Layered energy balancing method for series-parallel battery energy storage system

Abstract

The invention provides a layered energy balancing method for a series-parallel battery energy storage system, and the method comprises the following steps: S1, building a relational expression between the periodic average current and the inductive current of a single battery based on the working time sequence of a switching group of the series-parallel battery energy storage system; s2, based on the relational expression of the periodic average current and the inductive current of the single battery, establishing a residual energy state (SOC) model of the single battery subsystem by adopting an ampere-hour integral method, and deducing an average SOC model of the battery subsystem; and S3, on the basis of the average SOC model of the battery subsystem, a layered equalization control strategy is designed, the inductive current reference value of the series-parallel battery energy storage system is obtained through the layered equalization control strategy, and the inductive current is the inductive current in the Boost converter. According to the invention, the SOC equalization of the single batteries in the battery pack and the SOC equalization among the battery packs are realized, so that the SOC equalization of all the single batteries is realized.

Description

Technical Field

[0001] The present invention relates to the field of automation control, and in particular to a hierarchical energy balancing method for a series-parallel battery energy storage system. Background Art

[0002] With the rapid development of society, the demand for energy has also increased. Solving the energy consumption problem of the development of the automobile industry, vigorously developing new energy electric vehicles, using clean energy instead of fossil energy, adhering to the development direction of electrification, networking, and intelligence, focusing on integration and innovation, breaking through key core technologies, and optimizing the industrial development environment have become the beacon for the development of the electric vehicle industry.

[0003] In order to meet application requirements, it is usually necessary to connect multiple batteries in series and parallel to form a battery pack. However, the differences in characteristics between single batteries will lead to a reduction in the available capacity of the energy storage system and a shortened service life. In addition, the charging and discharging behavior of the battery will also have a great impact on its service life. For example, high-frequency mutation current will damage the battery performance. Lithium-ion batteries have dynamic nonlinear characteristics, and the research on key technologies for their reliability directly affects the quality and overall performance of electric vehicles. Therefore, studying the energy balancing method of lithium-ion battery packs is of great significance to improving the operating efficiency, stability, safety, and reducing costs of large-scale energy storage systems. Summary of the invention

[0004] The present invention aims to at least solve the technical problems existing in the prior art, and in particular innovatively proposes a hierarchical energy balancing method for a series-parallel battery energy storage system.

[0005] In order to achieve the above-mentioned object of the present invention, the present invention provides a hierarchical energy balancing method for a series-parallel battery energy storage system, the key of which is that it includes the following steps:

[0006] S1, based on the working sequence of the switch group of the series-parallel battery energy storage system, establish the relationship between the average current of a single battery cycle and the inductor current;

[0007] The series-parallel battery energy storage system includes m battery subsystems, each battery subsystem includes n pairs of switch groups and a Boost converter, the n pairs of switch groups are used to connect n batteries in series, wherein each pair of switch groups is connected to one battery; the switch can be a MOS tube, an IGBT, etc.

[0008] The positive poles of the m battery subsystems are connected to the positive pole of the power source / load through a bus, the negative poles of the m battery subsystems are connected to the negative pole of the power source / load through a bus, and the battery subsystems are connected in parallel; 1≤i≤m, 1≤j≤n; energy is transmitted between the battery subsystem and the load / power source, and between the battery subsystems through the energy bus.

[0009] S2, based on the relationship between the average current of a single battery cycle and the inductor current, the remaining energy state (SOC) model of a single battery subsystem is established using the ampere-hour integration method, and the average SOC model of the battery subsystem is derived;

[0010] S3, based on the average SOC model of the battery subsystem, design a hierarchical balancing control strategy, and obtain the inductor current reference value of the series-parallel battery energy storage system through the hierarchical balancing control strategy, wherein the inductor current is the inductor current in the Boost converter.

[0011] Preferably, the S1 comprises:

[0012] In addition to being the power switch of the multi-input single-output four-switch Buck-Boost converter, the working state of the switch group also determines whether the corresponding battery cell is connected to the series battery group. For each battery in the same battery subsystem, in order to reduce the fluctuation of the converter input voltage, it is set that only one battery is bypassed at the same time. When the other batteries are connected to the circuit, the batteries are bypassed in turn: when the jth battery B of the ith battery subsystem ij When bypassed (1≤i≤m,1≤j≤n), the working state of the input switch group corresponding to the battery satisfies:

[0013] Q ij1 =0 and Q ij2 =1,

[0014] Among them, Q ij1 and Q ij2 Indicates the state of the switch group corresponding to the battery cell, with 1 indicating that the switch is on and 0 indicating that the switch is off.

[0015] Assume T1 is the duty cycle of the input switch group, define d ij Q is the switch ij2 The duty cycle is (1-d ij ) is the switch Q ij1 The duty cycle, i ij is the battery current, i Li is the inductor current. When battery B ij When bypassed, the battery current is 0. Otherwise, the battery current is equal to the inductor current, that is, the battery current satisfies:

[0016] When the circuit is running in steady state, the average inductor current in period T1 is considered to be a constant. Therefore, after detecting the inductor current, the average current of each battery cell in one cycle can be calculated through the duty cycle, which satisfies: in, For a working cycle of battery B ij The average value of the current.

[0017] Preferably, S2 includes:

[0018] For battery B ij , the remaining energy state (SOC) at time t is obtained by the ampere-hour integration method, that is:

[0019]

[0020] Among them, SOC ij (t0) is battery B ij SOC at time t0;

[0021] Q is the battery capacity,

[0022] i ij is the battery current, and the capacity of all batteries in the same subsystem is the same.

[0023] Find the battery B in one cycle ij The SOC change value is:

[0024]

[0025] in, For a working cycle of battery B ij The average value of the current.

[0026] Combining the above formula, we can deduce:

[0027] Among them, d ij Q is the switch ij2 The duty cycle, corresponding to (1-d ij ) is the switch Q ij1 Duty cycle;

[0028] ΔSOC ij It is determined by the input switch duty cycle and the inductor current.

[0029] For each battery in the same battery subsystem, the inductor current is the same, so the control d ij Adjust the change rate of SOC of each battery cell. When the battery pack is discharged, the inductor current i Li >0, then d ij The larger the value, the more time the corresponding battery is bypassed and the smaller the SOC decreases. Therefore, the smaller the SOC of the battery, the smaller the actual working d ij should be larger, so as to achieve the difference in the output energy of each battery cell; when the battery pack is charged, i Li <0, then d ij The larger the value, the smaller the SOC rise. Therefore, the smaller the SOC of the battery, the smaller the actual working d ij It should be smaller.

[0030] Among them, for the same battery subsystem, the duty cycle of each switch group satisfies:

[0031] The output terminals of each battery subsystem are connected in parallel to the DC bus. By controlling the input and output power of the battery subsystem, energy balance between the battery subsystems is achieved. For the ith battery subsystem, the average SOC of all batteries in the battery subsystem is used to represent the energy status of the battery pack, which is defined as SOC i ,but: SOC ij For battery B ij Combined with the above formula, the remaining energy state (SOC) model of a single battery subsystem is derived:

[0032]

[0033] Wherein, T1 represents the switch group control period of the i-th battery subsystem;

[0034] i Li represents the inductor current of the i-th battery subsystem.

[0035] The change in the average SOC of the battery subsystem within a cycle is determined by its inductor current. By controlling the inductor current, energy balance between the battery subsystems is achieved.

[0036] Preferably, the hierarchical balancing control strategy of S3 is a master-slave control structure, the slave controller is the controller of each battery subsystem, used for circuit control of the local battery subsystem, and the master controller is used to generate a current reference value of the slave controller;

[0037] The slave controller uploads the converter input voltage, output voltage, inductor current and other parameters of the local battery subsystem to the master controller, and completes the SOC (SOC i ) and the SOC of a single battery in the battery subsystem (SOC ij ) estimates, and generates a current reference value as a control reference value for each slave controller according to the SOC state, and transmits the updated SOC and control instructions to each slave controller:

[0038] The goal of inter-group balancing between battery subsystems is to achieve its SOC by adjusting the output power of each battery subsystem. i A steady-state value is reached, which is the average SOC value of all battery subsystems.

[0039] The goal of balancing within the battery subsystem group is to achieve its SOC by adjusting the working time (one working cycle) of the battery cells. ijA steady-state value is reached, which is the average SOC value of all batteries in the battery subsystem.

[0040] In the main controller, the bus voltage is detected and the voltage compensator G is used to v (s) to generate the total input current reference value i of the battery system refall , expressed as:

[0041] i refall =G v (s)(v ref -v bus ),

[0042] Among them, G v (s) is the transfer function, representing the voltage compensator;

[0043] v ref Indicates the voltage reference value;

[0044] v bus Indicates the bus voltage;

[0045] And the average value i refall / m is set as the input current reference value of each subsystem, and the average value i refall / m and battery subsystem SOC reference value SOC avg By comparison, the SOC error value ΔSOC of the i-th battery subsystem is obtained. i , and through the energy balance algorithm between groups f mod Generate the current reference value of this subsystem:

[0046]

[0047] Among them, i refi represents the current reference value of the i-th subsystem;

[0048] K mod is the gain parameter;

[0049] For all battery subsystems, the local input current reference satisfies:

[0050] The reference current of the slave controller comes from two parts: one part is the local input current reference value i from the master controller. refall / m; the other part is the energy balance algorithm between groups f mod (ΔSOC i ) generates a current reference value i refi Therefore, the current reference value from the controller is (i refall / m+i refi ), and through the current compensator G i(s) and the PWM signal generating circuit generate a PWM waveform to control the converter.

[0051] Preferably, it also includes: determining the gain parameter K in the balancing control strategy according to the system charging and discharging state mod The value range of

[0052] When the battery system is discharged, the battery subsystem with a larger SOC is expected to have a higher discharge capacity, and vice versa, the smaller the discharge capacity is expected. Therefore, K mod The value should be greater than 0.

[0053] To ensure that all battery subsystems are discharged during the discharge process, K mod Satisfy the constraints:

[0054]

[0055] Among them, I ref is the steady-state value of the battery subsystem inductor current, and I ref >0.

[0056] According to ΔSOC i Further analysis of the symbols yields:

[0057]

[0058] Among them, when ΔSOC i = 0, the second term of the constraint is always 0, K mod Therefore, it is necessary to pass SOC i ≠0 for K mod Constraints are made, and the following analysis is the same. Finally, K is obtained under discharge mod The value range of is: When the battery system is charging, I ref <0, therefore, for a battery subsystem with a larger SOC, the desired charging capacity is lower, and vice versa, the desired charging capacity is larger, therefore, K mod The value of K is still greater than 0. mod Satisfy the constraints: According to ΔSOC i Further analysis of the symbols gives the formula:

[0059]

[0060] Finally, the charging condition K mod The value range of is:

[0061]

[0062] In summary, we can get K under the condition of battery subsystem charging and discharging. modThe value range of is:

[0063]

[0064] Among them, | | is the absolute value;

[0065] I ref Indicates i ref The steady-state value of i ref is the current reference value of the subsystem;

[0066] SOC i represents the energy of the ith battery subsystem;

[0067] |·| max Indicates the maximum absolute value.

[0068] For battery balancing within the group, the battery charge and discharge energy is adjusted by adjusting the working time of the battery cells, which is equivalent to adjusting the duty cycle of the switch group.

[0069] Preferably, the master controller is also used to generate control instructions for all slave controllers, that is, the duty cycle of a single battery:

[0070] The duty cycle of a single battery consists of two parts: one part is the steady-state value of the duty cycle of all batteries in the group, which is 1 / n here; the other part is based on SOC ij Compared with the SOC reference value SOC iavg Compare and get the jth battery error ΔSOC in the group ij , and through the energy balance algorithm within the group f sub The duty cycle difference of the battery is generated:

[0071]

[0072] Where, Δd ij represents the current reference value of the jth battery in the i-th subsystem;

[0073] K isub is the gain parameter.

[0074] For all battery cells, the duty cycle difference satisfies:

[0075] Preferably, it also includes: determining the gain parameter K in the balancing control strategy according to the system charging and discharging state isub The value range of

[0076] When the i-th battery subsystem is discharging, the battery cell with a larger SOC is expected to have a higher discharge capacity, and vice versa, the smaller the discharge capacity is expected. Therefore, K isub The value should be greater than 0.

[0077] Since the duty cycle needs to meet the condition: 0≤d ij ≤1, therefore, K isu The constraints need to be met: Among them, SOC iavg is the average SOC value of all battery cells in the group. ij Further analysis of the symbols yields:

[0078]

[0079] Finally, we get K when the battery subsystem is discharged. isub The value range of is:

[0080]

[0081] When the i-th battery subsystem is charged, the battery cell with a larger SOC is expected to have a lower charge capacity, and vice versa, the charge capacity is expected to be higher. Therefore, K isub The value should be less than 0. Combined with ΔSOC ij By analyzing the symbol of the battery subsystem, we can get K isub The value range of is:

[0082]

[0083] As the balance progresses, SOC i Towards SOC avg , SOC ij Towards SOC iavg Therefore, it is necessary to adjust K according to the initial value of SOC. mod and K isub The value of is constrained.

[0084] Preferably, the battery subsystem adopts a voltage and current double closed-loop PI control structure to achieve control of system voltage and current:

[0085] The battery subsystem adopts a voltage and current double closed-loop PI control structure, in which the voltage compensator is k pv , k iv are proportional gain and integral gain respectively; the current compensator is k pi , k ii are proportional gain and integral gain respectively, and s is a representation of the signal in the frequency domain. The controller parameters are designed by analyzing the open-loop frequency domain characteristics of the voltage loop and the current loop. The system stability requirements must be met, and the cutoff frequency of the current loop must be much larger than that of the voltage loop, so that its dynamic response speed is faster, it can be adjusted quickly, and it has stronger anti-interference ability.

[0086] In summary, due to the adoption of the above technical solution, the present invention realizes the SOC balance of battery cells in a battery pack and the SOC balance between battery packs, thereby realizing the SOC balance of all battery cells. By analyzing the gain parameters of the energy balance algorithm between groups and the energy balance algorithm within a group, the value range is obtained, so that the energy flow direction of each battery subsystem is the same under charging / discharging conditions, avoiding the additional energy loss caused by the back and forth transfer of energy.

[0087] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0089] Figure 1 It is a schematic diagram of a layered energy balancing method for a series-parallel battery energy storage system proposed by the present invention.

[0090] Figure 2 It is a circuit diagram of a series-parallel battery balancing system based on a multi-input single-output four-switch Buck-Boost converter in a series-parallel battery energy storage system hierarchical energy balancing method proposed by the present invention;

[0091] Figure 3 It is a timing diagram of the power switch and main working voltage and current of the circuit in a hierarchical energy balancing method of a series-parallel battery energy storage system proposed by the present invention;

[0092] Figure 4 It is a master-slave control structure in a hierarchical energy balancing method for a series-parallel battery energy storage system proposed by the present invention;

[0093] Figure 5 It is a voltage and current double closed-loop PI control structure in a series-parallel battery energy storage system hierarchical energy balancing method proposed by the present invention; DETAILED DESCRIPTION

[0094] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0095] like Figure 1The figure shows a schematic diagram of a hierarchical energy balancing method for a series-parallel battery energy storage system proposed by the present invention. It includes: S1, designing the converter working mode, designing the working sequence (the order and duration of opening and closing) of the multi-input single-output converter switch group, and establishing the relationship between the average current of a single battery cycle and the inductor current; S2, establishing the SOC model of a single battery based on the ampere-hour integration method, and deriving the average SOC model of the battery subsystem; S3, designing a hierarchical balancing control strategy, adopting a master-slave control structure, the master controller generates a current reference value of the slave controller, and discussing the value range of the gain parameter in the balancing control algorithm according to the system charging and discharging state; S4, the battery subsystem adopts a voltage and current double closed-loop PI control structure to track the current reference value.

[0096] like Figure 2 As shown, it is a circuit diagram of a series-parallel battery balancing system based on a multi-input single-output four-switch Buck-Boost converter in a hierarchical energy balancing method for a series-parallel battery energy storage system proposed by the present invention. In the figure, n batteries are connected in series through n pairs of switch groups and connected to the low-voltage side or battery side of the Boost converter. The n pairs of switch groups and the Boost converter constitute a multi-input single-output four-switch Buck-Boost converter. The above components constitute a complete battery subsystem. The output ends of the m battery subsystems are connected to the energy bus, and all the battery subsystems are in parallel relationship. The load or power supply is also connected to the energy bus. Energy is transmitted between the battery subsystem and the load / power supply, and between the battery subsystem and the battery subsystem through the energy bus.

[0097] The series-parallel battery balancing system includes m battery subsystems Mi, the positive electrode of the battery subsystem Mi is connected to the positive electrode of the power supply / load through the bus, and the negative electrode of the battery subsystem Mi is connected to the negative electrode of the power supply / load through the bus; a plurality of battery subsystems Mi are connected in parallel; the battery subsystem Mi includes a battery pack Packi and a converter Fi; the battery pack Packi includes batteries Bi1 to Bin, and the converter Fi includes MOS tubes Qij1 and Qij2, MOS tubes Qi1, MOS tubes Qi2, and a converter Fi. Inductor Li and capacitor Ci, where 1≤i≤m, 1≤j≤n; the connection relationship between the battery pack Packi and the converter Fi is: the positive electrode of the battery Bi1 is connected to the drain of the MOS tube Qi11, the negative electrode of the battery Bi1 is connected to the source of the MOS tube Qi12, the positive electrode of the battery Bi2 is connected to the drain of the MOS tube Qi21, the negative electrode of the battery Bi2 is connected to the source of the MOS tube Qi22, ..., the positive electrode of the battery Bin is connected to the drain of the MOS tube Qin1, and the negative electrode of the battery Bin is connected to the MOS tube Q The source of MOS tube Qi11 is connected to the drain of MOS tube Qi12, the source of MOS tube Qi21 is connected to the drain of MOS tube Qi22, and the source of MOS tube Qin1 is connected to the drain of MOS tube Qin2; the source of MOS tube Qi11 and the drain of MOS tube Qi21 are connected to one end of inductor Li, and the other end of inductor Li is connected to the source of MOS tube Qi1 and the drain of MOS tube Qi2; the drain of MOS tube Qi1 is connected to one end of capacitor Ci and the positive electrode of the bus, and MOS The source of transistor Qi2 is connected to the other end of capacitor Ci and the negative electrode of the bus; the negative electrode of battery Bi1 and the source of MOS transistor Qi12 are connected to the source of MOS transistor Qi21 and the drain of MOS transistor Qi22, the negative electrode of battery Bi2 and the source of MOS transistor Qi22 are connected to the source of MOS transistor Qi31 and the drain of MOS transistor Qi32, ..., the negative electrode of battery Bi(n-1) and the source of MOS transistor Qi(n-1)2 are connected to the source of MOS transistor Qin1 and the drain of MOS transistor Qin2.

[0098] like Figure 3 As shown, the power switch and main working voltage and current timing diagram of the circuit in the hierarchical energy balancing method of a series-parallel battery energy storage system proposed by the present invention are specifically the series battery group voltage, battery current, inductor current, converter output voltage and converter output current. Based on the multi-input single-output four-switch Buck-Boost converter balancing circuit working in boost mode, in addition to being the power switch of the multi-input single-output four-switch Buck-Boost converter, its working state also determines whether the corresponding battery cell is connected to the series battery group.

[0099] In order to reduce the fluctuation of the converter input voltage, only one battery is bypassed at the same time, and the other batteries are connected to the circuit to work. The batteries are bypassed in turn. For example, when the jth battery B of the i-th battery subsystem ij When bypassed, the working state of all switch groups at the input end meets: Q ij1 =0 and Q ij2 =1, where Q ij1 and Q ij2 Indicates the state of the switch group corresponding to the battery cell, and 1 indicates that the switch is on, and 0 indicates that the switch is off. Set T1 as the duty cycle of the input switch group, define d ij Q is the switch ij2 The duty cycle, corresponding to (1-d ij ) is the switch Q ij1 The duty cycle, i ij is the battery current. Assume T2 is the duty cycle of the converter power switch group, define d Oi Q is the switch i2 The duty cycle, corresponding to (1-d Oi ) is the switch Q i1 The duty cycle, i Li is the inductor current, v Oi is the output voltage, i Oi is the output current. In the above process, the working sequence of the power switch and the main voltage and current is as follows Figure 2 When battery B ij When bypassed, the battery current is 0. Otherwise, the battery current is equal to the inductor current, that is, the battery current satisfies: When the circuit is running in steady state, the average inductor current in period T1 is considered to be a constant. Therefore, after detecting the inductor current, the average current of each battery cell in one cycle can be calculated through the duty cycle, which satisfies: in, For a working cycle of battery B ij The average value of the current.

[0100] like Figure 4 The figure shows the master-slave control structure in the hierarchical energy balancing method of a series-parallel battery energy storage system proposed by the present invention. The slave controller refers to the controller of each battery subsystem, which is responsible for the circuit control of the local battery subsystem, and the master controller is responsible for generating control instructions for all slave controllers. The inter-group balancing goal between battery subsystems is to achieve its SOC by adjusting the output power of each battery subsystem. i The steady-state value is reached, which is the average SOC value of all battery subsystems. The goal of balancing within the battery subsystem group is to achieve its SOC by adjusting the working time of the battery cells. ijThe steady-state value is reached, that is, the average SOC value of all batteries in the battery subsystem. The slave controller uploads the corresponding battery subsystem's converter input voltage, output voltage, inductor current and other parameters to the master controller, completes the SOC estimation of the battery subsystem and the SOC of a single battery in the battery subsystem in the master controller, generates control reference values ​​for each slave controller based on the SOC state, and transmits the updated SOC and control instructions to each slave controller.

[0101] In the main controller, the bus voltage is detected and the voltage compensator G is used to v (s) to generate the total input current reference value i of the battery system refall , denoted as i refall =G v (s)(v ref -v bus ), and set the local input current reference value of each subsystem to the average value i refall / m. By comparing with the battery subsystem SOC reference value SOC avg By comparison, the SOC error value of the i-th battery subsystem is obtained, and the inter-group energy balancing algorithm f mod (ΔSOC i ) generates the current reference value of the subsystem. For all battery subsystems, the local input current reference value satisfies:

[0102] The reference current of the slave controller comes from two parts: one part is the local input current reference value i from the master controller. refall / m; the other part is the energy balance algorithm between groups f mod (ΔSOC i ) generates a current reference value i refi Therefore, the current reference value from the controller is (i refall / m+i refi ), and through the current compensator G i (s) and PWM signal generating circuit G PWM (s) Generate PWM waveform to control the converter. For battery balancing within the group, the battery charge and discharge energy is adjusted by adjusting the working time of the battery cells, which is equivalent to adjusting the duty cycle of the switch group. The duty cycle of a single battery consists of two parts: one is the steady-state value of the duty cycle of all batteries in the group, which is 1 / n here; the other is based on the SOC ij The error is obtained by comparing it with the SOC reference value within the group, and then the energy balance algorithm within the group is used to calculate the error. sub (ΔSOC ij ) generates the duty cycle difference Δd of the battery ij For all battery cells, the duty cycle difference satisfies:

[0103] like Figure 5 As shown in FIG. 1 , a voltage and current double closed-loop PI control structure in a series-parallel battery energy storage system hierarchical energy balancing method proposed by the present invention is shown. The battery subsystem adopts a voltage and current double closed-loop PI control structure, where v ref is the voltage reference value, err V and err I are voltage error and current error respectively, G v (s) is the voltage compensation link, G i (s) is the current compensation link, G PWM (s) is the gain of the PWM signal generating circuit, H v (s) is the voltage acquisition network gain, H i (s) is the current acquisition network gain, G vd (s) is the transfer function of the battery subsystem output voltage to duty cycle, G vi (s) is the transfer function of the battery subsystem output voltage to the inductor current. The voltage compensator is k pv , k iv are proportional gain and integral gain respectively; the current compensator is k pi , k ii They are proportional gain and integral gain respectively. The controller parameters are designed by analyzing the open-loop frequency domain characteristics of the voltage loop and the current loop. The system stability requirements must be met, and the cutoff frequency of the current loop must be much larger than that of the voltage loop, so that its dynamic response speed is faster, it can be adjusted quickly, and it has stronger anti-interference ability.

[0104] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A hierarchical energy balancing method for a series-parallel battery energy storage system, characterized in that: The steps include: S1, based on the working sequence of the switch group of the series-parallel battery energy storage system, establish the relationship between the average current of a single battery cycle and the inductor current; The series-parallel battery energy storage system includes m battery subsystems, each battery subsystem includes n pairs of switch groups and a Boost converter, the n pairs of switch groups are used to connect n batteries in series, wherein each pair of switch groups is connected to one battery; The positive electrodes of the m battery subsystems are connected to the positive electrode of the power source / load through the bus, the negative electrodes of the m battery subsystems are connected to the negative electrode of the power source / load through the bus, and the battery subsystems are connected in parallel; 1≤i≤m, 1≤j≤n; S2, based on the relationship between the average current of a single battery cycle and the inductor current, the remaining energy state (SOC) model of a single battery subsystem is established using the ampere-hour integration method, and the average SOC model of the battery subsystem is derived; S3, based on the average SOC model of the battery subsystem, design a hierarchical balancing control strategy, and obtain the inductor current reference value of the series-parallel battery energy storage system through the hierarchical balancing control strategy, wherein the inductor current is the inductor current in the Boost converter.

2. A hierarchical energy balancing method for a series-parallel battery energy storage system according to claim 1, characterized in that: The S1 includes: For each battery in the same battery subsystem, only one battery is bypassed at the same time, and the other batteries are connected to the circuit to work. The batteries are bypassed in turn: when the jth battery B of the i-th battery subsystem ij When bypassed, the working state of the input switch group corresponding to the battery satisfies: Q ij1 =0 and Q ij2 =1, Among them, Q ij1 and Q ij2 Indicates the state of the switch group corresponding to the battery cell, with 1 indicating that the switch is on and 0 indicating that the switch is off; Assume T1 is the duty cycle of the input switch group, define d ij Q is the switch ij2 The duty cycle is (1-d ij ) is the switch Q ij1 The duty cycle, i ij is the battery current, i Li is the inductor current; when battery B ij When bypassed, the battery current is 0. Otherwise, the battery current is equal to the inductor current, that is, the battery current satisfies: When the circuit is running in steady state, the average inductor current in period T1 is considered to be a constant. Therefore, after detecting the inductor current, the average current of each battery cell in one cycle can be calculated through the duty cycle, which satisfies: in, For a working cycle of battery B ij The average value of the current.

3. A hierarchical energy balancing method for a series-parallel battery energy storage system according to claim 1, characterized in that: The S2 includes: For battery B ij , the remaining energy state at time t is obtained by the ampere-hour integration method, that is: Among them, SOC ij (t0) is battery B ij SOC at time t0; Q is the battery capacity; i ij is the battery current, and all batteries have the same capacity; Find the battery B in one cycle ij SOC change value: Among them, i ij For a working cycle of battery B ij The average value of the current; Combining the above formula, we can deduce: Among them, d ij Q is the switch ij2 The duty cycle, (1-d ij ) is the switch Q ij1 Duty cycle; For the i-th battery subsystem, the average SOC of all batteries in the battery subsystem is used to represent the energy status of the battery pack, which is defined as SOC i ,but: SOC ij For battery B ij SOC; combined with the above formula, the remaining energy state model ΔSOC of a single battery subsystem is derived i : Wherein, T1 represents the switch group control period of the i-th battery subsystem; i Li represents the inductor current of the i-th battery subsystem.

4. A hierarchical energy balancing method for a series-parallel battery energy storage system according to claim 1, characterized in that: The hierarchical balancing control strategy of S3 is a master-slave control structure, where the slave controller is a controller of each battery subsystem and is used for circuit control of the local battery subsystem, and the master controller is used to generate a current reference value of the slave controller; The slave controller uploads the converter input voltage, output voltage, and inductor current of the local battery subsystem to the master controller, completes the SOC estimation of the battery subsystem and the SOC of a single battery in the battery subsystem in the master controller, and generates a current reference value as a control reference value for each slave controller according to the SOC state; In the main controller, the bus voltage is detected and the voltage compensator G is used to v (s) to generate the total input current reference value i of the battery system refall , expressed as: i refall =G v (s)(v ref -v bus ), Among them, G v (s) is the transfer function, representing the voltage compensator; v ref Indicates the voltage reference value; v bus Indicates the bus voltage; And the average value i refall / m is set as the input current reference value of each subsystem, and the average value i refall / m and battery subsystem SOC reference value SOC avg By comparison, the SOC error value ΔSOC of the i-th battery subsystem is obtained. i , and through the energy balance algorithm between groups f mod Generate the current reference value of this subsystem: Among them, i refi represents the current reference value of the i-th subsystem; K mod is the gain parameter; For all battery subsystems, the local input current reference satisfies: The reference current of the slave controller comes from two parts: one part is the local input current reference value i from the master controller. refall / m; the other part is the energy balance algorithm between groups f mod (ΔSOC i ) generates a current reference value i refi Therefore, the current reference value from the controller is (i refall / m+i refi ).

5. A hierarchical energy balancing method for a series-parallel battery energy storage system according to claim 4, characterized in that: Also includes: Determine the gain parameter K in the balancing control strategy according to the system charging and discharging status mod The value range of Battery subsystem charging and discharging K mod The value range of is: Among them, | | is the absolute value; I ref Indicates i ref The steady-state value of i ref is the current reference value of the subsystem; SOC i represents the energy of the i-th battery subsystem; |·| max Indicates the maximum absolute value.

6. A hierarchical energy balancing method for a series-parallel battery energy storage system according to claim 4, characterized in that: The master controller is also used to generate control instructions for all slave controllers, that is, the duty cycle of a single battery: The duty cycle of a single battery consists of two parts: one part is the steady-state value of the duty cycle of all batteries in the group, which is 1 / n here; the other part is based on SOC ij Compared with the SOC reference value SOC iavg Compare and get the jth battery error ΔSOC in the group ij , and through the energy balance algorithm within the group f sub The duty cycle difference of the battery is generated: Where, Δd ij represents the current reference value of the jth battery in the i-th subsystem; K isub is the gain parameter.

7. A hierarchical energy balancing method for a series-parallel battery energy storage system according to claim 6, characterized in that: Also includes: Determine the gain parameter K in the balancing control strategy according to the system charging and discharging status isub The value range of When the battery subsystem is discharged, K isub The value range of is: Battery subsystem charging condition K isub The value range of is: As the balance progresses, SOC i Towards SOC avg , SOC ij Towards SOC iavg Therefore, it is necessary to adjust K according to the initial value of SOC. mod and K isub The value of is constrained.

8. A hierarchical energy balancing method for a series-parallel battery energy storage system according to claim 1, characterized in that: The battery subsystem adopts a voltage and current double closed-loop PI control structure to achieve control of system voltage and current.

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