Discharge equalization control method and battery system

Abstract

The application discloses a discharge equalization control method and a battery system, which are applied to a battery assembly. The battery assembly comprises a plurality of parallelly connected battery modules. Each battery module comprises an energy storage unit and N DC / DC conversion units connected with the energy storage unit. The output ends of the N DC / DC conversion units are parallelly connected. The method comprises the following steps: obtaining a resistance signal for representing a virtual impedance in a current battery module line based on average output currents of all the battery modules; and constructing a voltage outer loop based on the resistance signal, constructing N current inner loops with the same voltage outer loop output signal as a reference current, and respectively generating driving signals to control corresponding DC / DC conversion units to work. The control method can improve the current sharing response speed of the parallelly connected battery modules during discharge, can refine the current sharing regulation granularity, and can improve the utilization rate of the battery modules.

Description

Technical Field

[0001] This invention relates to the field of discharge control technology, specifically to a discharge equalization control method and a battery system. Background Technology

[0002] With the rise of new energy industries such as wind power, photovoltaic power, and electric vehicles, high-power energy storage systems are being widely used. Existing high-power energy storage systems generally integrate battery modules in series or parallel. In particular, when connected in parallel, they can be used with devices such as DC / DC converters to meet the power expansion needs while outputting the required current.

[0003] For this type of parallel battery system, due to differences in battery cell performance, DC / DC converter, and line parameters, uneven load current distribution can occur during parallel operation. To address this, several current sharing control techniques have been proposed in the prior art to ensure balanced discharge of the battery system, such as the master-slave power supply method, the average current automatic current sharing method, and the maximum current automatic current sharing method. However, these methods suffer from poor real-time performance and coarse adjustment, resulting in poor current sharing performance. This still leads to increased SOC dispersion among the battery modules in the battery system and reduces the utilization rate of the battery modules. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects or problems in the prior art and to provide a discharge equalization control method and a battery system. This control method can improve the current sharing response speed of parallel battery modules during discharge, refine the granularity of current sharing adjustment, and improve the utilization rate of battery modules.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A discharge equalization control method is applied to a battery module, which includes several parallel battery modules. Each battery module includes an energy storage unit and N DC / DC converters connected to the energy storage unit. The outputs of the N DC / DC converters are connected in parallel to connect to an electrical load. For each battery module, the method includes: obtaining a current signal based on the average output current of all battery modules, wherein the average output current of all battery modules is the sum of the average output currents of the N DC / DC converters in each battery module; comparing the current signal with the current output current of the current battery module, and performing proportional-integral modulation... After the holiday, a resistance adjustment signal is obtained, where the current output current of the current battery module is the sum of the output currents of the N DC / DC converter units in the current battery module; the preset static resistance value is adjusted based on the resistance adjustment signal to obtain a resistance signal, which is used to represent the virtual impedance in the current battery module circuit; a corrected reference voltage is obtained based on the resistance signal; a voltage outer loop is constructed based on the corrected reference voltage, and a current inner loop is constructed using the output signal of the voltage outer loop as a reference current; the current inner loop includes N independent control loops; a drive signal is generated based on the output signal of each current inner loop to control the operation of the corresponding DC / DC converter unit.

[0007] Furthermore, the voltage outer loop uses the output voltage of one of the DC / DC conversion units in the current battery module as the feedback voltage, and generates the voltage outer loop output signal after proportional-integral adjustment; each current inner loop uses the output current of the corresponding DC / DC conversion unit as the feedback current, and generates the current inner loop output signal after proportional-integral adjustment.

[0008] Furthermore, the correction reference voltage is obtained based on the resistance signal, specifically including: obtaining a voltage signal based on the resistance signal and the current output current of the battery module; adjusting the reference voltage with the voltage signal as a reference to obtain the correction reference voltage.

[0009] Furthermore, the current signal is obtained by adjusting the ratio of the average output current of all battery modules to the average SOC of all battery modules and the SOC of the current module.

[0010] Furthermore, the resistance adjustment signal is obtained by subtracting the current signal from the current signal and the current output current of the battery module to obtain the deviation signal, and then performing proportional-integral adjustment on the deviation signal.

[0011] Furthermore, the voltage signal is obtained by multiplying the resistance signal by the current output current of the battery module; the correction reference voltage is obtained by subtracting the reference voltage from the voltage signal; and the drive signal is obtained by PWM modulation of the current inner loop output signal.

[0012] Furthermore, based on a preset voltage range, the voltage signal is limited to obtain a corrected voltage signal, and a corrected reference voltage is obtained based on the corrected voltage signal.

[0013] Furthermore, the present invention also provides a battery system, the battery assembly comprising a plurality of parallel battery modules, each battery module comprising an energy storage unit, N DC / DC converter units connected to the energy storage unit, and a control unit; the output terminals of the N DC / DC converter units are connected in parallel for connecting to an electrical load; the control unit comprises: a current signal generation unit adapted to obtain a current signal based on the average output current of all battery modules, wherein the average output current of all battery modules is the sum of the average output currents of the N DC / DC converter units in all battery modules; and a resistance signal generation unit adapted to compare the current signal with the current output current of the current battery module, obtain a resistance adjustment signal after proportional-integral adjustment, and adjust a preset static value based on the resistance adjustment signal. The system comprises: a resistance value generation unit, which generates a resistance signal based on the resistance signal and the current output current of the battery module; a correction reference voltage generation unit, which adjusts the reference voltage using the voltage signal as a reference to obtain a correction reference voltage; a loop control unit, which constructs an outer voltage loop based on the correction reference voltage and constructs an inner current loop using the output signal of the outer voltage loop as a reference current; the inner current loop includes N independent control loops; and a drive control unit, which generates a drive signal based on the output signal of each inner current loop to control the operation of the corresponding DC / DC converter unit.

[0014] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0015] In the discharge equalization control method provided by this invention, for a parallel system in which each battery includes one battery and N DC / DC conversion units, the N DC / DC conversion units use the same voltage outer loop output signal as the reference current of their respective current inner loops, thereby generating N independent drive signals to drive different DC / DC conversion units to work. In this way, the current sharing response speed of the voltage and current dual-loop control strategy can be effectively improved, thereby improving the output real-time performance of the battery module integrated in parallel and improving the utilization rate of the battery module.

[0016] The voltage signal is obtained based on the resistance signal and the current output current of the battery module. The resistance signal is used to represent the virtual impedance in the battery module circuit. By increasing the virtual impedance, the droop control of the DC / DC conversion unit is realized, eliminating the unbalanced impedance between the DC / DC conversion units of different battery modules, so as to make the power output balanced. Furthermore, since the virtual impedance does not add actual resistance in the circuit, it does not consume power.

[0017] Furthermore, since the battery module only needs to control the DC / DC converter unit to work according to the drive signal, the drive signal changes accordingly when the battery module is added or removed in the system cabinet, so that the battery module can still output appropriate power. Therefore, the addition or removal of battery modules in the system cabinet will not affect the discharge of a battery module that is already in operation, thus facilitating the expansion of the energy storage system and the hot-swapping of battery modules.

[0018] Furthermore, the resistance signal is obtained by adjusting a preset static resistance value using a resistance adjustment signal. Real-time adjustment of the static resistance value allows the obtained voltage signal to more accurately reflect the virtual impedance in the circuit, and avoids deviations from actual requirements when using only the static resistance value for droop control. Moreover, the resistance adjustment signal is obtained through the current signal and the current output current of the battery module. The current signal can be obtained by establishing a communication link, resulting in superior real-time control and effectively improved current sharing response speed.

[0019] By limiting the voltage signal based on a preset voltage range, the obtained corrected voltage signal can make a more appropriate adjustment to the corrected reference voltage and avoid excessive voltage signal drop.

[0020] This control method is applicable to battery modules containing N DC / DC converter units connected in parallel. It can adjust the reference voltage through a voltage signal and control the N DC / DC converter units with an independent current inner loop. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic diagram showing the parallel connection of the output terminals of two DC / DC converter units of each battery module in an embodiment of the battery system provided by the present invention;

[0023] Figure 2 A schematic diagram showing the series connection of the output terminals of two DC / DC converter units of each battery module in an embodiment of the battery system provided by the present invention;

[0024] Figure 3 A schematic diagram of the control loop when the output terminals of two DC / DC converter units of each battery module are connected in parallel in an embodiment of the discharge equalization control method provided by the present invention;

[0025] Figure 4A schematic diagram of the control loop when the outputs of the two DC / DC converter units of each battery module are connected in series in an embodiment of the discharge equalization control method provided by the present invention. Figure 1 ;

[0026] Figure 5 A schematic diagram of the control loop when the outputs of the two DC / DC converter units of each battery module are connected in series in an embodiment of the discharge equalization control method provided by the present invention. Figure 2 . Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise expressly defined, the use of terms such as "first," "second," or "third" in the claims, description, and accompanying drawings of this invention is for distinguishing different objects and not for describing a specific order.

[0029] Unless otherwise expressly defined, in the claims, description, and accompanying drawings of this invention, the use of directional terms such as "center," "lateral," "longitudinal," "horizontal," "vertical," "top," "bottom," "inner," "outer," "upper," "lower," "front," "rear," "left," "right," "clockwise," and "counterclockwise" to indicate orientation or positional relationships is based on the orientation and positional relationships shown in the accompanying drawings and is only for the convenience of describing the invention and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the specific scope of protection of this invention.

[0030] Unless otherwise expressly defined, the terms "fixed connection" or "fixed connection" used in the claims, description and drawings of this invention should be interpreted broadly to refer to any connection in which there is no displacement or relative rotation relationship between the two parties, including non-removable fixed connection, detachable fixed connection, integral connection and fixed connection by other means or components.

[0031] In the claims, description and accompanying drawings of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0032] This invention provides a battery system comprising at least one battery assembly, each battery assembly comprising a plurality of parallel battery modules, each battery module comprising at least one energy storage unit and at least one DC / DC converter unit, wherein the DC / DC converter unit is used to connect the energy storage unit and the electrical load.

[0033] Specifically, in this embodiment, each battery module includes an energy storage unit and two DC / DC conversion units, as shown in the figure. Figure 1 and Figure 2 In two implementations, the outputs of these two DC / DC converter units can be switched between parallel and series connections, and are connected to a DC / DC converter via a bus. This DC / DC converter then supplies power to the load via the DC bus. Of course, in other embodiments, the DC / DC converter is not necessary; the battery module can directly supply power to the load, with the two built-in DC / DC converter units adjusting the output voltage and current.

[0034] In this battery system, each battery module also includes a control unit, which includes a current signal generation unit, a resistance signal generation unit, a voltage signal generation unit, a correction reference voltage generation unit, a loop control unit, and a drive control unit.

[0035] Specifically, the current signal generation unit is adapted to obtain a current signal based on the average output current of all battery modules; the resistance signal generation unit is adapted to compare the current signal with the current output current of the current battery module, and obtain a resistance signal after proportional-integral adjustment; the voltage signal generation unit is adapted to obtain a voltage signal based on the resistance signal and the current output current of the current battery module; the correction reference voltage generation unit is adapted to adjust the reference voltage with the voltage signal as a reference to obtain a correction reference voltage; the loop control unit is adapted to construct a voltage outer loop based on the correction reference voltage, and construct a current inner loop with the voltage outer loop output signal as a reference current; the drive control unit is adapted to generate a drive signal based on the current inner loop output signal to control the operation of the DC / DC conversion unit.

[0036] Furthermore, the control unit is configured to implement a discharge equalization control method through the aforementioned components. This discharge equalization control method, for each battery module, includes the following steps:

[0037] S100: Obtain the current signal based on the average output current of all battery modules;

[0038] S200: Compares the current signal with the current output current of the battery module, and obtains the resistance adjustment signal after proportional-integral regulation;

[0039] S300: Adjusts the preset static resistance value based on the resistance adjustment signal to obtain the resistance signal;

[0040] S400: Obtains the voltage signal based on the resistance signal and the current output current of the battery module;

[0041] S500: Using a voltage signal as a reference, adjust the reference voltage to obtain a corrected reference voltage;

[0042] S600: Constructs an outer voltage loop based on a modified reference voltage, and constructs an inner current loop using the output signal of the outer voltage loop as a reference current.

[0043] S700: Based on the current inner loop output signal, a drive signal is generated to control the operation of the DC / DC converter unit.

[0044] Specifically, firstly Figure 3 The above method is illustrated using the example of the parallel connection of the output terminals of the two DC / DC converter units within the battery module shown.

[0045] Reference Figure 1 Within the battery module, the positive output terminals of two DC / DC conversion units are connected in parallel to the positive bus, and the negative output terminals are connected in parallel to the negative bus. Both the positive and negative buses are connected to a DC / DC converter, which adjusts the output voltage to the DC bus. Here, the corresponding DC / DC conversion units within each battery module are labeled as the first conversion unit and the second conversion unit, respectively.

[0046] Through CAN communication, the output current of each first conversion unit and each second conversion unit can be collected. The battery management module (BMS) built into the battery system can obtain the average output current of all first conversion units and the average output current of all second conversion units. The sum of the two is used as the input information of the current signal generation unit in the generation control unit.

[0047] In this embodiment, the generation of the current signal also references the SOC of the battery module. Specifically, the current signal can be obtained by adjusting the ratio of the average SOC of all battery modules to the SOC of the current battery module based on the average output current of all battery modules. It should be noted that the average SOC of the battery modules and the SOC of the current battery module referred to here can be obtained from the power output information of the entire battery module or from the power output information of the cells within each battery module; no limitation is made here.

[0048] Specific reference Figure 3The sum of the average output current of all first conversion units and the average output current of all second conversion units is used as the first input information, and the ratio of the average SOC of all battery modules to the SOC of the current module is used as the second input information. Multiplying these two values ​​yields the final current signal. Alternatively, as a basic implementation, the current signal can be generated without referring to the battery module SOC, i.e., directly based on the average output current of all battery modules.

[0049] Reference Figure 3 After obtaining the current signal, the difference between the current signal and the current output current of the current battery module is calculated to obtain a deviation signal. This deviation signal is then subjected to proportional-integral adjustment to obtain a resistance adjustment signal. The current output current of the current battery module is the sum of the output currents of the first conversion unit and the second conversion unit.

[0050] Reference Figure 3 After obtaining the resistance adjustment signal, the preset static resistance value is adjusted based on the resistance adjustment signal to obtain a resistance signal. The resistance signal is then multiplied by the current output current of the battery module to obtain a voltage signal. In this embodiment, the final voltage signal is obtained by multiplying the resistance signal obtained by adjusting the static resistance value with the current output current of the battery module. The resistance signal obtained by adjusting the resistance signal can more accurately reflect the virtual impedance in different lines, thus making the obtained voltage signal more accurate.

[0051] Reference Figure 3 After obtaining the voltage signal, the difference between the reference voltage and the voltage signal is calculated to obtain the corrected reference voltage. In this embodiment, after obtaining the voltage signal, the voltage signal is further limited based on a preset voltage range to obtain the corrected voltage signal, and the final corrected reference voltage is obtained based on the corrected voltage signal; the limiting operation can avoid excessive voltage signal drop leading to distortion in the adjustment of the reference voltage.

[0052] Reference Figure 3 After obtaining the corrected reference voltage, a voltage outer loop is constructed based on the corrected reference voltage. The voltage outer loop can use the output voltage of either the first or second conversion unit as the feedback voltage. In this embodiment, the output voltage of the first conversion unit is selected as the feedback voltage. The voltage deviation signal is obtained by subtracting the corrected reference voltage and the feedback voltage. After performing proportional-integral adjustment on the voltage deviation signal, the voltage outer loop output signal is obtained. The voltage outer loop output signal is used as the reference current to construct the current inner loop, that is, the voltage outer loop output signal is the current inner loop reference.

[0053] Reference Figure 3Since it includes two DC / DC conversion units, it also includes two current inner loops, which are labeled as the first current inner loop and the second current inner loop, respectively. Both use the output signal of the voltage outer loop as the reference current. The first current inner loop corresponds to the first conversion unit, and it uses the output current of the first conversion unit as the feedback current. The difference between the reference current and the feedback current is used to obtain the current deviation signal. After proportional-integral adjustment of the current deviation signal, the output signal of the current inner loop is obtained. Similarly, the second current inner loop corresponds to the second conversion unit, and it uses the output current of the second conversion unit as the feedback current.

[0054] After obtaining the two inner current loop output signals, PWM modulation is performed to obtain the corresponding drive signal, which is then used to control the operation of the corresponding DC / DC converter unit.

[0055] Secondly, with Figure 4 and Figure 5 The above method is illustrated using the example of the output terminals of the two DC / DC converter units in the battery module being connected in series.

[0056] Reference Figure 2 The negative output terminal of the first conversion unit in the battery module is connected to the positive output terminal of the second conversion unit. The positive output terminal of the first conversion unit serves as the positive terminal of the battery module, and the negative output terminal of the second conversion unit serves as the negative terminal of the battery module. The positive and negative terminals of the battery module are then connected to positive and negative buses, which are connected to a DC / DC converter. The output voltage is adjusted to the DC bus through the DC / DC converter.

[0057] Reference Figure 4 and Figure 5Since the output terminals of the two DC / DC converters within the battery module are connected in series, the first and second converters are controlled independently by two control loops. Therefore, the above-mentioned discharge equalization control method can be as follows: Based on the average output current of all battery modules, obtain a first current signal and a second current signal; compare the first current signal, the second current signal, and the output current of the corresponding DC / DC converter in the current battery module, and obtain a first resistance adjustment signal and a second resistance adjustment signal after proportional-integral adjustment; adjust a preset static resistance value based on the first resistance adjustment signal and the second resistance adjustment signal to obtain a first resistance signal and a second resistance signal; based on the first resistance signal, the second resistance signal, and the output current of the corresponding DC / DC converter in the current battery module, obtain a first voltage signal and a second voltage signal; adjust the reference voltage using the first voltage signal and the second voltage signal as references to obtain a first corrected reference voltage and a second corrected reference voltage; construct voltage outer loops based on the first corrected reference voltage and the second corrected reference voltage, and construct current inner loops using the output signals of the two voltage outer loops as reference currents; generate drive signals based on the output signals of the two current inner loops to control the operation of the corresponding DC / DC converters.

[0058] Specifically, the control of the first conversion unit will be used as an example for explanation. The control of the second conversion unit can be explained with reference to the explanation of the first conversion unit.

[0059] The output current of each first conversion unit can be acquired through CAN communication. The average output current of all first conversion units can be obtained through the battery management module (BMS) built into the battery system, which serves as the input information for the current signal generation unit in the generation control unit.

[0060] In this embodiment, the generation of the first current signal also references the SOC of the battery module. Specifically, the first current signal can be obtained by adjusting the ratio of the average SOC of all battery modules to the SOC of the current battery module based on the average output current of all battery modules. It should be noted that the average SOC of the battery modules and the SOC of the current battery module referred to here can be obtained from the power output information of the entire battery module or from the power output information of the cells within each battery module; no limitation is made here.

[0061] Specific reference Figure 4 The average output current of all first conversion units is used as the first input information, and the ratio of the average SOC of all battery modules to the SOC of the current module is used as the second input information. Multiplying these two values ​​yields the final first current signal. Alternatively, as a basic implementation, the first current signal can be generated without referring to the battery module SOC, i.e., it can be obtained directly based on the average output current of all battery modules.

[0062] Reference Figure 4 After obtaining the first current signal, the difference between the first current signal and the current output current of the current battery module is calculated to obtain a deviation signal. This deviation signal is then subjected to proportional-integral adjustment to obtain the first resistance adjustment signal. The current output current of the current battery module is the output current of the first conversion unit.

[0063] Reference Figure 4 After obtaining the first resistance adjustment signal, the preset static resistance value is adjusted based on the first resistance adjustment signal to obtain the first resistance signal. The first resistance signal is then multiplied by the current output current of the battery module to obtain the first voltage signal. Here, the current output current of the battery module is the output current of the first conversion unit. In this embodiment, the final first voltage signal is obtained by multiplying the first resistance signal by the current output current of the battery module. The first resistance signal obtained by adjusting the first resistance signal can more accurately reflect the virtual impedance in different lines, thus making the obtained voltage signal more accurate.

[0064] Reference Figure 4 After obtaining the first voltage signal, the difference between the reference voltage and the first voltage signal is calculated to obtain the first corrected reference voltage. In this embodiment, after obtaining the first voltage signal, the first voltage signal is further limited based on a preset voltage range to obtain a corrected voltage signal, and the final corrected reference voltage is obtained based on the corrected voltage signal; the limiting operation can prevent the first voltage signal from dropping excessively, which could lead to distortion in the adjustment of the reference voltage.

[0065] Reference Figure 4 After obtaining the first corrected reference voltage, a voltage outer loop is constructed based on the first corrected reference voltage, with the output voltage of the first conversion unit serving as the feedback voltage. The voltage deviation signal is obtained by subtracting the first corrected reference voltage from the feedback voltage. After performing proportional-integral adjustment on the voltage deviation signal, the voltage outer loop output signal is obtained. The voltage outer loop output signal is used as the reference current to construct a current inner loop, i.e., the voltage outer loop output signal serves as the current inner loop reference.

[0066] Reference Figure 4 The inner current loop uses the output current of the first conversion unit as the feedback current. The difference between the reference current and the feedback current is used to obtain the current deviation signal. This current deviation signal is then subjected to proportional-integral regulation to obtain the inner current loop output signal. After obtaining the inner current loop output signal, it is PWM modulated to obtain the corresponding drive signal, which controls the operation of the first conversion unit.

[0067] In the discharge equalization control method provided by this invention, a voltage signal is generated to adjust the reference voltage, and a voltage outer loop is constructed based on the adjusted reference voltage. Then, a dual-loop control strategy of the voltage outer loop and the current inner loop is used to generate a drive signal to control the operation of the DC / DC converter unit. This method effectively improves the current sharing response speed of the dual-loop control strategy, thereby improving the real-time output performance of battery modules integrated in parallel and increasing the utilization rate of the battery modules. The voltage signal is obtained based on the resistance signal and the current output current of the battery module. The resistance signal represents the virtual impedance in the DC / DC converter unit circuit. By increasing the virtual impedance, droop control of the DC / DC converter unit is achieved, eliminating the unbalanced impedance between the DC / DC converter units of different battery modules, thus... Power output is balanced; furthermore, since the virtual impedance does not add actual resistance to the line, it does not consume power; and since the battery module only needs to control the DC / DC converter unit according to the drive signal, the drive signal changes accordingly when battery modules are added or removed from the system cabinet, allowing the battery modules to still output appropriate power. Therefore, adding or removing battery modules in the system cabinet will not affect the discharge of any battery module that is already in operation, thus facilitating the expansion of the energy storage system and hot-swapping of battery modules. In addition, the resistance signal is obtained by adjusting the preset static resistance value through the resistance adjustment signal. After real-time adjustment of the static resistance value, the obtained voltage signal can more accurately reflect the virtual impedance in the line, and can also avoid the deviation from actual requirements when using only the static resistance value for droop control. Moreover, the resistance adjustment signal is obtained through the current signal and the current output current of the current battery module. The current signal can be obtained by establishing a communication link, which is more effective in real-time control and improves the current sharing response speed.

[0068] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. A discharge equalization control method, characterized in that: This is applied to a battery assembly, which includes several battery modules connected in parallel. Each battery module includes an energy storage unit and N DC / DC conversion units connected to the energy storage unit. The outputs of the N DC / DC conversion units are connected in parallel to connect to an electrical load. For each of the battery modules, the method includes: A current signal is obtained based on the average output current of all battery modules, wherein the average output current of all battery modules is the sum of the average output currents of the N DC / DC conversion units in all battery modules. The current signal is compared with the current output current of the current battery module, and after proportional-integral adjustment, the resistance adjustment signal is obtained. The current output current of the current battery module is the sum of the output currents of the N DC / DC conversion units in the current battery module. The preset static resistance value is adjusted based on the resistance adjustment signal to obtain a resistance signal, which is used to represent the virtual impedance in the current battery module circuit. The corrected reference voltage is obtained based on the resistance signal; A voltage outer loop is constructed based on a modified reference voltage, and a current inner loop is constructed using the output signal of the voltage outer loop as a reference current. The current inner loop includes N independent control loops. A drive signal is generated based on the output signal of each current inner loop to control the corresponding DC / DC converter unit.

2. The discharge equalization control method as described in claim 1, characterized in that, The voltage outer loop uses the output voltage of one of the DC / DC conversion units in the current battery module as the feedback voltage, and generates the voltage outer loop output signal after proportional-integral adjustment; each current inner loop uses the output current of the corresponding DC / DC conversion unit as the feedback current, and generates the current inner loop output signal after proportional-integral adjustment.

3. The discharge equalization control method as described in claim 1, characterized in that, The method of obtaining the corrected reference voltage based on the resistance signal specifically includes: obtaining a voltage signal based on the resistance signal and the current output current of the battery module; and adjusting the reference voltage with the voltage signal as a reference to obtain the corrected reference voltage.

4. The discharge equalization control method as described in claim 1, characterized in that, The current signal is obtained by adjusting the ratio of the average output current of all battery modules to the average SOC of all battery modules and the SOC of the current module.

5. The discharge equalization control method as described in claim 1, characterized in that, The resistance adjustment signal is obtained by subtracting the current signal from the current signal and the current output current of the battery module to obtain the deviation signal, and then performing proportional-integral adjustment on the deviation signal.

6. The discharge equalization control method as described in claim 1, characterized in that, The voltage signal is obtained by multiplying the resistance signal by the current output current of the battery module; The corrected reference voltage is obtained by subtracting the reference voltage from the voltage signal. The driving signal is obtained by PWM modulation of the current inner loop output signal.

7. The discharge equalization control method as described in claim 1, characterized in that, Based on a preset voltage range, the voltage signal is limited to obtain a corrected voltage signal, and the corrected reference voltage is obtained based on the corrected voltage signal.

8. A battery system, characterized in that, include: A battery assembly, comprising a plurality of parallel battery modules, each battery module comprising an energy storage unit, N DC / DC conversion units connected to the energy storage unit, and a control unit; The output terminals of N DC / DC converter units are connected in parallel to connect to electrical loads. The control unit includes: The current signal generation unit is adapted to obtain a current signal based on the average output current of all battery modules, wherein the average output current of all battery modules is the sum of the average output currents of the N DC / DC conversion units in all battery modules. The resistance signal generation unit is adapted to compare the current signal and the output current of the current battery module, obtain the resistance adjustment signal after proportional-integral adjustment, and adjust the preset static resistance value based on the resistance adjustment signal to obtain the resistance signal; wherein, the output current of the current battery module is the sum of the output currents of N DC / DC conversion units in the current battery module, and the resistance signal is used to represent the virtual impedance in the current battery module circuit; A voltage signal generation unit is adapted to obtain a voltage signal based on a resistance signal and the current output current of the battery module; The correction reference voltage generation unit is adapted to adjust the reference voltage using a voltage signal as a reference to obtain a correction reference voltage; The loop control unit is adapted to construct an outer voltage loop based on a modified reference voltage and to construct an inner current loop using the output signal of the outer voltage loop as a reference current; the inner current loop includes N independent control loops. The drive control unit is adapted to generate drive signals based on the output signal of each current inner loop to control the operation of the corresponding DC / DC conversion unit.

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