Battery self-heating circuit and control method

Abstract

The invention discloses a battery self-heating circuit and a control method, and relates to the technical field of battery self-heating, the battery self-heating circuit is composed of a heating circuit, a charging control circuit, a current detection circuit and a charger, the charging control circuit comprises a first charging control circuit and a second charging control circuit, and the battery pack can be charged by the charger through the first charging control circuit or the second charging control circuit while the battery pack is subjected to alternating current self-heating by utilizing the heating circuit; the battery pack can be charged while being heated, and heat can be dissipated to assist in heating during charging, so that the heating efficiency of the battery pack at a low temperature is effectively improved, and the charging time of the battery is shortened.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a battery self-heating circuit and control method. Background Technology

[0002] With the increasing popularity of new energy vehicles in cold regions, the low-temperature performance degradation of lithium-ion batteries has become a core technological bottleneck restricting the all-weather application of electric vehicles. When the ambient temperature is below 0°C, the following chain of degradation effects will occur inside the battery. Existing battery low-temperature heating technologies mainly use fixed frequency and current amplitude to perform AC self-heating of the battery pack, which generates very little heat, resulting in low heating efficiency of the battery pack. Summary of the Invention

[0003] To address the aforementioned technical problems, embodiments of the present invention provide a battery self-heating circuit and control method, which solves the problem of low heating efficiency in existing battery low-temperature self-heating circuits.

[0004] A first aspect of this invention provides a battery self-heating circuit, including a heating circuit, a charging control circuit, a current detection circuit, and a charger, wherein... The heating circuit includes an LC resonant circuit and a high-frequency switching circuit. The LC resonant circuit is configured to be connected in parallel with the battery pack, the high-frequency switching circuit is connected in parallel with the LC resonant circuit, and the current detection circuit is connected in series with the battery pack. The charging control circuit includes a first charging control circuit and a second charging control circuit connected in parallel. The first terminals of the first charging control circuit and the second charging control circuit are respectively connected to the positive terminal of the battery pack, and the second terminals of the first charging control circuit and the second charging control circuit are respectively connected to the positive terminal of the charger. The negative terminal of the charger is used to connect to the negative terminal of the battery pack. The first charging control circuit is used to open the path between the charger and the battery pack when the temperature of the battery pack is greater than or equal to the third preset temperature threshold, so that the charger outputs a first current value to charge the battery pack. The second charging control circuit is used to open the path between the charger and the battery pack when the temperature of the battery pack is lower than the third preset temperature threshold, so that the charger outputs a second current value to charge the battery pack, wherein the second current value is less than the first current value.

[0005] In one possible implementation of the first aspect, the LC resonant circuit includes an inductor and a capacitor, and the high-frequency switching circuit includes a first switch and a second switch, wherein... The first end of the inductor is connected to the positive terminal of the battery pack, the second end of the inductor is connected to the first end of the capacitor, the second end of the capacitor is connected to the first transistor of the first switch, and the second end of the second switch is connected to the negative terminal of the battery pack. The second end of the inductor is also connected to the first end of the second switch, and the second end of the second switch is connected to the negative terminal of the battery pack.

[0006] In one possible implementation of the first aspect, the first charging control circuit includes a third switching transistor, wherein, The first end of the third switch is connected to the positive terminal of the battery pack, and the second end of the third switch is connected to the positive terminal of the charger.

[0007] The second charging control circuit includes a fourth switching transistor and a diode, wherein, The first end of the diode is connected to the positive terminal of the battery pack, the second end of the diode is connected to the first end of the fourth switching transistor, and the second end of the fourth switching transistor is connected to the positive terminal of the charger.

[0008] In one possible implementation of the first aspect, the charging control circuit can also be replaced by a charge / discharge switch circuit, wherein, The charge / discharge switch circuit includes a discharge switch transistor and a charge switch transistor. The first end of the discharge switch transistor is connected to the positive terminal of the battery pack, the second end of the discharge switch transistor is connected to the first end of the charge switch transistor, and the second end of the charge switch transistor is connected to the positive terminal of the charger.

[0009] To address the same technical problem, a second aspect of this invention provides a battery self-heating control method, which is implemented using the battery self-heating circuit of the first aspect of this invention.

[0010] Obtain the first actual temperature value of the battery pack in self-heating mode; Based on the first actual temperature value, determine the duty cycle of the heating circuit for heating the battery pack and the charging strategy of the charging control circuit for charging the battery pack. The closing state of each component in the heating circuit is controlled according to the duty cycle to make the heating circuit conduct. When the battery pack is heated by the heating circuit after it is turned on, the first charging control circuit or the second charging control circuit is controlled to charge and heat the battery pack according to the charging strategy until the temperature of the battery pack is greater than the fourth preset temperature threshold and the heating of the battery pack is stopped. The charging of the battery pack is stopped when the state of charge of the battery pack reaches the target state of charge.

[0011] In one possible implementation of the second aspect, determining the duty cycle for heating the battery pack by the heating circuit based on a first actual temperature value includes: If the first actual temperature value is less than the third preset temperature threshold, then the duty cycle is determined to be the maximum duty cycle of the heating circuit.

[0012] In one possible implementation of the second aspect, the charging strategy for the charging control circuit to charge the battery pack is determined based on a first actual temperature value, including: If the first actual temperature value is less than the second preset temperature threshold, then the charging strategy is determined to be the first charging strategy, wherein the first charging strategy is: Close the fourth switch in the second charging control circuit to obtain the current discharge current value of the battery pack in self-heating mode; Determine the charger's output current value based on the current discharge current value; The battery pack is charged based on the output current value.

[0013] In one possible implementation of the second aspect, the charging strategy for the charging control circuit to charge the battery pack is determined based on a first actual temperature value, including: If the first actual temperature value is greater than or equal to the second preset temperature threshold and less than the third preset temperature threshold, then the charging strategy is determined to be the second charging strategy, wherein the second charging strategy is: Close the fourth switch in the second charging control circuit and obtain the current voltage, actual state of charge value and output voltage of the battery pack in self-heating mode; Based on the actual state of charge and the current voltage, the efficiency of the heating circuit in heating the battery pack is calculated to obtain the first efficiency; Based on the output voltage, the efficiency of the second charging control circuit in heating the battery pack is calculated to obtain the second efficiency. Based on the battery pack's performance parameters, the heat dissipation efficiency is obtained. The first efficiency and the second efficiency are added together to obtain the third efficiency. The output current of the charger and the duty cycle of the heating circuit for heating the battery are determined based on the heat dissipation efficiency and the third efficiency.

[0014] In one possible implementation of the second aspect, the charging strategy for the charging control circuit to charge the battery pack is determined based on a first actual temperature value, including: If the first actual temperature value is greater than or equal to the third preset temperature threshold and less than the fourth preset temperature threshold, then the charging strategy is determined to be the third charging strategy, wherein the third charging strategy is: Close the third switch in the first charging control circuit; The charger's output current is gradually increased according to a preset growth rate to charge the battery pack.

[0015] The technical solution of this invention has the following advantages: The battery self-heating circuit provided in this embodiment of the invention comprises a heating circuit, a charging control circuit, a current detection circuit, and a charger. The heating circuit includes an LC resonant circuit and a high-frequency switching circuit. The LC resonant circuit is connected in parallel with the battery pack, and the high-frequency switching circuit is connected in parallel with the LC resonant circuit. The current detection circuit is connected in series with the battery pack. The charging control circuit consists of a first charging control circuit and a second charging control circuit connected in parallel. When the battery pack is at a low temperature, the heating circuit performs AC self-heating on the battery pack. Simultaneously, the second charging control circuit connects the charger and the battery pack, allowing the charger to charge the battery pack with a small current. This achieves simultaneous heating and charging of the battery pack, and the charging process also dissipates heat to assist in heating, effectively improving the heating efficiency of the battery pack at low temperatures and reducing the charging time. Furthermore, once the battery pack is no longer in a low-temperature state, such as when the temperature exceeds the third preset threshold, the second charging control circuit opens the path between the charger and the battery pack, allowing the charger to charge the battery pack with a large current, thus enabling the battery pack to be charged quickly. In summary, this battery self-heating circuit enables the battery pack to continue to increase its capacity during the low-temperature heating process, without having to wait for the battery to finish heating before charging, thereby shortening the overall low-temperature charging time. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the circuit module of the battery self-heating circuit in an embodiment of the present invention; Figure 2 This is a schematic diagram of the overall circuit structure of the battery self-heating circuit in an embodiment of the present invention; Figure 3 This is a schematic diagram of another overall circuit structure of the battery self-heating circuit in an embodiment of the present invention; Figure 4 This is a flowchart of the control method for the battery self-heating control method in an embodiment of the present invention; Figure 5 This is a schematic diagram of the battery self-heating current waveform in an embodiment of the present invention. Figure 6 This is a schematic diagram of another battery self-heating current waveform in an embodiment of the present invention. The reference numerals in the accompanying drawings are as follows: 100, heating circuit; 200, charging control circuit; 300, current detection circuit; 400, charger; 101, current detection circuit; 102, high-frequency switching circuit; 201, first charging control circuit; 202, second charging control circuit; 11, inductor; 21, capacitor; 31, first switching transistor; 32, second switching transistor; 33, third switching transistor; 34, fourth switching transistor; 41, diode; 500, charge / discharge switching circuit; 35, discharge switching transistor; 36, charging switching transistor. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can also refer to the internal connection of two components; it can be a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] The battery self-heating circuit provided in this embodiment of the invention, such as... Figure 1 As shown, the battery self-heating circuit includes a heating circuit 100, a charging control circuit 200, a current detection circuit 300, and a charger 400, wherein... The heating circuit 100 includes an LC resonant circuit 101 and a high-frequency switching circuit 102. The LC resonant circuit 101 is configured to be connected in parallel with the battery pack, the high-frequency switching circuit 102 is connected in parallel with the LC resonant circuit 101, and the current detection circuit 300 is connected in series with the battery pack. The charging control circuit 200 includes a first charging control circuit 201 and a second charging control circuit 202 connected in parallel. The first terminals of the first charging control circuit 201 and the second charging control circuit 202 are respectively connected to the positive terminal of the battery pack, and the second terminals of the first charging control circuit 201 and the second charging control circuit 202 are respectively connected to the positive terminal of the charger 400. The negative terminal of the charger 400 is connected to the negative terminal of the battery pack. The first charging control circuit 201 is used to connect the charger 400 and the battery pack when the temperature of the battery pack is greater than or equal to the third preset temperature threshold, so that the charger 400 outputs a first current value to charge the battery pack. The third preset temperature threshold is determined based on the charging performance parameters of the battery pack. The second charging control circuit 202 is used to connect the charger 400 and the battery pack when the temperature of the battery pack is lower than the third preset temperature threshold, so that the charger 400 outputs a second current value to charge the battery pack, wherein the second current value is less than the first current value.

[0021] like Figure 1 As shown, the battery self-heating circuit consists of at least a heating circuit 100, a charging control circuit 200, and a charger 400. The heating circuit 100 is connected in parallel with the battery pack. Specifically, the heating circuit 100 includes an LC resonant circuit 101 and a high-frequency switching circuit 102. The first terminal of the LC resonant circuit 101 is connected to the positive terminal of the battery pack, and the second terminal of the LC resonant circuit 101 is connected to the negative terminal of the battery pack, thereby heating the battery pack. The battery pack can also provide electrical energy input to the LC resonant circuit 101. Simultaneously, the high-frequency switching circuit 102 is connected in parallel with the LC resonant circuit 101, i.e., as shown... Figure 2 As shown, the two ends of the high-frequency switching circuit 102 are connected to the two ends of the LC resonant circuit 101, sharing the same two connection points. Through this parallel connection, the high-frequency switching circuit 102 can control the operating state of the LC resonant circuit 101, such as adjusting the current on / off state or frequency, thereby achieving precise control of the heating process and meeting the heating requirements of the battery pack.

[0022] The charging control circuit 200 consists of a first charging control circuit 201 and a second charging control circuit 202. The first terminals of both circuits are connected to the positive terminal of the battery pack, and their second terminals are connected to the positive terminal of the charger 400. The negative terminal of the charger 400 is connected to the negative terminal of the battery pack. Specifically, the first terminal of the first charging control circuit 201 is connected to the positive terminal of the battery pack, and its second terminal is connected to the positive terminal of the charger 400. Similarly, the first terminal of the second charging control circuit 202 is also connected to the positive terminal of the battery pack, and its second terminal is also connected to the positive terminal of the charger 400. Simultaneously, the negative terminal of the charger 400 is directly connected to the negative terminal of the battery pack, forming a circuit. The first charging control circuit 201 and the second charging control circuit 202 are connected in parallel. When the charger 400 is connected to a power source, current can flow to the battery pack through either the first charging control circuit 201 or the second charging control circuit 202, thus completing the charging process. Because the two charging control circuits 200 are connected in parallel, one of them can be flexibly controlled to operate according to actual charging needs. Combined with monitoring data from the current detection module, precise control of the battery pack's charging status can be achieved. For example, when the battery pack's temperature is low, such as below the third preset temperature threshold, the second charging control circuit 202 opens the path between the charger 400 and the battery pack, causing the charger 400 to output a second current value to charge the battery pack. When the battery pack is not in a low-temperature state, such as above or equal to the third preset temperature threshold, the first charging control circuit opens the path between the charger 400 and the battery pack, causing the charger 400 to output a first current value to charge the battery pack. It should be noted that the second current value is mainly a small current value, such as 0.1C to 0.3C. The first current value is mainly a large current value, such as 0.5C to 2C. The specific value can be determined according to actual needs, where C is the rated capacity of the battery pack. The upper limit of the first current value cannot exceed the maximum continuous charging current of the battery cell. The third preset temperature threshold is determined based on the charging performance parameters of the battery pack, such as the critical lithium plating temperature, thermal runaway trigger threshold, or overvoltage tolerance.

[0023] In addition, a current detection circuit 300 is connected in series in the power supply circuit of the battery pack to monitor the charging current flowing through the battery pack in real time. That is, the first terminal of the current detection circuit 300 is connected to the second terminal of the heating circuit 100 and the negative terminal of the charger 400, respectively, and the second terminal of the detection resistor is connected to the negative terminal of the battery pack.

[0024] It should be noted that the battery pack is composed of multiple cells connected in series and parallel.

[0025] In one embodiment, the LC resonant circuit 101 includes an inductor 11 and a capacitor 21, and the high-frequency switching circuit 102 includes a first switching transistor 31 and a second switching transistor 32, wherein... The first end of the inductor 11 is used to connect to the positive terminal of the battery pack, the second end of the inductor 11 is connected to the first end of the capacitor 21, the second end of the capacitor 21 is connected to the first tube of the first switch 31, and the second end of the second switch 32 is used to connect to the negative terminal of the battery pack. The second end of the inductor 11 is also connected to the first end of the second switch 32, and the second end of the second switch 32 is connected to the negative terminal of the battery pack.

[0026] like Figure 2 As shown, the heating circuit 100 includes an inductor 11, a capacitor 21, a first switching transistor 31, and a second switching transistor 32. The inductor 11 and capacitor 21 form an LC resonant circuit 101, and the first switching transistor 31 and second switching transistor 32 form a high-frequency switching circuit 102. The specific connections of each component are as follows: the first end of the inductor 11 is directly connected to the positive terminal of the battery pack, and the second end of the inductor 11 is connected to the first end of the capacitor 21. The first end of the second switching transistor 32 is also connected to the second end of the inductor. The second end of the capacitor 21 is directly connected to the first end of the first switching transistor 31. Through the cooperation of the capacitor and inductor, voltage fluctuations in the circuit are reduced, ensuring stable operation of the switching transistors. The first switch 31 and the second switch 32 are used to control the on / off state and regulate the current of the heating circuit 100. The second terminals of the first switch 31 and the second switch 32 are connected in parallel and then connected to the negative terminal of the battery pack to form the common ground terminal of the heating circuit 100. This ensures that the current from both switches can eventually flow back to the negative terminal of the battery pack, forming a complete current loop.

[0027] During operation, after the third switch 33 is turned on, the LC circuit begins its first cycle of oscillation, and the LC resonant frequency is: In the formula, Indicates the inductance value. This indicates the capacitance value.

[0028] When the system detects that the positive terminal voltage of capacitor element 21 reaches 0V, the system sends a high-level pulse. The first high-level pulse drives the second switch 32 to close. At this time, battery current flows out from the positive terminal, recorded as the forward current, charging the LC resonant unit. The current flowing through the inductor continues to increase. When the forward current reaches its maximum value, the system sends a low-level pulse to drive the second switch 32 to open, achieving the purpose of soft turn-off. The time for the first high-level pulse to drive the second switch 32 to close is recorded as [missing information]. .

[0029] After the second switch 32 is turned off, due to the phase difference between the resonant voltage and current, the forward current continues to charge the capacitor 21. As the capacitor charge increases, the forward current gradually decreases until it reaches zero, which is represented by the positive half-cycle of a sine wave. When the voltage of the capacitor 21 reaches its maximum value, the forward current decreases to 0. The voltage at the positive terminal of the capacitor 21 is more than twice the battery voltage, and the current begins to flow back to the positive terminal of the battery, which is recorded as the reverse current. As the charge stored in the LC gradually decreases, the voltage at the positive terminal of the capacitor 21 decreases accordingly. The reverse current first increases and then decreases, which is represented by the negative half-cycle of a sine wave. When the voltage drops to 0V, the system pulse signal drives the second switch 32 to close again, achieving the soft-start purpose. The time when the first pulse low level drives the second switch 32 to turn off is recorded as... PWM pulse drive signal period The duty cycle of the PWM high level is denoted as LC resonant frequency From a theoretical perspective, maintaining Unchanged, Changed The size can be adjusted to change the amplitude of the alternating current.

[0030] In one embodiment, the first charging control circuit 201 includes a third switching transistor 33, wherein, The first end of the third switch 33 is connected to the positive terminal of the battery pack, and the second end of the third switch 33 is connected to the positive terminal of the charger 400.

[0031] like Figure 2 As shown, the first charging control circuit 201 is the main charging circuit, which includes a third switch 33, which is the main charging switch for the battery pack. Specifically, the first terminal of the third switch 33 is connected to the positive terminal of the battery pack, and the second terminal of the third switch 33 is connected to the positive terminal of the charger 400. During operation, when the temperature of the battery pack reaches or exceeds a fourth preset temperature threshold, the first switch 31, the second switch 32, and the fourth switch 34 are disconnected, and the third switch 33 is closed, allowing the main charging circuit to charge the battery pack.

[0032] It should be noted that the first switch 31, the second switch 32, the third switch 33 and the fourth switch 34 are all metal-oxide-semiconductor field-effect transistors or integrated circuits with switching functions.

[0033] In one embodiment, the second charging control circuit 202 includes a fourth switching transistor 34 and a diode 41, wherein, The first end of diode 41 is connected to the positive terminal of the battery pack, the second end of diode 41 is connected to the first end of the fourth switch 34, and the second end of the fourth switch 34 is connected to the positive terminal of the charger 400.

[0034] In this embodiment, the second charging control circuit 202 includes a fourth switch 34 and a diode 41. Specifically, the first terminal of diode 41 is connected to the positive terminal of the battery pack, the second terminal of diode 41 is connected to the first terminal of the fourth switch 34, and the second terminal of the fourth switch 34 is connected to the positive terminal of the charger 400. The fourth switch 34 is responsible for opening or closing the DC charging circuit. When using the charger 400, the fourth switch 34 can adjust the charging current value through a pulse switch. The diode 41 prevents high-frequency alternating current from flowing back into the charger 400, thus avoiding damage to the charger 400. Furthermore, the diode 41 is selected with a fast recovery time of less than 50ns to quickly prevent resonant current from flowing back into the charger 400. The fast recovery time refers to the time required for diode 41 to switch from the conducting state to the cutoff state, or from the reverse cutoff state to a state capable of withstanding reverse voltage.

[0035] In one embodiment, the charging control circuit 200 can also be replaced by a charge / discharge switch circuit 500, wherein, The charge / discharge switch circuit 500 includes a discharge switch transistor 35 and a charge switch transistor 36. The first end of the discharge switch transistor 35 is connected to the positive terminal of the battery pack, the second end of the discharge switch transistor 35 is connected to the first end of the charge switch transistor 36, and the second end of the charge switch transistor 36 is connected to the positive terminal of the charger.

[0036] In this embodiment, the charging control circuit 200 can also be replaced by the charge / discharge switch circuit 500, that is, the high-side same-port charge / discharge switch circuit of the battery management system can be reused as the charging control circuit. Figure 3 As shown, the charge / discharge switch circuit 500 includes a discharge switch transistor 35 and a charge switch transistor 36. The first terminal of the discharge switch transistor 35 is connected to the positive terminal of the battery pack, and the second terminal of the discharge switch transistor 35 is connected to the first terminal of the charge switch transistor 36. The second terminal of the charge switch transistor 36 is connected to the positive terminal of the charger. When charging the battery pack, the discharge switch transistor 35 is closed, and the charge switch transistor 36 is opened. The charging pulse current enters the positive terminal of the battery pack through the diode of the charge switch transistor 36, achieving charging and heating when the battery is low on power.

[0037] It should be noted that both the discharge switch 35 and the charge switch 36 are metal-oxide-semiconductor field-effect transistors or integrated circuits with switching functions.

[0038] The battery self-heating control method provided in this embodiment of the invention, such as... Figure 4 As shown, Figure 4 The flowchart shows a battery self-heating control method, which includes steps S101 to S104, each step specifically including: S101. Obtain the first actual temperature value of the battery pack in self-heating mode; like Figure 4 As shown, firstly, the battery management system acquires the temperature of multiple monitoring points inside the battery pack. When the lowest temperature falls below a first preset temperature threshold, the self-heating mode is activated. Then, the temperature sensor obtains the first actual temperature value of the battery pack in self-heating mode in real time.

[0039] S102. Based on the first actual temperature value, determine the duty cycle of the heating circuit for heating the battery pack and the charging strategy of the charging control circuit for charging the battery pack.

[0040] In this embodiment, the duty cycle for the heating circuit to heat the battery pack and the charging strategy for the charging control circuit to charge the battery pack are determined based on the pre-set temperature-duty cycle and charging strategy correspondence.

[0041] In one embodiment, determining the duty cycle for the heating circuit to heat the battery pack based on a first actual temperature value includes: If the first actual temperature value is less than the third preset temperature threshold, then the duty cycle is determined to be the maximum duty cycle of the heating circuit.

[0042] In this embodiment, when the first actual temperature value is less than the third preset temperature threshold, the maximum duty cycle is set so that the heating circuit outputs the maximum amplitude high-frequency AC current to heat the battery pack until the first actual temperature value is greater than the fourth preset temperature threshold. Then, the heating circuit is disconnected, the LC oscillation heating is turned off, the fourth switch is disconnected, and the third switch is closed.

[0043] It should be noted that the heating stage of the battery pack in self-heating mode and the charging strategy adopted for the battery pack are different depending on the first actual temperature value. Specifically, when the first actual temperature value is less than the first preset temperature threshold, the battery pack's self-heating mode is in the heating-dominant, charge-discharge balance stage. At this time, the duty cycle is determined to be the maximum duty cycle of the heating circuit. For example, if the first preset temperature threshold is -20℃, when the first actual temperature value is less than -20℃, it is in the heating-dominant, charge-discharge balance stage. The maximum duty cycle in the heating circuit is set so that the heating circuit outputs the maximum amplitude high-frequency AC current to heat the battery pack. At the same time, the fourth switch is closed, and the charging control circuit uses the first charging strategy to charge the battery pack.

[0044] When the first actual temperature value is greater than or equal to the first preset temperature threshold but less than the second preset temperature threshold, the amplitude of the high-frequency sudden current output by the heating circuit remains unchanged, and a command is sent to the charger or the charging current value is adjusted through the second charging control circuit, so that the average battery current is thus... *Battery pack rated capacity, e.g., 0.1C. When the first actual temperature value is greater than the second preset temperature threshold but less than the third preset temperature threshold, the amplitude of the LC resonant high-frequency alternating current of the heating circuit is appropriately reduced, while the charger output current continues to increase to charge the battery pack, so that the average current entering the battery is... *Battery pack rated capacity, such as 0.2C. The above method allows for dynamic adjustment of the high-frequency alternating current amplitude; the resonant frequency of the heating circuit is determined by the size of the inductor and capacitor components.

[0045] It should be noted that the second preset temperature threshold can be set to -10℃, -5℃ or 0℃, and the third preset temperature threshold can be set to 5℃, 10℃ or 15℃, which can be set according to actual needs.

[0046] In one embodiment, based on a first actual temperature value, a charging strategy for the charging control circuit to charge the battery pack is determined, including: If the first actual temperature value is less than the second preset temperature threshold, then the charging strategy is determined to be the first charging strategy, wherein the first charging strategy is: Close the fourth switch in the second charging control circuit to obtain the current discharge current value of the battery pack in self-heating mode; Determine the charger's output current value based on the current discharge current value; The battery pack is charged based on the output current value.

[0047] In this embodiment, if the first actual temperature value is less than the second preset temperature threshold, the charging control circuit determines the charging strategy for the battery pack to be the first charging strategy. For example, if the second preset temperature threshold is 0°C and the first actual temperature value is less than 0°C, the charging control circuit uses the first charging strategy to charge the battery pack. Specifically, when the first actual temperature value is less than the second preset temperature threshold, the charging control circuit uses the first charging strategy to charge the battery pack. The first charging strategy involves closing the fourth switch, starting the second charging control circuit to DC charge the battery pack, and sending instructions to the charger based on the real-time acquired state of charge value and open-circuit voltage of the battery pack in self-heating mode, or adjusting the charging current value through pulses in the second charging control circuit, so that the average current entering the battery is zero, that is, setting the charger to charge with a small current, so that the average current flowing into and out of the battery is close, so that the battery continues to heat up, that is, the current output at the current stage is equal to the current discharge current value of the battery pack. For example, when the charger is set to output a 7A current, after the fourth switch of the second charging control circuit is closed, the anode TP1 current waveform is as follows. Figure 5Channel CH4 has a horizontal bottom line, the cutoff current of diode 41 is 0A, and the peak value is the maximum current value of the charger pulse output. The charging behavior of diode 41 is approximately sinusoidal DC pulse charging. The current waveform of TP3 at the positive terminal of the battery pack is shown in channel CH2 of the figure below. It is a sinusoidal AC pulse with symmetrical positive and negative half-axis. No DC component current enters the battery. The reason is that the amount of charge brought in by the DC pulse per unit time is just consumed by the battery internal resistance and the heat generated by the LC resonant circuit. There is no excess charge left to enter the battery, thus achieving current balance.

[0048] In one embodiment, based on a first actual temperature value, a charging strategy for the charging control circuit to charge the battery pack is determined, including: If the first actual temperature value is greater than or equal to the second preset temperature threshold and less than the third preset temperature threshold, then the charging strategy is determined to be the second charging strategy, wherein the second charging strategy is: Close the fourth switch in the second charging control circuit and obtain the current voltage, actual state of charge value and output voltage of the battery pack in self-heating mode; Based on the actual state of charge and the current voltage, the efficiency of the heating circuit in heating the battery pack is calculated to obtain the first efficiency; Based on the output voltage, the efficiency of the second charging control circuit in heating the battery pack is calculated to obtain the second efficiency. Based on the battery pack's performance parameters, the heat dissipation efficiency is obtained. The first efficiency and the second efficiency are added together to obtain the third efficiency. The output current of the charger and the duty cycle of the heating circuit for heating the battery are determined based on the heat dissipation efficiency and the third efficiency.

[0049] In this embodiment, if the first actual temperature value is greater than or equal to the second preset temperature threshold and less than the third preset temperature threshold, the charging strategy is determined to be the second charging strategy. For example, if the third preset temperature threshold is 15°C, and the first actual temperature value is greater than or equal to 0°C and less than 15°C, the charging control circuit uses the second charging strategy to charge the battery pack. Specifically, if the first actual temperature value is greater than or equal to the second preset temperature threshold and less than the third preset temperature threshold, the charging control circuit uses the second charging strategy to charge the battery pack. Specifically, the second charging strategy involves closing the fourth switch in the second charging control circuit and, based on the real-time acquired state data of the battery pack in self-heating mode and the output voltage of the charger, the state data includes at least the current voltage and the actual state of charge value. Specifically, if the lowest temperature cell is detected to have reached the second preset temperature threshold, the output current of the charger is increased in a ramp-up manner, the battery temperature continues to rise, and the amplitude of the LC resonant high-frequency alternating current remains unchanged. The system sends a command to the charger to increase the voltage and current, so that the average current flowing into and out of the battery is... * Rated capacity of the battery pack.

[0050] It should be noted that the charger's output current can be determined based on the AC self-heating efficiency and the DC pulse self-heating efficiency. Specifically, the battery pack's heat dissipation efficiency is calculated using the heat dissipation efficiency formula. When the heat dissipation efficiency is greater than the AC and DC heating rates, the DC current output by the charger and the amplitude of the LC high-frequency alternating current in the heating circuit should be increased to increase the heating rate until the battery temperature stabilizes. If the battery temperature continues to rise during charging, exceeding the battery's maximum withstand temperature, the AC and DC heating currents should be gradually reduced until the battery temperature stabilizes. The ambient heat dissipation efficiency is calculated using the following formula: In the formula, This refers to the amount of battery temperature reduction during the cooling process. The specific heat capacity of the battery pack materials. For battery quality, For heat dissipation efficiency, This refers to the surface area for heat dissipation of the battery pack. For heat dissipation coefficient, The average temperature difference between the battery and the environment during the cooling process. This refers to the cooling time of the battery pack.

[0051] The heating efficiency of the heating circuit for heating the battery pack, i.e., the first efficiency, is calculated using the following formula: In the formula, The total energy consumed by the battery during the heating process. This is the total voltage of the battery pack. The remaining charge after the battery is heated. This represents the remaining charge of the battery before it is heated. This refers to the total battery capacity. This is a unit for converting between coulombs and capacity; 1 mAh = 1 * 10^6 mAh. -3 A * 3600s = 3.6C The first efficiency refers specifically to the ratio of the energy actually absorbed by the battery during the standalone AC self-heating process to the total energy consumed by the battery.

[0052] The specific formula for calculating the charging efficiency, or second efficiency, of the battery pack controlled by the second charging control circuit is as follows: In the formula, The DC pulse current entering the battery pack generates heat. The increase in temperature for AC + DC heating. This is the output voltage of the charger. Indicates the LC resonant unit switch Closure duration, For the quality of the battery pack, The specific heat capacity of the battery pack materials. The formula for calculating the heat absorbed during the heating process of the battery pack is as follows: In the formula, To absorb heat during the battery pack's heating process. For battery pack quality, For the specific heat capacity of the battery pack, This represents the increase in battery temperature.

[0053] As an example of this embodiment, when the charger output current increases to 18A, the waveform of the anode TP1 current is as follows. Figure 6 As shown in channel CH4, the overall current was increased by 6A, and the current waveform was approximately sinusoidal with a peak-to-peak value of 18A; the current waveform at the positive electrode TP3 of the battery pack is as follows. Figure 5 The CH2 channel features peak-to-peak compression of the sine wave, reducing the power consumption of the LC resonant circuit. Excess energy is transferred to the battery, improving heating efficiency and allowing more power to remain in the battery.

[0054] In one embodiment, based on a first actual temperature value, a charging strategy for the charging control circuit to charge the battery pack is determined, including: If the first actual temperature value is greater than or equal to the third preset temperature threshold and less than the fourth preset temperature threshold, then the charging strategy is determined to be the third charging strategy, wherein the third charging strategy is: Close the third switch in the first charging control circuit; The charger's output current is gradually increased according to a preset growth rate to charge the battery pack.

[0055] In this embodiment, if the first actual temperature value is greater than or equal to the third preset temperature threshold and less than the fourth preset temperature threshold, then the charging strategy is determined to be the third charging strategy. For example, if the fourth preset temperature threshold is 20°C, and the first actual temperature value is greater than or equal to 15°C and less than 20°C, then the charging strategy is determined to be the third charging strategy. Specifically, if the first actual temperature value is greater than or equal to the third preset temperature threshold and less than the fourth preset temperature threshold, then the amplitude of the LC resonant high-frequency alternating current is appropriately reduced, and the charger output current is further increased, so that the average current flowing into and out of the battery is... *Battery pack rated capacity. (Among them,) Greater than , The preferred value is 0.2. The preferred value is 0.1, which can be determined according to actual needs.

[0056] If the first actual temperature value is greater than the fourth preset temperature threshold, the charging control circuit uses the third charging strategy to charge the battery pack. This stage is primarily charging with AC self-heating as an auxiliary process. Specifically, when the battery temperature rises to the third preset temperature threshold, the heating circuit is disconnected, the fourth switch is turned off, and the main charging MOSFET (the third switch) is turned on. The battery management system sends a command to the charger to gradually increase the output current value according to a preset growth rate, putting the battery in a fast charging state. Then, the battery temperature continues to be monitored. If the first actual temperature value rises to the maximum current the battery pack can withstand, the charger's output current is reduced. If the first actual temperature value drops below the second temperature threshold, the third switch is disconnected, and the heating circuit and the second charging control circuit are re-energized, thus initiating the AC self-heating and DC pulse self-heating stages. This repeated charging and heating operation continues until the first actual temperature value exceeds the fourth preset temperature threshold, switching to pure charging mode. This cycle continues until the battery is fully charged.

[0057] It should be noted that the appropriate alternating current amplitude and charger output current value can also be selected based on AC and DC heating evaluation models. The specific formula is as follows: in, The score for heating and charging synergy performance. The heating efficiency of the heating circuit for heating the battery pack. To control the charging efficiency of the battery pack by the second charging control circuit. For battery pack charging rate, The rate of change of battery internal resistance. To indicate the degree of battery aging, Because the DC output current of the charger (400) is a positive half-cycle sinusoidal pulse current input into the battery under the action of LC resonant high-voltage AC, the cumulative output power of the charger during the heating process is time. The integral of the internal current. During this stage, the voltage of the resonant capacitor is the same as the battery voltage, and no reverse current is generated. Therefore, the charger output current enters the battery through diode 41.

[0058] The specific calculation method is the ratio of the battery capacity C2 minus the initial battery capacity C1 after the charging and heating process is completed to the heating time. The specific calculation method involves charging and heating the battery with a certain AC / DC current for 100 cycles, and then calculating the ratio of the increase in the battery's AC internal resistance to its initial AC internal resistance. The higher the value, the more severe the battery aging. The specific calculation method is to assess the battery capacity degradation rate. If the initial discharge capacity of the battery is C0, and after 100 cycles of charging and heating, the battery discharge capacity becomes C1, then the degree of battery aging is determined. = (C0 - C1) / C0, The larger the value, the greater the degree of battery aging, and the smaller the evaluation model value.

[0059] S103. Control the closing state of each component in the heating circuit according to the duty cycle so that the heating circuit is turned on.

[0060] In this embodiment, the battery management system controls the closing state of various components, such as the high-frequency switching circuit, in the heating circuit according to a determined duty cycle, thereby turning on the heating circuit. Based on a determined charging strategy, the charging control circuit is controlled to charge the battery pack.

[0061] S104. When heating the battery pack using the conducting heating circuit, the charging control circuit is controlled to charge and heat the battery pack according to the charging strategy until the temperature of the battery pack is greater than the fourth preset temperature threshold, and the heating of the battery pack is stopped. The charging of the battery pack is stopped when the state of charge of the battery pack reaches the target state of charge.

[0062] In this embodiment, the heating circuit, once activated, generates heat through an LC resonant circuit to heat the battery pack. Simultaneously, the charging control circuit charges the battery pack according to a predetermined charging strategy. During heating and charging, the system continuously monitors the temperature; when the battery pack temperature exceeds a fourth preset temperature threshold, heating is stopped; when the battery pack reaches the target state of charge, charging is stopped.

[0063] The charging control circuit, following a predetermined charging strategy, causes the charger to output DC power. This DC power, under the influence of a high-frequency alternating current (LC), is converted into DC pulses to charge the battery pack. Simultaneously, it generates heat to heat the battery pack. The heat generated inside the battery by the DC pulse component is significantly greater than the heat generated by the high-frequency alternating current. Specifically, the heating circuit's method of heating the battery pack is AC self-heating, while the method of heating the battery pack while charging is DC pulse heating.

[0064] The reason why batteries introduce DC pulse self-heating at low temperatures is that, below 0°C, the DC internal resistance of a lithium battery is much greater than its AC internal resistance, generating heat according to Joule's law. Battery self-heating is mainly caused by internal resistance R and the current flowing through the cell. The formula for calculating the low-temperature DC internal resistance of a battery cell is: in, This indicates the voltage across the battery when it is open-circuited. This indicates the voltage across the battery terminals when it discharges. Indicates the discharge current. This indicates the current when the circuit is open, typically 0A.

[0065] As an example of this embodiment, consider the nominal AC internal resistance of a certain single-cell lithium battery. The resistance is 0.4mΩ, and the measured resistance at -20℃ is 0.5mΩ. The open-circuit voltage of the cell at low temperature is 3.297V. When discharged with a load resistor, the discharge current is 11A. At this time, the measured voltage across the cell is 2.741V, and the DC internal resistance is... = (3.2974V-2.7414V) / (11A-0A)=50.5mΩ. Subtracting the discharge return line resistance of about 10mΩ, the DC internal resistance of the battery cell is about 40mΩ, which is 80 times the AC internal resistance.

[0066] A certain single-cell lithium battery has a surface temperature of -27℃. When discharged by an electronic load with a discharge current of 12A, the surface temperature of cell B2 rises to 33℃ after 20 minutes, a temperature rise of 60℃, with a temperature rise rate of 3℃ / min. At the same low temperature, heating the cell with an AC pulse current of 12A (effective AC current) results in a temperature rise of 28℃ after 28 minutes, with a temperature rise rate of 1℃ / min, which is one-third of the DC heating rate. Larger capacity cells have lower AC internal resistance. To rapidly heat the cell at low temperatures, relying solely on AC internal resistance requires a significant increase in the effective value of the AC current, necessitating a larger LC energy storage inductor inductance and size, thus increasing costs.

[0067] It should be noted that the first preset temperature threshold can be determined according to the actual characteristics of the battery pack, such as -30℃, -25℃, or -20℃. The fourth preset temperature threshold is preferably 20℃ and can be set according to actual needs. The target state of charge is preferably 100% and can be set according to actual needs. The first actual temperature value refers to the temperature of the battery pack in self-heating mode as monitored in real time.

[0068] When AC self-heating and DC pulse self-heating work together to heat the battery pack, the total heat generated inside the battery pack is: In the formula, This refers to the total heat generated inside the battery pack. This is the effective value of the DC current. The low-temperature equivalent DC internal resistance of the battery. This is the effective value of the high-frequency alternating current. The battery's low-temperature AC equivalent internal resistance, The duration of combined AC self-heating and DC pulse self-heating for heating the battery pack.

[0069] This invention enables AC self-heating even when the battery pack has zero charge, without the need to reserve sufficient charge for heating. Furthermore, the rate of AC self-heating and DC pulse self-heating is faster than that of AC self-heating alone. Moreover, the battery charge continuously increases during the heating process, eliminating the need to wait for the battery to fully heat up before recharging, thus shortening the overall low-temperature charging time.

[0070] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0071] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A battery self-heating circuit, characterized in that, It includes a heating circuit (100), a charging control circuit (200), a current detection circuit (300), and a charger (400), wherein, The heating circuit (100) includes an LC resonant circuit (101) and a high-frequency switching circuit (102), wherein the LC resonant circuit (101) is configured to be connected in parallel with the battery pack, the high-frequency switching circuit (102) is connected in parallel with the LC resonant circuit (101), and the current detection circuit (300) is configured to be connected in series with the battery pack. The charging control circuit (200) includes a first charging control circuit (201) and a second charging control circuit (202) connected in parallel. The first terminals of the first charging control circuit (201) and the second charging control circuit (202) are respectively used to connect to the positive terminal of the battery pack. The second terminals of the first charging control circuit (201) and the second charging control circuit (202) are respectively connected to the positive terminal of the charger (400). The negative terminal of the charger (400) is used to connect to the negative terminal of the battery pack. The first charging control circuit (201) is used to open the path between the charger (400) and the battery pack when the temperature of the battery pack is greater than or equal to a third preset temperature threshold, so that the charger (400) outputs a first current value to charge the battery pack. The second charging control circuit (202) is used to open the path between the charger (400) and the battery pack when the temperature of the battery pack is less than the third preset temperature threshold, so that the charger (400) outputs a second current value to charge the battery pack, wherein the second current value is less than the first current value.

2. The battery self-heating circuit as described in claim 1, characterized in that, The LC resonant circuit (101) includes an inductor (11) and a capacitor (21), and the high-frequency switching circuit (102) includes a first switching transistor (31) and a second switching transistor (32), wherein, The first end of the inductor (11) is used to connect to the positive terminal of the battery pack, the second end of the inductor (11) is connected to the first end of the capacitor (21), the second end of the capacitor (21) is connected to the first tube of the first switch (31), and the second end of the second switch (32) is used to connect to the negative terminal of the battery pack. The second end of the inductor (11) is also connected to the first end of the second switch (32), and the second end of the second switch (32) is connected to the negative terminal of the battery pack.

3. The battery self-heating circuit as described in claim 1, characterized in that, The first charging control circuit (201) includes a third switching transistor (33), wherein, The first end of the third switch (33) is used to connect to the positive terminal of the battery pack, and the second end of the third switch (33) is connected to the positive terminal of the charger (400).

4. The battery self-heating circuit as described in claim 1, characterized in that, The second charging control circuit (202) includes a fourth switching transistor (34) and a diode (41), wherein, The first end of the diode (41) is connected to the positive terminal of the battery pack, the second end of the diode (41) is connected to the first end of the fourth switch (34), and the second end of the fourth switch (34) is connected to the positive terminal of the charger (400).

5. The battery self-heating circuit as described in claim 1, characterized in that, The charging control circuit (200) can also be replaced by a charge / discharge switch circuit (500), wherein, The charge / discharge switch circuit (500) includes a discharge switch tube (35) and a charge switch tube (36), wherein the first end of the discharge switch tube (35) is connected to the positive terminal of the battery pack, the second end of the discharge switch tube (35) is connected to the first end of the charge switch tube (36), and the second end of the charge switch tube (36) is connected to the positive terminal of the charger (400).

6. A battery self-heating control method, characterized in that, For implementation via the battery self-heating circuit as described in any one of claims 1-5, comprising: Obtain the first actual temperature value of the battery pack in self-heating mode; Based on the first actual temperature value, determine the duty cycle of the heating circuit for heating the battery pack and the charging strategy of the charging control circuit for charging the battery pack. The closing state of each component in the heating circuit is controlled according to the duty cycle to make the heating circuit conduct. When the heating circuit is turned on to heat the battery pack, the first charging control circuit or the second charging control circuit is controlled to charge the battery pack according to the charging strategy until the temperature of the battery pack is greater than the fourth preset temperature threshold and the heating of the battery pack is stopped, and the charging of the battery pack is stopped when the state of charge of the battery pack reaches the target state of charge.

7. The battery self-heating control method as described in claim 6, characterized in that, Determining the duty cycle for heating the battery pack by the heating circuit based on the first actual temperature value includes: If the first actual temperature value is less than the third preset temperature threshold, then the duty cycle is determined to be the maximum duty cycle of the heating circuit.

8. The battery self-heating control method as described in claim 6 or 7, characterized in that, The step of determining the charging strategy for the charging control circuit to charge the battery pack based on the first actual temperature value includes: If the first actual temperature value is less than the second preset temperature threshold, then the charging strategy is determined to be the first charging strategy, wherein the first charging strategy is: Close the fourth switch in the second charging control circuit to obtain the current discharge current value of the battery pack in self-heating mode; Based on the current discharge current value, determine the output current value of the charger; The battery pack is charged based on the output current value.

9. The battery self-heating control method as described in claim 6 or 7, characterized in that, The step of determining the charging strategy for the charging control circuit to charge the battery pack based on the first actual temperature value includes: If the first actual temperature value is greater than or equal to the second preset temperature threshold and less than the third preset temperature threshold, then the charging strategy is determined to be the second charging strategy, wherein the second charging strategy is: Close the fourth switch in the second charging control circuit and obtain the current voltage, actual state of charge value and output voltage of the battery pack in self-heating mode; Based on the actual state of charge value and the current voltage, the efficiency of the heating circuit in heating the battery pack is calculated to obtain a first efficiency; Based on the output voltage, the efficiency of the second charging control circuit in heating the battery pack is calculated to obtain the second efficiency; Based on the performance parameters of the battery pack, the heat dissipation efficiency is obtained. The first efficiency and the second efficiency are added together to obtain the third efficiency. The output current of the charger and the duty cycle of the heating circuit for heating the battery are determined based on the heat dissipation efficiency and the third efficiency.

10. The battery self-heating control method as described in claim 6 or 7, characterized in that, The step of determining the charging strategy for the charging control circuit to charge the battery pack based on the first actual temperature value includes: If the first actual temperature value is greater than or equal to the third preset temperature threshold and less than the fourth preset temperature threshold, then the charging strategy is determined to be the third charging strategy, wherein the third charging strategy is: Close the third switch in the first charging control circuit; The output current of the charger is gradually increased according to a preset growth rate to charge the battery pack.

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