A high-frequency large-current equalization circuit and control method for a power battery

Abstract

The application belongs to the technical field of battery equalization, and provides a high-frequency large-current equalization circuit and control method for power batteries. The equalization circuit comprises a plurality of battery monomers. Odd battery monomers are controlled for energy equalization by a first transformer module, and even battery monomers are controlled for energy equalization by a second transformer module. Two adjacent battery monomers are connected to the primary side of the first transformer module and the primary side of the second transformer module through a group of shared switching tubes. The first transformer module and the second transformer module each comprise a transformer, a primary-side switching tube and a secondary-side switching tube. The group of shared switching tubes, the primary-side switching tube and the secondary-side switching tube are each connected to a microcontroller. The microcontroller selects an equalization type by comparing the voltage of each battery monomer with the average voltage of all battery monomers, and then controls the switching tube on the corresponding side of the transformer corresponding to the battery monomer or the storage battery to be turned on or turned off through a PWM pulse signal.

Description

Technical Field

[0001] This invention belongs to the field of battery balancing technology, specifically relating to a high-frequency, high-current balancing circuit and control method for power batteries. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the increasingly widespread application of high-capacity lithium-ion battery packs in new energy vehicles and energy storage systems, electric vehicles are placing increasingly higher demands on the performance of their power batteries. However, due to variations in battery cell manufacturing processes and usage, inconsistencies in battery capacity can occur after a period of use. This inconsistency can further lead to overcharging and over-discharging of individual battery cells, affecting the driving range of electric vehicles and the lifespan of the batteries. To address this inconsistency, battery cell balancing is necessary. In the field of battery balancing, current balancing circuits are mainly classified into passive balancing and active balancing based on whether energy is dissipated.

[0004] Passive balancing, also known as dissipative balancing, dissipates excess energy by connecting a power-dissipating resistor in parallel across each battery cell, causing it to heat up. Active balancing, on the other hand, redistributes energy through a balancing circuit, transferring energy from higher-energy cells to lower-energy cells, achieving energy-free balancing. Passive balancing circuits are simple and low-cost, but they have low balancing current, and excess energy is wasted as heat, resulting in low overall system efficiency. In the field of active balancing, most balancing circuits use inductors, capacitors, and numerous switching devices, making integration difficult. Some use transformers for energy exchange, but these require many switching devices, and transformers can experience insufficient demagnetization and magnetic saturation during use. For example, Chinese invention patent application number (CN201910561137.7) proposes a battery pack balancing module, system, and control method based on a bidirectional flyback converter. This invention uses a transformer for energy exchange, with the primary and secondary side conduction and turn-off times dynamically adjusted according to the voltage ratio, and the balancing current is adjustable. However, the inventors discovered that a set of batteries required a transformer, and each battery required four switching transistors, resulting in a complex circuit topology, low integration, and inconsistent current balancing, leading to a long balancing time. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a high-frequency, high-current balancing circuit and control method for power batteries. By improving the balancing circuit topology, the invention divides individual battery cells into odd and even groups, with adjacent cells sharing a single set of switching transistors, enabling bidirectional energy flow. For n batteries, only 8 + 2·n switching transistors are needed, and the original secondary-side switching transistors of the transformer require only one PWM signal control, saving a significant number of components and achieving high integration. Furthermore, the optimized control strategy dynamically adjusts the PWM signal duty cycle, promptly demagnetizes the transformer, and rationally sets transformer and circuit parameters to achieve high-current balancing, improving balancing speed and efficiency.

[0006] According to some embodiments, the present invention adopts the following technical solution:

[0007] Firstly, the present invention provides a high-frequency, high-current balancing circuit for power batteries.

[0008] A high-frequency, high-current balancing circuit for a power battery includes several battery cells. Odd-numbered battery cells are controlled by a first transformer module for energy balancing, while even-numbered battery cells are controlled by a second transformer module. Adjacent battery cells are connected to the primary side of the first transformer module and the primary side of the second transformer module by sharing a set of switching transistors.

[0009] Both the first transformer module and the second transformer module include a transformer, a primary-side switch transistor, and a secondary-side switch transistor. A set of primary-side switch transistors is connected between the primary side of the first transformer and the primary side of the second transformer and the set of switch transistors. A secondary-side switch transistor and a battery are connected to the secondary side of the first transformer and the secondary side of the second transformer.

[0010] The set of switching transistors, the primary-side switching transistors, and the secondary-side switching transistors are all connected to the microcontroller. The microcontroller selects the equalization type by comparing the voltage of each battery cell with the average voltage of all battery cells, and then controls the switching transistors on or off on the corresponding side of the transformer corresponding to the battery cell or the battery through PWM pulse signals to perform equalization control of the charging and discharging of the battery cells.

[0011] Furthermore, the sum of the number of switching transistors in the set of switching transistors, the primary-side switching transistors, and the secondary-side switching transistors is equal to 8 + 2·n, where n is the number of individual battery cells.

[0012] Furthermore, both the first and last battery cells are connected to the primary-side switching transistors via a set of switching transistors.

[0013] Furthermore, the secondary side of the first transformer and the secondary side of the second transformer share a set of batteries.

[0014] Furthermore, the balancing types include charging balancing and discharging balancing.

[0015] Furthermore, both the set of switching transistors and the set of primary-side switching transistors include two switching transistors.

[0016] Furthermore, the microcontroller is connected to a voltage acquisition module, which is used to acquire the voltage value of each battery cell and send it to the microcontroller.

[0017] Secondly, the present invention provides a high-frequency high-current equalization circuit control method for power batteries.

[0018] A method for controlling a high-frequency, high-current balancing circuit for a power battery, comprising the high-frequency, high-current balancing circuit for a power battery as described in the first aspect, including:

[0019] Obtain the voltage of all individual battery cells and calculate the average voltage of all individual battery cells;

[0020] Calculate the difference between the voltage of each individual battery cell and the average voltage of all individual battery cells to determine the maximum positive voltage difference and the maximum negative voltage difference;

[0021] If the maximum positive voltage difference is greater than the absolute value of the maximum negative voltage difference, then all the switches on the primary side of the transformer corresponding to the battery cell that generates the maximum positive voltage difference are turned on, and the switches on the secondary side are turned off, in order to perform discharge equalization.

[0022] If the absolute value of the maximum negative voltage difference is greater than the maximum positive voltage difference, then the secondary-side switch of the transformer corresponding to the battery cell that generates the maximum negative voltage difference is turned on, and all switches on the primary side are turned off to perform charging equalization.

[0023] Furthermore, during the discharge equalization, the following conditions are met:

[0024]

[0025] Where V0 is the voltage across the secondary inductor, V1 is the voltage across the primary inductor, N1 is the number of turns in the primary coil, N2 is the number of turns in the secondary coil, t1 is the primary conduction time, and t2-t1 is the secondary conduction time.

[0026] Furthermore, during the charging equalization process, the following conditions are met:

[0027]

[0028] Where V0 is the voltage across the secondary inductor, V1 is the voltage across the primary inductor, N1 is the number of turns in the primary coil, N2 is the number of turns in the secondary coil, t1 is the primary conduction time, and t2-t1 is the secondary conduction time.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) The present invention divides the battery cells into two groups of odd and even, and adjacent battery cells share a set of switching transistors, allowing energy to flow bidirectionally. By sharing a MOS switch array, this circuit can balance several series-connected battery cells. Compared with traditional equalization circuits, it can reduce the number of switching devices by about 50%, resulting in low cost and high integration.

[0031] (2) The circuit topology is equipped with a PWM duty cycle dynamic adjustment module, which maximizes the timely demagnetization of the transformer and reduces the voltage stress on the MOSFET.

[0032] (3) The present invention is simple to control. The switching on and off of the primary and secondary sides of the transformer only requires one PWM signal.

[0033] (4) The present invention can continuously balance with high frequency and high current, which can significantly shorten the balancing time and improve working efficiency. Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0035] Figure 1 This is a schematic diagram of the circuit topology of the present invention;

[0036] Figure 2(a) shows the working state of the primary and secondary sides of the transformer and the direction of current flow when the battery cell B1 is discharging and the PWM is on.

[0037] Figure 2(b) shows the working state of the transformer and the direction of current flow on the primary and secondary sides when the battery cell B1 is discharging under PWM.

[0038] Figure 3 It shows the PWM control signal and the current waveforms corresponding to the first and second sides during the equalization process.

[0039] Figure 4 This is a flowchart of the control method of the present invention;

[0040] Figure 5 This is a simulation diagram of the current change during charging equalization at 100kHz in an embodiment of the present invention.

[0041] Figure 6 This is a simulation diagram of the current change during discharge equalization at 100kHz in an embodiment of the present invention.

[0042] Figure 7 This is a simulation diagram of the battery voltage change throughout the entire process at 100kHz in an embodiment of the present invention. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0044] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0045] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0046] In this invention, terms such as "connected" and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0047] Example 1

[0048] This embodiment provides a high-frequency, high-current balancing circuit for power batteries.

[0049] A high-frequency, high-current balancing circuit for a power battery includes several battery cells. Odd-numbered battery cells are controlled by a first transformer module for energy balancing, while even-numbered battery cells are controlled by a second transformer module. Adjacent battery cells are connected to the primary side of the first transformer module and the primary side of the second transformer module by sharing a set of switching transistors.

[0050] Both the first transformer module and the second transformer module include a transformer, a primary-side switch transistor, and a secondary-side switch transistor. A set of primary-side switch transistors is connected between the primary side of the first transformer and the primary side of the second transformer and the set of switch transistors. A secondary-side switch transistor and a battery are connected to the secondary side of the first transformer and the secondary side of the second transformer.

[0051] The set of switching transistors, including the primary-side and secondary-side transistors, are all connected to a microcontroller. The microcontroller selects the balancing type by comparing the voltage of each individual battery cell with the average voltage of all battery cells. It then controls the switching transistors on or off the corresponding side of the transformer associated with each battery cell or the battery via PWM pulse signals to achieve balanced charging and discharging control of the battery cells. Specifically, the microcontroller controls the PWM signal, which drives the switching transistors connected to the battery to turn on and off, further realizing the transfer of energy between batteries.

[0052] Figure 1 For example, the circuit topology diagram. Figure 1 As shown, taking a battery pack with a total of 12 cells as an example, they are divided into two groups: odd and even. The individual cells are B1, B3, B5, B7, B9, and B... 11 For odd-numbered arrays, B2, B4, B6, B8, B 10 and B 12 For even-numbered arrays, two battery groups are equipped with a total of 32 MOSFETs and two transformers. Each pair of adjacent cells shares a set of switching transistors. Charge / discharge equalization of odd-numbered cells is achieved through transformer T1, while charge / discharge equalization of even-numbered cells is achieved through transformer T2. The transformers operate in bidirectional flyback mode. Assuming that cell B1 has the highest voltage, it will perform discharge equalization (…). Figure 2(a)-Figure 2(b) During a PWM equalization cycle, the circuit operates in three states: Phase 1: Primary side is on, secondary side is off; Phase 2: Primary side is off, secondary side is on; Phase 3: Both primary and secondary sides are off. During this process, the PWM signal and the primary and secondary currents are as follows... Figure 3 As shown. The working process will now be explained:

[0053] Transformer energy storage stage (0-t1):

[0054] During the PWM positive pulse, switching transistors Q1, Q2, and Q... 14 Q 15 On, Q 16 Turn off. The primary circuit of the transformer is turned on. The induced electromotive force (EMF) across the primary inductor is approximately equal to the terminal voltage of the individual battery cell, with the direction being "positive at the top and negative at the bottom." A "negative at the top and positive at the bottom" induced EMF is generated on the secondary side. The secondary side is turned off. The energy of the individual battery cell is temporarily stored in the transformer in the form of magnetic energy. Because the PWM cycle is very short, we can assume that the magnitude of the induced EMF in the inductor remains constant during one PWM cycle, equal to the voltage V1 across the individual battery cell. The primary current I1 increases linearly, with a rate of change of:

[0055]

[0056] Where V1 is the voltage across the primary inductor, L is the magnetizing inductance (ignoring the effect of leakage inductance), and the maximum primary current is:

[0057]

[0058] Where t1 is the primary conduction time.

[0059] The average current during one PWM cycle is:

[0060]

[0061] Among them, t w This is the time of one PWM cycle.

[0062] During this process, the magnetic flux flowing through the iron core gradually increases, and the increase in magnetic flux is:

[0063]

[0064] Where N1 is the number of turns of the primary coil.

[0065] Transformer energy release stage (t1-t2):

[0066] During the PWM negative pulse, switching transistors Q1, Q2, and Q3... 14 Q 15 Off, Q 16 When the primary side is turned off, an induced electromotive force (EMF) with negative at the top and positive at the bottom is generated on the primary side. Consequently, an induced EMF with positive at the top and negative at the bottom is generated on the secondary side. The transformer secondary circuit is now conducting. The magnitude of the induced EMF across the secondary inductor is approximately equal to the voltage across the lead-acid battery. At this time, current flows on the secondary side, and the secondary current I2 decreases linearly. The magnetic flux gradually decreases, and the amount of magnetic flux decreases is:

[0067]

[0068] Where V0 is the voltage across the secondary inductor, N2 is the number of turns in the secondary coil, and t2-t1 is the conduction time of the secondary side.

[0069] Circuit resting stage (t2-t) w )

[0070] During this process, all switches remain off. The circuit is left idle, allowing excess energy in the transformer to fully dissipate. Q 16 Keeping it off prevents the lead-acid battery from reverse-charging the transformer, while the secondary side current is always controlled by switch Q. 16 The body diode is maintained.

[0071] Example 2

[0072] This embodiment provides a high-frequency, high-current balancing circuit control method for power batteries (flowchart shown below). Figure 4 As shown):

[0073] The average voltage of the 12 batteries was collected and calculated, denoted as V. aver .

[0074] Calculate the difference between the voltage of each battery cell and the average voltage, and denot it as V. dif .

[0075] V dif The maximum positive pressure difference in the middle is denoted as V. max1 .

[0076] V dif The maximum negative pressure difference in the middle is denoted as V. max2 .

[0077] If V max1 >V max2 The corresponding MOSFET is turned on to perform discharge equalization.

[0078] If V max1 <V max2 The corresponding MOSFET is turned on to perform charging equalization.

[0079] PWM pulse signal settings:

[0080] Based on the above control method, the individual battery cells requiring equalization are determined, and the type of equalization (charging / discharging) needs to be determined. Simultaneously, to ensure the transformer operates continuously in the linear region, the required ΔΦ must be satisfied. + =ΔΦ - From formulas (4) and (5), we can obtain:

[0081] During discharge equalization:

[0082]

[0083] further:

[0084]

[0085] During charging equalization:

[0086]

[0087] further:

[0088]

[0089] To verify the feasibility of the model, a simulation experiment was conducted. PWM pulse signal settings: A sawtooth wave with an amplitude of 1 and a frequency of 100kHz was used as the carrier wave, and the output signal obtained by formula (7) or (9) was used as the modulation wave. The two were combined to form the required PWM pulse signal. The switching frequency of the MOSFET was equal to the frequency of the sawtooth wave, 100kHz. The simulation step size was set to 1e-6, and the simulation time was set to 45. The transformer magnetizing inductance was set to 2μH (ignoring the influence of leakage inductance), and a 12V lead-acid battery was used on the secondary side. The voltage equalization threshold was set to 5mV.

[0090] Example:

[0091] Battery cell B1-B 12 The initial voltages are set as follows: B1 = 3.41V, B2 = 3.18V, B3 = 3.38V, B4 = 3.11V, B5 = 3.34V, B6 = 3.04V, B7 = 3.29V, B8 = 2.96V, B9 = 3.28V, B... 10 =2.94V, B 11 =3.24V, B 12 = 2.93V. The average voltage of the 12 batteries is 3.175V, the maximum positive voltage difference is 0.234V (B1), and the maximum negative voltage difference is 0.245V (B12). Therefore, the voltage of battery cell B is... 12 First, charging equalization is performed, and the current changes are as follows: Figure 5 As shown, then battery cell B1 undergoes discharge equalization, and the current changes as follows. Figure 6 As shown, the average equalization current is approximately 2A. The voltage changes throughout the process are as follows: Figure 7 As shown, the voltage of all 12 batteries is around 3.2V, which meets the consistency requirements.

[0092] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-frequency, high-current balancing circuit for a power battery, characterized in that, It includes several battery cells, wherein odd-numbered battery cells are controlled by a first transformer module for energy balancing, and even-numbered battery cells are controlled by a second transformer module for energy balancing. Adjacent battery cells are connected to the primary side of the first transformer module and the primary side of the second transformer module by sharing a set of switching transistors. Both the first transformer module and the second transformer module include a transformer, a primary-side switch transistor, and a secondary-side switch transistor. A set of primary-side switch transistors is connected between the primary side of the first transformer and the primary side of the second transformer and the set of switch transistors. A secondary-side switch transistor and a battery are connected to the secondary side of the first transformer and the secondary side of the second transformer. The set of switching transistors, the primary-side switching transistors, and the secondary-side switching transistors are all connected to the microcontroller. The microcontroller selects the equalization type by comparing the voltage of each battery cell with the average voltage of all battery cells, and then controls the switching transistors on or off on the corresponding side of the transformer corresponding to the battery cell or the battery through PWM pulse signals to perform equalization control of the charging and discharging of the battery cells.

2. The high-frequency, high-current balancing circuit for power batteries according to claim 1, characterized in that, The sum of the number of switching transistors in the set of switching transistors, the primary-side switching transistors, and the secondary-side switching transistors is equal to 8 + 2·n, where n is the number of individual battery cells.

3. The high-frequency, high-current balancing circuit for power batteries according to claim 1, characterized in that, The first and last battery cells are both connected to the primary-side switching transistors via a set of switching transistors.

4. The high-frequency, high-current balancing circuit for power batteries according to claim 1, characterized in that, The secondary side of the first transformer and the secondary side of the second transformer share a set of batteries.

5. The high-frequency, high-current balancing circuit for power batteries according to claim 1, characterized in that, The balancing types include charging balancing and discharging balancing.

6. The high-frequency, high-current balancing circuit for power batteries according to claim 1, characterized in that, Both the set of switching transistors and the set of primary-side switching transistors consist of two switching transistors.

7. The high-frequency, high-current balancing circuit for power batteries according to claim 1, characterized in that, The microcontroller is connected to a voltage acquisition module, which is used to acquire the voltage value of each battery cell and send it to the microcontroller.

8. A control method for a high-frequency, high-current balancing circuit of a power battery, characterized in that, The high-frequency, high-current equalization circuit for power batteries according to any one of claims 1-7 includes: Obtain the voltage of all individual battery cells and calculate the average voltage of all individual battery cells; Calculate the difference between the voltage of each individual battery cell and the average voltage of all individual battery cells to determine the maximum positive voltage difference and the maximum negative voltage difference; If the maximum positive voltage difference is greater than the absolute value of the maximum negative voltage difference, then all the switches on the primary side of the transformer corresponding to the battery cell that generates the maximum positive voltage difference are turned on, and the switches on the secondary side are turned off, in order to perform discharge equalization. If the absolute value of the maximum negative voltage difference is greater than the maximum positive voltage difference, then the secondary-side switch of the transformer corresponding to the battery cell that generates the maximum negative voltage difference is turned on, and all switches on the primary side are turned off to perform charging equalization.

9. The high-frequency high-current balancing circuit control method for power batteries according to claim 8, characterized in that, During the discharge equalization, the following conditions are met: Where V0 is the voltage across the secondary inductor, V1 is the voltage across the primary inductor, N1 is the number of turns in the primary coil, N2 is the number of turns in the secondary coil, t1 is the primary conduction time, and t2-t1 is the secondary conduction time.

10. The high-frequency high-current equalization circuit control method for power batteries according to claim 8, characterized in that, During the charging equalization process, the following conditions are met: Where V0 is the voltage across the secondary inductor, V1 is the voltage across the primary inductor, N1 is the number of turns in the primary coil, N2 is the number of turns in the secondary coil, t1 is the primary conduction time, and t2-t1 is the secondary conduction time.

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