Balanced charging method and apparatus for battery pack, and computer program product

Abstract

Provided in the present application are a balanced charging method and apparatus for a battery pack, and a computer program product. Charging current control consists of two stages, i.e., a "pulse square-wave excitation" stage and a "multi-stage current-reduction charging" stage. During the pulse square-wave excitation stage, the parameter identification of an equivalent circuit model and the joint estimation of state variables are realized, thereby providing reliable battery parameters for a subsequent balancing process. During the multi-stage current-reduction charging stage, a flyback converter is used to control a balanced current of each battery cell, and the battery cells remain in a charging state throughout a balancing process, thereby effectively mitigating the impact of a hysteresis voltage.

Description

Battery pack equalization charging method, device and computer program product

[0001] Cross-reference to related applications

[0002] The present application claims priority to the Chinese patent application No. 202410640772.5, filed on May 22, 2024, and entitled "Battery pack equalization charging method, device and computer program product", the content of the above application is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the field of new energy vehicle and energy storage battery technology, in particular, to a battery pack equalization charging method, device and computer program product. BACKGROUND

[0004] In the field of new energy vehicles and energy storage, high-voltage battery packs are core components composed of hundreds or thousands of single cells connected in series. However, subtle differences in manufacturing processes and actual use often lead to significant inconsistencies in voltage, state of charge (SOC), and decay rate between cells, which restricts the overall available capacity of the battery pack. To effectively improve this situation, precise battery equalization control is crucial, as it not only significantly improves battery performance, but also effectively extends battery life.

[0005] Currently, most equalization control strategies mainly rely on calculating the average SOC as a reference, and comparing the actual SOC of the single cell with this average to determine its imbalance state. However, traditional equalization methods often introduce hysteresis voltage because the battery single cell needs both charging and discharging, which leads to non-linear efficiency that is difficult to accurately quantify, and seriously interferes with the estimation accuracy of SOC during current reversal, thereby affecting the accuracy of the entire equalization control.

[0006] SUMMARY

[0007] The purpose of the embodiments of the present application is to provide a battery pack equalization charging method, device and computer program product to solve the problem that the traditional equalization method often introduces hysteresis voltage because the battery single cell needs both charging and discharging, which leads to non-linear efficiency that is difficult to accurately quantify, and seriously interferes with the estimation accuracy of SOC during current reversal, thereby affecting the accuracy of the entire equalization control.

[0008] The battery pack equalization charging method provided by the embodiments of the present application comprises:

[0009] In the first charging phase, a continuous square wave charging current is used to charge the battery pack, obtain the equivalent circuit model and model parameters, and the state quantity of each battery single cell of the battery pack;

[0010] In the second charging stage, the battery pack is charged by using a multi-stage descending current charging current, and the equalization current of each battery cell is controlled by using the flyback converter according to the equivalent circuit model, the model parameters and the state quantity of each battery cell of the battery pack.

[0011] In the above technical solution, the charging current composition includes two stages of "pulse square wave excitation" and "multi-stage descending current charging". In the pulse square wave excitation stage, the equivalent circuit model parameter identification and state quantity joint estimation are realized to provide reliable battery parameters for the subsequent equalization process. In the multi-stage descending current charging stage, the equalization current of each battery cell is controlled by using the flyback converter, and the single battery is always in a charging state in the equalization process, so that the influence of the hysteresis voltage is effectively controlled.

[0012] In some optional embodiments, the equalization current of each battery cell is controlled by using the flyback converter according to the equivalent circuit model, the model parameters and the state quantity of each battery cell of the battery pack, including:

[0013] According to the state quantity and the imbalance judgment condition of each battery cell, the equalization capacity demand of each battery cell is obtained;

[0014] According to the equalization capacity demand of each battery cell, the average equalization current of each battery cell is obtained;

[0015] According to the average equalization current, the control period of the MOS tube of the flyback converter is obtained;

[0016] According to the control period and the equivalent circuit model and the model parameters, the target voltage of the battery cell is obtained;

[0017] The target voltage tracking is performed by adjusting the control period to control the equalization current to realize the equalization charging.

[0018] In the above technical solution, the concept of average equalization current is used to indirectly control the actual equalization current by using the characteristics of the flyback converter. Specifically, the equalization current is controlled by target voltage tracking, and based on the relationship between the average equalization current and the actual equalization current, the consistency goal of the final remaining available capacity is achieved through the energy transfer between the battery cell and the power supply.

[0019] In some optional embodiments, after obtaining the state quantity of each battery cell of the battery pack, the method further includes:

[0020] According to the state quantity of each battery cell, a first battery cell with the minimum capacity value in each battery cell is determined;

[0021] The capacity value of the first battery cell is taken as a reference value C0, and the SOC of the first battery cell is taken as a reference SOC0; the capacity values of the remaining battery cells are C jSOC of the rest of the battery cells is SOC j ;

[0022] The SOC j is normalized to obtain the SOC j ’:

[0023] In some optional embodiments, the imbalance judgment condition is that: starting the balancing in the case that |ΔSOC j | is greater than a set threshold ε; wherein, ΔSOC j = SOC′ j - SOC0.

[0024] The balancing capacity requirement ΔC j of each battery cell: ΔC j = ΔSOC j × C0.

[0025] In some optional embodiments, according to the balancing capacity requirement of each battery cell, the average balancing current of each battery cell is obtained, comprising:

[0026] According to the reference battery cell charging current and SOC change relationship table, the time t s required for the reference battery cell to charge from SOC0 to full is queried;

[0027] According to the balancing capacity requirement of each battery cell and the time t s , the average balancing current I j of each battery cell is obtained:

[0028] In some optional embodiments, the flyback converter comprises a transformer, a primary MOS tube and a secondary MOS tube;

[0029] The primary side of the transformer is connected to the battery cell, and the secondary side is connected to the power supply;

[0030] For the battery cell starting the balancing, if ΔSOC j is greater than 0, the battery cell is the rich end, the primary MOS tube is in the on state, and the secondary MOS tube is in the off state; if ΔSOC j is less than 0, the battery cell is the poor end, the primary MOS tube is in the off state, and the secondary MOS tube is in the on state.

[0031] In some optional embodiments, in the case that the battery cell is the rich end, according to the average balancing current, the control period of the MOS tube of the flyback converter is obtained, comprising:

[0032] The voltage and current relationship of the flyback converter is:

[0033] wherein, L1 is the primary inductance, U t is the real-time voltage value of the battery cell measured by the BMS, i is the primary current value;

[0034] The remaining capacity that needs to be met in the control period is:

[0035] wherein, U i is the terminal voltage of the battery cell at the current time; D is the duty cycle of the primary MOS tube; T is the first control period; L1 is the primary inductance;

[0036] The first control period T is:

[0037] In some optional embodiments, the equivalent circuit model includes a first-order RC circuit model;

[0038] According to the control period and the equivalent circuit model and the model parameters, the target voltage of the battery cell is obtained, including:

[0039] According to the first-order RC circuit model and the model parameters, the target voltage U d is obtained:

[0040] wherein, the first instantaneous charging current i L = I t - ΔI; I t is the dry circuit charging current at the current time; the first instantaneous equalization current U D is the polarization voltage; U’ D is the derivative of the state equation of the polarization voltage; C D is the polarization capacitance; R D is the polarization resistance; R i is the ohmic resistance; U oc is the OCV terminal voltage.

[0041] In some optional embodiments, by adjusting the control period, target voltage tracking is performed to control the equalization current to achieve equalization charging, including:

[0042] The real-time voltage value U t of the battery cell is discretized to obtain the state space equation of the flyback converter at this time:

[0043] wherein, U t [k] is the voltage of the battery cell at time k; i k is the instantaneous equalization current at time k; T s is the time step of the simulation calculation;

[0044] The state equation of the control target is expressed as: U d [k+1] = A d U d [k]

[0045] wherein U d [k] is a constant vector in a control cycle, A d is a unit matrix;

[0046] The target voltage tracking in a cycle is realized by adjusting the error value e[k] = 0 at the time k; wherein e[k] = U t [k] - U d [k].

[0047] In some optional embodiments, the target voltage tracking in a cycle is realized by adjusting the error value e[k] = 0 at the time k, including:

[0048] The state space equation of the flyback converter and the state equation of the control target are combined into a matrix form as:

[0049] The new extended state space equation is:

[0050] wherein,

[0051] Then e[k] is:

[0052] wherein C a = [I - I].

[0053] The cost function is defined as:

[0054] wherein Q is a state weight coefficient matrix, S is a terminal value weight coefficient matrix, and R is an input weight coefficient matrix;

[0055] Let C a T SC a = S a , C a T QC a = Q a , then the cost function is converted to:

[0056] According to the converted cost function and the new extended state space equation, the tracking of the target voltage is realized by solving the LQR tracking problem.

[0057] In some optional embodiments, in the case that the battery cell is at the low end, the control period of the MOS tube of the flyback converter is obtained according to the average equalization current, including:

[0058] The remaining capacity to be met in the control period is:

[0059] Wherein, U' i is the terminal voltage of the battery cell at the current time; D' is the duty cycle of the secondary MOS tube; T' is the second control period; L2 is the secondary inductance.

[0060] The second control period T' is:

[0061] In some optional embodiments, the equivalent circuit model includes a first-order RC circuit model.

[0062] According to the control period and the equivalent circuit model and the model parameters, the target voltage of the battery cell is obtained, including:

[0063] According to the first-order RC circuit model and the model parameters, the target voltage U d is obtained.

[0064] Wherein, the second instantaneous charging current i' L = I t + nΔI'; I t is the main circuit charging current at the current time, n is the turns ratio of the primary and secondary coils, ΔI' is the second instantaneous equalization current; U D is the polarization voltage; U' D is the derivative of the state equation of the polarization voltage; C D is the polarization capacitance; R D is the polarization resistance; R i is the ohmic resistance; U oc is the OCV terminal voltage.

[0065] The embodiments of the present application also provide a battery pack equalization charging device, including: a processor, a network interface, a memory and a computer program; the computer program is loaded into the memory; the computer program is executed by the processor to perform the method of any one of the above.

[0066] The embodiments of the present application also provide a computer program product, including computer programs / instructions, which are executed by a processor to implement the steps of the method of any one of the above. BRIEF DESCRIPTION OF DRAWINGS

[0067] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those of ordinary skill in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0068] Fig. 1 is a flow chart of a battery pack equalization charging method according to an embodiment of the present application;

[0069] Fig. 2 is a charging current waveform diagram according to an embodiment of the present application;

[0070] Fig. 3 is a waveform diagram of capacity process noise change in the algorithm execution process according to an embodiment of the present application;

[0071] Fig. 4 is a topological structure diagram of a battery cell equalization circuit according to an embodiment of the present application;

[0072] Fig. 5 is a primary and secondary side current waveform diagram according to an embodiment of the present application;

[0073] Fig. 6 is a topological structure diagram of a battery pack equalization circuit according to an embodiment of the present application;

[0074] Fig. 7 is a diagram of actual capacity change of a battery cell according to an embodiment of the present application. DETAILED DESCRIPTION

[0075] The technical solutions of the embodiments of the present application will be described below in combination with the drawings in the embodiments of the present application.

[0076] At present, most equalization control strategies take the calculation of SOC average value as a reference, and judge the imbalance state based on the difference between the actual SOC of a single cell and the average value. However, this method often produces the opposite effect when dealing with single cell battery cells with large capacity attenuation rate and high SOC during charging. In addition, due to the hysteresis voltage generated by the battery cell during charging and discharging, and the difficulty in accurately quantifying the nonlinear efficiency of this process, the estimation accuracy of the SOC is seriously affected during the current commutation stage.

[0077] Based on the multi-time scale adaptive Kalman filtering algorithm, the SOC and the available capacity of the battery cell can be jointly estimated, and the product of the two can be used as the basis for judging the equalization control. However, the accuracy of the output of this algorithm is seriously dependent on the external excitation, and there is a lack of judgment basis for the convergence of the output results of this joint estimation algorithm.

[0078] In addition, since only the main circuit current can be measured during the charging and discharging process, even if the equalization control is started in combination with the equalization circuit, the equalization current cannot be directly measured, which makes it difficult to realize the equalization control based on the equalization current. Therefore, it is usually necessary to rely on the real-time measurement of the cell terminal voltage to realize the closed-loop control of the equalization.

[0079] Therefore, regardless of the energy consumption type or the power transfer type, there is currently a lack of a clear and logical equalization control method that can uniformly define the imbalance state of the single cells in the battery pack. This limits the further development and application of the equalization control technology to some extent.

[0080] Therefore, please refer to Figure 1, which is a flow chart of a battery pack equalization charging method according to an embodiment of the present application, which specifically includes:

[0081] Step 100, in the first charging stage, the battery pack is charged by using a continuous square wave charging current, the equivalent circuit model and model parameters are obtained, and the state quantity of each battery cell of the battery pack is obtained.

[0082] Step 200, in the second charging stage, the battery pack is charged by using a multi-stage current reduction charging current, and the equalization current of each battery cell is controlled by using a flyback converter according to the equivalent circuit model, the model parameters, and the state quantity of each battery cell of the battery pack.

[0083] In the embodiment of the present application, the charging current composition includes two stages of "pulse square wave excitation" and "multi-stage current reduction charging". In the pulse square wave excitation stage, the equivalent circuit model parameter identification and state quantity joint estimation are realized, which provides reliable battery parameters for the subsequent equalization process. In the multi-stage current reduction charging stage, the equalization current of each battery cell is controlled by using a flyback converter, and the single cell is always in a charging state during the equalization process, which effectively controls the influence of the hysteresis voltage.

[0084] In some optional embodiments, step 200 specifically includes:

[0085] Step 210, obtaining the equalization capacity demand of each battery cell according to the state quantity and the imbalance judgment condition of each battery cell;

[0086] Step 220, obtaining the average equalization current of each battery cell according to the equalization capacity demand of each battery cell;

[0087] Step 230, obtaining the control period of the MOS tube of the flyback converter according to the average equalization current;

[0088] Step 240, obtaining the target voltage of the battery cell according to the control period, the equivalent circuit model and the model parameters;

[0089] Step 250, target voltage tracking is performed by adjusting the control period to control the equalization current to achieve equalization charging.

[0090] In the technical solution, the concept of average equalization current is used to indirectly control the actual equalization current by using the characteristics of the flyback converter. Specifically, the equalization current is controlled by target voltage tracking. Based on the relationship between the average equalization current and the actual equalization current, the consistency goal of the final remaining available capacity is achieved through energy transfer between the battery monomer and the power supply.

[0091] In some optional embodiments, after obtaining the state quantity of each battery monomer of the battery pack, the method further comprises: determining a first battery monomer with the minimum capacity value among the battery monomers according to the state quantity of each battery monomer; taking the capacity value of the first battery monomer as a reference value C0, and taking the SOC of the first battery monomer as a reference SOC0; and taking the capacity value of the remaining battery monomers as C j , and taking the SOC of the remaining battery monomers as SOC j . j j

[0092] In some optional embodiments, the imbalance judgment condition is: starting equalization when |ΔSOC j | is greater than a set threshold ε; wherein ΔSOC j = SOC' j - SOC0; and the equalization capacity requirement ΔC j of each battery monomer is: ΔC j = ΔSOC j × C0.

[0093] In some optional embodiments, the average equalization current of each battery monomer is obtained according to the equalization capacity requirement of each battery monomer, comprising: querying the required time t s of the reference battery core from SOC0 to full charge according to the reference battery core charging current and SOC change relationship table; and obtaining the average equalization current I j of each battery monomer according to the equalization capacity requirement of each battery monomer and the time t s .

[0094] In some optional embodiments, the flyback converter comprises a transformer, a primary MOS tube and a secondary MOS tube; the primary side of the transformer is connected to the battery monomer, and the secondary side is connected to the power supply; for the battery monomer starting equalization, if ΔSOC j is greater than 0, the battery monomer is a rich end, the primary MOS tube is in an on state, and the secondary MOS tube is in an off state; if ΔSOC j ​​If the value is less than 0, the battery cell is a loss end, the primary side MOS tube is in an off state, and the secondary side MOS tube is in an on state.

[0095] In some optional embodiments, in the case of the battery cell being a rich end, the control period of the MOS tube of the flyback converter is obtained according to the average equalization current, including:

[0096] The voltage and current relationship of the flyback converter is:

[0097] Wherein, L1 is the primary side inductance, U t is the real-time voltage value of the battery cell measured by the BMS, and i is the primary side current value;

[0098] The remaining capacity that needs to be met in the control period is:

[0099] Wherein, U i is the terminal voltage of the battery cell at the current time; D is the duty cycle of the primary side MOS tube; T is the first control period; L1 is the primary side inductance;

[0100] The first control period T is:

[0101] In some optional embodiments, the equivalent circuit model includes a first-order RC circuit model; the target voltage of the battery cell is obtained according to the control period and the equivalent circuit model and the model parameters, including: the target voltage U d is obtained according to the first-order RC circuit model and the model parameters.

[0102] Wherein, the first instantaneous charging current i L = I t - ΔI; I t is the dry circuit charging current at the current time; the first instantaneous equalization current U D is the polarization voltage; U' D is the derivative of the state equation of the polarization voltage; C D is the polarization capacitance; R D is the polarization resistance; R i is the ohmic internal resistance; U oc is the OCV terminal voltage.

[0103] In some optional embodiments, the target voltage tracking is performed by adjusting the control period to control the equalization current to realize equalization charging, including: discretizing the real-time voltage value U t of the battery cell to obtain the state space equation of the flyback converter at this time:

[0104] wherein, U t [k] is the voltage of the battery cell at time k; i k is the instantaneous equalization current at time k; T s is the time step of the simulation calculation; the state equation of the control target is expressed as: U d [k+1] = A d U d [k]

[0105] wherein, U d [k] is a constant vector within a control cycle, A d is a unit matrix; the target voltage tracking within a cycle is realized by adjusting the error value e[k] = 0 at time k; wherein, e[k] = U t [k] - U d [k].

[0106] In some optional embodiments, the target voltage tracking within a cycle is realized by adjusting the error value e[k] = 0 at time k, including: the state space equation of the flyback converter and the state equation of the control target are combined into a matrix form as:

[0107] Then the new extended state space equation is:

[0108] wherein,

[0109] Then e[k] is:

[0110] wherein, C a = [I - I].

[0111] The cost function is defined as:

[0112] wherein Q is a state weight coefficient matrix, S is a terminal value weight coefficient matrix, and R is an input weight coefficient matrix; let C a T SC a = S a , C a T QC a = Q a , then the cost function is converted to:

[0113] According to the converted cost function and the new extended state space equation, the tracking of the target voltage is realized by solving the LQR tracking problem.

[0114] In some optional embodiments, in the case that the battery cell is at the low end, the control period of the MOS tube of the flyback converter is obtained according to the average equalization current, and the remaining capacity that needs to be met in the control period is:

[0115] wherein U' i is the terminal voltage of the battery cell at the current moment; D' is the duty cycle of the secondary MOS tube; T' is the second control period; and L2 is the secondary inductance. The second control period T' is:

[0116] In some optional embodiments, the equivalent circuit model comprises a first-order RC circuit model; and the target voltage of the battery cell is obtained according to the control period and the equivalent circuit model and the model parameters, which comprises: the target voltage U d is obtained according to the first-order RC circuit model and the model parameters.

[0117] wherein the second instantaneous charging current i' L = I t + nΔI'; I t is the charging current in the main circuit at the current moment, n is the turns ratio of the primary and secondary coils, ΔI' is the second instantaneous equalization current; U D is the polarization voltage; U' D is the derivative of the state equation of the polarization voltage; C D is the polarization capacitance; R D is the polarization resistance; R i is the ohmic resistance; and U oc is the OCV terminal voltage.

[0118] The working process of the battery pack equalization charging method of the embodiments of the present application will be described in detail below with reference to a specific embodiment.

[0119] First, please refer to FIG. 2, which is a charging current waveform diagram provided by the present embodiment. The charging current composition comprises two stages, namely “pulse square wave excitation” and “multi-stage current reduction charging”. Through continuous square wave charging current excitation, the equivalent circuit model parameter identification, state quantity joint estimation and convergence judgment are realized. On this basis, the health degree monitoring is performed according to the internal resistance of the battery cell. The specific method is:

[0120] The monomer charging OCV-SOC relationship curve obtained by the experiment, the real-time measured monomer battery OCV and the main circuit current value under the pulse square wave current are input, the recursive least square algorithm with a forgetting factor is run, and the model parameter (including a first-order RC circuit model and a second-order RC circuit model, for example, for the second-order RC circuit model, including ohmic internal resistance R0, electrochemical polarization internal resistance R1, concentration polarization internal resistance R2, electrochemical polarization capacitance C1, and concentration polarization capacitance C2) is stimulated and identified. On this basis, the SOC and the actual available capacity of each monomer are estimated by running a multi-time scale adaptive EKF, and the health degree of the battery monomer is evaluated by calculating the ratio of the previously set battery monomer aging internal resistance threshold value and the identified internal resistance value.

[0121] In addition, macro time scale process noise is also used for estimation algorithm convergence judgment. Please refer to FIG. 3, which is a waveform diagram of the capacity process noise change in the algorithm execution process provided by the embodiment. As can be seen from the figure, with the progress of the algorithm, the process noise Q continuously decreases and reaches close to 0 at a macro time scale of 150. This shows that the algorithm can quickly reach convergence, providing a reliable condition for subsequent balancing.

[0122] After obtaining the estimation results of each battery monomer in the “pulse square wave excitation” stage, the battery monomer with the minimum capacity value is determined, and the capacity of this monomer is taken as the reference value, denoted as C0, and the SOC value is denoted as SOC0, and the normalization conversion of SOC is completed. Let the SOC value of the remaining monomers at this time be SOC j , the capacity be C j , and the normalized SOC value of each monomer be SOC′ j Then:

[0123] When the following conditions are met, start balancing: ΔSOC j =|SOC′ j -SOC0|≥ε(3.2)

[0124] and take it as the imbalance judgment condition, and extract the balancing capacity requirement ΔC j of each monomer: ΔC j =ΔSOC j ×C0(3.3)

[0125] By looking up the known reference battery charging current and SOC change relationship table, the remaining charging current trajectory and time course are obtained, and the time course of the reference battery from SOC0 to full charge is t s At this time, the average balancing current of each monomer can be obtained:

[0126] Therefore the final purpose of the method is to make the remaining available capacity of each battery cell equal to the reference cell, i.e. to ensure that the reference cell is fully charged after the SOC0= SOC' is met by controlling the equalization current j .

[0127] Please refer to Figure 4 and Figure 5, the basic equalization process of using flyback converter to control the single cell equalization current is: the left side of the flyback converter (i.e. the primary side of the transformer) is connected to the battery cell, and the right side is connected to the 12v power supply. For a battery cell that meets the equalization condition, when ΔSOC j >0, it is called the rich end, and the MOS tube M1 in the primary side is in the on state when the discharge operation is enabled, at which time its equalization current ΔI rises in the primary winding until it reaches the preset I max ; when ΔSOC j <0, it is called the poor end, and the MOS tube M2 in the secondary side is in the on state when the charging operation is enabled, at which time its equalization current ΔI' rises in the secondary winding until it reaches the preset I' max .

[0128] When the primary MOS tube M1 switches to the off state, the energy stored in the primary side of the transformer will be coupled to the secondary side in accordance with the principle of energy conservation, at which time the equalization current I t will flow in the secondary side of the transformer. At the same time, the MOS tube M2 in the secondary side is immediately turned on, and the primary side current gradually decreases to zero.

[0129] Alternatively, the secondary MOS tube M2 switches to the off state, and the energy stored in the secondary side of the transformer will be coupled to the primary side in accordance with the principle of energy conservation, at which time the equalization current I t will flow in the primary side of the transformer. At the same time, the MOS tube M1 in the primary side is immediately turned on, and the secondary side current gradually decreases to zero.

[0130] Repeat the above process until the transfer process of the equalization current in the flyback converter is completed.

[0131] The following is the derivation of the target transient charging current and the target voltage transformation and equalization control process in the control cycle for the rich end:

[0132] Let the time when the MOS tube M1 is turned on be T on , the time when it is turned off be T off , and the duty cycle of the MOS tube M1 be D. Since the equalization current cannot be directly and accurately measured, the real-time voltage of each single cell battery can be obtained by the BMS. Therefore, according to the characteristics of the flyback converter, the voltage of the single cell battery is used to indirectly reflect the size of the equalization current. The voltage and current relationship of the flyback converter is:

[0133] where L1 is the primary inductance, Ut denoted as , where is the real-time voltage value of the battery cell measured by the BMS, and i is the primary current value.

[0134] Combining the above equation with the remaining capacity condition that must be satisfied within one equilibrium period, we have:

[0135] Among them, U i Let be the terminal voltage of the battery cell at the current moment; D be the duty cycle of the primary-side MOSFET; T be the first control cycle; and L1 be the primary-side inductance. From the above equation, we have:

[0136] Due to the average equalization current I j It is known that if the duty cycle of MOSFET M1 is determined, the control period T can be determined.

[0137] The above describes the capacity transfer process based on the average equalization current within one cycle. The following section introduces the target voltage tracking process. From Equation 3.5, we have:

[0138] Where ΔI is the change in primary current, i.e., instantaneous equilibrium current; U t The voltage value is the current value measured by the BMS; T is the control period.

[0139] From the above equation, we can obtain the peak value of the primary current of the flyback converter within one control cycle (the primary current of the flyback converter rises from 0). Combining the first-order RC circuit model and the model parameters determined through prior identification, we have:

[0140] First instantaneous charging current: i L =I t -ΔI(3.10)

[0141] Among them, I t The current charging current of the main circuit at the current moment; the first instantaneous equalization current. U D U' is the polarization voltage; D C is the derivative of the state equation for the polarization voltage. D For polarization capacitors; R D R is the polarization resistor. i U is the internal resistance of ohms; oc This is the voltage at the OCV terminal.

[0142] The target voltage U can be obtained from the above two equations. d Discretizing Equation 3.5 above yields the state-space equation of the flyback converter at this point:

[0143] Among them U t[k] is the voltage of the battery cell at time k; i k I[k] is the current of the primary side at time k, i.e., the instantaneous equalization current; T s T is the time step of the simulation calculation.

[0144] The state equation of the control target can be expressed as: U d [k+1] = A d U d [k](3.12)

[0145] Since U d [k] is a constant vector within a control period, A d is a unit matrix.

[0146] Definition: e[k] = U t [k] - U d [k](3.13)

[0147] e[k] is the error value at time k.

[0148] The target voltage tracking within a period can be achieved by adjusting e[k] = 0.

[0149] The state space equation of the flyback converter and the state equation of the control target are combined into a matrix form:

[0150] The new extended state space equation can be expressed as:

[0151] Where A a , B a and other matrices correspond to the above equations one by one.

[0152] At this time, e[k] can be rewritten as:

[0153] Where C a = [I - I]. Define the cost function:

[0154] Where Q is the state weight coefficient matrix, S is the terminal value weight coefficient matrix, and R is the input weight coefficient matrix. Let C a T SC a = S a , C a T QC a = Q a , which can be converted to:

[0155] Solve:

[0156] It can be seen that it satisfies the standard form of LQR tracking problem, so the tracking of target voltage can be realized by solving the LQR tracking problem. The specific process is as follows:

[0157] First, the feedback gain matrix F is obtained, that is, F = lqr(Aa, Ba, Qa, Sa, R) (3.20)

[0158] Define the number of system running steps, so the system input in one step is:

[0159] Then the response of the system is:

[0160] At this time, the extended state equation matrix is updated as: a [k] = [U t [k+1] ; U d [k]] (3.23)

[0161] Continue the loop calculation with the new extended state equation. As can be seen from equation 3.5, changing the value of control period T can change the value of , so by adjusting the period T in each time step, the closed-loop control of the trajectory tracking of the target voltage is finally realized.

[0162] The equilibrium process of the depleted end is similar to that of the rich end. At this time, the 12V power supply charges the battery monomer. Turn on the secondary MOS tube M2 and turn off the primary MOS tube M1. To achieve equilibrium conditions, the following relationship must be established:

[0163] Where U′ i is the terminal voltage of the battery monomer at the current time; D′ is the duty ratio of the secondary MOS tube; T′ is the second control period; L2 is the secondary inductance.

[0164] Then we have:

[0165] Since the average equilibrium current I j is known, the control period T′ can be determined if the duty ratio of the MOS tube is determined. Where L2 = n 2 L1. The target voltage tracking process of the depleted end is similar to that of the rich end, the main difference is that when calculating the instantaneous charging current i′ L , it should be: i′ L = I t + nΔI′

[0166] Where I tis the charging current; n is the turns ratio of the primary and secondary coils, ΔI' is the second instantaneous equalization current; taking n = 3, then L2 = 31.5 μH. The equalization process of the deficient end is the same as that of the rich end, which will not be described here.

[0167] By repeating the above equalization in each control period T n , the equalization target is achieved, i.e., each battery monomer has the same remaining available capacity when the charging is completed.

[0168] Please refer to FIG. 6, which is a schematic diagram of the battery pack equalization circuit topology of the embodiment of the application. The embodiment takes three battery monomers as an example, and sets the initial SOC values to be 0.1, 0.15 and 0.2 respectively, and the rated capacities to be 110 ah, 105 ah and 90 ah respectively. The change curve of the actual capacity of the battery core finally obtained according to the above method is shown in FIG. 7. It can be seen that after the pulse square wave excitation, with the opening of the equalization control, the remaining available capacities of the three monomers gradually tend to be consistent, and the equalization target is achieved.

[0169] The embodiment of the application also provides a battery pack equalization charging device, which comprises a processor, a network interface, a memory and a computer program; the computer program is loaded into the memory; and the computer program is run by the processor to execute the method as any one of the above.

[0170] The embodiment of the application also provides a computer program product, which comprises computer programs / instructions, and the computer programs / instructions are executed by a processor to implement the steps of the method as any one of the above.

[0171] In the embodiments provided in the application, it should be understood that the disclosed devices and methods can be implemented in other manners. The above-described device embodiments are only schematic. For example, the division of the units is only a logical function division. There can be another division manner for the actual implementation, for example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections between the units can be indirect couplings or communication connections through some interfaces, devices or units, and can be electrical, mechanical or in other forms.

[0172] In addition, the units described as separate components can or can not be physically separate, and the components displayed as units can or can not be physical units. That is, they can be located in one place, or can be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purposes of the embodiments.

[0173] Further, each functional module in each embodiment of the present application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part. In this article, relationship terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations.

[0174] The above merely provides an embodiment of the present application, and is not intended to limit the protection scope of the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A battery pack equalization charging method characterized by, The method comprises the following steps: In the first charging stage, the battery pack is charged by using a continuous square wave charging current, equivalent circuit model and model parameters, and state quantities of each battery cell of the battery pack are obtained; In the second charging stage, the battery pack is charged by using a multi-stage current reduction charging current, and the equalization current of each battery cell is controlled by using a flyback converter according to the equivalent circuit model, the model parameters, and the state quantities of each battery cell of the battery pack.

2. The method of claim 1, wherein, The control of the equalization current of each battery cell by using the flyback converter according to the equivalent circuit model, the model parameters, and the state quantities of each battery cell of the battery pack comprises the following steps: The equalization capacity demand of each battery cell is obtained according to the state quantity and the imbalance judgment condition of each battery cell; The average equalization current of each battery cell is obtained according to the equalization capacity demand of each battery cell; The control period of the MOS tube of the flyback converter is obtained according to the average equalization current, the equivalent circuit model, and the model parameters; The target voltage of the battery cell is obtained according to the control period, the equivalent circuit model, and the model parameters; The target voltage tracking is performed by adjusting the control period, so that the equalization current is controlled to realize the equalization charging.

3. The method of claim 2, wherein, After the state quantities of each battery cell of the battery pack are obtained, the following steps are further included: The first battery cell with the minimum capacity value is determined according to the state quantities of each battery cell. The capacity value of the first battery cell is taken as a reference value C0, the SOC of the first battery cell is taken as a reference SOC0; the capacity values of the remaining battery cells are C j , and the SOCs of the remaining battery cells are SOC j . normalizing the SOC j j : ​ 4. The method of claim 3, wherein, The imbalance judging condition is: in case that |ΔSOC j equalization is started; wherein, ΔSOC j = SOC' j -SOC0; the equalization capacity requirement ΔC of the respective battery cell j : ΔC j = ΔSOC j × C0.

5. The method of claim 4, wherein, The average equalization current of each battery cell is obtained according to the equalization capacity demand of each battery cell, which comprises the following steps: According to the reference battery cell charging current and SOC change relationship table, the time t required for the reference battery cell to change from SOC0 to full charge is queried s ; According to the equalization capacity requirement of each battery cell and time t s , the average equalization current I j of each battery cell is obtained:

6. The method of claim 5, wherein, The flyback converter comprises a transformer, a primary MOS tube, and a secondary MOS tube; The primary side of the transformer is connected to the battery cell, and the secondary side of the transformer is connected to the power supply; For the battery monomer starting equalization, if ΔSOC j is greater than 0, the battery monomer is rich in electricity, and the primary side MOS tube is in the on state, and the secondary side MOS tube is in the off state; if ΔSOC j is less than 0, the battery monomer is poor in electricity, and the primary side MOS tube is in the off state, and the secondary side MOS tube is in the on state.

7. The method of claim 6, wherein, In the case that the battery cell is a rich power end, the control period of the MOS tube of the flyback converter is obtained according to the average equalization current, which comprises the following steps: The voltage and current relationship of the flyback converter is: Wherein, L1 is the primary inductance, U t is the real-time voltage value of the battery cell measured by the BMS, and i is the primary current value. The remaining capacity that needs to be satisfied in the control period is: wherein U i is the terminal voltage of the battery cell at the current time; D is the duty cycle of the primary MOSFET; T is the first control period; L1 is the primary inductance; The first control period T is:

8. The method of claim 7, wherein, The equivalent circuit model comprises a first-order RC circuit model; The target voltage of the battery cell is obtained according to the control period, the equivalent circuit model, and the model parameters, which comprises the following steps: According to the first-order RC circuit model and the model parameters, the target voltage U d : wherein the first transient charging current i L = I t - ΔI; I t is the current moment dry road charging current; the first transient equalization current U D is the polarization voltage; U' D is the derivative of the state equation for the polarization voltage; C D is the polarization capacitance; R D is the polarization resistance; R i is the ohmic internal resistance; U oc is the OCV terminal voltage.

9. The method of claim 8, wherein, The target voltage tracking is performed by adjusting the control period, so that the equalization current is controlled to realize the equalization charging, which comprises the following steps: The battery cell real-time voltage value U t Discretization, get the state space equation of flyback converter at this time: wherein U t [k] is the voltage of the battery cell at time k; i k is the instantaneous equalization current at time k; T s is the time step of the simulation calculation; The state equation of the control target is expressed as: U d [k+1] = A d U d [k] wherein U d [k] is a constant vector over a control period, A d is a unit matrix; The target voltage tracking in one period is realized by adjusting the error value e[k] = 0 at time k; wherein e[k] = U t [k] - U d [k].

10. The method of claim 9, wherein, The target voltage tracking in a period is realized by adjusting the error value e[k] = 0 at time k, which comprises the following steps: Combining the state-space equations of the flyback converter and the state-space equations of the control objective into a matrix form has: The new extended state space equation is then: wherein, e[k] is then: where C a = [I - I]; Define the cost function: Wherein Q is a state weight coefficient matrix, S is a terminal value weight coefficient matrix, and R is an input weight coefficient matrix; Let C a T SC a = S a , C a T QC a = Q a The cost function is then transformed to: According to the converted cost function and the new extended state space equation, the target voltage tracking is realized by solving the LQR tracking problem.

11. The method of claim 6, wherein, In the case that the battery cell is a poor power end, the control period of the MOS tube of the flyback converter is obtained according to the average equalization current, which comprises the following steps: The remaining capacity that needs to be satisfied in the control period is: Among them, U′ i The current terminal voltage of the battery cell; D′ is the duty cycle of the secondary MOSFET; T′ is the second control cycle; L2 is the secondary inductor; The second control period T' is:

12. The method of claim 11, wherein, The equivalent circuit model comprises a first-order RC circuit model; The target voltage of the battery cell is obtained according to the control period, the equivalent circuit model, and the model parameters, which comprises the following steps: According to the first-order RC circuit model and the model parameters, the target voltage U d : wherein the second instantaneous charging current i' L = I t + nΔI'; I t is the main line charging current at the current moment, n is the turns ratio of the primary and secondary coils, ΔI' is the second instantaneous balancing current; U D is the polarization voltage; U' D is the derivative of the state equation of the polarization voltage; C D is the polarization capacitance; R D is the polarization resistance; R i is the ohmic internal resistance; U oc is the OCV terminal voltage.

13. A battery pack equalization charging device, characterized by, The method comprises the following steps: The processor, the network interface, the memory, and the computer program are included; the computer program is loaded into the memory; The computer program is run by the processor to execute the method of any one of claims 1-12.

14. A computer program product comprising computer programs / instructions, characterized in that, The computer program / instructions are executed by the processor to realize the steps of the method of any one of claims 1-12.

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