A battery self-heating device based on LC topology and its control method

Abstract

The present invention discloses a battery self-heating device based on LC topology, which belongs to the technical field of battery self-heating. The battery self-heating device based on LC topology includes a switch bridge and a boost capacitor. The switch bridge adopts a MOS tube. On the one hand, the switch bridge is connected to the boost capacitor. On the other hand, the battery is connected in series with the inductor and capacitor and connected to the switch bridge. The battery self-heating device based on LC topology of the present invention can directly charge and discharge the battery, generate high-frequency ripple current, and can adjust the impedance and output current according to the frequency, and has a good AC output function. The present invention also discloses a battery heating control method, which can obtain the frequency and amplitude of the heating current with the best heating effect according to the health status, charge state, temperature and polarization voltage of the battery with the assistance of a frequency impedance meter, and determine the duty cycle and frequency of the PWM signal used to control the MOS tube in the switch bridge accordingly, so as to achieve precise heating control.

Description

Technical Field

[0001] The present invention relates to the technical field of battery self-heating, and more particularly to a battery self-heating device based on LC topology and a control method thereof. Background Art

[0002] Electric vehicles are currently gaining popularity worldwide at an unprecedented rate, thanks to their numerous advantages, including environmental friendliness, energy efficiency, and convenience. More and more consumers are choosing electric vehicles for daily commuting, and they are becoming increasingly common on city roads. However, lithium batteries, the core power source of electric vehicles, face significant challenges. At low temperatures, lithium ion diffusion slows, reducing available capacity, lowering electrolyte conductivity, increasing battery internal resistance, and decreasing charge and discharge efficiency. Furthermore, during low-temperature charging, lithium metal can precipitate on the negative electrode surface, causing short circuits or thermal runaway. Therefore, power lithium battery systems require intelligent thermal management systems to provide low-temperature heating, high-temperature heat dissipation, and thermal insulation.

[0003] In addition, the new battery has a stable internal structure, smoother lithium ion transmission, and a more stable response to the AC heating frequency. However, the thermal time constant of the aged battery changes due to factors such as the loss of electrode active materials and changes in the interface between the electrode and the electrolyte. The AC heating frequency originally suitable for new batteries cannot accurately match the real-time thermal requirements of the battery in the later stages of battery aging. There are also adaptation issues in the heating amplitude. After the battery ages, its heat generation mechanism becomes more complex, and the demand for heating amplitude is not static. In the early stages, the battery can maintain a good operating temperature state under conventional amplitude AC heating. But in the later stages, the internal resistance of the battery increases, and the self-heating capacity changes. A higher amplitude heating may be required to maintain a suitable temperature, but the existing AC heating system makes it difficult to flexibly adjust the current amplitude to the required level.

[0004] CN115868065A discloses a battery heating method and system. This system uses a three-phase full-bridge converter to control the charge and discharge cycles between a battery pack and an inductive load (motor windings), combined with an external auxiliary heating mechanism (PTC heater or heating film) to achieve battery heating. During the discharge phase, the auxiliary heating mechanism is connected in parallel with the battery to increase external heating and internal resistance heat generation. During the charging phase, the auxiliary heating mechanism is disconnected, and the energy stored in the inductive load is fed back to the battery, optimizing heating efficiency. This battery heating method and system has the following drawbacks: It requires the motor to be in an inoperative state, making it unsuitable for systems without a motor. If improperly controlled, the motor may be damaged by stalled rotors and overheating.

[0005] CN112736327A discloses a low-temperature battery assembly heating device based on LC resonance. This device uses an LC resonant circuit combined with a full-bridge switch to generate a pulsed discharge current. This circuit generates heat through the battery's internal resistance, while simultaneously heating the battery's exterior with a PTC heater, achieving simultaneous internal and external heating. This LC resonance-based low-temperature battery assembly heating device has the following drawbacks: the LC resonant frequency is fixed and cannot adapt to changes in impedance due to battery aging or different operating conditions. Summary of the Invention

[0006] In view of the problems that the existing technology requires motor auxiliary heating or uses the fixed resonant frequency of the LC resonant circuit for battery self-heating, the motor may be damaged due to stalled rotor overheating and cannot adapt to battery aging or impedance changes under different operating conditions. The present invention proposes a battery self-heating device based on LC topology and its control method.

[0007] According to one aspect of the present invention, a battery self-heating device based on an LC topology includes: a switching bridge and a boost capacitor C2, the switching bridge includes an upper bridge arm and a lower bridge arm, the upper bridge arm includes a first MOS transistor Q1 and a second MOS transistor Q2, the lower bridge arm includes a third MOS transistor Q3 and a fourth MOS transistor Q4, wherein the drain of the first MOS transistor Q1 is connected to the drain of the second MOS transistor Q2 and is connected to the first end of the boost capacitor C2, the source of the third MOS transistor Q3 is connected to the source of the fourth MOS transistor Q4 and is connected to the second end of the boost capacitor C2, and the drain of the second MOS transistor Q2 is connected to the drain of the third MOS transistor Q3 and the drain of the fourth MOS transistor Q4. The source and the drain of the third MOS transistor Q3 are connected to a first node, the source of the first MOS transistor Q1 and the drain of the fourth MOS transistor Q4 are connected to a second node, the negative electrode of the battery is connected to the second node, the positive electrode of the battery is connected in series with the capacitor C1 and the inductor L1, and is connected to the first node through one end of the capacitor C1 or the inductor L1, wherein the first MOS transistor Q1 and the third MOS transistor Q3 are configured to be controlled by a first PWM control signal to be turned on or off simultaneously, and the second MOS transistor Q2 and the fourth MOS transistor Q4 are configured to be controlled by a second PWM control signal to be turned on or off simultaneously.

[0008] In the above aspect, further, a ratio C1 / C2 of the capacitance of the capacitor C1 to the boost capacitor C2 is 100-300.

[0009] In the above aspect, further, the battery includes any one of the following: a single battery, multiple batteries, a battery module, a battery pack consisting of multiple batteries or battery modules, and a PACK battery formed by connecting multiple battery cells in series.

[0010] In the above aspect, further, the MOS transistor is a silicon carbide MOS transistor.

[0011] According to another aspect of the present invention, a battery heating control method is disclosed. The battery heating control method is based on the battery self-heating device based on LC topology of the present invention. The battery heating control method includes: real-time monitoring of battery parameters, wherein the battery parameters include the battery health state SOH, state of charge SOC, temperature T and polarization voltage. ; Perform EIS testing on the battery based on specific battery parameters to construct multiple frequency impedance tables, wherein the specific battery parameters are the state of health (SOH), state of charge (SOC), and temperature (T) selected according to the EIS test settings; upon receiving a heating request, based on the battery parameters monitored in real time, search the corresponding frequency impedance table for the target frequency f of the heating current with the best heating effect, and calculate the target frequency f based on the battery impedance corresponding to the target frequency f and the polarization voltage of the battery. The target amplitude I of the heating current is calculated; based on the target frequency f and the target amplitude I of the heating current, the duty cycle and frequency of the first PWM control signal and the second PWM control signal are obtained.

[0012] In the above aspect, further, the frequency impedance table is constructed by: and denote the maximum and minimum values ​​of the SOH of the battery under consideration, is the sampling interval for the battery SOH; and represent the maximum and minimum values ​​of the SOC of the battery under consideration, is the sampling interval for the battery SOC; and denote the maximum and minimum values ​​of the temperature T of the battery under consideration, is the sampling interval of the battery temperature T; the battery is tested by EIS at a preset resolution using a current with a frequency f of 0.01 Hz to 10 kHz to obtain the battery impedance at different current frequencies f under a specific SOH-SOC-T , the battery impedance Including real impedance Re and imaginary impedance , expressed as , the number m of frequency impedance tables obtained is expressed by the following formula:

[0013] .

[0014] In the above aspect, further, when the difference between adjacent impedances in the frequency impedance table exceeds a set threshold, 、 and Perform adaptive adjustments and update the frequency impedance table synchronously.

[0015] In the above aspect, further, the duty cycle and frequency of the first PWM control signal and the second PWM control signal are obtained in the following manner: first, the frequency of the first PWM control signal and the second PWM control signal is determined to be equal to the target frequency f of the heating current; thereafter, the duty cycle of the first PWM control signal and the second PWM control signal is determined according to the amplitude I of the heating current.

[0016] In the above aspect, further, a closed-loop feedback control method is used to determine the duty cycle of the first PWM control signal and the second PWM control signal, including: real-time monitoring of the amplitude I of the heating current; calculating the error value between the measured value and the expected value of the amplitude I of the heating current; adjusting the duty cycle of the first PWM control signal and the second PWM control signal according to the error value; repeating the above steps until the error value is less than the set threshold.

[0017] In the above aspect, further, the polarization voltage is controlled when the battery is heated. ,Will Take and The smaller of is the upper limit voltage of charging, is the lower limit discharge voltage, is the static open circuit voltage.

[0018] The beneficial effects of the present invention are:

[0019] (1) The present invention abandons the motor-assisted heating method and adopts the MOS switch bridge and LC series topology to directly charge and discharge the battery to achieve self-heating, avoiding the limitations brought by reliance on the motor, such as the inapplicability of the system without a motor and the damage caused by motor stalling and overheating. It simplifies the system structure and improves the directness and efficiency of heating.

[0020] (2) The present invention dynamically optimizes the frequency and amplitude of the heating current based on the battery EIS test data, which can accurately match the thermal requirements of the battery under different aging conditions throughout its life cycle. It solves the problems of changes in the thermal time constant of aging batteries and the difficulty in adapting the AC heating frequency and amplitude, ensuring that the battery can be properly heated at different stages of use.

[0021] (3) The battery self-heating device based on LC topology of the present invention adopts silicon carbide MOS tube, which can generate high-frequency ripple current of 200kHz-500kHz. Compared with the traditional heating method which is limited by the IGBT switching frequency (generally ≤50kHz), it can significantly increase the heating speed, reduce the battery heating time, and improve the use efficiency.

[0022] (4) The LC topology used in the present invention can adjust the impedance and output current according to the frequency, and has a good AC current output function. At the same time, it also has overvoltage and short-circuit protection functions, which enhances the safety and stability of the circuit.

[0023] (5) The battery heating control method of the present invention controls the polarization voltage within a reasonable range through the battery management system BMS to avoid lithium plating.

[0024] (6) The battery heating control method of the present invention can obtain the target frequency and amplitude of the heating current for optimal heating effect based on parameters such as the battery's state of health (SOH), state of charge (SOC), temperature (T), and polarization voltage, with the assistance of a frequency-impedance table, and accordingly determine the duty cycle and frequency of the PWM control signal. Furthermore, when the difference between adjacent impedances in the frequency-impedance table exceeds a set threshold (e.g., 10%), the relevant sampling interval is adaptively adjusted and the frequency-impedance table is updated to achieve precise heating control. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention and make other features, objects and advantages of the present invention more apparent. The accompanying drawings and descriptions of the exemplary embodiments of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0026] In addition, throughout the drawings, the same or similar reference numerals represent the same or similar elements. It should be understood that the drawings are schematic and that the elements and components are not necessarily drawn to scale.

[0027] In the attached figure:

[0028] Figure 1 is a circuit diagram of an embodiment of a battery self-heating device based on LC topology of the present invention;

[0029] Figure 2 1 is a schematic diagram of current flow in the first stage of the starting operation of an embodiment of the battery self-heating device based on the LC topology of the present invention;

[0030] Figure 3 1 is a timing diagram of an oscillation waveform of the first stage of oscillation operation of an embodiment of a battery self-heating device based on an LC topology of the present invention;

[0031] Figure 4 1 is a schematic diagram of current flow in the second stage of the starting operation of an embodiment of the battery self-heating device based on the LC topology of the present invention;

[0032] Figure 5 1 is a timing diagram of an oscillation waveform in the second stage of the oscillation operation of an embodiment of the battery self-heating device based on the LC topology of the present invention;

[0033] Figure 6 1 is a schematic diagram of current flow in the third stage of the starting operation of an embodiment of the battery self-heating device based on the LC topology of the present invention;

[0034] Figure 7 is a timing diagram of an oscillation waveform of the third stage in the oscillation operation of an embodiment of the battery self-heating device based on the LC topology of the present invention;

[0035] Figure 8 1 is a schematic diagram of current flow in the fourth stage of the starting operation of an embodiment of the battery self-heating device based on the LC topology of the present invention;

[0036] Figure 9 1 is a timing diagram of an oscillation waveform of the fourth stage of oscillation operation of an embodiment of a battery self-heating device based on an LC topology of the present invention;

[0037] Figure 10 1 is a schematic diagram of current flow in a state 1 in which the inductor L1 and the capacitor C1 are charged and the boost capacitor C2 reaches a first maximum voltage according to an embodiment of the battery self-heating device based on the LC topology of the present invention;

[0038] Figure 11 1 is a schematic diagram of current flow in a state 1 in which the current charges the inductor L1 and the capacitor C1 and the boost capacitor C2 decreases from a first maximum voltage to a minimum voltage according to an embodiment of the battery self-heating device based on the LC topology of the present invention;

[0039] Figure 12 1 is a ripple current timing diagram of an embodiment of a battery self-heating device based on an LC topology according to the present invention in state 1;

[0040] Figure 13 1 is a schematic diagram of current flow in a state 2 of an embodiment of a battery self-heating device based on an LC topology of the present invention, in which the current is discharged through the inductor L1 and the capacitor C1;

[0041] Figure 14 1 is a ripple current timing diagram of an embodiment of a battery self-heating device based on an LC topology of the present invention in state 2;

[0042] Figure 15 1 is a schematic diagram of current flow in a state 3 in which the inductor L1 and the capacitor C1 are charged and the boost capacitor C2 reaches the second maximum voltage according to an embodiment of the battery self-heating device based on the LC topology of the present invention;

[0043] Figure 161 is a schematic diagram of current flow in a state 3 in which the inductor L1 and the capacitor C1 are charged and the boost capacitor C2 decreases from the second maximum voltage to the minimum voltage according to an embodiment of the battery self-heating device based on the LC topology of the present invention;

[0044] Figure 17 1 is a ripple current timing diagram of an embodiment of a battery self-heating device based on an LC topology according to the present invention in state 3;

[0045] Figure 18 1 is a schematic diagram of current flow in a state 4 of an embodiment of a battery self-heating device based on an LC topology of the present invention, in which the current is discharged through the inductor L1 and the capacitor C1;

[0046] Figure 19 1 is a ripple current timing diagram of an embodiment of a battery self-heating device based on an LC topology of the present invention in state 4;

[0047] Figure 20 is a flow chart of a battery heating control method of the present invention. DETAILED DESCRIPTION

[0048] Embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be construed as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present disclosure. It should be understood that the drawings and embodiments of the present disclosure are for illustrative purposes only and are not intended to limit the scope of protection of the present disclosure.

[0049] like Figure 1As shown, the battery self-heating device based on the LC topology of the present invention includes a switching bridge and a boost capacitor C2. The switching bridge includes an upper bridge arm and a lower bridge arm. The upper bridge arm includes a first MOS transistor Q1 and a second MOS transistor Q2, and the lower bridge arm includes a third MOS transistor Q3 and a fourth MOS transistor Q4. The drain of the first MOS transistor Q1 and the drain of the second MOS transistor Q2 are connected, and are connected to the first end of the boost capacitor C2. The source of the third MOS transistor Q3 and the source of the fourth MOS transistor Q4 are connected, and are connected to the second end of the boost capacitor C2. The source of the second MOS transistor Q2 and the drain of the third MOS transistor Q3 are connected to a first node, the source of the first MOS transistor Q1 and the drain of the fourth MOS transistor Q4 are connected to a second node, the negative electrode of the battery is connected to the second node, and the positive electrode of the battery is connected in series with the capacitor C1 and the inductor L1, and is connected to the first node through one end of the capacitor C1 or the inductor L1. The gates of the first and third MOS transistors Q1 and Q3 are S1, and the gates of the second and fourth MOS transistors Q2 and Q4 are S2. The present invention applies a first PWM control signal and a second PWM control signal to S1 and S2, respectively, to control the simultaneous disconnection of the first and third MOS transistors Q1 and Q3, as well as the simultaneous disconnection of the second and fourth MOS transistors Q2 and Q4. The battery self-heating device based on an LC topology performs high-frequency resonant charging and discharging on a resonant inductor and capacitor, causing the battery connected in series to perform high-frequency current charging and discharging, thereby achieving ripple current output and thus completing the battery's ripple self-heating function.

[0050] In one embodiment of the present invention, the ratio C1 / C2 of the capacitance of the capacitor C1 to the boost capacitor C2 is 100-300. The present invention selects the capacitance of the boost capacitor C2 to be much smaller than the capacitance C1 of the LC topology, so that the boost capacitor C2 relies on the inductive freewheeling charging to boost the voltage, and then realizes the reverse high-voltage instantaneous discharge of the boost capacitor C2 to charge the battery. Figure 1 As shown, in one embodiment of the present invention, the capacitance value of capacitor C1 is set to 1mF, and the capacitance value of C2 is set to 5uF. In this case, C1 / C2 is 200. The reason is that the capacity of the boost capacitor C2 is small, and it can charge and discharge quickly, generating a large ripple current; the capacity of the capacitor C1 is large, which can smooth the output voltage while allowing the ripple current to pass. If the ratio of C1 / C2 is too small (for example, less than 100), the amplitude of the ripple current may be insufficient and the battery cannot be effectively heated. On the other hand, the ratio of C1 / C2 will also affect the frequency of the ripple current. If the ratio is too large (for example, more than 300), the frequency of the ripple current may be too low, resulting in reduced heating efficiency. Therefore, the ratio of C1 / C2 is within a certain range to ensure that energy can be efficiently transferred from the boost capacitor to the battery internal resistance. According to tests, this ratio is selected to be between 100 and 300 as the preferred range.

[0051] In various embodiments of the present invention, a battery can refer to a single battery, multiple batteries, a battery module, or a battery pack composed of multiple batteries or battery modules, particularly a battery pack formed by multiple strings of battery cells connected in series. In various embodiments of the present invention, the battery is connected in series with an LC topology to form an LC source, and an oscillatory ripple high current charging and discharging heating is achieved through a switching bridge.

[0052] In various embodiments of the present invention, the MOS tube in the battery self-heating device can adopt a silicon carbide MOS tube (SiCMOSFET), and the upper limit switching frequency can reach 200KHz to 500KHz. Compared with IGBT, it has the advantages of small size, large output current, high voltage resistance and wide operating frequency range.

[0053] The LC topology used in the present invention consists of a series connection of inductors and capacitors, capable of adjusting impedance and output current according to frequency, providing excellent AC current output function, as well as overvoltage and short-circuit protection. Specifically, the LC series circuit exhibits a certain impedance characteristic for AC signals. At the resonant frequency, the total impedance Z is minimum, allowing AC current to pass smoothly. When the input voltage is constant, changes in impedance cause changes in output current, thereby achieving frequency-dependent impedance and output current adjustment. When an AC signal is input, as long as the frequency is appropriate, an AC current path is formed in the circuit, enabling AC current output. For AC signals that deviate from the resonant frequency, although the total impedance of the inductor and capacitor is not zero, AC current can still be output. When the current needs to be increased, the current frequency can be shifted toward the resonant frequency, while when the current needs to be reduced, the current frequency can be shifted away from the resonant frequency. In addition, when a voltage spike occurs in the circuit, capacitor C1 absorbs excess energy through charging, limiting the voltage surge. When the current suddenly changes during a short circuit, inductor L1 generates a reverse electromotive force, suppressing the sharp rise in current.

[0054] See Figures 2 to 19 The working principle of the battery self-heating device based on LC topology of the present invention is now described in detail. The battery self-heating device based on LC topology of the present invention has two operations when starting heating, namely, the starting operation and the heating operation, wherein the starting operation is to charge the boost capacitor C2. Figure 3 、 Figure 5 、 Figure 7 、 Figure 9 、 Figure 12 、 Figure 14 、 Figure 17 and Figure 19 In the figure, the horizontal axis represents time, the vertical axis represents amplitude, and from top to bottom they are the capacitor voltage of the boost capacitor, the battery current, the first PWM signal applied to S1, and the second PWM signal applied to S2.

[0055] like Figure 2As shown, this is the first stage of the oscillation operation: the first MOS tube Q1 and the third MOS tube Q3 are turned on, and the current charges the LC circuit through the body diode of the second MOS tube Q2 and the first MOS tube Q1 to store energy. This first stage corresponds to Figure 3 The t in the oscillation waveform timing diagram a to t b .

[0056] like Figure 4 As shown, this is the second stage of the oscillation operation: by applying a control signal of 0 to S1 to turn off all MOS tubes, the loop current flows through the body diode of the second MOS tube Q2 and the body diode of the fourth MOS tube Q4 to charge and boost the boost capacitor C2. This second stage corresponds to Figure 5 The t in the oscillation waveform timing diagram b to t c .

[0057] like Figure 6 As shown, this is the third stage of the oscillation operation: by applying a control signal of 1 to S1 to turn on the second MOS tube Q2 and the fourth MOS tube Q4, the circuit freewheeling current passes through the second MOS tube Q2 and the fourth MOS tube Q4, and continues to charge and boost the boost capacitor C2. This third stage corresponds to Figure 7 The t in the oscillation waveform timing diagram c to t d .

[0058] like Figure 8 As shown, it is the fourth stage in the oscillation operation: by applying a control signal of 0 to S1 to turn off all MOS tubes, the loop current flows through the body diode of the second MOS tube Q2 and the body diode of the fourth MOS tube Q4 to charge and boost the boost capacitor C2. This fourth stage corresponds to Figure 9 The t in the oscillation waveform timing diagram d to t e .

[0059] The four stages of the above oscillation start-up operation charge the boost capacitor C2 through multiple cycles, and the boost capacitor C2 can be charged and discharged normally, thereby achieving a ripple current output state.

[0060] The heating operation of the battery self-heating device based on the LC topology of the present invention is now described.

[0061] See Figures 10 to 12 In state 1 of the heating operation, a control signal of 1 is applied to S1 of the second MOS transistor Q2 and the fourth MOS transistor Q4 to turn them on, and a control signal of 0 is applied to S2 of the first MOS transistor Q1 and the third MOS transistor Q3 to turn them off. Figure 10 Corresponding to Figure 12 From t1 to t2 in the ripple current timing diagram, the boost capacitor C2 reaches the first maximum voltage. Figure 11 Corresponding to Figure 12 From t2 to t3 in the ripple current timing diagram, the boost capacitor C2 drops from the first maximum voltage to the minimum voltage. In state 1, the current charges the inductor L1 and the capacitor C1.

[0062] See Figure 13 and Figure 14 In the state 2 of the heating operation, the S1 control signal of the second MOS transistor Q2 and the fourth MOS transistor Q4 is set to 0 to turn them off, and the S2 control signal of the first MOS transistor Q1 and the third MOS transistor Q3 is set to 0 to turn them off. The current flows as follows Figure 13 As shown, Figure 13 Corresponding to Figure 14 In the ripple current timing diagram, the current is discharged from t3 to t4. In state 2, the current is discharged through the inductor L1 and the capacitor C1.

[0063] See Figures 15 to 17 In state 3 of the heating operation, the control signal of S1 of the second MOS transistor Q2 and the fourth MOS transistor Q4 is set to 0 to turn them off, and at the same time, a control signal of 1 is applied to S2 of the first MOS transistor Q1 and the third MOS transistor Q3 to turn them on. Figure 15 Corresponding to Figure 17 From t4 to t5 in the ripple current timing diagram, the boost capacitor C2 reaches the second maximum voltage. Figure 16 Corresponding to Figure 17 From t5 to t6 in the ripple current timing diagram, the boost capacitor C2 drops from the second maximum voltage to the minimum voltage. In state 3, the current charges the inductor L1 and the capacitor C1.

[0064] See Figure 18 and Figure 19 In the heating operation state 4, the S1 control signal of the second MOS transistor Q2 and the fourth MOS transistor Q4 is set to 0 to turn them off, and the S2 control signal of the first MOS transistor Q1 and the third MOS transistor Q3 is set to 0 to turn them off. The current flows as follows Figure 18 As shown, Figure 18 Corresponding to Figure 19 In state 4, the current is discharged through inductor L1 and capacitor C1.

[0065] See Figure 20 The present invention also discloses a battery heating control method, which can be applied to the battery self-heating device based on LC topology of the present invention. The battery heating control method includes: real-time monitoring of battery parameters, wherein the battery parameters include the battery health state SOH, state of charge SOC, temperature T and polarization voltage. ; Based on specific battery parameters, an EIS (Electrochemical Impedance Spectroscopy) test is performed on the battery to construct multiple frequency impedance tables, wherein the specific battery parameters are the health state SOH, the state of charge SOC and the temperature T selected according to the EIS test settings, that is, the specific battery parameters refer to the battery parameters that meet the test points for the EIS test on the battery, which are described in detail below; when a heating request is received, based on the battery parameters monitored in real time, the target frequency f of the heating current with the best heating effect is searched in the corresponding frequency impedance table, and the battery impedance corresponding to the target frequency f and the polarization voltage of the battery are calculated based on the battery impedance corresponding to the target frequency f. The target amplitude I of the heating current is calculated, and the target frequency f of the heating current is, for example, 100 Hz to 100 kHz; based on the target frequency f and the target amplitude I of the heating current, the duty cycle and frequency of the first PWM control signal and the second PWM control signal are obtained, wherein the frequency of the PWM control signal affects the frequency of the heating current, and thus affects the heating impedance; the duty cycle of the PWM control signal affects the amplitude of the heating current.

[0066] State of health SOH, state of charge SOC, temperature T and polarization voltage Both can be obtained by the Battery Management System (BMS), where the polarization voltage It is the difference between the actual working voltage and the open circuit voltage due to the internal polarization effect during the charge and discharge process of the battery. It can be monitored and controlled in real time by the battery management system BMS.

[0067] Since the main sources of heat generation during battery pulse heating are ohmic internal resistance heat generation and polarization internal resistance heat generation, it is necessary to calculate the maximum heat generation of ohmic internal resistance and polarization internal resistance in the electrochemical impedance data. This can be done by finding the frequency and amplitude of the heating current for better battery heating effect through the battery heating equation.

[0068] The advantages of the battery heating control method of the present invention are that, on the one hand, the best heating effect can be obtained according to the battery parameters; on the other hand, the amplitude of the heating current is proportional to the polarization voltage of the battery. The larger the polarization voltage, the faster the heating speed, but the larger the polarization voltage is, the better it is. By controlling the polarization voltage within a reasonable range through the battery management system BMS, lithium plating can be avoided and overcharging or over-discharging can be prevented. It can be understood that the battery management system BMS is an electronic system for monitoring and managing batteries. Its main functions include battery status monitoring, state of charge SOC estimation, health state SOH assessment, safety protection and energy management. Battery status monitoring includes real-time monitoring of single cell voltage, temperature, charge and discharge current and total voltage; state of charge SOC estimation includes open circuit voltage under static state Calculate SOC; health state SOH assessment includes comprehensive SOH assessment through data such as internal resistance change and number of cycles; safety protection includes overcharge / over-discharge protection, overcurrent protection and temperature protection; energy management includes dynamic adjustment of charging and discharging power according to SOC and temperature.

[0069] The frequency and amplitude of the heating current that achieves the best heating effect can be found based on the battery heating equation. The details are as follows:

[0070] Battery self-heating heat generation Mainly composed of real impedance Heat generation, imaginary impedance Does not participate in heat generation. Since the battery itself has heat dissipation, according to the law of conservation of energy, it can be concluded that the battery actually brings about temperature rise. Battery cooling The battery heat dissipation is determined by the battery surface area, heat transfer coefficient and the temperature difference between the battery and the environment. It can be expressed by the following formula:

[0071] (1)

[0072] Where, is the heat transfer coefficient, which represents the amount of heat transferred between the battery surface and the environment per unit area per unit time, and is affected by the battery temperature; S is the surface area of ​​the battery, that is, the total area in contact with the environment; is the actual temperature of the battery, that is, the temperature reached by the battery during operation; is the ambient temperature, that is, the temperature of the environment where the battery is located.

[0073] Since the ambient temperature is constant, the battery temperature continues to rise. Therefore, the shorter the heating time, the smaller the heat loss. Therefore, in the design process, only The largest one is fine.

[0074] Battery heating is mainly caused by the real impedance, that is,

[0075] (2)

[0076] Among them, the current , is the polarization voltage, It is composed of real impedance and imaginary impedance, which can be expressed as , we can get:

[0077] (3)

[0078] Substituting (3) into (2) we can get

[0079] (4)

[0080] in, is the polarization voltage, t is the time the battery generates heat during operation, and It can be obtained through a frequency impedance table.

[0081] In one embodiment of the present invention, the frequency impedance table can be constructed in the following manner: and denote the maximum and minimum values ​​of the SOH of the battery under consideration, is the sampling interval for the battery SOH; and represent the maximum and minimum values ​​of the SOC of the battery under consideration, is the sampling interval for the battery SOC; and denote the maximum and minimum values ​​of the temperature T of the battery under consideration, is the sampling interval of the battery temperature T. The EIS test setting is to set the above 、 and , thereby obtaining the test points of battery parameters for EIS test of the battery. The battery is tested by EIS with a current of 0.01Hz to 10kHz at a preset resolution to obtain the battery impedance at different current frequencies f under a specific SOH-SOC-T. , the number m of frequency impedance tables obtained is expressed by the following formula:

[0082] (5)

[0083] For example, the battery can be tested for EIS in sequence by controlling a single variable among SOH, SOC, and T. For example, the battery SOH ranges from 100% to 70%, with intervals of 5% (batteries with SOH below 70% are generally considered scrapped), with a total of 7 specific SOHs; the battery SOC ranges from 100% to 0%, with intervals of 10%, with a total of 11 specific SOCs; the temperature T ranges from -40°C to 10°C, with intervals of 5°C (when heated above 10°C, the heating effect of the present invention will significantly decrease, so the heating method of the present invention generally heats the battery to 10°C), with a total of 11 specific Ts. Each time a specific parameter is fixed, and all points are swept from 0.01Hz to 10kHz (with a resolution of, for example, 0.01Hz) (under normal circumstances, the battery's available frequency ranges from hundreds of hertz to thousands of hertz, so this frequency range is fully covered). A total of 11*11*7=847 frequency impedance tables can be obtained, and each frequency impedance table is as follows:

[0084]

[0085] Since t in formula (4) is a constant, When the time and current are constant, it is also a constant, so we need to make The largest, just need to find The maximum value of . The corresponding maximum value , we can find the corresponding target frequency f of the heating current in the frequency-impedance table, and further substitute the corresponding impedance at the target frequency f into formula (3) to obtain the target amplitude I of the current.

[0086] When determining the corresponding frequency impedance table to be referenced, if the current battery parameters correspond exactly to the test point of the EIS test on the battery, the frequency impedance table corresponding to the current battery parameters can be referenced. If the current battery parameters do not correspond to the test point of the EIS test on the battery, the frequency impedance table corresponding to the previous adjacent test point of the current battery parameters can be determined as the reference frequency impedance table. For example, in 、 and With the above settings, if the current battery parameters are as follows: SOH is 92%, SOC is 88%, and T is 2°C, then you should refer to the frequency impedance table corresponding to SOH of 95%, SOC of 90%, and T of 0°C.

[0087] In one embodiment of the present invention, when the difference between adjacent impedances in the frequency impedance table exceeds 10%, ΔSOH, ΔSOC, and ΔT may be adaptively adjusted, and the frequency impedance table may be updated synchronously.

[0088] Specifically, when the difference between adjacent impedances exceeds 10%, if SOC and T remain unchanged, the battery ages quickly, that is, the SOH changes significantly, then the battery should be appropriately reduced. , for example, from 5% to 3%, so that more data points can be obtained in the SOH change range, accurately reflecting the impact of battery aging on impedance; if the aging rate is slow, it can be increased moderately , such as adjusting from 5% to 7%, reducing the number of sampling times, improving efficiency and ensuring data representativeness. If SOH and T remain unchanged, the battery impedance varies greatly in different SOC ranges. For example, if the battery internal resistance changes greatly at low SOC, the battery impedance can be reduced in the low SOC range. , adjust from 10% to 5%, and carefully analyze the impedance change law at low SOC; if the impedance changes are relatively stable in each SOC interval, you can increase , such as adjusting from 10% to 15%, reducing unnecessary sampling and improving efficiency. If SOH and SOC remain unchanged, when the battery temperature T changes drastically, such as when the battery performance fluctuates greatly in a low temperature environment, then reduce , change from 5℃ to 3℃, closely monitor the effect of temperature on impedance; if the temperature has little effect on battery impedance, increase , such as adjusting from 5℃ to 7℃, to reduce the sampling workload while ensuring the validity of temperature-related data.

[0089] After adjustment, the battery is retested with the adjusted intervals, and the real impedance, imaginary impedance, and total impedance data in the frequency impedance table are updated to ensure that they match the actual state of the battery, providing an accurate basis for the subsequent calculation of the target frequency and amplitude of the heating current, and ensuring that the battery heating process is efficient and safe.

[0090] In one embodiment of the present invention, the duty cycle and frequency of the PWM control signal are obtained in the following manner: first, the frequency of the PWM control signal is determined to be equal to the target frequency f of the heating current; thereafter, the duty cycle of the PWM control signal is determined according to the amplitude I of the heating current.

[0091] Specifically, when determining the duty cycle of the PWM control signal based on the amplitude of the heating current, I, a closed-loop feedback control approach can be employed to monitor the amplitude of the heating current in real time and compare it with the desired amplitude. Based on the comparison result, the duty cycle of the PWM control signal is automatically adjusted to stabilize the heating current amplitude near the desired value. As described above, the desired value of the heating current amplitude is determined by the polarization voltage and the battery impedance corresponding to the target frequency of the heating current. A current sensor can be used to measure the heating current amplitude in real time, and the measured value is fed back to a controller. The controller compares the measured current amplitude with the desired current amplitude and calculates an error value. Based on the error value, a PID control algorithm, for example, is used to calculate the duty cycle increment that needs to be adjusted, and the duty cycle of the PWM signal is updated. The above steps are repeated until the error value is less than a set threshold.

[0092] During the battery heating process, reasonable control of the polarization voltage is crucial to avoiding lithium plating. Polarization voltage is the difference between the actual voltage and the circuit voltage during battery charging and discharging. Lithium plating is the phenomenon of lithium metal precipitation on the surface of the negative electrode during low-temperature charging, which will seriously affect the performance and safety of the battery. The polarization voltage is related to the reaction rates of charge transfer, ion diffusion, etc. inside the battery. An increase in polarization voltage means that the reaction resistance inside the battery increases, and the ion diffusion rate may not keep up with the reaction requirements. This situation is more serious when charging at low temperatures, and lithium ions accumulate on the electrode surface, easily forming lithium dendrites. Reasonable control of the polarization voltage can maintain a balance between ion diffusion and charge transfer reactions, reduce lithium ion accumulation, and reduce the risk of lithium plating.

[0093] In one embodiment of the present invention, the duty cycle of the PWM control signal of the MOS tube in the battery self-heating device of the present invention can be controlled by the battery management system BMS to control the amplitude of the heating current, thereby controlling the polarization voltage when heating the battery. ,Will Take and The smaller of the two, thus avoiding the lithium precipitation phenomenon, where is the upper limit voltage of charging, is the lower limit discharge voltage, is the static open circuit voltage, where and It is the specification parameter of the battery itself, which is determined when the battery is designed, such as the ternary lithium battery 4.2V / cell, 2.5V / cell, It needs to be collected through the battery management system BMS.

[0094] The battery management system BMS can directly collect , and then calculate and ,Pick and The smaller of Then the battery self-heating device of the present invention is controlled according to the target Adjust the amplitude or frequency of the heating current in real time. When approaching the threshold, the heating power is reduced to avoid exceeding the limit.

Claims

1. A battery self-heating device based on LC topology, characterized in that: include: A boost capacitor C2 and a switch bridge composed of MOS transistors, the switch bridge includes an upper bridge arm and a lower bridge arm, the upper bridge arm includes a first MOS transistor Q1 and a second MOS transistor Q2, and the lower bridge arm includes a third MOS transistor Q3 and a fourth MOS transistor Q4, wherein: The drain of the first MOS transistor Q1 is connected to the drain of the second MOS transistor Q2, and is connected to the first end of the boost capacitor C2. The source of the third MOS transistor Q3 is connected to the source of the fourth MOS transistor Q4, and is connected to the second end of the boost capacitor C2. The source of the second MOS transistor Q2 and the drain of the third MOS transistor Q3 are connected to a first node. The source of the first MOS transistor Q1 and the drain of the fourth MOS transistor Q4 are connected to a second node. The negative electrode of the battery is connected to the second node. The positive electrode of the battery is connected in series with the capacitor C1 and the inductor L1, and is connected to the first node through one end of the capacitor C1 or the inductor L1. The first MOS transistor Q1 and the third MOS transistor Q3 are configured to be controlled by the first PWM control signal to be turned on or off simultaneously, and the second MOS transistor Q2 and the fourth MOS transistor Q4 are configured to be controlled by the second PWM control signal to be turned on or off simultaneously.

2. The battery self-heating device based on LC topology according to claim 1, characterized in that: The capacitance ratio C1 / C2 of the capacitor C1 and the boost capacitor C2 is 100-300.

3. The battery self-heating device based on LC topology according to claim 1, characterized in that: The battery includes any one of the following: a single battery, multiple batteries, a battery module, a battery pack consisting of multiple batteries or battery modules, and a PACK battery formed by connecting multiple battery cells in series.

4. The battery self-heating device based on LC topology according to claim 1, characterized in that: The MOS tube is a silicon carbide MOS tube.

5. A battery heating control method, characterized in that: The battery self-heating device based on LC topology according to any one of claims 1 to 4, comprising: Real-time monitoring of battery parameters, including battery health status SOH, state of charge SOC, temperature T and polarization voltage ; Performing an EIS test on the battery based on specific battery parameters to construct a plurality of frequency impedance tables, wherein the specific battery parameters are a state of health (SOH), a state of charge (SOC), and a temperature (T) selected according to an EIS test setting; When a heating request is received, based on the real-time monitored battery parameters, the target frequency f of the heating current with the best heating effect is found in the corresponding frequency impedance table, and the battery impedance corresponding to the target frequency f and the polarization voltage of the battery are calculated. Calculate the target amplitude I of the heating current; Based on the target frequency f and the target amplitude I of the heating current, the duty ratio and the frequency of the first PWM control signal and the second PWM control signal are obtained.

6. The battery heating control method according to claim 5, characterized in that: The frequency impedance table is constructed in the following way: make and denote the maximum and minimum values ​​of the SOH of the battery under consideration, is the sampling interval for the battery SOH; and represent the maximum and minimum values ​​of the SOC of the battery under consideration, is the sampling interval for the battery SOC; and denote the maximum and minimum values ​​of the temperature T of the battery under consideration, is the sampling interval of the battery temperature T; Perform EIS test on the battery with a current frequency f of 0.01Hz to 10kHz at a preset resolution to obtain the battery impedance at different current frequencies f under a specific SOH-SOC-T , the battery impedance Including real impedance Re and imaginary impedance , expressed as , the number m of frequency impedance tables obtained is expressed by the following formula: 。 7. The battery heating control method according to claim 6, characterized in that: When the difference between adjacent impedances in the frequency impedance table exceeds the set threshold, 、 and Perform adaptive adjustments and update the frequency impedance table synchronously.

8. The battery heating control method according to claim 5, characterized in that: The duty cycle and frequency of the first PWM control signal and the second PWM control signal are obtained by: First, the frequencies of the first PWM control signal and the second PWM control signal are determined to be equal to the target frequency f of the heating current; Thereafter, the duty ratios of the first PWM control signal and the second PWM control signal are determined according to the amplitude I of the heating current.

9. The battery heating control method according to claim 8, characterized in that: Determining the duty ratio of the first PWM control signal and the second PWM control signal by adopting a closed-loop feedback control method includes: Real-time monitoring of the amplitude I of the heating current; Calculate the error between the measured value and the expected value of the amplitude I of the heating current; adjusting the duty cycle of the first PWM control signal and the second PWM control signal according to the error value; Repeat the above steps until the error value is less than the set threshold.

10. The battery heating control method according to any one of claims 5 to 9, characterized in that: Also includes: Controlling the polarization voltage when heating the battery ,Will Take and The smaller of is the upper limit voltage of charging, is the lower limit voltage of discharge, is the static open circuit voltage.

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