5 or 6, characterized in that: In the inter-module SOC balance control loop, the average SOC value of the battery system SOC ref The calculation formula is as follows: Among them, SOC i_j represents 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: The 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)。 8. The method according to claim 5 or 6, characterized in that: In the SOC balance control loop within the i-th module, the SOC average value SOC i , and the SOC value SOC of the jth power unit of the i-th module i_j The difference passes 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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