Lithium ion battery self-heating device and control method

Abstract

The invention relates to a lithium ion battery self-heating device and a control method, and belongs to the technical field of battery low-temperature self-heating. The device comprises an H-bridge commutation circuit formed by four controllable switch elements, a connection inductor connected between middle points of left and right bridge arms of an H-bridge, a first inductor connected in series with a lithium ion battery, and a filter capacitor connected in parallel with a DC side of the H-bridge. The method comprises the following steps: analyzing a space operation state of a topological structure to deduce a battery end steady-state current expression; establishing a circuit simulation model, and inputting the element parameters and the control parameters into the model to obtain simulation values; actual control parameters are adjusted through the simulation values and input into a control panel; according to the self-heating topological structure, the amplitude and the frequency of the self-heating current can be adjusted within a certain range, the phenomena of capacity reduction and power reduction of the lithium ion battery at a low temperature can be improved, and the service life of the lithium ion battery is prolonged. And a structural reference is provided for the low-temperature alternating-current heating design of the power battery system.

Description

Technical Field

[0001] This invention belongs to the field of battery low-temperature self-heating technology, and relates to a lithium-ion battery self-heating device and control method. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, grid energy storage, and portable electronic devices due to their high energy density and long cycle life. However, in low-temperature environments, the internal electrochemical reaction rate of the battery decreases significantly, internal resistance increases, and usable capacity and power output decrease markedly, severely affecting vehicle starting performance and the reliability of energy storage systems. Therefore, preheating the battery through certain methods before putting it into normal operation has become a critical issue that must be addressed in low-temperature applications.

[0003] In existing technologies, one approach involves placing heating elements, PTC heaters, or liquid cooling / liquid heating systems outside the battery pack to transfer heat to the cells via an external heat source. While this method has a relatively straightforward structure, it requires additional heating elements, piping, and control systems, resulting in complex system integration, high costs, and the need for heat to penetrate the casing and interface materials to reach the active materials. This leads to slow response times, low thermal efficiency, and issues such as large temperature gradients, localized overheating, or areas remaining at low temperatures, making it difficult to balance safety and energy utilization efficiency.

[0004] Another approach utilizes the battery itself as a heat source, achieving "self-heating" by applying a specific waveform of current in the battery circuit. Existing self-heating topologies often employ a half-bridge or full-bridge structure, directly applying an alternating voltage across the battery terminals to generate Joule heat from the battery's internal resistance. However, these circuits generally suffer from a large DC component in the self-heating current, severe current waveform distortion, and high harmonic content, leading to increased polarization of the battery electrodes, additional losses, and electromagnetic interference. Simultaneously, they place significant voltage and current stress on power devices and conductors. Currently, there is a lack of a battery self-heating topology and its control method that can simultaneously achieve controllable current waveforms, suppressed DC bias, manageable device stress, and ease of engineering implementation under low-temperature conditions. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a self-heating device and control method for lithium-ion batteries. This topology, by introducing a combination of connecting inductance and battery series inductance into the traditional H-bridge structure, and combining it with a control strategy based on analytical modeling and simulation tuning, enables the battery to generate a self-heating current with controllable waveform, adjustable amplitude, and limited DC component under low-temperature conditions. This allows for more comprehensive and accurate control of the battery temperature change over time, improving self-heating efficiency while ensuring battery safety and power device reliability. This invention is applicable to single lithium-ion batteries and power battery modules composed of multiple cells connected in series and parallel, providing a compact and flexible technical solution for the rapid activation and safe operation of electric vehicles, grid-side energy storage systems, etc., in low-temperature environments.

[0006] To achieve the above objectives, the present invention provides the following technical solution: On one hand, the present invention provides a self-heating device for a lithium-ion battery, comprising: an H-bridge commutation circuit composed of four controllable switching elements, a connecting inductor connected between the midpoints of the left and right arms of the H-bridge, a first inductor connected in series with the lithium-ion battery, and a filter capacitor connected in parallel on the DC side of the H-bridge. The positive and negative DC buses of the H-bridge are respectively connected to the positive and negative terminals of the DC power supply or the battery module. The left and right bridge arms are each composed of two controllable switching elements connected in series, and the midpoint of each bridge arm serves as the connection terminal. One end of the connecting inductor is connected to the midpoint of the left bridge arm, and the other end is connected to the midpoint of the right bridge arm. It is used to carry alternating current under different bridge arm conduction combinations. The lithium-ion battery is connected in series with the first inductor and then connected to the DC bus to withstand and generate the self-heating current during the self-heating operation. The filter capacitor is connected across the two ends of the DC bus to stabilize the DC bus voltage and suppress the high-frequency voltage ripple introduced by the self-heating process.

[0007] This device generates an alternating current with a specific frequency and amplitude in the connecting inductor by controlling the on and off of the controllable switching elements in the H-bridge. This alternating current forms an approximately sinusoidal self-heating current in the battery through the first inductor, thereby generating ohmic heat using the battery's internal resistance to achieve battery self-heating.

[0008] Furthermore, the lithium-ion battery is at least one of nickel-cobalt-manganese battery, lithium iron phosphate battery, lithium cobalt oxide battery, lithium nickel oxide battery, lithium manganese oxide battery, and lithium manganese phosphate battery; The capacitor is a ceramic capacitor, an electrolytic capacitor, a thin film capacitor, a mica / paper capacitor, an electrochemical supercapacitor, or a variable capacitor. The first inductor and the connecting inductor are air-core inductors, magnetic core power inductors, chokes, adjustable inductors, or various types of transformers; The controllable switching elements include: power MOSFETs, IGBTs, various thyristors, relays / solid-state relays, or new-generation SiC / GaN devices.

[0009] On the other hand, the present invention provides a control method for a self-heating device of a lithium-ion battery, comprising the following steps: S1: Establish an equivalent circuit model of the lithium-ion battery self-heating device, analyze the spatial operating state of the H-bridge under various switch combinations, and derive the analytical expression of the steady-state current at the battery terminal. S2: Select the parameter ranges of the first inductor, connecting inductor, and filter capacitor based on the analytical expression of the steady-state current, and input the circuit element parameters and control parameters in the equivalent circuit model to obtain the simulation results of the battery terminal current; S3: Determine the target control parameters based on the simulation results, write the target control parameters into the control board, and make the control board output a switch drive signal to control the conduction and cutoff of each controllable switch element in the H-bridge, thereby generating a self-heating current in the battery that meets the preset waveform and amplitude requirements.

[0010] Furthermore, the circuit parameters of the self-heating topology in step S1 include at least one or more of the following: the nominal voltage and capacity of the battery, the inductance value of the first inductor, the inductance value of the connecting inductor, the capacitance value of the filter capacitor, the DC bus voltage, the switching frequency, and the modulation coefficient.

[0011] Furthermore, the establishment of the equivalent circuit model in step S1 includes: taking each controllable switching element in the H-bridge as a switching function, writing the voltage and current differential equations of the connecting inductor, the first inductor, and the battery under different switching combinations, and solving the differential equations using the averaging method or the fundamental equivalent method to obtain the analytical expression of the steady-state current at the battery terminal as a function of the modulation coefficient and the switching frequency.

[0012] Furthermore, the analytical expression for the steady-state current at the battery terminal includes the DC component and the AC component of the battery self-heating current. The analytical expression is solved to obtain the target AC component amplitude and frequency under the condition that the DC component does not exceed a preset limit.

[0013] Furthermore, in step S3, the switch drive signal output by the control board adopts a diagonal pair drive method, where the two controllable switch elements on the same bridge arm are mutually complementary and conduction is performed, and a dead time is set between each conduction and turn-off to avoid bridge arm shoot-through.

[0014] Furthermore, the switch drive signal is a carrier-based pulse width modulation signal, wherein the carrier is a triangular wave or a sawtooth wave with a carrier frequency of 2 kHz to 50 kHz, and the modulation signal is a sine wave or a quasi-sine wave, thereby generating an approximately sinusoidal self-heating current in the connecting inductor.

[0015] Furthermore, step S3 also includes: acquiring the battery terminal current, comparing the acquired actual self-heating current with the target self-heating current calculated according to the steady-state current analytical expression, and obtaining the current deviation; and performing closed-loop adjustment on the modulation coefficient and / or duty cycle of the switch drive signal according to the current deviation, so that the actual self-heating current approaches the target self-heating current.

[0016] Furthermore, step S3 also includes: collecting the battery temperature, starting self-heating when the battery temperature is lower than the preset lower limit temperature, stopping self-heating when the battery temperature reaches the preset upper limit temperature, and setting a temperature hysteresis between the upper limit temperature and the lower limit temperature.

[0017] The lithium-ion battery self-heating device of the present invention can be used for single cells or battery modules. In the application scenario of battery modules, an independent self-heating unit can be set at each module level. By measuring the temperature and status information of different modules respectively, the self-heating power of each module can be independently controlled to achieve zoned preheating and temperature equalization of the battery pack.

[0018] The lithium-ion battery self-heating device and control method of the present invention can be applied to the low-temperature preheating of the power battery system of electric vehicles. Before the cold start of the vehicle, the battery temperature is raised to a suitable working range by short-term self-heating, thereby improving the low-temperature power performance and energy consumption of the vehicle.

[0019] The lithium-ion battery self-heating device and control method of the present invention can be applied to grid-side energy storage systems, backup power supplies for communication base stations, and industrial power supply systems in low-temperature environments, providing a reliable means of battery temperature management for the deployment and operation of the above systems in cold regions.

[0020] The beneficial effects of this invention are as follows: By comprehensively constraining the self-heating current waveform, DC bias, current change rate, and device voltage and current stress, this invention establishes a technical solution that can efficiently and accurately preheat lithium-ion batteries in low-temperature environments. Compared with existing self-heating methods, this invention has a more compact topology, a wider range of adjustable control parameters, and is applicable to a wider variety of battery types. It can provide important support for the structural design and safe operation of power battery systems and has good engineering application value and promotion prospects.

[0021] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the self-heating topology of the lithium-ion battery in this invention; Figure 2 This is a flowchart of the control method for the lithium-ion battery self-heating device of the present invention; Figure 3 This is a schematic diagram of the simulation design in this invention; Figure 4 The diagram shows the simulation results in this invention, where (a) is the steady-state current simulation waveform and (b) is the steady-state current simulation FFT analysis. Figure 5 This is a diagram showing the experimental results of this invention. Detailed Implementation

[0023] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed 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 are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0024] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0025] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0026] Example 1: Lithium-ion batteries have advantages such as high energy density, high power density, long cycle life, and fast charging, making them the mainstream power source for electric vehicles and energy storage systems. However, in low-temperature environments, the internal resistance of lithium-ion batteries increases significantly, usable capacity decreases, charge / discharge rate capability is limited, and even safety hazards such as lithium deposition may occur, severely restricting the range and reliability of electric vehicles in cold regions.

[0027] Common low-temperature preheating methods in existing technologies include external heating elements, coolant circulation heating, and simple self-heating achieved through high-current charging and discharging. These solutions either require additional heating devices, resulting in complex structures and large space requirements, or suffer from low heating efficiency, uneven temperature distribution, or difficulty in precisely controlling the heating current waveform, leading to large DC bias and significant impact on battery aging. Therefore, constructing a battery self-heating topology and control method with adjustable heating power, controllable current waveform, and low DC bias without significantly increasing system complexity and cost has significant engineering application value.

[0028] like Figure 1 As shown, this invention provides a self-heating topology for a lithium-ion battery, comprising an H-bridge consisting of four controllable switching elements, a self-heating connecting inductor, a battery-connected first inductor, and a filter capacitor connected in parallel on the DC side of the H-bridge. The positive and negative DC buses of the H-bridge are respectively connected to the positive and negative terminals of a DC power supply or a battery module. The left and right arms are each composed of two controllable switching elements connected in series, with the midpoint of each arm serving as the connection terminal. One end of the connecting inductor is connected to the midpoint of the left arm, and the other end is connected to the midpoint of the right arm, used to carry alternating current under different arm conduction combinations. The lithium-ion battery is connected in series with the first inductor and then connected to the DC bus, used to withstand and generate the self-heating current during self-heating operation. The filter capacitor is connected across the DC bus to stabilize the DC bus voltage and suppress high-frequency voltage ripple introduced during the self-heating process. By controlling the on and off of the controllable switching elements in the H-bridge, an alternating current with a specific frequency and amplitude is generated in the connecting inductor. This alternating current forms an approximately sinusoidal self-heating current in the battery through the first inductor, thereby generating ohmic heat using the battery's internal resistance to achieve battery self-heating.

[0029] Lithium-ion batteries include at least one of the following: nickel-cobalt-manganese batteries, lithium iron phosphate batteries, lithium cobalt oxide batteries, lithium nickel oxide batteries, lithium manganese oxide batteries, and lithium manganese phosphate batteries.

[0030] The controllable switching elements include power MOSFETs, IGBTs, various thyristors (SCR / TRIAC, etc.), relays / solid-state relays, and new-generation SiC / GaN devices. Different withstand voltage levels and rated current specifications can be selected according to the battery voltage level and self-heating power requirements.

[0031] The inductor can be an air-core inductor, a magnetic core power inductor, a choke, an adjustable inductor, or various transformers. Different withstand voltage ratings and rated current specifications can be selected according to the battery voltage level and self-heating power requirements. The first inductor is used to limit the rise and fall rate of the self-heating current at the battery terminal, reduce voltage spikes and electromagnetic interference caused by current changes, and filter out high-frequency current components. The connecting inductor is used to shape the connecting current waveform, improve the harmonic characteristics of the self-heating current, and together with the first inductor, determine the spectral distribution of the self-heating current.

[0032] Capacitors include: ceramic capacitors, electrolytic (aluminum / tantalum / solid) capacitors, film capacitors, mica / paper capacitors, electrochemical supercapacitors, and variable capacitors. The capacitance value of the filter capacitor is selected according to the allowable voltage ripple of the DC bus, the switching frequency, and the magnitude of the self-heating current. It is used to reduce the dynamic disturbance of the DC bus voltage during the self-heating process and ensure the normal operation of other power-consuming units in the system.

[0033] Example 2: like Figure 2 As shown, this embodiment provides a control method for the topology described in Embodiment 1, including the following steps: 1. By analyzing the spatial operating state of the self-heating topology, an equivalent circuit model including the battery, the first inductor, the connecting inductor, the filter capacitor, and the H-bridge switching function is established. The voltage and current differential equations of the connecting inductor and the battery circuit under different switching combinations are written. Under the assumption of periodic steady state, the above differential equations are averaged or treated with fundamental equivalents to derive the steady-state analytical expression between the self-heating current at the battery end and the modulation coefficient, switching frequency, and inductor and capacitor parameters. 2. Based on the steady-state analytical expression of the battery terminal self-heating current, and combined with the target self-heating power, the allowable DC component limit, and the DC bus voltage ripple limit, the parameter ranges of the first inductor, connecting inductor, and filter capacitor are initially selected; a simulation model of the self-heating topology is established in the circuit simulation platform, and the circuit component parameters and control parameters such as switching frequency, modulation method, and modulation coefficient are input into the simulation model to obtain the simulation results of the battery terminal self-heating current waveform, peak value, current RMS value, and DC component under different parameter combinations; 3. Based on the simulation results, adjust the circuit parameters and control parameters to determine the target control parameters that meet the target self-heating power, limit the DC component, and reduce the voltage and current stress of the devices. Write the target control parameters into the control board. The control board outputs a switch drive signal according to the target control parameters to control the conduction and cutoff of the controllable switching elements in the H-bridge, so that the battery generates a self-heating current that meets the preset amplitude, frequency, and waveform requirements.

[0034] Furthermore, in the equivalent circuit model, the battery can adopt an equivalent internal resistance model or an equivalent circuit model composed of an open-circuit voltage source and a series-parallel RC network. The battery internal resistance and equivalent circuit parameters can be obtained through constant current charge-discharge test and AC impedance test.

[0035] Furthermore, in the self-heating control method, the spatial operating state analysis includes dividing the space into several typical operating intervals. The operating intervals include the charging interval of the connecting inductor, the discharging interval of the connecting inductor, and the commutation interval near the current zero crossing. By solving the voltage and current relationship of each interval piecewise, an analytical expression for the self-heating current that is closer to the actual operating state is obtained.

[0036] Furthermore, the switch drive signal adopts sinusoidal pulse width modulation (SPWM), triangular carrier modulation, or other carrier modulation methods, and the carrier frequency is preferably in the range of 2kHz to 50kHz to balance self-heating efficiency, electromagnetic compatibility performance, and control board computing resources.

[0037] Furthermore, the control board is a digital controller based on DSP, MCU or FPGA. The control board is equipped with a non-volatile storage unit for storing target control parameters and an analog acquisition module for acquiring current, voltage and temperature signals. It can calculate and output the corresponding gate drive signal in real time according to the target control parameters.

[0038] Furthermore, the self-heating control method also includes acquiring the self-heating current at the battery terminal, comparing the acquired actual self-heating current with the target self-heating current determined according to the analytical model or simulation results to obtain the current deviation, and performing closed-loop adjustment of the modulation coefficient and / or duty cycle according to the current deviation to make the amplitude and waveform of the actual self-heating current approach the target self-heating current.

[0039] Furthermore, the self-heating control method also includes collecting the battery temperature, starting self-heating when the battery temperature is lower than a preset lower limit temperature, and stopping self-heating when the battery temperature reaches a preset upper limit temperature. A temperature hysteresis is set between the upper limit temperature and the lower limit temperature to avoid control oscillations caused by frequent start-stop cycles.

[0040] Furthermore, the self-heating circuit can be used for single cells or battery modules. In battery module application scenarios, an independent self-heating unit can be set at each module level. By measuring the temperature and status information of different modules, the self-heating power of each module can be independently controlled to achieve zoned preheating and temperature equalization of the battery pack.

[0041] Furthermore, the lithium-ion battery self-heating circuit and self-heating control method described in this invention can be applied to the low-temperature preheating of the power battery system of electric vehicles. Before the cold start of the vehicle, the battery temperature is raised to a suitable working range through short-term self-heating, thereby improving the low-temperature power performance and energy consumption of the vehicle.

[0042] Furthermore, the lithium-ion battery self-heating circuit and self-heating control method described in this invention can be applied to grid-side energy storage systems, backup power supplies for communication base stations, and industrial power supply systems in low-temperature environments, providing reliable battery temperature management methods for the deployment and operation of these systems in cold regions.

[0043] Example 3: This embodiment provides specific operating steps for a lithium-ion battery self-heating device control method, including: Step 101: Analyze the spatial operating state of the topology to derive the expression for the steady-state current at the battery terminal.

[0044] Based on the circuit topology described in Example 1, the spatial operating states of the circuit are divided according to the on and off combinations of each switch in the H-bridge. The current flow path, voltage application direction, and charging and discharging relationship of inductors and capacitors are analyzed under different switching states, and corresponding equivalent circuits are established.

[0045] According to the switching formula, we have:

[0046]

[0047] Taking the Fourier transform of the switching function, we have:

[0048] in, For SPWM duty cycle, ; This is the SPWM switching angular frequency.

[0049] When the SPWM switching angular frequency is much higher than the load frequency, it can be ignored. The harmonic terms, thus having At this time there is

[0050]

[0051] Since the load-side voltage loop equation is:

[0052] Under ideal conditions:

[0053] in , The phase angle of the modulated wave is given, and the modulated waves of the left and right bridge arms are mutually different. ; It is the modulation ratio (the ratio of the modulation amplitude to the carrier amplitude).

[0054] Therefore, we obtain the following formula:

[0055] make , In order to be in SPWM fundamental voltage output under control law The amplitude of is then expressed by the following formula:

[0056] Let its steady-state solution be Then its steady-state equation can be expressed as:

[0057] After unfolding, you get

[0058] Therefore we have:

[0059] Solving for:

[0060] Let the complete solution be A is an undetermined coefficient. The time constant of the transient component and , initial conditions Substituting into the above equation, we have Therefore, we can obtain:

[0061] Therefore, there is

[0062] The first part is The steady-state component is expressed as The latter part is the transient component. Since the time constant is very small, the transient component can be ignored to simplify the analysis, thus we have

[0063] The battery terminal voltage can be approximately expressed as the open circuit voltage OCV and The sum of, where the current The resistance changes over time. It is only related to temperature. This relationship is expressed as follows:

[0064] Furthermore, according to Kirchhoff's voltage law, we have:

[0065] Bring into We have the following expressions:

[0066] According to Kirchhoff's voltage law, we have:

[0067] Therefore, we obtain:

[0068] Transform the above expression into the following form:

[0069] in:

[0070]

[0071] In steady state, i is a periodic function, which can be Fourier transformed into the following form:

[0072] Since higher-order terms are filtered by capacitors, we take n=2. Lower-order terms are also filtered, so we take an approximate solution as follows:

[0073] After substituting, we get

[0074] Therefore, we obtain the following relationship:

[0075] Solving

[0076] in This represents the DC offset of the steady-state current at the battery terminals. This represents the amplitude of the AC component of the steady-state current at the battery terminal. . Step 102: Establish a circuit simulation model of the self-heating topology, input the relevant circuit component parameters and control parameters into the model to obtain simulation values. The circuit parameters are shown in Table 1.

[0077] Table 1

[0078] Based on the steady-state current analytical relationship obtained in step 101, a circuit simulation model is established according to the self-heating topology. The first inductor, connection inductor, filter capacitor, and battery equivalent parameters are input into the simulation model. The simulation model is shown below. Figure 3 The experimental battery parameters are shown in Table 2. Control parameters such as duty cycle, modulation frequency, and dead time were set, and the simulation program was run to obtain the simulation results of the battery terminal current. Figure 4 As shown in (a) and (b), the simulation values ​​provide a direct way to evaluate the current waveform, DC bias, and heating effect under different parameter combinations.

[0079] Table 2

[0080] Step 103: Adjust the actual control parameters accordingly using the obtained simulation values ​​and input them into the control board; Based on the simulation values ​​obtained in step 102, the control parameters such as modulation ratio and modulation frequency are adjusted accordingly according to the differences. The simulation is repeated until the preset safety and heating performance requirements are met, thereby determining a set of target control parameters. The target control parameters are written into the control program of the control board as the control configuration for subsequent actual operation.

[0081] Step 104: The control board controls the switching elements in the self-heating topology to turn on and off according to the set control parameters; After the target control parameters are written, the control board generates switching drive signals in real time according to the preset modulation method and control parameters. This controls the on / off state of each switching element in the H-bridge, causing the self-heating topology to switch between different spatial operating states according to a predetermined pattern. This generates a self-heating current in the battery that meets the preset waveform and amplitude requirements, achieving low-temperature heating of the lithium-ion battery. Experimental results are shown in [Figure number missing]. Figure 5 .

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A self-heating device for lithium-ion batteries, characterized in that: include: The circuit consists of an H-bridge converter circuit composed of four controllable switching elements, a connecting inductor connected between the midpoints of the left and right arms of the H-bridge, a first inductor connected in series with the lithium-ion battery, and a filter capacitor connected in parallel on the DC side of the H-bridge. The positive and negative DC buses of the H-bridge are respectively connected to the positive and negative terminals of the DC power supply or the battery module. The left and right bridge arms are each composed of two controllable switching elements connected in series, and the midpoint of each bridge arm serves as the connection terminal. One end of the connecting inductor is connected to the midpoint of the left bridge arm, and the other end is connected to the midpoint of the right bridge arm. It is used to carry alternating current under different bridge arm conduction combinations. The lithium-ion battery is connected in series with the first inductor and then connected to the DC bus to withstand and generate the self-heating current during the self-heating operation. The filter capacitor is connected across the two ends of the DC bus to stabilize the DC bus voltage and suppress the high-frequency voltage ripple introduced by the self-heating process.

2. The self-heating device for lithium-ion batteries according to claim 1, characterized in that: The lithium-ion battery is at least one of nickel-cobalt-manganese battery, lithium iron phosphate battery, lithium cobalt oxide battery, lithium nickel oxide battery, lithium manganese oxide battery, and lithium manganese phosphate battery. The capacitor is a ceramic capacitor, an electrolytic capacitor, a thin film capacitor, a mica / paper capacitor, an electrochemical supercapacitor, or a variable capacitor. The first inductor and the connecting inductor are air-core inductors, magnetic core power inductors, chokes, adjustable inductors, or various types of transformers; The controllable switching elements include: power MOSFETs, IGBTs, various thyristors, relays / solid-state relays, or new-generation SiC / GaN devices.

3. A control method for a self-heating device of a lithium-ion battery, characterized in that: Includes the following steps: S1: Establish an equivalent circuit model of the lithium-ion battery self-heating device, analyze the spatial operating state of the H-bridge under various switch combinations, and derive the analytical expression of the steady-state current at the battery terminal. S2: Select the parameter ranges of the first inductor, connecting inductor, and filter capacitor based on the analytical expression of the steady-state current, and input the circuit element parameters and control parameters in the equivalent circuit model to obtain the simulation results of the battery terminal current; S3: Determine the target control parameters based on the simulation results, write the target control parameters into the control board, and make the control board output a switch drive signal to control the conduction and cutoff of each controllable switch element in the H-bridge, thereby generating a self-heating current in the battery that meets the preset waveform and amplitude requirements.

4. The control method for the self-heating device of a lithium-ion battery according to claim 3, characterized in that: The circuit parameters of the self-heating topology described in step S1 include at least one or more of the following: the nominal voltage and capacity of the battery, the inductance value of the first inductor, the inductance value of the connecting inductor, the capacitance value of the filter capacitor, the DC bus voltage, the switching frequency, and the modulation coefficient.

5. The control method for the self-heating device of a lithium-ion battery according to claim 3, characterized in that: The establishment of the equivalent circuit model in step S1 includes: taking each controllable switching element in the H-bridge as the switching function, writing the voltage and current differential equations of the connecting inductor, the first inductor and the battery under different switching combinations, and solving the differential equations by using the averaging method or the fundamental equivalent method to obtain the analytical expression of the steady-state current of the battery terminal as a function of the modulation coefficient and the switching frequency.

6. The control method for the self-heating device of a lithium-ion battery according to claim 3, characterized in that: The analytical expression for the steady-state current at the battery terminal includes the DC component and the AC component of the battery self-heating current. The analytical expression is solved to obtain the target AC component amplitude and frequency under the condition that the DC component does not exceed the preset limit.

7. The control method for the self-heating device of a lithium-ion battery according to claim 3, characterized in that: The switch drive signal output by the control board in step S3 adopts a diagonal pair drive method, in which the two controllable switch elements on the same bridge arm are mutually complementary and conduction is performed, and a dead time is set between each conduction and turn-off to avoid bridge arm shoot-through.

8. The control method for the self-heating device of a lithium-ion battery according to claim 3, characterized in that: The switch drive signal is a carrier-based pulse width modulation signal. The carrier is a triangular wave or a sawtooth wave with a carrier frequency of 2 kHz to 50 kHz. The modulation signal is a sine wave or a quasi-sine wave, thereby generating an approximately sinusoidal self-heating current in the connecting inductor.

9. The control method for the self-heating device of a lithium-ion battery according to claim 3, characterized in that: Step S3 further includes: acquiring the battery terminal current, comparing the acquired actual self-heating current with the target self-heating current calculated according to the analytical expression of the steady-state current, and obtaining the current deviation; and performing closed-loop adjustment of the modulation coefficient and / or duty cycle of the switch drive signal according to the current deviation, so that the actual self-heating current approaches the target self-heating current.

10. The control method for the self-heating device of a lithium-ion battery according to claim 3, characterized in that: Step S3 further includes: collecting battery temperature, starting self-heating when the battery temperature is lower than the preset lower limit temperature, stopping self-heating when the battery temperature reaches the preset upper limit temperature, and setting a temperature hysteresis between the upper limit temperature and the lower limit temperature.

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