Battery module double-target equalization circuit and method based on double multi-winding flyback transformers

Abstract

The invention discloses a battery module double-target equalization circuit and method based on double multi-winding flyback transformers, a battery module is formed by connecting n single batteries numbered according to a position sequence in a positive-negative connection and series mode, and the equalization circuit is provided with one multi-winding flyback transformer on each of the left side and the right side of the battery module. The right side multi-winding flyback transformer II is used for discharging equalization of a high-electric-quantity battery, the left side multi-winding flyback transformer is used for charging equalization of a low-electric-quantity battery, and primary windings of the flyback transformers on the two sides are connected with the whole battery module through MOS tubes and diodes. And the upper end and the lower end of each secondary winding are respectively connected with the corresponding battery through one MOS tube and one diode to form a loop. According to the equalization method, the difference values relative to the SOC mean value in the single batteries are compared in real time, and the high-electric-quantity or low-electric-quantity battery with the large difference value is selected for charging and discharging, so that the equalization speed is improved.

Description

Technical Field

[0001] The present invention belongs to the field of power electronic converters, and in particular relates to a dual-target balancing circuit and method for a battery module based on a dual multi-winding flyback transformer. Background Art

[0002] At present, energy storage systems based on lithium batteries have become an indispensable part of smart grid construction. Among them, energy storage battery technology, as a key technology, has not only promoted the rapid development of electric vehicles, but also promoted the intelligence of large-scale distributed power grids.

[0003] In order to obtain a voltage level that meets the requirements of practical application engineering, multiple single lithium batteries are usually connected in series to obtain high voltage and large capacity. Due to manufacturing processes, materials, and attenuation rates, the internal resistance of the battery module will increase with the increase of charging and discharging time, while the capacity will gradually decrease. This change in turn will reduce the available capacity of the series battery pack and even cause safety hazards due to overcharging and over-discharging. Therefore, in order to improve the safety and reliability of energy storage modules and extend their cycle life, the key technology of battery balancing must be used to reduce the inconsistency of the battery pack.

[0004] Battery balancers can be divided into energy-consuming balancers and non-energy-consuming balancers. Among them, energy-consuming balancers consume excess energy in batteries with higher SOC by connecting resistors in parallel to single cells. They have simple structures, low costs, and are easy to implement, but they have large losses and low efficiency. In addition, the circuit temperature rises significantly during the balancing process, which can easily cause safety hazards. Common structures in non-energy-consuming balancers include capacitors and their derivative topologies, inductors and their derivative topologies, transformers and their derivative topologies, etc. Among them, the balancing topology based on inductors or capacitors has a huge disadvantage. Energy cannot be directly transferred between single cells, and energy will cause excessive losses during step-by-step transmission. This disadvantage is particularly obvious for battery pack modules with too many series connections. In view of the shortcomings of the inductor and capacitor balancing circuit, a transformer-based balancing method is used to shorten the balancing path and improve the balancing efficiency. For example, a topology based on a flyback converter has the advantage that energy can be transferred between any single cells, but only a single battery can be charged and discharged at the same time, which affects the battery balancing speed. Summary of the invention

[0005] The present invention provides a dual-target balancing circuit and method for a battery module based on a dual multi-winding flyback transformer. The balancing circuit is easy to expand and can realize the integration of balancing control of the charging and discharging process, so that the single battery with the largest difference is balanced first, thereby improving the balancing speed.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] A dual-target balancing circuit for a battery module based on a dual multi-winding flyback transformer, wherein the battery module is composed of n single batteries numbered in sequence and connected in series with positive and negative electrodes, and the balancing circuit includes two multi-winding flyback transformers, 2n+2 MOS tubes and 2n+2 diodes;

[0008] The positive terminal of the i-th single cell is connected to the negative electrode of the 2i-1th diode, and the negative terminal of the i-th single cell is connected to the positive terminal of the 2i-1th MOS tube; the same-name terminal and the opposite-name terminal of the i-th winding on the secondary side of the multi-winding flyback transformer I are connected to the positive electrode of the 2i-1th diode and the negative terminal of the 2i-1th MOS tube respectively;

[0009] The primary side like-name terminal of the multi-winding flyback transformer I is connected to the positive electrode of the 2n+1th diode, the negative electrode of the 2n+1th diode is connected to the positive electrode of the 2n+1th MOS tube, and the negative electrode of the 2n+1th MOS tube is connected to the negative electrode of the nth single cell; the primary side opposite-name terminal of the multi-winding flyback transformer I is connected to the positive electrode of the first single cell;

[0010] The positive terminal of the i-th single cell is connected to the positive terminal of the 2i-th diode, and the negative terminal of the i-th single cell is connected to the negative terminal of the 2i-th MOS tube; the same-name terminal and the opposite-name terminal of the i-th winding on the secondary side of the multi-winding flyback transformer II are connected to the negative terminal of the 2i-1-th diode and the positive terminal of the 2i-1-th MOS tube respectively;

[0011] The primary side like-name end of the multi-winding flyback transformer II is connected to the negative electrode of the nth single cell; the primary side opposite-name end of the multi-winding flyback transformer II is connected to the positive electrode of the 2n+2th diode, the negative electrode of the 2n+2th diode is connected to the positive electrode of the 2n+2th MOS tube, and the negative electrode of the 2n+2th MOS tube is connected to the positive electrode of the 1st single cell.

[0012] Furthermore, the single battery is replaced by a battery pack.

[0013] A dual-target balancing method for a battery module based on a dual multi-winding flyback transformer, using the above-mentioned battery module balancing circuit based on a dual flyback transformer, comprises:

[0014] Step 1: Obtain the SOC of each single battery in real time and extract the maximum SOC max and minimum SOC min , and calculate and update the average SOC of all single cells average , the first difference Δ1 and the second difference Δ2:

[0015] Δ1=SOC max -SOC average

[0016] Δ2=SOC average -SOC min

[0017] Step 2, compare the first difference Δ1 with the second difference Δ2, if Δ1>Δ2, start the multi-winding flyback transformer II to discharge the high-power single battery in the battery module; if Δ1<Δ2, start the multi-winding flyback transformer I to charge the low-power single battery in the battery module.

[0018] Furthermore, the starting multi-winding flyback transformer II is used to discharge the high-capacity single battery in the battery module, including:

[0019] Step A1, find the battery module with SOC greater than SOC average All single cells;

[0020] Step A2, connecting the loops formed between the high-capacity batteries found in step A1 and the secondary windings of the multi-winding flyback transformer II, disconnecting the other loops, and maintaining the high-capacity battery discharge time of a preset length, so that the single cells store the electricity in the multi-winding flyback transformer II;

[0021] Step A3, disconnect the loops formed between these high-capacity batteries and the secondary measuring windings of the multi-winding flyback transformer II, and close and turn on the 2n+2th MOS tube, while keeping the remaining loops disconnected, and maintaining the overall battery charging time of a preset length, so that the power stored in the multi-winding flyback transformer II can be transferred to the entire battery module.

[0022] Furthermore, the starting multi-winding flyback transformer I is used to charge low-power single cells in the battery module, including:

[0023] Step B1, find the battery module with SOC less than SOC average All single cells;

[0024] Step B2, closing and conducting the 2n+1th MOS tube, so that the loop formed between the entire battery module and the primary winding of the multi-winding flyback transformer I is conducted, and the other loops are disconnected, and the overall battery discharge time of the preset time is maintained, so that the entire battery module charges the primary winding of the multi-winding flyback transformer I;

[0025] Step B3, disconnect the loop formed between the entire battery module and the primary winding of the multi-winding flyback transformer I, and connect the loops formed between the single cells found in step B1 and the secondary windings of the multi-winding flyback transformer I respectively, and disconnect the remaining loops, and maintain the low-battery charging time of a preset time to transfer the power stored in the primary winding of the multi-winding flyback transformer I to the low-battery found in step B1.

[0026] Furthermore, between step 1 and step 2, step 1.5 is also included: calculating and updating the range difference ΔSOC=SOC of all single cells max -SOC min Only when the extreme difference ΔSOC is greater than the preset threshold value, step 2 is executed to balance the charge and discharge of the battery module. Otherwise, step 2 is not executed, that is, the charge and discharge balance of the battery module is not performed.

[0027] Furthermore, after executing step A3 or step B3, the process returns to step 1 to enter the next round of balancing the battery modules.

[0028] Furthermore, all n single cells in the battery module are clustered to divide single cells with high power and single cells with low power.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) Easy to expand. The flyback transformer used in the present invention has a wide input voltage range, so the balancing object can be a single battery or a battery pack, making the balancing circuit of the battery module easy to expand;

[0031] (2) Fast balancing speed. The battery module dual-target balancing circuit of the present invention can directly transfer balancing energy between any number of single cells and battery modules, shortening the balancing path and effectively reducing the time required for balancing a large number of series-connected batteries. The battery module dual-target balancing method of the present invention can balance the single cells with the largest differences first, thereby improving the balancing speed.

[0032] (3) Simple control. Only two sets of flyback transformers are needed, and the control signals required for the primary and secondary sides of the transformers are simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The balancing circuit topology based on the dual multi-winding flyback transformer proposed by the present invention;

[0034] Figure 2 This is a working principle diagram of the flyback transformer on the right side of the balancing circuit proposed by the present invention;

[0035] Figure 3This is a working principle diagram of the flyback transformer on the left side of the balancing circuit proposed by the present invention;

[0036] Figure 4 This is a flow chart of the dual-objective equilibrium strategy of the present invention. DETAILED DESCRIPTION

[0037] The following is a detailed description of an embodiment of the present invention. This embodiment is based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process to further explain the technical solution of the present invention.

[0038] Example 1

[0039] This embodiment provides a dual-target balancing circuit for a battery module based on a dual multi-winding flyback transformer. Figure 1 As shown, the battery module is composed of n single cells numbered in sequence and connected in series with positive and negative terminals, the n single cells are marked as B1, B2, ..., Bn in sequence, and the balancing circuit includes 2 multi-winding flyback transformers, 2n+2 MOS tubes and 2n+2 diodes.

[0040] The positive terminal of the i-th single cell is connected to the negative electrode of the 2i-1th diode, and the negative terminal of the i-th single cell is connected to the positive terminal of the 2i-1th MOS tube; the same-name end and the opposite-name end of the i-th winding on the secondary side of the multi-winding flyback transformer I are connected to the positive electrode of the 2i-1th diode and the negative terminal of the 2i-1th MOS tube respectively; i=1,2,……,n.

[0041] The primary side like-name terminal of the multi-winding flyback transformer I is connected to the positive electrode of the 2n+1th diode, the negative electrode of the 2n+1th diode is connected to the positive electrode of the 2n+1th MOS tube, and the negative electrode of the 2n+1th MOS tube is connected to the negative electrode of the nth single cell; the primary side opposite-name terminal of the multi-winding flyback transformer I is connected to the positive electrode of the 1st single cell.

[0042] The positive terminal of the i-th single cell is connected to the positive terminal of the 2i-th diode, and the negative terminal of the i-th single cell is connected to the negative terminal of the 2i-th MOS tube; the same-name end and the opposite-name end of the i-th winding on the secondary side of the multi-winding flyback transformer II are connected to the negative electrode of the 2i-1-th diode and the positive terminal of the 2i-1-th MOS tube respectively; i=1,2,……,n.

[0043] The primary side like-name end of the multi-winding flyback transformer II is connected to the negative electrode of the nth single cell; the primary side opposite-name end of the multi-winding flyback transformer II is connected to the positive electrode of the 2n+2th diode, the negative electrode of the 2n+2th diode is connected to the positive electrode of the 2n+2th MOS tube, and the negative electrode of the 2n+2th MOS tube is connected to the positive electrode of the 1st single cell.

[0044] Example 2

[0045] This embodiment provides a dual-target balancing method for a battery module based on a dual multi-winding flyback transformer, using the battery module balancing circuit based on a dual flyback transformer described in Example 1, referring to Figure 2 As shown, including:

[0046] Step 1: Obtain the SOC of each single battery in real time and extract the maximum SOC max and minimum SOC min , and calculate and update the average SOC of all single cells average , range ΔSOC, first difference Δ1 and second difference Δ2:

[0047] ΔSOC=SOC max -SOC min

[0048] Δ1=SOC max -SOC average

[0049] Δ2=SOC average -SOC min

[0050] Step 1.5, determine whether the range difference ΔSOC is greater than a preset threshold β. When ΔSOC>β is satisfied, continue to execute step 2 to balance the charge and discharge of the battery module. Otherwise, do not execute step 2, that is, do not balance the charge and discharge of the battery module.

[0051] Step 2, compare the first difference Δ1 with the second difference Δ2, if Δ1>Δ2, start the multi-winding flyback transformer II to discharge the high-power single battery in the battery module; if Δ1<Δ2, start the multi-winding flyback transformer I to charge the low-power single battery in the battery module.

[0052] Among them, the starting multi-winding flyback transformer II is used to discharge the high-capacity single battery in the battery module, including:

[0053] Step A1, find the battery module with SOC greater than SOC average All single cells.

[0054] Step A2: connect the loops formed between the high-capacity batteries found in step A1 and the secondary windings of the multi-winding flyback transformer II (by closing the MOS tubes on the control loop), disconnect the other loops, and maintain the high-capacity battery discharge time of a preset length, so that the single cells store the power in the multi-winding flyback transformer II. Figure 3 Shown by the red line.

[0055] Step A3, disconnect the loops formed between these high-capacity batteries and the secondary windings of the multi-winding flyback transformer II (by disconnecting the MOS tubes on the control loop), and close and conduct the 2n+2 MOS tubes, while keeping the remaining loops disconnected, and maintaining the overall battery charging time of the preset duration, so that the power stored in the multi-winding flyback transformer II is transferred to the entire battery module. Figure 3 Shown by the blue line.

[0056] After executing step A3, return to step 1 to enter the next round of balancing the battery modules.

[0057] In addition, the starting multi-winding flyback transformer I is used to charge low-power single cells in the battery module, including:

[0058] Step B1, find the battery module with SOC less than SOC average All single cells.

[0059] Step B2, close and conduct the 2n+1th MOS tube, so that the loop formed between the entire battery module and the primary winding W1 of the multi-winding flyback transformer I is connected, and the other loops are disconnected, and the overall battery discharge time of the preset time is maintained, so that the entire battery module charges the primary winding W1 of the multi-winding flyback transformer I. Figure 4 Shown by the red line.

[0060] Step B3, disconnect the loop formed between the entire battery module and the primary winding W1 of the multi-winding flyback transformer I, and connect the loops formed between the low-power single batteries found in step B1 and the secondary windings of the multi-winding flyback transformer I (by closing the MOS tube on the control loop), and disconnect the other loops, and keep the low-power battery charging time for a preset time to transfer the power stored in the primary winding of the multi-winding flyback transformer I to the low-power batteries found in step B1. Figure 4 Shown by the blue line.

[0061] After executing step B3, return to step 1 to enter the next round of balancing the battery modules.

[0062] The battery module dual-target balancing circuit and method of the present invention can ensure that the charge state of each battery in the battery pack is kept in a relatively balanced state, so as to improve the overall performance and life of the battery module.

[0063] The above embodiments are preferred embodiments of the present application. Ordinary technicians in this field can also make various changes or improvements on this basis. Without departing from the overall concept of the present application, these changes or improvements should fall within the scope of protection required by the present application.

Claims

1. A dual-target balancing circuit for a battery module based on a dual multi-winding flyback transformer, characterized in that: The battery module is composed of n single batteries numbered in sequence and connected in series with positive and negative electrodes, and the balancing circuit includes two multi-winding flyback transformers, 2n+2 MOS tubes and 2n+2 diodes; The positive terminal of the i-th single cell is connected to the negative electrode of the 2i-1th diode, and the negative terminal of the i-th single cell is connected to the positive terminal of the 2i-1th MOS tube; the same-name terminal and the opposite-name terminal of the i-th winding on the secondary side of the multi-winding flyback transformer I are connected to the positive electrode of the 2i-1th diode and the negative terminal of the 2i-1th MOS tube respectively; The primary side like-name terminal of the multi-winding flyback transformer I is connected to the positive electrode of the 2n+1th diode, the negative electrode of the 2n+1th diode is connected to the positive electrode of the 2n+1th MOS tube, and the negative electrode of the 2n+1th MOS tube is connected to the negative electrode of the nth single cell; the primary side opposite-name terminal of the multi-winding flyback transformer I is connected to the positive electrode of the first single cell; The positive terminal of the i-th single cell is connected to the positive terminal of the 2i-th diode, and the negative terminal of the i-th single cell is connected to the negative terminal of the 2i-th MOS tube; the same-name terminal and the opposite-name terminal of the i-th winding on the secondary side of the multi-winding flyback transformer II are connected to the negative terminal of the 2i-1-th diode and the positive terminal of the 2i-1-th MOS tube respectively; The primary side like-name end of the multi-winding flyback transformer II is connected to the negative electrode of the nth single cell; the primary side opposite-name end of the multi-winding flyback transformer II is connected to the positive electrode of the 2n+2th diode, the negative electrode of the 2n+2th diode is connected to the positive electrode of the 2n+2th MOS tube, and the negative electrode of the 2n+2th MOS tube is connected to the positive electrode of the 1st single cell.

2. The battery module dual-target balancing circuit based on dual multi-winding flyback transformer according to claim 1, characterized in that: The single battery is replaced by a battery pack.

3. A dual-target balancing method for battery modules based on dual multi-winding flyback transformers, using the battery module balancing circuit based on dual flyback transformers according to claim 1, characterized in that: include: Step 1: Obtain the SOC of each single battery in real time and extract the maximum SOC max and minimum SOC min , and calculate and update the average SOC of all single cells average , the first difference Δ1 and the second difference Δ2: Δ1=SOC max -SOC average Δ2=SOC average -SOC min Step 2, compare the first difference Δ1 with the second difference Δ2, if Δ1>Δ2, start the multi-winding flyback transformer II to discharge the high-power single battery in the battery module; if Δ1<Δ2, start the multi-winding flyback transformer I to charge the low-power single battery in the battery module.

4. The dual-target balancing method for battery modules based on dual multi-winding flyback transformers according to claim 3 is characterized in that: The starting multi-winding flyback transformer II is used to discharge the high-capacity single battery in the battery module, including: Step A1, find the battery module with SOC greater than SOC average All single cells; Step A2, connecting the loops formed between the high-capacity batteries found in step A1 and the secondary windings of the multi-winding flyback transformer II, disconnecting the other loops, and maintaining the high-capacity battery discharge time of a preset length, so that the single cells store the electricity in the multi-winding flyback transformer II; Step A3, disconnect the loops formed between these high-capacity batteries and the secondary measuring windings of the multi-winding flyback transformer II, and close and turn on the 2n+2th MOS tube, while keeping the remaining loops disconnected, and maintaining the overall battery charging time of a preset length, so that the power stored in the multi-winding flyback transformer II can be transferred to the entire battery module.

5. The dual-target balancing method for battery modules based on dual multi-winding flyback transformers according to claim 3, characterized in that: The starting multi-winding flyback transformer I is used to charge low-power single cells in the battery module, and includes: Step B1, find the battery module with SOC less than SOC average All single cells; Step B2, closing and conducting the 2n+1th MOS tube, so that the loop formed between the entire battery module and the primary winding of the multi-winding flyback transformer I is conducted, and the other loops are disconnected, and the overall battery discharge time of the preset time is maintained, so that the entire battery module charges the primary winding of the multi-winding flyback transformer I; Step B3, disconnect the loop formed between the entire battery module and the primary winding of the multi-winding flyback transformer I, and connect the loops formed between the single cells found in step B1 and the secondary windings of the multi-winding flyback transformer I respectively, and disconnect the remaining loops, and maintain the low-battery charging time of a preset time to transfer the power stored in the primary winding of the multi-winding flyback transformer I to the low-battery found in step B1.

6. The dual-target balancing method for battery modules based on dual multi-winding flyback transformers according to claim 4 or 5, characterized in that: Step 1.5 is also included between step 1 and step 2: Calculate and update the range of all single cells ΔSOC = SOC max -SOC min Only when the extreme difference ΔSOC is greater than the preset threshold value, step 2 is executed to balance the charge and discharge of the battery module. Otherwise, step 2 is not executed, that is, the charge and discharge balance of the battery module is not performed.

7. The dual-target balancing method for battery modules based on dual multi-winding flyback transformers according to claim 6, characterized in that: After executing step A3 or step B3, return to step 1 to enter the next round of balancing the battery modules.

8. The dual-target balancing method for battery modules based on dual multi-winding flyback transformers according to claim 3, characterized in that: All n single cells in the battery module are clustered to divide the single cells with high power and the single cells with low power.

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