CN116039341B

CN116039341B - Motor heating method, computer equipment, readable storage medium and electric vehicle

Info

Publication number: CN116039341B
Application number: CN202310333480.2A
Authority: CN
Inventors: 陈子豪; 曹然
Original assignee: Zhejiang Zero Run Technology Co Ltd; Zhejiang Lingsheng Power Technology Co Ltd
Current assignee: Zhejiang Zero Run Technology Co Ltd; Zhejiang Lingsheng Power Technology Co Ltd
Priority date: 2023-03-28
Filing date: 2023-03-28
Publication date: 2023-06-30
Anticipated expiration: 2043-03-28
Also published as: CN116039341A

Abstract

The invention discloses a motor heating method, computer equipment, readable storage medium and an electric vehicle, and relates to the technical field of new energy automobiles; wherein the heating mode comprises at least a rapid heating mode, and the rapid heating mode is set in a state that the motor is at rest or locked-rotor; starting the rapid heating mode, and inputting direct current and high-frequency voltage to a direct shaft of the motor; the motor heating method has the advantages of low cost, high heating efficiency and higher comfort level for users.

Description

Motor heating method, computer equipment, readable storage medium and electric vehicle

Technical Field

The invention relates to the technical field of new energy automobiles, in particular to a motor heating method, computer equipment, a readable storage medium and an electric vehicle.

Background

The performance of the power battery of the electric automobile is reduced along with the reduction of the ambient temperature in the daily use process. The low temperature can raise the viscosity of the electrolyte of the battery, thereby reducing the charge and discharge performance of the battery and greatly reducing the cruising ability of the electric automobile. In addition, the low temperature environment can also affect the comfort of personnel in the cabin. Therefore, in order to ensure the charge and discharge performance of the battery and to improve the comfort in the cabin, the battery and the cabin need to be heated in a low-temperature environment.

In order to solve the problems of the electric automobile in the low-temperature environment, a special heating device is usually arranged in the whole automobile system. Among them, the most widely used and straightforward is to achieve heating using positive temperature coefficient (Positive Temperature Coefficient, PTC) thermistors. However, the scheme has the problems of high cost, large occupied space, increased parts of the whole vehicle and the like.

Therefore, how to effectively utilize the existing modules in the electric vehicle system to heat, and reduce or replace the special heating devices becomes one of important research directions. In the whole vehicle architecture, the motor in the electric drive system is the element closest to the PTC, so it can be studied how to use the motor for sufficient heating.

In the traditional motor auxiliary heating method, current is mostly only conducted in the direction of a motor direct axis, and the current can be in a direct current or alternating current mode, but the current is controlled by a controller to beat and dynamically respond, and even if the current is conducted, the frequency is not very high, so that the traditional scheme mainly utilizes copper loss of the motor to heat, and the heat generated by the iron loss of the motor is limited. For example, in the chinese patent application No. 202080019346X, a motor controller, a heat exchange system and a current injection method are provided for improving the heating efficiency of a motor. The motor controller includes a control device and an inverter circuit. The control device is used for controlling the inverter circuit to input alternating current to the motor, wherein the alternating current has direct current bias and is used for heating the motor; the inverter circuit is used for outputting the alternating current to a direct axis or a zero axis of the motor under the control of the control device.

The inventors of the present application found that in the above-described scheme, the alternating current is realized by using switching power devices in an inverter, and that in view of the cost, the switching frequency of the power devices is generally selected to be within 20kHz, a sine wave equal to (or close to) the frequency of the switching power devices cannot be modulated when modulating the sine wave alternating current by using the alternating current. In addition, the frequency of the sine wave alternating current which is generally modulated is not more than 1/5 of the frequency of the switching power device under the limitation of the bandwidth of the current loop. On the one hand, noise with different degrees can be generated at the frequency, the frequency falls in the acceptable range of human ears, and the tolerance degree of different individuals to the noise is inconsistent, so that the alternating current is output to the direct axis or the zero axis of the motor to heat the motor, and bad experience is brought to users; on the other hand, when the iron loss of the motor is increased by using the alternating current for heating, the heating power and the frequency of the alternating current are positively correlated in a certain range, and the heating quantity of the iron loss is low due to the limitation of the current frequency (lower than 1/5 of the frequency of a switching power device).

In summary, how to develop a motor heating method, a computer device, a readable storage medium and an electric vehicle with low cost, high heating efficiency and high comfort for users under the condition of fully utilizing the existing structure, not additionally adding devices or improving the existing system with low cost is a urgent problem to be solved by those skilled in the art.

Disclosure of Invention

The present invention aims to solve one of the technical problems in the related art to a certain extent. Therefore, the invention provides a motor heating method, computer equipment, a readable storage medium and an electric vehicle, which have the advantages of low cost, high heating efficiency and higher comfort level for users.

In order to achieve the above object, the present invention adopts the following technical scheme in a first aspect:

a motor heating method is used for supplying heat to a heat exchange system of an electric vehicle in a low-temperature environment, and comprises the following steps,

determining a heating mode of the motor according to the operating state of the motor in response to the heating start signal; wherein the heating mode comprises at least a rapid heating mode, and the rapid heating mode is set in a state that the motor is at rest or locked-rotor;

and starting the rapid heating mode, and inputting direct current and high-frequency voltage to a direct shaft of the motor.

According to the scheme, on the basis that the copper loss of the motor is increased to heat by using direct current, high-frequency voltage is injected into the direct shaft of the motor to increase the iron loss and heat generation of the motor, the direct-current motor is directly applied to the existing structure, any additional equipment is not required to be additionally added, and the copper loss and the iron loss of the motor are fully utilized. The high-frequency voltage can be directly modulated by an inverter circuit (of a system containing an alternating current motor), an energy storage element and an additional control element are not needed, and the method is not limited. In addition, when the high-frequency voltage is modulated by the switching power device in the inverter circuit, the frequency of the modulated high-frequency voltage can be close to or equal to the frequency of the switching power device, and compared with the modulation alternating current, the frequency conversion has little damage. The frequency of the selected switching power device is higher, especially more than 20kHz, so that the hearing range of the human ear can be exceeded, and the influence of noise on a user is reduced. Even though the frequency of the selected switching power device does not exceed 20kHz, compared with the scheme adopting alternating current, the frequency is hardly broken in the modulation process, so that even if noise exists, the frequency is higher, compared with low-frequency noise, the high-frequency noise is easily absorbed by obstacles in the propagation process, and the bad experience of the noise to users can be greatly reduced. At the same time, the frequency is increased to correspondingly increase the heating power of the iron loss.

Optionally, the waveform of the high-frequency voltage is a square wave. The square wave modulation mode is relatively simple, the change of the existing circuit is small, and for example, the square wave can be modulated directly through a direct current chopper circuit.

Optionally, the waveform of the high-frequency voltage is a unipolar square wave, a bipolar square wave or any one of composite square waves formed by combining unipolar and bipolar square waves. These waveforms all fall into the category of square waves, which are relatively easy to modulate.

Optionally, the working states of the motor comprise a static state, a locked rotor state, a low-speed running state and a high-speed running state;

when the rotating speed of the motor is 0r/min, setting the motor to be in a static state or a locked-rotor state;

when the rotating speed of the motor is less than or equal to Nr/min, setting the motor to a low-speed running state;

when the rotating speed of the motor is greater than Nr/min, setting the motor to be in a high-speed running state;

wherein N is E [2500,3500].

The heating mode is further set according to the working state of the motor and the heating starting signal, so that the motor is divided into more adjacent use scenes.

Optionally, the heating start signal is generated by a vehicle control terminal or when the battery temperature detection module detects that the temperature is lower than a preset value. The method is characterized in that an active mode and a passive mode are adopted to generate a starting signal respectively, wherein the active mode is mainly used at a vehicle control end, a user judges that the temperature is too low through a sense of body (a seat or an environment) and operates the vehicle control end, the passive mode is mainly used for detecting the temperature of a battery pack through a battery temperature detection module, and when the battery temperature detection module detects that the temperature is lower than a preset value, the starting signal is generated to prevent the battery pack from working at a low temperature and affecting the performance. Both of the two modes combine the requirements of the actual scene, and the division is quite reasonable and necessary.

Optionally, the heating mode further includes a normal heating mode and a dynamic heating mode;

wherein the normal heating mode is configured in a motor stationary or locked-rotor state or in a motor low-speed operation state; the dynamic heating mode motor is configured in a low speed operating state.

The heating modes are further subdivided, more choices are provided for users, and different requirements of the users are met.

Optionally, in the dynamic heating mode, the direct current or/and the high-frequency high-voltage is/are input to the direct shaft of the motor, and the heating power is dynamically adjusted along with the output torque power of the motor, and the adjusting step includes:

obtaining a maximum current value of sustainable operation of a motor controller;

determining a phase current minimum operation value and a maximum torque Tm which can be output under the current according to the heating power requirement;

when the motor set running torque is lower than the maximum torque Tm, the current vector angle under the synchronous rotation coordinate system is adjusted, the given current vector is redistributed, and the residual current is used for heating all under the condition that the output torque reaches the required value.

Under the condition of meeting the requirement of torque output, namely meeting active power, the remaining reactive power is dynamically distributed to be used for heating, and the total power is maintained to be stable as far as possible within the maximum current value of sustainable operation of the controller.

Compared with the existing scheme adopting thermistor heating, the method does not need to use extra equipment or increase the volume and cost of the system, and the method can directly heat by using inherent equipment (a motor) of the system, so that the cost and the space are saved.

The method provides more than two heating modes and provides a diversified choice for users. In addition, under the condition of equal heating power, the current generated by injecting high-frequency square wave voltage is lower than the alternating current (used for heating), and the alternating current is safer relatively.

In addition, the invention also provides a computer device in a second aspect, comprising a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to realize the motor heating method.

The computer equipment provided by the invention is similar to the reasoning process of the beneficial effects of the motor heating method, and is not repeated here.

Also, the present invention provides in a third aspect a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, implements the above-described motor heating method.

Meanwhile, the invention also provides an electric vehicle in a fourth aspect, the electric vehicle comprises a motor, a controller and a heat exchange system, and the electric vehicle adopts the motor heating method in the first aspect to supply heat to the heat exchange system in a low-temperature environment;

or the electric vehicle has the computer device described in the second aspect;

or the electric vehicle has a computer-readable storage medium as described in the third aspect, which implements the motor heating method as described in the first aspect when being executed by a processor.

These features and advantages of the present invention will be disclosed in more detail in the following detailed description and the accompanying drawings. The best mode or means of the present invention will be described in detail with reference to the accompanying drawings, but is not limited to the technical scheme of the present invention. In addition, these features, elements, and components are shown in plural in each of the following and drawings, and are labeled with different symbols or numerals for convenience of description, but each denote a component of the same or similar construction or function.

Drawings

The invention is further described below with reference to the accompanying drawings:

fig. 1 is a schematic block diagram of a motor heating method according to the present invention.

Fig. 2 is a flowchart of the operation of the motor of the present invention in the normal heating mode.

Fig. 3 is a flowchart of the operation of the motor of the present invention in the rapid heating mode.

Fig. 4 is a timing diagram of the high frequency voltage of the present invention between one switching cycle and the original control signal.

Fig. 5 is a waveform diagram of three-phase current output of the motor after injection of high frequency voltage (square wave) into the direct axis of the motor according to the present invention.

Fig. 6 is a graph showing actual operation results of three-phase current of the motor in the normal heating mode according to the present invention.

Fig. 7 is a graph showing actual operation results of three-phase current of the motor in the rapid heating mode according to the present invention.

Fig. 8 is a graph comparing the heating power variation of the direct axis of the motor according to the present invention under the condition of injecting different voltage and current amplitudes.

Detailed Description

Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The examples in the embodiments are intended to illustrate the present invention and are not to be construed as limiting the present invention.

Reference in the specification to "one embodiment" or "an example" means that a particular feature, structure, or characteristic described in connection with the embodiment itself can be included in at least one embodiment of the present patent disclosure. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

Prior to the description of the embodiments, the related technical background of the present invention will be briefly described. In the electric drive system of the new energy automobile, the consumed power of the motor can be divided into two parts: the mechanical power used for generating torque to drive an external load to operate and the lost power for generating heat dissipation are characterized in that the first part of power is related to the rotating speed of the motor and the output torque and is used for doing useful work and cannot be used for heating, and the second part of power is the useful work consisting of copper loss and iron loss of the motor and can be dissipated into the environment in a heat form. Therefore, the motor needs to fully utilize the power of the second part of the motor to ensure that the copper consumption and the iron consumption of the motor are as large as possible.

The copper loss refers to the loss generated by the AC/DC current flowing through the copper conductor, and since the application object of the embodiment of the invention is a permanent magnet synchronous motor, the copper loss is generated only at the stator side, and the heating power is I ² R represents the effective value of current flowing through the copper conductor, and R represents the total resistance of the copper conductor. As can be seen from the expression, there are two ways to increase the copper consumption of the motor, one is to increase the current through the motor windings, and the other is to increase the resistance of the motor windings. Obviously, after the motor is produced, the stator resistance cannot be changed in a large range, so the only way to increase the copper loss is to increase the effective value of the winding current.

The term "iron loss" means a loss of magnetic flux generated by an alternating magnetic field in a core cast of a ferromagnetic material, and includes hysteresis loss, eddy current loss, parasitic loss, and the like. In the permanent magnet synchronous motor, the stator and the rotor are cast by using iron cores, so that iron loss can be generated in the stator and the rotor. Because the motor is a complex multivariable, nonlinear and strongly coupled system, the analytic relationship between the losses and the alternating magnetic field is difficult to obtain, and accurate quantitative analysis cannot be performed. However, from prior experience, it is known that the qualitative relationship between the iron loss and the current flowing through the windings, i.e. the higher the frequency of the current flowing through the stator windings of the motor, the greater the amplitude, the greater the resulting iron loss. Therefore, in order to obtain a larger iron loss, it is necessary to increase the frequency and amplitude of the current flowing through the winding as much as possible. The invention increases heating power according to the principles of increasing copper loss and iron loss, and compared with the scheme of increasing iron loss by alternating current in the background art, the invention adopts high-frequency voltage to increase iron loss, and the invention is described below with specific implementation.

Examples:

the invention increases heating power according to the principles of increasing copper consumption and iron consumption, as shown in fig. 1, and in this embodiment, a motor heating method is provided, which is applied to a motor of an electric vehicle and is used for supplying heat to a heat exchange system of the electric vehicle in a low-temperature environment. According to the method, under the conditions that the existing structure in the electric vehicle is fully utilized, no additional equipment is added or the existing system is improved in low cost, direct current and high-frequency voltage are input to the direct shaft of the motor in a superposition mode, copper loss generated by the direct current and iron loss generated by the high-frequency voltage are fully utilized for heating, and the method is low in cost, high in heating efficiency and higher in user comfort. Specifically, according to the operation condition of the motor, the heating is further divided into two modes of static locked-rotor heating and rotating (or dynamic, i.e. in a low-speed operation state of the motor) heating, and in addition, in the static locked-rotor heating, two modes of rapid heating and normal heating exist.

The motor heating method in this embodiment includes the following steps:

and judging the working state of the motor.

The current working state of the motor comprises a static state, a locked-rotor state, a low-speed running state and a high-speed running state. When the rotating speed of the motor is 0r/min, setting the motor to be in a static state or a locked-rotor state; when the rotating speed of the motor is less than or equal to Nr/min, setting the motor to a low-speed running state; and when the rotating speed of the motor is larger than Nr/min, setting the motor to be in a high-speed running state, wherein N is E [2500,3500]. In this embodiment, n=3000 r/min is taken as an example, and the motor is set to a low-speed operation state when the motor rotation speed is equal to or less than 3000 r/min. And when the rotating speed of the motor is greater than 3000r/min, setting the motor to be in a high-speed running state.

And acquiring a heating start signal.

The heating start signal is generated by a user operating at a vehicle control end or when the battery temperature detection module detects that the temperature is lower than a preset value.

The temperature detected by the battery temperature detection module is the temperature of the battery pack, so as to avoid the battery from operating at a low temperature. And thus generates a heating start signal to heat the battery when the temperature is lower than a preset value. The user can actively select the setting by operating the vehicle control end, namely, under the condition of starting the vehicle (namely, when the vehicle is in the vehicle), the setting can be remotely set by the application of the mobile terminal, and then the setting is transmitted by utilizing the wireless communication between the mobile terminal and the electric vehicle, so that the motor enters a heating mode in advance, and the motor does not need to output torque at the moment, so that all power can be used for heating on copper loss and iron loss.

In response to the heating start signal, a heating mode of the motor is determined based on an operating state of the motor.

The heating modes include a normal heating mode, a rapid heating mode, and a dynamic heating (i.e., rotational heating) mode.

Wherein the normal heating mode is configured in a motor stationary or locked-rotor state or in a motor low-speed operation state; the rapid heating mode is configured in a motor stationary or locked-rotor state; the dynamic heating mode motor is configured in a low speed operating state.

When the motor is in a stationary or locked-rotor state, the user can select only one of the normal heating mode and the rapid heating mode to operate. When the motor is in a low-speed operation state, the user can select only one of the normal heating mode and the dynamic heating mode to operate.

It should be noted that, the heating modes (in the static or locked state) are divided into a rapid heating mode and a normal heating mode, and the main reason is that high-frequency whistle may be generated during the rapid heating process, so that for some users with abnormal sensitivity, when the system does not need rapid heating, a more comfortable normal heating mode can be selected.

And according to the determined heating mode starting, inputting a heating power supply corresponding to the heating mode to a direct shaft of the motor, wherein the heating power supply comprises direct current and high-frequency voltage, the direct current mainly utilizes copper loss to generate heat, and the high-frequency voltage mainly utilizes iron loss to generate heat.

It should be noted that the waveform of the high-frequency voltage is a square wave (which may be a unipolar square wave or a bipolar square wave, or any one of composite square waves formed by combining unipolar and bipolar waves), a triangular wave, a trapezoidal wave, and a sawtooth wave, where the square wave modulation mode is relatively simple, and the change of the existing circuit is less, and in this embodiment, the inverter is directly used to control the space vector pulse width modulation.

In order to reduce the adverse effect of noise, the frequency of the high-frequency voltage is preferably controlled to be above 18kHz, in this embodiment, 5kHz or 10kHz, even though the frequency is within the range of human ears, the frequency of the noise generated by the alternating current is still higher (5 times to 10 times higher than the frequency of the noise generated by the alternating current), and the higher frequency is easier to be absorbed by obstacles, so that the noise generated by the alternating current has smaller influence on users under the same sound insulation measure.

More specifically, when the normal heating mode is started, a direct current is input to the direct shaft of the motor. The normal heating mode mainly uses copper loss of the stator winding of the motor to heat, constant direct current is injected into the direct shaft of the motor, at the moment, the generated power is dissipated on the inherent resistance of the stator winding, and the resistance is used for continuous heating. The normal heating mode is specifically implemented as follows:

a complete normal heating mode execution flow chart is shown in fig. 2. Firstly, the controller receives a heating instruction in a static locked state of the motor, namely, a user selects a normal heating mode in the heating modes, and generates a heating starting signal. The controller then obtains the current rotor position from the motor position encoder to determine the direct and quadrature axis positions. Then, the current loop of the controller starts to work, the set value of the direct axis is set to be the maximum current value, the value is set to be-400A in the system, the set value of the quadrature axis is set to be zero, no effective torque component is generated in the heating process of the injected current, and the system is kept to be stationary at the current position. Wherein the direct current set point is ramped up to a maximum value, reducing the step shock of the system. Further, since the motor is in a stationary state, although a current is applied to the synchronous rotation coordinate system, the three-phase current obtained by the final control still assumes a direct current state. Finally, the current loop controls the current of the orthogonal axis at a set value, so that the system is ensured to continuously heat until a heating stopping instruction is received, namely the heating starting signal disappears.

When the rapid heating mode is started, direct current and high-frequency voltage are simultaneously input to the direct shaft of the motor, and in the system, the amplitude of the injection voltage is 40% of the direct current bus voltage, and the maximum injectable voltage is 57.7%. The rapid heating mode is to inject additional high-frequency voltage based on direct current injection in the normal heating mode, and fully utilizes copper loss of the motor stator winding and iron loss of the stator and rotor windings to heat. The specific implementation of the rapid heating mode is as follows:

a complete rapid heating mode execution flow chart is shown in fig. 3. First, the controller receives a heating command in a state in which the motor is stationary locked, i.e., the user selects a rapid heating mode among the heating modes. The controller then obtains the current rotor position from the motor position encoder and determines the current straight and quadrature axis positions. The previous two steps are consistent with the normal heating mode. The reference value of the controller current loop is then ramped up to a set maximum value, i.e., to-400A, while the high frequency injection voltage, here 40% dc bus voltage, is added to the output control dc voltage. The form of the high frequency injection voltage and its relationship to the original control signal is shown in fig. 4 during a switching cycle, where the injection voltage will change positively and negatively once during a PWM cycle. Because the control system adopts a double-sampling double-updating control mode, the positive direct-axis voltage is accumulated in the first half period, the negative direct-axis voltage is accumulated in the second half period, the average value of the direct-axis voltage output in one switching period is ensured to be zero, and no bias current is generated. After the injection of the high frequency voltage square wave signal, the three-phase current output value of the motor is shown in fig. 5, where ia represents the a-phase current waveform, ib represents the B-phase current waveform, and ic represents the C-phase current waveform. As can be seen from the figure, the switching frequency of the switching tube is 5kHz, and the frequency of the high-frequency current excited by the injection voltage coincides with the switching frequency. Fig. 5 shows three-phase current waveforms of the motor in the case of injecting only high-frequency voltage, the direct current injection is set to 0A, the motor rotor is positioned at 330 degrees in the electrical angle during testing, the current ripple generated on the a-phase current is maximum, the peak-peak value reaches 110A, the ripple generated by the C-phase current is minimum, and the peak-peak value is about 20A along with the injection of the high-frequency voltage.

In addition, since the high-frequency voltage signal and the direct current signal are injected on the direct shaft of the motor, no effective torque component is generated, and the static state of the motor can be maintained. Finally, the current loop controls the average value of the three-phase currents to a reference value, and heating is continued until a heating stopping command is received. Since the high frequency voltage signal is injected, the current loop controls the average current of one switching cycle to the target value at the time of control, which requires that the sampling point must be set in the middle of the zero vector, ensuring that no ripple current is sampled.

The actual running results of the three-phase current of the motor under the working conditions of the normal heating mode and the rapid heating mode are shown in fig. 6 and 7. In accordance with fig. 5, ia, ib, and ic appearing in fig. 6 and 7 represent A, B, C three-phase currents of the motor, respectively. In fig. 6, the injected direct current is set to-400A, the injected high frequency voltage is set to 0V, and after the three-phase currents ia, ib and ic are respectively 380A, -80A and-320A, which satisfy the three-phase currents and are zero, when the motor rotor position is stopped. In fig. 7, the injection dc setting was kept-400A, and the injection high frequency voltage was changed from 0V to 140.8V (40% of the dc bus voltage of the present system was 352V). By comparing the two experimental results, it can be found that after the high-frequency voltage is additionally injected, relatively wide ripple waves are added to the original three-phase current which presents direct current, and the magnitude of the ripple wave amplitude and the magnitude of the direct current amplitude of each three-phase current are related to the position of the motor rotor. The closer to the rotor straight axis, the larger the phase current DC amplitude and ripple amplitude.

In addition, high-frequency current excited by high-frequency voltage is injected, so that the effective value of current acting in a three-phase winding of the motor is increased, copper loss is increased, and on the other hand, the iron loss of a stator and a rotor is greatly increased due to alternating change of phase current, and the heating power of the motor is increased from two aspects. The high-frequency voltage injection has the advantages that the control of the current loop is bypassed, the injection frequency is not limited by the bandwidth of the current loop, and the signal injection with the same frequency as the switching frequency can be realized, so that the iron loss of the motor is further improved. The disadvantage is that audible high frequency howling occurs during injection, and because the tolerance of different people to the high frequency howling is not consistent, two modes of operation are provided for the user to choose from in this embodiment. In the occasion that needs rapid heating, the user can bear the trouble of high-frequency howling for a short time, so that the rapid heating mode is selected, high-frequency voltage is additionally injected, and the temperature rise of the system is accelerated. Under the situation that the heating speed is not required strongly, a user can select a normal heating mode, only direct current is injected, no high-frequency howling is generated at the moment, but the heating power is limited, and the heating speed of the system is low.

The ultimate power of heat generated by the two heating modes is mainly limited by the temperature rise conditions of all components of the electric drive system, and a great amount of experimental tests prove that the three-phase copper bar connected with the controller and the motor is the component which has the highest temperature rise in the whole system but cannot be quickly replaced by heat. Therefore, the voltage and current mixed injection amplitude described in the heating method provided in this embodiment needs to be obtained through testing in a temperature rise bottoming experiment. The test is used on the one hand to determine the amplitude of the injected voltage current and on the other hand to determine the limit power value at which the electric drive system can stably sustain heating.

As shown in fig. 8, the heating power variation condition under the condition of different injection voltages and current amplitudes is shown in fig. 8, and the rated bus voltage of the motor adopted by the system is 352V. The horizontal axis of the histogram represents the proportion of the amplitude of the injected high-frequency voltage to the voltage of the direct-current bus, and the vertical axis represents the heating power value under the corresponding working condition. When the high-frequency voltage is not injected, the system is in a normal heating mode, and when the direct current is injected from left to right and is-200A, -300A, -400A, the heating power is sequentially 1.3kW, 2.15kW and 2.43kW; when the amplitude of the injected high-frequency voltage is 30% of the amplitude of the direct-current bus, the heating power under the condition of the same direct-current amplitude injection is 2.6kW, 3.49kW and 3.84kW in sequence; when the amplitude of the injected high-frequency voltage is 40% of the amplitude of the direct-current bus, the heating power under the condition of the same direct-current amplitude injection is 4.3kW, 5.32kW and 5.71kW in sequence. From the experimental results, it can be seen that the heating power is continuously increased with the increase of the magnitudes of the injected direct current and the high frequency voltage.

As mentioned above, the amplitude cannot be increased infinitely, and through tests, the injection DC amplitude-300A is selected in the system, and the high-frequency voltage amplitude which is 40% of the DC bus is a working point which can stably and continuously run, and the heating power at the moment is 5.32kW.

It should be noted that when the inverter is controlled using space vector pulse width modulation and the system is operating in the linear region, the maximum injectable high frequency voltage does not exceed 57.7% of the dc bus. Meanwhile, the current loop also needs to be controlled to inject direct current, so that the selection of the high-frequency voltage needs to be further limited according to the parameter characteristics of the system in order to ensure that the current loop has enough adjusting capability.

When the dynamic heating mode is started, the direct current or the high-frequency high voltage can be input in a superimposed manner on the basis of the driving current input to the direct shaft of the motor, or the heat can be generated by inputting the direct current and the high-frequency high voltage in a superimposed manner. In this embodiment, copper loss heating is described by superimposing a direct current on a direct axis.

When the motor is in a low-speed running state and the rotating speed is lower than 3000 rpm, the user can automatically start the dynamic heating mode, namely the rotary heating mode after selecting the heating mode. The specific principle of the implementation of the rotary heating mode is as follows:

first, the controller receives a command for (rotational) heating, at which time the motor should be in a rotational control output torque state. In the conventional torque control, the motor running operating point is determined according to the maximum torque current ratio, and the motor phase current is small under the condition of low speed and low torque, and the loss generated by the motor phase current cannot generate enough heat. Therefore, in order to realize motor heating in a low-speed low-torque state, a reference command value of a current loop needs to be adjusted, and the motor heating power is ensured. The reference command value of the current loop is changed to a given value in a slope mode, so that the operation impact of the motor caused by mode switching is reduced as much as possible. After the rotary heating mode is switched, the current loop keeps the motor to output stable torque according to the set heating working point, and heating is continuously performed until a heating stopping instruction is received. After the heating command is stopped, the reference value of the current loop is gradually reduced to the maximum torque current ratio working point, and the current loop is switched into the initial control mode after the torque is stable.

The rotary heating mode is to heat by copper loss and iron loss of the motor together, and the heating power mainly comes from the copper loss under the condition of low speed and low torque. When the motor is in a rotating operation condition, the controller can utilize the current loop to regulate the three-phase current of the motor according to the maximum torque current ratio. At this time, three-phase current will form losses in the stator and the rotor in the form of alternating current, the three-phase current first generates copper losses in the stator windings, the magnitude of which is proportional to the effective value of the current, while alternating three-phase current will generate iron losses in the stator and the rotor, the magnitude of which is related to both the amplitude and the frequency of the current.

Therefore, under the condition that the motor operates at high torque or high speed, the iron loss and copper loss generated by the three-phase current per se already meet the heating power requirement, and the operating working point of the motor does not need to be changed. If the motor operates in a low-speed low-torque state, the three-phase current is small in amplitude and low in frequency, and the heating power requirement cannot be met by the iron loss and the copper loss, so that the working point of the motor needs to be changed.

To confirm the operating point of the motor in the aforementioned spin-up mode, first, the present embodiment tests the maximum current that the controller (i.e., the driver) can continuously and stably operate at a low rotational speed. Then, a phase current minimum operating limit and a maximum torque Tm that the current can output are determined according to the required heating power. When the motor set operating torque exceeds the aforementioned Tm, the system will operate in a maximum torque to current ratio state. When the set running torque of the motor is lower than the Tm, the running current amplitude of the motor is not reduced, and the AC-DC axis current is redistributed by adjusting the current vector angle under the synchronous rotation coordinate system, so that the output torque is ensured to reach a given value. At this time, most of the current is applied to the motor straight shaft, the reluctance torque part is removed, and the remaining current is converted into heating power as a loss. Finally, under the working conditions of different rotating speeds, the current distribution condition of the alternating-direct axis is manufactured into a two-dimensional lookup table, and the current distribution at the non-tested working point is obtained through linear interpolation lookup table.

It should be noted that, in an alternative embodiment, for heating the motor by using high frequency and high voltage to generate iron loss in the dynamic heating mode, the principle of high frequency and high voltage generation is basically consistent with that of locked-rotor heating, and the positive and negative values of the square wave voltage are alternated by superposing a square wave signal consistent with the switching frequency on the output of the direct-axis current loop. In view of the large saliency of the motor for vehicles, the generated pulsating current may cause torque pulsation even if a high-frequency voltage is injected into the straight shaft. The optimal implementation mode can be flexibly selected by a person skilled in the art by controlling the ratio of the injected high-frequency voltage, balancing the torque pulsation and the heating efficiency according to the actual situation.

After the heating start signal disappears, only the heating power corresponding to the heating mode is stopped from being input. At this time, if the motor still needs to maintain the low-speed operation state, the driving current still proceeds normally.

It should be noted that, when the user cancels the heating command (i.e., cancels the selection of the heating mode), and stops generating the start heating signal when the temperature detection module detects that the temperature rises to the preset value, neither start heating signal appears, and the input of the heating power to the direct axis of the motor is stopped.

In summary, the motor heating method provided by the embodiment of the invention can flexibly determine the heating mode according to the operation condition of the motor, and can switch between the two modes of rapid heating and normal heating according to the heating requirement of a user when the motor is in the locked state. Particularly, in the rapid heating mode, the high-frequency voltage and direct current mixed injection mode provided by the embodiment can fully utilize copper loss and iron loss of the motor under the condition of not changing a hardware circuit, and improves the heating power of the motor. The direct application of the battery pack is that the battery pack is heated by replacing high-voltage PTC in a new energy automobile under the condition of low temperature.

Meanwhile, the embodiment also provides a computer device, which comprises a memory and a processor, wherein the memory stores a computer program, and the computer program when executed by the processor causes the processor to execute the steps of the motor heating method.

Those skilled in the art will appreciate that implementing all or part of the processes in the methods of the embodiments described above may be accomplished by computer programs to instruct related hardware. Accordingly, the computer program may be stored in a non-volatile computer readable storage medium, which when executed, performs the method of any of the above embodiments. Any reference to memory, storage, database, or other medium used in embodiments provided herein may include non-volatile and/or volatile memory. The nonvolatile memory can include Read Only Memory (ROM), programmable ROM (PROM), electrically Programmable ROM (EPROM), electrically Erasable Programmable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double Data Rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous Link DRAM (SLDRAM), memory bus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), among others.

The embodiment also provides an electric vehicle, which comprises a motor, a controller and a heat exchange system, wherein the electric vehicle supplies heat for the heat exchange system by adopting the motor heating method under a low-temperature environment;

or the electric vehicle is provided with the computer equipment;

or the electric vehicle has the above-described computer-readable storage medium, and the computer program when executed by the processor implements the above-described motor heating method.

The above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that the present invention includes but is not limited to the accompanying drawings and the description of the above specific embodiment. Any modifications which do not depart from the functional and structural principles of the present invention are intended to be included within the scope of the appended claims.

Claims

1. A motor heating method for supplying heat to a heat exchange system of an electric vehicle in a low temperature environment, the motor heating method comprising the steps of:

determining a heating mode of the motor according to the operating state of the motor in response to the heating start signal; the working states of the motor comprise a static state, a locked rotor state, a low-speed running state and a high-speed running state; the heating modes comprise a rapid heating mode, a normal heating mode and a dynamic heating mode; the rapid heating mode is set in a state that the motor is stationary or locked; the normal heating mode is configured in a motor stationary or locked-rotor state or in a motor low-speed running state; the dynamic heating mode motor is configured in a low-speed operation state; starting the rapid heating mode, and inputting direct current and high-frequency voltage to a direct shaft of the motor;

when the rotating speed of the motor is 0r/min, the motor is in a static state or a locked-rotor state; when the rotating speed of the motor is less than or equal to Nr/min, the motor is in a low-speed running state; when the rotating speed of the motor is greater than Nr/min, the motor is in a high-speed running state; wherein N is E [2500,3500].

2. The motor heating method according to claim 1, wherein the waveform of the high-frequency voltage is a square wave.

3. The motor heating method according to claim 2, wherein the waveform of the high-frequency voltage is any one of a unipolar square wave, a bipolar square wave, or a composite square wave formed by combining unipolar and bipolar.

4. A motor heating method according to any one of claims 1 to 3, wherein the heating start signal is generated by a vehicle control terminal or when the battery temperature detection module detects that the temperature is lower than a preset value.

5. The motor heating method according to claim 1, wherein in the dynamic heating mode, while inputting a direct current or/and a high-frequency high-voltage to a direct shaft of the motor, the heating power is dynamically adjusted according to an output torque power of the motor, the adjusting step includes:

when the motor set running torque is lower than the maximum torque Tm, the current vector angle under the synchronous rotation coordinate system is adjusted, and the given current vector is redistributed.

6. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor implements the motor heating method of any one of claims 1 to 5 when executing the computer program.

7. A computer-readable storage medium, on which a computer program is stored, characterized in that the computer program, when executed by a processor, implements the motor heating method of any one of claims 1 to 5.

8. An electric vehicle, characterized in that the electric vehicle comprises a motor, a controller and a heat exchange system, and the electric vehicle supplies heat to the heat exchange system in a low-temperature environment by adopting the motor heating method according to any one of claims 1-5;

or the electric vehicle has the computer device as claimed in claim 6;

or the electric vehicle having a computer-readable storage medium as claimed in claim 7, which computer program, when executed by a processor, implements the motor heating method of any one of claims 1 to 5.