Balancing control circuit for prolonging service life of battery energy storage system

Abstract

An equalization control circuit for prolonging the service life of a battery energy storage system comprises a battery management system and an equalization circuit module electrically connected with the battery management system. The equalization circuit module comprises an inter-cell equalization circuit and an inter-module equalization circuit; the n single batteries of the whole module are averagely divided into m battery packs, each battery pack comprises k single batteries, m is greater than or equal to 2, and k is greater than or equal to 2; the inter-cell equalization circuit is arranged between every two adjacent single batteries in the battery pack; k single batteries connected in series in each battery pack are regarded as a whole, the positive electrode of the first battery serves as the positive electrode of the battery pack, the negative electrode of the kth battery serves as the negative electrode of the battery pack, the inter-module equalization circuit is connected between the positive electrode and the negative electrode of each battery pack, and the inter-module equalization circuit is further connected with the whole module through the transformer. According to the utility model, the electric quantity transfer between the adjacent single batteries in the battery pack and the bidirectional electric quantity transfer from any battery pack between the battery modules to the whole can be realized.

Description

Technical Field

[0001] The utility model relates to the technical field of battery energy storage, in particular to a balancing control circuit for improving the life of a battery energy storage system. Background Art

[0002] Lithium-ion batteries have been widely used as the main energy source for various devices due to their high power density, strong reliability, long life, and low environmental pollution. In order to meet the voltage requirements of the equipment, it is often necessary to connect multiple single lithium-ion batteries in series.

[0003] However, due to differences in the manufacturing process, operating conditions and working environment of lithium-ion batteries, the decay speed of the single cells after combination is inconsistent, which leads to the inconsistency of the internal resistance, capacity and voltage of the battery. This inconsistency makes the overall performance of the battery pack lower than the sum of the performance of the single cells in the group, which eventually leads to rapid aging and retirement of the battery, and may have an impact on the environment.

[0004] In order to effectively solve the inconsistency problem of battery packs, balancing control is a necessary means. Balancing control refers to the use of balancing topology circuits and effective control strategies in an effective balancing architecture to achieve balancing of battery packs. Commonly used balancing architectures include adjacent battery cell balancing architectures, balancing architectures between any battery cells, and balancing architectures from battery cells to battery packs.

[0005] Some existing balancing circuits on the market currently have the following problems: (1) Unable to control the balancing current: Due to the characteristics of the circuit design, the magnitude of the current in most balancing circuits during the balancing process is mainly determined by the differential voltage between the capacitor and the battery, and these parameters are not easy to control in practical applications. Therefore, the magnitude of the current cannot be directly controlled, which may cause the battery to be overcharged or over-discharged. (2) Only the terminal voltage can be used as the balancing standard: The circuit determines whether balancing is required by comparing the terminal voltages of each battery; however, the terminal voltage of the battery cannot fully reflect its internal state, such as the battery's state of charge or health. Therefore, using only the terminal voltage as the balancing standard may not achieve the optimal balancing of the battery state. Utility Model Content

[0006] The purpose of the utility model is to overcome the above-mentioned deficiencies in the prior art and provide a balancing control circuit for increasing the life of a battery energy storage system.

[0007] The technical solution of the present utility model is: an equalization control circuit for improving the lifespan of a battery energy storage system, including a battery management system and an equalization circuit module electrically connected to the battery management system; the equalization circuit module includes an inter-cell equalization circuit and an inter-module equalization circuit; the n single cells of the entire module are evenly divided into m battery packs, each battery pack contains k single cells, where m≥2 and k≥2; the inter-cell equalization circuit is provided between every two adjacent single cells within the battery pack, which is equivalent to including k - 1 inter-cell equalization circuits in each battery pack; considering the k series-connected single cells in each battery pack as a whole, the positive electrode of the first cell is used as the positive electrode of the battery pack, and the negative electrode of the kth cell is used as the negative electrode of the battery pack. The inter-module equalization circuit is connected between the positive and negative electrodes of each battery pack, and the inter-module equalization circuit is also connected to the entire module through a transformer.

[0008] Further, the inter-cell equalization circuit adopts a Buck - Boost equalization topology structure, including an inductor, switching transistor Q1, and switching transistor Q2, and a diode is anti-parallel connected to each switching transistor.

[0009] Further, one end of the inductor is connected between the negative electrode of the adjacent battery B k-1 and the positive electrode of battery B k ; the other end of the inductor is respectively connected to the source electrode of switching transistor Q1 and the drain electrode of switching transistor Q2; the drain electrode of switching transistor Q1 is connected to the positive electrode of battery B k-1 ; the source electrode of switching transistor Q2 is connected to the negative electrode of battery B k ; the opening and closing of switching transistors Q1 and Q2 are controlled by a pulse width modulation wave to achieve equalization.

[0010] Further, the inter-module equalization circuit adopts an equalization topology structure of a flyback transformer, and the transformer is a flyback transformer.

[0011] Further, each inter-module equalization circuit includes switching transistors Q3 and Q4. All inter-module equalization circuits share a flyback transformer. One end of the primary winding of the flyback transformer is connected to the positive electrode of the battery pack j 1 < j < m; the other end of the primary winding is connected to the negative electrode of the battery pack j through switching transistor Q3; one end of the secondary winding of the flyback transformer is connected to the positive electrode of battery pack 1, and the other end of the secondary winding is connected to the negative electrode of battery pack m through switching transistor Q4; diodes D3 are anti-parallel connected to switching transistors Q3, and diode D4 is anti-parallel connected to switching transistor Q4; the opening and closing of switching transistors Q3 and Q4 are controlled by a pulse width modulation wave.

[0012] Further, the battery management system communicates with the equalization circuit module through a CAN bus.

[0013] Furthermore, the battery management system mainly includes a battery status monitoring module, a signal processing module, a signal execution module and a protection circuit module; the battery status monitoring module is used to monitor the status information of each single battery in the battery pack in real time; the signal processing module is used to perform data processing and analysis based on the monitored battery status information, and formulate a balancing strategy; the signal execution module is used to control the working state of the balancing circuit module through an adjustable PWM control signal according to the instructions of the signal processing module.

[0014] Furthermore, the m battery packs include m inter-module balancing circuits.

[0015] Furthermore, the battery management system is used to determine whether to perform balancing according to the state of charge SOC of the single battery, and to achieve balancing by controlling the opening and closing of the switch tubes Q1 and Q2 of the inter-cell balancing circuit through a pulse width modulation wave PWM.

[0016] Furthermore, the battery management system is used to determine whether to perform balancing according to the average SOC of the battery pack, and to achieve balancing by controlling the opening and closing of the switch tubes Q3 and Q4 of the inter-module balancing circuit through a pulse width modulation wave PWM.

[0017] Beneficial effects of the utility model:

[0018] (1) By setting up inter-cell balancing circuits and inter-module balancing circuits, it is possible to achieve the transfer of power between adjacent single cells in a battery pack and the bidirectional transfer of power between any battery packs to the whole battery module.

[0019] (2) The use of a layered active balancing architecture based on a Buck-Boost circuit and a flyback transformer can significantly improve the balancing effect of the battery pack. Compared with traditional adjacent active balancing, this layered active balancing mechanism can shorten the balancing time and improve the balancing efficiency. On the other hand, it can improve the inconsistency problem of the battery pack and increase the charge and discharge capacity of the entire battery module, while also extending the life of the battery energy storage system.

[0020] (3) The battery management system is used to monitor the battery's state of charge (SOC) in real time, and use this as the basis for battery power transfer. The balancing strategy can be adjusted during the battery charging and discharging process, and balancing is achieved by PWM controlling the switch tube of the balancing circuit to optimize the battery's charging and discharging efficiency.

[0021] (4) The prior art has the limitation that there is a current return phenomenon in the transformer, which will cause power loss and reduce battery efficiency. The present invention can effectively avoid this problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the equalization control circuit of an embodiment of the utility model;

[0023] Figure 2 It is a Buck-Boost balanced topology structure for active balancing between cells in the embodiment of the utility model;

[0024] Figure 3 This is a balanced topology structure of a flyback transformer with active balance between modules in the embodiment of the utility model. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown: A balancing control circuit for improving the life of a battery energy storage system, including a battery management system and a balancing circuit module, wherein the battery management system mainly includes a battery status monitoring module, a signal processing module, a signal execution module and a protection circuit module. The battery status monitoring module is used to monitor the voltage, current, temperature and other parameters of each single battery in the battery pack in real time; the signal processing module performs data processing and analysis based on the monitored battery status information, and formulates a balancing strategy; the signal execution module controls the working state of the balancing circuit module through an adjustable PWM control signal according to the instructions of the signal processing module; the balancing circuit module includes an inter-cell balancing circuit and an inter-module balancing circuit, which are used to achieve power balancing in the battery pack and power transfer between modules; the protection circuit module is used to monitor the overcharge and over-discharge status of the battery pack, and take corresponding protection measures to ensure the safe operation of the battery. Since the hardware modules of the battery management system are already existing technologies, they will not be described in detail here.

[0027] In this embodiment, the balancing strategy is the key to improving the battery life. Specifically, the implementation of the balancing strategy is divided into two levels: active balancing between cells and active balancing between modules. The balancing strategy is formulated based on the state of charge (SOC) as the balancing standard.

[0028] like Figure 1As shown: This embodiment is implemented based on the active balancing architecture of adjacent single cells and the active balancing architecture of a single battery pack to the entire module. The n single cells of the entire module are evenly divided into m battery packs, each of which contains k single cells (n=k·m). Each battery pack includes k-1 inter-cell balancing circuits, and m battery packs include m inter-module balancing circuits. Among them, the m battery packs all adopt the architecture of active balancing of adjacent batteries, that is, there is an inter-cell balancing circuit between all adjacent single cells in the battery pack to balance the single cells, and this balancing behavior is called active balancing between cells. In addition, the k single cells connected in series in each battery pack are regarded as a whole, the positive electrode of the first battery is used as the positive electrode of the battery pack, and the negative electrode of the kth battery is used as the negative electrode of the battery pack. At the same time, these m battery packs are balanced using the active balancing architecture from a single battery pack to the entire module, and this balancing behavior is called active balancing between modules. The battery current, voltage, temperature and other information are collected by the battery management system (BMS) and transmitted through the CAN bus.

[0029] Specifically, the active balancing between cells adopts the Buck-Boost balancing topology, such as Figure 2 As shown. An inter-cell balancing circuit is set between each two adjacent single batteries (hereinafter referred to as batteries), such as between battery B1 and battery B2, between battery B2 and battery B3, etc. of battery B1. k-1 With battery B k There is an inter-cell balancing circuit between the two cells, where k≥2. Each inter-cell balancing circuit includes an inductor, a switch tube Q1 and a switch tube Q2, and each switch tube is connected in reverse parallel with a diode. One end of the inductor is connected to the adjacent battery B k-1 The negative electrode of battery B k The other end of the inductor is connected to the source of the switch tube Q1 and the drain of the switch tube Q2; the drain of the switch tube Q1 is connected to the battery B k-1 The positive electrode of the switch tube Q2 is connected to the battery B k The current will flow bidirectionally between the battery cells through the inductor, and the BMS will decide whether to balance the cells according to the state of charge (SOC) of the cells. Specifically, balancing is achieved by controlling the opening and closing of the switches Q1 and Q2 through pulse width modulation (PWM).

[0030] For example, the inter-cell balancing circuit between battery B1 and battery B2 has one end of the inductor L1 connected between the negative electrode of battery B1 and the positive electrode of battery B2, and the other end connected to the source of switch tube Q1 and the drain of switch tube Q2; the drain of switch tube Q1 is connected to the positive electrode of battery B1, the source of switch tube Q2 is connected to the negative electrode of battery B2, and switch tube Q1 is anti-parallel connected to diode D1, and switch tube Q2 is anti-parallel connected to diode D2. Similarly, the inter-cell balancing circuit between battery B2 and battery B3 is also configured in this way, which will not be described in detail here.

[0031] When the BMS detects that SOC1 is greater than SOC2 and decides to balance, PWM will control the switch tube Q1. The specific balancing process is as follows: First, PWM inputs a high-level signal to the switch tube Q1 to turn on Q1. At this time, the current I flows from the battery B1 into the inductor L1 for storage, and the current path is: B1+→Q1→L1→B1-→B1+. Next, PWM inputs a low-level signal to the switch tube Q1 to close Q1, so that the inductor L1 generates a reverse electromotive force and continues to supply current. The diode D2 is turned on, and the inductor L1 transfers the stored electricity to the battery B2. The current path becomes: L1→B2+→B2-→D2→L1, thereby completing the transfer of electricity. Correspondingly, if you need to transfer electricity from B2 to B1, you only need to control the switch tube Q2 in the same way.

[0032] In this embodiment, in terms of active balancing between modules, whether balancing operation is required is determined based on the average SOC of the battery pack. When the average SOC difference between modules exceeds the set threshold, the inter-module balancing circuit is turned on to transfer power to achieve power balancing. In this way, the power difference between different battery packs can be balanced to prevent some battery packs from reaching the upper or lower limit too early and affecting the performance and life of the entire module.

[0033] Active balancing between modules uses a flyback transformer balancing topology, such as Figure 3 As shown. This balancing topology realizes the power transfer between the battery pack and the entire module by utilizing the magnetic field and electric field conversion function of the flyback transformer. In this structure, the primary winding of the flyback transformer T is connected in parallel with the battery pack through a switch tube (i.e., a metal oxide semiconductor field effect tube MOSFET), while the secondary winding is connected to the entire module through a MOSFET. The battery management system (BMS) estimates the average state of charge (SOC) of the battery pack and decides whether to balance. Then, balancing is achieved by controlling the opening and closing of the switch tubes Q3 and Q4 through a pulse width modulation wave (PWM).

[0034] Specifically, each inter-module balancing circuit includes switch tubes Q3 and Q4, and each inter-module balancing circuit shares a flyback transformer T. One end of the primary winding of the flyback transformer T is connected to a battery pack (e.g., a battery pack j, 1 < j <The positive electrode of <m), the other end of the primary winding is connected to the battery pack through the switching transistor Q3 j <The negative electrode; one end of the secondary winding of the flyback transformer T is connected to the positive electrode of the battery pack 1, and the other end of the secondary winding is connected to the negative electrode of the battery pack m through the switching transistor Q4. And so on, the other module-to-module balancing circuits are also connected in this way, that is, the primary windings of the flyback transformer T are all connected in parallel with both ends of the corresponding battery pack through the switching transistor Q3, and the secondary windings of the flyback transformer T are connected in parallel between the battery pack 1 and the battery pack m through the switching transistor Q4, which is equivalent to connecting the entire module. Among them, a diode D3 is anti-parallel connected to each switching transistor Q3 of the module-to-module balancing circuit, and a diode D4 is anti-parallel connected to the switching transistor Q4. The switching transistors Q3 and Q4 are controlled to open and close by a pulse width modulation wave (PWM).

[0035] <For example, assuming that the BMS detects that the average SOC value of a certain battery pack m is too high and decides to perform balancing, the PWM wave will control the switching transistor Q3. The specific process is as follows: First, the PWM inputs a high-level signal to Q3 to turn Q3 on. At this time, the voltage U1 of the battery pack m is applied to the primary winding of the flyback transformer T, and the magnitude of the induced electromotive force generated by the secondary winding is U2. Since the diode D3 is reverse cut off at this time, the primary winding is equivalent to an inductor for storing the electric quantity transferred from the battery pack m. When Q3 is turned on until t = To, the current in the primary winding reaches the maximum value. This process completes the conversion of electrical energy to magnetic energy through the transformer, and the magnetic flux increases at this time. Then, the PWM inputs a low-level signal to Q3 to turn Q3 off. No current passes through the primary winding, the secondary winding induces an electromotive force, the diode D3 conducts, the primary winding releases the electric quantity, and transfers it to the entire module. When t = T, the current in the secondary winding drops to the minimum value. This process completes the conversion of magnetic energy to electrical energy through the transformer, and the magnetic flux decreases at this time.

[0036] <It can be seen from this that the voltage value output by the secondary winding is related to the turn ratio of the primary and secondary sides of the flyback transformer, the conduction duty cycle of the MOSFET, and the magnitude of the primary voltage value. On the contrary, if it is necessary to realize the process of transferring the electric quantity from the module to the battery pack, only the switching transistor Q4 needs to be controlled.

[0037] <It can be understood that the batteries in this embodiment include but are not limited to lithium iron phosphate batteries, ternary batteries, lead-acid batteries, and fuel cells.

[0038] In summary, the balancing architecture of this embodiment divides the batteries into multiple groups, wherein the cell-to-cell balancing circuit based on the Buck-Boost balancing topology circuit is used within the group, and the module-to-module balancing circuit based on the flyback transformer is used between the groups. This architecture effectively solves the problem of slow balancing speed between adjacent single cells due to the large number of batteries. At the same time, the active balancing structure with the flyback transformer as the core is used between the groups, which can transfer power from any battery pack to the entire module, and has better flexibility.

[0039] The main advantage of the utility model is that, through the layered active balancing architecture, energy transfer between adjacent battery cells and modules in the battery pack is realized, which effectively solves the inconsistency problem of the battery pack, improves the charge and discharge capacity of the battery, and thus significantly improves the life of the battery energy storage system. The layered balancing architecture can reduce the number of flyback transformers used, while reducing the circuit volume and reducing costs. The method and device of the present invention are simple, easy to implement, and have strong practicality.

Claims

1. A balancing control circuit for improving the life of a battery energy storage system, comprising a battery management system and a balancing circuit module electrically connected to the battery management system; characterized in that: The balancing circuit module includes an inter-cell balancing circuit and an inter-module balancing circuit; the n single cells of the entire module are evenly divided into m battery packs, each battery pack contains k single cells, where m≥2, k≥2; the inter-cell balancing circuit is provided between each adjacent single cell in the battery pack, which is equivalent to each battery pack including k-1 inter-cell balancing circuits; the k single cells connected in series in each battery pack are regarded as a whole, wherein the positive electrode of the first battery is used as the positive electrode of the battery pack, and the negative electrode of the kth battery is used as the negative electrode of the battery pack, and the inter-module balancing circuit is connected between the positive and negative electrodes of each battery pack, and the inter-module balancing circuit is also connected to the entire module via a transformer.

2. The balancing control circuit for improving the life of a battery energy storage system according to claim 1, characterized in that: The cell-to-cell balancing circuit adopts a Buck-Boost balancing topology structure, including an inductor, a switch tube Q1 and a switch tube Q2, and each switch tube is anti-parallel connected to a diode.

3. The balancing control circuit for improving the life of a battery energy storage system according to claim 2, characterized in that: One end of the inductor is connected to the adjacent battery B k-1 The negative electrode of battery B k The other end of the inductor is connected to the source of the switch tube Q1 and the drain of the switch tube Q2; the drain of the switch tube Q1 is connected to the battery B k-1 The positive electrode of the switch tube Q2 is connected to the battery B. k The negative pole of the resistor is connected to the resistor; the balance is achieved by controlling the opening and closing of the switch tubes Q1 and Q2 through the pulse width modulation wave.

4. The balancing control circuit for improving the life of a battery energy storage system according to claim 1, characterized in that: The inter-module balancing circuit adopts a balancing topology structure of a flyback transformer, and the transformer is a flyback transformer.

5. The balancing control circuit for improving the life of a battery energy storage system according to claim 4, characterized in that: Each inter-module balancing circuit includes switching transistors Q3 and Q4. Each inter-module balancing circuit shares a flyback transformer. One end of the primary winding of the flyback transformer is connected to the positive electrode of the battery pack. j The positive electrode of 1< j <m; the other end of the primary winding is connected to the negative electrode of the battery pack through the switching transistor Q3. j One end of the secondary winding of the flyback transformer is connected to the positive electrode of battery pack 1, and the other end of the secondary winding is connected to the negative electrode of battery pack m through the switching transistor Q4; a diode D3 is anti-parallel connected to each switching transistor Q3, and a diode D4 is anti-parallel connected to the switching transistor Q4; the opening and closing of the switching transistors Q3 and Q4 are controlled by a pulse width modulation wave.

6. The balancing control circuit for improving the life of a battery energy storage system according to claim 1, characterized in that: The battery management system communicates with the balancing circuit module via the CAN bus.

7. The balancing control circuit for improving the life of a battery energy storage system according to claim 1, characterized in that: The battery management system mainly includes a battery status monitoring module, a signal processing module, a signal execution module and a protection circuit module; the battery status monitoring module is used to monitor the status information of each single battery in the battery pack in real time; the signal processing module is used to perform data processing and analysis based on the monitored battery status information, and formulate a balancing strategy; the signal execution module is used to control the working state of the balancing circuit module through an adjustable PWM control signal according to the instructions of the signal processing module.

8. The balancing control circuit for improving the life of a battery energy storage system according to claim 1, characterized in that: The m battery packs include m inter-module balancing circuits.

9. The balancing control circuit for improving the life of a battery energy storage system according to claim 3, characterized in that: The battery management system is used to determine whether to perform balancing according to the state of charge SOC of the single battery, and to achieve balancing by controlling the opening and closing of the switch tubes Q1 and Q2 of the balancing circuit between the cells through the pulse width modulation wave PWM.

10. The balancing control circuit for improving the life of a battery energy storage system according to claim 5, characterized in that: The battery management system is used to determine whether to perform balancing according to the average SOC of the battery pack, and to achieve balancing by controlling the opening and closing of the switch tubes Q3 and Q4 of the inter-module balancing circuit through a pulse width modulation wave PWM.

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