Battery low-temperature heating circuit for electric automobile
By using series resistance and bidirectional pulse current heating in the battery low-temperature heating circuit, combined with internal and external heating, the problems of lithium plating and SOC imbalance in electric vehicle lithium-ion batteries under low-temperature conditions are solved, achieving rapid heating and charging and reducing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-11
- Publication Date
- 2026-03-13
AI Technical Summary
In low-temperature environments, the performance of lithium-ion batteries in electric vehicles degrades, and problems such as lithium plating and SOC imbalance occur. Existing heating strategies are either costly or have low heating rates.
The battery low-temperature heating circuit employs a battery string, switch, inverter bridge, and motor. It uses series resistors and bidirectional pulse current for heating, combined with internal and external heating, and adjusts the resistance value and current frequency to optimize the heating rate and SOC balance.
It improves the battery heating rate, reduces the risk of lithium plating, enables fast charging and SOC balance, and reduces production costs.
Smart Images
Figure CN121663034A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electric vehicle power battery management technology, and more specifically to a low-temperature heating circuit for electric vehicle batteries. Background Technology
[0002] In recent years, the electric vehicle industry has developed rapidly. Lithium-ion batteries, with their advantages of high energy density, environmental friendliness, and lack of memory effect, are the primary power source for electric vehicles. However, the performance of lithium-ion batteries degrades significantly in cold environments. Studies have shown that the capacity of lithium-ion batteries decreases by only 5% at -40°C compared to their capacity at room temperature. Furthermore, rapid charging at low temperatures may lead to lithium plating, further reducing battery capacity and posing safety hazards.
[0003] Low-temperature preheating is crucial for ensuring the normal operation of electric vehicles, especially in extremely cold regions. Batteries primarily employ two heating methods: external heating and internal heating. External heating utilizes hot air, liquids, and metals to heat the battery; however, due to the long heat transfer distance, this method suffers from significant energy loss and poor temperature uniformity. Internal heating can be further divided into self-heating and heating using an external power source, each with its own advantages.
[0004] Several heating strategies have been proposed to reduce battery damage during internal heating. These strategies effectively balance the rate of temperature rise and lithium deposition, but require an external AC power source, making them costly for electric vehicle applications.
[0005] Self-heating can reduce heating costs. However, a drawback is that the inductance and capacity must meet stringent requirements, which increases the production cost of electric vehicles. High-frequency AC heating reduces the risk of lithium plating to some extent, but its heating rate is lower than that of low-frequency current heating.
[0006] Therefore, self-heaters with low frequency, low cost, and low lithium deposition risk have significant research value. Bidirectional pulsed current heating achieves a good balance between heating rate and battery degradation. Studies show that the battery can function even under low temperature, high current, overcharge, or over-discharge conditions. Meanwhile, improving the heating rate and addressing slow and difficult charging are major problems in the current environment, and increasing heat generation by adding a few components has become a popular research direction. Although internal and external heating each have their drawbacks, combining internal and external heating—ensuring that internal heating does not damage the battery—can significantly increase the heating rate.
[0007] Currently, dual-motor driven electric vehicles are widely used in various environments. Therefore, it is necessary to specifically study the heating circuit and control method of the power battery of dual-motor driven electric vehicles, and solve the problem of unbalanced SOC of the two batteries when charging them in parallel on a 400V high-voltage platform after preheating.
[0008] Therefore, how to propose a low-temperature heating circuit for electric vehicle batteries, solve the lithium plating problem by preheating the power battery of single-motor or dual-motor electric vehicles, and avoid the SOC imbalance problem that occurs after the two batteries are preheated are problems that urgently need to be solved by those skilled in the art. Summary of the Invention
[0009] In view of this, the present invention provides a low-temperature heating circuit for batteries in electric vehicles, which solves the lithium plating problem by preheating the power battery of single-motor or dual-motor driven electric vehicles, and avoids the SOC imbalance problem that occurs after the two batteries have been preheated. To achieve the above objectives, the present invention adopts the following technical solution:
[0010] A low-temperature heating circuit for batteries in electric vehicles includes: a battery string, a switch S0, a combination switch, a resistor, an inverter bridge, and a motor. The battery string includes a first battery and a second battery connected in series. The positive and negative terminals of the first battery are connected to the positive and negative terminals of the second battery through the combination switch. The positive terminal of the first battery is connected to the upper arm of the inverter bridge, and the negative terminal of the second battery is connected to the lower arm of the inverter bridge. The inverter bridge is connected to the motor. The neutral point lead of the Y-connected stator winding of the motor is connected to the series connection point of the two batteries through the resistor and the switch S0.
[0011] Optionally, the combination switch includes switch S1, switch S2 and switch S3, wherein the negative terminal of the first battery is connected to the positive terminal of the second battery through switch S1; the positive terminal of the first battery is connected to the positive terminal of the second battery through switch S2; and the negative terminal of the first battery is connected to the negative terminal of the second battery through switch S3.
[0012] Optional features also include a charging port.
[0013] When the vehicle is parked and there is a need for low-temperature preheating, switches S0 and S1 are closed, and switches S2 and S3 are open, and the electric vehicle enters the low-temperature preheating state.
[0014] When the charging gun is not connected to the charging port and there is no need for low-temperature preheating, switches S0, S2, and S3 are open, and switch S1 is closed. The electric vehicle enters the motor drive state, which is powered by two 400V batteries connected in series. The DC bus voltage of the inverter bridge is 800V.
[0015] When an electric vehicle connected to an 800V busbar is connected to a 400V charging station charging gun, switches S0 and S1 are open, and switches S2 and S3 are closed. The first battery and the second battery are charged in parallel, and the electric vehicle enters the charging state.
[0016] When an electric vehicle connected to an 800V charging station is connected to an 800V charging gun, switches S0, S2, and S3 are open, and switch S1 is closed, and the electric vehicle enters the charging state.
[0017] Optionally, it also includes: controlling the current of the motor stator winding through a closed-loop negative feedback control method so that the current flowing through each phase stator winding is a symmetrical alternating current with the same frequency and phase, thereby generating an alternating current with opposite polarities for heating the two batteries.
[0018] Optionally, the method further includes: using a series resistor R0 to introduce a DC component into the AC heating current flowing through the battery, with the resistance value of R0 being positively correlated with the desired magnitude of the DC component; and conducting the heat generated by the series resistor R0 to the battery through a medium, thus simultaneously heating the battery internally and externally. A current sensor detects the current flowing through the stator windings, thereby controlling the opening and closing of the switching transistor and obtaining the AC current across the battery. For example, a heat pipe can be used to conduct the heat dissipated by the resistor to the battery, increasing the contact area between the heat pipe and the battery to improve heat transfer and generation. The series resistor enables control over battery durability and speed.
[0019] Optionally, the resistance value of the series resistor R0 is selected based on the battery SOC and battery temperature. Different resistance values are selected for different battery SOCs and battery temperatures. The resistance value is positively correlated with the battery SOC and negatively correlated with the battery temperature.
[0020] Optionally, the series resistor R0 is composed of multiple wide-line metal films connected in series or in parallel, and the resistance value of the series resistor is changed by switching on and off through a switch connected to the wide-line metal films.
[0021] Optionally, it also includes: changing the magnitude and frequency of the current flowing through the stator winding, thereby changing the motor losses, and thus changing the DC component of the battery heating current, wherein the larger the desired DC component, the larger the given values of the magnitude and frequency of the current flowing through the stator winding.
[0022] Optionally, this also includes using real-time detected battery SOC, battery temperature, and battery SOH to consult a calibration table and obtain the optimal current amplitude and frequency as the stator current frequency and amplitude setpoints. This allows for adjustment of motor losses, rapid temperature rise, and reduction of lithium plating risk. The principle for setting motor losses and resistance R0 is: the greater the detected motor loss, the greater the current or frequency of the stator winding. During charging, a minimum temperature threshold is set for the battery SOC; if the temperature falls below this threshold, the battery is heated.
[0023] Optionally, it also includes: the battery string supplies power to two sets of motors, the positive terminal of the first battery is connected to the upper arm of the two inverter bridges, the negative terminal of the first battery is connected to the positive terminal of the second battery, the negative terminal of the second battery is connected to the lower arm of the two inverter bridges, the two inverter bridges are respectively connected to two motors, and the two motors are connected to the series connection point of the two batteries through the Y-connection neutral point lead of the stator winding through the resistor and switch R0.
[0024] Optionally, it also includes: switches S0, S4, S5 and S6, a first detection unit, a first control unit, a second detection unit and a second control unit, the first control unit controls the switching transistor to turn on and off, and the second control unit controls the switching to turn on and off; the first detection unit detects the current through the stator winding of the three-phase motor, and the second detection unit detects the temperature and SOC of the first battery and the second battery;
[0025] The neutral point of the stator windings of the two motors is connected in a Y-type connection to the negative terminal of the first battery and the positive terminal of the second battery through switch S0. The negative terminal of the first battery and the positive terminal of the second battery are connected through switch S6. One end of the power input port is connected to the lower end of switch S6 through switch S4, and the other end is connected to the upper end of switch S6 through switch S5.
[0026] The second control unit controls switch S0 and switch S6 to be off, and switches S4 and S5 to be on, so as to charge the first battery and the second battery in parallel.
[0027] The second control unit controls switch S4 and switch S5 to be off, and switches S0 and S6 to be on, to carry out the SOC equalization process or heating process of the first battery and the second battery.
[0028] The second control unit controls switches S0, S4, and S5 to be off, and switch S6 to be on, so that the battery is connected in series to drive the three-phase motor via the inverter.
[0029] Optionally, the resistor is a variable resistor with four operating modes: when switches S7, S8, and S9 are all off, the resistance value is R1+R2+R3; when switch S7 is closed, the resistance value is R2+R3; when switch S9 is closed, the resistance value is R1+R2; and when switches S8 and S9 are closed, the resistance value is R1, where R3 = 2R1 = 2R2.
[0030] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a low-temperature heating circuit for electric vehicle batteries, which has the following beneficial effects:
[0031] This invention proposes a low-temperature heating circuit for electric vehicle batteries, comprising: a battery string, an inverter bridge, and a motor. The battery string includes a first battery and a second battery connected in series. The positive terminal of the first battery is connected to the upper arm of the inverter bridge, and the negative terminal is connected to the second battery. The negative terminal of the second battery is connected to the lower arm of the inverter bridge. The inverter bridge is connected to the motor, and the neutral point lead of the motor's Y-type stator winding is connected to the series connection point of the two batteries via a resistor. This invention (1) increases the heating rate by adding a resistor and proposes a corresponding heating strategy considering the overall circuit efficiency, thereby accelerating internal heating. (2) It realizes the multi-functionality of the circuit, including functions such as fast battery charging, low-temperature battery preheating, battery SOC balancing, and battery-driven motor operation. (3) It combines internal and external battery heating, thereby improving the overall temperature rise rate of the battery. (4) By adjusting the resistance, it reduces the risk of lithium plating in the battery and increases the heat generation rate of the battery. Attached Figure Description
[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.
[0033] Figure 1 This invention provides a schematic diagram of a low-temperature heating circuit for batteries in electric vehicles.
[0034] Figure 2 A flowchart illustrating the optimized strategy for resistance-regulated heating provided by this invention.
[0035] Figure 3 The schematic diagram of the dual-motor low-temperature preheating circuit provided by the present invention.
[0036] Figure 4 The schematic diagram of the dual-motor automotive preheating integrated circuit provided by the present invention.
[0037] Figure 5The schematic diagram of the 400V voltage platform charging circuit provided by the present invention.
[0038] Figure 6 This is a schematic diagram of the variable resistor R0 structure provided by the present invention.
[0039] Figure 7 The schematic diagram of the electric vehicle driving circuit provided by the present invention. Detailed Implementation
[0040] 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.
[0041] This invention provides a low-temperature heating circuit for electric vehicle batteries. By connecting a variable resistor R0 in series, a bipolar pulse heating current with a DC component is obtained, reducing the risk of lithium plating during charging and improving the heat generation rate. It achieves a combination of efficient internal and external heating, significantly improving the battery's temperature rise rate. A variable resistor adjustment optimization strategy is proposed, with different resistor selections under different SOC conditions. This method also possesses multi-functional integrated control capabilities for rapid battery self-heating, fast charging, driving modes, and SOC balancing, effectively solving the problem of slow heating and SOC balancing of power batteries under low-temperature conditions.
[0042] This invention discloses a low-temperature heating circuit for batteries in electric vehicles, comprising: a battery string, a switch S0, a combination switch, a resistor, an inverter bridge, and a motor. The battery string includes a first battery and a second battery connected in series. The positive and negative terminals of the first battery are connected to the positive and negative terminals of the second battery through the combination switch. The positive terminal of the first battery is connected to the upper arm of the inverter bridge, and the negative terminal of the second battery is connected to the lower arm of the inverter bridge. The inverter bridge is connected to the motor, and the neutral point lead of the Y-connected stator winding of the motor is connected to the series connection point of the two batteries through the resistor and the switch S0.
[0043] Furthermore, the combination switch includes switch S1, switch S2 and switch S3. The negative terminal of the first battery is connected to the positive terminal of the second battery through switch S1; the positive terminal of the first battery is connected to the positive terminal of the second battery through switch S2; and the negative terminal of the first battery is connected to the negative terminal of the second battery through switch S3.
[0044] Furthermore, it also includes: switches S0, S4, S5 and S6, a first detection unit, a first control unit, a second detection unit and a second control unit, the first control unit controls the switching transistors to open and close, and the second control unit controls the switches to open and close; the first detection unit detects the current through the stator windings of the three-phase motor, and the second detection unit detects the temperature and SOC of the first battery and the second battery;
[0045] The neutral point of the stator windings of the two motors is connected in a Y-type connection to the negative terminal of the first battery and the positive terminal of the second battery through switch S0. The negative terminal of the first battery and the positive terminal of the second battery are connected through switch S6. One end of the power input port is connected to the lower end of switch S6 through switch S4, and the other end is connected to the upper end of switch S6 through switch S5.
[0046] The second control unit controls switch S0 and switch S6 to be off, and switches S4 and S5 to be on, so as to charge the first battery and the second battery in parallel.
[0047] The second control unit controls switch S4 and switch S5 to be off, and switches S0 and S6 to be on, to carry out the SOC equalization process or heating process of the first battery and the second battery.
[0048] The second control unit controls switches S0, S4, and S5 to be off, and switch S6 to be on, so that the battery is connected in series to drive the three-phase motor via the inverter.
[0049] Furthermore, the resistor is a variable resistor with four operating modes: when switches S7, S8, and S9 are all off, the resistance value is R1+R2+R3; when S7 is closed, the resistance value is R2+R3; when switch S9 is closed, the resistance value is R1+R2; and when switches S8 and S9 are closed, the resistance value is R1, where R3 = 2R1 = 2R2.
[0050] Furthermore, the upper arm of the inverter is composed of multiple sets of sub-elements connected in series, the sub-elements including parallel-connected switching transistors and diodes, and the lower arm of the inverter is composed of multiple sets of sub-elements connected in series, the sub-elements including parallel-connected switching transistors and diodes, and the inverter is a switching transistor bridge.
[0051] In a specific implementation, the variable resistor includes multiple control elements connected in series. Each control element includes a resistor connected in parallel and a control switch. The resistance change of the variable resistor is positively correlated with the battery's State of Charge (SOC). By controlling the switching on and off of the switch via closed-loop negative feedback, an AC pulse current is generated in the winding. This, in turn, generates a bipolar pulse current with a DC component in the battery due to the influence of the variable resistor R0, significantly improving the battery's heat generation rate. This DC component is positively correlated with the resistance value. The series resistor increases internal heat generation within the battery, and the resistor itself also dissipates a significant amount of heat, which can be conducted to the battery through a medium. This combination of internal and external heating significantly improves the battery's temperature rise rate. The selection of the resistor is optimized based on the battery's SOC and frequency changes; a higher resistance results in a higher heat generation rate. This approach comprehensively considers battery durability and heat generation rate, selecting different resistance values at different SOCs to prioritize battery durability at low SOCs and prioritize heat generation rate at high SOCs.
[0052] In a specific implementation, the method also includes balancing the battery's state of charge (SOC), the specific process of which includes:
[0053] The upper or lower bridge arm is turned on, allowing the two batteries to charge and discharge each other through the upper bridge arm switch and the lower bridge arm diode or the lower bridge arm switch and the upper bridge arm diode. The battery SOC is detected by the battery management system (BMS).
[0054] The positive terminal of the first battery is connected to the upper arm of the inverter, and the negative terminal of the first battery is connected to the positive terminal of the second battery. The negative terminal of the second battery is connected to the lower arm of the inverter. The inverter outputs through the neutral point of the Y-type stator winding and is connected to the series connection point of the two batteries through a variable resistor. When the SOC of the first battery is greater than that of the second battery, the upper arm switch is turned on. The first battery discharges and flows into the stator winding of the three-phase motor through the upper arm, flows out through the neutral point, and the current flows into the negative terminal of the first battery and the positive terminal of the second battery. The current of the second battery charges the second battery, and the current of the lower arm merges with the current of the upper arm and flows into the three-phase motor winding.
[0055] This invention solves the problem of SOC imbalance between batteries and realizes circuit multifunctionality; it reduces the risk of lithium plating in batteries and improves the heat generation rate of internal preheating by series resistors; it further improves the internal heat generation rate of batteries by dynamically adjusting the resistance value; and it maximizes the battery temperature rise rate by combining internal and external heating.
[0056] In a specific embodiment, a low-temperature heating circuit for a battery in an electric vehicle specifically includes: an efficiency-based resistance adjustment optimization strategy to control battery durability and rate of change; the heating circuit principle circuit is as follows: Figure 1As shown, the positive and negative terminals of the two battery packs are connected together, and the other positive and negative terminals are connected to the two ends of the inverter bridge respectively. A variable resistor R0 is added to the line connecting the neutral point lead of the Y-connection of the motor stator winding and the midpoint of the two batteries.
[0057] By controlling the switching transistors to turn on and off using a closed-loop negative feedback control method, the current flowing through the motor stator windings is controlled, ensuring that the current flowing through the stator windings is a symmetrical alternating current. This generates alternating currents of opposite polarity for heating the two batteries, thus heating their internal structure. This internal heating method allows for rapid preheating of the batteries at low temperatures. The presence of the variable resistor R0 adds a DC component to the battery heating current, significantly increasing the battery's heat generation rate; the larger the DC component, the higher the battery's heat generation rate.
[0058] Internal heating generates heat from within the battery itself. While increasing internal heat generation, the resistor itself also dissipates a significant amount of heat. This heat can be transferred to the battery via heat pipes. Increasing the contact area between the heat pipes and the battery further enhances thermal conductivity and heat generation. Combining internal and external heating significantly improves the battery's temperature rise rate.
[0059] In specific implementation methods, such as Figure 2 The diagram illustrates an optimized heating strategy based on resistance regulation. The selection of the resistance value is crucial to this optimization. Increasing the resistance value increases the DC component of the heating current, thereby increasing the discharge current, decreasing the charging current, lowering the polarization voltage during charging, improving the heating rate, and reducing the risk of lithium plating. The internal heat generation of the battery is related to the amplitude and frequency of the current flowing through it, more specifically, to the effective value of the current. Increasing the resistance increases the effective value of the battery current, thus increasing internal heat generation. Simultaneously, increasing the resistance also increases the heat generated by the resistor itself, thereby accelerating external heating.
[0060] Of course, while increasing resistance accelerates both internal and external heating, it also has adverse effects, namely, reduced efficiency. Therefore, under different circumstances, the selection of resistance should be considered in combination with efficiency and heat generation rate.
[0061] The frequency of battery current and the state of charge (SOC) of the battery both affect the efficiency and heat generation rate as a function of resistance. At low SOC, a small resistance should be selected, sacrificing some heat generation rate to ensure sufficient battery durability. At medium SOC, the frequency has a greater impact; a small resistance should be selected at low frequencies and a large resistance at high frequencies. At high SOC, a large resistance should be selected to maximize the heat generation rate.
[0062] In specific implementation methods, such as Figure 3The diagram shows the SOC balancing circuit of a dual-motor tram, which also has a low-temperature preheating function. Battery BT1's positive terminal is connected to the upper arm of both inverter bridges, and its negative terminal is connected to battery BT2. Battery BT2's negative terminal is connected to the lower arm of both inverter bridges. The two inverter bridges are connected to the two motors respectively. The two motors are connected to the series connection point of the two batteries via the neutral point of their Y-type stator windings. When the two batteries have different SOCs, for example, BT1's SOC is greater than BT2's, BT1 needs to discharge to charge BT2. By turning on the two upper arms Q1, Q2, Q3, Q7, Q8, and Q9, BT1 discharges through the upper arms into the three-phase motor windings and out through the Y neutral point. The current then flows into the negative terminal of BT1 and the positive terminal of BT2, charging BT2 through the current in BT2. Finally, the current from BT1 merges with the current from the upper arms through the diodes in the lower arms and flows into the three-phase motor windings. If the SOC of BT2 is greater than that of BT1, then the lower bridge arm will conduct Q4, Q5, Q6, Q10, Q11, and Q12, for the same reason as above.
[0063] In a specific embodiment, the present invention proposes a multifunctional control method for the low-temperature heating circuit of a dual-motor driven electric vehicle, which includes controlling the heating circuit and the charging circuit, so as to realize multiple functions in a single circuit, including battery charging, battery discharging to drive the motor, self-heating through the motor circuit, and balancing the unequal SOC of the two batteries during charging or heating.
[0064] like Figure 4 The example shown illustrates a dual-motor application. This circuit, capable of the aforementioned functions, consists of three parts: first, the charging section, which includes a charging pile interface, switches S4, S5, and S6, and two batteries BT1 and BT2; next, the converter section, composed of two switching bridges, each including upper and lower bridge arms, with a total of 12 switching transistors Q1-Q12; and finally, the two three-phase motors, each composed of three inductors. The two batteries are connected in series with their positive and negative terminals connected. The two motors are connected to the series connection point of the two batteries via a Y-connection neutral point lead of the stator winding, through switch S0 and a resistor. The other end of the stator winding is connected to the midpoint of the inverter bridge arm.
[0065] The first detection unit includes a current sensor on the stator winding of a three-phase motor, whose detection signal is input to the first control unit to control the switching transistor's on / off state. The second detection unit is a battery management system (BMS), whose detection signal is input to the first and second control units to control the switching transistor and the switch's on / off state.
[0066] In a specific implementation, the charging process is as follows: After the second detection unit (BMS) detects the connection to the charging pile, it controls the second control unit (PDU) to close switches S4 and S5, while other switches are turned off, thus connecting batteries BT1 and BT2 in parallel. Figure 5As shown, it can be charged simultaneously under a 400V voltage platform to achieve fast charging.
[0067] Preheating process: The second control unit closes control switches S0 and S6, and turns off other switches. The specific circuit is as follows: Figure 3 As shown.
[0068] When the battery temperature falls below a certain threshold, the preheating circuit is activated by the second detection unit. The preheating current is an alternating current. The control method for R0 is as follows: Figure 6 As shown, it has four operating modes, meaning four resistance values are available: When switches S7, S8, and S9 are all off, the resistance value is R1 + R2 + R3; when switch S7 is closed, the resistance value is R2 + R3; when switch S9 is closed, the resistance value is R1 + R2; and when switches S8 and S9 are closed, the resistance value is R1, where R3 = 2R1 = 2R2. The AC current can be obtained using a closed-loop negative feedback control method. A current sensor detects the current flowing through the stator windings, thereby controlling the opening and closing of the switches and obtaining the AC current across the battery.
[0069] In a specific implementation, to prevent lithium plating, the optimal preheating current frequency and amplitude are first obtained through table lookup or online calculation at different temperatures and battery SOCs. Then, based on real-time battery SOC, battery temperature, and battery SOH, a calibration table is consulted to obtain the optimal current amplitude and frequency as the setpoints for the stator current frequency and amplitude. This achieves adjustment of motor losses, rapid heating, and reduction of the risk of lithium plating. The principle for setting motor losses and resistance R0 is: the greater the detected motor loss, the greater the current magnitude or frequency of the stator winding. Changing the magnitude and frequency of the current flowing through the stator winding changes the motor loss, thereby changing the DC component of the battery heating current. Specifically, the greater the magnitude and frequency of the current flowing through the stator winding, the greater the motor loss and the greater the DC component. Since the battery temperature may decrease during extremely low-temperature charging, a minimum temperature threshold needs to be set for each battery SOC during charging. If the temperature is too low, the battery needs to be reheated.
[0070] The calibration table is set according to the following principles: the lower the battery temperature, the smaller the battery current, and the smaller the inductor current needs to be, or the battery current frequency needs to be increased; the higher the battery SOC, the smaller the battery current, and the smaller the inductor current needs to be, or the battery current frequency needs to be increased.
[0071] In a specific implementation, if an imbalance in the State of Charge (SOC) of the two batteries is detected after charging is complete, continued use is permitted. Figure 3The preheating circuit performs a battery SOC balancing process. When the SOC of battery BT1 is less than that of battery BT2, the two lower bridge arms Q4, Q5, Q6, Q10, Q11, and Q12 are turned on, and BT2 charges BT1. The charging current gradually decreases as the SOC approaches the same level until the second detection unit detects that the SOCs of the two batteries are the same. When the SOC of battery BT1 is greater than that of battery BT2, the two upper bridge arms Q1, Q2, Q3, Q7, Q8, and Q9 are turned on, and BT1 charges BT2. Similarly, the charging current gradually decreases as the SOC approaches the same level until the second detection unit detects that the SOCs of the two batteries are the same level.
[0072] After all processes are completed and the car is fully charged, the driving mode can be activated. The second control unit opens switches S0, S4, and S5, and closes switch S6. The two motors are then driven by the two batteries connected in series. Figure 7 As shown, the inverter bridge acts as an inverter, converting the near-DC power generated by the power battery into three-phase AC power through a three-phase inverter, which drives the AC motor and thus propels the car.
[0073] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.
[0074] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A low-temperature heating circuit for a battery in an electric vehicle, characterized in that, include: The system comprises a battery string, a switch S0, a combination switch, a resistor, an inverter bridge, and a motor. The battery string includes a first battery and a second battery connected in series. The positive and negative terminals of the first battery are connected to the positive and negative terminals of the second battery through the combination switch. The positive terminal of the first battery is connected to the upper arm of the inverter bridge, and the negative terminal of the second battery is connected to the lower arm of the inverter bridge. The inverter bridge is connected to the motor. The neutral point lead of the Y-connected stator winding of the motor is connected to the series connection point of the two batteries through the resistor and the switch S0.
2. The low-temperature heating circuit for a battery in an electric vehicle according to claim 1, characterized in that, The combination switch includes switch S1, switch S2 and switch S3. The negative terminal of the first battery is connected to the positive terminal of the second battery through switch S1; the positive terminal of the first battery is connected to the positive terminal of the second battery through switch S2; and the negative terminal of the first battery is connected to the negative terminal of the second battery through switch S3.
3. The low-temperature heating circuit for a battery in an electric vehicle according to claim 1, characterized in that, It also includes a charging port. When the vehicle is parked and there is a need for low-temperature preheating, switches S0 and S1 are closed, and switches S2 and S3 are open, and the electric vehicle enters the low-temperature preheating state. When the charging gun is not connected to the charging port and there is no need for low-temperature preheating, switches S0, S2, and S3 are open, and switch S1 is closed. The electric vehicle enters the motor drive state, which is powered by two 400V batteries connected in series. The DC bus voltage of the inverter bridge is 800V. When an electric vehicle connected to an 800V busbar is connected to a 400V charging station charging gun, switches S0 and S1 are open, and switches S2 and S3 are closed. The first battery and the second battery are charged in parallel, and the electric vehicle enters the charging state. When an electric vehicle connected to an 800V charging station is connected to an 800V charging gun, switches S0, S2, and S3 are open, and switch S1 is closed, and the electric vehicle enters the charging state.
4. A low-temperature heating circuit for a battery in an electric vehicle according to claim 1, characterized in that, Also includes: By controlling the current of the motor stator windings through a closed-loop negative feedback control method, the current flowing through each phase of the stator windings is made into a symmetrical alternating current with the same frequency and phase, thereby generating an alternating current with opposite polarities for the two batteries to heat the batteries internally.
5. A low-temperature heating circuit for a battery in an electric vehicle according to claim 1, characterized in that, Also includes: By using a series resistor R0, the AC heating current flowing through the battery has a DC component. The value of the series resistor R0 is positively correlated with the magnitude of the required DC component. The heat generated by the series resistor R0 is conducted to the battery through a medium, thus simultaneously heating the battery internally and externally.
6. A low-temperature heating circuit for a battery in an electric vehicle according to claim 5, characterized in that, The resistance value of the series resistor R0 is selected based on the battery SOC and battery temperature. Different resistance values are selected for different battery SOC and battery temperature. The resistance value is positively correlated with the battery SOC and negatively correlated with the battery temperature.
7. A low-temperature heating circuit for a battery in an electric vehicle according to claim 6, characterized in that, The series resistor R0 is composed of multiple wide-line metal films connected in series or in parallel, and the resistance value of the series resistor is changed by switching on and off the switch connected to the wide-line metal films.
8. A low-temperature heating circuit for a battery in an electric vehicle according to claim 1, characterized in that, Also includes: Changing the magnitude and frequency of the current flowing through the stator winding alters the motor losses, which in turn changes the DC component of the battery heating current. The larger the desired DC component, the larger the given values of the current magnitude and frequency flowing through the stator winding.
9. A low-temperature heating circuit for a battery in an electric vehicle according to claim 8, characterized in that, It also includes using real-time detected battery SOC, battery temperature, and battery SOH to look up calibration tables and obtain the optimal current amplitude and frequency as the setpoint values for the stator current frequency and amplitude.
10. A low-temperature heating circuit for a battery in an electric vehicle according to claim 1, characterized in that, Also includes: The battery string supplies power to two sets of motors. The positive terminal of the first battery is connected to the upper arm of the two inverter bridges, the negative terminal of the first battery is connected to the positive terminal of the second battery, and the negative terminal of the second battery is connected to the lower arm of the two inverter bridges. The two inverter bridges are connected to the two motors respectively. The two motors are connected to the series connection point of the two batteries through the neutral point lead of the stator winding Y-connection, through the resistor and switch R0.
11. A low-temperature heating circuit for a battery in an electric vehicle according to claim 10, characterized in that, Also includes: Switches S0, S4, S5, and S6; a first detection unit, a first control unit, a second detection unit, and a second control unit; the first control unit controls the on / off state of the switching transistors, and the second control unit controls the on / off state of the switches; the first detection unit detects the current passing through the stator windings of the three-phase motor, and the second detection unit detects the temperature and SOC of the first and second batteries; The neutral point of the stator windings of the two motors is connected in a Y-type connection to the negative terminal of the first battery and the positive terminal of the second battery through switch S0. The negative terminal of the first battery and the positive terminal of the second battery are connected through switch S6. One end of the power input port is connected to the lower end of switch S6 through switch S4, and the other end is connected to the upper end of switch S6 through switch S5. The second control unit controls switch S0 and switch S6 to be off, and switches S4 and S5 to be on, so as to charge the first battery and the second battery in parallel. The second control unit controls switch S4 and switch S5 to be off, and switches S0 and S6 to be on, to carry out the SOC equalization process or heating process of the first battery and the second battery. The second control unit controls switches S0, S4, and S5 to be off, and switch S6 to be on, so that the battery is connected in series to drive the three-phase motor via the inverter.