Battery equalization circuit and battery equalization method based on MMC module

Abstract

The application discloses a battery equalization circuit and method based on MMC module, wherein a single battery and an MMC module are connected in series to form an equalization unit, and a plurality of equalization units are connected in cascade to form an equalization module, wherein the equalization module and a subsequent voltage stabilization module can realize independent control of front and rear stages; in the charging and discharging process, the application compares the difference between the voltage variation of the single battery and the output value of the fuzzy controller to determine whether the single battery is connected to the circuit or bypassed, so that the electric quantity of the single battery in the battery pack is kept consistent; the application also compares the output voltage with the required voltage to determine whether the voltage stabilization circuit needs to be started, so as to ensure that the output voltage of the whole battery pack is kept stable in the equalization process. The application has the fault removal function, can reduce the energy loss in the battery equalization process, improve the battery equalization speed and energy transfer efficiency, and can solve the pseudo equalization problem caused by the battery aging.

Description

Technical Field

[0001] This invention relates to the field of battery management technology, and in particular to a battery balancing circuit and battery balancing method based on an MMC module. Background Technology

[0002] To meet the high voltage or high power requirements of electric vehicles, a large number of individual battery cells need to be connected in series and parallel to form battery packs. Due to differences in manufacturing processes and usage environments, inconsistencies in the parameters of individual battery cells will gradually accumulate with repeated charging and discharging, leading to a decrease in the usable capacity of the battery pack, a shorter cycle life, and potential safety issues due to overcharging and over-discharging. Therefore, battery balancing circuits are needed to perform battery balancing.

[0003] However, in related technologies, the battery equalization circuit and the voltage regulation circuit must work simultaneously, and energy transfer is usually carried out using inductors, capacitors and a large number of switching devices. This process inevitably results in significant energy loss, and also causes the equalizer to be bulky and costly. Furthermore, the equalization current of the equalization circuit is limited by the maximum current allowed by the battery, resulting in a slow equalization speed. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the first objective of this invention is to provide a battery balancing circuit based on an MMC module, which, while addressing the issues of reduced usable battery pack capacity and shortened cycle life caused by battery inconsistency, reduces energy loss during battery balancing, improves battery balancing speed and energy transfer efficiency, and resolves the pseudo-balancing problem caused by battery aging.

[0005] The second objective of this invention is to provide a battery balancing method based on an MMC module.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] A battery balancing circuit based on an MMC module includes:

[0008] The equalization module includes multiple cascaded equalization units. Each equalization unit includes a single battery cell and an MMC module. The MMC module includes a first switch located in the upper bridge arm and a second switch located in the lower bridge arm. The single battery cell is connected in series with the MMC module. The negative terminal of the single battery cell in each equalization unit is connected to the connection point of the upper and lower bridge arms of the MMC module in the next equalization unit. The connection point of the upper and lower bridge arms of the MMC module in the first equalization unit is led out as the positive terminal of the equalization module. The negative terminal of the single battery cell in the last equalization unit is used as the negative terminal of the equalization module. The equalization module is used to control the switch in the MMC module to connect or bypass the corresponding single battery cell to the circuit in order to equalize the single battery cell.

[0009] A voltage regulator module is connected to the equalization module, and the voltage regulator module is used to regulate the output voltage of the battery pack composed of individual cells.

[0010] Optionally, the first and second switches in the MMC module are connected in reverse series, and both the first and second switches are MOSFET switching devices.

[0011] Optionally, the first switch and the second switch can be independently controlled by two trigger pulses.

[0012] Optionally, the voltage regulator module includes a main switch, one end of which is connected to the positive terminal of the equalization module, and the other end of which serves as the positive terminal of the voltage regulator module. The battery equalization circuit achieves independent control of the equalization module and the voltage regulator module through the main switch.

[0013] Optionally, the voltage regulator module further includes a first switch, a second switch, an inductor, a capacitor, and a diode. The first switch is a single-pole double-throw switch. The first terminal of the single-pole double-throw switch is connected to the positive terminal of the equalization module. The second terminal of the single-pole double-throw switch is connected to the cathode of the diode. The third terminal of the single-pole double-throw switch is connected to the first terminal of the inductor. The second terminals of the inductor and the capacitor are both connected to the negative terminal of the equalization module and serve as the negative terminal of the voltage regulator module. The anode of the diode is connected to the second terminal of the second switch and the first terminal of the capacitor, respectively. The first terminal of the second switch is connected to the other end of the main switch transistor. The second switch is normally closed.

[0014] Optionally, the voltage regulator module starts when the main switch is turned off, and shuts down when the main switch is turned on.

[0015] To achieve the above objectives, a second aspect of the present invention provides a battery balancing method based on an MMC module, applied to the battery balancing circuit described above, comprising:

[0016] Step S1: Detect the voltage of each individual cell and calculate the voltage difference between adjacent sampling times for each individual cell;

[0017] Step S2: Sort the voltage differences of each individual cell to determine the maximum and minimum voltage differences;

[0018] Step S3: Calculate the difference between the maximum and minimum voltage difference to obtain the maximum voltage difference value;

[0019] Step S4: Determine whether the voltage difference between each individual cell is greater than zero. When the voltage difference between each individual cell is greater than zero, use the terminal voltage of the individual cell corresponding to the maximum voltage difference as the input voltage of the charging fuzzy controller. When the voltage difference between each individual cell is less than zero, use the terminal voltage of the individual cell corresponding to the maximum voltage difference as the input voltage of the discharging fuzzy controller, and obtain the output value of the corresponding fuzzy controller.

[0020] Step S5: Calculate the difference between the voltage difference of each individual cell and the minimum voltage difference. When the difference between the voltage difference of each individual cell and the minimum voltage difference is greater than the output value, the corresponding individual cell is bypassed until the battery equalization process ends.

[0021] Optionally, in step S5, the corresponding single battery cell is bypassed, including: driving the first switch in the MMC module connected to the corresponding single battery cell to disconnect and the second switch to close, so that the single battery cell is bypassed.

[0022] Optionally, before step S4, the method further includes constructing the charging fuzzy controller and the discharging fuzzy controller. The steps of constructing the charging fuzzy controller and the discharging fuzzy controller include: determining the capacity change accuracy required for battery equalization; obtaining aging test data of the single cell model used, and extracting the voltage change difference from the aging test data according to the capacity change accuracy; and constructing the charging fuzzy controller and the discharging fuzzy controller with the single cell terminal voltage as input and the voltage change difference as output.

[0023] Optionally, the battery balancing method further includes: when the battery balancing process is started, the main switch in the voltage regulator module is simultaneously turned off to start the voltage regulation process, until the voltage difference between the battery pack output voltage and the preset voltage is less than a preset threshold after the battery balancing process is completed, then the main switch is controlled to close to end the voltage regulation process.

[0024] Compared with the prior art, the present invention has at least the following technical effects:

[0025] 1. Traditional equalization circuits and voltage regulation circuits must work simultaneously, and usually use inductors, capacitors and a large number of switching devices for energy transfer. This process inevitably results in significant energy loss and causes the equalizer to be bulky and costly. However, the battery equalization circuit provided by this invention does not require energy transfer during the equalization process, and the front and rear circuits can be controlled independently, thereby further reducing energy loss and solving the problems of bulky size and high cost to a certain extent.

[0026] 2. The balancing current of traditional circuits is limited by the maximum allowable current of the battery, that is, the sum of the battery operating current and the balancing current cannot exceed the maximum allowable current specified by the battery. However, the battery balancing circuit based on MMC of the present invention essentially changes the connection structure of the battery, so that it does not contain additional balancing devices, thereby making the balancing current the same as the charging and discharging current of the battery. As a result, the balancing current of the battery balancing circuit of the present invention is greater than the balancing current of the traditional balancing topology, which facilitates the improvement of balancing speed.

[0027] 3. The battery balancing circuit based on MMC of the present invention has a redundancy mechanism, thereby having a fault clearing function, which greatly increases the safety and reliability of the battery pack.

[0028] 4. The MMC-based battery balancing method of the present invention can overcome the pseudo-balancing phenomenon caused by battery aging by eliminating the influence of battery ohmic internal resistance and polarization internal resistance.

[0029] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the battery balancing circuit structure based on the MMC module according to an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram of the working principle of the battery balancing circuit based on the MMC module according to an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram of the equalization module circuit structure according to an embodiment of the present invention.

[0033] Figures 4(a)-4(b) This is a schematic diagram illustrating the working principle of the voltage regulator module in the first and second stages according to an embodiment of the present invention.

[0034] Figure 5 This is a flowchart of a battery balancing method based on an MMC module according to an embodiment of the present invention.

[0035] Figure 6 This is a flowchart illustrating the specific workflow of the battery balancing method based on the MMC module according to an embodiment of the present invention. Detailed Implementation

[0036] The following describes this embodiment in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0037] The following description, with reference to the accompanying drawings, illustrates a battery balancing circuit and battery balancing method based on an MMC module.

[0038] Figure 1 This is a schematic diagram of the battery balancing circuit structure based on the MMC module according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the working principle of the battery balancing circuit based on the MMC module according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the equalization module circuit structure according to an embodiment of the present invention.

[0039] like Figure 1-3 As shown, the battery balancing circuit includes an balancing module, which comprises multiple cascaded balancing units. Each balancing unit includes a single battery cell and an MMC (Modular Multilevel Converter) module, with the single battery cell connected in series with the MMC module. The MMC module includes a first switch located on the upper bridge arm and a second switch located on the lower bridge arm. The first and second switches are connected in reverse series. Both the first and second switches are MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) switching devices, and the first and second switches can be independently controlled by two trigger pulses.

[0040] For example, the first equalization unit includes a single cell B1 and an MMC module consisting of a first switch MS1 located on the upper bridge arm and a second switch MX1 located on the lower bridge arm; the nth equalization unit includes a single cell Bn and an MMC module consisting of a first switch MSn located on the upper bridge arm and a second switch MXn located on the lower bridge arm.

[0041] Furthermore, the negative terminal of the individual battery in each equalization unit is connected to the connection point of the upper and lower bridge arms of the MMC module in the next adjacent equalization unit. The connection point of the upper and lower bridge arms of the MMC module in the first equalization unit is led out as the positive terminal of the equalization module, and the negative terminal of the individual battery (Bn) in the last equalization unit is used as the negative terminal of the equalization module. The equalization module is used to control the switching transistors (upper and lower bridge arm switching transistors) in the MMC module to connect the corresponding individual battery to the circuit or bypass it, so that the individual battery is in a static state or a charging (discharging) state, thereby achieving the same remaining power of each individual battery and thus achieving individual battery equalization.

[0042] like Figure 1-2 As shown, the battery balancing circuit also includes a voltage regulator module connected to the balancing module. The voltage regulator module is used to regulate the output voltage of the battery pack composed of individual cells. The voltage regulator module includes a main switch M, one end of which is connected to the positive terminal of the balancing module, and the other end of which serves as the positive terminal of the voltage regulator module. The battery balancing circuit can achieve independent control of the balancing module and the voltage regulator module through the main switch M.

[0043] Furthermore, the voltage regulator module also includes a first switch S0, a second switch S, an inductor L, a capacitor C, and a diode D. The first switch S0 is a single-pole double-throw switch. The first terminal (1) of the single-pole double-throw switch is connected to the positive terminal of the equalization module. The second terminal (2) of the single-pole double-throw switch is connected to the cathode of the diode D. The third terminal (3) of the single-pole double-throw switch is connected to the first terminal of the inductor L. The second terminals of the inductor L and the second terminals of the capacitor C are both connected to the negative terminal of the equalization module (Bn), and serve as the negative terminal of the voltage regulator module. The anode of the diode D is connected to the second terminal of the second switch S and the first terminal of the capacitor C, respectively. The first terminal of the second switch S is connected to the other terminal of the main switch M. The second switch S is normally closed.

[0044] When the main switch M is open, the voltage regulator module starts; when the main switch M is closed, the voltage regulator module shuts down. When the main switch M is open, i.e., when the voltage regulator module is started, its operation can be divided into the following two stages:

[0045] Phase 1 P1: The second switch S remains closed, and the operation of the voltage regulator circuit is controlled by the first switch S0. The two operating processes within one cycle are as follows: Figure 4(a) and 4(b) As shown in Figure 4(a), when the first switch S0 is at terminal 1, the first switch S0 is in the on state, and the power supply E supplies power to the inductor L through the first switch S0, so that it stores energy, in the direction shown in Figure 4(a). At the same time, the capacitor C maintains the output voltage basically constant and supplies power to the load R.

[0046] In the second stage P2, the first switch S0 is turned on at terminal 2. The energy stored in the inductor L is released to the load R and the capacitor C through the second switch S and the diode D, respectively. At this time, the energy stored in the capacitor C will supply power to the load R in the first stage, realizing the continuity of the current. The direction is shown in Figure 4(b). It can be seen that the polarity of the load R voltage is negative at the top and positive at the bottom, which is opposite to the polarity of the power supply voltage.

[0047] It should be noted that by changing the duty cycle of the second switch S and the first switch S0, the output voltage of the voltage regulator module can be either higher or lower than the power supply voltage, thereby achieving voltage regulation output of the circuit.

[0048] In this embodiment, an improvement is made to the traditional voltage regulator circuit. Figure 1-2 The improved voltage regulator circuit shown in the medium voltage regulator module, in this embodiment, achieves independent control of the front and rear stages of the entire battery equalization circuit by adding a main switch transistor M to the main voltage regulator circuit. That is, by controlling the opening and closing of the main switch transistor M, the start-up of the voltage regulator module can be controlled, which can reduce the loss in the battery equalization process. In addition, by controlling the duty cycle of the second switch S and the first switch S0, the circuit can achieve regulated output.

[0049] Figure 5 This is a flowchart of a battery balancing method based on an MMC module according to an embodiment of the present invention. Figure 5 As shown, the battery balancing method includes:

[0050] Step S1: Detect the voltage of each individual cell and calculate the voltage difference between adjacent sampling times for each individual cell.

[0051] Step S2: Sort the voltage differences of each individual cell to determine the maximum and minimum voltage differences.

[0052] Step S3: Calculate the difference between the maximum and minimum voltage difference to obtain the maximum voltage difference value.

[0053] Step S4: Determine whether the voltage difference between each individual cell is greater than zero. When the voltage difference between each individual cell is greater than zero, use the terminal voltage of the individual cell corresponding to the maximum voltage difference as the input voltage of the charging fuzzy controller. When the voltage difference between each individual cell is less than zero, use the terminal voltage of the individual cell corresponding to the maximum voltage difference as the input voltage of the discharging fuzzy controller, and obtain the output value of the corresponding fuzzy controller.

[0054] Step S5: Calculate the difference between the voltage difference of each individual cell and the minimum voltage difference. When the difference between the voltage difference of an individual cell and the minimum voltage difference is greater than the output value, the corresponding individual cell is bypassed until the battery equalization process ends.

[0055] In step S5, the corresponding single battery cell is bypassed, including: driving the first switch in the MMC module connected to the corresponding single battery cell to turn off and the second switch to turn on, so that the single battery cell is bypassed.

[0056] It should be noted that before step S4, the battery balancing method further includes constructing a charging fuzzy controller and a discharging fuzzy controller. The steps of constructing the charging fuzzy controller and the discharging fuzzy controller include: determining the capacity change accuracy required for battery balancing; obtaining aging test data of the single cell model used, and extracting the voltage change difference from the aging test data according to the capacity change accuracy; and constructing the charging fuzzy controller and the discharging fuzzy controller with the single cell terminal voltage as input and the voltage change difference as output.

[0057] Figure 6 This is a flowchart illustrating the specific workflow of the battery balancing method based on the MMC module according to an embodiment of the present invention. The following is a detailed explanation... Figure 5 and Figure 6 The battery balancing method based on the MMC module in this embodiment will be described in detail. Before the description, it should be noted that when the balancing function is not enabled, the upper arm switches of the MMC module are all in the closed state, while the lower arm switches are all in the open state.

[0058] The battery balancing method specifically includes:

[0059] Step S100: Determine the capacity change accuracy required for battery equalization, where the capacity change accuracy represents the accuracy parameter of battery capacity consistency.

[0060] Step S101: Obtain aging test data for the model of the single cell used, and extract the voltage change difference from the aging test data based on the capacity change accuracy.

[0061] Step S102: Using the terminal voltage of a single battery cell as input and the voltage change difference as output, construct a charging fuzzy controller and a discharging fuzzy controller, thereby completing the design of the charging fuzzy controller and the discharging fuzzy controller in advance.

[0062] Step S103: Through Figure 2 The battery status acquisition device measures the voltage u of each individual battery cell.

[0063] Step S104: Calculate the voltage difference Δu between adjacent sampling times of each individual cell, where Δu i =u i (t)-u i (t-1), where Δu i Let u be the voltage difference between adjacent sampling times of the i-th individual cell. i (t) represents the terminal voltage of the i-th individual cell at the current time, ui (t-1) represents the terminal voltage of the i-th cell at the previous moment, t represents the current time, and t-1 represents the time of the previous moment.

[0064] Step S105: Sort the voltage differences of each individual cell, i.e., the calculated Δu, and obtain Δu max >……>Δu min , where Δu max The maximum voltage difference, Δu min This represents the minimum voltage difference.

[0065] Step S106: Calculate Δu max With Δu min The difference is obtained to obtain the maximum value of the pressure difference ΔU difmax Alternatively, first calculate the absolute value of the voltage difference between each individual cell, |Δu dif |, that is, the absolute value of the difference in voltage change between each battery |Δu dif | and then obtain the maximum pressure difference ΔU from it. difmax .

[0066] Step S107: Determine whether the voltage difference Δu between each individual cell is greater than zero. If it is greater than zero, it indicates that the charging process is underway, and ΔU is... difmax The corresponding terminal voltage u of the single cell Bi i As the input voltage of the charging fuzzy controller, the output value DOVV of the charging fuzzy controller is obtained at this time, and then the formula ΔU is used. diff =Δu i -Δu min Calculate the difference between the voltage difference of each individual cell and the minimum voltage difference, where ΔU diff Let ΔU be the difference between the voltage difference of the i-th individual cell and the minimum voltage difference, then... diff Compare with the output value DOVV, and if it is greater than the output value DOVV, then... Figure 2 The drive signal generator outputs a drive signal to control the ΔU. diff In the MMC module connected to the corresponding single cell Bi, the upper arm switch (first switch) is turned off, and the lower arm switch (second switch) is turned on to bypass the corresponding single cell Bi until the battery equalization process is complete. If ΔU diff If the value is less than the output value DOVV, then proceed directly to the next sampling process.

[0067] If Δu is less than 0, it indicates that the discharge process is underway, and ΔU will be... difmax The corresponding terminal voltage u of the single cell Bj j As the input voltage of the discharge fuzzy controller, the output value DOVV of the discharge fuzzy controller is obtained at this time, and then the value is calculated using the formula ΔU.diff =Δu i -Δu min Calculate the difference between the voltage difference of each individual cell and the minimum voltage difference, then convert ΔU to... diff Compare with the output value DOVV, and if it is greater than the output value DOVV, then... Figure 2 The drive signal generator outputs a drive signal to control the ΔU. diff In the MMC module connected to the corresponding single cell Bj, the upper arm switch (first switch) is turned off, and the lower arm switch (second switch) is turned on to bypass the corresponding single cell Bj until the battery equalization process is completed. If ΔU diff If the value is less than the output value DOVV, then proceed directly to the next sampling process.

[0068] Meanwhile, when the battery equalization process is started, the main switch M in the voltage regulator module can be turned off to start the voltage regulation process. The voltage regulation process continues until the voltage difference between the battery pack output voltage and the preset voltage is less than the preset threshold after the equalization process is completed. Then, the main switch M is controlled to close to end the voltage regulation process. The voltage regulation process has two stages as described above, namely stages P1 and P2.

[0069] It should be noted that the advantages of the battery balancing circuit in this embodiment are mainly reflected in:

[0070] (1) Traditional equalization circuits and voltage regulation circuits must work simultaneously, and usually use inductors, capacitors and a large number of switching devices for energy transfer. This process inevitably results in large energy loss and causes the equalizer to be bulky and costly. However, the battery equalization circuit provided by this invention does not require energy transfer during the equalization process, and the front and rear circuits can be controlled independently, thereby further reducing energy loss and solving the problems of bulky size and high cost to a certain extent.

[0071] (2) The equalization current of the traditional circuit is limited by the maximum allowable current of the battery, that is, the sum of the battery working current and the equalization current cannot exceed the maximum allowable current specified by the battery. However, the battery equalization circuit based on MMC of the present invention essentially changes the connection structure of the battery, so that it does not contain additional equalization devices, thereby making the equalization current the same as the charging and discharging current of the battery. As a result, the equalization current of the battery equalization circuit of the present invention is greater than the equalization current of the traditional equalization topology, which facilitates the improvement of equalization speed.

[0072] (3) The battery balancing circuit based on MMC in this embodiment has a redundancy mechanism, which has a fault clearing function, greatly increasing the safety and reliability of the battery pack.

[0073] The advantages of the battery balancing method in this embodiment are mainly reflected in:

[0074] The pseudo-equilibrium phenomenon caused by battery aging can be overcome by eliminating the influence of the battery's ohmic internal resistance and polarization internal resistance. The verification principle is as follows:

[0075] First, the relationship between terminal voltage and open-circuit voltage is as follows:

[0076] U o =U OCV +U R +U P (1)

[0077] Among them, U o U represents the terminal voltage. OCV U represents the open-circuit voltage. R U represents the ohmic voltage, which is the voltage across the battery's internal ohmic resistance. P This represents the polarization voltage.

[0078] The ohmic voltage changes over time as follows:

[0079] U R =IR+ΔU R (2)

[0080] In the formula, ΔU R The voltage change is caused by the battery's internal resistance as the battery ages, where I represents the current flowing through the battery's internal resistance and R represents the battery's internal resistance.

[0081] The polarization voltage changes with time as follows:

[0082] U P =U P0 +ΔU P (3)

[0083] In the formula, ΔU P U represents the voltage change caused by the polarization internal resistance as the battery ages. P0 This represents the initial value of the polarization voltage.

[0084] Since the sampling time interval is very small, we assume that the voltage changes of the ohmic voltage and polarization voltage are the same at adjacent sampling times under ideal conditions. Then, the terminal voltage change of the same single cell can be derived from formula (1):

[0085] ΔU O =U O (t n )-U o (t n-1 )=ΔU OCV (4)

[0086] In the formula, ΔU O U represents the change in terminal voltage of a single cell. O (t nU represents the current terminal voltage of a single cell. o (t n-1 ) represents the terminal voltage of a single cell at the previous moment, t n t represents the current time. n-1 Let ΔU be the time of the previous moment, n represent the nth individual cell, and ΔU be the time of the previous moment. OCV This represents the change in open-circuit voltage of a single cell.

[0087] Therefore, the difference in voltage change between different individual cells is:

[0088] ΔU dif =ΔU ocvi -ΔU ocvj (5)

[0089] In the formula, ΔU dif ΔU represents the difference in voltage change between different individual cells. ocvi Let ΔU be the change in open-circuit voltage of the i-th cell. ocvj Let be the change in open-circuit voltage of the j-th individual cell.

[0090] Therefore, the open-circuit voltage U OCV Only related to the change in terminal voltage ΔU O It is related to the ohmic voltage and polarization voltage, so the difference in voltage change is used as the equilibrium variable to overcome the influence of battery aging on the ohmic internal resistance and polarization internal resistance, thereby overcoming the pseudo-equilibrium phenomenon caused by the ohmic internal resistance and polarization internal resistance.

[0091] In summary, the present invention, through the aforementioned battery balancing circuit structure and battery balancing strategy, can significantly improve the energy transfer efficiency and balancing speed of the entire balancing system, and significantly improve the pseudo-balancing phenomenon caused by battery aging.

[0092] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0093] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A battery balancing method based on an MMC module, wherein the battery balancing method is applied to a battery balancing circuit, the battery balancing circuit comprising: The equalization module includes multiple cascaded equalization units. Each equalization unit includes a single battery cell and an MMC module. The MMC module includes a first switch located in the upper bridge arm and a second switch located in the lower bridge arm. The single battery cell is connected in series with the MMC module. The negative terminal of the single battery cell in each equalization unit is connected to the connection point of the upper and lower bridge arms of the MMC module in the next equalization unit. The connection point of the upper and lower bridge arms of the MMC module in the first equalization unit is led out as the positive terminal of the equalization module. The negative terminal of the single battery cell in the last equalization unit is used as the negative terminal of the equalization module. The equalization module is used to control the switch in the MMC module to connect or bypass the corresponding single battery cell to the circuit in order to equalize the single battery cell. A voltage regulator module is connected to the equalization module, and the voltage regulator module is used to regulate the output voltage of the battery pack composed of individual cells. The battery balancing method is characterized by comprising: Step S1: Detect the voltage of each individual cell and calculate the voltage difference between adjacent sampling times for each individual cell; Step S2: Sort the voltage differences of each individual cell to determine the maximum and minimum voltage differences; Step S3: Calculate the difference between the maximum and minimum voltage difference to obtain the maximum voltage difference value; Step S4: Determine whether the voltage difference between each individual cell is greater than zero. When the voltage difference between each individual cell is greater than zero, use the terminal voltage of the individual cell corresponding to the maximum voltage difference as the input voltage of the charging fuzzy controller. When the voltage difference between each individual cell is less than zero, use the terminal voltage of the individual cell corresponding to the maximum voltage difference as the input voltage of the discharging fuzzy controller, and obtain the output value of the corresponding fuzzy controller. The individual cell corresponding to the maximum voltage difference is the same as the individual cell corresponding to the maximum voltage difference. Step S5: Calculate the difference between the voltage difference of each individual cell and the minimum voltage difference. When the difference between the voltage difference of each individual cell and the minimum voltage difference is greater than the output value, the corresponding individual cell is bypassed until the battery equalization process ends.

2. The battery balancing method based on an MMC module as described in claim 1, characterized in that, In step S5, the corresponding single battery cell is bypassed, including: driving the first switch in the MMC module connected to the corresponding single battery cell to disconnect and the second switch to close, so that the single battery cell is bypassed.

3. The battery balancing method based on an MMC module as described in claim 1, characterized in that, Before step S4, the method further includes constructing the charging fuzzy controller and the discharging fuzzy controller. The steps of constructing the charging fuzzy controller and the discharging fuzzy controller include: Determine the required accuracy of capacity change for battery equalization; Acquire aging test data for the model of the single cell used, and extract the voltage change difference from the aging test data based on the capacity change accuracy. The charging fuzzy controller and the discharging fuzzy controller are constructed using the terminal voltage of a single battery cell as input and the voltage change difference as output.

4. The battery balancing method based on an MMC module as described in claim 1, characterized in that, Also includes: When the battery balancing process is started, the main switch in the synchronous control voltage regulator module is turned off to start the voltage regulation process. The voltage regulation process continues until the voltage difference between the battery pack output voltage and the preset voltage is less than the preset threshold after the battery balancing process is completed. Then, the main switch is controlled to close to end the voltage regulation process.

5. The battery balancing method based on an MMC module as described in claim 1, characterized in that, The first and second switches in the MMC module are connected in reverse series, and both the first and second switches are MOSFET switching devices.

6. The battery balancing method based on an MMC module as described in claim 1, characterized in that, The first and second switching transistors are independently controlled by two trigger pulses.

7. The battery balancing method based on an MMC module as described in claim 1, characterized in that, The voltage regulator module includes a main switch transistor. One end of the main switch transistor is connected to the positive terminal of the equalization module, and the other end of the main switch transistor serves as the positive terminal of the voltage regulator module. The battery equalization circuit achieves independent control of the equalization module and the voltage regulator module through the main switch transistor.

8. The battery balancing method based on an MMC module as described in claim 7, characterized in that, The voltage regulator module further includes a first switch, a second switch, an inductor, a capacitor, and a diode. The first switch is a single-pole double-throw switch. The first terminal of the single-pole double-throw switch is connected to the positive terminal of the equalization module. The second terminal of the single-pole double-throw switch is connected to the cathode of the diode. The third terminal of the single-pole double-throw switch is connected to the first terminal of the inductor. The second terminals of the inductor and the capacitor are both connected to the negative terminal of the equalization module and serve as the negative terminal of the voltage regulator module. The anode of the diode is connected to the second terminal of the second switch and the first terminal of the capacitor, respectively. The first terminal of the second switch is connected to the other end of the main switch transistor. The second switch is normally closed.

9. The battery balancing method based on an MMC module as described in claim 8, characterized in that, When the main switch is turned off, the voltage regulator module starts; when the main switch is turned on, the voltage regulator module turns off.

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