An adaptive configuration hybrid battery system and active balancing control method thereof

Abstract

The present invention discloses an adaptive configuration hybrid battery system and an active balancing control method thereof. By designing a free hybrid battery energy storage system structure with adaptive switching of BU connection mode, and proposing a universal battery SOC balancing control strategy for the structure, the battery energy storage system can adaptively switch the series and parallel connection mode of each BU in the system for different types of loads, and more effectively meet the needs of various complex loads. At the same time, the present invention also performs battery output voltage modulation and SOC balance control through the proposed SOC balancing control strategy, realizing active SOC balancing control between batteries under any connection mode.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery balancing control, and more specifically, relates to an adaptive configuration hybrid battery system and an active balancing control method thereof. Background Art

[0002] Battery energy storage systems can provide power to many electronic devices or power systems, such as electric vehicles, mobile phones, computers, and computer centers. The batteries in the battery energy storage system can provide high voltage to the load by connecting in series, or they can provide high current to the load by connecting in parallel. The voltage level of the battery itself is usually difficult to meet the load requirements, so a DC-DC converter is used to increase the voltage level of the battery. In a battery energy storage system, even if the models of the batteries are the same, they may have different states of charge (SOC) when working due to various factors such as temperature, aging, and factory manufacturing. This difference may cause a battery to be overcharged or over-discharged, which may cause a fire or explosion in serious cases.

[0003] Traditional battery balancing methods mostly use passive balancing methods, that is, connecting resistors in parallel at the battery ends to consume excess energy in the form of resistor heat. However, this method is inefficient and the heat generation has a great impact on battery thermal control. In order to solve the problems of passive balancing heat release and long balancing time, active balancing using components such as inductors, capacitors, power converters and transformers has also been applied. However, existing active balancing control methods are mostly aimed at control structures of battery series connection. For mixed series and parallel battery structures, how to achieve balance between each battery is an urgent problem to be solved.

[0004] For example, document 1 "Yuan Cao and Jaber A. Abu Qahouq. Hierarchical SOC Balancing Controller for Battery Energy Storage System. IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, vol. 68, no. 10, pp. 9386-9397" proposes a SOC balancing strategy for battery packs in series and battery cells in parallel. In the structure of this document, N battery cells are connected in parallel to form a battery pack, and N such battery packs are connected in series to power the system. The parallel battery cells control the switches connected to each other through PWM signals, so that each battery is turned on successively rather than at the same time, and then the DC-DC duty cycle connected to each battery pack is controlled according to the control strategy proposed in the article. When a battery cell with a larger SOC is turned on, the corresponding DC-DC duty cycle is larger. The average value of the SOC of the parallel battery cells is regarded as the SOC of the battery pack. For a battery pack in series, the larger the SOC, the larger the voltage required to be provided. Therefore, when controlling the battery voltage, the larger the SOC of the battery pack, the larger the output voltage reference value corresponding to the battery pack. The battery output voltage and SOC are controlled in the above manner.

[0005] In addition, Reference 2 "Balancing Charge / Discharge Management for Series / Parallel Battery Packs. In 2012 7th IEEE Conference on Industrial Electronics and Applications (ICIEA), pp. 613-618" proposes a battery hybrid structure that can realize the conversion of batteries from all series connection to all parallel connection. This structure also consists of N cells forming a battery pack, and then N such battery packs form a system. The difference is that all battery cells in a battery pack in Reference 1 share a converter, while each battery cell in this article is only connected to its own converter. When in the discharge stage, the control switch allows each battery pack to be connected in series to achieve a high voltage output of the system. When in the charging stage, the control switch allows each battery pack to be connected in parallel to achieve that all batteries are charged under the same voltage conditions. At the same time, under different connection conditions, a method similar to Reference 1 is used to perform SOC balancing.

[0006] Since there are many methods for battery SOC balancing, an effective battery balancing method can ensure the safe and reliable operation of the battery energy storage system. However, the existing SOC balancing methods are mostly targeted at a specific battery connection method, and lack a control strategy for unified SOC balancing of batteries under different connection structures, especially for complex battery systems with mixed series and parallel connections. At present, there is a lack of a universal control strategy for achieving SOC balancing when the batteries are mixed. The control strategy proposed in document 1 of the prior art is only for the battery system structure of first parallel and then series connection, and it is impossible to change the battery system configuration according to the load demand. The structure proposed in document 2 discusses the parallel connection and series connection of the battery separately, and only discusses parallel control during discharge and only discusses series control during charging. For the load of the actual battery energy storage system, sometimes a simple series or parallel connection cannot meet the demand, and the battery needs to be connected in series and parallel. Sometimes it is even necessary to switch the battery from a certain connection method to another connection method while still achieving SOC balancing between batteries. These are all technical deficiencies under the current technical background.

[0007] Therefore, there is an urgent need to design an adaptive configuration hybrid battery system and its active balancing control method, which can adaptively adjust and control the common series-parallel hybrid structure configuration of the battery to adapt to different load requirements, thereby achieving SOC balancing between batteries under any connection mode. Summary of the invention

[0008] 1. Technical issues to be resolved

[0009] Based on the defects mentioned in the above background technology, the present invention discloses an adaptive configuration hybrid battery system and its active balancing control method, by designing a battery energy storage system structure that adaptively switches the BU connection mode, and proposes a universal battery SOC balancing control strategy for the structure, so that the battery energy storage system can adaptively switch the series and parallel connection mode of each BU in the system for different types of loads, and more effectively meet the needs of various complex loads. At the same time, the present invention also performs battery output voltage modulation and SOC balance control through the proposed SOC balancing control strategy, and realizes active SOC balancing control between batteries under any connection mode.

[0010] (II) Technical solution

[0011] The present invention discloses an adaptive configuration hybrid battery system, wherein each battery is connected to a DC-DC converter to form a battery unit. The adaptive configuration hybrid battery system comprises N battery units. In the first to Nth battery units, there are K switches responsible for controlling the series connection. s1 ,K s2 ,…,K s(N-1) , responsible for controlling the parallel connected switches are Kp11 ,K p12 ,…,K pN1 and K pN2 , the positive terminal of the output terminal of the first battery cell is connected to K p12 One end of K is connected to the positive electrode of the load. p12 The other end is connected to each K pi1 The i-th K pi1 The other end is connected to the positive electrode of the output end of the i-th battery unit; the negative electrode of the output end of the i-1-th battery unit is connected to the positive electrode of the output end of the i-th battery unit through the switch K s(i-1) The positive electrode of the output terminal of the i-th battery cell is connected. In addition, the negative electrode of the output terminal of the first battery cell is connected in series with K p11 With N-1 K pi2 One end of each K pi2 The other end of each battery is connected to the negative electrode of the output terminal of the i-th battery unit, and the negative electrode of the output terminal of the N-th battery unit is connected to the negative electrode of the output terminal of the K pN2 The other end is connected to the negative terminal of the load.

[0012] Preferably, the DC-DC converter is specifically a BOOST boost converter, and the battery parameters in the 1st to Nth battery units are the same.

[0013] Preferably, the adaptive configuration hybrid battery system includes the following four states (a) to (d): (a) N battery cells are fully connected in series; (b) N battery cells are fully connected in parallel; (c) d battery cells are first connected in series, and then the other Nd battery cells are connected in parallel; (d) d battery cells are first connected in parallel, and then the other Nd battery cells are connected in series.

[0014] In addition, the present invention also discloses an active balancing control method for the adaptive configuration hybrid battery system as described above, setting the parallel connection parameters of N battery units to par 1～N , the series parameter is ser 1～N And the series charge reference value is SOC s_ref The parallel charge reference value is SOC p_ref , in the initialization setting par 1～N =ser 1～N =1, calculate the parameters according to the four states (a) to (d):

[0015] When in full series connection (a), the parallel parameters of each battery unit are 1～N The default value is 1. The series parameter ser of each series connected battery cell 1～N Set to N / N, then the SOC in the series circuit s_ref for SOC BU_i is the state of charge of the ith battery cell.

[0016] Preferably, the calculation of each parameter according to the four states (a) to (d) further includes:

[0017] When in full parallel state (b), the series parameter ser of each battery unit is 1～N The default value is 1. The parallel parameters of each parallel connected battery unit are 1～N Set to N, then the SOC of each battery unit in the parallel circuit p_ref is the average SOC value of each battery cell connected in parallel, that is

[0018] Preferably, the calculation of each parameter according to the four states (a) to (d) further includes:

[0019] When there are d series and Nd parallel connections (c), the parallel parameter par of the d series connected battery cells is 1～d The default value is 1. 1～d Set to N / d, the parallel parameter par of Nd parallel connected battery cells d+1～N is N, their series parameter ser d+1～N The default value is 1, and SOC s_ref and SOC p_ref Satisfies the following formula:

[0020]

[0021]

[0022] Preferably, the calculation of each parameter according to the four states (a) to (d) further includes:

[0023] When the number of parallel connections is d and the number of series connections is Nd (d), the series parameter value ser of the d parallel connected battery cells is 1～d The default value is 1. Their parallel parameters par 1～d Set to d, Nd series battery cells series parameter ser d+1～N is N / N, and their parallel parameter par d+1～N The default value is 1, and SOC s_ref and SOC p_ref Satisfies the following formula:

[0024]

[0025]

[0026] Preferably, the active balancing control method includes a voltage control loop, and the voltage control loop includes a formula for calculating the switching duty cycle of the DC-DC converter in the 1st to Nth battery cells:

[0027]

[0028] Among them, a1~a N and b1~b N are the voltage multiples and duty cycle multiples of N battery cells, V bus is the load voltage, V1~V N are the output voltages of 1 to N battery cells, G BU_vol (z) is the transfer function, D1~D N The actual duty cycle of the DC-DC control switches in 1 to N battery cells respectively.

[0029] Preferably, the active balancing control method includes a series SOC control loop, wherein the series SOC control loop includes a circuit for calculating the voltage multiples a1 to a N The formula is:

[0030]

[0031]

[0032] Among them, SOC INs_i is the SOC input value of the series connected battery cell, G BU_SOC (z) is the transfer function.

[0033] Preferably, the active balancing control method includes a parallel SOC control loop, wherein the parallel SOC control loop includes a circuit for calculating the duty cycle multiples b1 to b2. N The formula is:

[0034]

[0035]

[0036] Among them, SOC INp_i is the parallel SOC input value of the i-th battery unit, G BU_SOC (z) is the transfer function.

[0037] (III) Beneficial effects

[0038] 1. The present invention proposes an adaptive configuration battery series-parallel hybrid structure, connecting each battery unit (Battery Unit, hereinafter referred to as BU) with a series-parallel switch, and changing the series-parallel connection structure of the system by controlling the on-off of the switch, aiming to adaptively adjust the battery series-parallel hybrid structure configuration to adapt to different loads or power requirements. In this structure, each battery unit as an energy storage structure is connected to a Boost DC-DC converter to form a BU. The proposed control strategy realizes output voltage modulation and SOC balance control of the battery system by controlling the duty cycle of the DC-DC in the battery unit.

[0039] 2. The present invention also proposes a universal battery SOC balancing control strategy under a hybrid structure, which gives specific control means to different BUs by judging the battery connection mode, inputs the terminal voltage of each BU, the terminal voltage of each battery and the current signal into the controller, obtains the corresponding DC-DC duty cycle, and outputs PWM waves to achieve voltage control and SOC balancing. In addition, for the parallel parameter par used to assist in controlling the reference voltage value of each BU in different connection modes 1～N and the concatenation parameter ser 1～N and SOC s_ref and SOC p_ref The SOC balancing control strategy of the present invention specifically designs a voltage control loop, a series SOC control loop and a parallel control loop, which can realize the active balancing of the SOC of the battery inside the BU under various connection modes, and dynamically control the SOC multipliers a1~a N and b1~b N , which can effectively affect the reference voltage or output duty cycle of the voltage control loop, so that the BU with high SOC outputs more voltage and the BU with low SOC outputs less voltage.

[0040] 3. The adaptive configuration circuit and its balancing control method of the present invention are highly versatile. When facing high voltage loads, the adaptive configuration hybrid battery system of the present invention can adopt a full-series or multi-series and less-parallel structure; when facing high current loads, a full-parallel or multi-parallel and less-series structure can be adopted; when charging, a full-parallel structure can be adopted for equal voltage charging; the system configuration can be freely adjusted through the switch matrix at the output end. After determining the specific structure, the proposed SOC balancing control strategy will assign different parameters to each BU according to the connection structure, realize SOC balancing under various connection structures, and there is no need to change the structure of the control strategy according to the connection structure of the BU, and at the same time, it can realize the unified modulation control of the output load voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments:

[0042] Figure 1 It is a schematic diagram of the structure of the adaptive configuration hybrid battery system in the present invention, which is a battery energy storage system structure with adaptive switching BU connection mode.

[0043] Figure 2 Figure 1 is a simplified schematic diagram of different BU connection modes of the present invention, wherein (a) shows a full series connection of BUs; (b) shows a full parallel connection of BUs; (c) shows a d-series (Nd)-parallel connection, which means that d BUs are first connected in series and then other BUs are connected in parallel; (d) shows a d-parallel (Nd)-series connection, which means that d BUs are first connected in parallel and then other BUs are connected in series.

[0044] Figure 3 The figure is a flow chart of control parameter setting of the active balancing control method proposed by the present invention.

[0045] Figure 4 For the present invention Figure 1 The control strategy system block diagram of the battery energy storage system under the hybrid structure is shown in the figure, where (a) is the voltage control loop structure; (b) is the SOC control loop structure of the series BU; (c) is the SOC control loop structure of the parallel BU. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in 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 making creative work are within the scope of protection of the present invention.

[0047] In order to adapt to different load or power requirements, the structure of the adaptive configuration hybrid battery system proposed in the present invention is as follows: Figure 1 As shown, in this structure, each battery is connected to a DC-DC converter to form a battery unit (hereinafter referred to as BU). The proposed control strategy realizes output voltage modulation and SOC balance control of the battery system by controlling the duty cycle of the DC-DC in the battery unit.

[0048] The DC-DC converter in each battery cell can be a Boost circuit. In order to reduce power consumption, the specific Figure 1 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 12 This MOS tube is controlled by the logic inside the synchronous chip, which is connected to the main control signal S11 The signals of the MOS tube are complementary. When the chip is not working, the MOS tube S 12 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 DC-DC converter of the present invention can also be other DC-DC converters.

[0049] by Figure 1 Take the first battery unit BU#1 in the example, B1 represents battery No. 1, and the two capacitors C, inductor L and MOS switch S connected to it. 11 and S 12 The DC-DC converter (i.e. synchronous type BOOST boost circuit, S 11 and S 12 Signal complement), B1 and the DC-DC together form Battery Unit #1, namely BU #1. B1 represents the voltage across battery B1, I B1 represents the current flowing through battery B1, V1 represents the output voltage of BU#1, I1 represents the output current of BU#1, and D1 represents the DC-DC input main switch S in BU#1. 11 The duty cycle of the PWM signal. N such BUs can be freely set in the entire battery energy storage system, and they are connected to each other through series-parallel conversion switches.

[0050] In order to realize the adaptive configuration of hybrid connection and to count the specific connection status during hybrid connection, in the 1st to Nth battery cells, the switches responsible for controlling the series connection are K s1 ,K s2 ,…,K s(N-1) , responsible for controlling the parallel connected switches are K p11 ,K p12 ,…,K pN1 and K pN2 , the connection methods of each switch are as follows:

[0051] The positive terminal of the output terminal of the first battery cell is connected to K p12 One end of K is connected to the positive electrode of the load. p12 The other end is connected to each K pi1 The i-th K pi1 The other end is connected to the positive electrode of the output end of the i-th battery unit; the negative electrode of the output end of the i-1-th battery unit is connected to the positive electrode of the output end of the i-th battery unit through the switch K s(i-1) The positive electrode of the output terminal of the i-th battery cell is connected. In addition, the negative electrode of the output terminal of the first battery cell is connected in series with K p11 With N-1 K pi2 One end of each Kpi2 The other end of each battery is connected to the negative electrode of the output terminal of the i-th battery unit, and the negative electrode of the output terminal of the N-th battery unit is connected to the negative electrode of the output terminal of the K pN2 The other end of the switch is connected to the negative pole of the load. Therefore, in the switch responsible for controlling the parallel connection, switch K p12 and K pN2 Responsible for controlling whether the positive and negative poles of the parallel connected battery units BU are directly connected in parallel with the load. Other parallel connection switches are responsible for the parallel connection between BU and BU. The output voltage of the entire battery energy storage system is V bus , that is, the load voltage, the output current is I bus , that is, the load current.

[0052] The following Figure 1 The voltage and current output conditions are analyzed when the circuit is in four mixed states:

[0053] (a) Full series connection: When the load is a high voltage and low current load, each BU is connected in series, such as Figure 2 As shown in Figure (a) in the figure. At this time, the switch K responsible for controlling the series connection s1 ,K s2 To K s(N-1) Fully closed, responsible for controlling the parallel switch K p11 ,K p12 To K pN1 ,K pN2 The output voltage of the battery energy storage system is equal to the sum of the output voltages of each BU, and the output currents of each BU are equal, which is equal to the output current of the battery energy storage system, as shown in equations (1) and (2).

[0054] V bus =V1+V2+...+V N (1)

[0055] I bus =I1=I2=...=I N (2)

[0056] (b) Full parallel: When the load is a high current and low voltage load, each BU is connected in parallel, such as Figure 2 As shown in Figure (b). At this time, the switch K responsible for controlling the parallel connection p11 ,K p12 To K pN1 ,K pN2 All are closed, responsible for controlling the series switch K s1 ,K s2 To K s(N-1) All disconnected. The output current of the battery energy storage system is equal to the sum of the output currents of each BU, and the output voltages of each BU are equal, which is equal to the output voltage of the battery energy storage system, as shown in equations (3) and (4).

[0057] V bus =V1=V2=...=V N (2)

[0058] I bus =I1+I2+...+I N (3)

[0059] (c) d-series (Nd) parallel: When the load is in the middle state, the simple series connection cannot meet the current requirement, and the simple parallel connection cannot meet the voltage requirement. It is necessary to connect d BUs in series to increase the output voltage, and then connect other BUs in parallel with the series branch composed of d BUs to increase the output current. The structure of d-series multi-parallel is shown in Figure 1. Figure 2 As shown in Figure (c). At this time, the switch K responsible for controlling the series connection s1 ,K s2 To K s(d-1) Fully closed, K sd To K s(N-1) Fully disconnected, responsible for controlling the parallel switch K pd2 To K pN1 Fully closed, responsible for controlling the switch K directly connected in parallel with the load p12 and K pN2 Fully closed. The output current of the battery energy storage system is equal to the sum of the output current of the series branch and the output current of the parallel BU. The output voltage of the parallel BU is equal to the output voltage of the series branch, which is equal to the output voltage of the battery energy storage system, as shown in equations (5) and (6). In this connection method, the value of d should be selected according to the load demand and generally cannot exceed half of the total number of BUs. If it is too small, the load demand cannot be met. If it is too large, the output voltage of the battery energy storage system will be too large, the output current will be insufficient, and the output voltage borne by the parallel BU will be too large, which is not good for the health of the battery.

[0060] V bus =V1+V2+...+V d =V d+1 =... =V N (4)

[0061] I bus =I i +I d+1 +...+I N ,i=1,2,...,d (5)

[0062] (d) d parallel (Nd) series: When the load is a high voltage and low current load, the simple series connection cannot meet the current requirement, and the simple parallel connection cannot meet the voltage requirement. If the value of d is increased on the basis of the d series multi-parallel structure to increase the output voltage of the system, it will cause the parallel BU to overload, which is not conducive to the normal operation of the battery. Therefore, it is necessary to connect d BUs in parallel to increase the output current, and then connect other BUs in series with the parallel branch composed of these d BUs to increase the output voltage. The structure of d parallel multi-string is as follows Figure 2 As shown in Figure (d). At this time, the switch K responsible for controlling the parallel connection p11 ,K p12 To K pd1 Fully closed, K pd2 To K pN1 ,K pN2 Fully disconnected, responsible for controlling the series switch K sd To K s(N-1) Fully closed. The output current of the battery energy storage system is equal to the output current of the parallel branch, and the output voltage is equal to the output voltage of the parallel branch plus the output voltage of other series BUs, as shown in equations (7) and (8). In this connection mode, the value of d should be selected according to the load demand and generally cannot exceed half of the total number of BUs. If it is too small, it will not be able to meet the load demand. If it is too large, it will cause the output current of the battery energy storage system to be too large, the output voltage to be insufficient, and the output current borne by the series BU to be too large, which is not good for the health of the battery.

[0063] V bus =V i +V d+1 +...+V N ,i=1,2,...,d (6)

[0064] I bus =I1+I2+...+I d =I d+1 =...=I N (7)

[0065] for Figure 2 The control parameter settings of BU under the four different connection modes (a) to (d) are shown in Figure 3 .exist Figure 3 In the example, assume that the total number of BUs in the battery energy storage system is N, and set the parallel parameter par 1～N and the concatenation parameter ser 1～N , which is used as a circuit structure parameter to assist in controlling the reference voltage value of each BU in different connection modes, and to set the parameter SOC s_ref and SOC p_ref Used to calculate the SOC reference value of each BU in the series circuit and parallel circuit of the battery energy storage system.

[0066] See also Figure 3 As shown, the present invention also judges in sequence Figure 1 Does the circuit belong to Figure 2 In the four cases (a) to (d), if so, execute the corresponding par 1～N and / or ser 1～N Parameter assignment, and calculate the corresponding parameter SOC s_ref and SOC p_ref If not, continue to judge the next situation until all four situations are judged in sequence. 1～N =ser 1～N =1, perform the following steps:

[0067] Step 1: When all BUs in the battery energy storage system are connected in series, the parallel parameters of each BU are 1～N The default value is 1. The serial parameters of each serially connected BU are ser. 1～N Set to N / N (total number of BUs / total number of BUs in the series loop). At this time, the SOC reference value SOC of each BU in the series loop is s_ref is the average SOC value of each BU connected in series, which is specifically SOC BU_i is the state of charge of the i-th battery unit BU.

[0068] Step 2: When all BUs in the battery energy storage system are connected in parallel, the series parameters of each BU are 1～N The default value is 1. The parallel parameters of each parallel connected BU are par. 1～N Set to N (the total number of BUs in the parallel circuit), then the SOC reference value SOC of each BU in the parallel circuit is p_ref is the average SOC value of each BU connected in parallel, that is

[0069] Step 3: When there are d BUs in series and Nd BUs in parallel in the battery energy storage system, these d BUs form a series circuit, and their parallel parameters par 1～d The default value is 1. 1～d Set to N / d, the SOC reference value SOC of each BU in this series circuit s_ref is the average SOC value of each BU connected in series. In addition, this series circuit and the remaining Nd BUs connected in parallel form a parallel circuit, so the number of BUs in the parallel circuit is still N, and the parallel parameter par of these Nd BUs d+1～N is N, their series parameter ser d+1～NThe default is 1. When calculating the SOC reference value, the series circuit is considered as a whole, so the SOC reference value SOC of Nd BUs in the parallel circuit is p_ref SOC is the SOC of each BU connected in parallel and the average SOC of the series circuit s_ref The average value of . That is, it satisfies the following formula:

[0070]

[0071]

[0072] Step 4: When there are d BUs in parallel and Nd BUs in series in the battery energy storage system, these d BUs form a parallel circuit, and their series parameter value ser 1～d The default value is 1. Their parallel parameters par 1～d Set to d, the SOC reference value SOC of each BU in this parallel circuit p_ref is the average SOC value of each BU connected in parallel. In addition, this parallel circuit and the remaining Nd BUs connected in series form a series circuit, so the number of BUs in the series circuit is still N, and the series parameter ser of these Nd BUs is d+1～N is N / N, and their parallel parameter par d+1～N The default is 1. When calculating the SOC reference value, the parallel circuit is considered as a whole, so the SOC reference value SOC of Nd BUs in the series circuit is s_ref SOC is the SOC of each BU connected in series and the average SOC of the parallel circuit p_ref The average value of . That is, it satisfies the following formula:

[0073]

[0074]

[0075] The SOC balancing control strategy for the battery energy storage system structure with adaptive switching BU connection mode proposed in the present invention is as follows: Figure 4 As shown in the figure, the control strategy depends on Figure 3 The calculated circuit parameters par 1～N ,ser 1～N , SOC s_ref and SOC p_ref The SOC balancing control strategy proposed in the present invention can achieve SOC balancing of batteries inside BU under various connection modes. The proposed SOC balancing control strategy consists of a voltage control loop, a series SOC control loop and a parallel SOC control loop.

[0076] Voltage control loop: Voltage control loop such as Figure 4As shown in Figure (a). The voltage control of the battery is realized by the voltage compensator, whose input is the difference between the measured voltage of the BU and the expected voltage, and the output is the duty cycle of the DC-DC. The expected voltage is calculated from the load voltage. The load voltage is divided by the total number of BUs N to obtain the voltage expected to be allocated to each BU, which is called the pre-allocated voltage. Then different series parameters ser are allocated according to the connection method of the BU. 1～N And the parallel parameter par 1～N , the BUs connected in series will change the pre-allocated voltage of each BU in the branch according to the number of BUs in the series branch, which is equivalent to the pre-allocated voltage multiplied by the total number of BUs / total number of BUs in series. The BUs connected in parallel need to bear a voltage value equal to the output voltage of the parallel branch. The output voltage of the parallel branch is equal to the pre-allocated voltage multiplied by the number of BUs in the parallel branch. When the BUs are in series connection, the corresponding voltage multiples a1 to a1 will be allocated according to the SOC of the battery in the series branch. N , so that the BU with more SOC outputs more voltage, and the BU with less SOC outputs less voltage. For BUs in parallel connection, their output voltage values ​​should be equal, but due to the different SOCs of the batteries, the terminal voltages of the batteries are not the same, so different DC-DC duty cycles need to be allocated. The desired duty cycle is multiplied by b1 to b through the SOC multiplier. N times to obtain the actual duty cycle D1 to D corresponding to the DC-DC N , the voltage control loop is shown in equation (9).

[0077]

[0078] Among them, a1~a N and b1~b N is the voltage ratio and duty cycle ratio, V bus is the load voltage, V1~V N are the output voltages of 1 to N battery cells, G BU_vol (z) is a transfer function, preferably a transfer function of a PI proportional integral controller, D1~D N The actual duty cycle of the DC-DC control switches in 1 to N battery cells respectively.

[0079] Series SOC control loop: Figure 4 Figure (b) is responsible for controlling the BU in series connection. When the BU is in series connection, the BU's parallel parameter par defaults to 1. For the BU in this series connection, the BU's output reference voltage is adjusted by controlling its voltage multiplier, and then the BU's output voltage is controlled by the voltage control loop. Therefore, for the BU in series connection, its series SOC input value SOC INs_i It is equal to its actual SOC value SOC BU_iWhen the BU is in parallel connection mode, the parallel parameter par of the BU is equal to the number of BUs in parallel (must be greater than 1). For the BU in this parallel connection mode, the output voltage of the BU can be adjusted by controlling its duty cycle. Therefore, it is necessary to set its series SOC input value SOC INs_i Set as the expected series SOC value SOC s_ref , so that the voltage ratio of the BU is 1. The series SOC control loop is shown in equations (10) and (11), which can calculate a1~a N .

[0080]

[0081]

[0082] Parallel SOC control loop: Figure 4 Figure (c) is responsible for controlling the BUs in parallel connection. When the BUs are in parallel connection, the parallel parameter par of the BU is equal to the number of BUs in parallel (must be greater than 1). For the BUs in parallel connection, the output voltage of the BU can be adjusted by controlling its duty cycle. Therefore, for the BUs in parallel connection, its parallel SOC input value SOC INp_i It is equal to its actual SOC value SOC BU_i When the BU is in series connection, the BU's parallel parameter par defaults to 1. For the BU in this series connection, the BU's output reference voltage can be adjusted by controlling its voltage multiplier, and then the BU's output voltage can be controlled through the voltage control loop. Therefore, its parallel SOC input value SOC INp_i Set as the parallel SOC expected value SOC p_ref , so that the duty cycle of the BU is 1. The parallel SOC control loop is shown in equations (12) and (13), which can calculate b1~b N .

[0083]

[0084]

[0085] In formulas (10) to (13), G BU_SOC (z) is a transfer function, which may also be preferably a transfer function of a PI proportional-integral controller.

[0086] The actual value of the battery's state of charge (SOC) can be calculated by the coulomb counting method. The coulomb counting method can calculate the battery's SOC based on the rate of change of the battery's SOC. After a given discharge time, the actual value of the battery's state of charge (SOC) is shown in formula (14).

[0087]

[0088] Among them, SOC initial_i represents BU#i, i.e., the initial state of charge SOC of the i-th battery unit, t1 to t2 represent the start and end time of current sampling, I Bi It represents the discharge current of the battery, and C represents the nominal capacity of the battery.

[0089] In summary, the present invention proposes a battery series-parallel hybrid structure, connecting each BU to a series-parallel switch, and changing the series-parallel connection structure of the system by controlling the on and off of the switch; a corresponding battery SOC balancing control strategy suitable for the hybrid structure is also proposed, which gives different BUs specific control means by judging the battery connection method. The terminal voltage of each BU, the terminal voltage of each battery, and the current signal are input into the controller to obtain the corresponding DC-DC duty cycle, and the PWM wave is output to achieve voltage control and SOC balancing; the proposed SOC balancing control strategy can dynamically control the SOC multiplier a1 to a N and b1 to b N , and at the same time comprehensively consider the circuit parameters par that represent the characteristics of the hybrid structure 1～N ,ser 1～N , SOC s_ref , SOC p_ref And the state of charge SOC of each battery BU_i The actual situation can be calculated effectively to finally calculate the reference voltage or output duty cycle that affects the voltage control loop, so that the BU with high SOC outputs more voltage and the BU with low SOC outputs less voltage. It is worth mentioning that the control structure has strong versatility.

[0090] Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An adaptive configuration hybrid battery system, characterized in that: Each battery is connected to a DC-DC converter to form a battery unit. The self-adaptive hybrid battery system includes N battery units. In the first to N battery units, there are K switches responsible for controlling the series connection. s1 ,K s2 ,…,K s(N-1) , responsible for controlling the parallel connected switches are K p11 ,K p12 ,…,K pN1 and K pN2 , the positive terminal of the output terminal of the first battery cell is connected to K p12 One end of K is connected to the positive electrode of the load. p12 The other end is connected to each K pi1 The i-th K pi1 The other end is connected to the positive electrode of the output end of the i-th battery unit; the negative electrode of the output end of the i-1-th battery unit is connected to the positive electrode of the output end of the i-th battery unit through the switch K s(i-1) The positive terminal of the output terminal of the i-th battery cell is connected; in addition, the negative terminal of the output terminal of the first battery cell is connected to the positive terminal of the i-th battery cell through the K p11 With N-1 K pi2 One end of each K pi2 The other end of each battery is connected to the negative electrode of the output terminal of the i-th battery unit, and the negative electrode of the output terminal of the N-th battery unit is connected to the negative electrode of the output terminal of the K pN2 The other end is connected to the negative pole of the load; The self-adaptive hybrid battery system includes the following four states (a) to (d): (a) N battery units are all connected in series; (b) N battery units are all connected in parallel; (c) d battery units are first connected in series, and then the other Nd battery units are connected in parallel; (d) First, d battery cells are connected in parallel, and then the other Nd battery cells are connected in series.

2. The adaptive configuration hybrid battery system according to claim 1, characterized in that: The DC-DC converter is specifically a BOOST boost converter, and the battery parameters in the 1st to Nth battery units are the same.

3. An active balancing control method for an adaptive configuration hybrid battery system as claimed in claim 1, characterized in that: Set the parallel connection parameter of N battery cells to par 1～N , the series parameter is ser 1～N And the series charge reference value is SOC s_ref The parallel charge reference value is SOC p_ref , in the initialization setting par 1～N =ser 1～N =1, calculate the parameters according to the four states (a) to (d): When in full series connection (a), the parallel parameters of each battery unit are 1～N The default value is 1. The series parameter ser of each series connected battery cell 1～N Set to N / N, then the SOC in the series circuit s_ref for SOC BU_i is the state of charge of the ith battery cell.

4. The active balancing control method according to claim 3, characterized in that: The calculation of each parameter according to the four states (a) to (d) also includes: When in full parallel state (b), the series parameter ser of each battery unit is 1～N The default value is 1. The parallel parameters of each parallel connected battery unit are 1～N Set to N, then the SOC of each battery unit in the parallel circuit p_ref is the average SOC value of each battery cell connected in parallel, that is 5. The active balancing control method according to claim 4, characterized in that: The calculation of each parameter according to the four states (a) to (d) also includes: When there are d series connections and Nd parallel connections (c), the d parallel parameters of the d battery cells are 1～d The default value is 1, which is unchanged. 1～d Set to N / d, the parallel parameter of Nd battery cells is d+1～N is the series parameter ser of N, Nd battery cells d+1～N The default value is 1, and SOC s_ref and SOC p_ref Satisfies the following formula:

6. The active balancing control method according to claim 5, characterized in that: The calculation of each parameter according to the four states (a) to (d) also includes: When the number of cells is d in parallel and Nd in series (d), the series parameter value ser of the d cells is 1～d The default value is 1, which is unchanged. The parallel parameter par of d battery cells 1～d Set to d, Nd battery cells series parameter ser d+1～N N / N, the parallel parameter par of Nd battery cells d+1～N The default value is 1, and SOC s_ref and SOC p_ref Satisfies the following formula:

7. The active balancing control method according to claim 6, characterized in that: The active balancing control method includes a voltage control loop, and the voltage control loop includes a formula for calculating the switching duty cycle of the DC-DC converter in the first to Nth battery cells: Among them, a1~a N and b1~b N are the voltage multiples and duty cycle multiples of N battery cells, V bus is the load voltage, V1~V N are the output voltages of 1 to N battery cells, G BU_vol (z) is the transfer function, D1~D N The actual duty cycle of the DC-DC control switches in 1 to N battery cells respectively.

8. The active balancing control method according to claim 7, characterized in that: The active balancing control method includes a series SOC control loop, wherein the series SOC control loop includes a circuit for calculating the voltage multiples a1 to a2. N The formula is: Among them, SOC INs_i is the SOC input value of the series connected battery cell, G BU_SOC (z) is the transfer function.

9. The active balancing control method according to claim 8, characterized in that: The active balancing control method includes a parallel SOC control loop, wherein the parallel SOC control loop includes a circuit for calculating the duty cycle multiples b1 to b2. N The formula is: Among them, SOC INp_i is the parallel SOC input value of the i-th battery unit, G BU_SOC (z) is the transfer function.

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