SOC balance control and EIS test method based on modular dual-output battery system

Abstract

According to the SOC balance control and EIS test method based on the modular dual-output battery system, the circuit topology can carry out high-low voltage dual-output power supply at the same time, a multi-winding transformer is adopted, so that a plurality of batteries share one transformer, and the number of windings is reduced; besides, a control strategy of combining a voltage control loop and an SOC balance control loop is adopted, so that the SOC balance of the battery can be realized, and the output voltage can be accurately adjusted; a time division multiplexing strategy is utilized to carry out the EIS test of the battery on the premise that the normal charging and discharging of the battery and the SOC balance process are not interfered, and reliable data support is provided for the performance analysis of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of high- and low-voltage dual-output battery systems, and in particular to a SOC balancing control and EIS testing method based on a modular dual-output battery system. Background Art

[0002] In today's energy sector, battery technology is widely used in key industries such as new energy vehicles and large-scale energy storage. As these applications place increasing demands on battery performance, battery system balancing and electrochemical impedance spectroscopy (EIS) testing have become hot topics of concern.

[0003] In practical applications, due to variations in manufacturing processes, operating environments, and cycle life, batteries often experience inconsistent state of charge (SOC) during operation. SOC imbalance can affect the overall performance of the battery pack, reduce energy efficiency, accelerate battery degradation, shorten battery life, and even lead to the risk of thermal runaway. To address SOC imbalance, researchers have proposed various SOC balancing methods, including passive balancing of batteries with high SOC using resistors, and active balancing methods that redistribute energy between batteries using energy storage elements such as capacitors, inductors, and transformers. For example, Michael Evzelman et al. proposed a dual-output battery system architecture and battery balancing control method for series and parallel outputs in the paper "Active Balancing System for Electric Vehicles With Incorporated Low-Voltage Bus [J]. IEEE Transactions on Power Electronics, vol. 31, no. 11, pp. 7887-7895, 2016." This structure connects a full-bridge converter to each battery cell. By controlling the converter's phase shift, the charge and discharge current of each cell is adjusted to achieve cell balancing. This battery system can power both high- and low-voltage loads simultaneously, but it still suffers from high system costs and the inability to stably regulate the low-voltage output.

[0004] EIS testing, an important electrochemical analysis technique, applies AC signals of varying frequencies to a battery to obtain impedance information at the corresponding frequencies, enabling in-depth analysis of key information such as the electrochemical reaction processes within the battery and the battery's state. Due to its non-invasive nature and ability to provide rich internal information, EIS testing plays a key role in battery management system optimization and fault diagnosis. However, currently used EIS testing methods face numerous challenges. Firstly, each battery needs to be individually connected to a test device, and only one battery can be measured at a time. This testing method is time-consuming for long battery packs and struggles to meet the demand for rapid and efficient acquisition of large amounts of battery EIS data. Secondly, existing EIS testing often relies on specialized testing equipment, requiring the battery to be disconnected from the operating system for offline testing and analysis. This makes it impossible to obtain real-time impedance data online while the battery is operating normally. This not only reduces testing efficiency but also makes it difficult to meet the practical needs of dynamic monitoring and timely regulation of battery status, limiting its widespread adoption in large-scale battery applications.

[0005] In summary, existing battery systems have shortcomings in balancing control and EIS testing. Moreover, the battery balancing and EIS testing structures are independent of each other, and two sets of circuit structures need to be constructed separately to implement the corresponding functions. This undoubtedly greatly increases the complexity and difficulty of system design, and seriously hinders the integration and miniaturization of the system. Summary of the Invention

[0006] (1) Technical issues to be solved

[0007] Based on this, the present invention provides an SOC balancing control and EIS testing method based on a modular dual-output battery system to solve the problems mentioned in the background technology, such as the inability to stably adjust the low-voltage output and high system cost of the dual-output battery system structure; the EIS test requires offline measurement, and the efficiency of testing long battery packs is low; battery balancing and EIS testing require different circuit structures to be constructed to achieve the desired results.

[0008] (2) Technical solution

[0009] To achieve the above objectives, the present invention provides an SOC balancing control and EIS testing method based on a modular dual-output battery system, wherein the system includes a controller and m battery balancing modules, wherein the battery balancing module includes a battery cell and a balancing unit;

[0010] The battery unit includes n batteries connected in series;

[0011] The balancing unit includes n switching tubes, n inductors, a multi-winding transformer, a diode, and a filter capacitor; the multi-winding transformer includes n primary windings and one secondary winding to form a transformer with n+1 windings;

[0012] In the battery balancing module, battery B ij With switch tube M i-j After connecting in series, they are respectively connected with the inductor L i-j , multi-winding transformer M si A primary winding of the multi-winding transformer M is connected in parallel; si The secondary winding and diode S ai After connecting in series, it is then connected to the filter capacitor C i Parallel; switch tube M of the balancing unit i-j 、Inductor L i-j , multi-winding transformer M si , diode S ai and filter capacitor C i A flyback converter is formed. The subscript i represents the number of the cell balancing module, and i∈[1,m]. The subscript j represents the number of the battery in the cell balancing module, and j∈[1,n]. Since the switch tube, inductor, primary winding of the multi-winding transformer and battery have a corresponding relationship, the same subscript j is used to represent them. In other words, each balancing unit includes n flyback converters, and these n flyback converters share the secondary winding of the multi-winding transformer, a diode, and a filter capacitor.

[0013] The battery cells of m battery balancing modules are connected in series in sequence, so that m×n batteries are connected in series to supply power to the high-voltage load. The positive and negative output electrodes of the balancing cells in the m battery balancing modules are connected in parallel to supply power to the low-voltage load, thereby achieving dual output of high and low voltage loads.

[0014] The battery balancing module has three operating modes, namely the first mode, the second mode and the third mode;

[0015] In the first mode, among the n batteries in the battery balancing module, only one battery B ij The corresponding connected switch tube M i-j The switch tubes connected to the other batteries are all disconnected. At this time, the current flows through the switch tube M i-j Enter the primary side excitation inductance L i-j , inductance L i-j The current in the transformer increases gradually; while the secondary side of the transformer is ai It cannot conduct in the reverse direction, so no current flows; the load is connected through the output capacitor C i The energy stored in it is used to work;

[0016] In the second mode, battery B ij The corresponding connected switch tube M i-j Disconnect, transformer M si The excitation current in the primary side flows in the reverse direction on the primary side because the inductor current cannot change suddenly, transferring the energy stored in the excitation inductor on the primary side in the first mode to the low voltage output end, so that the diode S ai Forward conduction to achieve energy transfer;

[0017] In the third mode, the switch tubes corresponding to all batteries are disconnected to prevent two batteries from being turned on at the same time, affecting the output voltage stability, and to avoid voltage spikes caused by coupling between multiple batteries.

[0018] Preferably, the SOC balance control method of the system is: using a voltage control loop and an SOC balance control loop in combination to achieve SOC balance and output voltage regulation;

[0019] For a battery balancing module, the voltage compensator G c_vol(s) The measured output voltage V out and the reference output voltage V out_ref The difference between the two is taken as input, and the duty cycle coefficient D it As the output, where the subscript i is the number of the battery balancing module, the voltage closed-loop control circuit is realized;

[0020] SOC Compensator G c_soc(s) Each battery B ij The true value of SOC ij ,j∈[1,n] and reference SOC value SOC out_ref The difference between the two is taken as input, and each battery B ij Corresponding SOC coefficient α ij ,j∈[1,n] as the output, and then the SOC coefficient α ij With the voltage compensator output D it Multiplying them, we can get each battery B ij Corresponding switch tube M i-j Duty cycle D ij ,j∈[1,n];

[0021] Each battery B ij Corresponding SOC coefficient α ij is generated by the SOC balance control loop; SOC out_ref It is obtained by the average SOC value of all batteries in the battery balancing module, as shown in the following formula:

[0022]

[0023] SOC balance compensator G c_soc(s)The input is obtained by the difference between the actual SOC value of the battery and the SOC reference value. Its output is usually a number between -1 and 0. In order to control it between 0 and a positive value, a fixed value of 1 is usually added to the output value of the SOC compensator, thereby adjusting the SOC coefficient α corresponding to each battery. ij Adjust to the required range; the SOC coefficient α corresponding to each battery ij And the relationship is shown in the following formula, where n is the number of batteries in the battery balancing module;

[0024]

[0025] α1+α2+…+α n =n.

[0026] Preferably, the EIS test method of the system is:

[0027] For example, when the AC impedance of a battery cell needs to be measured in a battery balancing module, a sinusoidal disturbance signal with a small duty cycle is added during the conduction period of the switch tube corresponding to each battery using the time-division multiplexing method. ac , whose frequency is f p , with an amplitude of D ac ;

[0028] Specifically, to measure battery B ij For example, the disturbance signal is modulated by PWM control technology; when no EIS test is performed, a stable duty cycle is generated by comparing the carrier wave and the modulation wave; at this time, the modulation wave only has battery B i2 The DC signal D dc ; During the EIS test, the modulation wave d(t) is ij The DC signal D dc , and the disturbance signal d is also superimposed ac , as shown in the following formula, at this time, the duty cycle of periodic changes is obtained by comparing the carrier wave and the modulating wave;

[0029] d(t)=D dc +D ac ·sin(2πf p t)

[0030] Disturbance signal d ac The output voltage of the flyback converter V out , the battery's DC voltage V Bij_dc and the battery's DC current I cij_dc A relatively small sine wave is superimposed on each of them, as shown in the following formula:

[0031]

[0032] Among them, v Bij(t) and i cij (t) is the jth battery B in the i-th battery balancing module ij Voltage and current; I ac Indicates the amplitude of the superimposed sinusoidal current, V ac Indicates the amplitude of the superimposed sinusoidal voltage; represents the phase of the superimposed sinusoidal voltage, represents the phase of the superimposed sinusoidal currents; all these sinusoids have a frequency of f p ;

[0033] By measuring the peak value V of the battery voltage during a disturbance cycle Bij_pp and the peak value of the battery current I cij_pp , the battery B can be determined according to the following formula ij The AC impedance of Bij (f p ) indicates that at frequency f p Lower battery B ij AC impedance;

[0034]

[0035] The frequency f is determined by the following formula p The phase of the battery AC impedance is ∠z Bmn (f p ):

[0036]

[0037] Preferably, the disturbance signal d ac The magnitude is within 4% of the battery's stable duty cycle value.

[0038] Preferably, the carrier wave is a sawtooth wave.

[0039] Preferably, the controller is a micro control unit MCU.

[0040] Preferably, the SOC compensator and the voltage compensator are both PI controllers.

[0041] (3) Beneficial effects

[0042] As can be seen from the above technical solution, the SOC balancing control and EIS testing method based on a modular dual-output battery system proposed in the present invention has the following beneficial effects:

[0043] The proposed modular dual-output battery system can simultaneously power two outputs: a high-voltage output generated by multiple batteries connected in series, and a low-voltage output generated by flyback converters connected in parallel. This design utilizes a multi-winding transformer, with multiple batteries sharing a single transformer. This reduces the number of windings, avoids the need for a high-power converter and additional cell balancing circuits, and effectively reduces system cost, size, and integration, making it more suitable for space-constrained applications such as new energy vehicles and large-scale energy storage.

[0044] 2. A control strategy combining a voltage control loop and an SOC balance control loop is adopted. Through the voltage compensator and the SOC balance compensator, the duty cycle of the corresponding switch tube of each battery is adjusted according to the difference between the output voltage and the reference voltage, as well as the difference between the actual SOC of the battery and the reference SOC, and the battery discharge rate is dynamically changed. This can not only achieve battery SOC balance, but also accurately adjust the output voltage of the battery balancing module (i.e., low-voltage output).

[0045] 3. Utilizing a time-sharing multiplexing strategy, we conduct EIS testing on batteries without interfering with normal charging, discharging, and SOC balancing. During the on-time period of each battery's corresponding MOS switch, we add a small duty cycle sinusoidal perturbation signal. By measuring the battery voltage and current fluctuations, we calculate the magnitude and phase of the battery's AC impedance, providing reliable data support for battery performance analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0047] Figure 1 This is a schematic diagram of the structure of the modular dual-output battery system in the present invention;

[0048] Figure 2 Schematic diagrams of three operating modes of the system of the present invention; (a) shows the first mode, (b) shows the second mode, (c) shows the third mode, and (d) also shows the first mode;

[0049] Figure 3 The following are timing diagrams of the excitation inductor current in three operating modes of the system of the present invention;

[0050] Figure 4 Figure 1 is a block diagram of the balancing control of a modular dual-output battery system according to the present invention; (a) is the voltage control loop, and (b) is the SOC balancing control loop;

[0051] Figure 5Schematic diagram of the principle of EIS testing of the present invention; (a) is a schematic diagram of the principle of obtaining the duty cycle by comparing the carrier and the modulation wave; (b) is a schematic diagram of the principle of obtaining the duty cycle when no EIS test is performed; (c) is a schematic diagram of the principle of obtaining the duty cycle when an EIS test is performed. DETAILED DESCRIPTION

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0053] like Figure 1 As shown, the modular dual-output battery system of the present invention includes a controller and m battery balancing modules, wherein the battery balancing module includes a battery unit and a balancing unit;

[0054] The battery unit includes n batteries connected in series;

[0055] The balancing unit includes n switching tubes, n inductors, a multi-winding transformer, a diode and a filter capacitor; the multi-winding transformer includes n primary windings and one secondary winding to form a transformer with n+1 windings.

[0056] In the battery balancing module, battery B ij (where the subscript i represents the number of the battery balancing module, and i∈[1,m]; the subscript j represents the number of the battery in the battery balancing module, and j∈[1,n]) and the switch tube M i-j (The subscript i represents the number of the battery balancing module, and the subscript j represents the number of the switch tube in the battery balancing module. Since the switch tube has a corresponding relationship with the battery, the same subscript is used, and the same is true below) After being connected in series, they are respectively connected to the inductor L i-j , multi-winding transformer M si A primary winding of the multi-winding transformer M is connected in parallel; si The secondary winding and diode S ai After connecting in series, it is then connected to the filter capacitor C i Parallel. The switch tube M of the balancing unit i-j 、Inductor L i-j , multi-winding transformer M si , diode S ai and filter capacitor C iA flyback converter is formed. That is, each balancing unit includes n flyback converters, and these n flyback converters share a secondary winding of a multi-winding transformer, a diode, and a filter capacitor.

[0057] In the battery balancing module, both ends of each battery are connected to a flyback converter of the balancing unit to perform a balanced discharge operation.

[0058] In this way, the battery cells of m battery balancing modules are connected in series in sequence, so that m×n (the system includes m battery balancing modules, and each battery balancing module contains n batteries) batteries are connected in series to power the high-voltage load, and the positive and negative output electrodes of the balancing cells in the m battery balancing modules are connected in parallel to power the low-voltage load, thereby achieving dual output of high and low voltage loads.

[0059] The modular dual-output battery system connects batteries in series, which not only generates high voltage but also reduces the voltage through a multi-winding transformer to power low-voltage loads. It also has the functions of battery balancing and EIS testing.

[0060] In this embodiment, the controller is a micro control unit MCU, and the switch tube is a MOS tube.

[0061] Under the control of the controller, the battery balancing module has three operating modes: the first mode, the second mode, and the third mode. Figure 2 As shown, the present invention uses two batteries B i1 and B i2 (i.e. n=2) as an example for analysis and explanation.

[0062] like Figure 2 As shown in (a), in the first mode, only one battery B among the two batteries in the battery balancing module is i1 The corresponding connected switch tube M i-1 conduction, other batteries (such as B i2 ) The corresponding connected switch tubes are all disconnected, and the current flows through the switch tube M i-1 Enter the primary side excitation inductance L i-1 , inductance L i-1 The current in the secondary side increases gradually. ai It cannot conduct in the reverse direction, so no current flows. The load is connected through the output capacitor C i In this mode, the conduction state of the switch tube and the timing change of the excitation inductor current are as follows: Figure 3 Middle t 10 -t 11 Stages shown.

[0063] like Figure 2(b) shows that in the second mode, battery B i1 The corresponding connected switch tube M i-1 Disconnect, transformer M si The excitation current in the primary side flows in the reverse direction on the primary side because the inductor current cannot change suddenly, transferring the energy stored in the excitation inductor on the primary side in the first mode to the low voltage output end, so that the diode S ai In this mode, the conduction state of the switch tube and the timing change of the excitation inductor current are as follows: Figure 3 Middle t 11 -t 12 Stages shown.

[0064] like Figure 2 As shown in (c), in the third mode, all the switches connected to the batteries are disconnected to prevent two batteries from being turned on at the same time, affecting the output voltage stability, and to avoid voltage spikes caused by coupling between multiple batteries. In this mode, the conduction state of the switch tube and the timing change of the excitation inductor current are shown as follows: Figure 3 Middle t 13 -t 20 Stages shown.

[0065] like Figure 2 As shown in (d), there is only one battery B among the two batteries in the battery balancing module. i2 The corresponding connected switch tube M i-2 conduction, other batteries (such as B i1 ) The corresponding connected switch tubes are all disconnected. At this time, the system is also in the first mode, and the current flows through the switch tube M i-2 Enter the primary side excitation inductance L i-2 , inductance L i-2 The current in the winding gradually increases. This mode mainly completes the switching of the working battery, realizes the storage of excitation energy, and creates conditions for the subsequent energy transfer to the secondary winding. In this mode, the conduction state of the switch tube and the timing change of the excitation inductor current are as follows: Figure 3 Middle t 20 -t 21 Stages shown.

[0066] The balance control strategy of the modular dual-output battery system of the present invention is to achieve SOC balance and output voltage regulation by combining the voltage control loop and the SOC balance control loop. The control block diagram is as follows: Figure 4 As shown (only one battery balancing module is provided as an illustration). Voltage compensator G c_vol(s) The measured output voltage V out and the reference output voltage V out_ref The difference between the two is taken as input, and the duty cycle coefficient D it(where the subscript i is the number of the battery balancing module) as the output to realize the voltage closed-loop control circuit. c_soc(s) Each battery B ij The true value of SOC ij ,j∈[1,n] and reference SOC value SOC out_ref The difference between the two is taken as input, and each battery B ij Corresponding SOC coefficient α ij ,j∈[1,n] as the output, and then the SOC coefficient α ij With the voltage compensator output D it Multiplying them, we can get each battery B ij Corresponding switch tube M i-j Duty cycle D ij ,j∈[1,n]. The SOC compensator G used in the present invention c_soc(s) and voltage compensator G c_vol(s) Both are PI controllers.

[0067] Each battery B ij Corresponding SOC coefficient α ij It is generated by the SOC balance control loop. out_ref It is the average SOC value of all batteries in the battery balancing module, as shown in formula (1). SOC balance compensator G c_soc(s) The input is obtained by the difference between the actual SOC value of the battery and the SOC reference value. Its output is usually a number between -1 and 0. In order to control it between 0 and a positive value, a fixed value of 1 is usually added to the output value of the SOC compensator, thereby adjusting the SOC coefficient α corresponding to each battery. ij Adjust to the required range. The SOC coefficient α corresponding to each battery ij And their relationship is shown in formulas (2) and (3), where n is the number of batteries in the battery balancing module.

[0068]

[0069] α1+α2+…+α n =n (3)

[0070] Through the above analysis, when the output voltage on the secondary side is not equal to the expected voltage, the balancing algorithm controls the battery with a higher SOC to operate at a higher duty cycle and provide a higher proportion of electrical energy to the load, so that the SOC of each battery tends to be balanced.

[0071] The topology of the dual-output modular battery system proposed in this invention can not only achieve SOC balance, but also measure the AC impedance of the battery. Taking a battery balancing module as an example, when the AC impedance of the battery cell needs to be measured, a sinusoidal disturbance signal d with a small duty cycle is added during the conduction period of the switch corresponding to each battery using a time-division multiplexing method. ac , whose frequency is f p , with an amplitude of D ac .like Figure 5 (a) shows the measurement of battery B i2 For example, the disturbance signal is modulated by PWM control technology. Figure 5 As shown in (b), when no EIS test is performed, by comparing the carrier wave (sawtooth wave) and the modulation wave (only battery B i2 The DC signal D dc ) to generate a stable duty cycle (such as Figure 5 (b) is shown in the lower half). Figure 5 As shown in (c), during the EIS test, the modulation wave d(t) is not only i2 The DC signal D dc , and the disturbance signal d is also superimposed ac , as shown in formula (4); at this time, the duty cycle of periodic changes (such as Figure 5 (shown in the lower half of (c)).

[0072] Disturbance signal d ac The output voltage of the flyback converter V out , the battery's DC voltage V Bij_dc and the battery's DC current I cij_dc A relatively small sine wave is superimposed on both, as shown in formulas (5) and (6). Bij (t) and i cij (t) is the jth battery B in the i-th battery balancing module ij Voltage and current; I ac Indicates the amplitude of the superimposed sinusoidal current, V ac Indicates the amplitude of the superimposed sinusoidal voltage; represents the phase of the superimposed sinusoidal voltage, represents the phase of the superimposed sinusoidal current. The frequency of all these sinusoids is f p By measuring the peak value of the battery voltage V Bij_pp and the peak value of the battery current I cij_pp , the battery B can be determined according to formula (7) ij The AC impedance of Bij (f p ) indicates that at frequency fp Lower battery B ij If there is a phase offset between the battery voltage and the battery current, or if phase information is required, the phase offset at frequency f can be determined according to formula (8). p The phase of the battery AC impedance is ∠z Bmn (f p ).

[0073] d(t)=D dc +D ac ·sin(2πf p t) (4)

[0074]

[0075] In this embodiment, the disturbance signal d ac The amplitude is very small, generally only accounting for 4% of the given duty cycle of the battery (i.e., the stable duty cycle value). Assume that the stable duty cycle value of a battery is set to 0.167 when no EIS test is performed, and the disturbance signal d ac The amplitude is only 0.0067. During the EIS test, the duty cycle value changes from 0.160 to 0.174 in a sinusoidal manner. The experiment proves that under such a small duty cycle disturbance, the secondary side output voltage V of the system under normal discharge conditions is not affected. out_dc and its cell balancing function.

[0076] The integrated EIS test function enables the system to monitor the battery's AC impedance in real time during operation, obtaining information about the battery's internal electrochemical processes, providing a strong basis for battery performance analysis and health assessment. This multifunctional integration eliminates the need for additional testing equipment, simplifies battery management processes, and improves the system's intelligence and overall performance.

[0077] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be covered by the scope of protection of the present invention.

Claims

1. A SOC balance control and EIS test method based on a modular dual-output battery system, characterized in that: The system includes a controller and m battery balancing modules, wherein the battery balancing module includes a battery unit and a balancing unit; The battery unit includes n batteries connected in series; The balancing unit includes n switching tubes, n inductors, a multi-winding transformer, a diode, and a filter capacitor; the multi-winding transformer includes n primary windings and one secondary winding to form a transformer with n+1 windings; In the battery balancing module, battery B ij With switch tube M i-j After connecting in series, they are respectively connected with the inductor L i-j , multi-winding transformer M si A primary winding of the multi-winding transformer M is connected in parallel; si The secondary winding and diode S ai After connecting in series, it is then connected to the filter capacitor C i Parallel; switch tube M of the balancing unit i-j 、Inductor L i-j , multi-winding transformer M si , diode S ai and filter capacitor C i A flyback converter is formed. The subscript i represents the number of the cell balancing module, and i∈[1,m]. The subscript j represents the number of the battery in the cell balancing module, and j∈[1,n]. Since the switch tube, inductor, primary winding of the multi-winding transformer and battery have a corresponding relationship, the same subscript j is used to represent them. In other words, each balancing unit includes n flyback converters, and these n flyback converters share the secondary winding of the multi-winding transformer, a diode, and a filter capacitor. The battery cells of m battery balancing modules are connected in series in sequence, so that m×n batteries are connected in series to supply power to the high-voltage load. The positive and negative output electrodes of the balancing cells in the m battery balancing modules are connected in parallel to supply power to the low-voltage load, thereby achieving dual output of high and low voltage loads. The battery balancing module has three operating modes, namely the first mode, the second mode and the third mode; In the first mode, among the n batteries in the battery balancing module, only one battery B ij The corresponding connected switch tube M i-j The switch tubes connected to the other batteries are all disconnected. At this time, the current flows through the switch tube M i-j Enter the primary side excitation inductance L i-j , inductance L i-j The current in the transformer increases gradually; while the secondary side of the transformer is ai It cannot conduct in the reverse direction, so no current flows; The load is connected through the output capacitor C i The energy stored in it is used to work; In the second mode, battery B ij The corresponding connected switch tube M i-j Disconnect, transformer M si The excitation current in the primary side flows in the reverse direction on the primary side because the inductor current cannot change suddenly, transferring the energy stored in the excitation inductor on the primary side in the first mode to the low voltage output end, so that the diode S ai Forward conduction to achieve energy transfer; In the third mode, the switch tubes corresponding to all batteries are disconnected to prevent two batteries from being turned on at the same time, affecting the output voltage stability, and to avoid voltage spikes caused by coupling between multiple batteries.

2. The method according to claim 1, characterized in that The SOC balance control method of the system is: using a voltage control loop and an SOC balance control loop in combination to achieve SOC balance and output voltage regulation; For a battery balancing module, the voltage compensator G c_vol(s) The measured output voltage V out and the reference output voltage V out_ref The difference between the two is taken as input, and the duty cycle coefficient D it As the output, where the subscript i is the number of the battery balancing module, the voltage closed-loop control circuit is realized; SOC Compensator G c_soc(s) Each battery B ij The true value of SOC ij ,j∈[1,n] and reference SOC value SOC out_ref The difference between the two is taken as input, and each battery B ij Corresponding SOC coefficient α ij ,j∈[1,n] as the output, and then the SOC coefficient α ij With the voltage compensator output D it Multiplying them, we can get each battery B ij Corresponding switch tube M i-j Duty cycle D ij ,j∈[1,n]; Each battery B ij Corresponding SOC coefficient α ij is generated by the SOC balance control loop; SOC out_ref It is obtained by the average SOC value of all batteries in the battery balancing module, as shown in the following formula: SOC balance compensator G c_soc(s) The input is obtained by the difference between the actual SOC value of the battery and the SOC reference value. Its output is usually a number between -1 and 0. In order to control it between 0 and a positive value, a fixed value of 1 is usually added to the output value of the SOC compensator, thereby adjusting the SOC coefficient α corresponding to each battery. ij Adjust to the required range; the SOC coefficient α corresponding to each battery ij And the relationship is shown in the following formula, where n is the number of batteries in the battery balancing module; α1+α2+…+α n ＝n。 3. The method according to claim 2, characterized in that The EIS test method of the system is: For example, when the AC impedance of a battery cell needs to be measured in a battery balancing module, a sinusoidal disturbance signal with a small duty cycle is added during the conduction period of the switch tube corresponding to each battery using the time-division multiplexing method. ac , whose frequency is f p , with an amplitude of D ac ; Specifically, to measure battery B ij For example, the disturbance signal is modulated by PWM control technology; when no EIS test is performed, a stable duty cycle is generated by comparing the carrier wave and the modulation wave; At this time, the modulated wave only has battery B i2 The DC signal D dc ; During the EIS test, the modulation wave d(t) is ij The DC signal D dc , and the disturbance signal d is also superimposed ac , as shown in the following formula, at this time, the duty cycle of periodic changes is obtained by comparing the carrier wave and the modulating wave; d(t)=D dc +D ac ·sin(2πf p t) Disturbance signal d ac The output voltage of the flyback converter V out , the battery's DC voltage V Bij_dc and the battery's DC current I cij_dc A relatively small sine wave is superimposed on each of them, as shown in the following formula: Among them, v Bij (t) and i cij (t) is the jth battery B in the i-th battery balancing module ij Voltage and current; I ac Indicates the amplitude of the superimposed sinusoidal current, V ac Indicates the amplitude of the superimposed sinusoidal voltage; represents the phase of the superimposed sinusoidal voltage, represents the phase of the superimposed sinusoidal currents; all these sinusoids have a frequency of f p ; By measuring the peak value V of the battery voltage during a disturbance cycle Bij_pp and the peak value of the battery current I cij_pp , the battery B can be determined according to the following formula ij The AC impedance of Bij (f p ) indicates that at frequency f p Lower battery B ij AC impedance; The frequency f is determined by the following formula p The phase of the battery AC impedance is ∠z Bmn (f p ):

4. The method according to claim 3, characterized in that The disturbance signal d ac The magnitude is within 4% of the battery's stable duty cycle value.

5. The method according to claim 3, characterized in that The carrier wave is a sawtooth wave.

6. The method according to claim 1, characterized in that The controller is a micro control unit MCU.

7. The method according to claim 2, characterized in that The SOC compensator and the voltage compensator are both PI controllers.

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