Types and applications of drive motors for new energy vehicles

China's automotive motors have obvious comparative advantages under the conditions of global resources and have great potential for development. From the perspective of the industrial chain of new energy vehicles, the beneficiaries will be mainly concentrated in the field of core components. The current situation of the domestic vehicle-driven motor industry: a small industry in the motor industry, but the manufacturing threshold is high, and there are still many gaps and deficiencies in the motor drive system, but domestic policy support will accelerate the pace of the industry.

As one of the core components of new energy vehicles (batteries, motors, electronic control), the drive motor and its control system have considerable future development prospects.

Introduction to the drive motor system

New energy vehicles have three advantages: environmental protection, economy and simplicity. It is particularly obvious in pure electric vehicles: the electric motor replaces the fuel engine, which is driven by a motor without an automatic transmission. Compared with the automatic transmission, the motor has simple structure, mature technology and reliable operation.

The speed when the traditional internal combustion engine can generate torque is limited to a narrow range, which is why traditional internal combustion engine cars need a large and complex transmission mechanism; while the motor can generate torque in a relatively wide speed range, and there is no need for a shift transmission device in the process of pure electric vehicles, which is easy to operate. Easy, low noise.

Compared with hybrid vehicles, pure electric vehicles use a single electric energy source. The electronic control system greatly reduces the internal mechanical transmission system of the vehicle, and the structure is more simplified. It also reduces the energy loss and noise caused by friction of mechanical components, saving the internal space and weight of the car. The motor drive control system is the main executive structure in the exercise of new energy vehicles. The drive motor and its control system are one of the core components (battery, motor, electronic control) of new energy vehicles. Its driving characteristics determine the main performance index of vehicle driving. It is an important component of electric vehicles.

The three categories of fuel cell vehicle FCV, hybrid vehicle HEV and pure electric vehicle EV in electric vehicles should be driven by electric motors. Choosing the right electric motor is an important factor to improve the cost performance of all kinds of electric vehicles. Therefore, the research and development or improvement can meet the performance of the vehicle driving process at the same time. It is important to drive the motor with the characteristics of robustness and durability, low cost and high efficiency.

The drive motor system is one of the three core components of new energy vehicles. The motor drive control system is the main execution structure in the exercise of new energy vehicles. Its driving characteristics determine the main performance index of the vehicle. It is an important component of electric vehicles. The entire drive system of an electric vehicle includes two parts: the motor drive system and its mechanical transmission mechanism. The motor drive system is mainly composed of motor, power converter, controller, various detection sensors and power supply.

Motors are generally required to have two functions: electric power and power generation. According to the type, several types of motors such as DC, AC, permanent magnet brushless or switched magnetoresistance can be selected, as shown in Figure 3. According to the selected motor type, the power converter has DC/DC power converter, DC/AC power converter and other forms. Its function is to convert the DC of the battery into a DC, AC or pulse power supply of the corresponding voltage level according to the driving current requirements of the selected motor.

The motor is a rotating electromagnetic machine operated by applying the principle of electromagnetic induction, which is used to realize the conversion of electrical energy to mechanical energy. When running, it absorbs electrical power from the electrical system and outputs mechanical power to the mechanical system. The motor drive system is mainly composed of a motor and a controller (inverter). The cost ratio of the drive motor and the motor controller is about 1:1. According to the design principle and classification method, the specific structure and cost composition of the motor are also different. The control system of the motor is mainly adjusted.

The operating state of the motor enables it to meet the purpose of different operating requirements of the whole vehicle. For different types of motors, the principle and mode of the control system are very different.

Compare the applications, advantages and disadvantages of four commonly used motor drive systems.

1. The basic requirements for electric vehicle motors are as follows:

(1) The motor has a compact structure, small size, limited packaging size, and must be specially designed according to the specific product.

(2) Light weight to reduce the overall weight of the vehicle. Aluminum alloy shells should be used as much as possible, and the rotation speed should be high at the same time to reduce the quality of the whole vehicle, increase the adaptability of the motor to the car body, and expand the available space of the car body.

(3) High reliability and controllable failure mode to ensure passengers.

(4) Provide torque control with good dynamic performance.

(5) High efficiency and high power density. It is necessary to ensure high efficiency in a wide speed and torque range to reduce power loss and improve the driving mileage of a single charge.

(6) Low cost to reduce the overall cost of vehicle production.

(7) Wide speed regulation range. It should include a constant torque zone and a constant power zone. The constant torque of low-speed operation output is large to meet the requirements of rapid start-up, acceleration, load climbing and other requirements of vehicles. High-speed operation output constant power, with a large speed regulation range to meet the requirements of flat pavement, overtaking and other high-speed driving.

(8) High instantaneous power and strong overload capacity. It is necessary to ensure that the car has a load capacity of 4 to 5 times to meet the requirements of accelerated driving and climbing in a short period of time.

(9) Good environmental adaptability. To adapt to the different regional environments of the car itself, it can work normally even in harsh environments, with good high temperature and humidity resistance.

(10) High braking regeneration efficiency. When the car slows down, feedback braking can be realized, energy can be recovered and fed back to the battery, so that electric vehicles have energy utilization.

(11) Other. The structure is simple, the price is low, it is suitable for mass production, the noise is low at runtime, and it is convenient to use and maintain.

(12) Unlike general industrial motors, the drive motor used for automobiles should have the characteristics of wide speed regulation range, large starting torque, high backup power and high efficiency. In addition, it also requires high reliability, high temperature and moisture resistance, simple structure, low cost, simple maintenance, suitable for large-scale production, etc. In the future, China's electric vehicle drive motor system will develop towards permanent magnetization, digitization and integration.

2. Application of asynchronous motor (induction motor) in new energy vehicles

(1) Introduction of asynchronous motor

The induction motor is also known as the "asynchronous motor", that is, the rotor is placed in a rotating magnetic field. Under the action of the rotating magnetic field, it obtains a torque, so the rotor rotates. The rotor is a rotating conductor, usually in the shape of a squirrel cage. The stator is the non-rotating part of the motor, and the main task is to generate a rotating magnetic field. The rotating magnetic field is not achieved by mechanical methods. Instead, it is connected to the digital pair of electromagnets by alternating current to change its magnetic mass cycle, so it is equivalent to a rotating magnetic field. This kind of motor does not have a brush or collector ring like a DC motor. According to the type of alternating current used, there are single-phase motors and three-phase motors.

(2) Characteristics of asynchronous motors

Asynchronous motors have the following advantages: compact structure, strong and durable; reliable operation and convenient maintenance; low price, small size and light quality; good environmental adaptability; low torque pulsation and low noise. AC asynchronous motors have low cost and high reliability. Even if the inverter is damaged and short-circuited, it will not produce anti-elm, so there is no possibility of sudden braking.

Therefore, it is widely used in large and high-speed electric vehicles. The power capacity of the three-phase cage asynchronous motor covers a wide range, from a few watts to a few kilowatts. It can adopt air cooling or liquid cooling, with high cooling freedom, good adaptability to the environment, and can realize regenerative braking. Compared with DC motors with the same power, the efficiency is higher and the weight is about half lighter.

At the same time, it has the following disadvantages: the power factor is low, and the reactive current must be absorbed from the power grid to establish a magnetic field during operation; the control is complex, which is easily affected by motor parameters and load changes; the rotor is not easy to dissipate heat; the speed regulation performance is poor, and the speed regulation range is narrow.

Advantage analysis: The special motor for new energy vehicles generates action by obtaining limited energy from the battery, so it is required to be very efficient in various environments. Therefore, the performance requirements are stricter than that of general industrial motors. The motor suitable for electric vehicles needs to meet several characteristics: small lightweight (solidity) from high speed, (long driving mileage after one charge), constant output characteristics in a large range under low speed and high torque, long service life, high reliability, low noise and low cost. However, in reality, motors that fully meet the above characteristics have not yet been developed. At present, the motors more suitable for new energy vehicles are AC asynchronous motors and PM motors.

(3) Control system of asynchronous motor

Since the AC three-phase induction motor cannot directly use direct current, an inverter device is required for conversion control. When a new energy vehicle is decelerated or braked, the motor is in the state of power generation braking to charge the battery and realize the conversion of mechanical energy into electrical energy. In new energy vehicles, the PWM power inverter composed of power semiconductor devices converts the direct current provided by the battery power supply into alternating current that can adjust the frequency and amplitude.

The control methods of three-phase asynchronous motor inverter mainly include V/f constant control method, change rate control method, vector control method and direct torque control method (DTC). Before the 1990s, the main

The first two control methods are used, but because the speed control range is small and the torque characteristics are not ideal, it is not suitable for electric vehicles that need to start and speed frequently. At present, the latter two control methods are currently in the mainstream.

(4) Application status of asynchronous motor

In the United States, asynchronous motors are more widely used, which is also artificially related to road conditions. In the United States, highways already have a certain scale. Except for big cities, cars generally continue to drive at a certain high speed, so asynchronous motors can operate at high speed and are widely used at high speed. In China, with the development of highway scale, the application of AC asynchronous motors in new energy vehicles will become more and more important.

3. Application of permanent magnet brushless motor in new energy vehicles

With the rapid development of power electronics technology, microelectronics technology, microcomputer technology, rare earth permanent magnet materials, sensor technology and motor control theory in recent years, AC drive technology has gradually matured.

Compared with the existing series or excitation brush DC motor drive system, the permanent magnet brushless motor has the advantages of high power density, small size, high efficiency, simple and strong structure, easy maintenance, etc., and the operation and maintenance cost of the electric vehicle driving system using permanent magnet brushless motor as the driving element is low. It adopts a fully digital and modular structure design, which makes the driver interface flexible, the control ability stronger and more comfortable to operate. The application of energy feedback braking technology can reduce the wear of brake pads and increase the driving mileage of the car.

Therefore, based on the development needs and technology status of the electric vehicle market, the design and development of a reliable, low-cost and high-performance all-digital electric vehicle permanent magnet brushless motor drive system is of great practical significance for the development of the electric vehicle industry.

(1) Introduction to permanent magnet synchronous motor

There are two ways to establish the air gap magnetic field required for electromechanical energy conversion in the motor. One is to generate a magnetic field with current in the motor winding. This method requires not only a special winding and corresponding device, but also the continuous supply of energy to maintain the current flow, such as ordinary DC motors and synchronous motors. The other is that the permanent magnet generates a magnetic field, which can simplify the motor structure and save energy. The motor that generates a magnetic field by a permanent magnet is a permanent magnet motor.

It uses permanent magnets to establish a synchronous motor of excitation magnetic field. Its stator generates a rotating magnetic field, and the rotor is made of permanent magnet material. In order to convert energy, a synchronous generator needs a DC magnetic field to generate the DC current of this magnetic field, which is called the excitation current of the generator. According to the supply mode of excitation current, generators that obtain excitation current from other power sources are called excitation generators, and those that obtain excitation power from the generator itself are called self-exciting generators.

(2) Characteristics of permanent magnet synchronous motor

Permanent magnet synchronous motor has the following advantages: large power factor, high efficiency and high power density; simple structure, easy maintenance, long service life and high reliability; good speed regulation performance and high accuracy; good instantaneous characteristics, low momentary momentary inertia, fast response speed; high frequency, large output torque, speed and braking performance It is better than other types of motors; the electronic power device is used as the reversing device, with flexible drive and strong controllability; the shape and size are flexible and diverse, which is convenient for shape design; the motor is small in size and light in mass after using rare earth permanent magnet material.

However, the permanent magnet synchronous motor also has the following disadvantages: the motor cost is high; in the constant power mode, the operation is more complex, and the cost of the control system is high; the weak magnetic ability is poor, and the speed regulation range is limited; the power range is small, affected and limited by the magnetic material process, the high power is only a few tens Large loss and low efficiency; when the permanent magnet material is affected by vibration, high temperature and overload current, its magnetic conductivity may decline or demagnetize, which will reduce the performance of the permanent magnet motor. In serious cases, it will also damage the motor. It must be strictly controlled during use so that it does not overload. The magnetic field of the permanent magnet material is immutable. If you want to increase the power of the motor, its volume will be very large; the corrosion resistance is poor; it is not easy to assemble.

(3) Advantages of permanent magnet motor as a driving motor

1 Torque, high power density and high starting torque. The air gap magnetic density of the permanent magnet motor can be greatly improved, and the motor index can achieve a good design, so that the volume of the motor can be reduced and the weight can be reduced, and the volume, weight and materials used in the rare earth permanent magnet motor of the same capacity can be reduced by about 30%. The permanent magnet drive motor has a large starting torque, which can provide an effective starting torque when the car starts to meet the operating needs of the car.

2 The energy index is good. When the Y-series motor works under 60% load, the efficiency decreases by 15%, the power factor decreases by 30%, and the energy index decreases by 40%. However, the efficiency and power factor of the permanent magnet motor have decreased very little. When the motor has only 20% load, its energy index is still more than 80% of the full load. At the same time, the constant torque area of the permanent magnet brushless synchronous motor is relatively long, extending to about 50% of the high speed of the motor, which is of great help to improve the low-speed power performance of the car.

3 Energy saving. After the rare earth permanent magnet material is embedded in the rotor, the rotor runs synchronously with the stator magnetic field during normal operation. The rotor winding has no sensory current, and there is no rotor resistance and hysteresis loss, which improves the motor efficiency. The permanent magnet motor can not only reduce the resistance loss, but also effectively improve the power factor. For example, the permanent magnet synchronous motor can maintain high efficiency and power factors in the 25-120 rated load range.

4 Simple structure and high reliability. With permanent magnet material excitation, the excitation coil in the original excitation motor can be replaced by one or more permanent magnets. The components are greatly reduced, the structure is greatly simplified, and the process of the motor is improved. Moreover, the mechanical reliability of the motor operation is greatly enhanced and the service life is increased. There is no resistance loss in the rotor winding, there is almost no reactive current in the stator winding, and the motor temperature rises low, which can also cool the whole vehicle.

However, the load of the system is reduced to further improve the efficiency of the operation of the whole vehicle.

(4) Control system of permanent magnet synchronous motor

The control technology of permanent magnet motor is similar to that of induction motor, and the control strategy mainly focuses on improving the characteristics of low-speed torque and high-speed constant power. At present, the permanent magnet synchronous motor often adopts vector control at low speed, including air gap magnetic field orientation, rotor flux direction, stator flux direction, etc. When running at high speed, permanent magnet synchronous motors usually adopt weak magnetic control.

(5) Application status of permanent magnet motor

The design theory, calculation method, detection technology and manufacturing technology of rare earth permanent magnet motor are constantly improving and developing, and the performance and reliability of permanent magnet materials are constantly improving. The rapid development of power electronics technology, large-scale integrated circuits and computer technology has also promoted the development of permanent magnet drive motors. With the rapid development of hybrid vehicles and pure electric vehicles in the future, permanent magnet drive motors will usher in a period of more rapid development. Its development trend will also show the following characteristics: high power density, high torque density, high controllability, high performance, high price ratio, etc. to meet the actual needs of hybrid vehicles and pure electric vehicles.

4. Application of switched reluctance motors in new energy vehicles

(1) Introduction to switched reluctance motor

Switched Reluctance Drive (SRD) is a new generation of stepless speed regulation system developed after frequency conversion speed regulation system and brushless DC motor speed regulation system. It integrates modern microelectronic technology, digital technology, power electronics technology and infrared light. High-tech optical, machine and electrical integration integrating electrical technology and modern electromagnetic theory, design and production technology. It has the advantages of both DC and AC speed regulation systems.

The switched reluctance motor covers various high and low speed drive speed regulation systems with a power range of 10W to 5MW. The switched reluctance motor has many potential fields and can be widely used in various situations where speed regulation is needed (electric vehicle drive, general industry, household appliances, textile machinery, electric transmission system, etc.).

Working principle of switched reluctance motor: The operation of the switched reluctance motor follows the principle of small magnetoresistance - the magnetic flux should always be closed along the path of small magnetic resistance. When the iron core with a certain shape moves to a small reluctance position, it must overlap its main axis with the axis of the magnetic field.

(2) Characteristics of switched reluctance motor

Its structure is simpler than that of any other motor. There are no slip rings, windings and permanent magnets on the rotor of the motor, but there is a simple centralized winding on the stator. The end of the winding is short, and there is no inter-phase crossover wiring, so it is easy to maintain and repair. Therefore, the reliability is good, and the rotation speed can reach 15,000r/min. The efficiency can reach 85-93 percent, which is higher than the AC induction motor. The loss is mainly in the stator, and the motor is easy to cool; the rotor element permanent magnet is easy to achieve the torque-speed characteristics of various special requirements, and it is maintained in a wide range. It is more suitable for the power performance requirements of electric vehicles.

The switched reluctance motor also has the advantages of running in a wide speed and torque range, flexible control, four-ebegible operation, fast response speed and low cost. Good process, suitable for high speed, strong environmental adaptability; the direction of the motor torque is independent of the direction of the winding current; suitable for frequent start-stop and forward and reverse conversion operation; small starting current, large torque; many controllable parameters, good speed regulation performance; strong regenerative braking ability; the materials of stator and rotor are made of silicon steel. Tablets, easy to obtain and recycle.

However, the switched reluctance motor has the disadvantages of large torque fluctuation, requiring a position detector, and the nonlinear characteristics of the system. The magnetic field is jumping rotation, and the control system is complex. It will generate a large pulse current for the DC power supply. The position detector is the key device of the switched reluctance motor, and its performance has an important impact on the control operation of the switched reluctance motor. Because the switched reluctance motor is a double-convex structure, there are inevitably torque fluctuations, and noise is the main disadvantage of the switched reluctance motor.

However, research in recent years has shown that with reasonable design, manufacturing and control technology, the noise of the switched reluctance motor can be completely suppressed. In addition, due to the large fluctuation of the output torque of the switched reluctance motor and the large fluctuation of the DC current of the power converter, a very

Large filter capacitor.

(3) Control system of switched reluctance motor

The core of the switched reluctance motor drive system is the switched reluctance motor (SRM), which involves multidisciplinary knowledge such as motor, power electronics, microcomputer, control, photoelectric conversion, angle measurement, etc. The structure is relatively complex, and the control system requirements are relatively unique. The control methods of induction motors and permanent magnet synchronous motors are usually difficult to meet the control requirements of the system. At present, electric vehicles are rarely used. Its main research direction is model research.

Because the switched reluctance motor has obvious nonlinear characteristics, the system is difficult to model, and the general linear control method is not suitable for the switching reluctance motor system. At present, fuzzy logic control and neural network control are mainly used.

Its control system includes power converters, controllers and position sensors, and speed detectors.

1 Power converter

The excitation winding of the switched reluctance motor, whether through forward current or reverse current, its torque direction remains unchanged and the future is reversed. Each phase only needs a small power switching tube. The power converter circuit is relatively simple, and there will be no straight-through failure. It has good reliability. It is easy to realize the soft start and four-quadrant operation of the system, and has a strong regenerative braking ability. The cost is lower than that of the inverter control system of AC three-phase induction motor.

2 Controller

The controller is composed of microprocessors, digital logic circuits and other components. According to the command entered by the driver, the microprocessor analyzes and processes the rotor position of the motor feedback from the position detector and the current detector, and makes decisions in an instant, and issues a series of execution commands to control the switched reluctance motor to adapt to the operation of electric vehicles under different conditions. The performance of the controller and the flexibility of adjustment depend on the performance of the microprocessor's software and hardware.

3 Position detector

The switching reluctance motor requires a high-precision position detector to provide the change signal of the position, speed and current of the motor rotor for the control system, and requires a high switching frequency to reduce the noise of the switched reluctance motor.

5. Application of DC motor in new energy vehicles

DC motors can be divided into two types: permanent magnet DC motors and winding excitation motors. Generally, the former is used for low power and the latter is used for high power. The latter is mainly discussed below.

(1) Introduction to DC motor

DC motor: a rotary motor that converts DC electrical energy into mechanical energy (DC motor) or converts mechanical energy into DC electrical energy (DC generator).

The structure of the DC motor should be composed of two parts: fixed and rotor. The stationary part of the DC motor is called the stator, and the main function of the stator is to generate a magnetic field. The rotating part during operation is called the rotor. Its main function is to generate electromagnetic torque and induced electromotive force. It is the hub for the energy conversion of the DC motor, so it is usually called armature, which is composed of a rotating shaft, armature core, armature winding, commutator and fan.

Brushed DC motors are widely used in situations where adjustable speed and good speed regulation performance are required, as well as frequent starting, braking and reVERSing.

(2) Characteristics of DC motor

DC motor has the following advantages: simple structure; with excellent electromagnetic torque control characteristics, can achieve constant torque below the base speed and constant power above the base speed, which can meet the requirements of the car for low-speed high torque, high-speed and low-torque of the power source; it can start frequently and quickly, brake and reverse; the speed regulation is smooth, stepless Wide circumference; strong anti-overload ability, able to withstand frequent impact loads; simple control method, only need to be controlled by voltage, no need to detect the magnetic position.

However, it also has the following disadvantages: it is equipped with an electric brush and a directional device. When running at high speed and high load, the surface of the directional device is easy to generate electric sparks. At the same time, the maintenance of the directional converter is difficult, and it is difficult to develop to large capacity and high speed. In addition, electric sparks Large volume and mass. Among them, the electromagnetic interference generated by electric sparks will be fatal to highly electronic electric vehicles. With the development of electronic force technology and control theory, compared with other drive systems, the application of DC motors in electric vehicles has been at a disadvantage and has been gradually eliminated.

(3) Control system of DC motor

The DC motor control system is mainly composed of a chopper and a controller. According to the needs of the output torque of the DC motor, the input voltage and current of the motor are controlled by the chopper to control and drive the operation of the DC motor.

6. Comparison of various motors

Let's first compare the development history of various motors. There is a long history of commercialization of brush DC motors, general synchronous motors, induction motors and brushed magnet motors. Their products are constantly updated and are still being used so far. Surface permanent magnet synchronous motors that have been commercialized since the 1980s have entered the market with switched reluctance motors, built-in permanent magnet synchronous motors and new synchronous reluctance motors developed since the 1990s, and have been applied in electric vehicles and hybrid vehicles.

Then compare which new energy vehicles are widely used in various motors. Asynchronous motors are mainly used in pure electric vehicles, permanent magnet synchronous motors are mainly used in hybrid vehicles, and switched reluctance motors are mainly used in passenger cars. Judging from the application of different types of new energy vehicle drive motors in China, AC asynchronous induction motors and switched reluctance motors are mainly used in new energy commercial vehicles, especially new energy buses. There are fewer practical installation applications of switched reluctance motors; permanent magnet synchronous motors are mainly used in new energy passenger vehicles.

Compare the development status of various motors in China

(1) AC asynchronous motor drive system China has established a development platform for asynchronous motor drive systems with independent intellectual property rights, forming a development, manufacturing, testing and service system for small-volume production. The product performance basically meets the needs of the whole vehicle, and the high-power asynchronous motor system has been widely used in all kinds of electric buses. Through demonstration operation and small-scale market-oriented applications, the product reliability has been preliminarily verified.

(2) The switched reluctance motor drive system has formed the ability to optimize design and independently research and development. Through the rational design of the motor structure and the improvement of control technology, the product performance basically meets the needs of the whole vehicle. Some companies have an annual production capacity of 2,000 sets, which can meet the needs of small batches of supporting equipment. At present, some products have been equipped with vehicle demonstration and operation, with good results.

(3) Domestic enterprises of brushless DC motor drive system have effectively improved the performance of brushless DC motor products through reasonable design and improved control technology, basically meeting the needs of electric vehicles; they have initially had electromechanical integrated design capabilities.

(4) The permanent magnet synchronous motor drive system has formed a certain R&D and production capacity, and different series of products have been developed, which can be applied to various electric vehicles. Some technical indicators of the product are close to the international advanced level, but the overall level is still a certain gap from that of foreign countries. It basically has the integrated design ability of permanent magnet synchronous motors; most companies are still in small-scale trial production, and a few companies have invested in the establishment of special production lines for vehicle drive motor systems.

(5) Permanent magnet motor materials The main materials of permanent magnet motor are neodymium iron boron magnetic steel, silicon steel, etc. Some companies have mastered the overall magnetic charging technology of motor rotor magnets first assembled and then magnetized. The operating temperature of neodymium-iron boron permanent magnets developed in China can be 280°C, but the technical level is still far from that of Germany and Japan. Silicon steel is an important magnetic material for manufacturing motor cores. Its cost accounts for about 20% of the motor body. Its thickness has a great impact on iron consumption. Japan has produced 0.27mm silicon steel sheets for automotive motors, and only 0.35mm silicon steel sheets have been developed in China.

Future prospects of new energy vehicle drive motors

The current development directions of new energy vehicle drive motors are as follows: small and lightweight; torque characteristics; long service life, high reliability; low noise; low price. With the passage of time, the development of new energy drive motors shows the following trends:

1 Motor body permanent magnetization: Permanent magnet motors have the advantages of high torque density, high power density and high reliability. China has the world's rich rare earth resources, so high-performance permanent magnet motors are an important development direction for automotive drive motors in China.

2 Digitalization of motor control: The emergence of special chips and digital signal processors promotes the digitization of motor controllers, improves the control accuracy of the motor system, and effectively reduces the system volume.

3 Motor system integration: Through electromechanical integration (motor and engine integration or motor and gearbox integration) and controller integration, it is conducive to reducing the weight and volume of the drive system and can effectively reduce the manufacturing cost of the system.

Let's talk about a variety of future motors. With the rapid development of new energy vehicle drive technology, many new structures or new concept motors have been put into research. Among them, the new permanent magnet brushless motor is one of the current promising motors, including hybrid excitation type, wheel hub type, double stator type, memory type and magnetic gear composite type. In addition, amorphous motors have also begun to enter the field of new energy vehicles. As a new generation of high-performance motors, their own advantages will certainly play a huge role in promoting the development of the new energy vehicle industry.

(1) Hybrid excitation motor

The topology of the motor is changed, and the main magnetic field of the motor is generated by two excitation sources, which realizes the adjustment and control of the main magnetic field of the motor, and improves the speed regulation, driving performance or voltage regulation characteristics of the motor. It not only inherits many characteristics of permanent magnet motors, but also has the advantages of smooth and adjustable air gap magnetic field of electric excitation motors. Such as permanent magnet switched reluctance motor and permanent magnet synchronous reluctance motor.

(2) Double stator permanent magnet motor

The double stator motor is a new type of permanent magnet brushless motor that increases the number of stators on the basis of the constant volume of the existing motor, so that the number of air gaps can be changed from one layer to two or more layers. Due to the superposition of torque, the electromagnetic torque acting on the rotor will also increase accordingly, thus improving the overall torque density and power density of the motor. Due to the high mechanical integration of this kind of motor, it has the characteristics of fast response, good dynamic characteristics, high utilization rate of structural materials and flexible driving.

(3) Memory motor

The memory motor is also known as the magnetic flux controllable permanent magnet motor. The difference from the general permanent magnet motor is that the magnetization degree of the permanent magnet material itself can be changed in a very short time by applying magnetization or demagnetization potential, and its magnetization degree can also be retained after magnetization and demagnetization. Therefore, it has a wider speed regulation range and can avoid additional excitation losses. In essence, it is a new and simple weak magnetic control technology.

(4) Magnetic gear permanent magnet brushless composite motor

The motor is a composite motor that integrates a brushless DC drive motor and a coaxial magnetic gear. The so-called coaxial magnetic gear is a high-performance, non-contact variable speed transmission device based on the principle of adjustable harmonics. This motor cleverly uses the hollow part of the rotor in the coaxial magnetic gear to embed the motor stator.

Among them, the tire is directly riveted on the external rotor of the gear, which realizes the integration of motor, magnetic gear and tire, and effectively improves the space utilization rate.

(5) Amorphous motor

Amorphous motor is a new type of energy-saving and pollution-free motor that uses amorphous alloys to replace traditional silicon steel sheets as iron core materials. It has low loss and high efficiency at high frequency. Compared with ordinary motors of the same standard, its volume and quality are greatly reduced, which improves the utilization rate of energy and resources.

For the same new energy vehicles, the use of amorphous motors can increase their driving mileage by more than 30%, while in the case of the same mileage, the battery can save 30%. In short, amorphous motors will become the next generation of motors to replace traditional motors with their advantages such as high power density.