Multiplexing type switched capacitor equalization circuit for single battery string and control method of multiplexing type switched capacitor equalization circuit

Abstract

The invention discloses a multiplexing switched 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 and the battery modules are correspondingly arranged, and each battery module is connected to the multiplexed capacitor network through the corresponding switch array. All the switch arrays adopt pulse phase shift control, and when the switch arrays are alternately driven, the multiplexed capacitor network can transfer the energy of the high-voltage battery modules in the battery string to the low-voltage battery modules, and can also transfer the energy of the high-voltage single batteries in the battery modules to the low-voltage single batteries. And voltage balance of the whole battery string can be finally realized through continuous charging and discharging of the capacitor network. According to the invention, the voltage equalization of the single cell string is completed through the multiplexed capacitor network, and the circuit is of great significance to the miniaturization and compactness design of a single cell string equalization circuit.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemical energy storage, and in particular to a multiplexed switch capacitor equalization circuit for a single battery string and a control method thereof. Background Art

[0002] At present, electrochemical energy storage systems based on lithium-ion batteries are booming. In order to meet the application requirements of high voltage and high power of energy storage systems, it is inevitable to connect a large number of battery cells in series. However, simply connecting the battery cells in series will cause the voltage between the battery cells in the battery string to be unbalanced during operation, which will lead to overcharge and over-discharge problems in individual battery cells, reduce the performance of the entire energy storage system, and even cause catastrophic safety accidents. The voltage balancing circuit can achieve voltage balancing between battery cells in the battery string, which is of great significance to ensure the safe and efficient operation of the energy storage system.

[0003] Lithium-ion battery voltage balancing circuits can be divided into two categories: passive balancing and active balancing. Passive balancing circuits use resistance energy dissipation to make the voltage of each battery cell gradually approach the battery cell with the lowest voltage. Passive balancing circuits will reduce the efficiency of the energy storage system and aggravate thermal management problems, so active balancing circuits have become an important direction for future development. Active balancing circuits use transformers, inductors, capacitors and other components to transfer energy between high and low voltage battery cells, thereby achieving voltage balancing between battery cells. In particular, the switched capacitor balancing circuit has many advantages, such as fast balancing speed, high balancing efficiency, small size, and no need for closed-loop control. It is a popular balancing solution.

[0004] However, the capacitor network in the existing switched capacitor balancing circuit uses a large number of capacitors, and the withstand voltage of the capacitors is high, and this situation will be aggravated as the length of the battery string increases. Therefore, it is urgent to propose a new switched capacitor balancing circuit and its control method, which can reduce the number and withstand voltage of the capacitors as much as possible while ensuring the performance of the balancing circuit, thereby reducing the cost and volume of the balancing circuit and improving the reliability of the balancing circuit. Summary of the invention

[0005] In view of the deficiencies of the above-mentioned prior art, the present invention aims to propose a multiplexed switched capacitor balancing circuit for a single battery string and a control method thereof, so as to solve the problems of excessive number of capacitors and excessive withstand voltage when the existing switched capacitor balancing circuit is used for a high-voltage battery string, and to achieve a low-cost and miniaturized design of a single battery string balancing circuit.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: In a first aspect, the present invention proposes a multiplexed switch capacitor balancing circuit for a single battery string, comprising a switch array and a capacitor network; the switch array is arranged corresponding to the battery modules in the battery string, and each battery module is connected to the multiplexed capacitor network through the corresponding switch array; the capacitor network is used to achieve voltage balancing between unbalanced battery modules in the battery string and between unbalanced battery cells in the battery module.

[0007] As a further improvement of the present invention, the switch array is composed of switch tubes, and 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 switch tubes, and the number of switch tubes 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, and the switch tubes are N-channel MOSFETs of exactly the same model and parameters.

[0008] As a further improvement of the present invention, the switch array corresponding to each battery module uses two cycles of T , duty cycle is 1 / 2 m The phase difference is T / 2 m Square wave signal control, m is the number of battery modules connected in series in a battery string.

[0009] As a further improvement of the present invention, the capacitor network adopts one of a classical structure, a double-layer structure, a chain structure, a star structure, and a triangle structure, and the capacitance of each capacitor in the capacitor network is exactly the same.

[0010] In a second aspect, the present invention proposes a control method for a multiplexed switch capacitor equalization circuit for a single battery string, which is implemented based on the multiplexed switch capacitor equalization circuit for a single battery string, and includes: The switch arrays corresponding to all battery modules adopt pulse phase shift control to achieve the reuse of capacitor networks; When the voltages between all battery modules in the battery string are in a balanced state, but the voltages between battery cells in the battery module are not balanced, when the switch array corresponding to the battery module is driven, the capacitor network transfers the energy of the battery cells with higher voltages in the battery module to the battery cells with lower voltages, and the voltages between the battery cells in the battery module are balanced through the continuous charging and discharging of the capacitor network; When the voltages between all battery cells in a battery module are in a balanced state, but the voltages between battery modules in a battery string are unbalanced, when the switch arrays corresponding to the unbalanced battery modules are alternately driven, the capacitor network transfers the energy of the battery modules with higher voltages in the battery string to the battery modules with lower voltages, and the voltage balance between the battery modules in the battery string is achieved through continuous charging and discharging of the capacitor network.

[0011] As a further improvement of the present invention, the pulse phase shift control strategy is: The switch array corresponding to each battery module uses two cycles. T , duty cycle is 1 / 2 m The phase difference is T / 2 m The square wave signal is used to control m is the number of battery modules connected in series in the battery string; The conduction time of all switches in the switch array in each switching cycle is T / 2 m , and any two adjacent switch tubes are in complementary conduction or simultaneously turned off state; Phase shift the two square waves of the switch array corresponding to the first battery module in sequence T / m , get the rest m - Driving signal of the switch array corresponding to one battery module; At each moment, only one switch array is driven, that is, only one battery module is in working state, thereby realizing the reuse of the capacitor network.

[0012] As a further improvement of the present invention, when the voltages between the battery modules are in a balanced state, but the voltages between the battery cells in the battery module are unbalanced, the balancing process is specifically as follows: When the switch array corresponding to the unbalanced battery module is driven, the battery module balances the voltage between the battery cells through the capacitor network; When the switch tube corresponding to the battery cell with higher voltage in the battery module is turned on, the capacitor network is charged and the energy of the battery cell with higher voltage is transferred to the capacitor network; When the switch tube corresponding to the battery cell with lower voltage in the battery module is turned on, the capacitor network discharges and transfers the energy of the capacitor network to the battery cell with lower voltage; By continuously switching between the two working states of the capacitor network, the energy of the battery cells with higher voltage in the battery module is transferred to the battery cells with lower voltage, thereby achieving voltage balance between the battery cells in the battery module.

[0013] As a further improvement of the present invention, when the voltages between the battery cells in each battery module are in a balanced state, and the voltages between the battery modules are unbalanced, the balancing process is specifically 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 to transfer 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 is continuously discharged to transfer the energy of the capacitor network to the battery module with lower voltage; By continuously switching the charging and discharging states through the capacitor network, the energy of the battery module with higher voltage in the battery string is transferred to the battery module with lower voltage, so as to achieve voltage balance between the battery modules in the battery string.

[0014] The beneficial effects of the present invention are: In the multiplexed switched capacitor balancing circuit proposed in the present invention, all battery modules share a capacitor network, and the voltage balancing of the entire battery string is achieved by means of pulse phase shift control. However, the capacitor network in the existing switched capacitor balancing circuit requires the use of a large number of capacitors, and the number of capacitors increases as the battery string becomes longer. Compared with the existing switched capacitor balancing circuit, the balancing circuit proposed in the present invention greatly reduces the number of capacitors required for battery string balancing, thereby reducing the cost and volume of the balancing circuit while ensuring excellent balancing performance, which is of great significance to the miniaturization and compact design of the battery string balancing circuit.

[0015] The balancing circuit proposed in the present invention divides the battery group into multiple battery modules, and realizes the voltage balancing of the battery string through a reused capacitor network. The maximum withstand voltage of the capacitor is about the voltage of one battery module. The maximum withstand voltage of the capacitor in the existing switch capacitor balancing circuit is about the voltage of the entire battery string. Therefore, the maximum withstand voltage of the capacitor in the balancing circuit proposed in the present invention is reduced exponentially. In high-voltage applications, the withstand voltage of the capacitor in the existing switch capacitor balancing circuit will be very high, which will lead to problems such as reduced reliability and increased volume of the balancing circuit. The balancing circuit proposed in the present invention can effectively solve the high withstand voltage problem of the capacitor in the balancing circuit in high-voltage applications, thereby ensuring the safe and reliable operation of the balanced battery group.

[0016] The balancing circuit proposed in the present invention is the same as the existing switched capacitor balancing circuit. The switch array corresponding to each battery module is controlled by a pair of complementary square wave signals with constant period and duty cycle, which reduces the complexity of the control algorithm and eliminates the hardware conditions required for closed-loop control. In addition, when the length of the battery string increases, the balancing circuit only needs to increase the switch array corresponding to the battery module, without changing the structure of the capacitor network. Therefore, the balancing circuit proposed in the present invention is very easy to implement and expand. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1is a schematic diagram of a multiplexed switched capacitor balancing circuit for a single battery string in an embodiment of the present invention; Figure 2 is a schematic diagram of various types of capacitor networks in an embodiment of the present invention; Figure 3 Schematic diagram of a switch array pulse phase shift control signal in an embodiment of the present invention; FIG. 4 is a schematic diagram of voltage balancing between battery cells in a battery module according to an embodiment of the present invention, where (a) is a capacitor C i, j To charge, place the battery cells B t, i+1 ~ B t, j The energy is transferred to the capacitor; (b) the capacitor C i, j Discharge the capacitor C i, j The energy is transferred to the battery cells B t, i ~ B t, j-1 process; FIG5 is a schematic diagram of voltage balancing between battery modules in a battery string according to an embodiment of the present invention, wherein (a) is a process of transferring energy from a battery module to a capacitor network during balancing; and (b) is a process of transferring energy from a capacitor network to a battery module during balancing. DETAILED DESCRIPTION

[0019] In order to make the purpose and technical solution of the present invention clearer and easier to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, wherein the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0021] Embodiment 1 like Figure 1 As shown, this embodiment proposes a multiplexed switch capacitor balancing circuit for a single battery string, which mainly includes a switch array and a capacitor network.

[0022] Preferably, the battery string is composed of a plurality of battery modules connected in series, and each battery module is composed of a plurality of battery cells connected in series. The switch array is arranged corresponding to the battery modules in the battery string, and each battery module is connected to the reused capacitor network through the corresponding switch array. The capacitor network is used to achieve voltage balance between unbalanced battery modules in the battery string and between unbalanced battery cells in the battery module.

[0023] Preferably, 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 switch tubes, and the number of switch tubes 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. All switch tubes use N-channel MOSFETs with exactly the same model and parameters.

[0024] Preferably, Figure 1 The capacitor network in the embodiment uses a triangular structure as an example. The capacitor network of the equalization circuit of the present invention can also be Figure 2 There are many types of structures, such as the classic structure, double-layer structure, chain structure, star structure, etc. shown in the figure. The capacitance of each capacitor in the capacitor network is exactly the same.

[0025] Embodiment 2 This embodiment proposes a control method for a multiplexed switched capacitor balancing circuit for a single battery string, using the multiplexed capacitor balancing circuit for a single battery string, the topology of the balancing circuit is as follows: Figure 1 The specific plan is as follows: The switch arrays corresponding to all battery modules adopt pulse phase shift control to achieve the reuse of capacitor networks; When the voltages between all battery modules in the battery string are in a balanced state, but the voltages between battery cells in the battery module are not balanced, when the switch array corresponding to the battery module is driven, the capacitor network transfers the energy of the battery cells with higher voltages in the battery module to the battery cells with lower voltages, and the voltages between the battery cells in the battery module are balanced through the continuous charging and discharging of the capacitor network; When the voltages between all battery cells in a battery module are in a balanced state, but the voltages between battery modules in a battery string are unbalanced, when the switch arrays corresponding to the unbalanced battery modules are alternately driven, the capacitor network transfers the energy of the battery modules with higher voltages in the battery string to the battery modules with lower voltages, and the voltage balance between the battery modules in the battery string is achieved through continuous charging and discharging of the capacitor network.

[0026] Preferably, Figure 3 As shown in the figure, the pulse phase shift control strategy is as follows: The switch array corresponding to each battery module uses two cycles. T , duty cycle is 1 / 2 m The phase difference is T / 2 m The square wave signal is used to control m is the number of battery modules connected in series in the battery string; The conduction time of all switches in the switch array in each switching cycle is T / 2 m, and any two adjacent switch tubes are in complementary conduction or simultaneously turned off state; Shift the phases of the two square waves of the switch array corresponding to the first battery module in sequence T / m , get the rest m - Driving signal of the switch array corresponding to one battery module; When the switch array corresponding to each battery module is driven, the corresponding battery module is connected to the capacitor network. At each moment, only one switch array is in working state, that is, only one battery module is connected to the capacitor network, thereby realizing the reuse of the capacitor network.

[0027] Preferably, as shown in FIG. 4 , when the voltages between the battery modules are in a balanced state, and the voltages between the battery cells in the battery module are unbalanced, the balancing process is specifically as follows: Assume t Unbalanced battery cells within a battery module B t, j The voltage is higher than the battery cell B t, i The voltage of t When the switch array corresponding to the first battery module is driven, t The battery modules start voltage balancing; As shown in Figure 4(a), when the switch tube with an even number in the switch array is turned on, the capacitor C i, j To charge, place the battery cells B t, i+1 ~ B t, j The energy is transferred to the capacitor C i, j ; As shown in Figure 4(b), when the odd-numbered switches in the switch array are turned on, the capacitor C i, j Discharge the capacitor C i, j The energy is transferred to the battery cells B t, i ~ B t, j-1 ; By continuously switching between the two working states mentioned above, the battery cells can be B t, j The energy is transferred to the battery cells B t, i , and ultimately achieve voltage balance between battery cells in the battery module.

[0028] Preferably, as shown in FIG5 , when the voltages between the battery cells in each battery module are in a balanced state, and the voltages between the battery modules are unbalanced, the balancing process is specifically as follows: Assuming unbalanced battery modules in a battery string B k The voltage is higher than the battery module B h Voltage; As shown in Figure 5(a), when k When the switch array corresponding to each battery module is driven, k When the switch tube with an even or odd sequence number in the switch array corresponding to the first battery module is turned on, the capacitor network is continuously charged. k The energy of each battery module is transferred to the capacitor network; As shown in Figure 5(b), when h When the switch array corresponding to each battery module is driven, h When the switch tube with an even or odd sequence number in the switch array corresponding to the first battery module is turned on, the capacitor network continues to discharge and transfers the energy of the capacitor network to the first h Battery modules; The battery module is continuously switched between charging and discharging states by the capacitor network. B k The energy is transferred to the battery module B h , and ultimately achieve voltage balance between battery modules in the battery string.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does 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 balancing circuit for a single battery string, characterized in that: including a switch array and a capacitor network; The switch array is arranged corresponding to the battery modules in the battery string, and each battery module is connected to the reused capacitor network through the corresponding switch array; The capacitor network is used to achieve voltage balance between unbalanced battery modules in a battery string and between unbalanced battery cells in a battery module.

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 switch tubes. 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 switch tubes. The number of switch tubes 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.

3. The multiplexed switched capacitor equalization circuit for a single battery string according to claim 2, characterized in that: The switch tube adopts N-channel MOSFET with exactly the same model and parameters.

4. The multiplexed switched capacitor equalization circuit for a single battery string according to claim 2, characterized in that: The switch array corresponding to each battery module uses two cycles. T , duty cycle is 1 / 2 m The phase difference is T / 2 m Square wave signal control, m is the number of battery modules connected in series in a battery string.

5. 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 classic structure, double-layer structure, chain structure, star structure, and triangle structure, and the capacitance of each capacitor in the capacitor network is exactly the same.

6. A control method for a multiplexed switch capacitor equalization circuit for a single battery string, implemented based on the multiplexed switch capacitor equalization circuit for a single battery string according to any one of claims 1 to 5, characterized in that: include: The switch arrays corresponding to all battery modules adopt pulse phase shift control to achieve the reuse of capacitor networks; When the voltages between all battery modules in the battery string are in a balanced state, but the voltages between battery cells in the battery module are not balanced, when the switch array corresponding to the battery module is driven, the capacitor network transfers the energy of the battery cells with higher voltages in the battery module to the battery cells with lower voltages, and the voltages between the battery cells in the battery module are balanced through the continuous charging and discharging of the capacitor network; When the voltages between all battery cells in a battery module are in a balanced state, but the voltages between battery modules in a battery string are unbalanced, when the switch arrays corresponding to the unbalanced battery modules are alternately driven, the capacitor network transfers the energy of the battery modules with higher voltages in the battery string to the battery modules with lower voltages, and the voltage balance between the battery modules in the battery string is achieved through continuous charging and discharging of the capacitor network.

7. The method for controlling a multiplexed switched capacitor equalization circuit for a single battery string according to claim 6, characterized in that: The pulse phase shift control strategy is: The switch array corresponding to each battery module uses two cycles. T , duty cycle is 1 / 2 m The phase difference is T / 2 m The square wave signal is used to control m is the number of battery modules connected in series in the battery string; The conduction time of all switches in the switch array in each switching cycle is T / 2 m , and any two adjacent switch tubes are in complementary conduction or simultaneously turned off state; Shift the phases of the two square waves of the switch array corresponding to the first battery module in sequence T / m , get the rest m - Driving signal of the switch array corresponding to one battery module; At each moment, only one switch array is driven, that is, only one battery module is in working state, thereby realizing the reuse of the capacitor network.

8. The method for controlling a multiplexed switched capacitor equalization circuit for a single battery string according to claim 6, characterized in that: When the voltages between the battery modules are in a balanced state, but the voltages between the battery cells in the battery module are not balanced, 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 the battery cells through the capacitor network; When the switch tube corresponding to the battery cell with higher voltage in the battery module is turned on, the capacitor network is charged and the energy of the battery cell with higher voltage is transferred to the capacitor network; When the switch tube corresponding to the battery cell with lower voltage in the battery module is turned on, the capacitor network discharges and transfers the energy of the capacitor network to the battery cell with lower voltage; By continuously switching between the two working states of the capacitor network, the energy of the battery cells with higher voltage in the battery module is transferred to the battery cells with lower voltage, thereby achieving voltage balance between the battery cells in the battery module.

9. The method for controlling a multiplexed switched capacitor equalization circuit for a single battery string according to claim 6, characterized in that: When the voltage between the battery cells in each battery module is in a balanced state, but the voltage between the 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 to transfer 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 is continuously discharged to transfer the energy of the capacitor network to the battery module with lower voltage; By continuously switching the charging and discharging states through the capacitor network, the energy of the battery module with higher voltage in the battery string is transferred to the battery module with lower voltage, so as to achieve voltage balance between the battery modules in the battery string.

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