A battery heating circuit based on transformer and electric vehicle

Abstract

The present application provides a transformer-based battery heating circuit and electric vehicle, relating to the field of power battery technology. In this battery heating circuit, a first sub-battery and a second sub-battery are connected in series to form a first battery half-bridge circuit, a third sub-battery and a fourth sub-battery are connected in series to form a second battery half-bridge circuit, and the first battery half-bridge circuit and the second battery half-bridge circuit are connected in parallel. The transformer is provided with a primary side and a secondary side, with the two ends of the secondary side connected to the midpoint of the first battery half-bridge circuit and the midpoint of the second battery half-bridge circuit, respectively, and one end of the primary side connected to one of a set of preset endpoints. A three-phase motor is connected to the other end of the primary side and a three-phase inverter, respectively, and the three-phase motor is connected to the transformer via a heating relay. This battery heating circuit achieves the technical advantages of low component heat generation during battery heating, can be used while the vehicle is in motion, and has minimal impact on the motor's power.

Description

Technical Field

[0001] The present application relates to the technical field of power batteries, and in particular to a transformer-based battery heating circuit and an electric vehicle. Background Art

[0002] Currently, new energy vehicles (NEVs) are vehicles that use unconventional fuels as their power source (or use conventional fuels with new onboard power units), integrating advanced technologies in vehicle power control and drive to create advanced technical principles, new technologies, and new structures. New energy vehicles include pure electric vehicles and hybrid electric vehicles.

[0003] Due to the poor low-temperature performance of electric vehicle power batteries, methods are currently needed to increase battery temperature at low temperatures. Common battery heating methods typically use methods such as positive temperature coefficient (PTC) resistors and heat generated by the electric drive system to heat the cold-spot fluid, which then heats the battery, achieving indirect heating. Alternatively, a motor controller can charge and discharge the motor windings, generating an AC current within the battery. This heat is then heated by the battery's internal resistance, a process known as direct internal resistance heating, or self-heating. Among these commonly used battery heating methods, indirect heating is highly inefficient, with a significant amount of heat not effectively transferred to the battery and dissipated into the environment. Heat transfer is slow, requiring heat to be transferred to the battery through the cold-spot fluid and the battery's external structure, resulting in a slow temperature rise. Battery heating is uneven, with cells closer to the cold-spot fluid experiencing a faster temperature rise. Traditional direct heating methods using motor windings suffer from a low heating current frequency, typically around 2 kHz, which is highly sensitive to the human ear and produces a high level of noise. These methods are difficult to use while the vehicle is in motion and can easily cause torque jitter or affect motor power output. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a transformer-based battery heating circuit and an electric vehicle, which can achieve the technical effects of less component heat generation when heating the battery, heating in driving state, and little impact on the motor power.

[0005] In a first aspect, an embodiment of the present application provides a transformer-based battery heating circuit, comprising a battery pack, a transformer, a three-phase inverter, a heating relay, and a three-phase motor;

[0006] The battery pack includes a first sub-battery, a second sub-battery, a third sub-battery, and a fourth sub-battery, wherein the first sub-battery and the second sub-battery are connected in series to form a first battery half-bridge circuit, the third sub-battery and the fourth sub-battery are connected in series to form a second battery half-bridge circuit, and the first battery half-bridge circuit and the second battery half-bridge circuit are connected in parallel;

[0007] The transformer is provided with a primary side and a secondary side, the two ends of the secondary side are respectively connected to the midpoint of the first battery half-bridge circuit and the midpoint of the second battery half-bridge circuit, and one end of the primary side is connected to one of the endpoints of a preset endpoint set, the preset endpoint set including the midpoint of the second battery half-bridge circuit, the positive pole of the DC bus, the negative pole of the DC bus, the internal level point of the battery, the positive and negative bus capacitor voltage divider point, the midpoint of the DC bus capacitor, and the second battery half-bridge;

[0008] The three-phase motor is connected to the other end of the primary side and the three-phase inverter respectively, and the three-phase motor is connected to the transformer through the heating relay.

[0009] In the above implementation process, when battery heating is required, the heating relay is closed, and the three-phase current of the three-phase motor is controlled through the PWM modulation of the three-phase inverter regardless of whether the vehicle is in the parked or running state, so that the three-phase motor generates corresponding torque (in the driving state, it drives the vehicle to run; when the vehicle is stationary, it outputs zero torque); the PWM modulation of the three-phase inverter will generate a common-mode voltage in the three-phase motor, and the common-mode voltage acts on the transformer and generates an alternating current on the secondary side of the transformer. The alternating current flows through the internal resistance of each sub-battery in the battery pack, and the battery is heated and heated, thereby improving the performance of the battery in a low-temperature environment and enhancing the vehicle's endurance and power; thus, the battery heating circuit can achieve the technical effects of less component heat generation when heating the battery, heating in the driving state, and little impact on the motor power.

[0010] Furthermore, the three-phase inverter includes three power switch tube assemblies, one end of the power switch tube assembly is connected to one end of the first battery half-bridge circuit, and the other end of the power switch tube assembly is connected to the other end of the second battery half-bridge circuit.

[0011] Furthermore, the power switch tube assembly includes two power switch tubes, and the two power switch tubes are connected in series.

[0012] Furthermore, the three-phase motor is provided with three cables, and the three cables are respectively connected to the three power switch tube assemblies.

[0013] Furthermore, the battery heating circuit further includes a capacitor, and the capacitor and the heating relay are connected in series.

[0014] Furthermore, the battery heating circuit further includes a first relay, which is connected in series to one end of the first battery half-bridge circuit.

[0015] Furthermore, the battery heating circuit further includes a second relay, which is connected in series to the other end of the first battery half-bridge circuit.

[0016] In the above implementation process, the first relay and the second relay are respectively the positive and negative relays of the battery pack.

[0017] Furthermore, the three-phase motor is a star-connected three-phase motor.

[0018] Furthermore, the three-phase motor is one of a permanent magnet synchronous motor, a brushless motor, and an asynchronous motor.

[0019] In a second aspect, an embodiment of the present application provides an electric vehicle, comprising the transformer-based battery heating circuit described in any one of the first aspects.

[0020] Other features and advantages disclosed in the present application will be described in the following description, or some features and advantages can be inferred or determined without doubt from the description, or can be learned by implementing the above-mentioned technology disclosed in the present application.

[0021] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0023] Figure 1a A circuit diagram of a first transformer-based battery heating circuit provided in an embodiment of the present application;

[0024] Figure 1b A circuit diagram of a second transformer-based battery heating circuit provided in an embodiment of the present application;

[0025] Figure 1c A circuit diagram of a third transformer-based battery heating circuit provided in an embodiment of the present application;

[0026] Figure 1d A circuit diagram of a fourth transformer-based battery heating circuit provided in an embodiment of the present application;

[0027] Figure 1e A circuit diagram of a fifth transformer-based battery heating circuit provided in an embodiment of the present application;

[0028] Figure 1fA circuit diagram of a sixth transformer-based battery heating circuit provided in an embodiment of the present application;

[0029] Figure 1g A circuit diagram of a seventh transformer-based battery heating circuit provided in an embodiment of the present application;

[0030] Figure 2 A simplified model schematic diagram of a transformer-based battery heating circuit provided in an embodiment of the present application;

[0031] Figure 3 A circuit diagram of a battery heating circuit for a battery stack provided in an embodiment of the present application;

[0032] Figure 4 A circuit diagram of a battery heating circuit for batteries connected in series according to an embodiment of the present application;

[0033] Figure 5 A circuit diagram of the first single-cell half-bridge provided in an embodiment of the present application;

[0034] Figure 6 A circuit diagram of a second single-cell half-bridge provided in an embodiment of the present application;

[0035] Figure 7 A schematic diagram of a circuit in which the primary circuit provided in an embodiment of the present application is connected to one phase of a motor. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0037] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and should not be understood as indicating or implying relative importance.

[0038] The embodiment of the present application provides a transformer-based battery heating circuit and an electric vehicle, which can be used in the battery heating process; when battery heating is required, the heating relay is closed, and no matter whether the vehicle is in the parked or running state, the three-phase current of the three-phase motor is controlled through the PWM modulation of the three-phase inverter, so that the three-phase motor generates corresponding torque (in the driving state, it drives the vehicle to run; when the vehicle is stationary, it outputs zero torque); the PWM modulation of the three-phase inverter will generate a common-mode voltage in the three-phase motor, and the common-mode voltage acts on the transformer and generates an alternating current on the secondary side of the transformer. The alternating current flows through the internal resistance of each sub-battery in the battery pack, and the battery is heated and heated, thereby improving the performance of the battery in a low-temperature environment and enhancing the vehicle's endurance and power; thus, the battery heating circuit can achieve the technical effects of less component heat generation when heating the battery, heating in the driving state, and little impact on the motor power.

[0039] See Figure 1a , Figure 1a This is a circuit diagram of a first transformer-based battery heating circuit provided in an embodiment of the present application. The transformer-based battery heating circuit includes a battery pack 100, a transformer 200, a three-phase inverter 300, a heating relay Ka and a three-phase motor 400.

[0040] Illustratively, the battery pack 100 includes a first battery sub-battery U1, a second battery sub-battery U2, a third battery sub-battery U3, and a fourth battery sub-battery U4. The first battery sub-battery U1 and the second battery sub-battery U2 are connected in series to form a first battery half-bridge circuit, the third battery sub-battery U3 and the fourth battery sub-battery U4 are connected in series to form a second battery half-bridge circuit, and the first battery half-bridge circuit and the second battery half-bridge circuit are connected in parallel.

[0041] In some embodiments, the first and second battery sub-cells U1 and U2 are symmetrical, and the third and fourth battery sub-cells U3 and U4 are symmetrical. The voltages of the first and third battery sub-cells U1 and U3 are the same, and the voltages of the second and fourth battery sub-cells U2 and U4 are the same. The first and second battery sub-cells U1 and U2, and the third and fourth battery sub-cells U3 and U4 are connected in series to form two "half-bridge" circuits, which are then connected in parallel to form a "full-bridge."

[0042] Optionally, the first sub-battery U1 and the third sub-battery U3 have different capacities, and the second sub-battery U2 and the fourth sub-battery U4 have different capacities, so as to maintain consistent temperature rise.

[0043] Exemplarily, the transformer 200 is provided with a primary side and a secondary side, the two ends of the secondary side are respectively connected to the midpoint of the first battery half-bridge circuit and the midpoint of the second battery half-bridge circuit, and one end of the primary side is connected to one of the endpoints of a preset endpoint set, and the preset endpoint set includes the midpoint of the second battery half-bridge circuit, the positive pole of the DC bus, the negative pole of the DC bus, the internal level point of the battery, the positive and negative bus capacitor voltage divider points, and the midpoint of the DC bus capacitor of the second battery half-bridge.

[0044] For example, Figure 1a In the illustrated embodiment, one end of the primary side is connected to the midpoint of the second battery half-bridge circuit. A secondary side of a transformer 200 is connected between the midpoints of the first and second battery half-bridge circuits. One end of the primary side of transformer 200 is also connected to the midpoint of the second battery half-bridge circuit, meaning that this end is also connected to the opposite-signal terminal of the secondary side. The transformer ratio is designed based on the battery voltage, internal resistance, and required heating power.

[0045] For example, a transformer is a device that uses the principle of electromagnetic induction to change AC voltage. Its main components are a primary coil, a secondary coil, and an iron core (magnetic core). Its main functions include voltage conversion, current conversion, impedance conversion, and isolation. According to their use, they can be divided into power transformers and special transformers (furnace transformers, rectifier transformers, industrial frequency test transformers, voltage regulators, mining transformers, audio transformers, medium frequency transformers, high frequency transformers, impulse transformers, instrument transformers, electronic transformers, reactors, mutual inductors, etc.). Among them, the primary side of the transformer 200 refers to the input side of the voltage, and the secondary side refers to the output side of the voltage after the voltage is converted by the transformer.

[0046] Exemplarily, the three-phase motor 400 is connected to the other end of the primary side of the transformer 200 and the three-phase inverter 300 respectively, and the three-phase motor 400 is connected to the transformer 200 via a heating relay Ka.

[0047] For example, the heating relay Ka can be used to cut off the circuit for protection in the event of a vehicle failure, and can also be used to cut off the circuit and stop battery heating when there is no need for battery heating.

[0048] For example, when battery heating is required, the heating relay Ka is closed, and the three-phase current of the three-phase motor is controlled by the PWM modulation of the three-phase inverter 300 regardless of whether the vehicle is in the parked or running state, so that the three-phase motor 400 generates corresponding torque (in the driving state, it drives the vehicle to run; when the vehicle is stationary, it outputs zero torque); the PWM modulation of the three-phase inverter 300 will generate a common-mode voltage in the three-phase motor 400, and the common-mode voltage acts on the transformer and generates an alternating current on the secondary side of the transformer. The alternating current flows through the internal resistance of each sub-battery in the battery pack 100, and the battery generates heat and heats up, thereby improving the performance of the battery in a low-temperature environment and enhancing the vehicle's endurance and power. Therefore, the battery heating circuit can achieve the technical effects of less component heat generation when heating the battery, heating in the driving state, and little impact on the motor power.

[0049] For example, pulse width modulation (PWM) is an analog control method that modulates the bias of a transistor base or field-effect transistor gate based on changes in the corresponding load to change the on-time of the transistor or field-effect transistor, thereby changing the output of a switching power supply. This method can maintain a constant output voltage despite changes in operating conditions and is a very effective technique for controlling analog circuits using digital signals from a microprocessor. It is widely used in many fields, from measurement and communications to power control and conversion.

[0050] In some embodiments, the three-phase inverter 300 can be controlled using SPWM (sinusoidal PWM modulation), SVPWM (space vector PWM modulation) or other modulation methods, such as DPWM (discontinuous PWM modulation); it should be noted that the PWM modulation method of the three-phase inverter 300 here is only an example and not a limitation.

[0051] Exemplarily, the three-phase inverter 300 includes three power switch tube assemblies, one end of the power switch tube assembly is connected to one end of the first battery half-bridge circuit, and the other end of the power switch tube assembly is connected to the other end of the second battery half-bridge circuit.

[0052] Exemplarily, the power switch tube assembly includes two power switch tubes, which are connected in series.

[0053] Exemplarily, the three power switch tube assemblies include six power switch tubes Q1 to Q6 , namely, six semiconductor power switch tubes of the three-phase inverter 300 that drive the three-phase motor 400 to operate.

[0054] In some embodiments, the power switch tube of the power switch tube assembly may be a semiconductor power switch device such as a field effect transistor, an insulated gate bipolar transistor, or the like.

[0055] Exemplarily, the three-phase motor is provided with three cables, and the three cables are respectively connected to three power switch tube assemblies.

[0056] Exemplarily, the battery heating circuit further includes a capacitor, and the capacitor and the heating relay are connected in series.

[0057] For example, the transformer 200 is connected to the three-phase motor 400 via a capacitor Cn and a heating relay Ka. The capacitor Cn isolates the DC current to prevent the transformer 200 from saturating, and resonates with the common-mode inductance of the three-phase motor 400 and the leakage inductance of the transformer 200.

[0058] It should be noted that when the primary circuit of the transformer is connected, because the primary coil, capacitor Cn (i.e., resonant capacitor), and heating relay Ka are all connected in series, their relative order does not affect the circuit. When the primary coil, capacitor Cn, and heating relay Ka are connected in series, all circuits of different arrangements are equivalent.

[0059] In some embodiments, the transformer 200 is connected to the neutral point of the three-phase motor 400 connected in star connection via a capacitor Cn and a heating relay Ka.

[0060] Exemplarily, the battery heating circuit further includes a first relay K1 , which is connected in series to one end of the first battery half-bridge circuit.

[0061] Exemplarily, the battery heating circuit further includes a second relay K2 , which is connected in series to the other end of the first battery half-bridge circuit.

[0062] For example, the first relay K1 and the second relay K2 are respectively the positive relay and the negative relay of the battery pack 100 .

[0063] Exemplarily, the three-phase motor 400 is a star-connected three-phase motor.

[0064] For example, during PWM modulation, the three-phase inverter 300 controls the three-phase current of the three-phase motor 400, thereby enabling the motor 400 to generate the torque required by the vehicle. These PWM modulations generate a high-frequency common-mode voltage at the neutral point of the star-connected three-phase motor 400. The primary frequency component of this high-frequency common-mode voltage is the switching frequency of the three-phase inverter bridge (i.e., the three-phase inverter 300).

[0065] Exemplarily, the three-phase motor is one of a permanent magnet synchronous motor, a brushless motor, and an asynchronous motor.

[0066] For example, an embodiment of the present application provides an electric vehicle, the electric vehicle comprising Figure 1a The transformer-based battery heating circuit shown.

[0067] For example, one end of the "primary circuit" (i.e., the primary coil + capacitor Cn + heating relay Ka) in the battery heating circuit provided in the embodiment of the present application is connected to the neutral point of the motor, which is one of the optional connection methods; in some embodiments, when there is a coupling capacitor in the battery heating circuit, one end of the primary circuit can be connected to the midpoint of the battery bridge in addition to being connected in the following manner.

[0068] See Figure 1b , Figure 1b A circuit diagram of a second transformer-based battery heating circuit provided in an embodiment of the present application; Figure 1b As shown, one end of the primary circuit is connected to the positive pole of the DC bus; optionally, one end of the primary circuit can be connected to the left end or the right end of K1, which is not limited here.

[0069] See Figure 1c , Figure 1c A circuit diagram of a third transformer-based battery heating circuit provided in an embodiment of the present application; Figure 1c As shown, one end of the primary circuit is connected to the negative pole of the DC bus; the principle is the same as above, and it can be connected to the left or right end of K2, which is not limited here.

[0070] See Figure 1d , Figure 1d A circuit diagram of a fourth transformer-based battery heating circuit provided in an embodiment of the present application; Figure 1d As shown, one end of the primary circuit is connected to the internal level point of the battery. The internal level point of the battery can be any level point inside the battery, not necessarily the middle point.

[0071] See Figure 1e , Figure 1e A circuit diagram of a fifth transformer-based battery heating circuit provided in an embodiment of the present application; Figure 1e As shown, the capacitor Cn becomes a "three-terminal capacitor" (divided into capacitor Cn1 and capacitor Cn2), with its two ends connected across the positive and negative busbars (i.e., the positive and negative busbar capacitors divide the voltage), and the center point connected to the primary circuit (at this time, the primary circuit = heating relay Ka + primary coil).

[0072] For example, Figure 1e Compared with the connection shown Figures 1a to 1dThe advantages of the connection method shown are: after the circuit is powered on (K1 and K2 are closed), the initial voltage of capacitors Cn1 and Cn2 is basically the same as the voltage during stable operation. When the circuit starts to heat up, there is little transient resonance such as the voltage of capacitors Cn1 and Cn2 and the current flowing through the primary side from the start of operation to the steady-state resonance. This is beneficial to reducing the transient maximum voltage and maximum current on components such as the transformer and capacitor Cn (= Cn1 + Cn2), thereby helping to reduce the specification requirements for these components and achieve cost reduction.

[0073] For example, Figures 1a to 1d In the connection method shown, the initial voltage on capacitor Cn after power-on is generally zero. During steady-state resonant heating, the voltage is approximately half the DC bus voltage. Therefore, there is a transition process from the initial state to the steady state. During this process, there will be instantaneous large values ​​of the voltage across capacitor Cn and the primary current. This requires components to use larger specifications, which will lead to increased costs.

[0074] See Figure 1f , Figure 1f A circuit diagram of a sixth transformer-based battery heating circuit provided in an embodiment of the present application; Figure 1f As shown, the primary circuit is connected to the midpoint of the DC bus capacitor Cdc, and the DC bus capacitor Cdc is divided into two parts (capacitor Cdc1 and capacitor Cdc2), with equal capacitance. This connection method also has the advantage of small transient process, but the DC bus capacitor Cdc becomes complex and the cost is high.

[0075] See Figure 1g , Figure 1g A circuit diagram of a seventh transformer-based battery heating circuit provided in an embodiment of the present application; Figure 1g As shown, in Figure 1f On this basis, the capacitor Cn is omitted, and the DC bus capacitor takes into account both the resonance and DC isolation functions; this connection method needs to take into account the normal DC bus voltage stabilization function of the DC bus capacitor Cdc, and the resonance and DC isolation function during heating.

[0076] See Figure 2 , Figure 2 A simplified model diagram of a transformer-based battery heating circuit provided in an embodiment of the present application.

[0077] For example, if the transformation ratio of the transformer 200 is large enough so that the primary current of the transformer 200 is negligible compared to the secondary current, then Figure 1a The circuit can be simplified to Figure 2 The circuit model shown.

[0078] Exemplarily, Ucom is the common-mode voltage of the three-phase motor 400 relative to the midpoint of the series battery pack 100; Ls is the common-mode inductance, including the common-mode inductance of the three-phase motor 400, the leakage inductance of the transformer 200 and the stray inductance of the cable; Lm is the excitation inductance of the transformer 200; and R is the internal resistance of the entire battery pack 100.

[0079] For example, when the vehicle is stopped, regardless of whether SPWM or SVPWM modulation is used, Ucom is a square wave with a frequency equal to the switching frequency of the three-phase inverter bridge. When the vehicle is running, the Ucom waveform deviates from the square wave, but the frequency of the main component remains the switching frequency of the three-phase inverter bridge. Therefore, to simplify the analysis, it can be assumed that Ucom is a sine wave with a frequency equal to the three-phase inverter bridge frequency.

[0080]

[0081] Among them, the function η(f s / f ac ,m) is the adjustment coefficient of the common mode voltage amplitude under different working conditions, which is the motor current frequency f ac and the voltage utilization factor m of the three-phase inverter 300.

[0082] When the vehicle stops and the three-phase motor 400 is stationary, under the condition of adopting SVPWM modulation or SPWM modulation, the following are obtained:

[0083]

[0084] Valid values ​​are:

[0085]

[0086] according to Figure 2 In the circuit described above, assuming that Lm is much larger than Ls and can be ignored, the effective value of the current on the internal resistance R can be calculated as:

[0087]

[0088] Wherein, the transformation ratio of the transformer 200 is n=Np / Ns, f r is the resonant frequency of Ls and Cn, Z r is the resonant impedance, and their relationship with Ls and Cn is as follows:

[0089]

[0090]

[0091] The current flowing through the neutral point of the motor is:

[0092]

[0093] From Equation 4 and Equation 7, we can get:

[0094]

[0095] For example, the working modes of the battery heating circuit provided in the embodiments of the present application are as follows:

[0096] Ls is basically controlled by the common-mode inductance of the three-phase motor 400 and has a very small adjustable range. Therefore, the main adjustable quantities of the circuit are the capacity of Cn and the transformer ratio n.

[0097] Choose Cn so that f s ≈f r , then:

[0098]

[0099]

[0100] On this basis, n is selected according to the heating power P required by the battery, that is:

[0101]

[0102] At this time there are:

[0103]

[0104] In this mode, it can be seen from Equation 4 that by adjusting the switching frequency f s , the heating power can be adjusted within a certain range. When battery heating is not required at all, the heating relay Ka is switched.

[0105] The transformer-based battery heating circuit provided in the example of this application has a small common-mode current flowing through the motor during operation, and therefore has the following advantages: a) when heating the battery, components such as the three-phase motor 400 generate less heat; b) when heating the battery while driving, the impact on dynamic performance is small.

[0106] For example, because the battery heating circuit operates in a resonant state and transformer 200 transforms the battery's internal resistance, which is very small on the secondary side, to a larger resistance on the primary side, the circuit has a high power factor, resulting in a relatively low current flowing through the motor's neutral point and minimal motor heating. During driving mode heating, the current flowing through the midpoint is relatively low, and the current distributed across the motor's three phases is only one-third of the midpoint current. Therefore, only a small amount of current capacity is required from the three motor phases for battery heating, leaving the majority of the remaining capacity available to drive the motor. This minimizes the impact on the motor's output capacity during driving mode.

[0107] In some implementation scenarios, for a certain electric drive system, the battery voltage is 400V, the internal resistance of the entire package is 20mΩ, the common-mode inductance of the motor is 15uH, the rated switching frequency of the inverter is 10kHz, the rated current of each of the three phases of the inverter is 300A effective value, the short-time peak current is 530A effective value, and the target battery heating power is 20kW. The transformer ratio is selected as 9, Cn = 16.9uF. At this time, the effective value of the neutral current is only 111A, and after being evenly distributed to the three phases, each phase is only 37A, which is much less than the rated current and peak current. However, at this time, the battery heating current on the secondary side of the transformer reaches 1000A, which can enable the battery to obtain a heating power of 20kW.

[0108] For example, the resonant frequency f r You can choose a switching frequency much higher than the normal one, such as 20kHz. When heating is required, the switching frequency f s Increase to close to f r When heating is required, the temperature is very low, which allows the inverter switching frequency to be increased, thereby increasing the inverter's heat generation to heat the cold zone liquid.

[0109] Optionally, the connection method between the transformer 200 and the battery pack 100 can be varied in many ways, and the number of transformers 200 and battery packs 100 can be multiple. This example only uses two transformer combinations. For example, the transformer 200 can have primary sides connected in parallel or series, secondary sides connected in parallel or series, multiple secondary sides each forming a "battery full bridge", multiple battery full bridges connected in series or parallel, and so on. Various other combinations are possible.

[0110] See Figure 3 and Figure 4 , Figure 3 This is a circuit diagram of a battery heating circuit for a battery stack provided in an embodiment of the present application. Figure 4 This is a circuit diagram of a battery heating circuit with batteries connected in series according to an embodiment of the present application; wherein the battery pack 100 includes eight sub-batteries U1 to U8 and two transformers 200.

[0111] In some embodiments, while heating the battery, the heat generated by the battery can be used to heat the cold zone liquid, and then heat the crew cabin through a heat pump or other means.

[0112] In some embodiments, injecting a high-frequency alternating current into a battery can be used to measure the internal impedance of the battery, thereby obtaining the temperature and health status of the battery.

[0113] See Figure 5 , Figure 5 This is a circuit diagram of the first single-battery half-bridge provided in an embodiment of the present application.

[0114] In some implementation scenarios, if the battery pack cannot be split into two half-bridges, a set of capacitors can be used to implement a half-bridge, such as Figure 5 As shown, capacitors Cb1 and Cb2 are used to form a half bridge.

[0115] See Figure 6 , Figure 6 This is a circuit diagram of the second single-battery half-bridge provided in an embodiment of the present application.

[0116] Optionally, the DC bus capacitor Cdc of the motor three-phase inverter may be split into two parts Cdc1 and Cdc2 to form a capacitor half-bridge.

[0117] See Figure 7 , Figure 7 A schematic diagram of a circuit in which the primary circuit provided in an embodiment of the present application is connected to one phase of a motor.

[0118] For example, Figures 1a to 6 For all the connection methods shown, the other end of the primary circuit can be connected directly to one phase of the motor instead of the neutral point of the motor, such as Figure 7 The principle is basically the same, except that the primary side of the transformer changes from the common mode voltage of the neutral point of the motor to the voltage of one of the three phases.

[0119] It should be noted that in Figures 1a to 7 In the circuit shown, even if not marked in the circuit diagram, the three-phase inverter 300 includes a DC bus capacitor Cdc by default.

[0120] In the several embodiments provided in this application, it should be understood that the functional modules in each embodiment can be integrated together to form an independent part, or each module can exist separately, or two or more modules can be integrated to form an independent part.

[0121] The foregoing is merely an embodiment of the present application and is not intended to limit the scope of protection of the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included within the scope of protection of the present application. It should be noted that similar reference numerals and letters represent similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined or explained in subsequent figures.

[0122] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

[0123] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

Claims

1. A transformer-based battery heating circuit, characterized in that: Includes battery pack, transformer, three-phase inverter, heating relay and three-phase motor; The battery pack includes a first sub-battery, a second sub-battery, a third sub-battery, and a fourth sub-battery, wherein the first sub-battery and the second sub-battery are connected in series to form a first battery half-bridge circuit, the third sub-battery and the fourth sub-battery are connected in series to form a second battery half-bridge circuit, and the first battery half-bridge circuit and the second battery half-bridge circuit are connected in parallel; The transformer is provided with a primary side and a secondary side, the two ends of the secondary side are respectively connected to the midpoint of the first battery half-bridge circuit and the midpoint of the second battery half-bridge circuit, and one end of the primary side is connected to one of the endpoints of a preset endpoint set, the preset endpoint set including the midpoint of the second battery half-bridge circuit, the positive pole of the DC bus, the negative pole of the DC bus, the internal level point of the battery, the positive and negative bus capacitor voltage divider point, and the midpoint of the DC bus capacitor; The three-phase motor is connected to the other end of the primary side and the three-phase inverter respectively, and the three-phase motor is connected to the transformer through the heating relay; The transformation ratio of the transformer is determined according to the battery voltage, the battery internal resistance, and the battery heating power. When the battery heating circuit operates in a resonant state, the secondary resistance and the primary resistance are transformed by the transformer.

2. The transformer-based battery heating circuit according to claim 1, characterized in that The three-phase inverter includes three power switch tube assemblies, one end of the power switch tube assembly is connected to one end of the first battery half-bridge circuit, and the other end of the power switch tube assembly is connected to the other end of the second battery half-bridge circuit.

3. The transformer-based battery heating circuit according to claim 2, characterized in that: The power switch tube assembly includes two power switch tubes, and the two power switch tubes are connected in series.

4. The transformer-based battery heating circuit according to claim 2, characterized in that The three-phase motor is provided with three cables, and the three cables are respectively connected to the three power switch tube assemblies.

5. The transformer-based battery heating circuit according to claim 1, characterized in that The battery heating circuit further includes a capacitor, which is connected in series with the heating relay.

6. The transformer-based battery heating circuit according to claim 1, characterized in that The battery heating circuit further includes a first relay connected in series to one end of the first battery half-bridge circuit.

7. The transformer-based battery heating circuit according to claim 6, characterized in that The battery heating circuit further includes a second relay connected in series to the other end of the first battery half-bridge circuit.

8. The transformer-based battery heating circuit according to claim 1, characterized in that The three-phase motor is a star-connected three-phase motor.

9. The transformer-based battery heating circuit according to claim 1 or 8, characterized in that: The three-phase motor is one of a permanent magnet synchronous motor, a brushless motor and an asynchronous motor.

10. An electric vehicle, characterized in that: The electric vehicle comprises the transformer-based battery heating circuit according to any one of claims 1 to 9.

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