A multi-mode resonant converter for electric vehicle power battery and control method thereof

Abstract

The present invention provides a multi-mode resonant converter for electric vehicle power batteries and a control method thereof, relating to the field of optimized control of automotive power batteries. The converter includes a battery-side full-bridge unit, a resonant circuit, a high-frequency transformer, and a DC-side full-bridge unit; the battery-side full-bridge unit converts the input voltage of the battery into a high-frequency square wave, which flows through the resonant circuit and the high-frequency transformer into the DC-side full-bridge unit, outputting a DC voltage; the resonant circuit can adaptively switch between LLC operating mode and LLCC operating mode; the resonant circuit and the battery can form an LC loop through a predetermined switching tube, and controllable heat is generated by the ohmic effect of the battery's internal resistance. The present invention integrates the resonant circuit with the battery thermal management function, forms a closed loop with the resonant network and the battery through switch control, and directly utilizes the ohmic effect of the battery's internal resistance to achieve internal heating. No external heating device is required, and energy transmission and battery preheating are simultaneously completed in a low-temperature environment.

Description

Technical Field

[0001] The present invention relates to the field of optimized control of automotive power batteries, and in particular to a multi-mode resonant converter for an electric vehicle power battery and a control method thereof. Background Art

[0002] Lithium-ion batteries are an important energy storage technology currently used in a variety of portable electronic devices and electric vehicles. However, lithium-ion batteries face several challenges in low-temperature environments, which poses certain problems for the operation and use of electric vehicles in cold climates. Lithium-ion batteries face multiple performance challenges in low-temperature conditions. First, the battery's charge and discharge rates are limited, resulting in a decrease in the battery's energy storage and release capabilities, and thus a reduction in battery capacity, making it unable to meet the normal operating requirements of the device or vehicle. Second, because the movement of lithium ions between the electrolyte and electrodes slows at low temperatures, the chemical reaction activity within the battery decreases, resulting in increased resistance and internal resistance, which affects battery performance. Finally, the performance of lithium-ion batteries in low-temperature environments may become unstable, with irregular discharge curves and uneven energy output. These issues collectively lead to reduced performance of lithium-ion batteries in low-temperature environments, posing challenges for applications such as electric vehicles. Summary of the Invention

[0003] Purpose of the invention: In order to solve the above problems, the present invention proposes a multi-mode resonant converter for electric vehicle power batteries and its control method. The converter has two functions: integrated internal heating and bidirectional power transmission. For higher voltage gain requirements, the resonant network is configured as LLC working mode. For lower voltage gain, the switch S can be dynamically controlled to a , configuring the resonant network to operate in LLCC mode. Furthermore, a heating control circuit is placed within the loop. The switching devices and additional power devices within this heating control circuit, combined with the capacitive elements and winding inductance that are turned on and off, form an LC oscillating circuit to generate a high-frequency alternating current. This high-frequency alternating current continuously flows through the lithium-ion battery, thereby heating it. Simultaneously, the heating circuit allows current to circulate between the battery's internal resistance and the resonant network. This current circulation generates power loss through the battery's internal resistance, effectively heating the battery. Based on this, a multi-objective particle swarm optimization algorithm is used to dynamically adjust the heating parameters. The optimization algorithm establishes a multi-objective function that includes energy efficiency and heating time. Using this algorithm, the algorithm determines the optimal heating current for each 1°C temperature rise, achieving a balance between rapid preheating and performance recovery.

[0004] In a first aspect of the present invention, a multi-mode resonant converter for an electric vehicle power battery is proposed, comprising a battery-side full-bridge unit, a switchable resonant circuit, a high-frequency transformer, and a DC-side full-bridge unit.

[0005] The battery of the electric vehicle is connected to the battery-side full-bridge unit, which converts the battery input voltage into a high-frequency square wave. The square wave flows through the switchable resonant circuit and the high-frequency transformer into the DC-side full-bridge unit to output a DC voltage.

[0006] The switchable resonant circuit is connected to the switch tube S a Adaptive switching between LLC working mode and LLCC working mode, LLC resonance is used when the voltage gain is high, and LLC resonance is converted when the voltage gain is low; H The switchable resonant circuit and the battery form an LC loop, and the ohmic effect of the internal resistance of the battery is used to generate controllable heat.

[0007] In a further embodiment of the first aspect, the battery side full-bridge unit is an H-bridge inverter, whose input end is connected to the battery and is used to convert the input voltage of the battery into a high-frequency square wave; the battery side full-bridge unit includes switch tubes S1, S2, S3, and S4, each of which is connected in parallel with a diode D S1 、D S2 、D S3 、D S4 ; The switch tube S1 and the switch tube S4 form a pair of bridge arms, and the switch tube S2 and the switch tube S3 form another pair of bridge arms, which are alternately turned on; the output end of the battery side full-bridge unit is connected to the switchable resonant circuit.

[0008] In a further embodiment of the first aspect, the switchable resonant circuit includes a resonant inductor L r , resonant capacitor C r , bypass capacitor C s , excitation inductance L m , switch tube S H , switch tube S a ;Resonant inductor L r and the resonant capacitor C r The main resonant path is formed in series, connecting the output end of the battery side full bridge and the primary winding of the high-frequency transformer; the switch tube S a With the resonant inductor L r Series, used to switch resonant mode; bypass capacitor C s Set on the resonant path, used to adjust the resonant frequency; the switch tube S H The switchable resonant circuit and the battery form an LC loop; the excitation inductor L m is the equivalent parallel inductance of the high-frequency transformer, which participates in resonance.

[0009] In a further embodiment of the first aspect, the primary winding of the high-frequency transformer is connected to the output end of the switchable resonant circuit; the secondary winding of the high-frequency transformer is connected to the input end of the DC side full-bridge unit; and the transformation ratio of the high-frequency transformer is 1:N.

[0010] In a further embodiment of the first aspect, the DC side full-bridge unit is a synchronous rectifier H-bridge, the input end of the synchronous rectifier H-bridge is connected to the secondary winding of the high-frequency transformer, the output end of the synchronous rectifier H-bridge outputs a DC voltage V0, and the high-frequency ripple is filtered out by the filter capacitor C0; the synchronous rectifier H-bridge includes switch tubes S5, S6, S7, and S8, and each switch tube is connected in parallel with a diode D S5 、D S6 、D S7 、D S8 ; The switch tube S5 and the switch tube S8 form a pair of bridge arms, and the switch tube S6 and the switch tube S7 form another pair of bridge arms.

[0011] In a further embodiment of the first aspect, when the switch tube S H When turned on, the battery heating mode is entered, and the battery heating mode is divided into mode 1 and mode 2 according to the time period;

[0012] The period from t0 to t2 is mode 1. At this time, the battery, switches S1 and S3, and the resonant capacitor C r , resonant inductor L r , switch tube S H A circuit is formed; at time t0, switches S1 and S3 are turned on to achieve ZVS; from t0 to t1, the battery is discharged into the resonant circuit; from t1 to t2, the energy stored in the resonant circuit is dissipated through its internal impedance to charge the battery;

[0013] The period from t2 to t4 is mode 2. At this time, the battery, switches S2, S4, and resonant capacitor C r , resonant inductor L r , switch tube S H A circuit is formed; at time t2, the switches S2 and S4 are turned on to achieve ZCS; during the period from t2 to t3, the battery is charged through the resonant circuit; during the period from t3 to t4, the battery is discharged.

[0014] In a further embodiment of the first aspect, the circuit equation of mode one is as follows:

[0015]

[0016] The circuit equation for mode 2 is as follows:

[0017]

[0018] Where, is the net equivalent resistance value; is the internal resistance of the battery; is the on-resistance value of the switch tube; is the resonant circuit loss component, where is the inductance L r The resistance value, is the capacitance C r resistance value; is the open circuit voltage of the battery; is the capacitance C r voltage; is the inductance L r of current.

[0019] In a further embodiment of the first aspect, the heating current The expression is as follows:

[0020]

[0021] Where, Indicates the duration of the switching cycle.

[0022] In a further embodiment of the first aspect, the ohmic effect of the internal resistance of the battery is used to generate controllable heat, satisfying the following relationship:

[0023]

[0024] Where m is the battery mass, c is the battery specific heat capacity, S is the battery surface area, is the ambient temperature, is the battery temperature, h is the equivalent heat transfer coefficient, is the heat generated in the battery due to ohmic losses.

[0025] Based on the multi-mode resonant converter disclosed in the first aspect and further embodiments thereof, the second aspect of the present invention discloses a control method for the multi-mode resonant converter, and the specific steps are as follows:

[0026] Step 1: Obtain the battery initial temperature and state of charge (SOC) and their corresponding battery internal resistance;

[0027] Step 2: Set the battery temperature range, i.e. the initial battery temperature and the target battery temperature. Each 1°C rise in battery temperature is recorded as a stage.

[0028] Step 3: Determine the heating current range corresponding to the jth stage ;

[0029] Step 4: In the heating current range Within the range, take a current value every ΔI and calculate the energy efficiency corresponding to different heating currents. , heating time t and power consumption ΔSOC;

[0030] Step 5: The energy efficiency corresponding to different heating currents in the jth stage and heating time t for normalization;

[0031] Step 6: Set the objective function ,in is the weighting factor, is the normalized energy efficiency, is the normalized heating time; find the objective function value corresponding to different heating current values in the jth stage;

[0032] Step 7: Establish a multi-objective particle swarm optimization algorithm based on the objective function value calculated in step 6;

[0033] Step 8: Use the multi-objective particle swarm optimization algorithm to solve the optimal heating current for each 1°C temperature rise stage and form the optimal heating current sequence; calculate the switching tube S with the optimal heating current sequence. H The switching frequency heats the battery and produces controllable heat in line with the desired level.

[0034] In a further embodiment of the second aspect, the minimum value of the heating current in step three is satisfy:

[0035] ;

[0036] Maximum heating current This is the maximum discharge current specified by the battery factory.

[0037] In a further embodiment of the second aspect, the calculation formula for the heating time t in step 4 is as follows:

[0038]

[0039] Where, is the heating current, is the internal resistance of the battery, h is the equivalent heat transfer coefficient, S is the surface area of the battery, is the ambient temperature, is the battery temperature, is the heat generated in the battery due to ohmic loss, is the heat dissipation power between the battery and the external environment; ΔT is the temperature change of the battery in a stage.

[0040] In a further embodiment of the second aspect, the energy efficiency in step 4 The calculation formula is as follows:

[0041]

[0042] Where, 、 represent the initial SOC and final SOC respectively; 、 Represent the ambient temperature and the final temperature of the battery respectively; is the energy storage function, which is used to describe the relationship between the total stored energy and the temperature T:

[0043] .

[0044] In a further embodiment of the second aspect, the calculation formula for the power consumption ΔSOC in step 4 is as follows:

[0045]

[0046] Where Cap is the rated capacity of the battery; is the heating current of the jth stage; is the heating time of the jth stage; N is the total number of heating stages.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] (1) The multi-mode resonant converter proposed in this paper integrates internal heating and bidirectional power transmission. By dynamically switching between LLC and LLCC resonant network structures, it can flexibly respond to different voltage gain requirements. Combining zero voltage switching (ZVS) and zero current switching (ZCS) technologies, it effectively reduces switching losses and achieves efficient bidirectional power transmission. The coordinated control of the battery-side and DC-side full-bridge units supports the bidirectional flow of energy between the energy storage system and the external circuit, meeting the energy interaction requirements under complex operating conditions.

[0049] (2) The resonant circuit is integrated with the battery thermal management function. Through switch control, the resonant network and the battery form a closed loop circuit, and the ohmic effect of the battery's internal resistance is directly used to achieve internal heating. The two-stage cycle heating mode is combined with the ZVS / ZCS switching mechanism to achieve autonomous energy circulation between the battery and the resonant network. No external heating device is required, and energy transmission and battery preheating are completed simultaneously in low-temperature environments.

[0050] (3) The control method for a multi-mode resonant converter proposed in this invention optimizes battery heating based on a multi-objective particle swarm optimization algorithm, establishing a collaborative optimization model that includes heating rate and energy efficiency. Through a normalized objective function and an adaptive constraint strategy, a balance between rapid preheating and performance recovery is achieved while ensuring battery safety, significantly improving the overall system performance under extreme temperature conditions. This method is suitable for applications such as new energy vehicles that have strict thermal management requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 14 is a topology diagram of a multi-mode resonant converter in an embodiment.

[0052] Figure 2 FIG. 4 is a flow chart of a control method for a multi-mode resonant converter in an embodiment.

[0053] Figure 3 is the equivalent circuit of the converter during the interval from t0 to t1 in the embodiment.

[0054] Figure 4 is the equivalent circuit of the converter during the interval from t1 to t2 in the embodiment.

[0055] Figure 5 Schematic diagram of the heating mode at time t0~t2 in the embodiment.

[0056] Figure 6 Schematic diagram of the heating mode at time t2 to t4 in the embodiment. DETAILED DESCRIPTION

[0057] In the following description, numerous specific details are provided to provide a more thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without one or more of these details. In other instances, certain technical features well known in the art have not been described to avoid confusion with the present invention.

[0058] This embodiment discloses a multi-mode resonant converter for electric vehicle power batteries, such as Figure 1 As shown in the figure, the converter has two functions: integrated internal heating and bidirectional power transmission. It adopts a composite resonant network structure, including a battery-side full-bridge unit, an LLC / LLCC switchable resonant circuit, a high-frequency transformer, and a DC-side full-bridge unit. Adaptive switching between LLC and LLCC operating modes is achieved through dynamic control of the switch: LLC resonance is used at high voltage gain, and LLCC resonance is converted at low voltage gain. Zero voltage / current switching technology is also used to reduce losses. The heating function module is innovatively integrated, and the switching S is controlled by the switch S. H The resonant network and the battery form an LC loop, leveraging the ohmic effect of the battery's internal resistance to generate controllable heat. A dual-stage cyclic heating mode was designed, employing ZVS / ZCS switching technology to achieve bidirectional energy circulation between the battery and the resonant network. A multi-objective particle swarm optimization algorithm was used to dynamically adjust heating parameters. The optimization algorithm established a multi-objective function encompassing energy efficiency and heating time, employing a multi-objective particle swarm optimization algorithm to determine the optimal heating current for each 1°C temperature rise, achieving a balance between rapid preheating and performance recovery.

[0059] Circuit Configuration of Power Transfer Mode The proposed bidirectional multi-resonant converter in power transfer mode consists of battery side full-bridge units (S1-S4), resonant network, high-frequency transformer and DC side full-bridge units (S5-S8). The resonant circuit consists of series resonant capacitor C r , resonant inductor L r and the magnetizing inductance L m In addition, the S a , C P Through the series resonant inductor L r The connection forms an LLCC resonant network. At the same time, the operating mode is controlled according to the change of input voltage.

[0060] See Figure 3 In the first subinterval, from t0 to t1, switches S1 and S3 are turned on. The resonant current lags behind the switch voltage, allowing the switch to turn on at zero voltage. At the same time, the primary resonant circuit components resonate, transferring energy from the battery side to the DC link side. At time t1, the excitation current i lm =Equal to the resonant current, the secondary current is reduced to zero. Therefore, the secondary side switches S5 and S8 can be turned off by zero current switching (ZCS). At time t1, switches S1 and S3 are turned off. The resonant current discharges the drain-source capacitance of switches S2 and S4 to zero, and the drain-source capacitance of switches S1 and S3 is charged to V b .

[0061] See Figure 4 During the period from t1 to t2, the voltage drop across S2 and S4 is zero due to the forward bias of the switch body diodes. Therefore, switches S2 and S4 achieve zero voltage switching (ZVS), and body diodes DS6 and DS7 conduct. Simultaneously, the resonant circuit resonates, transferring energy from the battery to the DC link.

[0062] Battery heating mode circuit configuration Battery heating topology in the switch tube S H When turned on, a series LC resonant network is combined with an H-bridge network.

[0063] See Figure 5 , Mode 1 [t0~t2]: Among them, the battery, MOSFET switch tubes S1, S3, capacitor C r 、Inductor L r , switch tube S HA circuit is formed. At time t0, switches S1 and S3 are turned on under ZCS conditions. During the period t0 to t1, the battery discharges into the resonant circuit. During the interval t1 to t2, the energy stored in the resonant network is dissipated through its internal impedance, charging the battery. The heating circuit allows current to circulate between the battery's internal resistance and the resonant network. This current generates power loss (heat) through the battery's internal resistance. In this mode, the losses in switches S1 and S3 are reduced due to ZVS shutdown.

[0064] See Figure 6 , Mode 2 [t2~t4]: Among them, the battery, MOSFET switch tubes S2, S4, capacitor C r 、Inductor L r , switch tube S H The circuit is formed. Switches S2 and S4 are turned on at ZCS at time t2. From t2 to t3, the battery is charged by current through the resonant circuit. During t3-t4, the battery is discharged. This phenomenon contributes to the generation of heat within the entire battery. In addition, the switch tube achieves ZVS shutdown, reducing switching losses. Therefore, this topology allows energy to be transferred between the battery and the resonant network, providing internal heat for the battery. By selecting appropriate resonant network components and switching frequency f sw The heating rate can be adjusted.

[0065] The circuit equation for mode 1 is as follows:

[0066]

[0067] The circuit equation for mode 2 is as follows:

[0068]

[0069] in, is the net equivalent resistance value; is the internal resistance of the battery; is the on-resistance value of the switch tube; is the resonant circuit loss component, where is the inductance L r The resistance value, is the capacitance C r resistance value; is the open circuit voltage of the battery; is the capacitance C r voltage; is the inductance L r of current.

[0070] Derivation of heating current The expression:

[0071]

[0072] The heat generated inside the battery depends mainly on the ohmic losses in the battery's internal resistance, with some heat generated due to electrochemical heating at the AC frequency.

[0073]

[0074] is the heat generated by ohmic loss in the battery, m is the battery mass, c is the battery specific heat capacity, S is the battery surface area, is the ambient temperature, is the battery temperature, and h is the equivalent heat transfer coefficient.

[0075] The main goal of the proposed multi-objective particle swarm optimization heating is to achieve the preheating of the lithium battery in the shortest possible time and to quickly improve and restore its various performances to a certain extent. The overall flow chart is shown in Figure 2 , the specific steps are as follows:

[0076] Step 1: Obtain the battery's initial temperature and state of charge (SOC) and their corresponding battery internal resistance, and then proceed to step 2.

[0077] Step 2: Set the battery temperature range, i.e. the initial battery temperature and the target battery temperature. Each 1°C rise in battery temperature is considered a stage, and then proceed to step 3.

[0078] Step 3: Determine the heating current range corresponding to the jth stage , execute step 4;

[0079] Step 4: In the heating current range corresponding to the jth stage, take a current value every ΔI and calculate the energy efficiency corresponding to different heating currents. , heating time t and power consumption ΔSOC, proceed to step five;

[0080] Step 5: The energy efficiency corresponding to different heating currents in the jth stage Normalize the heating time t so that the optimization objective function contains two variables and execute step 6;

[0081] Among them, the conversion method is expressed as:

[0082]

[0083] is the maximum value of the sample data, is the minimum value of the sample data. The sample data referred to here is the objective function value obtained when the battery is heated with different discharge currents in the jth stage.

[0084] Step 6: Set the objective function , find the objective function value corresponding to different heating current values in the jth stage, and execute step 7;

[0085] Step 7: Based on the results of step 6, a multi-objective particle swarm optimization algorithm is established:

[0086] 1) First, initialize the parameters: set the current values according to the actual object, the dimension is one-dimensional, the dimension is represented by m, set the current population size n, and its acceleration constants c1 and c2, etc.

[0087] 2) Then the population is initialized: Initializing the population means generating a random matrix, including the initial position x(i) and velocity v(i) of the current particle, and calculating the fitness of each current value particle. Let For the optimal position of the individual, compare the fitness of each particle and determine the optimal position of the population .

[0088] 3) Fixed inertia weight setting ω=0.5.

[0089] 4) Update particle velocity:

[0090]

[0091] in, is the velocity of particle i at time step t, is the new velocity of particle i at time step t+1, ω is the inertia weight, 、 is the acceleration constant, 、 is a random number uniformly distributed in [0,1] generated at time step t, is the historical optimal position of particle i at time step t, is the global optimal position of the group at time step t, is the current position of particle i at time step t.

[0092] 5) Update particle position:

[0093]

[0094] Constraint function:

[0095]

[0096] in, is the new position of particle i at time t+1, To constrain the function, limit x to the interval [a, b].

[0097] 6) Evaluate each particle.

[0098] 7) Finally, check whether the optimization end condition is met. If it is met, the optimization ends. Otherwise, set t = t + 1 and go to step 4) to continue the optimization until the end condition is met.

[0099] Step 8: After the battery heating experiment is completed, the optimized current and heating time in each stage are obtained, and then the optimal discharge heating current in each stage of the heating process is obtained.

[0100] As a preference, the initial value of j in step 3 is 1, and the specific method for determining the heating current range corresponding to the j-th battery temperature is: the minimum value of the heating current satisfy ; Maximum value of heating current The maximum discharge current specified by the battery factory; is the heating current, is the internal resistance of the battery, h is the equivalent heat transfer coefficient, S is the surface area of the battery, is the ambient temperature, is the battery temperature, is the heat generated in the battery due to ohmic loss, It is the heat dissipation power between the battery and the external environment.

[0101] Preferably, the polynomial formula between the total stored energy and the temperature is:

[0102]

[0103] Energy efficiency The calculation formula is:

[0104]

[0105] in, 、 represent the initial SOC and final SOC respectively; 、 They represent the initial temperature (i.e., ambient temperature) and final temperature of the battery, respectively.

[0106] The calculation formula for heating time t is:

[0107]

[0108] ΔT is the temperature change of the battery in one stage. In the present invention, ΔT=1.

[0109] The method for calculating the SOC consumption in stage i is:

[0110]

[0111] Cap is the rated capacity of the battery; is the heating current of the jth stage; is the heating time of the jth stage; N is the total number of heating stages.

[0112] The heating current has a monotonic relationship with the switching frequency, so the switching frequency is selected as the control input. The corresponding frequency is calculated based on the obtained optimal current sequence, thereby realizing the optimal heating strategy of the heater.

[0113] The technical process of the control method of the multi-mode resonant converter disclosed in the above embodiments can be implemented in whole or in part through software, hardware, firmware or any other combination.

[0114] When implemented using hardware, the above embodiments can be run on an electronic device by compiling all or part of the operating logic and computational processes into software. The electronic device includes a processor, a memory, a communication interface, and a communication bus. The processor, memory, and communication interface communicate with each other via the communication bus. The memory is used to store at least one executable instruction that causes the processor to execute the technical process of the multi-mode resonant converter control method disclosed in the above embodiments.

[0115] When implemented using software, the above embodiments can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions or computer programs. If the above method is implemented in the form of a software function module and sold or used as an independent product, it can also be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the embodiment of the present application can be embodied in the form of a software product, which is essentially or contributes to the relevant technology. The software product is stored in a storage medium and includes several instructions for enabling an electronic device (which can be a personal computer, server, or network device, etc.) to execute all or part of the methods described in each embodiment of the present application. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a magnetic disk, or an optical disk. In this way, the embodiments of the present application are not limited to any specific hardware, software, or firmware, or any combination of hardware, software, and firmware.

[0116] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A control method for a multi-mode resonant converter for an electric vehicle power battery, characterized in that: The converter includes: a battery-side full-bridge unit, a switchable resonant circuit, a high-frequency transformer, and a DC-side full-bridge unit; Connecting the battery of the electric vehicle to the battery-side full-bridge unit, the battery-side full-bridge unit converts the input voltage of the battery into a high-frequency square wave, which flows through the switchable resonant circuit and the high-frequency transformer into the DC-side full-bridge unit to output a DC voltage; The switchable resonant circuit is connected to the switch tube S a Adaptive switching between LLC and LLCC operating modes: LLC resonance is used at high voltage gain, while LLC resonance is used at low voltage gain. Through the switch tube S H The switchable resonant circuit and the battery form an LC loop, and the ohmic effect of the internal resistance of the battery is used to generate controllable heat; When the switch tube S H When turned on, the battery heating mode is entered, and the battery heating mode is divided into mode 1 and mode 2 according to the time period; The period from t0 to t2 is mode 1. At this time, the battery, switches S1 and S3, and the resonant capacitor C r , resonant inductor L r , switch tube S H A circuit is formed; at time t0, switches S1 and S3 are turned on to achieve ZVS; from t0 to t1, the battery is discharged into the resonant circuit; from t1 to t2, the energy stored in the resonant circuit is dissipated through its internal impedance to charge the battery; The period from t2 to t4 is mode 2. At this time, the battery, switches S2, S4, and resonant capacitor C r , resonant inductor L r , switch tube S H A circuit is formed; at time t2, switches S2 and S4 are turned on to achieve ZCS; from t2 to t3, the battery is charged through the resonant circuit; from t3 to t4, the battery is discharged; The control method includes: Step 1: Obtain the battery initial temperature and state of charge (SOC) and their corresponding battery internal resistance; Step 2: Set the battery temperature range, i.e. the initial battery temperature and the target battery temperature. Each 1°C rise in battery temperature is recorded as a stage. Step 3: Determine the heating current range corresponding to the jth stage ; Step 4: In the heating current range Within the range, take a current value every ΔI and calculate the energy efficiency corresponding to different heating currents. , heating time t and power consumption ΔSOC; the energy efficiency The calculation formula is as follows: Where, 、 represent the initial SOC and final SOC respectively; 、 Represent the ambient temperature and the final temperature of the battery respectively; is the energy storage function, which is used to describe the relationship between the total stored energy and temperature; Step 5: The energy efficiency corresponding to different heating currents in the jth stage and heating time t for normalization; Step 6: Set the objective function ,in is the weighting factor, is the normalized energy efficiency, is the normalized heating time; find the objective function value corresponding to different heating current values in the jth stage; Step 7: Establish a multi-objective particle swarm optimization algorithm based on the objective function value calculated in step 6; Step 8: Use the multi-objective particle swarm optimization algorithm to solve the optimal heating current for each 1°C temperature rise stage and form the optimal heating current sequence; calculate the switching tube S with the optimal heating current sequence. H The switching frequency heats the battery and produces controllable heat in line with the desired level.

2. The control method of a multi-mode resonant converter for an electric vehicle power battery according to claim 1, characterized in that: The battery-side full-bridge unit is an H-bridge inverter, whose input end is connected to the battery and is used to convert the battery input voltage into a high-frequency square wave; The battery side full bridge unit includes switch tubes S1, S2, S3, and S4, each of which is connected in parallel with a diode D S1 、D S2 、D S3 、D S4 ; Switch tube S1 and switch tube S4 form a pair of bridge arms, and switch tube S2 and switch tube S3 form another pair of bridge arms, which are alternately turned on; The output end of the battery-side full-bridge unit is connected to a switchable resonant circuit.

3. The control method of a multi-mode resonant converter for an electric vehicle power battery according to claim 1, characterized in that: The switchable resonant circuit includes a resonant inductor L r , resonant capacitor C r , bypass capacitor C p , excitation inductance L m , switch tube S H , switch tube S a ; Resonant inductor L r and the resonant capacitor C r A main resonant path is formed in series, connecting the output end of the battery-side full bridge and the primary winding of the high-frequency transformer; Switch tube S a With the resonant inductor L r Series connection for switching resonant mode; Bypass capacitor C p Set on the resonant path to adjust the resonant frequency; The switch tube S H The switchable resonant circuit and the battery form an LC loop; The excitation inductance L m is the equivalent parallel inductance of the high-frequency transformer, which participates in resonance.

4. The control method for a multi-mode resonant converter for an electric vehicle power battery according to claim 1, characterized in that: The primary winding of the high-frequency transformer is connected to the output end of the switchable resonant circuit; the secondary winding of the high-frequency transformer is connected to the input end of the DC side full-bridge unit; the transformation ratio of the high-frequency transformer is 1:N.

5. The control method of a multi-mode resonant converter for an electric vehicle power battery according to claim 4, characterized in that: The DC side full-bridge unit is a synchronous rectifier H-bridge, the input end of the synchronous rectifier H-bridge is connected to the secondary winding of the high-frequency transformer, and the output end of the synchronous rectifier H-bridge outputs a DC voltage V0, and the high-frequency ripple is filtered out by the filter capacitor C0; The synchronous rectifier H bridge includes switch tubes S5, S6, S7, and S8, each of which is connected in parallel with a diode D S5 、D S6 、D S7 、D S8 ; The switch tube S5 and the switch tube S8 form a pair of bridge arms, and the switch tube S6 and the switch tube S7 form another pair of bridge arms.

6. The control method of a multi-mode resonant converter for an electric vehicle power battery according to claim 1, characterized in that: The circuit equation for mode 1 is as follows: The circuit equation for mode 2 is as follows: Where, is the net equivalent resistance value; is the internal resistance of the battery; is the on-resistance value of the switch tube; is the resonant circuit loss component, where is the inductance L r The resistance value, is the capacitance C r resistance value; is the open circuit voltage of the battery; is the capacitance C r voltage; is the inductance L r Current; Heating current The expression is as follows: Where, Indicates the duration of the switching cycle; The ohmic effect of the battery's internal resistance is used to generate controllable heat, satisfying the following relationship: Where m is the battery mass, c is the battery specific heat capacity, S is the battery surface area, is the ambient temperature, is the battery temperature, h is the equivalent heat transfer coefficient, is the heat generated in the battery due to ohmic losses.

7. The control method of a multi-mode resonant converter for an electric vehicle power battery according to claim 1, characterized in that: The minimum value of the heating current in step 3 satisfy ; Maximum heating current The maximum discharge current specified by the battery factory; The calculation formula for the heating time t in step 4 is as follows: Where, is the heating current, is the internal resistance of the battery, h is the equivalent heat transfer coefficient, S is the surface area of the battery, is the ambient temperature, is the battery temperature, is the heat generated in the battery due to ohmic loss, is the heat dissipation power between the battery and the external environment; ΔT is the temperature change of the battery in a stage; m is the battery mass, and c is the battery specific heat capacity.

8. The control method for a multi-mode resonant converter for an electric vehicle power battery according to claim 1, characterized in that: Energy storage function Used to describe the relationship between total stored energy and temperature T: The calculation formula for the power consumption ΔSOC in step 4 is as follows: Where Cap is the rated capacity of the battery; is the heating current of the jth stage; is the heating time of the jth stage; N is the total number of heating stages.

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