An improved power battery module power equalization system and control method

Abstract

The application discloses an improved power battery module electric quantity equalization system and a control method. j If |SOC j -SOC m |> SOC m * 5%, it is determined that the single battery needs to participate in the electric quantity equalization, the time required for the equalization of each single battery is calculated, and the equalization scheme of the single battery needing to participate in the electric quantity equalization is judged: if ΔSOC j > 0, the corresponding electric quantity needs to be extracted from the single battery; and if ΔSOC j < 0, the corresponding single battery needs to be supplemented with electric quantity. The application can reduce electric quantity loss and overall heat generation, and is helpful to improve the energy utilization rate of the whole battery pack.

Description

Technical Field

[0001] This invention belongs to the field of electric vehicle technology, specifically relating to an improved power battery module power balancing system and control method. Background Technology

[0002] The power battery is the primary energy carrier and power source of electric vehicles, and a crucial component. Currently, the commonly used power battery model consists of numerous individual cells within a battery pack. Due to manufacturing precision issues, these individual cells inevitably exhibit inconsistencies in internal resistance, capacity, and other parameters. These inconsistencies lead to variations in power output and temperature during operation. The "barrel principle" is well-known, and the overall capacity of the battery pack depends on the individual cell with the lowest energy or voltage. This significantly reduces the overall capacity utilization of the battery pack, thereby decreasing the actual usable capacity.

[0003] To address this issue, electric vehicle battery packs are generally equipped with a charge balancing module to balance the voltage and charge of each individual cell within the pack as quickly as possible. Currently, there are two main balancing modes: active balancing and passive balancing. The former transfers energy from high-energy cells to low-energy cells, while the latter dissipates the charge from high-energy cells as heat. Active balancing typically involves a balancing control circuit between series-connected batteries. After detecting an imbalance, it extracts excess charge, transfers it to an inductor or capacitor, and then redistributes it to the lower-energy cells. However, this energy transfer takes considerable time and involves numerous circuits and capacitors, resulting in energy loss. Passive balancing selects the higher-energy cells based on the number of lower-energy cells, dissipating the excess energy as heat. This method is more efficient and has a simpler circuit structure, but it results in significant energy loss and generates substantial heat during the balancing process, potentially leading to overall operational instability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an improved power battery module power balancing system and control method. The system calculates the balanced power of each individual battery cell based on its current power level, reducing the time for power to travel between individual cells and capacitors, thereby reducing power loss and overall heat generation, and helping to improve the energy utilization rate of the entire battery pack.

[0005] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0006] An improved control method for a power battery module power balancing system:

[0007] S1, when the temperature of the battery module is between 15℃ and 40℃, the equalization control module determines whether the voltage difference of the largest single cell is greater than the set voltage threshold. If so, proceed to S1; otherwise, continue to acquire battery module temperature information.

[0008] S2, based on the current voltage data of each individual battery cell and the capacity of the battery module, estimates the current value passing through the battery module according to the Kalman filter algorithm;

[0009] S2.1, Establish a Thevenin equivalent circuit model for each individual cell and perform online parameter identification for the Thevenin equivalent circuit model;

[0010] S2.2, Based on the voltage data of the individual cells and the identified parameters, the current of the individual cells is estimated;

[0011] S2.3, determine whether the maximum difference in the current of each individual battery cell is less than the set current threshold. If so, the current of the battery module is taken as the average value of the individual batteries. Otherwise, the online parameter identification of the Thevenin equivalent circuit model is performed again.

[0012] S3, calculate the SOC of the i-th individual cell based on the current value passing through the battery module, and sort all individual cell SOC values ​​from low to high, denoted as SOC. j , where j = 1, 2, 3...N, and N is the total number of individual cells;

[0013] S4, if |SOC j -SOC m |>SOC m *5%, determining that individual cells need to participate in charge balancing, and calculating the balancing time required for each individual cell, where SOC m This represents the SOC value of a single battery cell after equalization.

[0014] S5, determine the individual battery balancing scheme that needs to participate in the power balancing: if ΔSOC j If ΔSOC > 0, then the corresponding amount of electricity needs to be drawn from the individual battery cells. j If ΔSOC is less than 0, then the corresponding individual battery cell needs to be recharged; where ΔSOC... j =SOC j -SOC m .

[0015] Furthermore, the SOC m The calculation process is as follows:

[0016] a. Assume the initial SOC of a single cell after equalization is SOC. X，n , where n = 1, 2, ...;

[0017] b. Calculate W respectively in the first dichotomy A1 = |SOC1 - A1| + |SOC2 - A1| + |SOC3 - A1| + … + |SOC N - A1|, W B1 = |SOC1 - B1| + |SOC2 - B1| + |SOC3 - B1| + … + |SOC N - B1|, where A1 is the median of SOC1 and and B1 is and the median of SOC N ;

[0018] c. If W A1 < W B1 , then A1 is SOC X，1 , determine the interval where A1 is located as the dominant interval and proceed to the next step, otherwise select B1 and its dominant interval

[0019] d. Starting from the second dichotomy, follow the procedures in b and c. Each time, divide the previously obtained dominant interval into two equal intervals, and substitute the medians A n and B n of these two intervals into W An and W Bn , then compare the magnitudes of W An and W Bn to determine whether to select A n or B n as the SOC X，n for this time; where: W An = |SOC1 - A n | + |SOC2 - A n | + |SOC3 - A n | + … + |SOC N - A n |, W Bn = |SOC1 - B n | + |SOC2 - B n | + |SOC3 - B n | + … + |SOC N - B n |;

[0020] e. If |SOC X , n+1 - SOC X , n | < SOC1 * 2%, then determine that the current SOC X , n is the SOC m , otherwise return to d.

[0021] Furthermore, the SOC m The following conditions must be met:

[0022] (1) SOC1 <SOC m <SOC N ;

[0023] (2) The sum of the changes in the electrical charge of all individual cells, W, is minimized: W = |ΔSOC1| + |ΔSOC2| + |ΔSOC3| + ... + |ΔSOC N |, where ΔSOC j To balance the charge of individual cells to SOC m The numerical change experienced, i.e., ΔSOC j =SOC j -SOC m .

[0024] Furthermore, the SOC of the i-th single cell satisfies the formula:

[0025]

[0026] Where c n For the capacity of the battery module, I k Δt represents the current of the battery module, and Δt represents the sampling time step.

[0027] Furthermore, the time required for the individual battery to be equalized is: Where c n For the capacity of the battery module, C c The set charge / discharge rate.

[0028] Furthermore, the parameter identification specifically involves identifying parameters in the discrete-time state-space model. The open-circuit voltage in the discrete-time state-space model is determined by using polynomial fitting to obtain the OCV-SOC relationship of each individual cell.

[0029] An improved power battery module power balancing system includes: a series battery module, a battery management system, a balancing control module, a balancing device, and a voltage detection module. The balancing control module is communicatively connected to the battery management system, and the battery management system is also communicatively connected to the voltage detection module. The balancing control module and the voltage detection module are also electrically connected to the balancing and detection bus, respectively. The series battery module and the balancing device are both electrically connected to the detection bus.

[0030] The above technical solution also includes a main control circuit, which includes a current limiter, diodes, photorelays and inductors. One end of each of the N photorelays is electrically connected to the positive terminal of each of the N individual cells in the battery module, and the other end is connected to the equalization and detection bus. One end of each of the N inductors is electrically connected to the negative terminal of each of the N individual cells in the battery module, and the other end is connected to the equalization and detection bus.

[0031] In the above technical solution, the equalization device includes a supercapacitor, which is electrically connected to the equalization and detection bus via a diode.

[0032] In the above technical solution, the equalization device further includes an equalization step-down DC / DC converter, a supercapacitor electrically connected to the equalization step-down DC / DC converter, and the equalization step-down DC / DC converter electrically connected to the equalization and detection bus via a current limiter.

[0033] The beneficial effects of this invention are as follows: Compared with the current technology, the method proposed in this invention can obtain the current value of the battery module and the SOC of the individual cells while ensuring the balancing accuracy. It can further determine whether the individual cells need to participate in the power balancing, calculate the balancing time required for each individual cell, and determine the balancing scheme of the individual cells that need to participate in the power balancing. This reduces the flow of power between the balancing branch and the supercapacitor, reduces energy loss, improves the balancing rate, and at the same time improves the capacity utilization of the battery module and improves the safety status of the battery module. Attached Figure Description

[0034] Figure 1 This is a simplified circuit diagram of the power battery module balancing system described in this invention;

[0035] Figure 2 This is a flowchart of the control method for the power battery module balancing system described in this invention;

[0036] Figure 3 This is a diagram of the Thevenin equivalent circuit model described in this invention. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0038] like Figure 1As shown, the power battery module power balancing system of the present invention includes a series battery module, a battery management system, a balancing control module, a balancing device, a voltage detection module, and a main control circuit. The balancing device consists of a supercapacitor and a balancing step-down DC / DC converter. The main control circuit includes a current limiter, a diode, a photorelay, and an inductor. The balancing control module is communicatively connected to the battery management system, which is also communicatively connected to the voltage detection module. The balancing control module and the voltage detection module are also electrically connected to the balancing and detection bus, respectively. The supercapacitor is electrically connected to the balancing step-down DC / DC converter, which is then electrically connected to the balancing and detection bus via a current limiter. The supercapacitor is then electrically connected to the balancing and detection bus via a diode. One end of each of the N photorelays is electrically connected to the positive electrode of each of the N individual batteries in the battery module, and the other end is connected to the balancing and detection bus. One end of each of the N inductors is electrically connected to the negative electrode of each of the N individual batteries in the battery module, and the other end is connected to the balancing and detection bus. The signal injection terminal of the photorelay is connected to the signal generation terminal of the balancing control module. When the operating voltage of the battery module differs from the voltage of the main control circuit, a balanced step-down DC / DC converter is used to unify the voltage; a current limiter is used to prevent excessive current and overload; an inductor acts as a damper when abnormal current fluctuations occur; and a diode allows current to flow in one direction and prevents backflow.

[0039] The voltage detection module detects the voltage and temperature of all individual cells in the battery module within milliseconds and sends the data to the battery management system for storage. It first determines whether power balancing is needed, then calculates and selects the balancing scheme that requires the least amount of power to flow, and sends the data to the balancing control module. The balancing control module sends a PWM signal to the target balancing photorelay to activate the corresponding balancing branch, and performs the corresponding power extraction or replenishment on only one target individual cell at a time.

[0040] like Figure 2 As shown, a control method for a power battery module power balancing system specifically includes the following steps:

[0041] S1, the equalization control module reads the battery module temperature information from the battery management system.

[0042] S2, when the temperature is between 15℃ and 40℃, the voltage detection module continuously collects the terminal voltage data of each individual battery and sends it to the battery management system. The battery management system stores the data and sends it to the equalization control module.

[0043] S3, the equalization control module determines whether the maximum voltage difference of a single cell is greater than the set voltage threshold (0.05V). If yes, proceed to the next step; otherwise, the equalization ends and returns to S1.

[0044] S4, the equalization control module estimates the current value through the battery module based on the current terminal voltage data of each individual battery cell and the capacity of the battery module, using a Kalman filter algorithm. Specifically:

[0045] S4.1, 20 OCV data points were obtained through open-circuit voltage (OCV) testing, and the OCV-SOC relationship diagram of each individual cell was obtained using a polynomial fitting method. A sixth-order polynomial was used for fitting: OCV=α0+α1·SOC+α2·SOC 2 +α3·SOC 3 +α4·SOC 4 +α5·SOC 5 +α6·SOC 6 , where α0, α1, α2, α3, α4, α5, and α6 are coefficients;

[0046] S4.2, establish a Thevenin equivalent circuit model for each individual cell (e.g., Figure 3 As shown), the main parameters include the ohmic internal resistance R0, the diffusion internal resistance R1, and the diffusion capacitance C1; using Kirchhoff's law, the dynamic equation (continuous-time equation) of the Thevenin equivalent circuit model can be written as: The state of charge (SOC) of a single cell is defined by the ampere-hour measurement method, and its expression is: Simultaneously define a state vector x = [SOC U] c ] T The discrete-time state-space model can be obtained as follows: This discrete-time state-space model is used for parameter identification; where: U t U is the terminal voltage. c U is the voltage in the R1C1 loop. ocv for OCV, I t Let τ be the load current, τ = R1C1 be time, Δt be the sampling time step, η be the coulomb efficiency, and Q be the load current. cap Where k is the available battery capacity, x is the time step, and k is the time step. k Let I be the state vector at time k. t,k Let U be the load current at time k. t,k Let SOC be the terminal voltage at time k. k Let U be the state of charge (SOC) of a single cell at time k. C,k Let k be the voltage in the R1C1 loop at time k;

[0047] S4.3, The recursive least squares method with genetic factors is used to identify the parameters of the Thevenin model online;

[0048] S4.4, Based on the obtained voltage data of the individual cells and the identified Thevenin model parameters, write the state equation and measurement equation for estimating the current of the individual cells:

[0049] Because batteries age during use, causing changes in the parameters of the Thevenin model, Kalman filtering can improve the accuracy of current measurements. Based on the principles of Kalman filtering, the current estimation algorithm for a single battery cell is described below:

[0050]

[0051] in: Q ~ (0, R), where R represents a matrix; U i,OCV,k U represents the open-circuit voltage of the i-th individual cell at time k; i,t,k U represents the terminal voltage of the i-th individual cell at time k; i,1,k K represents the RC loop voltage of the i-th cell in the Thevenin model at time k; t Kalman gain; Q is process noise; F is the state transition matrix; H is the transformation matrix from state variables to measurements (observations), and both matrices F and H are set as identity matrices; ΔR i,0 U represents the difference in ohmic internal resistance R0 between the i-th cell and the cell with the lowest voltage; min,t,k R represents the terminal voltage of the lowest voltage cell at time k-1; i,0 P represents the ohmic internal resistance of the i-th cell. k P represents the covariance estimate. t I represents the updated posterior estimate covariance, β represents the measurement noise covariance, and I i,k This represents the current of the i-th individual cell at time k;

[0052] S4.5, determine whether the maximum difference between the current values ​​of each individual battery cell calculated in the previous step is less than the set current threshold (1mA). If so, take the average current, i.e., the current through the battery module is... If not, jump back to S4.3 and repeat the corresponding steps with the sampled voltage at the new time.

[0053] S5, according to formula Calculate the SOC of the i-th single cell, where c n The initial SOC value of a single cell is obtained by checking the OCV-SOC after a long period of rest, which is the capacity of the battery module.

[0054] S6. Sort all the obtained SOC values ​​of individual cells from low to high, and denote them as SOC. j(j=1,2,3...N); Based on the SOC value of each individual cell, the equalized SOC value of the individual cell is calculated using an iterative method and denoted as SOC. m SOC m The following conditions must be met:

[0055] (1) SOC1 <SOC m <SOC N ;

[0056] (2) Individual cell charge equalization to SOC m The numerical change experienced is denoted as ΔSOC. j (ΔSOC j =SOC j -SOC m The sum of the changes in the electrical charge of all individual cells is: W = |ΔSOC1| + |ΔSOC2| + |ΔSOC3| + ... + |ΔSOC N |, We need to select W as the smallest among all equilibrium solutions;

[0057] SOC m The specific calculation process is as follows:

[0058] a. Assume the initial SOC of a single cell after equalization is SOC. X，n (n = 1, 2, ...);

[0059] b. In the first bisection process, A1 is SOC1 and The median value, B1 is With SOC N The intermediate value, W is calculated separately in the first bisection method. A1 =|SOC1-A1|+|SOC2-A1|+|SOC3-A1|+…+|SOC N -A1|,W B1 =|SOC1-B1|+|SOC2-B1|+|SOC3-B1|+…+|SOC N -B1|;

[0060] c. Compare the results with those calculated in step b. If W A1 <W B1 Then A1 is considered to be the desired SOC. X，1 Determine the interval [SOC1, where A1 is located. If B1 is the dominant range, proceed to the next step; otherwise, select B1 as the desired SOC. X，1 and its advantageous range [ SOC N ];

[0061] d. Starting from the second bisection method, following the processes of steps b and c, each time the dominant interval obtained previously is evenly divided into two intervals, and the intermediate values A n and B n are substituted into W An and W Bn for calculation. Then, compare the magnitudes of W An and W Bn to determine whether to select A n or B n as the SOC obtained in this step X，n ; where: W An =|SOC1 - A n | + |SOC2 - A n | + |SOC3 - A n | + … + |SOC N - A n |, W Bn =|SOC1 - B n | + |SOC2 - B n | + |SOC3 - B n | + … + |SOC N - B n |;

[0062] e. Perform one more time based on each completion in step d to obtain SOC X，n+1 . If |SOC X , n+1 - SOC X，n | < SOC1 * 2%, then proceed to the next step; otherwise, repeat step d;

[0063] f. Determine that the current SOC X，n is the target SOC m .

[0064] S7. Compare SOC j with SOC m . If the difference exceeds 5% (|SOC j - SOC m | > SOC m * 5%), it is determined that the single cell needs to participate in charge equalization; here, 5% is used as the threshold. The smaller the set value, the better the battery charge equalization, but too small a value may cause waste of computing power.

[0065] S8. Further calculate the time required for equalization of each single cell. During this time, there is current passing through the equalization branch. That is, the time (milliseconds) from when the time relay just closes to when it opens during each charge equalization is: where C c is the set charge and discharge rate.

[0066] S9, ΔSOC determined by S6 j Determine the balancing strategy for each individual cell in the supercapacitor: if ΔSOC j If ΔSOC > 0, then the corresponding amount of electricity needs to be extracted from the individual cell; if ΔSOC j If the value is less than 0, then the corresponding cell needs to be recharged. At this time, the equalization control module sends PWM signals to the photorelays of one or more target cell branches in sequence, which turns on the corresponding equalization branches. The supercapacitor can quickly complete the power equalization of each cell, thereby extracting or compensating for the power of the target cell.

[0067] S10, this battery balancing process is now complete.

[0068] S11, The above equalization scheme is an equalization control scheme within a single battery pack. Based on this, multiple battery packs can be connected in series. According to the above scheme, after the power equalization within a single battery pack is completed, the power equalization work is completed for multiple battery packs.

[0069] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An improved control method of a power battery module power equalization system, characterized in that: S1, when the temperature of the battery module is between 15℃-40℃, the equalization control module judges whether the voltage difference of the maximum single battery is greater than the set voltage threshold value, if yes, S1 is performed, otherwise the battery module temperature information is continuously obtained; S2, based on the voltage data of each single battery and the capacity of the battery module, the current value through the battery module is estimated according to the Kalman filtering algorithm; S2.1, a Thevenin equivalent circuit model is established for each single battery, and online parameter identification is performed on the Thevenin equivalent circuit model; S2.2, the single battery current is estimated according to the voltage data of the single battery and the identified parameters; S2.3, it is judged whether the maximum difference of the calculated single battery current is less than the set current threshold value, if yes, the average value of the single battery current is taken as the current of the battery module, otherwise the online parameter identification of the Thevenin equivalent circuit model is re-performed; S3, calculating the SOC of the i-th single battery by the current value passing through the battery module, and sorting all single battery SOC values from low to high, denoted as SOC j where j = 1, 2, 3...N, N is the total number of single batteries; S4, if |SOC j -SOC m |>SOC m 5%, determine that the single battery needs to participate in the power balance, calculate the time required for each single battery balance, wherein SOC m is the single battery SOC value after balancing; S5, judging the monomer battery equalization scheme needed to participate in the electric quantity equalization: if ΔSOC j >0, the corresponding electric quantity needs to be extracted from the monomer battery, if ΔSOC j <0, the corresponding monomer battery needs to be supplemented with electric quantity; wherein ΔSOC j =SOC j -SOC m ; The SOC m The calculation process is: a.Assume the initial value of the balanced single battery SOC is SOC X，n where n = 1, 2,...; b. W is calculated in the first dichotomy respectively A1 = |SOC1-A1| + |SOC2-A1| + |SOC3-A1| + … + |SOC N -A1|, W B1 = |SOC1-B1| + |SOC2-B1| + |SOC3-B1| + … + |SOC N -B1|, wherein A1 is the intermediate value of SOC1 and , B1 is the intermediate value of SOC and SOC N ​ c. If W A1 <W B1 then A1 is SOC X，1 , determine the interval where A1 is located is the dominant interval, and go to the next step, otherwise select B1 and its dominant interval d. From the second dichotomy, according to the procedures of b and c, each time the advantage interval obtained in the previous time is evenly divided into two intervals, and the middle values A n and B n are substituted into W An and W Bn , respectively, and the sizes of W An and W Bn are compared to determine whether to select A n or B n as the SOC X，n of this time; wherein: W An = |SOC1-A n + |SOC2-A n + |SOC3-A n +... + |SOC N -A n |, W Bn = |SOC1-B n + |SOC2-B n + |SOC3-B n +... + |SOC N -B n |; e. If |SOC X , n +1 - SOC X , n| < SOC1*2%, then determine that the SOC X , n at this time is SOC m , otherwise return d.

2. The control method of the power battery module equalization system according to claim 1, characterized in that, The SOC m The following conditions must be met: (1) SOC1< SOC m SOC1< SOC N ; (2) The sum of the values of all the single cell power changes W is minimized: W = |ΔSOC1| + |ΔSOC2| + |ΔSOC3| +... + |ΔSOCN| N where ΔSOC j is the value change experienced by the single cell power balance to SOC m target j = SOC j - SOC m .

3. The control method of the power battery module equalization system according to claim 1, characterized in that, The SOC of the i-th single battery satisfies the formula: where c n is the capacity of the battery module, I k is the current of the battery module, and Δt is the sampling time step.

4. The control method of the power battery module equalization system according to claim 1, characterized in that, The time required for the single cell balancing is: where c n is the capacity of the battery module, C c is the set charge / discharge rate.

5. The control method of the power battery module equalization system according to claim 1, characterized in that, The parameter identification is specifically parameter identification on a discrete time state space model, and the open circuit voltage in the discrete time state space model is determined by using a polynomial fitting to obtain the OCV-SOC relationship of each single battery.

6. An equalization system for implementing the control method of any one of claims 1-5, characterized in that, It comprises: A series battery module, a battery management system, an equalization control module, an equalization device and a voltage detection module, the equalization control module is in communication connection with the battery management system, the battery management system is also in communication connection with the voltage detection module, the equalization control module and the voltage detection module are also respectively in electrical connection with the equalization and detection bus, and the series battery module and the equalization device are both in electrical connection with the detection bus.

7. The equalization system of claim 6, further comprising a total control circuit, the total control circuit comprising a current limiter, a diode, an optical relay and an inductor, one end of the N optical relays is respectively in electrical connection with the positive poles of the N single batteries in the battery module, and the other end is connected to the equalization and detection bus, one end of the N inductors is respectively in electrical connection with the negative poles of the N single batteries in the battery module, and the other end is connected to the equalization and detection bus.

8. The equalization system of claim 7, wherein the equalization device comprises a super capacitor, and the super capacitor is in electrical connection with the equalization and detection bus through a diode.

9. The equalization system of claim 7, wherein the equalization device further comprises an equalization buck DC / DC, the super capacitor is in electrical connection with the equalization buck DC / DC, and the equalization buck DC / DC is in electrical connection with the equalization and detection bus through a current limiter.

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