Multiplexed switched capacitor equalization circuit for a cell string and control method thereof

Abstract

The application discloses a multiplexed switch capacitor equalization circuit for a single battery string and a control method thereof, and relates to the field of electrochemical energy storage. The equalization circuit is composed of a switch array and a capacitor network. The battery string is divided into a plurality of battery modules. The switch array is arranged in correspondence with the battery modules. Each battery module is connected to the multiplexed capacitor network through the corresponding switch array. All the switch arrays are controlled by pulse phase shift. When the switch arrays are alternately driven, the multiplexed capacitor network can transfer the energy of high-voltage battery modules in the battery string to low-voltage battery modules, or transfer the energy of high-voltage battery cells in the battery modules to low-voltage battery cells. Through the continuous charging and discharging of the capacitor network, the voltage of the entire battery string can be finally balanced. The application completes the voltage balancing of the single battery string through the multiplexed capacitor network, and has important significance for the miniaturization and compact design of the single battery string equalization circuit.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to a multiplexed switched capacitor balancing circuit and its control method for a single battery string. Background Technology

[0002] Currently, electrochemical energy storage systems, primarily based on lithium-ion batteries, are rapidly developing. To meet the high-voltage, high-power application requirements of these systems, it is inevitable to connect a large number of individual battery cells in series. However, simply connecting individual cells in series can lead to voltage imbalances between them during operation, causing overcharging and over-discharging issues in some cells, reducing the overall performance of the energy storage system, and even causing catastrophic safety accidents. Voltage balancing circuits can achieve voltage balance among the individual cells within a battery string, which is crucial for ensuring the safe and efficient operation of energy storage systems.

[0003] Lithium-ion battery voltage equalization circuits can be divided into two categories: passive equalization and active equalization. Passive equalization circuits use resistors to dissipate energy, gradually bringing the voltage of each battery cell closer to that of the cell with the lowest voltage. Passive equalization circuits reduce the efficiency of the energy storage system and exacerbate thermal management problems; therefore, active equalization circuits have become an important direction for future development. Active equalization circuits use components such as transformers, inductors, and capacitors to transfer energy between high- and low-voltage battery cells, thereby achieving voltage equalization among the battery cells. In particular, switched-capacitor equalization circuits offer numerous advantages, including fast equalization speed, high equalization efficiency, small size, and no need for closed-loop control, making them a highly favored equalization solution.

[0004] However, existing switched-capacitor equalization circuits use a large number of capacitors in the capacitor network, and these capacitors have high voltage ratings. This problem worsens as the battery string length increases. Therefore, there is an urgent need to propose a new switched-capacitor equalization circuit and its control method that, while ensuring the performance of the equalization circuit, minimizes the number and voltage rating of capacitors, thereby reducing the cost and size of the equalization circuit and improving its reliability. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention aims to propose a reusable switched-capacitor balancing circuit and its control method for single-cell strings, thereby solving the problems of excessive number of capacitors and excessively high voltage withstand when existing switched-capacitor balancing circuits are used in high-voltage battery strings, and realizing a low-cost, miniaturized design for single-cell string balancing circuits.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention proposes a multiplexed switched-capacitor balancing circuit for a single battery string, comprising a switch array and a capacitor network; the switch array is configured corresponding to the battery modules within the battery string, and each battery module is connected to the multiplexed capacitor network through a corresponding switch array; the capacitor network is used to achieve voltage balancing between unbalanced battery modules within the battery string and between unbalanced individual battery cells within the battery module.

[0008] As a further improvement of the present invention, the switch array is composed of switching transistors, and the number of switch arrays required for the battery string is equal to the total number of series-connected battery modules. Each battery cell in the battery module is controlled by two switching transistors, and the number of switching transistors required for the switch array corresponding to each battery module is equal to twice the number of series-connected battery cells in the battery module. The switching transistors are N-channel MOSFETs with identical models and parameters.

[0009] As a further improvement of the present invention, the switch array corresponding to each battery module uses two cycles. T Duty cycle is 1 / 2 m Phase difference is T / 2 m Square wave signal control, m This represents the number of battery modules connected in series within the battery string.

[0010] As a further improvement of the present invention, the capacitor network adopts one of the following structures: classic structure, double-layer structure, chain structure, star structure, and triangular structure, and the capacitance value of each capacitor in the capacitor network is exactly the same.

[0011] Secondly, the present invention proposes a control method for a multiplexed switched capacitor equalization circuit for a single battery string, based on the aforementioned multiplexed switched capacitor equalization circuit for a single battery string, comprising:

[0012] All battery modules use pulse phase-shift control for their corresponding switch arrays, thereby enabling the reuse of the capacitor network;

[0013] When the voltage between all battery modules in the battery string is balanced, but the voltage between individual battery cells in the battery module is unbalanced, when the switch array corresponding to the battery module is driven, the capacitor network transfers the energy of the higher voltage battery cells in the battery module to the lower voltage battery cells. Through the continuous charging and discharging of the capacitor network, the voltage balance between individual battery cells in the battery module is achieved.

[0014] When the voltage of all individual cells in a battery module is balanced, but the voltage of the battery modules in a battery string is unbalanced, the switch array corresponding to the unbalanced battery modules is driven alternately. The capacitor network transfers the energy of the battery modules with higher voltage in the battery string to the battery modules with lower voltage. Through the continuous charging and discharging of the capacitor network, the voltage balance between the battery modules in the battery string is achieved.

[0015] As a further improvement of the present invention, the pulse phase shift control strategy is as follows:

[0016] Each battery module's corresponding switch array uses two cycles. T Duty cycle is 1 / 2 m Phase difference is T / 2 m The square wave signal is used for control, where m This refers to the number of battery modules connected in series within the battery string.

[0017] The conduction time of all switches in the switching array during each switching cycle is 100%. T / 2 m Furthermore, any two adjacent switches are either in a complementary on state or simultaneously off state.

[0018] The two square waves of the switch array corresponding to the first battery module are shifted in phase sequentially. T / m to obtain the rest m -Drive signals for the switch array corresponding to one battery module;

[0019] Only one switch array is driven at any given time, meaning only one battery module is in operation, thus enabling the reuse of the capacitor network.

[0020] As a further improvement of the present invention, when the voltage between each battery module is in a balanced state, but the voltage between individual battery cells within the battery module is unbalanced, the balancing process is specifically as follows:

[0021] When the switch array corresponding to the unbalanced battery module is driven, the battery module balances the voltage between individual battery cells through the capacitor network.

[0022] When the switching transistor corresponding to the higher voltage battery cell in the battery module is turned on, the capacitor network is charged, transferring the energy of the higher voltage battery cell to the capacitor network.

[0023] When the switching transistor corresponding to the lower voltage battery cell in the battery module is turned on, the capacitor network discharges, transferring the energy of the capacitor network to the lower voltage battery cell.

[0024] By continuously switching between two operating states of the capacitor network, the energy of the higher-voltage battery cells in the battery module is transferred to the lower-voltage battery cells, thereby achieving voltage balance among the battery cells in the battery module.

[0025] As a further improvement of the present invention, when the voltage between individual battery cells within each battery module is balanced, but the voltage between battery modules is unbalanced, the balancing process is specifically as follows:

[0026] When the switch array corresponding to the battery module with higher voltage in the battery string is driven, the capacitor network is continuously charged, transferring the energy of the battery module with higher voltage to the capacitor network.

[0027] When the switch array corresponding to the battery module with lower voltage in the battery string is driven, the capacitor network continuously discharges, transferring the energy of the capacitor network to the battery module with lower voltage.

[0028] By continuously switching between charging and discharging states through a capacitor network, energy from the battery modules with higher voltages within the battery string is transferred to the battery modules with lower voltages, thereby achieving voltage balance among the battery modules within the battery string.

[0029] The beneficial effects of this invention are as follows:

[0030] The multiplexed switched-capacitor balancing circuit proposed in this invention uses a single capacitor network for all battery modules, achieving voltage balancing across the entire battery string through pulse phase-shift control. In contrast, existing switched-capacitor balancing circuits require a large number of capacitors, and the number of capacitors increases with the length of the battery string. Compared to existing switched-capacitor balancing circuits, the balancing circuit proposed in this invention significantly reduces the number of capacitors required for battery string balancing, thereby reducing the cost and size of the balancing circuit while maintaining excellent balancing performance. This is of great significance for the miniaturization and compact design of battery string balancing circuits.

[0031] The equalization circuit proposed in this invention divides the battery pack into multiple battery modules and achieves voltage equalization of the battery string through a reused capacitor network. The maximum withstand voltage of the capacitor is approximately equal to the voltage of one battery module. In contrast, the maximum withstand voltage of the capacitor in existing switched-capacitor equalization circuits is approximately equal to the voltage of the entire battery string. Therefore, the maximum withstand voltage of the capacitor in the equalization circuit proposed in this invention is reduced by a factor of two. In high-voltage applications, the withstand voltage of the capacitor in existing switched-capacitor equalization circuits is very high, leading to problems such as reduced reliability and increased size of the equalization circuit. The equalization circuit proposed in this invention can effectively solve the problem of high withstand voltage of capacitors in equalization circuits for high-voltage applications, thereby ensuring the safe and reliable operation of the equalized battery pack.

[0032] The equalization circuit proposed in this invention is similar to existing switched-capacitor equalization circuits. Each battery module's corresponding switch array is controlled by a pair of complementary square wave signals with constant period and duty cycle. This reduces the complexity of the control algorithm and eliminates the hardware requirements for closed-loop control. Furthermore, as the battery string length increases, the equalization circuit simply needs to increase the number of switch arrays corresponding to the battery modules, without altering the capacitor network structure. Therefore, the equalization circuit proposed in this invention is very easy to implement and expand. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of a multiplexed switched capacitor balancing circuit for a single battery string in an embodiment of the present invention;

[0035] Figure 2 These are schematic diagrams of various types of capacitor networks in embodiments of the present invention;

[0036] Figure 3 This is a schematic diagram of the switch array pulse phase shift control signal in an embodiment of the present invention;

[0037] Figure 4 is a schematic diagram of voltage balancing between individual battery cells in the battery module in an embodiment of the present invention. (a) is a capacitor. C i, j Charge the battery cells B t, i+1 ~ B t, j (a) is the process of energy transfer to the capacitor; (b) is the capacitor. C i, j Discharge the capacitor. C i, j Energy transfer to battery cells B t, i ~ B t, j-1 process;

[0038] Figure 5 is a schematic diagram of voltage balancing between battery modules in the battery string in an embodiment of the present invention. (a) shows the process of energy transfer from the battery module to the capacitor network during the balancing process; (b) shows the process of energy transfer from the capacitor network to the battery module during the balancing process. Detailed Implementation

[0039] To make the objectives and technical solutions of this invention clearer and easier to understand, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0040] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0041] Example 1

[0042] like Figure 1 As shown, this embodiment proposes a multiplexed switched capacitor equalization circuit for a single battery string, which mainly includes a switch array and a capacitor network.

[0043] Preferably, the battery string consists of multiple battery modules connected in series, and each battery module consists of multiple individual battery cells connected in series. A switch array is configured corresponding to each battery module within the battery string, and each battery module is connected to a multiplexed capacitor network through its corresponding switch array. The capacitor network is used to achieve voltage equalization between unbalanced battery modules within the battery string and between unbalanced individual battery cells within a battery module.

[0044] Preferably, the number of switch arrays required for the battery string is equal to the total number of series-connected battery modules. Each battery cell within a battery module is controlled by two switching transistors, and the number of switching transistors required for the switch array corresponding to each battery module is equal to twice the number of series-connected battery cells within the battery module. All switching transistors are N-channel MOSFETs with identical model and parameters.

[0045] Preferred, Figure 1 The capacitor network in the example uses a triangular structure. The capacitor network of the equalization circuit described in this invention can also be... Figure 2 The diagram shows various types of capacitor networks, including classic structures, double-layer structures, chain structures, and star structures, where each capacitor has the same capacitance value.

[0046] Example 2

[0047] This embodiment proposes a control method for a multiplexed switched capacitor equalization circuit for a single battery string. The multiplexed capacitor equalization circuit for a single battery string has the following topology: Figure 1 As shown. The specific solution is as follows:

[0048] All battery modules use pulse phase-shift control for their corresponding switch arrays, thereby enabling the reuse of the capacitor network;

[0049] When the voltage between all battery modules in the battery string is balanced, but the voltage between individual battery cells in the battery module is unbalanced, when the switch array corresponding to the battery module is driven, the capacitor network transfers the energy of the higher voltage battery cells in the battery module to the lower voltage battery cells. Through the continuous charging and discharging of the capacitor network, the voltage balance between individual battery cells in the battery module is achieved.

[0050] When the voltage of all individual cells in a battery module is balanced, but the voltage of the battery modules in a battery string is unbalanced, the switch array corresponding to the unbalanced battery modules is driven alternately. The capacitor network transfers the energy of the battery modules with higher voltage in the battery string to the battery modules with lower voltage. Through the continuous charging and discharging of the capacitor network, the voltage balance between the battery modules in the battery string is achieved.

[0051] Preferred, such as Figure 3 As shown, the pulse phase-shift control strategy is as follows:

[0052] Each battery module's corresponding switch array uses two cycles. T Duty cycle is 1 / 2 m Phase difference is T / 2 m The square wave signal is used for control, where m This refers to the number of battery modules connected in series within the battery string.

[0053] The conduction time of all switches in the switching array during each switching cycle is 100%. T / 2 m Furthermore, any two adjacent switches are either in a complementary on state or simultaneously off state.

[0054] The two square waves of the switch array corresponding to the first battery module are shifted in phase sequentially. T / m to obtain the rest m -Drive signals for the switch array corresponding to one battery module;

[0055] When the switch array corresponding to each battery module is driven, the corresponding battery module is connected to the capacitor network. Only one switch array is in working state at any given time, that is, only one battery module is connected to the capacitor network, thereby realizing the reuse of the capacitor network.

[0056] Preferably, as shown in Figure 4, when the voltage between each battery module is in a balanced state, but the voltage between individual battery cells within a battery module is unbalanced, the balancing process is as follows:

[0057] Assuming the first t Uneven battery cells within a battery module B t, j The voltage is higher than that of the battery cells.B t, i The voltage when the first t When the switch array corresponding to the battery module is driven, then the first... t Each battery module begins voltage equalization;

[0058] As shown in Figure 4(a), when the even-numbered switch in the switch array is turned on, the capacitor... C i, j Charge the battery cells. B t, i+1 ~ B t, j Energy transferred to capacitor C i, j ;

[0059] As shown in Figure 4(b), when the switch transistor with an odd number in the switch array is turned on, the capacitor... C i, j Discharge the capacitor. C i, j Energy transfer to battery cells B t, i ~ B t, j-1 ;

[0060] By continuously switching between the two working states described above, the battery cells can be... B t, j Energy transfer to battery cells B t, i Ultimately, this achieves voltage balance among the individual battery cells within the battery module.

[0061] Preferably, as shown in Figure 5, when the voltage between individual cells within each battery module is balanced, but the voltage between battery modules is unbalanced, the balancing process is as follows:

[0062] Assuming unbalanced battery modules within the battery string B k The voltage is higher than that of the battery module. B h The voltage;

[0063] As shown in Figure 5(a), when the first k When the switch array corresponding to the battery module is driven, regardless of the number of modules... k When the switch transistor with an even or odd number in the switch array corresponding to the battery module is turned on, the capacitor network continuously charges, thus charging the first battery module. k The energy of each battery module is transferred to the capacitor network;

[0064] As shown in Figure 5(b), when the first h When the switch array corresponding to the battery module is driven, regardless of the number of modules...h When the switch in the switch array corresponding to each battery module is turned on (whether the switch number is even or odd), the capacitor network continuously discharges, transferring the energy of the capacitor network to the first switch. h One battery module;

[0065] By continuously switching between charging and discharging states through a capacitor network, the battery module... B k Energy transferred to the battery module B h Ultimately, this achieves voltage balance among the battery modules within the battery string.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A multiplexed switched capacitor equalization circuit for a single battery string, characterized in that, Including switch arrays and capacitor networks; The switch array is configured to correspond to the battery modules in the battery string. Each battery module is connected to the multiplexed capacitor network through the corresponding switch array. The number of switching transistors required for the switch array corresponding to each battery module is equal to twice the number of battery cells connected in series in the battery module. The capacitor network is used to achieve voltage equalization between unbalanced battery modules within a battery string and between unbalanced battery cells within a battery module. All battery modules use pulse phase-shift control for their corresponding switch arrays, thereby enabling the reuse of the capacitor network; When the voltage between all battery modules in the battery string is balanced, but the voltage between individual battery cells in the battery module is unbalanced, when the switch array corresponding to the battery module is driven, the capacitor network transfers the energy of the higher voltage battery cells in the battery module to the lower voltage battery cells. Through the continuous charging and discharging of the capacitor network, the voltage balance between individual battery cells in the battery module is achieved. When the voltage of all individual cells in a battery module is balanced, but the voltage of the battery modules in a battery string is unbalanced, the switch array corresponding to the unbalanced battery modules is driven alternately. The capacitor network transfers the energy of the battery modules with higher voltage in the battery string to the battery modules with lower voltage. Through the continuous charging and discharging of the capacitor network, the voltage balance between the battery modules in the battery string is achieved.

2. The multiplexed switched capacitor equalization circuit for a single battery string according to claim 1, characterized in that, The switch array is composed of switching transistors. The number of switch arrays required for the battery string is equal to the total number of battery modules connected in series. Each battery cell in the battery module is controlled by two switching transistors.

3. The multiplexed switched capacitor equalization circuit for a single battery string according to claim 2, characterized in that, The switching transistor is an N-channel MOSFET with the same model and parameters.

4. The multiplexed switched capacitor equalization circuit for a single battery string according to claim 1, characterized in that, The capacitor network adopts one of the following structures: classic structure, double-layer structure, chain structure, star structure, and triangle structure. The capacitance value of each capacitor in the capacitor network is exactly the same.

5. The multiplexed switched capacitor equalization circuit for a single battery string according to claim 1, characterized in that, Each battery module's corresponding switch array uses two cycles. T Duty cycle is 1 / 2 m Phase difference is T / 2 m Square wave signal control, m This represents the number of battery modules connected in series within the battery string.

6. The multiplexed switched capacitor equalization circuit for a single battery string according to claim 1, characterized in that, The pulse phase-shift control strategy is as follows: The conduction time of all switches in the switching array during each switching cycle is 100%. T / 2 m Furthermore, any two adjacent switches are either in a complementary on state or simultaneously off state. The two square waves of the switch array corresponding to the first battery module are shifted in phase sequentially. T / m to obtain the rest m -Drive signals for the switch array corresponding to one battery module; Only one switch array is driven at any given time, meaning only one battery module is in operation, thus enabling the reuse of the capacitor network.

7. The control method for a multiplexed switched capacitor equalization circuit for a single battery string according to claim 1, characterized in that, When the voltages between battery modules are balanced, but the voltages between individual battery cells within a battery module are unbalanced, the balancing process is as follows: When the switch array corresponding to the unbalanced battery module is driven, the battery module balances the voltage between individual battery cells through the capacitor network. When the switching transistor corresponding to the higher voltage battery cell in the battery module is turned on, the capacitor network is charged, transferring the energy of the higher voltage battery cell to the capacitor network. When the switching transistor corresponding to the lower voltage battery cell in the battery module is turned on, the capacitor network discharges, transferring the energy of the capacitor network to the lower voltage battery cell. By continuously switching between two operating states of the capacitor network, the energy of the higher-voltage battery cells in the battery module is transferred to the lower-voltage battery cells, thereby achieving voltage balance among the battery cells in the battery module.

8. The control method for a multiplexed switched capacitor equalization circuit for a single battery string according to claim 1, characterized in that, When the voltage between individual cells within each battery module is balanced, but the voltage between battery modules is unbalanced, the balancing process is as follows: When the switch array corresponding to the battery module with higher voltage in the battery string is driven, the capacitor network is continuously charged, transferring the energy of the battery module with higher voltage to the capacitor network. When the switch array corresponding to the battery module with lower voltage in the battery string is driven, the capacitor network continuously discharges, transferring the energy of the capacitor network to the battery module with lower voltage. By continuously switching between charging and discharging states through a capacitor network, energy from the battery modules with higher voltages within the battery string is transferred to the battery modules with lower voltages, thereby achieving voltage balance among the battery modules within the battery string.

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