Battery module equalization-low temperature self-heating integrated topological structure and control method

Abstract

The invention relates to a battery module equalization-low temperature self-heating integrated topological structure and a control method, and belongs to the technical field of battery management systems. The topological structure comprises a battery module, an inductor unit and an inductor direction switching unit. The control method comprises an active equalization control strategy and a variable-period self-heating control strategy. According to the active equalization control strategy, the electric energy of the single battery with high SOC is transferred to other single batteries by controlling the on and off of the MOSFET switch, so that the energy equalization of the battery module is realized. According to the variable-period self-heating control strategy, the inductance direction switching unit is controlled by generating two pairs of PWM signals with the phase angle difference of 180 degrees, so that alternating currents are generated among part of single batteries in the battery module, and therefore low-temperature self-heating of the battery module is achieved. According to the invention, the energy balance and low-temperature self-heating functions of the battery module are effectively realized, the comprehensive performance of the battery module is improved, and the service life of the battery module is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery management systems and relates to a battery module balancing-low-temperature self-heating integrated topological structure and a control method. Background Art

[0002] With the widespread use of electric vehicles and portable electronic devices, the performance and reliability of battery modules as energy storage units are crucial. During the use of battery modules, the inconsistency between single cells will lead to energy balance problems in the battery modules, affecting the performance and life of the battery modules. In addition, low temperature environments will have a significant impact on the performance of battery modules, resulting in problems such as reduced battery capacity and increased internal resistance, affecting the normal operation of battery modules.

[0003] At present, there are some technical solutions for the equalization and low-temperature self-heating problems of battery modules. For example, the traditional equalization method mainly relies on passive equalization, that is, transferring the electrical energy of a single cell with a high SOC to a single cell with a low SOC through a resistor or a diode, but its efficiency is low and has a certain impact on the battery life. In addition, the low-temperature self-heating method mainly includes external heating and internal heating. External heating requires an additional heating device, has low efficiency and high energy consumption; internal heating mainly relies on the chemical reaction of the battery itself to generate heat, but its heating rate is slow and has a certain impact on the battery life.

[0004] Therefore, there is an urgent need for a technical solution that can effectively solve the problems of battery module balancing and low-temperature self-heating. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a battery module balancing-low temperature self-heating integrated topology structure and control method.

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

[0007] A battery module balancing-low temperature self-heating integrated topology structure, comprising:

[0008] The battery module is composed of several single cells connected in series;

[0009] An inductor unit, comprising a plurality of inductors, one end of each inductor being connected to a single battery in the battery module, and the other end being connected to the inductor direction switching unit;

[0010] The inductor direction switching unit includes a plurality of MOSFET switches and is used for controlling the direction of the inductor current.

[0011] Furthermore, the inductor direction switching unit includes 2N MOSFET switches, where N is the number of single battery cells.

[0012] Furthermore, the MOSFET switches are arranged according to a certain rule so that each single battery is connected to two MOSFET switches.

[0013] A battery module balancing-low temperature self-heating integrated control method, comprising:

[0014] Determine a balancing target cell, the state quantity of which is greater than the average value of the state quantities of all cells in the battery module;

[0015] Control the inductor direction switching unit to discharge the target cell and transfer the electric energy to other cells;

[0016] The battery module is heated by generating a self-heating current.

[0017] Furthermore, the state quantity is the battery state of charge SOC.

[0018] Furthermore, the SOC of the balancing target cell is greater than a preset average SOC value of the battery module.

[0019] Further, the control inductor direction switching unit includes:

[0020] Generate PWM signal to control the on and off of MOSFET switch;

[0021] Different MOSFET switches are selected for control according to the position of the balancing target cell in the battery module.

[0022] Further, the generating of the self-heating current comprises:

[0023] Generate two pairs of PWM signals with a phase angle difference of 180°;

[0024] The inductor direction switching unit is controlled to generate an alternating current between some of the single cells in the battery module.

[0025] Furthermore, the number of the partial single cells is the same.

[0026] Further, the generating of the self-heating current comprises:

[0027] Determine the maximum cycle of the self-heating control strategy according to the terminal voltage limiting condition;

[0028] Use a maximum cycle PWM signal to drive the MOSFET switch to increase the self-heating effective current and heating rate.

[0029] The beneficial effects of the present invention are:

[0030] (1) The balancing and low-temperature self-heating functions are integrated into the same topology, which simplifies the design of the battery management system and reduces the system cost.

[0031] (2) The active balancing control strategy can effectively achieve energy balancing of the battery module and improve the capacity utilization and service life of the battery module.

[0032] (3) The variable cycle self-heating control strategy can effectively improve the heating rate, enable the battery module to quickly restore performance, and ensure the normal operation of the battery module in a low temperature environment.

[0033] (4) The maximum cycle of the self-heating control strategy is determined by the terminal voltage limit condition, thus avoiding the impact of high peak voltage on the safety of the battery module.

[0034] (5) The present invention is applicable to various types of battery modules and has high versatility and applicability.

[0035] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0037] Figure 1 A schematic diagram of a battery module balancing-low temperature self-heating integrated topology structure provided by an embodiment of the present invention;

[0038] Figure 2 The active balancing working modes of the battery module and the theoretical waveform of the inductor current provided by an embodiment of the present invention, (a) is mode 1; (b) is mode 2; (c) is L3; (d) is L2;

[0039] Figure 3 Self-heating working modes and current waveforms of the inductor and the battery provided by an embodiment of the present invention: (a) is mode 1; (b) is mode 2; (c) is mode 3; (d) is mode 4; (e) is the current waveform of the inductor and the battery;

[0040] Figure 4 The maximum cycles corresponding to different battery states provided by an embodiment of the present invention;

[0041] Figure 5 The change of each monomer SOC during the balancing process provided by an embodiment of the present invention;

[0042] Figure 6 The change of current and temperature of each monomer during the self-heating process provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0044] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0045] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0046] See also Figure 1 to Figure 6 The present invention provides a battery module balancing-low temperature self-heating integrated topology structure and control method, which controls the balancing current by formulating an active balancing control strategy to optimize the balancing process of the battery module. At the same time, a variable cycle self-heating control strategy is proposed to increase the heating rate, thereby effectively realizing the performance recovery of the battery module in a low temperature environment and improving the comprehensive performance and service life of the battery module.

[0047] The specific working process of the present invention is as follows:

[0048] (1) A battery module balancing-low temperature self-heating integrated topology

[0049] The overall structure is as follows Figure 1As shown, it includes: a battery module, an inductor unit, and an inductor direction switching unit. The battery module is composed of a number of single batteries (BT1, BT2, BT3...BTN), and the inductor direction switching unit includes 2N MOSFET switches (M 1,1 ~M N-1,1 , M 1,2 ~M N-1,2 , M N,1 , M N,2 ), there are N inductors (L1, L2...LN) in the circuit, the positive electrodes of which are connected to one end of the two MOSFET switches, and the negative electrodes are connected to the single cells. The battery module balancing-low temperature self-heating integrated topology structure of this embodiment is composed of a battery module formed by 8 single cells connected in series, 16 MOSFET switches and 8 inductors.

[0050] ①The working principle of active balancing mode is as follows:

[0051] In this topology, a peak-cutting balancing strategy is adopted to discharge the single cells with high SOC and transfer their electric energy to other single cells. That is, when the SOC of single cell BT3 in the battery module is 0.001 greater than the average SOC of the battery module, BT3 is identified as the execution target of active balancing. If the single cell is at both ends of the battery module, the active balancing execution component is only M 1,1 or M 7,2 , that is, discharge the battery BT1 or BT8 separately. If the single battery is in the middle of the battery module, the active balancing process is as follows Figure 2 shown.

[0052] Working mode 1: When the SOC of BT3 is 0.001 greater than the average SOC of the battery module, Figure 2 As shown in (a), t 3,0 Moment, M 3,1 When the inductor L3 is turned on, BT1-BT3 charges the inductor L3, and the inductor current I3 gradually increases. 3,1 Moment, M 3,1 Turn off, at this time the inductor current I3 reaches the peak value, M 3,2 The inductor L3 charges BT4-BT8, and the inductor current I3 decreases gradually. 3,2 When the time drops to 0, the cycle ends.

[0053] Working mode 2: Figure 2 As shown in (b), t 2,0 Moment, M 2,2 When the inductor L3 is turned on, BT3-BT8 charges the inductor L3, and the inductor current I2 gradually increases. 2,1 Moment, M 2,2 Turn off, at this time the inductor current I2 reaches the peak value, M 2,1The inductor L2 charges BT1 and BT2, and the inductor current I2 gradually decreases. 2,2 When the time drops to 0, the cycle ends.

[0054] ②The working principle of self-heating mode is as follows:

[0055] Balanced-self-heating topology self-heating working principle Figure 3 As shown. Two pairs of PWM signals with a phase angle difference of 180° are used to control the switching of the two MOSFETs. Since the number of monomers on both sides of the inductor is the same, the duty cycle of the PWM signal is 50%. During the self-heating process, four stable and alternating working modes are formed in one cycle, so that AC current is generated between BT+ (BT1-BT4) and BT- (BT5-BT8) in the battery pack.

[0056] Taking L4 as an example, working mode 1 [t0-t1, Figure 3 (a)]:At time t0, M 4,1 Connectivity, M 4,2 Turn off, inductor L4 charges BT+, and the inductor current I L4 Gradually decrease until the current drops to 0.

[0057] Working mode 2 [t1-t2, Figure 3 (b)]: At t1, the inductor current is 0, M 4,1 Stay connected, M 4,2 Keep off, BT+ power is transferred to inductor L4, current I L4 The absolute value increases.

[0058] Working mode three [t2-t3, Figure 3 (c)]: Contrary to modes 1 and 2, M 4,2 Connectivity, M 4,1 Turn off. Inductor L4 and BT- form a loop, the inductor charges BT-, and the current I L4 The absolute value gradually decreases until it reaches 0.

[0059] Working mode 4 [t3-t4, Figure 3 (d)]: At t3, the inductor current is 0, M 4,2 Stay connected, M 4,1 Keep off, BT+ power is transferred to inductor L4, current I L4 The absolute value increases.

[0060] Figure 3 (e) is the current waveform of the inductor and the battery.

[0061] (2) A battery module balancing-low temperature self-heating integrated control method

[0062] By determining the duty cycle of the PWM signal that controls each MOSFET and solving the relationship between the PWM signal cycles of different MOSFET switches, a PWM signal with complementary states is generated, so that the MOSFET switches are alternately turned on to achieve battery module balancing; the maximum cycle of the self-heating control strategy is obtained through the terminal voltage limit, and the MOSFET is driven with the maximum cycle PWM signal during the entire heating process, which can increase the self-heating effective current during the heating process, thereby increasing the heating rate.

[0063] ① The active balancing mode control method is as follows:

[0064] a. Determine the balance threshold

[0065] A peak-shaving balancing strategy is adopted, and the balancing variable is SOC, that is, the monomer with high SOC is discharged and its electric energy is transferred to other monomers, taking BT3 as an example.

[0066] like:

[0067] SOC max =SOC3

[0068]

[0069] Then BT3 is identified as the execution target of active balancing.

[0070] b. Calculate the inductor current

[0071] In t 3,0 Moment, M 3,1 When the inductor L3 is turned on, BT1-BT3 charges the inductor L3, and the inductor current I3 gradually increases. 3,1 At this moment, the inductor current I3 reaches its peak value, M 3,1 Shutdown, M 3,2 The inductor L3 charges BT4-BT8, and the inductor current I3 decreases gradually. 3,2 The inductor current in mode 1 is:

[0072]

[0073] Among them U 3,1 with U 3,2 are the terminal voltages where the inductor stores and releases energy, respectively; D is the duty cycle; T is the period; and L is the inductance.

[0074] To prevent the inductor L3 from working in a continuous state, so as to avoid the continuous increase of current and hysteresis saturation, let t 3,2 =T3, then the relationship between duty cycle and voltage is:

[0075]

[0076] Similarly, the calculation method of the inductor current in mode 2 is similar to that in mode 1.

[0077] c. Solve for M 2,2 With M 3,1 The relationship between the PWM signal period T2 and T3

[0078] First, integrate equation (2) and obtain Figure 2 The effective current of the blue and red parts in the middle is used to obtain the balanced effective charging current of BT1-BT2 and the balanced effective charging current of BT4-BT8. In order to ensure that the SOC of monomers other than BT3 does not change significantly during the active balancing process, the balanced effective current (average charging current) of BT1-BT2 and BT4-BT8 should be as equal as possible. Finally, the relationship between the PWM signal periods T2 and T3 of M2,2 and M3,1 is obtained.

[0079]

[0080] ② The self-heating mode control method is as follows:

[0081] The self-heating mode is to heat the battery at low temperature by generating self-heating current. 4,1 Connectivity, M 4,2 Turn off, inductor L4 charges BT+, and the inductor current I L4 Gradually decreases until the current drops to 0. At t1, the inductor current is 0, M 4,1 Stay connected, M 4,2 Keep off, BT+ power is transferred to inductor L4, current I L4 The absolute value increases. At t2, M 4,2 Connectivity, M 4,1 Turn off, inductor L4 and BT- form a loop, the inductor charges BT-, the current I L4 The absolute value gradually decreases until it reaches 0. At t3, the inductor current is 0, M 4,2 Stay connected, M 4,1 Keep off, BT+ power is transferred to inductor L4, current I L4 The absolute value increases.

[0082] a. Calculate the L4 inductor current and duration in each mode

[0083] Working mode 1:

[0084] The inductor current of L4 is:

[0085]

[0086] Among them, V a+ is the sum of the open circuit voltages of BT+ monomers, R a+It is the total path resistance composed of the BT+ monomer internal resistance and polarization internal resistance, MOSFET path internal resistance and inductor equivalent internal resistance.

[0087] At time t1, the inductor current is 0, and the duration of mode 1 is:

[0088]

[0089] Working mode 2:

[0090] The inductor current of L4 is:

[0091]

[0092] Working mode 2 duration:

[0093]

[0094] The duration and peak current derivation method of modes 3 and 4 are the same as those of modes 1 and 2, so they are not explained here. The same is true for L8 and L4, so they are not repeated here. For each monomer self-heating current, after the two inductor currents are disassembled on a half-cycle scale, the disassembled fragments can be pieced together to form the self-heating current waveform of the monomer in the entire cycle, as shown in Figure 2 As shown, it can be seen that the self-heating current waveforms of each monomer are consistent, so the states of each monomer during the self-heating process are consistent. After the self-heating current is known, the heat generation rate is calculated by the heat generation rate model in the battery model, and the temperature of each monomer is calculated by the thermal network model in the battery model.

[0095] b. Obtain the maximum cycle of the self-heating control strategy through the terminal voltage limit

[0096] For the self-heating topology with Buck-Boost converter as the basic unit, the self-heating peak current and effective current increase with the increase of period T, but the high peak current is accompanied by a high peak voltage. From the perspective of vehicle safety, the terminal voltage is usually limited to obtain the maximum period of the self-heating control strategy.

[0097] At t2, the maximum charging current I corresponding to BT- max :

[0098]

[0099] Therefore, for any monomer in BT-, the maximum terminal voltage should be lower than the limiting voltage V lim :

[0100] V max =I max (R+R1+R2)+OCV≤V lim

[0101] The maximum period of the self-heating control strategy is:

[0102]

[0103] Based on the above formula and battery parameters, the maximum cycle at different SOC and temperature can be determined. When the inductance is 0.01H, the maximum cycle is as follows: Figure 4 shown.

[0104] Ultimately, the above control method can achieve energy balance of the entire battery module and increase the effective current of self-heating during the heating process, thereby increasing the heating rate.

[0105] The MOSFET switches are all STP220N6F7, with an on-resistance of 5mΩ and an equivalent internal resistance of 2.4mΩ. When T = 3s, L = 1H, the initial SOC of different single cells is set, and the change of each single cell SOC during the balancing process is as follows Figure 5 When the states of each monomer are consistent, the SOC is 0.5, and the ambient temperature is -15°C. Self-heating analysis is performed under the conditions of T = 2s, L = 1H. The changes in the current and temperature of each monomer are shown in Figure 6 shown.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A battery module balancing-low temperature self-heating integrated topology structure, characterized in that: include: A battery module is composed of several single cells connected in series; An inductor unit, comprising a plurality of inductors, one end of each inductor being connected to a single battery in the battery module, and the other end being connected to the inductor direction switching unit; The inductor direction switching unit includes a plurality of MOSFET switches and is used for controlling the direction of the inductor current.

2. The battery module balancing-low temperature self-heating integrated topology structure according to claim 1 is characterized in that: The inductor direction switching unit includes 2N MOSFET switches, where N is the number of single battery cells.

3. The battery module balancing-low temperature self-heating integrated topology structure according to claim 1 or 2, characterized in that: The MOSFET switches are arranged according to a certain rule so that each single battery is connected to two MOSFET switches.

4. A battery module balancing-low temperature self-heating integrated control method, characterized in that: include: Determine a balancing target cell, the state quantity of which is greater than the average value of the state quantities of all cells in the battery module; Control the inductor direction switching unit to discharge the target cell and transfer the electric energy to other cells; The battery module is heated by generating a self-heating current.

5. The battery module balancing-low temperature self-heating integrated control method according to claim 4 is characterized in that: The state quantity is the battery state of charge SOC.

6. The battery module balancing-low temperature self-heating integrated control method according to claim 4 is characterized in that: The SOC of the balancing target cell is greater than a preset average SOC value of the battery module.

7. The battery module balancing-low temperature self-heating integrated control method according to claim 4, characterized in that: The control inductor direction switching unit comprises: Generate PWM signal to control the on and off of MOSFET switch; Different MOSFET switches are selected for control according to the position of the balancing target cell in the battery module.

8. The battery module balancing-low temperature self-heating integrated control method according to claim 4, characterized in that: The self-heating current generated comprises: Generate two pairs of PWM signals with a phase angle difference of 180°; The inductor direction switching unit is controlled to generate an alternating current between some of the single cells in the battery module.

9. The battery module balancing-low temperature self-heating integrated control method according to claim 8, characterized in that: The number of the partial single cells is the same.

10. The battery module balancing-low temperature self-heating integrated control method according to claim 4, characterized in that: The self-heating current generated comprises: Determine the maximum cycle of the self-heating control strategy according to the terminal voltage limiting condition; Use a maximum cycle PWM signal to drive the MOSFET switch to increase the self-heating effective current and heating rate.

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