Control circuit and module for performing active equalization on battery by using unit transformer

Abstract

The utility model discloses a control circuit and module for performing active equalization on a battery by using a unit transformer, in the control circuit, a main control unit is connected with a driving unit to control the on-off states of a first switch, a second switch, a first double-pole-double-throw switch, a second double-pole-double-throw switch and a third double-pole-double-throw switch; energy is transferred to a magnetic core in a unit transformer correspondingly connected with a battery pack where a bottom equalization battery cell is located so as to realize bottom equalization; according to the invention, energy is transferred to the transition secondary winding in the unit transformer correspondingly connected with the battery pack with the lowest average voltage in the i battery packs, so that the first switch corresponding to the battery pack with the lowest average voltage in the i battery packs is controlled to be switched on to discharge magnetism to realize top equalization; the active equalization technology of the high-voltage battery system is realized by adopting a unit transformer and a transition transformer aiming at the problem that the high-voltage battery system cannot be matched with a large magnetic core.

Description

Technical Field

[0001] The utility model relates to the technical field of realizing battery balancing control by using a transformer, and in particular to a control circuit and a module for actively balancing batteries by using a unit transformer. Background Art

[0002] With the development of modern science and technology, batteries as an energy storage device have been widely used in electric motorcycles, electric scooters and home storage systems. The main technical implementation of battery energy storage devices is to connect multiple storage cells in series to obtain a cell string to meet the system voltage requirements, and then connect multiple cell strings in parallel to achieve the required ampere-hour power.

[0003] Due to the limitation of production process, there are individual differences between battery cells, which are specifically manifested in the incomplete consistency of capacity and voltage. If the voltage exceeds the allowable range, the battery cell will be easily damaged. Furthermore, if the voltage exceeds the upper and lower limits (taking nanophosphate lithium-ion batteries as an example, the lower limit voltage is 2V and the upper limit voltage is 3.6V), the battery may be irreversibly damaged. At least one consequence is that the battery self-discharge rate is accelerated. In addition, as the number of charge and discharge times of multiple battery cells connected in series increases, the voltage difference between them will become more obvious. If effective measures are not taken to solve the problem of consistency, the storage capacity of the battery energy storage device will be affected at the least, and the damage to the battery cell will be caused at the worst, and even safety accidents such as explosions will be caused.

[0004] As a result, the "balancing technology" in the battery management system (BMS) has been vigorously developed. Battery balancing technology is divided into two categories: passive balancing and active balancing. In the charging scenario, assuming that the Nth battery cell reaches the upper limit of the operating voltage first, and the remaining battery cells are expected to continue to maintain the current charging current, it is necessary to connect a branch in parallel to the Nth battery cell to divert part of the energy. If the diverted energy is dissipated through resistance heat dissipation, it is defined as passive balancing. If the diverted energy can be stored and utilized again through transfer, it is defined as active balancing. The diversity of active balancing schemes lies in how to control these energy transfers.

[0005] Active balancing technology is divided into many categories. Common energy transfer methods in general circuits include: inductors, capacitors, transformers, converters (Buck / Boost, etc.), and the use of transformers to achieve energy transfer is a common technical route in the current active balancing solution. Among them, the technology that uses a multi-winding transformer and can manage the charge and discharge balance of a single battery cell is commonly used in bottom balancing and top balancing. When the bottom balancing strategy (Bottom balancing) is used in the discharge mode, the BMS identifies the battery cell with lower capacity, controls the primary side of the transformer to conduct, and transfers energy from the outside to the battery cell; when the top balancing strategy (Top balancing) is generally used in the charging mode, the BMS identifies the battery cell with higher capacity, controls the secondary side of the transformer to conduct, and transfers energy from the battery cell to the outside. The reason why different modes are adopted in charging and discharging is that during the system discharge process, if the voltage of a certain battery cell is too low, the entire system will enter the discharge low-voltage cut-off protection early. Therefore, bottom balancing is adopted to continuously charge the battery cell with too low voltage with the energy of the entire system (including all batteries) to increase the voltage of the battery cell with low voltage, so that the balanced system will not terminate the discharge early due to the battery cell with low voltage, wasting the power in other batteries that can continue to discharge, resulting in loss of the endurance of the battery energy storage device; conversely, during the system charging process, if the voltage of a certain battery cell is too high, the entire system will enter the charge overvoltage cut-off protection early. Therefore, top balancing is adopted to continuously extract the energy of the battery cell with high voltage to charge the entire system (including all batteries) to reduce the voltage of the battery cell with high voltage, so that the balanced system will not terminate the charging early due to the battery cell with high voltage, while other batteries are not fully charged at this time, resulting in a reduction in the overall battery capacity. For example, a Chinese patent application (CN20171064064.1) proposes an active balancing circuit to achieve bottom balancing of the battery cell when it is discharging or at rest and top balancing of the battery cell when it is charging or at rest. The active balancing circuit of this application is based on the above two different balancing modes, namely the bottom balancing mode and the top balancing mode, to avoid over-discharge and over-charge of the battery cell. A high-efficiency balancing technology is achieved through the clever coordination of two switching units. By adopting a building block design approach for multiple balancing function boards, the active balancing circuit can adapt to the requirements of different battery cells being connected in series, greatly improving flexibility.

[0006] For example, the Chinese patent application CN113872288 claims transformer balancing and CUK converter (Cuk converter is a single-tube non-isolated DC converter proposed by Slobodan Cuk of California Institute of Technology to improve Buck / Boost) balancing is an active balancing achieved by energy transfer. There is almost no energy loss during the balancing process, which greatly improves the efficiency and energy utilization of battery balancing. The method is to divide the total number of series cells N into N / 4 CUK battery groups that are multiples of 4, and take three steps to perform active balancing: Step 1) Use a transformer to complete the balancing between each battery group and the entire battery module. When the voltage of a battery group of 4 cells is higher, the energy of the battery group is transferred to the entire battery module. Conversely, when the voltage of a battery group of 4 cells is lower, the energy is transferred from the entire battery module to the battery group of the 4 cells. The first problem arises. There are 2 cells with the highest voltage and 2 cells with the lowest voltage among the 4 cells. As a result, the average voltage of the 4 cells is not too high or too low. Even if the software is used to force There is no way to adjust the single battery cell when charging the entire battery module from a certain battery pack, or from the entire battery module to a certain battery pack. If 4 high-voltage and low-voltage battery cells are in the same battery pack, then while the energy is delivered to the entire battery module based on the high voltage of a single battery cell in the battery pack, the energy of the single battery cell with too low voltage is also delivered to the entire battery module. Conversely, because the voltage of a single battery cell in the battery pack of 4 cells is too low, the entire battery module is forced to deliver energy to the battery pack of 4 cells, which will forcibly pour energy into the single battery cell with too high voltage, causing great problems for this battery grouping. The second problem is the efficiency difference. Even if energy is transferred from one battery pack to another, the energy is not actually transferred to a single battery cell. The solution has to use step 2 to further divide the battery pack into the first battery unit and the second battery unit, and then use CUK to balance the two battery units in the same battery pack. In addition to the extremely poor efficiency, it wastes the porters and generates unnecessary energy loss. If the two cells in the same battery unit are also one high and one low, the same problem as the high and low in the previous four cells will occur. When energy is transferred to a battery unit with two cells, one of which is high and the other is low, then the cell with the higher voltage will be mistakenly charged, and the cell that is originally too high in voltage and should be discharged will be charged, which will cause more imbalance, and if overcharging occurs, it will cause danger to the battery module.For this reason, the scheme also uses capacitors and inductors to make non-controllable. The two cells in the same battery unit use the so-called "bidirectional energy flow" of inductors and capacitors, that is, the energy distribution is left to nature, which can reduce the risk of overcharging the cell with too high voltage to a certain extent. However, because the cell with lower voltage in the two cells in the same battery unit is switched, the other cell with too high voltage is also charged first when it is just switched, and then the inductors and capacitors are slowly used to balance the two, which reduces the risk of overcharging to a certain extent, but it is still overcharged at the moment of switching. In order to further avoid the above risks, the scheme uses passive balancing in the last step 3. In the battery unit composed of two battery cells (which we call a single cell), passive balancing is used again to convert the battery cell with too high voltage into heat energy on the fixed resistor using a fixed resistor to achieve a balancing effect.

[0007] In the above existing solution, in step 1, a battery pack consisting of 4 cells is used, which makes it impossible to correctly judge whether a single cell is too high or too low, and the transfer of energy from the battery pack to the entire battery module will make the voltage of the cell with too low voltage even lower, or the transfer of energy from the entire battery module to a battery pack will make the voltage of the cell with too high voltage even higher. In step 2, the capacitor is used as an energy pool to the best of its ability to let the energy flow in both directions naturally, and finally in step 3, the resistor is used to passively balance the energy in the cell with higher voltage. It is both inefficient and risky, and in the end, passive balancing must be adopted, which is slow and wastes energy.

[0008] In order to improve the above problems, patent application disclosure technology CN114362305 transforms the above patent application disclosure technology CN113872288. Step C (corresponding to step 1 of the prior application CN113872288) is mainly that energy is no longer transported from the battery pack (the original single battery pack) to the entire battery module, or from the entire battery module to a certain battery pack (the original single battery pack), but is changed to be able to transport energy from a single battery pack to another battery pack. This causes the complexity of the winding group to increase significantly, and the complexity of the switching circuit is also greatly increased. However, this method does not solve the problem in the original patent that if half of the battery cells in a battery pack have a high voltage and the other half have a low voltage, and the battery pack voltage is standard after averaging, all the above problems are retained. Step C in CN114362305 (corresponding to step 1 in the prior application CN113872288) charges the battery pack with half of the battery cells having too high voltage, which causes the voltage of these battery cells with too high voltage to be higher. Energy is extracted from this battery pack with half of the battery cells having too high voltage, which causes the voltage of these battery cells with too low voltage to be lower. In step B of CN114362305 (corresponding to step 2 of the prior application CN113872288), a capacitor is used as an active balance for transferring energy between two battery cells in the same battery pack. Like the original CN113872288 architecture, the battery pack is divided into N / 4 battery packs, each of which is further divided into two battery cells. However, each battery pack is provided with a balancing capacitor. In step B of CN114362305 (corresponding to step 2 of the prior application CN113872288), the series voltage of the two cells of the battery cell with a higher voltage is first charged to the balancing capacitor, and then the balancing capacitor is discharged to the battery cell with a lower voltage. It is well known that active balancing using capacitors to transport energy has two disadvantages. The first is that the energy transported by capacitors is relatively small, so using multiple supercapacitors causes cost problems. Even so, the speed is still slower than that of inductors. The second is that if the capacitor is not current-limited, the current at the moment of conduction is extremely large, which will damage the battery. During the capacitor charging process, the charging current decreases rapidly, and the speed becomes slower. The frequency has to be increased desperately. The energy loss caused by the dielectric constant of the MOS switch and capacitor when it is turned on and off increases in proportion to the frequency. Even if the balancing capacitor is used to transport energy in two battery cells, the problem caused by one high and one low battery cell in the same battery cell in the original patent cannot be avoided. Step A of CN114362305 (corresponding to step 3 of the prior application CN113872288) still retains the passive balancing of the prior application CN113872288, that is, the original problem of all passive balancing is retained.

[0009] In fact, before 2010, the industry already had very good solutions to the existing problems of the above solutions, which are the so-called battery bottom balancing and top balancing methods. The technology uses a multi-winding transformer to balance the charge and discharge of a single battery cell. For example, on September 26, 2010, China's Electronic Enthusiasts website published an article on "Active Charging Balancing of Lithium Battery Packs". For another example, on November 25, 2013, Yifei.com quoted the Electronic Engineering Network's "Comprehensive Analysis of Active Charging Balancing Methods for Lithium-ion Battery Packs", which has a detailed explanation of bottom balancing and top balancing. The key point is that when the bottom balancing strategy (Bottom balancing) is often used in the discharge mode, the BMS identifies the battery cells with lower capacity in the module, controls the primary side of the transformer to be turned on, and transfers energy from the outside to the battery cells; when the top balancing strategy (Top balancing) is generally used in the charging mode, the BMS identifies the battery cells with higher capacity in the module, controls the secondary side of the transformer to be turned on, and transfers energy from the battery cells to the outside.

[0010] Another example is the active balancing circuit provided by Chinese patent application CN201710640641, which is used to achieve bottom balancing of the single cell when it is in a discharging or stationary state and top balancing when it is in a charging or stationary state. The active balancing circuit in this patent can be used to avoid over-discharge and over-charge of the single cell according to the above two different balancing modes, namely the bottom balancing mode and the top balancing mode. A high-efficiency balancing technology is achieved through the clever coordination of two switching units. By adopting a building block design method for multiple balancing function boards, the active balancing circuit can adapt to the requirements of different single cells connected in series, which greatly improves the flexibility.

[0011] By utilizing the top balancing and bottom balancing technologies, voltage compensation for a single battery cell can be achieved, so that all battery cells have the same voltage. This can solve the problems in the aforementioned CN114362305 and CN113872288 disclosed technologies, such as being unable to detect whether a single battery cell voltage is too high or too low, poor process efficiency, and doing a lot of useless work. High-voltage batteries are recharged to a higher level, and low-voltage batteries are discharged to a lower level. Energy is wasted as heat through passive balancing on resistors, generating energy waste and causing various problems in system heat dissipation.

[0012] However, most domestic articles, patents and foreign articles do not further explain why different modes are adopted in charging and discharging. The reason is that during the system discharge process, if the voltage of a certain battery cell is too low, the entire system will enter the discharge low-voltage cut-off protection early. Therefore, bottom balancing is adopted to continuously charge the battery cell with low voltage with the energy of the entire system to increase the voltage of the battery cell with low voltage, so that the balanced system will not terminate the discharge early due to the low voltage battery cell, wasting the power of other batteries that can continue to discharge, resulting in loss of endurance, and making all batteries Cell balancing, discharge until all cells are reduced to the discharge cut-off threshold together; conversely, during the charging process of the system, if the voltage of a certain cell is too high, the entire system will enter the charging overvoltage cut-off protection early. Therefore, top balancing is adopted to continuously extract the energy of the cell with high voltage to charge the entire system, so as to reduce the voltage of the cell with high voltage, so that the balanced system will not cut off the charging early due to the cell with high voltage, while other cells are not fully charged at this time, resulting in a reduction in the overall battery capacity. Top balancing can charge all cells to the charging cut-off threshold.

[0013] When using a transformer to achieve energy transfer, the system must have a multi-winding transformer and many switching circuits to complete this task. Both bottom balancing and top balancing technologies use a multi-winding transformer with a high-voltage primary side (primary side) and a low-voltage secondary side (secondary side). The turn ratio (N:1) of the high-voltage primary winding and the low-voltage secondary winding is the number of cells in series. Using the characteristics of the discontinuous conduction mode (DCM), in bottom balancing, the entire battery energy is first converted into magnetic energy through the primary winding and stored in the magnetic core in the first half of the DCM cycle, and then the current is transferred back to the secondary winding to charge a single cell in the second half of the cycle. In top balancing, the energy of a single cell is first converted into magnetic energy through the secondary winding and stored in the magnetic core, and then the current is transferred back to the primary winding to charge the entire battery.

[0014] When achieving energy transfer, the problems with existing control structures and methods in the industry are:

[0015] (1) Although the energy conversion in the theoretical N:1 transformer is lossless, the real-world transformer will have energy loss. In the N:1 or 1:N voltage conversion, there will be a lot of energy loss in the magnetic core and winding group. Generally, the higher the N:1 ratio, the greater the loss.

[0016] (2) During charging, top balancing is performed to perform a 1:N voltage conversion, transferring the energy of the cell with a higher voltage to the entire system (all cells). In addition to the relatively large loss caused when the low-voltage side is turned on, there is another technical problem: there is more than one cell with a higher voltage in the system. When energy is taken out from a cell with a higher voltage and recharged to the system (all cells), the energy of this cell with a higher voltage will also be recharged to other cells with a higher voltage.

[0017] Taking the commonly used home storage 48V100Ah system as an example, usually 16 iron-lithium batteries are connected in series to form a 51.2V. For ease of understanding, let's take an extreme case. Assume that there are 16 iron-lithium batteries in series, half of the number (i.e. 8) of the batteries are 3.6V, and the other half (i.e. 8) of the batteries are 2.8V. Then when energy is taken out from a 3.6V battery and recharged to the 16 batteries, the voltage of the other 7 3.6V batteries will exceed 3.6V, and then the BMS will find that the voltage of these 7 batteries is too high. Subsequently, the cells with a voltage exceeding 3.6V are top-balanced to extract their energy and then charge the energy back into the system (i.e. 16 cells). Before the 8th cell is top-balanced, the voltage of the 8th cell has been charged to a very high value, much higher than 3.6V, because the voltages of the other 7 cells are also high. This will reduce the service life of the cell string and affect the balancing effect. Therefore, the transformer balancing technology is not widely adopted in the industry.

[0018] In addition, when performing bottom balancing during discharge to perform N:1 voltage conversion, in addition to the loss problem, there is also the same technical problem as top balancing, that is, there is more than one battery cell with low voltage in the system. When energy is taken out from the entire system (all batteries) and charged to a battery cell with low voltage, energy will be taken out from other batteries with low voltage in the process of taking out energy. Similarly, in an extreme case, assuming that there are 16 iron-lithium batteries in series, half of the batteries are 3.6V and half of the batteries are 2.8V, then in the process of taking out energy from the 16 batteries and charging them to a 2.8V battery cell, energy is also taken out from the other 7 2.8V batteries. Then the BMS will find that the voltage of these 7 batteries is lower, and then energy is taken out from the 16 batteries in turn to charge the batteries that are already lower than 2.8V. Then, before charging the 8th battery cell with low voltage, the 7 bottom balancings have taken out the voltage of the 8th battery cell 7 times, making the 8th battery cell much lower than 2.8V at this time.

[0019] Therefore, the top or bottom balancing implemented by the existing transformer is a repetitive useless control method, which controls the voltage of the battery with too low voltage to be lower, and controls the voltage of the battery with too high voltage to be higher, which is an erroneous and harmful balancing control process.

[0020] In addition, for different numbers of battery cells connected in series, it is often necessary to reopen the mold and modify the automated equipment, which makes production difficult and costly. A standard transformer must be provided to adapt to different application scenarios of battery cells connected in series. For example, the transformers used when 16 iron-lithium battery cells are connected in series and 40 iron-lithium battery cells are connected in series are completely different. It is necessary to reopen a set of transformer molds and modify the automated production equipment accordingly, which makes production complicated and costly.

[0021] In addition, for high-voltage battery energy storage systems, when using transformers to achieve active balancing, it is impossible to match large magnetic cores when producing transformers. Therefore, due to the production and process limitations of transformers, the implementation of active balancing control using transformers in high-voltage battery energy storage systems is limited. Therefore, it is necessary to design corresponding technical solutions to solve the problems existing in the above active balancing control. Summary of the invention

[0022] The purpose of the utility model is to provide a control circuit and module for actively balancing batteries using a unit transformer, so as to solve the problem that when the above-mentioned existing batteries are actively balanced, the useless work control results are repeatedly performed, and the existing different numbers of series-connected battery cells often need to be re-opened. The mold and the automation equipment are modified, causing production difficulties, and the active balancing technology of large-voltage batteries cannot be matched with large magnetic cores.

[0023] The present invention provides a control circuit for actively balancing batteries using a unit transformer, comprising N battery cells connected in series, wherein the N battery cells are divided into i battery groups, where i is an integer greater than or equal to 2;

[0024] The control circuit further includes i unit transformers and i first switches, wherein the i unit transformers are respectively connected to the i battery packs in a one-to-one correspondence via one of the first switches;

[0025] The control circuit further includes N second switches; the N second switches are connected to the N battery cells in a one-to-one correspondence;

[0026] The unit transformer comprises a magnetic core, and a high-voltage primary winding and (M+1) secondary windings wound around the magnetic core, wherein the (M+1) secondary windings comprise M low-voltage secondary windings and 1 transition secondary winding;

[0027] The value of M corresponding to the unit transformer is the same as the number of cells in the battery pack connected to the unit transformer;

[0028] The M secondary windings in the unit transformer are respectively connected one by one to all the cells in the battery pack correspondingly connected to the unit transformer through one of the second switches;

[0029] The high-voltage primary winding of the unit transformer and the battery pack correspondingly connected to the unit transformer are connected in parallel via the first switch;

[0030] The control circuit further includes a transition transformer, i first double-pole double-throw switches, i second double-pole double-throw switches and i third double-pole double-throw switches, wherein the transition transformer includes a transition transformer primary winding and a transition transformer secondary winding;

[0031] The transition secondary windings in i of the unit transformers are respectively connected in parallel with the primary winding of the transition transformer via one of the first double-pole double-throw switches;

[0032] The high-voltage primary windings in i of the unit transformers are respectively connected in parallel with the secondary windings of the transition transformer via one of the second double-pole double-throw switches;

[0033] The transition secondary windings in i of the unit transformers are respectively connected in parallel with the secondary winding of the transition transformer via one of the third double-pole double-throw switches;

[0034] Furthermore, the control circuit further comprises an analog-to-digital conversion module, a driving unit and a main control unit, the analog-to-digital conversion module comprises N input terminals, and the N input terminals of the analog-to-digital conversion module are connected to the N battery cells in a one-to-one correspondence;

[0035] The main control unit is connected to the analog-to-digital conversion module to collect the voltage of each of the N battery cells through the analog-to-digital conversion module;

[0036] The driving unit is connected to the i first switches, the N second switches, the i first double-pole double-throw switches, the i second double-pole double-throw switches and the i third double-pole double-throw switches;

[0037] The main control unit is connected to the driving unit to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, and the second double-pole double-throw switch through the driving unit, thereby controlling the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer connected to the battery pack with the highest average voltage, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch, the transition transformer, and the second double-pole double-throw switch in sequence, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on to demagnetize the bottom balancing cell, and the cell with the lowest voltage among the N cells serves as the bottom balancing cell;

[0038] The cell with the highest voltage among the N cells is used as the top balancing cell. The main control unit controls the switch states of the first switch, the second switch, the first double-pole double-throw switch, the second double-pole double-throw switch and the third double-pole double-throw switch through the driving unit, thereby controlling the second switch corresponding to the top balancing cell to be turned on to magnetize the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding in the unit transformer connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch, the transition transformer and the third double-pole double-throw switch in sequence, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on for demagnetization.

[0039] Optionally, the N battery cells are equally divided into i battery groups; the number of battery cells in each of the i-1 battery groups is set to be the same, and the number of battery cells in the i-th battery group is the quotient plus the remainder of N divided by i.

[0040] Optionally, the N battery cells are 16 battery cells, and the i battery packs are 4 battery packs.

[0041] Optionally, the main control unit is further used to control the switching states of the first switch and the second switch through the driving unit, and then when the maximum voltage difference among the N battery cells is greater than or equal to the top balancing start threshold, control the switching states of the first switch, the second switch, the first double-pole double-throw switch, the second double-pole double-throw switch and the third double-pole double-throw switch, and then control the second switch corresponding to the top balancing battery cell to be turned on to magnetize the magnetic core of the unit transformer connected to the battery group where the top balancing battery cell is located, and then control the energy in the magnetic core of the unit transformer connected to the battery group where the top balancing battery cell is located to be transferred to the transition secondary winding in the unit transformer connected to the battery group with the lowest average voltage among the i battery groups through the transition secondary winding, the first double-pole double-throw switch, the transition transformer and the third double-pole double-throw switch in sequence, and then control the first switch corresponding to the battery group with the lowest average voltage among the i battery groups to be turned on for demagnetization;

[0042] The main control unit is further used to control the switch states of the first switch and the second switch through the driving unit when the voltage of the top balancing cell is greater than or equal to the top balancing end threshold, thereby controlling the second switch corresponding to the top balancing cell to be turned on to continue magnetizing the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding in the unit transformer connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch, the transition transformer, and the third double-pole double-throw switch in sequence, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on for demagnetization;

[0043] The main control unit is further configured to stop top balancing when the voltage of the top balancing cell is lower than the top balancing end threshold.

[0044] Optionally, the main control unit is further used to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, and the second double-pole double-throw switch through the driving unit when the maximum voltage difference among the N battery cells is greater than or equal to the bottom balancing start threshold, thereby controlling the first switch corresponding to the battery group with the highest average voltage among the i battery groups to be turned on, so as to magnetize the magnetic core of the unit transformer connected to the battery group with the highest average voltage, and then control the energy in the magnetic core of the unit transformer connected to the battery group with the highest average voltage to be transferred to the magnetic core of the unit transformer connected to the battery group where the bottom balancing battery cell is located through the first double-pole double-throw switch, the transition transformer, and the second double-pole double-throw switch in sequence, thereby controlling the second switch corresponding to the bottom balancing battery cell to be turned on for demagnetization;

[0045] The main control unit is further used to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, and the second double-pole double-throw switch through the driving unit when the voltage of the bottom balancing cell is less than or equal to the bottom balancing end threshold, thereby controlling the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer connected to the battery pack with the highest average voltage, and then control the energy in the magnetic core of the unit transformer connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch, the transition transformer, and the second double-pole double-throw switch in sequence, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on for demagnetization;

[0046] The main control unit is further configured to stop bottom balancing when the voltage of the bottom balancing cell is greater than the bottom balancing end threshold.

[0047] Optionally, the first switch and the second switch are high-frequency switches respectively.

[0048] Optionally, the main control unit and the driving unit are single chip microcomputers.

[0049] Optionally, the analog-to-digital conversion module includes a MUX multiplexing device, a differential amplifier module and an analog-to-digital converter connected in series.

[0050] Optionally, the first switch and the second switch are metal oxide semiconductor field effect transistors.

[0051] The utility model also provides a unit transformer module for actively balancing a battery, the unit transformer module is applied to any of the control circuits described above, and is used to actively balance N series-connected cells divided into i battery groups, where i is an integer greater than or equal to 2;

[0052] The unit transformer module includes i unit transformers, i first switches, a transition transformer, i first double-pole double-throw switches, i second double-pole double-throw switches and i third double-pole double-throw switches;

[0053] The i unit transformers are respectively connected to the i battery packs in a one-to-one correspondence through one of the first switches; the transition transformer includes a transition transformer primary winding and a transition transformer secondary winding;

[0054] The unit transformer includes a magnetic core, and a high-voltage primary winding and (M+1) secondary windings wound around the magnetic core, wherein the (M+1) secondary windings include M low-voltage secondary windings and 1 transition secondary winding; the value of M corresponding to the unit transformer is the same as the number of cells in the battery pack connected to the unit transformer; the M secondary windings in the unit transformer are respectively connected to all the cells in the battery pack connected to the unit transformer in a one-to-one correspondence through a different second switch;

[0055] The transition secondary windings in i of the unit transformers are respectively connected in parallel with the primary winding of the transition transformer via one of the first double-pole double-throw switches;

[0056] The high-voltage primary windings in i of the unit transformers are respectively connected in parallel with the secondary windings of the transition transformer via one of the second double-pole double-throw switches;

[0057] The transition secondary windings in the i unit transformers are respectively connected in parallel with the secondary winding of the transition transformer via one of the third double-pole double-throw switches.

[0058] Optionally, it further includes an analog-to-digital conversion module, a driving unit and a main control unit, wherein the analog-to-digital conversion module includes N input terminals, and the N input terminals of the analog-to-digital conversion module are used to be connected to the N battery cells in a one-to-one correspondence;

[0059] The main control unit is used to connect to the analog-to-digital conversion module, and collect the voltage of each of the N battery cells through the analog-to-digital conversion module;

[0060] The driving unit is used to connect the i first switches, the N second switches, the i first double-pole double-throw switches, the i second double-pole double-throw switches and the i third double-pole double-throw switches;

[0061] The cell with the lowest voltage among the N cells is used as the bottom balancing cell. The main control unit is further used to connect to the driving unit to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, and the second double-pole double-throw switch through the driving unit, thereby controlling the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer connected to the battery pack with the highest average voltage, and then control the energy in the magnetic core of the unit transformer connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch, the transition transformer, and the second double-pole double-throw switch in sequence, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on for demagnetization;

[0062] The cell with the highest voltage among the N cells is used as the top balancing cell. The main control unit is further used to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, the second double-pole double-throw switch and the third double-pole double-throw switch through the driving unit, thereby controlling the second switch corresponding to the top balancing cell to be turned on to magnetize the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding in the unit transformer connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch, the transition transformer and the third double-pole double-throw switch in sequence, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on for demagnetization.

[0063] The utility model provides a control circuit and module for actively balancing batteries using a unit transformer. The control circuit includes N battery cells connected in series, wherein the N battery cells are divided into i battery groups, where i is an integer greater than or equal to 2; the control circuit also includes i unit transformers and i first switches, wherein the i unit transformers are respectively connected to the i battery groups in a one-to-one correspondence through one of the first switches; the control circuit also includes N second switches; the N second switches are connected to the N battery cells in a one-to-one correspondence; the unit transformer includes a magnetic core, and a A high-voltage primary winding and (M+1) secondary windings, wherein the (M+1) secondary windings include M low-voltage secondary windings and 1 transition secondary winding; the value of M corresponding to the unit transformer is the same as the number of cells in the battery pack connected to the unit transformer; the M secondary windings in the unit transformer are respectively connected to all the cells in the battery pack corresponding to the unit transformer through a second switch; the high-voltage primary winding of the unit transformer is connected in parallel with the battery pack corresponding to the unit transformer through the first switch; the control circuit also The invention comprises a transition transformer, i first double-pole double-throw switches, i second double-pole double-throw switches and i third double-pole double-throw switches, wherein the transition transformer comprises a transition transformer primary winding and a transition transformer secondary winding; the transition secondary windings in i of the unit transformers are respectively connected in parallel with the transition transformer primary winding through one of the first double-pole double-throw switches; the high-voltage primary windings in i of the unit transformers are respectively connected in parallel with the transition transformer secondary winding through one of the second double-pole double-throw switches; the transition secondary windings in i of the unit transformers are respectively connected in parallel with the transition transformer secondary winding through one of the third double-pole double-throw switches. The double-throw switch is connected in parallel with the secondary winding of the transition transformer; and the control circuit further includes an analog-to-digital conversion module, a drive unit and a main control unit, the analog-to-digital conversion module includes N input terminals, and the N input terminals of the analog-to-digital conversion module are connected one-to-one with the N battery cells; the main control unit is connected to the analog-to-digital conversion module to collect the voltage of each of the N battery cells through the analog-to-digital conversion module; the drive unit is connected to the i first switches, the N second switches, the i first double-pole double-throw switches, the i second double-pole double-throw switches and the i third double-pole double-throw switches;The cell with the lowest voltage among the N cells is used as the bottom balancing cell. The main control unit is connected to the driving unit to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, and the second double-pole double-throw switch through the driving unit, thereby controlling the first switch corresponding to the battery group with the highest average voltage among the i battery groups to be turned on, so as to magnetize the magnetic core of the unit transformer connected to the battery group with the highest average voltage, and then control the energy in the magnetic core of the unit transformer connected to the battery group with the highest average voltage to be transferred to the magnetic core of the unit transformer connected to the battery group where the bottom balancing cell is located through the first double-pole double-throw switch, the transition transformer, and the second double-pole double-throw switch in sequence, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on for demagnetization; The cell with the highest voltage among the N cells is used as the top balancing cell. The main control unit controls the switch states of the first switch, the second switch, the first double-pole double-throw switch, the second double-pole double-throw switch and the third double-pole double-throw switch through the driving unit, thereby controlling the second switch corresponding to the top cell to conduct to magnetize the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding of the unit transformer connected to the battery pack with the lowest average voltage among the i battery packs through the first double-pole double-throw switch, the transition transformer and the third double-pole double-throw switch in sequence, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to conduct to discharge magnetism. ;

[0064] In the control circuit provided by the utility model, when realizing bottom balancing, the main control unit uses the characteristics of discontinuous conduction mode (DCM) to divide it into two DCM cycles. In the first half cycle of the first DCM, the first switch of the battery pack with the highest average voltage among the i battery packs is turned on to make it in an on state, so as to magnetize the magnetic core of the unit transformer corresponding to the battery pack with the highest average voltage, that is, to transfer the energy of the battery pack with the highest average voltage among the i battery packs. Then, in the second half cycle of the first DCM, the first switch of the battery pack with the highest average voltage among the i battery packs is turned off to make it in an off state, and the first double-pole double-throw switch connected to the transition secondary winding of the unit transformer corresponding to the battery pack with the highest average voltage and the transition transformer is controlled to be in an on state, thereby transferring the energy in the magnetic core of the unit transformer corresponding to the battery pack with the highest average voltage to the transition transformer. In the first half cycle of the second DCM, the first double-pole double-throw switch is turned off, and the second double-pole double-throw switch and the bottom balancing battery core are turned on. The first switch connected to the battery pack of the bottom balancing cell is used to transfer the energy in the transition transformer to the magnetic core in the unit transformer corresponding to the battery pack where the bottom balancing cell is located. In the second half cycle of the next DCM, the first switch connecting the second double-pole double-throw switch and the battery pack where the bottom balancing cell is located is disconnected, and the second switch connecting the bottom balancing cell and the secondary winding of the unit transformer corresponding to the battery pack where the bottom balancing cell is located is turned on, so that the energy in the magnetic core in the unit transformer corresponding to the battery pack where the bottom balancing cell is located is transferred to the bottom balancing cell for demagnetization, thereby realizing the bottom balancing of the battery pack with the highest average voltage to the single cell with the lowest voltage, thereby avoiding an erroneous and harmful balancing control process of controlling the voltage of the battery with too low a voltage to be lower. In addition, in the control circuit provided by the utility model, when realizing top balancing, the main control unit uses a discontinuous conduction mode (Discontinuous conduction mode) to control the voltage of the battery with too low a voltage to be lower. The characteristics of the DCM are divided into two DCM cycles. In the first half cycle of the first DCM, the second switch connected to the top balancing cell is turned on to make it in the on state, so as to magnetize the magnetic core of the unit transformer corresponding to the battery pack where the top balancing cell is located, that is, to transfer the energy of the top balancing cell to the magnetic core of the unit transformer corresponding to the battery pack where the top balancing cell is located. Then, in the second half cycle of the first DCM, the second switch connected to the top balancing cell is disconnected to make it in the off state, and the transition secondary winding of the unit transformer corresponding to the battery pack where the top balancing cell is located is turned on to connect the first double-pole double-throw switch of the transition transformer to make it in the on state, thereby transferring the energy in the magnetic core of the unit transformer corresponding to the battery pack where the top balancing cell is located to the transition transformer. In the first half cycle of the second DCM, the first double-pole double-throw switch is disconnected.The third double-pole double-throw switch is turned on, and the energy in the transition transformer is transferred to the core of the unit transformer corresponding to the battery group with the lowest average voltage through the transition secondary winding of the unit transformer corresponding to the battery group with the lowest average voltage, and then the third double-pole double-throw switch is disconnected in the second half of the second DCM cycle, and the first switch connecting the unit transformer corresponding to the battery group with the lowest average voltage and the battery group with the lowest average voltage is turned on, and the energy in the core of the unit transformer corresponding to the battery group with the lowest average voltage is transferred to the battery group with the lowest average voltage to achieve top balancing, so that the energy of the single battery cell with the highest voltage is transferred to the battery group with the lowest average voltage, thereby avoiding a wrong and harmful balancing control process of controlling the voltage of the battery with too high voltage to a higher level.

[0065] In addition, the problem of different numbers of existing series-connected battery cells, which often require the re-opening of molds and modification of automation equipment, causing production difficulties, is solved. In view of the fact that large-voltage batteries cannot match large magnetic cores, active balancing technology for top and bottom balancing of large-voltage batteries is achieved by using unit transformers and transition transformers. In addition, when the system voltage is very high, such as thousands of volts, it is necessary to use many battery packs in series. In this technical solution, multiple unit transformers and transition transformers are combined through the topology of the first switch, the second switch, the first double-pole double-throw switch, the second double-pole double-throw switch, and the third double-pole double-throw switch. Energy can be effectively transferred from the higher-voltage battery cells through the transition transformer, across the voltage gap between the unit voltages, and the energy can be transferred to the lower-voltage battery cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0067] Figure 1 A schematic diagram of the circuit connections of N cells in a control circuit for actively balancing batteries through a unit transformer provided in an embodiment of the utility model;

[0068] Figure 2 A schematic diagram of the connection between the transition transformer and the unit transformer in the control circuit for actively balancing the battery through the unit transformer provided in an embodiment of the utility model;

[0069] Figure 3a A schematic diagram of connecting components of a battery pack and a unit transformer 110 in a control circuit for actively balancing batteries through a unit transformer provided in an embodiment of the utility model;

[0070] Figure 3b A schematic diagram of the connection lines of the combined devices of a battery pack in a control circuit for actively balancing batteries using a unit transformer provided in an embodiment of the utility model;

[0071] Figure 4 A schematic diagram of the connection lines of a system assembly device using 16 battery cells in a control circuit for actively balancing batteries through a unit transformer provided in an embodiment of the utility model;

[0072] Figure 5 A schematic diagram of energy transfer during top balancing in a control circuit provided in an embodiment of the utility model;

[0073] Figure 6a A schematic diagram of the first half of the first cycle of energy transfer when the control circuit provided by the embodiment of the utility model performs top balancing;

[0074] Figure 6b A schematic diagram of the second half of the first cycle of energy transfer when the control circuit provided by the embodiment of the utility model performs top balancing;

[0075] Figure 6c A schematic diagram of the first half of the second cycle of energy transfer when the control circuit provided by the embodiment of the utility model performs top balancing;

[0076] Figure 6d A schematic diagram of the second half of the second cycle of energy transfer when the control circuit provided by the embodiment of the utility model performs top balancing;

[0077] Figure 7 A schematic diagram of energy transfer during bottom balancing in a control circuit provided in an embodiment of the utility model;

[0078] Figure 8a A schematic diagram of the first half of the first cycle of energy transfer when the control circuit provided by the embodiment of the utility model performs bottom balancing;

[0079] Figure 8b A schematic diagram of the second half of the first cycle of energy transfer when the control circuit provided by the embodiment of the utility model performs bottom balancing;

[0080] Figure 8c A schematic diagram of the first half of the second cycle of energy transfer when the control circuit provided by the embodiment of the utility model performs bottom balancing;

[0081] Figure 8d A schematic diagram of the second half of the second cycle of energy transfer when the control circuit provided by the embodiment of the utility model performs bottom balancing;

[0082] Fig. 9A schematic diagram of the structure of another unit transformer provided by an embodiment of the utility model;

[0083] Fig.10 A schematic diagram of a unit transformer module for actively balancing batteries provided in an embodiment of the utility model. DETAILED DESCRIPTION

[0084] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0085] The utility model provides a control circuit and module for actively balancing batteries by using a unit transformer and a transition transformer. The control circuit includes N battery cells connected in series, the N battery cells are divided into i battery groups, and i is an integer greater than or equal to 2; the control circuit also includes i unit transformers and i first switches, and the i unit transformers are respectively connected to the i battery groups in a one-to-one correspondence through a first switch; the control circuit also includes N second switches, and the N second switches are connected to the N battery cells in a one-to-one correspondence; the unit transformer includes a magnetic core, and a high-voltage primary winding and (M+1) secondary windings wound around the magnetic core, and the (M+1) secondary windings include M low-voltage secondary windings and 1 transition secondary winding; the value of M corresponding to the unit transformer is The number of cells in the battery pack connected to the unit transformer is the same; the M secondary windings in the unit transformer are connected to all the cells in the battery pack connected to the unit transformer through a second switch respectively; the high-voltage primary winding of the unit transformer is connected in parallel with the battery pack connected to the unit transformer through a first switch; the control circuit also includes a transition transformer, i first double-pole double-throw switches, i second double-pole double-throw switches and i third double-pole double-throw switches, the transition transformer includes a transition transformer primary winding and a transition transformer secondary winding; the transition secondary windings in the i unit transformers are connected in parallel with the transition transformer primary winding through a first double-pole double-throw switch respectively; the high-voltage primary windings in the i unit transformers are connected in parallel with the transition transformer primary winding through a second switch respectively. The double-pole double-throw switch is connected in parallel with the secondary winding of the transition transformer; the transition secondary windings in the i unit transformers are respectively connected in parallel with the secondary winding of the transition transformer through a third double-pole double-throw switch; and the control circuit also includes an analog-to-digital conversion module, a drive unit and a main control unit, the analog-to-digital conversion module includes N input terminals, and the N input terminals of the analog-to-digital conversion module are connected one-to-one with the N battery cells; the main control unit is connected to the analog-to-digital conversion module to collect the voltage of each of the N battery cells through the analog-to-digital conversion module; the drive unit is connected to i first switches, N second switches, i first double-pole double-throw switches, i second double-pole double-throw switches and i third double-pole double-throw switches; in the bottom balancing, the battery cell with the lowest voltage among the N battery cells is used as the bottom balancing voltage. The main control unit is connected to the driving unit to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, the second double-pole double-throw switch and the third double-pole double-throw switch through the driving unit, thereby controlling the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer connected to the battery pack with the highest average voltage, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch, the transition transformer and the second double-pole double-throw switch in sequence, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on for demagnetization;In the top balancing, the cell with the highest voltage among the N cells is used as the top balancing cell. The main control unit controls the switch states of the first switch, the second switch, the first double-pole double-throw switch, the second double-pole double-throw switch and the third double-pole double-throw switch through the driving unit, thereby controlling the second switch corresponding to the top balancing cell to conduct to magnetize the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding of the unit transformer connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch, the transition transformer and the third double-pole double-throw switch in sequence, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to conduct to discharge magnetism. ;

[0086] In the control circuit provided by the utility model, when bottom balancing is realized, the battery cell with the lowest voltage among the N battery cells is used as the bottom balancing battery cell. The main control unit uses the characteristics of the discontinuous conduction mode (DCM) to divide it into two DCM cycles. In the first half cycle of the first DCM, the first switch of the battery group with the highest average voltage among the i battery groups is turned on to make it in an on state, so as to magnetize the magnetic core of the unit transformer corresponding to the battery group with the highest average voltage, that is, to transfer the energy of the battery group with the highest average voltage among the i battery groups. Then, in the second half cycle of the first DCM, the first switch of the battery group with the highest average voltage among the i battery groups is turned off to make it in an off state, and the first double-pole double-throw switch connected to the transition secondary winding of the unit transformer corresponding to the battery group with the highest average voltage and the transition transformer is controlled to be turned on to make it in an on state, thereby transferring the energy in the magnetic core of the unit transformer corresponding to the battery group with the highest average voltage to the transition transformer, and the first double-pole double-throw switch is turned off in the first half cycle of the second DCM. The switch is turned on, and the first switch connecting the second double-pole double-throw switch and the battery pack where the bottom balancing cell is located is turned on, so that the energy in the transition transformer is transferred to the magnetic core in the unit transformer corresponding to the battery pack where the bottom balancing cell is located. In the second half cycle of the second DCM, the first switch connecting the second double-pole double-throw switch and the battery pack where the bottom balancing cell is located is disconnected, and the second switch connecting the bottom balancing cell and the secondary winding of the unit transformer corresponding to the battery pack where the bottom balancing cell is located is turned on, so that the energy in the magnetic core in the unit transformer corresponding to the battery pack where the bottom balancing cell is located is transferred to the bottom balancing cell for demagnetization, thereby realizing a method different from the traditional bottom balancing, ensuring that the energy is transported from the battery pack with the highest voltage to the battery cell with the lowest cell voltage, thereby avoiding an erroneous and harmful balancing control process of controlling the voltage of the battery that is already too low to be even lower.Furthermore, in the control circuit provided by the utility model, when top balancing is realized, the cell with the highest voltage among the N cells is used as the top balancing cell, and the main control unit uses the characteristics of discontinuous conduction mode (DCM) to divide the top balancing cell into two DCM cycles. In the first half cycle of the first DCM, the second switch connected to the top balancing cell is turned on to make it in an on state, so as to magnetize the magnetic core of the unit transformer corresponding to the battery pack where the top balancing cell is located, that is, to transfer the energy of the top balancing cell to the magnetic core of the unit transformer corresponding to the battery pack where the top balancing cell is located, and then in the second half cycle of the first DCM, the second switch connected to the top balancing cell is disconnected to make it in an off state, and the transition secondary winding of the unit transformer corresponding to the battery pack where the top balancing cell is located is turned on to connect the first double-pole double-throw switch of the transition transformer to make it in an on state, so as to transfer the energy in the magnetic core of the unit transformer corresponding to the battery pack where the top balancing cell is located to the transition transformer, and then in the second half cycle of the first DCM, the second switch connected to the top balancing cell is turned off to make it in an off state, and the transition secondary winding of the unit transformer corresponding to the battery pack where the top balancing cell is located is turned on to connect the first double-pole double-throw switch of the transition transformer to make it in an on state, so as to transfer the energy in the magnetic core of the unit transformer corresponding to the battery pack where the top balancing cell is located to the transition transformer. In the first half of the second DCM cycle, the first double-pole double-throw switch is disconnected, and the third double-pole double-throw switch is turned on, thereby transferring the energy in the transition transformer through the transition secondary winding of the unit transformer corresponding to the battery group with the lowest average voltage to the magnetic core of the unit transformer corresponding to the battery group with the lowest average voltage. Then, in the second half of the second DCM cycle, the third double-pole double-throw switch is disconnected, and the unit transformer corresponding to the battery group with the lowest average voltage is turned on to discharge the magnetism of the first switch connected to the battery group with the lowest average voltage, thereby transferring the energy in the magnetic core of the unit transformer corresponding to the battery group with the lowest average voltage to the battery group with the lowest average voltage, so as to achieve a different method from the traditional top balancing, and transfer the energy of the single battery cell with the highest voltage to the battery group with the lowest average voltage, thereby avoiding an erroneous and harmful balancing control process of controlling the voltage of the battery with too high a voltage to a higher level.

[0087] In addition, the problem of different numbers of existing series-connected battery cells, which often require re-opening molds and modifying automation equipment, causing production difficulties, is solved. In view of the fact that large-voltage batteries cannot match large magnetic cores, unit transformers and transition transformers are used to achieve active balancing technology for top and bottom balancing of large-voltage batteries.

[0088] In addition, when the system voltage is very high, such as thousands of volts, it is necessary to use many battery packs connected in series. In the present technical solution, multiple unit transformers and transition transformers are combined through a first switch, a second switch, a first double-pole double-throw switch, a second double-pole double-throw switch, and a third double-pole double-throw switch. The topology can effectively transfer energy from the higher-voltage battery cells through the transition transformer, across the voltage gap between the unit voltages, and transfer the energy to the lower-voltage battery cells.

[0089] like Figure 1As shown, a schematic diagram of the line connection of N battery cells in a control circuit for actively balancing batteries through a unit transformer is provided, wherein the control circuit includes N battery cells connected in series, and the N battery cells are divided into i battery groups, where i is an integer greater than or equal to 2; the control circuit also includes i unit transformers 110 and i first switches, and the i unit transformers 110 are respectively connected to the i battery groups in a one-to-one correspondence through a first switch; the control circuit also includes N second switches, and the N second switches are connected to the N battery cells in a one-to-one correspondence.

[0090] In the control circuit provided in this embodiment, the unit transformer 110 includes a magnetic core, a high-voltage primary winding wound around the magnetic core, and (M+1) secondary windings, and the (M+1) secondary windings include M low-voltage secondary windings and 1 transition secondary winding. The value of M corresponding to the unit transformer 110 is the same as the number of cells in the battery pack connected to the unit transformer 110.

[0091] In the control circuit provided in this embodiment, the M secondary windings in the unit transformer 110 are respectively connected one-to-one with all the battery cells in the battery pack correspondingly connected to the unit transformer 110 through a second switch; the high-voltage primary winding of the unit transformer 110 is connected in parallel with the battery pack correspondingly connected to the unit transformer 110 through a first switch.

[0092] like Figure 2 As shown, a connection diagram of a transition transformer and a unit transformer in a control circuit for actively balancing batteries through a unit transformer is provided. The control circuit provided in this embodiment also includes a transition transformer 120, i first double-pole double-throw switches 111, i second double-pole double-throw switches 112 and i third double-pole double-throw switches 113. The transition transformer 120 includes a transition transformer primary winding and a transition transformer secondary winding; the transition secondary windings in the i unit transformers 110 are respectively connected in parallel with the transition transformer primary winding through a first double-pole double-throw switch 111; the high-voltage primary windings in the i unit transformers 110 are respectively connected in parallel with the transition transformer secondary winding through a second double-pole double-throw switch 112; the transition secondary windings in the i unit transformers 110 are respectively connected in parallel with the transition transformer secondary winding through a third double-pole double-throw switch 113; and, as Figure 4As shown, the control circuit also includes an analog-to-digital conversion module 130, a drive unit 140 and a main control unit 150, the analog-to-digital conversion module 130 includes N input terminals, and the N input terminals of the analog-to-digital conversion module 130 are connected to the N battery cells in a one-to-one correspondence; the main control unit 150 is connected to the analog-to-digital conversion module 130 to collect the voltage of each of the N battery cells through the analog-to-digital conversion module 130; the drive unit 140 is connected to i first switches, N second switches, i first double-pole double-throw switches 111, i second double-pole double-throw switches 112 and i third double-pole double-throw switches 113; the main control unit 150 is connected to The driving unit 140 is connected to control the switch states of the first switch, the second switch, the first double-pole double-throw switch 111, the second double-pole double-throw switch 112 and the third double-pole double-throw switch 113 through the driving unit 140, and the battery cell with the lowest voltage among the N battery cells in the bottom balancing is used as the bottom balancing battery cell, and then the first switch corresponding to the battery group with the highest average voltage among the i battery groups is controlled to be turned on, so as to magnetize the magnetic core of the unit transformer 110 connected to the battery group with the highest average voltage, and then control the energy in the magnetic core of the unit transformer 110 connected to the battery group with the highest average voltage to flow in sequence. The magnetic flux is transferred to the magnetic core of the unit transformer 110 connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the second double-pole double-throw switch 112, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on for magnetic discharge; in the top balancing, the cell with the lowest voltage among the N cells is used as the top balancing cell, and the main control unit 150 controls the switch states of the first switch, the second switch, the first double-pole double-throw switch 111, the second double-pole double-throw switch 112, and the third double-pole double-throw switch 113 through the driving unit 140, thereby controlling the top The second switch corresponding to the balancing cell is turned on to magnetize the magnetic core of the unit transformer 110 connected to the battery group where the top balancing cell is located, and then the energy in the magnetic core of the unit transformer 110 connected to the battery group where the top balancing cell is located is controlled to be transferred to the transition secondary winding in the unit transformer 110 connected to the battery group with the lowest average voltage among the i battery groups through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the third double-pole double-throw switch 113 in sequence, and then the first switch corresponding to the battery group with the lowest average voltage among the i battery groups is controlled to be turned on for demagnetization.

[0093] In other embodiments, N does not necessarily need to be an integer multiple of i. When N is an integer multiple of i, the number of battery cells in each battery pack is N / i, that is, N battery cells are evenly divided into i battery groups. When N is not an integer multiple of i, the number of battery cells in the 1st to i-1th groups is set to be the same, the i-th group is the quotient of N divided by i plus the remainder, and the number of battery cells in the 1st to i-1th groups is the quotient of N divided by i. Regardless of whether N is an integer multiple of i, the ratio of the number of primary winding turns to the number of secondary winding turns corresponding to each battery pack is the number of battery cells in the battery pack.

[0094] For example, there are 13 battery cells in total, which are divided into 3 groups, N=13, i=3, the first and second groups are 4 battery cells, and the last group is 5 battery cells; for another example, there are 17 battery cells, which are divided into 4 groups, N=17, i=4, the first to third groups are 4 battery cells, and the fourth group is 5 battery cells.

[0095] However, when designing, we often do not decide how many groups there are first, but how many cells are in each group. Therefore, when there are more cells in each group and the remainder is large, the remainder can be formed into a separate group. For example, if each group is decided to have 8 cells, a total of 23 cells can be divided into three groups of 8+8+7.

[0096] like Figure 3a As shown, a schematic diagram of the connection between a battery pack and a unit transformer in a control circuit for actively balancing batteries through a unit transformer is provided. For example, 16 cells are divided into 4 battery packs, each battery pack includes 4 cells connected in series. Figure 3a The component connection structure of the battery pack 1 (i.e., the first battery pack) and the unit transformer 110 is shown. In this embodiment, the battery pack 1 includes 4 battery cells, namely, battery cells BAT_1, BAT_2, BAT_3 and BAT_4. The secondary winding of the unit transformer 110 is formed by 5 groups, the bottom group is a transition secondary winding, and the top 4 are low-voltage secondary windings, that is, the number of battery cells in the battery pack connected to the unit transformer 110 in this embodiment is 4, so M is 4, each battery cell is connected in series with a second switch, and the 4 battery cells (battery cells BAT_1, BAT_2, BAT_3 and BAT_4) are connected to the 4 second switches (second switches SW_S11, SW_S12, SW_S13 and SW_S14) in a one-to-one correspondence. The two ends of the battery pack are connected to the two ends of the high-voltage primary winding of the unit transformer 110 through the first switch SW_P1. Figure 3a The filter capacitor connected in parallel with the battery cell shown in FIG. 1 has no effect on the top balance control principle and the bottom balance control principle of the active balance control in the embodiment of the utility model, so it will not be described and explained here. Figure 3a The filter capacitors are shown in FIG.

[0097] like Figure 3bAs shown, a schematic diagram of the combined device connection line of a battery pack in a control circuit for actively balancing batteries using a unit transformer is provided. For example, 16 cells are divided into 4 battery packs, each battery pack includes 4 cells connected in series. Figure 3b A schematic diagram showing the connection lines of the combined devices of a battery pack is based on Figure 3a Each battery cell in the battery pack, and the second switch corresponding to each battery cell in the battery pack, and the first switch corresponding to the battery pack are schematically shown as a connection line of a combination device, the combination device is a schematic diagram of the connection line of the first battery pack 1, and the combination device includes all the battery cells (battery cells BAT_1, BAT_2, BAT_3 and BAT_4) divided into the single battery pack, and the second switch (second switch SW_S11, SW_S12, SW_S13 and SW_S14) in the battery unit to which each battery cell in the single battery pack belongs, and the first switch SW_P1 corresponding to the single battery pack. In the embodiment of the utility model, all the second switches and the first switch are high-frequency switches.

[0098] like Figure 3b As shown, in the schematic diagram of the combined device connection line, the control signal connection lines (SW_S11, SW_S12, SW_S13 and SW_S14) of the second switch in the battery unit to which each battery cell in the single battery pack belongs are identified on the left, as well as the control signal connection line SW_P1 of the first switch correspondingly connected to the single battery pack. In the schematic diagram of the combined device connection line, the positive electrode voltage signals (BAT_1, BAT_2, BAT_3 and BAT_4) of all the batteries in the single battery pack are identified on the right, and the negative electrode signal (BAT_1_negative) of one of the batteries is identified at the bottom on the right.

[0099] like Figure 4 As shown, a schematic diagram of the connection lines of a system combination device using 16 cells in a control circuit for actively balancing batteries through a unit transformer is provided. Figure 4 The system combination device shown is composed of the four above Figure 3b The combined devices of the battery pack shown are connected, and the four combined devices are combined device 411, combined device 412, combined device 413 and combined device 414, each of which is based on Figure 3a A schematic diagram of the connection of a combination of each battery cell in a battery pack, a second switch correspondingly connected to each battery cell in the battery pack, and a first switch correspondingly connected to the battery pack is shown.

[0100] For example, the combination device 411 is a schematic diagram of the connection lines of the first battery pack 1, and the combination device 411 includes all the battery cells (battery cells BAT_1, BAT_2, BAT_3 and BAT_4) divided into the single battery pack, and the second switches (second switches SW_S11, SW_S12, SW_S13 and SW_S14) in the battery cells to which each battery cell in the single battery pack belongs, and the first switch SW_P1 corresponding to the single battery pack.

[0101] Furthermore, the combination device 412 is a schematic diagram of the connection lines of the second battery pack 2, and the combination device 412 includes all the battery cells (battery cells BAT_5, BAT_5, BAT_7 and BAT_8) divided into the single battery pack (the second battery pack 2), and the second switches (second switches SW_S21, SW_S22, SW_S23 and SW_S24) in the battery cells to which each battery cell in the single battery pack belongs, and the first switch SW_P2 corresponding to the single battery pack.

[0102] Furthermore, the combination device 413 is a schematic diagram of the connection lines of the third battery pack 3, and the combination device 413 includes all the battery cells (battery cells BAT_9, BAT_10, BAT_11 and BAT_12) divided into the single battery pack (the third battery pack 3), and the second switches (second switches SW_S31, SW_S32, SW_S33 and SW_S34) in the battery cells to which each battery cell in the single battery pack belongs, and the first switch SW_P3 corresponding to the single battery pack.

[0103] Furthermore, the combination device 414 is a schematic diagram of the connection lines of the fourth battery pack 4, and the combination device 414 includes all the battery cells (battery cells BAT_13, BAT_14, BAT_15 and BAT_16) divided into the single battery pack (the fourth battery pack 4), and the second switches (second switches SW_S41, SW_S42, SW_S43 and SW_S44) in the battery cells to which each battery cell in the single battery pack belongs, and the first switch SW_P4 corresponding to the single battery pack.

[0104] like Figure 4As shown, in the embodiment of the utility model, the control circuit further includes an analog-to-digital conversion module 130, a driving unit 140 and a main control unit 150, and the analog-to-digital conversion module 130 includes N input terminals, and the N input terminals of the analog-to-digital conversion module 130 are connected one-to-one with N battery cells (i.e., 16 battery cells, namely BAT_1, BAT_2, BAT_3 and BAT_4, and BAT_5, BAT_7, BAT_8, and BAT_9, BAT_10, BAT_11 and BAT_12, and BAT_13, BAT_14, BAT_15 and BAT_16). Figure 4 As shown, the analog-to-digital conversion module 130 can be implemented by connecting a MUX multiplexing device, a differential amplifier module, and an analog-to-digital converter.

[0105] Preferably, the second switch and the first switch are high-frequency switches respectively.

[0106] Preferably, the main control unit 150 is a single chip microcomputer.

[0107] Preferably, the driving unit 140 is a demultiplexer logic circuit and a high-frequency switch pre-driving circuit.

[0108] Preferably, the analog-to-digital conversion module 130 includes a high-precision analog-to-digital converter.

[0109] Preferably, the analog-to-digital conversion module 130 includes a MUX (multiplexer) multiplexing device, a differential amplifier module and an analog-to-digital converter connected in series.

[0110] Preferably, the second switch and the first switch are MOS metal oxide semiconductor field effect transistors.

[0111] The main control unit 150 and the driving unit 140 are single chip microcomputers. If you want to directly connect the 16 cells to the analog-to-digital converter through the voltage divider resistor and perform analog-to-digital conversion ADC in single-ended input (Single Ended) mode, the accuracy of the ADC must be very high. In other embodiments, if you use an analog-to-digital converter with a lower accuracy, you can use a double-pole input and output MUX multiplexer device, and the double-pole output of the MUX is connected to a differential amplifier. The differential amplifier is used to convert the voltage of each cell into a single-ended output, and then the single-ended output voltage of the differential amplifier is connected to the analog-to-digital converter ADC.

[0112] In other embodiments, the analog-to-digital conversion module 130 is implemented by a high-precision analog-to-digital converter.

[0113] like Figure 4As shown, the main control unit 150 is connected to the analog-to-digital conversion module 130 to collect the voltage of each of the N battery cells through the analog-to-digital conversion module 130; the driving unit 140 is connected to i first switches (i.e., 4 first switches, namely SW_P1, SW_P2, SW_P3 and SW_P4) and N second switches (i.e., 16 second switches shown in this embodiment, namely SW_S11, SW_S12, SW_S13 and SW_S14, and SW_S21, SW_S22, SW_S23 and SW_S24, and SW_S31, SW_S32, SW_S33 and SW_S34 , and SW_S41, SW_S42, SW_S43 and SW_S44), the main control unit 150 is connected to the driving unit 140, and the battery cell with the lowest voltage among the N battery cells is used as the bottom balancing battery cell in the bottom balancing, so as to control the switch states of the first switch, the second switch, the first double-pole double-throw switch 111, the second double-pole double-throw switch 112 and the third double-pole double-throw switch 113 through the driving unit 140, and then control the first switch corresponding to the battery group with the highest average voltage among the i battery groups to be turned on, so as to magnetize the magnetic core of the unit transformer 110 connected to the battery group with the highest average voltage, and then control the battery group with the highest average voltage to be turned on. The energy in the magnetic core of the unit transformer 110 connected to the battery pack is transferred to the magnetic core of the unit transformer 110 connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the second double-pole double-throw switch 112 in sequence, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on for magnetic discharge; in the top balancing, the cell with the highest voltage among the N cells is used as the top balancing cell, and the main control unit 150 controls the first switch, the second switch, the first double-pole double-throw switch 111, the second double-pole double-throw switch 112 and the third double-pole double-throw switch 112 through the driving unit 140. 3, thereby controlling the second switch corresponding to the top balancing cell to conduct to magnetize the magnetic core of the unit transformer 110 connected to the battery group where the top balancing cell is located, and then controlling the energy in the magnetic core of the unit transformer 110 connected to the battery group where the top balancing cell is located to be transferred to the transition secondary winding in the unit transformer 110 connected to the battery group with the lowest average voltage among the i battery groups through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the third double-pole double-throw switch 113 in sequence, and then controlling the first switch corresponding to the battery group with the lowest average voltage among the i battery groups to conduct to discharge magnetism.

[0114] In the embodiment of the present invention, the main control unit 150 can be implemented by a main control chip.

[0115] In the embodiment of the utility model, the unit transformer 110 is constructed according to the principle of a flyback converter unit transformer 110. This type of unit transformer 110 can store energy in a magnetic field. If a low-frequency (e.g., 10kHz or lower) ferrite core is used, the air gap can be increased to increase the magnetic resistance to avoid magnetic saturation of the core material. However, if a toroidal unit transformer 110 is used, there is no need to increase the air gap for high-frequency switching (e.g., 50kHz).

[0116] In the embodiment of the utility model, the main control unit 150 controls the driving unit 140 to dynamically control the conduction of the second switch corresponding to different battery packs and different single cells under different voltage distribution conditions, and to perform flyback energy conversion with different primary and secondary side combinations. The specific process of magnetization and demagnetization is described here. The cell is turned on through the switch and the unit transformer 110. After the conduction, the current direction flows from the cell to the winding of the unit transformer 110. The current generated by the cell voltage in the winding of the unit transformer 110 gradually increases, and the electric energy is gradually converted into the magnetic flux in the magnetic core, that is, the electric energy is gradually converted into magnetic energy. In the embodiment of the utility model, this process of gradually establishing the magnetic flux is called "magnetization". On the contrary, the cell is turned on through the switch and the winding. After the conduction, the current direction flows back to the cell, and the magnetic flux in the magnetic core gradually decreases. We call the process of converting this magnetic energy back to the current through the winding and gradually flowing back to the cell "demagnetization".

[0117] The "magnetization" and "demagnetization" defined herein are different from the commonly used meanings in the industry and are only used to simplify and shorten the length of the text explanation in the description of the embodiments of the utility model. Outside the description of the embodiments of the utility model, the two definitions of "magnetization" and "demagnetization" used in the embodiments of the utility model are not applicable to the commonly used terms in the industry.

[0118] According to the above Figures 1 to 4 The structure of the control circuit shown schematically illustrates the control analysis of top equalization.

[0119] Taking the 48V100Ah, 16 iron-lithium cells in series with a nominal voltage of 51.2V, which are often used in home storage systems, as an example, when the 16 cells are divided into 4 groups (i.e. 4 battery groups), assuming that the voltage of the 7th cell BAT_7 is high, and the total voltage of the 4 cells (BAT_1, BAT_2, BAT_3 and BAT_4) in the first battery group 1 of the 4 battery groups is the lowest, that is, it is the battery group with the lowest voltage among the 4 battery groups, then top balancing is adopted when the system is charged. However, unlike the traditional top balancing that charges all cells, we group the cells and compare the group voltages to transfer energy from the single cell with the highest voltage BAT7 to the battery group with the lowest group voltage 1, so as to avoid the embarrassing situation of moving the energy of the highest voltage cell to other higher voltage cells. In the traditional top balancing, if the cells are not grouped, this effect cannot be achieved, and there must be a method to judge that the best effect can be achieved by moving energy from the cell with the highest voltage to the group with the lowest average voltage.

[0120] like Figure 5 The top balanced system without transition transformer is shown, so only one DCM cycle is needed. Figure 5 Only the connection structure between the cells and the unit transformer in the first battery pack and the second battery pack is shown. Figure 5 The left side shows the first half of the DCM cycle. First, SW_S23 corresponding to BAT_7 is turned on to magnetize the core, and then Figure 5 In the second half of the DCM cycle on the right, SW_S23 is disconnected and SW_P1 is turned on to discharge the cells BAT_1 to BAT_4 of the first battery pack 1.

[0121] In the above example, the battery pack with the lowest voltage is used as the basis for judging magnetic discharge. In this example, the number of cells in each battery pack is equal, so there is no difference between the battery pack with the lowest total voltage and the battery pack with the lowest average voltage as the basis for judging magnetic discharge. However, when the number of cells in the battery pack is different, the average value of the battery pack should be used as the basis for judging magnetic discharge.

[0122] Let's take an example to illustrate the situation where there is no group processing. Figure 5The voltages of cells BAT_5 to BAT_8 were originally 3.6V, while those of cells BAT_1 to BAT_4 were all 2.8V. If the traditional top balancing is used, BAT7 is turned on first to magnetize the core, and then all 16 cells are discharged together. In this way, the voltages of BAT_5, BAT_6, and BAT_8 will all be higher than 3.6V, becoming an overcharged state. In the subsequent top balancing process, the top balancing of cells BAT_5, BAT_6, and BAT_8 will continue in turn. When it comes to the last cell to be top balanced, it will be charged at least three times by top balancing after its voltage has exceeded the overcharge cut-off voltage, resulting in a very serious risk of overvoltage charging.

[0123] In the embodiment of the utility model, after being divided into 4 battery groups, the battery cell BAT_7 with the highest voltage is first turned on to magnetize the magnetic core, and then the first battery group 1 with the lowest voltage among the 4 battery groups is discharged, thereby solving the problem of transferring the energy of the battery cell with a relatively high voltage to the battery cell with a relatively high voltage in the traditional structure.

[0124] Although it is possible that the cell with the highest voltage and some cells with too low voltage will be grouped in the same battery pack, making this battery pack the group with the lowest voltage, it is possible that the cell with the highest voltage transfers energy to itself, but in the top balancing of a battery pack with 4 cells, the energy transferred out each time is 4 times the energy transferred back, and the cell with the highest voltage can be quickly turned into a cell with normal voltage through top balancing. Or it is possible that a cell with relatively high energy and some other cells with too low voltage are together to form the battery pack with the lowest voltage. However, in any case, it will never happen that several cells with relatively high voltage are in the same battery pack to form the group with the lowest voltage. Therefore, energy is always transferred from the cell with the highest voltage to each cell in the battery pack with the lowest voltage, avoiding the risk of very serious overvoltage charging, greatly reducing useless balancing operations, and improving the efficiency of active balancing control.

[0125] In the embodiment of the utility model, in the new battery cell series grouping structure, in the top balancing process, high-frequency switching is used to transfer energy from any one of the 16 battery cells to any group of 4 battery cells through the magnetic core, and high-frequency switching control technology is used to realize real-time confirmation and transfer from the battery cell with the highest voltage to the battery pack with the lowest group voltage. This is a method of adaptively transferring energy according to the battery cell voltage distribution status at all times, which further improves the efficiency of active balancing control.

[0126] Compared with the traditional top balancing structure, the grouped structure and adaptive energy transfer from the highest voltage cell to the lowest voltage group can greatly reduce the probability of transferring energy from a high voltage cell to a high voltage cell by several times, avoiding unnecessary waste and the situation where the cell voltage exceeds the overcharge protection cut-off voltage, and can ensure that the energy is effectively transferred from the highest voltage cell to the lower voltage cell with a high probability.

[0127] Following the above analysis of the battery cell with the highest voltage and some battery cells with lower voltage in the same battery pack, after the battery cell with the highest voltage carries energy to the group with lower voltage for a period of time, the voltage of the battery cell with the highest voltage is judged by a top balancing cutoff threshold and becomes normal. Then, it is possible that the voltage of this group becomes the lowest. Later, after other new battery cells with the highest voltage are replaced and magnetized into the magnetic core, the system will demagnetize the new group with the lowest voltage. The battery cell that once had the highest voltage and just dropped to the normal voltage is demagnetized again because the voltage of the battery pack it is in is the lowest, causing the voltage to rise again and may become the battery cell with the highest voltage.

[0128] Therefore, in order to prevent the battery cell with the highest voltage from becoming the battery cell with the highest voltage again, a top balancing cutoff threshold is set. The top balancing cutoff threshold should be a safety margin lower than the general overcharge cutoff voltage. Taking iron-lithium batteries as an example, the overcharge cutoff voltage is generally set to 3.6V, while the nominal value is 3.2V. The top balancing cutoff threshold is set to 3.2V, that is, a 3.6V battery cell must continue to transport energy to the group with the lowest voltage through top balancing until the 3.6V battery cell drops to 3.2V before the top balancing is stopped. Because the cell that once had the highest voltage is no longer the cell with the highest voltage after several top balancing, but top balancing must continue for this cell until the top balancing cutoff threshold is reached. Only then will top balancing begin for the next cell with the highest voltage. Since as before, in the top balancing with 4 cells as a group, the energy carried out each time is 4 times the energy carried back, this can avoid the voltage oscillation phenomenon caused by the voltage of the cell with the highest voltage just dropping to normal after top balancing, and then being charged and rising to above the overcharge cutoff protection voltage because other cells with low voltage in the group become the group with the lowest voltage.

[0129] When all the cells are close to the charging cut-off voltage but continue to charge, because the condition for starting the top balancing threshold cannot be met, a smaller top balancing starting threshold can be reset and the top balancing threshold can be set to the average voltage of all the cells, so that all the cells can be controlled to have the same voltage after the new top balancing threshold is controlled. In the process, a "safety margin" can be retained similar to the previous hysteresis control to avoid voltage oscillation during balancing. Since the above example can be used, it will not be repeated here.

[0130] Next, the top balancing process is analyzed in detail through an embodiment. The cell with the highest voltage among the 16 cells is used as the top balancing cell. The main control unit 150 controls the drive unit 140 to control the switch to achieve energy transfer. Figure 6a , 6b , 6c, and 6d, respectively, show the energy transfer process of each half cycle. Because the battery cell with the highest voltage and the group with the lowest average voltage are random, although the left and right sides of Figure 6 are different battery groups, the battery cells and the high-frequency switches are marked with the number of the first group. The left side of Figure 6 is the group where the top battery cell is located, and the right side of Figure 6 is the group with the lowest average voltage. Figure 6a , 6b 6c and 6d show a system with a transition transformer added. When realizing top balancing, two DCM cycles are required to complete a complete energy transfer process. The main control unit 150 uses the characteristics of the discontinuous conduction mode (DCM) to divide the DCM cycle into two DCM cycles. Figure 6a In the first half cycle of the first DCM, the second switch SW_S12 connected to the top balancing cell (in this embodiment, the second cell BAT_2 in the left group shown in the figure) is turned on to make it in the on state, so as to magnetize the magnetic core of the unit transformer 110 corresponding to the battery pack where the top balancing cell is located, that is, to transfer the energy of the top balancing cell to the magnetic core of the unit transformer 110 corresponding to the battery pack where the top balancing cell is located. Figure 6b As shown, then in the second half of the first DCM cycle, the second switch SW_S12 connected to the top balancing cell is disconnected to be in the off state, and the first double-pole double-throw switch 111 connecting the transition secondary winding of the unit transformer 110 corresponding to the battery pack where the top balancing cell (in this embodiment, the second cell BAT_2 of a group shown on the left in the figure) is located and the transition transformer 120 is turned on to be in the on state, thereby transferring the energy in the magnetic core of the unit transformer 110 corresponding to the battery pack where the top balancing cell (in this embodiment, the second cell BAT_2 of a group shown on the left in the figure) is located to the transition transformer 120. Figure 6c As shown, in the next DCM first half cycle (i.e., the first half cycle of the second cycle), the first double-pole double-throw switch 111 is turned off, and the third double-pole double-throw switch 113 is turned on, thereby transferring the energy in the transition transformer 120 to the magnetic core of the unit transformer 110 corresponding to the battery pack with the lowest average voltage through the transition secondary winding of the unit transformer 110 corresponding to the battery pack with the lowest average voltage. Figure 6dAs shown, the third double-pole double-throw is disconnected in the second half of the next second DCM cycle, and the unit transformer 110 corresponding to the battery pack with the lowest average voltage (the other battery pack on the right side of FIG. 6 ) is turned on, and the first switch SW_P1 connected to the battery pack with the lowest average voltage is turned on, thereby transferring the energy in the magnetic core of the unit transformer 110 corresponding to the battery pack with the lowest average voltage to the battery pack with the lowest average voltage (i.e., the battery pack on the right side of FIG. 6 ), so as to achieve top balancing, thereby avoiding an erroneous and harmful balancing control process of controlling the voltage of a battery with an excessively high voltage to a higher level.

[0131] Preferably, in an embodiment of the utility model, N battery cells are divided into i battery groups, N is an integer multiple of i, for example, N battery cells are 16 battery cells, and i battery groups are 4 battery groups. The control circuit and principle can refer to the example of 16 battery cells shown above.

[0132] In the embodiment of the utility model, the main control unit 150 is also used to control the switch states of the first switch and the second switch through the driving unit 140, and then when the maximum voltage difference among the N battery cells is greater than or equal to the top balancing start threshold, control the switch states of the first switch, the second switch, the first double-pole double-throw switch 111, the second double-pole double-throw switch 112 and the third double-pole double-throw switch 113, and then control the second switch corresponding to the battery cell with the highest voltage among the N battery cells to be turned on, and magnetize the magnetic core of the unit transformer 110 connected to the battery pack where the top balancing cell is located as the top balancing cell, and then control the energy in the magnetic core of the unit transformer 110 connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the third double-pole double-throw switch 113 in sequence to the transition secondary winding in the unit transformer 110 connected to the battery pack with the lowest average voltage among the i battery packs, and then control the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on for demagnetization.

[0133] As shown in the example of 16 battery cells above, the battery cell BAT_7 is the battery cell with the highest battery cell voltage. Therefore, in the embodiment of the present invention, the battery cell BAT_7 is the top balancing battery cell.

[0134] The main control unit 150 is further used to control the switch states of the first switch and the second switch through the driving unit 140 when the voltage of the top balancing cell is greater than the top balancing end threshold, thereby controlling the top balancing cell to continue to magnetize the magnetic core of the unit transformer 110 connected to the battery pack where the top balancing cell is located, and then controlling the energy in the magnetic core of the unit transformer 110 connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding in the unit transformer 110 connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the third double-pole double-throw switch 113 in sequence, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on for demagnetization.

[0135] As shown in the example of 16 battery cells, when the voltage of the battery cell BAT_7 is still greater than or equal to the top balancing end threshold, the switch states of the first switch and the second switch are controlled by the driving unit 140, thereby controlling the top balancing battery cell to continue to magnetize the magnetic core, and then the energy in the magnetic core of the unit transformer 110 connected to the battery pack where the top balancing battery cell is located is transferred to the transition secondary winding in the unit transformer 110 connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the third double-pole double-throw switch 113, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on for demagnetization.

[0136] When the voltage of the cell BAT_7 is less than the top balancing end threshold, the control circuit ends the current top balancing control, restarts the next round of top balancing start judgment, and then re-determines the next top balancing cell.

[0137] According to the above Figures 1 to 4The structure of the control circuit provided by the embodiment of the utility model shown in the figure analyzes the bottom balancing control, and takes the battery cell with the lowest voltage among the N battery cells as the bottom balancing battery cell. In the embodiment of the utility model, the main control unit 150 is connected to the driving unit 140 to control the switch states of the first switch, the second switch, the first double-pole double-throw switch 111, and the second double-pole double-throw switch 112 through the driving unit 140, thereby controlling the first switch corresponding to the battery group with the highest average voltage among the i battery groups to be turned on, so as to magnetize the magnetic core of the unit transformer 110 connected to the battery group with the highest average voltage, and then control the energy in the magnetic core of the unit transformer 110 connected to the battery group with the highest average voltage to be transferred to the magnetic core of the unit transformer 110 connected to the battery group where the bottom balancing battery cell is located through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the second double-pole double-throw switch 112 in sequence, thereby controlling the second switch corresponding to the bottom balancing battery cell to be turned on for demagnetization.

[0138] Taking the 48V100Ah, 16 iron-lithium battery cells connected in series that are commonly used in home storage as an example, after the 16 battery cells are divided into 4 battery groups, assuming that the voltage of the 7th battery cell is the lowest, and the total voltage of the 4 battery cells in the first battery group 1 among the 4 battery groups is the highest, bottom balancing is adopted during discharge.

[0139] like Figure 7 The bottom balancing system without a transition transformer is shown. Due to limited space, the connection structure between the cells in the first battery pack and the second battery pack and the unit transformer 110 is illustrated. Without a transition transformer, only one DCM cycle is needed to complete the energy transfer process. Figure 7 The left side is the first half of the DCM cycle. First, SW_P1 is turned on to magnetize the magnetic core from the cells BAT_1 to BAT_4 of the first battery pack 1. Then, press Figure 7 The middle right side is the second half of the DCM cycle, when SW_P1 is disconnected and SW_S23 corresponding to BAT_7 is turned on to discharge magnetism from the magnetic core to BAT_7.

[0140] In order to illustrate the superiority of the structure in which the high-voltage primary winding grouping magnetizes the magnetic core through the battery group connected to the i first switches in the embodiment of the utility model compared with the traditional structure in which only one winding on the primary side magnetizes the magnetic core through all the battery cores, for example, assuming that BAT_5 to BAT_8 of the second battery group 2 are originally 2.8V, and BAT_1 to BAT_4 of the first battery group 1 are all 3.6V, if the traditional bottom balancing treatment is that the second switches corresponding to all 16 battery cells of the system in the first half of the DCM cycle are turned on to magnetize the magnetic core, and then BAT_7 is discharged in the second half of the DCM cycle, then BAT_5, BAT_6, and BAT_8 are over-discharged, and the bottom balancing will continue to be performed on the three battery cells BAT_5, BAT_6, and BAT_8. When it is the turn of the last battery cell, it is possible that it has been discharged three more times when it is already below the over-discharge cut-off voltage, so that its voltage is already below the over-discharge cut-off voltage at that time, causing a very serious over-discharge risk.

[0141] In the embodiment of the utility model, after being divided into 4 battery groups, an adaptive method is used to first turn on the battery group with the highest average voltage to magnetize the magnetic core in the first half of the DCM cycle, and then discharge the magnetic core with the lowest voltage in the second half of the DCM cycle. This solves the problem of transferring the energy of the low-voltage battery cell to other battery cells in the traditional structure.

[0142] For example, in the embodiment of the utility model, the bottom balancing processing is to extract energy from the first battery group 1 with the highest average voltage in the group, BAT_1 to BAT_4 are all 3.6V, and use high-frequency switching to pass through the magnetic core to sequentially transfer the energy to BAT_5 to BAT_8 with a cell voltage of 2.8V. No energy will be transferred from the cell with too low voltage at all. This solves the problem of extracting energy from a cell with a low voltage to a cell with the lowest voltage.

[0143] Although it is possible that the battery cell with the lowest voltage and some battery cells with too high voltage will be grouped in the same battery pack, which may make this battery pack the group with the highest voltage, but because the group with the highest voltage in the first half of the cycle is that 4 battery cells magnetize the magnetic core, and the magnetic core demagnetizes a single battery cell (the battery cell with the lowest voltage) in the second half of the cycle, the current flowing into the battery cell when the magnetic core is demagnetized in the second half of the cycle is 4 times the current flowing out of the magnetic core when it is magnetized in the first half of the cycle, so soon the battery cell with the lowest voltage is no longer the battery cell with the lowest voltage.

[0144] Because in order to become the battery pack with the highest average voltage in the group, the voltages of other cells together with the cell with the lowest voltage must be relatively high to make this battery pack the battery pack with the highest average voltage in the group. Therefore, during the bottom balancing process, it is very likely that energy will not be extracted from other cells with lower voltages, but energy will be extracted from cells with higher voltages. For example, in the example above, the second battery pack is 4 2.8V and the first battery pack is 4 3.6V. All the cells with lower voltages are in the same battery pack. In the traditional bottom balancing operation, the energy of other cells with lower voltages will be extracted and transferred to the battery pack. However, according to the control circuit structure provided in the embodiment of the utility model and adopting an adaptive control method, energy is always transferred from the battery pack with the highest average voltage in other groups to the battery cell with the lowest voltage. In this way, all the battery cells with low voltage are concentrated in one group, and there will be no situation where energy is transferred from the battery cells with low voltage to make their voltage lower. And if the battery cell with the lowest voltage and some battery cells with high voltage are divided into the same battery group, it will not affect the operation of transferring energy from the battery pack with the highest average voltage in the group to the battery cell with the lowest voltage, and the battery cell with the lowest voltage will soon become of normal voltage.

[0145] The same principle applies to setting the top balancing cutoff threshold for top balancing. In order to prevent the battery cell with the lowest voltage from becoming normal and then immediately dropping below the over-discharge cutoff voltage in the subsequent bottom balancing, the bottom balancing cutoff threshold should be set higher than the general over-discharge cutoff voltage by a safety margin. For example, for lithium-ion batteries, the over-discharge cutoff voltage is generally set to 2.5V, and the nominal value is 3.2V. However, many bottom balancings are required to increase the voltage from 2.5V to 3.2V. Therefore, the bottom balancing cutoff threshold can be set to 2. 8V, only charge the battery cell with the lowest voltage to 2.8V first. When the new battery cell with the lowest voltage is replaced for bottom balancing, energy will not be extracted to charge the new battery cell with the lowest voltage, causing it to drop below the over-discharge cut-off voltage all of a sudden. This can avoid the voltage oscillation phenomenon caused by the voltage of the battery cell with the lowest voltage just rising to normal after bottom balancing and then falling below the over-discharge protection cut-off threshold. Also, other batteries with too low voltage will not be discharged too many times because of the process of constantly processing the battery cell with the lowest voltage to the bottom balancing threshold.

[0146] The control circuit structure provided by the embodiment of the utility model, in the top balancing of system charging, uses adaptive judgment and control to transfer energy from the battery cell with the highest voltage to the group with the lowest voltage, while in the bottom balancing of system discharging, uses adaptive judgment and control to transfer energy from the group with the highest voltage to the battery cell with the lowest voltage.

[0147] Next, the bottom balancing process is analyzed in detail through an embodiment, in which the main control unit 150 controls the driving unit 140 to control the switch to achieve energy transfer. Figure 8a , 8b 8c and 8d show a system with a transition transformer added, which is divided into two DCM cycles and shows the energy transfer process of each half cycle. Figure 8a As shown, when implementing bottom balancing, the cell with the lowest voltage among the N cells is the bottom balancing cell, and the bottom balancing cell and the battery group with the highest average voltage are random. Therefore, although the left and right sides of FIG. 8 are different battery groups, the identification numbers of the cells and each high-frequency switch are all marked with the number of the first group. The left side of FIG. 8 is the group with the highest average voltage, and the right side of FIG. 8 is the group where the bottom cell is located. Assuming that the bottom cell is BAT2, the main control unit 150 uses the characteristics of the discontinuous conduction mode (DCM) to add a transition transformer. When two DCM cycles are required to complete a complete bottom balancing, the battery group with the highest average voltage among the i battery groups (i.e., the battery group shown in this embodiment) is turned on in the first half cycle of the first DCM. Figure 8a The first switch SW_P1 of the left battery pack in the embodiment is turned on to switch on the battery pack with the highest average voltage (i.e., Figure 8a The core of the unit transformer 110 corresponding to the battery pack on the left in the figure is magnetized, that is, the energy of the battery pack with the highest average voltage among the i battery packs is transferred. Figure 8b As shown, then the battery pack with the highest average voltage among the i battery packs (i.e., the battery pack shown in this embodiment) is disconnected in the second half of the first DCM cycle. Figure 8b The first switch SW_P1 of the battery pack on the left in the figure is turned off, and the first double-pole double-throw switch 111 connecting the transition secondary winding of the unit transformer 110 corresponding to the battery pack with the highest average voltage and the transition transformer 120 is turned on, thereby transferring the energy in the magnetic core of the unit transformer 110 corresponding to the battery pack with the highest average voltage to the transition transformer 120. Figure 8c As shown, in the next DCM upper half cycle (i.e., the second DCM upper half cycle), the first double-pole double-throw switch 111 is turned off, and the second double-pole double-throw switch 112 and the bottom balancing cell (i.e., Figure 8c The battery pack (i.e., the battery pack shown in this embodiment) where the second battery cell BAT_2 of the battery pack on the right is located Figure 8c The first switch SW_P1 connected to the battery pack on the right in the figure) transfers the energy in the transition transformer 120 to the magnetic core in the unit transformer 110 corresponding to the battery pack where the bottom balancing cell (the second cell BAT_2 of the battery pack on the right) is located. Figure 8dAs shown, in the second half of the second DCM cycle, the second double-pole double-throw switch 112 and the battery pack where the bottom balancing cell is located are disconnected ( Figure 8d The first switch SW_P1 connected to the battery group on the right) is turned on, and the second switch connecting the bottom balancing cell (the second cell BAT_2 in the right group) and the secondary winding of the unit transformer 110 corresponding to the battery group where the bottom balancing cell is located is turned on, so that the energy in the magnetic core of the unit transformer 110 corresponding to the battery group where the bottom balancing cell is located is transferred to the second switch corresponding to the bottom balancing cell for demagnetization, thereby realizing bottom balancing and avoiding an erroneous and harmful balancing control process in which the voltage of the battery that is already too low is controlled to be even lower.

[0148] In the embodiment of the utility model, the main control unit 150 is also used to control the switch states of the first switch, the second switch, the first double-pole double-throw switch 111, and the second double-pole double-throw switch 112 through the driving unit 140 when the maximum voltage difference among the N battery cells is greater than or equal to the bottom balancing start threshold, thereby controlling the first switch corresponding to the battery group with the highest average voltage among the i battery groups to be turned on, so as to magnetize the magnetic core of the unit transformer 110 connected to the battery group with the highest average voltage, and then controlling the energy in the magnetic core of the unit transformer 110 connected to the battery group with the highest average voltage to be transferred to the magnetic core of the unit transformer 110 connected to the battery group where the bottom balancing battery cell is located through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the second double-pole double-throw switch 112 in sequence, thereby controlling the second switch corresponding to the bottom balancing battery cell to be turned on for demagnetization. As shown in the example of 16 battery cells above, the battery cell BAT_7 is the battery cell with the lowest battery cell voltage, so in the embodiment of the utility model, the battery cell BAT_7 is the bottom balancing battery cell.

[0149] In the embodiment of the utility model, the main control unit 150 is further used to control the switch states of the first switch, the second switch, the first double-pole double-throw switch 111, and the second double-pole double-throw switch 112 through the driving unit 140 when the voltage of the bottom balancing cell is less than or equal to the bottom balancing end threshold, thereby controlling the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer 110 connected to the battery pack with the highest average voltage, and then control the energy in the magnetic core of the unit transformer 110 connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer 110 connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the second double-pole double-throw switch 112 in sequence, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on for demagnetization.

[0150] As shown above, for the example of 16 battery cells, when the voltage of the battery cell BAT_7 is less than or equal to the bottom balancing end threshold, the switch states of the first switch, the second switch, the first double-pole double-throw switch 111, and the second double-pole double-throw switch 112 are controlled by the driving unit 140, so as to control the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer 110 connected to the battery pack with the highest average voltage, and then control the energy in the magnetic core of the unit transformer 110 connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer 110 connected to the battery pack where the bottom balancing battery cell is located through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the second double-pole double-throw switch 112 in sequence, so as to control the second switch corresponding to the bottom balancing battery cell to be turned on for demagnetization.

[0151] When the voltage of the cell BAT_7 is greater than the bottom balancing end threshold, the control circuit ends the current bottom balancing control, restarts the next round of bottom balancing start judgment, and then re-determines the next bottom balancing cell.

[0152] When all the cells are close to the discharge cut-off voltage but continue to discharge, because the condition for starting the bottom balancing threshold cannot be met, a smaller bottom balancing start threshold can be reset and the bottom balancing threshold can be set to the average voltage of all the cells to make all the cells have the same voltage after the bottom balancing. A "safety margin" can be retained similar to the previous hysteresis control to avoid voltage oscillation during balancing. Since the above example can be used as an example, I will not repeat it here.

[0153] The previous section analyzed the methods of system charging and discharging. The following section analyzes the system when it is at rest. This may be the case, for example, when the system is discharging for a while while the vehicle is driving. After the vehicle stops, the battery capacity is still very high and has not yet reached the state where charging is required, or the scheduled charging time has not yet arrived. It may also be that the battery has been placed in the warehouse for a long time. At this time, the voltages of the various cells may not be consistent. When the battery is taken out of rest or restarted, what needs to be ensured is that the system can provide the best discharge endurance when it is immediately discharged. Therefore, the battery in rest can regularly adopt the same bottom balancing method as the system in discharge, so that when the system enters the discharge state at any time from rest, all cells are maintained in the best discharge state with balanced voltage.

[0154] Because the magnetic flux needs to be connected in parallel and the energy needs to be switched from one set of windings to another, all primary and secondary windings are wound on the same magnetic core to achieve the effect of magnetic flux connection in parallel and magnetic energy being transferred from one set of coils to another through the magnetic flux. This results in the core structure shape, size and winding group configuration having to be changed according to the number of series cells in the application. When the number of series cells is large, there is often no ready-made winding frame with enough pins and a large enough core, so a new mold must be opened to manufacture a dedicated winding frame and core, and the existing automated equipment cannot cooperate with the new winding frame and core to make a suitable transformer.

[0155] To this end, we adopt unit transformer 110 to expand the system in a flexible combination manner to adapt to different numbers of series-connected battery cells.

[0156] The N cells are divided into i groups, and a separate unit transformer 110 is provided for each group. In order to reduce the types of unit standards, according to the commonly used 12V, 24V, 36V, 48V, 60V, 72V, and according to the voltage of the lithium iron battery, the number of series cells is 4 strings, 8 strings, 12 strings, 16 strings, 20 strings, and 24 strings, so the reasonable module is 4 strings.

[0157] However, to transfer energy from one unit transformer 110 to another unit transformer 110, a transition module is required. When considering using a capacitor or an inductor as a transition module, due to the high-pass characteristics of the capacitor, the instantaneous current of the capacitor transition is very large, which will damage the battery and must be limited. The current in the later stage is very small and the speed is very slow, which will cause the transition time to be too long. In order to solve this problem of small current in the later stage, the switching frequency can only be increased to keep the capacitor in the initial instant and the short initial large current. However, the loss of the semiconductor switch circuit at the switching instant is very large. Therefore, even if multiple supercapacitors are connected in parallel, the switching instant must be protected by current limiting to cause heating, and the current and voltage at the switching instant cannot be zero at the same time, and the current and voltage rise and fall period causes a large switching loss and heat. Therefore, the transition module chooses to adopt an inductive transformer structure, that is, the transition transformer 120 proposed in this embodiment. In order to reduce the number of transition modules, in addition to the unit transformer 110 with 4 strings of cells, the unit transformer 110 with 8 strings of cells can also be used. By using these two unit transformers 110 with different numbers of series cells, it is easy to combine the energy conversion and transmission systems required by different series numbers.

[0158] The number of secondary windings of the unit transformer 110, in addition to the original low-voltage secondary winding connected to the battery cell, is increased by a transition secondary winding connected to the transition module. The four secondary windings are each connected in parallel to a battery cell, that is, the original four or eight secondary windings are each connected to a battery cell, and the added transition secondary winding is not connected to any battery cell. The transition secondary winding also adopts the same switching mode as other secondary windings connected to the battery cell, except that the original part with the battery cell is left unconnected.

[0159] The transition secondary winding of each group of unit transformers 110 is connected to the primary winding side of the transition transformer 120 through a first double-pole double-throw switch, the secondary winding side of the transition transformer 120 is connected to the high-voltage primary winding side of i groups of unit transformers 110 through i second double-pole double-throw switches 112, and the secondary winding side of the transition transformer 120 is connected to the transition secondary winding side of i groups of unit transformers 110 through another i third double-pole double-throw switches 113.

[0160] The transition transformer 120 also adopts the flyback DCM control, which is explained from the bottom balance first. Assuming that the average group voltage of the 8 battery cells in the j-th group is the highest, and the voltage of the second battery cell among the 4 battery cells in the k-th group is the lowest, energy is to be transferred from the j-th group with the highest average group voltage to the second battery cell in the k-th group with the lowest average voltage. It is divided into two cycles. In the first cycle, energy is transferred from the 8 battery cells in the j-th group to the transition transformer 120 through the j-th unit transformer 110. In the second cycle, energy is transferred from the transition transformer 120 to the second battery cell among the 4 battery cells in the k-th group. The method is to turn on the primary winding of the unit transformer 110 of the j-th group in the first half of the first cycle to magnetize the magnetic core of the j-th unit transformer 110. Then, in the second half of the first cycle, the first switch on the primary side of the j-th unit transformer 110 is disconnected, and the first double-pole double-throw switch 111 connecting the transition secondary winding of the j-th unit transformer 110 and the primary winding of the transition transformer 120 is turned on. The j-th unit transformer 110 The magnetic core of the j-th unit transformer 110 discharges magnetism to the transition secondary winding of the j-th unit transformer 110, and the magnetic flux in the magnetic core of the unit transformer 110 is converted into the current in the transition secondary winding of the j-th group. The current in the transition secondary winding of the unit transformer 110 enters the primary winding of the transition transformer 120 through the first double-pole double-throw switch to magnetize the magnetic core of the transition transformer 120. In the first half of the second cycle, the first double-pole double-throw switch 111 connecting the primary winding of the transition transformer 120 and the transition secondary winding of the j-th unit transformer 110 is first disconnected, and the second double-pole double-throw switch 112 connecting the secondary winding of the transition transformer 120 and the primary winding of the k-th group unit transformer 110 is turned on. At the same time, the first switch of the primary winding of the k-th group unit transformer 110 is turned on, and the magnetic core of the transition transformer 120 discharges magnetism to the secondary winding of the transition transformer 120 to become current. The current enters the primary winding of the k-th group unit transformer 110 through the second double-pole double-throw switch 112 to magnetize the magnetic core of the k-th group unit transformer 110, and then as shown in Figure 8d In the second half of the second cycle, the second double-pole double-throw switch 112 connecting the secondary winding of the transition transformer 120 and the primary winding of the kth unit transformer 110 is first disconnected, and the first switch of the primary winding of the kth group unit transformer 110 is disconnected, and then the second switch of the second winding of the secondary of the kth group unit transformer 110 is turned on, and the magnetic core of the kth group unit transformer 110 discharges magnetism to the second winding of the secondary to become current that enters the corresponding battery core, completing the work of transferring energy from the jth group with the highest average voltage to the second battery core of the kth group with the lowest average voltage.

[0161] Next, the top balancing action is described. Assuming that the voltage of the second cell among the 8 cells in the jth group is the highest, and the average voltage of the 4 cells in the kth group is the lowest, energy is transferred from the second cell among the 8 cells in the jth group with the highest cell voltage to the 4 cells in the kth group with the lowest group average voltage. The process is divided into two cycles. In the first cycle, energy is transferred from the second cell in the jth group to the transition transformer 120 through the jth unit transformer 110. In the second cycle, energy is transferred from the transition transformer 120 to the 4 cells in the kth group. The method is to turn on the jth group in the first half of the first cycle. The second secondary winding switch of the jth unit transformer 110 magnetizes the magnetic core of the jth unit transformer 110, and then the second secondary winding switch of the jth unit transformer 110 is disconnected in the second half of the first cycle, and the first double-pole double-throw switch 111 connecting the transition secondary winding of the jth unit transformer 110 and the primary winding of the transition transformer 120 is turned on. The magnetic core of the jth unit transformer 110 discharges magnetism to the transition secondary winding of the jth unit transformer 110, and the magnetic flux in the magnetic core of the jth unit transformer 110 is converted into a current in the jth group transition secondary winding. The transition secondary winding of the jth unit transformer 110 The current in the winding enters the primary winding of the transition transformer 120 to magnetize the magnetic core of the transition transformer 120. Next, in the first half of the second cycle, the first double-pole double-throw switch 111 connecting the primary winding of the transition transformer 120 and the transition secondary winding of the j-th unit transformer 110 is disconnected, and the third double-pole double-throw switch 113 connecting the secondary winding of the transition transformer 120 and the transition secondary winding of the k-th group unit transformer 110 is conducted. The magnetic core of the transition transformer 120 discharges magnetism to the secondary winding of the transition transformer 120 to become current, and the current passes through the third double-pole double-throw switch 113 and enters the k-th group unit transformer 110. The transition secondary winding of the element transformer 110 magnetizes the magnetic core of the k-th group unit transformer 110, and then in the second half of the second cycle, the third double-pole double-throw switch 113 connecting the secondary winding of the transition transformer 120 and the transition secondary winding of the k-th group unit transformer 110 is disconnected, and the primary winding switch of the k-th group unit transformer 110 is turned on, and the magnetic core of the k-th group unit transformer 110 discharges magnetism to the primary winding to become current entering the corresponding 4 battery cells, completing the work of transferring energy from the second battery cell of the j-th group with the highest battery cell voltage to the 4 battery cells of the k-th group with the lowest group voltage.

[0162] like Fig. 9 As shown in FIG. 1 , another structure of the unit transformer 110 is shown. When the unit transformer 110 is connected to 8 cells, as shown in FIG. Fig. 9The 8-cell unit transformer 110 has two sets of windings on the primary side, each connected to 4 cells, and a total of 9 secondary windings, of which 8 windings are connected to one cell each, and the 9th winding is left unconnected as a transition secondary winding. The top balancing and bottom balancing operations are the same as above, but in this way, using an 8-cell unit transformer 110 in the case of 8 cells saves a transition secondary winding and a corresponding double-pole double-throw switch compared to using two 4-cell unit transformers 110.

[0163] like Fig.10 As shown, an embodiment of the utility model provides a unit transformer 110 module for actively balancing the battery. The unit transformer 110 module is applied to any of the above-mentioned control circuits to actively balance N series-connected battery cells divided into i battery groups, where i is an integer greater than or equal to 2.

[0164] The unit transformer 110 module includes i unit transformers 110, i first switches, a transition transformer 120, i first double-pole double-throw switches 111, i second double-pole double-throw switches 112 and i third double-pole double-throw switches 113;

[0165] The i unit transformers 110 are respectively connected to the i battery packs in a one-to-one correspondence through a first switch; the transition transformer 120 includes a transition transformer 120 primary winding and a transition transformer 120 secondary winding;

[0166] The unit transformer 110 includes a magnetic core, and a high-voltage primary winding and (M+1) secondary windings wound around the magnetic core, and the (M+1) secondary windings include M low-voltage secondary windings and 1 transition secondary winding; the value of M corresponding to the unit transformer 110 is the same as the number of cells in the battery pack connected to the unit transformer 110; the M secondary windings in the unit transformer 110 are respectively connected to all the cells in the battery pack connected to the unit transformer 110 through a different second switch in a one-to-one correspondence;

[0167] The transition secondary windings in the i unit transformers 110 are connected in parallel with the primary winding of the transition transformer 120 through a first double-pole double-throw switch 111;

[0168] The high-voltage primary windings in the i unit transformers 110 are connected in parallel with the secondary windings of the transition transformer 120 through a second double-pole double-throw switch 112;

[0169] The transition secondary windings in the i unit transformers 110 are connected in parallel with the secondary winding of the transition transformer 120 via a third double-pole double-throw switch 113 respectively.

[0170] Optionally, the unit transformer 110 module for actively balancing the battery provided in the embodiment of the present invention further includes: Figure 4 The analog-to-digital conversion module 130, the driving unit 140 and the main control unit 150 shown, the analog-to-digital conversion module 130 includes N input terminals, and the N input terminals of the analog-to-digital conversion module 130 are used to be connected to the N battery cells in a one-to-one correspondence;

[0171] The main control unit 150 is used to connect to the analog-to-digital conversion module 130 and collect the voltage of each of the N battery cells through the analog-to-digital conversion module 130;

[0172] A driving unit 140, used for connecting i first switches, N second switches, i first double-pole double-throw switches 111, i second double-pole double-throw switches 112 and i third double-pole double-throw switches 113;

[0173] The main control unit 150 is further used to connect to the driving unit 140, so as to control the switch states of the first switch, the second switch, the first double-pole double-throw switch 111, and the second double-pole double-throw switch 112 through the driving unit 140, and then control the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer 110 connected to the battery pack with the highest average voltage, and then control the energy in the magnetic core of the unit transformer 110 connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer 110 connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120, and the second double-pole double-throw switch 112 in sequence, and then control the second switch corresponding to the bottom balancing cell to be turned on for magnetization, and the cell with the lowest voltage among the N cells is used as the bottom balancing cell;

[0174] The main control unit 150 is further used to control the switch states of the first switch, the second switch, the first double-pole double-throw switch 111, the second double-pole double-throw switch 112 and the third double-pole double-throw switch 113 through the driving unit 140, thereby controlling the second switch corresponding to the battery cell with the highest voltage among the N battery cells to be turned on, so as to magnetize the magnetic core of the unit transformer 110 connected to the battery pack where the top balancing cell is located as the top balancing cell, and then control the energy in the magnetic core of the unit transformer 110 connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding in the unit transformer 110 connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch 111, the transition transformer 120 and the third double-pole double-throw switch 113 in sequence, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on for demagnetization.

[0175] In the embodiment of the present utility model, the bottom balance control can refer to the above bottom balance control method and Figures 8a-8d The schematic diagram and explanation of the bottom equalization control shown will not be repeated here.

[0176] In the description of the present invention, it should be understood that the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inside", "front", "center", "both ends" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0177] In addition, the terms "first", "second", "third" and "fourth" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first", "second", "third" and "fourth" may explicitly or implicitly include at least one of such features.

[0178] In the present utility model, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "screw-on" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the utility model according to the specific circumstances.

[0179] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0180] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A control circuit for actively balancing batteries using a unit transformer, characterized in that: Comprising N battery cells connected in series, the N battery cells are divided into i battery groups, where i is an integer greater than or equal to 2; The control circuit further includes i unit transformers and i first switches, wherein the i unit transformers are respectively connected to the i battery packs in a one-to-one correspondence through one of the first switches; The control circuit further includes N second switches; the N second switches are connected to the N battery cells in a one-to-one correspondence; The unit transformer comprises a magnetic core, and a high-voltage primary winding and (M+1) secondary windings wound around the magnetic core, wherein the (M+1) secondary windings comprise M low-voltage secondary windings and 1 transition secondary winding; The value of M corresponding to the unit transformer is the same as the number of cells in the battery pack connected to the unit transformer; The M secondary windings in the unit transformer are respectively connected one by one to all the cells in the battery pack correspondingly connected to the unit transformer through one of the second switches; The high-voltage primary winding of the unit transformer and the battery pack correspondingly connected to the unit transformer are connected in parallel via the first switch; The control circuit further includes a transition transformer, i first double-pole double-throw switches, i second double-pole double-throw switches and i third double-pole double-throw switches, wherein the transition transformer includes a transition transformer primary winding and a transition transformer secondary winding; The transition secondary windings in i of the unit transformers are respectively connected in parallel with the primary winding of the transition transformer via one of the first double-pole double-throw switches; The high-voltage primary windings in i of the unit transformers are respectively connected in parallel with the secondary windings of the transition transformer via one of the second double-pole double-throw switches; The transition secondary windings in i of the unit transformers are respectively connected in parallel with the secondary winding of the transition transformer via one of the third double-pole double-throw switches; Furthermore, the control circuit further comprises an analog-to-digital conversion module, a driving unit and a main control unit, the analog-to-digital conversion module comprises N input terminals, and the N input terminals of the analog-to-digital conversion module are connected to the N battery cells in a one-to-one correspondence; The main control unit is connected to the analog-to-digital conversion module to collect the voltage of each of the N battery cells through the analog-to-digital conversion module; The driving unit is connected to the i first switches, the N second switches, the i first double-pole double-throw switches, the i second double-pole double-throw switches and the i third double-pole double-throw switches; The cell with the lowest voltage among the N cells is used as the bottom balancing cell. The main control unit is connected to the driving unit to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, and the second double-pole double-throw switch through the driving unit, thereby controlling the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer connected to the battery pack with the highest average voltage, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch, the transition transformer, and the second double-pole double-throw switch in sequence, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on to demagnetize the bottom balancing cell; The cell with the highest voltage among the N cells is used as the top balancing cell. The main control unit controls the switch states of the first switch, the second switch, the first double-pole double-throw switch, the second double-pole double-throw switch and the third double-pole double-throw switch through the driving unit, thereby controlling the second switch corresponding to the top balancing cell to be turned on to magnetize the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding in the unit transformer connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch, the transition transformer and the third double-pole double-throw switch in sequence, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on for demagnetization.

2. The control circuit for actively balancing batteries using a unit transformer according to claim 1, characterized in that: The N battery cells are equally divided into i battery groups; the number of battery cells in each of the i-1 battery groups is set to be the same, and the number of battery cells in the i-th battery group is the quotient plus the remainder of N divided by i.

3. The control circuit for actively balancing batteries using a unit transformer according to claim 2, characterized in that: The N battery cells are 16 battery cells, and the i battery packs are 4 battery packs.

4. The control circuit for actively balancing batteries using a unit transformer according to claim 1, characterized in that: The main control unit is further used to control the switch states of the first switch and the second switch through the driving unit, and then when the maximum voltage difference among the N battery cells is greater than or equal to the top balancing start threshold, control the switch states of the first switch, the second switch, the first double-pole double-throw switch, the second double-pole double-throw switch and the third double-pole double-throw switch, and then control the second switch corresponding to the top balancing battery cell to be turned on to magnetize the magnetic core of the unit transformer connected to the battery pack where the top balancing battery cell is located, and then control the energy in the magnetic core of the unit transformer connected to the battery pack where the top balancing battery cell is located to be transferred to the transition secondary winding in the unit transformer connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch, the transition transformer and the third double-pole double-throw switch in sequence, and then control the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on to discharge magnetism; The main control unit is further used to control the switch states of the first switch and the second switch through the driving unit when the voltage of the top balancing cell is greater than or equal to the top balancing end threshold, thereby controlling the second switch corresponding to the top balancing cell to be turned on to continue magnetizing the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding in the unit transformer connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch, the transition transformer, and the third double-pole double-throw switch in sequence, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on for demagnetization; The main control unit is further configured to stop top balancing when the voltage of the top balancing cell is lower than the top balancing end threshold.

5. The control circuit for actively balancing batteries using a unit transformer according to claim 1, characterized in that: The main control unit is further used to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, and the second double-pole double-throw switch through the driving unit when the maximum voltage difference among the N battery cells is greater than or equal to the bottom balancing start threshold, thereby controlling the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer connected to the battery pack with the highest average voltage, and then control the energy in the magnetic core of the unit transformer connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer connected to the battery pack where the bottom balancing battery cell is located through the first double-pole double-throw switch, the transition transformer, and the second double-pole double-throw switch in sequence, thereby controlling the second switch corresponding to the bottom balancing battery cell to be turned on for demagnetization; The main control unit is further used to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, and the second double-pole double-throw switch through the driving unit when the voltage of the bottom balancing cell is less than or equal to the bottom balancing end threshold, thereby controlling the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer connected to the battery pack with the highest average voltage, and then control the energy in the magnetic core of the unit transformer connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch, the transition transformer, and the second double-pole double-throw switch in sequence, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on for demagnetization; The main control unit is further configured to stop bottom balancing when the voltage of the bottom balancing cell is greater than the bottom balancing end threshold.

6. The control circuit for actively balancing batteries using a unit transformer according to claim 1, characterized in that: The first switch and the second switch are high-frequency switches respectively.

7. The control circuit for actively balancing batteries using a unit transformer according to claim 1, characterized in that: The main control unit and the driving unit are single chip microcomputers.

8. The control circuit for actively balancing batteries using a unit transformer according to claim 1, characterized in that: The analog-to-digital conversion module comprises a MUX multiplexing device, a differential amplifier module and an analog-to-digital converter connected in series.

9. The control circuit for actively balancing batteries using a unit transformer according to claim 1, characterized in that: The first switch and the second switch are metal oxide semiconductor field effect transistors.

10. A unit transformer module for active balancing control of batteries, characterized in that: The unit transformer module is applied to the control circuit described in any one of claims 1 to 9, and is used to actively balance N series-connected cells divided into i battery groups, where i is an integer greater than or equal to 2; The unit transformer module includes i unit transformers, i first switches, a transition transformer, i first double-pole double-throw switches, i second double-pole double-throw switches and i third double-pole double-throw switches; The i unit transformers are respectively connected to the i battery packs in a one-to-one correspondence through one of the first switches; the transition transformer includes a transition transformer primary winding and a transition transformer secondary winding; The unit transformer includes a magnetic core, and a high-voltage primary winding and (M+1) secondary windings wound around the magnetic core, wherein the (M+1) secondary windings include M low-voltage secondary windings and 1 transition secondary winding; the value of M corresponding to the unit transformer is the same as the number of cells in the battery pack connected to the unit transformer; the M secondary windings in the unit transformer are respectively connected to all the cells in the battery pack connected to the unit transformer in a one-to-one correspondence through a different second switch; The transition secondary windings in i of the unit transformers are respectively connected in parallel with the primary winding of the transition transformer via one of the first double-pole double-throw switches; The high-voltage primary windings in i of the unit transformers are respectively connected in parallel with the secondary windings of the transition transformer via one of the second double-pole double-throw switches; The transition secondary windings in the i unit transformers are respectively connected in parallel with the secondary winding of the transition transformer via one of the third double-pole double-throw switches.

11. The unit transformer module for active balancing control of batteries according to claim 10, characterized in that: It also includes an analog-to-digital conversion module, a drive unit, and a main control unit, wherein the analog-to-digital conversion module includes N input terminals, and the N input terminals of the analog-to-digital conversion module are used to be connected to the N battery cells in a one-to-one correspondence; The main control unit is used to connect to the analog-to-digital conversion module, and collect the voltage of each of the N battery cells through the analog-to-digital conversion module; The driving unit is used to connect the i first switches, the N second switches, the i first double-pole double-throw switches, the i second double-pole double-throw switches and the i third double-pole double-throw switches; The cell with the lowest voltage among the N cells is used as the bottom balancing cell. The main control unit is further used to connect to the driving unit to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, and the second double-pole double-throw switch through the driving unit, thereby controlling the first switch corresponding to the battery pack with the highest average voltage among the i battery packs to be turned on, so as to magnetize the magnetic core of the unit transformer connected to the battery pack with the highest average voltage, and then control the energy in the magnetic core of the unit transformer connected to the battery pack with the highest average voltage to be transferred to the magnetic core of the unit transformer connected to the battery pack where the bottom balancing cell is located through the transition secondary winding, the first double-pole double-throw switch, the transition transformer, and the second double-pole double-throw switch in sequence, thereby controlling the second switch corresponding to the bottom balancing cell to be turned on for demagnetization; The cell with the highest voltage among the N cells is used as the top balancing cell. The main control unit is further used to control the switch states of the first switch, the second switch, the first double-pole double-throw switch, the second double-pole double-throw switch and the third double-pole double-throw switch through the driving unit, thereby controlling the second switch corresponding to the top balancing cell to be turned on to magnetize the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located, and then controlling the energy in the magnetic core of the unit transformer connected to the battery pack where the top balancing cell is located to be transferred to the transition secondary winding in the unit transformer connected to the battery pack with the lowest average voltage among the i battery packs through the transition secondary winding, the first double-pole double-throw switch, the transition transformer and the third double-pole double-throw switch in sequence, thereby controlling the first switch corresponding to the battery pack with the lowest average voltage among the i battery packs to be turned on for demagnetization.

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