Sustainable development of human coexistence with the environment and the global economy to make people desperately seeking a low-emissions and efficient use of resources, transport, use of electric vehicles is undoubtedly a promising solution.

Modern electric car is the integration of electrical, electronic, mechanical control, materials science and chemical technology and other high-tech composite products. Overall operating performance and economy depends primarily on the battery system and motor drive control system. Electric vehicle motor drive system generally consists of four main parts, namely the controller. Power converter, the motor and the sensor. Electric car motors currently used are generally DC motors, induction motors, switched reluctance motors and permanent magnet brushless motors.

1 electric car the basic requirements of the motor

Electric cars run, and general industrial applications different, very complex. Thus, the drive system requirements are very high.

1.1 Electric motor car should have a large instantaneous power, overload, overload factor should be 3 to 4), acceleration performance and long life characteristics.

1.2 Electric motor car should have a wide speed range, including constant torque region and constant power. In the constant torque region, it requires a low speed high torque to meet the requirements for starting and climbing; at constant power, low torque requirements of a high speed to meet the car on a flat surface capable of high-speed Claim.

1.3 electric vehicle motor should be able to achieve regenerative braking during deceleration of the vehicle, and the recovered energy is fed back to the battery, so that the electric vehicle has optimal energy utilization, which is in internal combustion engine vehicles can not be achieved.

1.4 electric vehicle motors should be within the entire operating range, with high efficiency, in order to improve a charge of driving range.

It also requires electric vehicle motor reliability, long-term work in harsh environments, simple structure, adapt to mass production, low noise operation, easy maintenance and low price.

2 electric vehicle motor types and control methods

2.1 DC Motor

There are major advantages of brush DC motor control is simple, mature technology. AC motors have unparalleled excellent control characteristics. In the early development of electric vehicles use more DC motors, even now, there are still using a DC motor to drive on some of the electric vehicles. However, due to the presence of mechanical commutator and brushes, not only to further improve the motor overload limit and speed, but if the long run, is bound to regular maintenance and replacement of brushes and commutator. In addition, the loss due to the presence on the rotor, so that the cooling difficulties, limiting further improve the quality of motor torque ratio. Given the existence of the above defects DC motor, the newly developed electric car has basically do not use direct current motor.

2.2 AC three-phase induction motor

Basic Performance 2.2.1 AC three-phase induction motor

Three-phase AC induction motor is the most widely used application of the motor. Its stator and rotor using silicon layers without mutual contact between the stator of the slip ring, commutator and other components. Simple structure, reliable and durable. AC induction motor power coverage is very broad, speed up to 12000 ~ 15000r / min. It can be air-cooled or liquid cooling, cooling high degree of freedom. Good adaptability to the environment, well enable regenerative braking feedback. Compared with the same power of the DC motor, high efficiency, reduced mass about half, cheap, and easy maintenance.

2.2.2 AC induction motor control system

Since the three-phase AC induction motor can not be used directly from the battery supply DC, AC three-phase induction motor having additional non-linear output characteristics. Therefore, in the AC three-phase induction motors for electric vehicles, needs to be applied in the inverter power semiconductor devices, the direct current into alternating current frequency and stroke amplitude can be adjusted to achieve the three-phase AC motor control. There are v / f control method, a slip frequency control method.

Vector control method, the field winding AC AC three-phase induction motor and frequency input AC three-phase induction motor end tone control, control AC three-phase induction motor flux and torque of the rotating magnetic field, to achieve change communication phase induction motor speed and torque output to meet the load requirements change characteristics, and be able to obtain maximum efficiency, so that the AC three-phase induction motor can be widely used in electric vehicles.

2.2.3 lack of AC three-phase induction motor

Three-phase AC induction motor power consumption is large, easy to heat the rotor at high speeds need to ensure the cooling of the AC three-phase induction motor, otherwise it will damage the motor. Three-phase AC induction motor of low power factor, so that the input power factor frequency transformer means is also low, requiring large-capacity inverter transformer means. Cost Three-phase AC induction motor control system is much higher than the three-phase AC induction motor itself, increasing the cost of electric vehicles. In addition, the AC three-phase induction motor speed control is also poor.

2.3 Permanent Magnet Brushless DC Motor

2.3.1 Basic performance permanent magnet brushless DC motor

Permanent magnet brushless DC motor is a high performance motors. Its biggest feature is the mechanical properties of the contact structure having an outer DC motor without brush composition. Additionally, it uses a permanent magnet rotor, no excitation loss: fever and armature windings mounted on the outside of the stator, heat is easy, therefore, there is no permanent magnet brushless DC motor commutation spark, no radio interference, long life and reliable operation , easy maintenance. In addition, its speed without mechanical change to the restrictions, if using air bearings or magnetic bearings, up to hundreds of thousands of revolutions per minute of running. Permanent magnet brushless DC motor system has higher energy density and higher efficiency, has a good prospect in electric vehicles.

2.3.2 Permanent Magnet Brushless DC Motor Control System

A typical permanent magnet brushless DC motor is a quasi-decoupled vector control system, since the permanent magnets can only produce a fixed amplitude of the magnetic field, and thus permanent magnet brushless DC motor system is ideally suited for operation in constant torque region, the general current hysteresis control or current feedback SPWM method to complete. To further expand the speed, permanent magnet brushless DC motor can also be used weakening control. Weakening control is the essence of the phase advance current phase angle, providing direct axis demagnetizing potential to weaken the stator winding flux.

2.3.3 lack of permanent magnet brushless DC motor

Permanent magnet brushless DC motor by the permanent magnet materials technology and limit the impact of such a small permanent magnet brushless DC motor power range, the maximum power is only tens of kilowatts. Permanent magnetic material is subjected to vibration, temperature and overload current role, its performance may be degraded or magnetic demagnetization phenomenon occurs, will degrade the performance of the permanent magnet motor, the motor will be serious damage, in use must be strictly controlled to not overloaded. Permanent magnet brushless DC motor in the constant power mode, manipulate complex, requiring a complex control system, so that the permanent magnet brushless DC motor drive system is high cost.

2.4 Switched Reluctance Motor

2.4.1 Basic performance Switched Reluctance Motor

Switched reluctance motor is a new type of electric motor, the system has many distinctive features: its structure is simpler than any other an electric motor, the rotor of the motor does not slip rings, winding and the permanent magnet, etc., but in the stator simple concentrated winding, the end windings short, there is no white jumper, easy repair and maintenance. Thus reliability, speed up to 15000 r / min. Efficiency up to 85% to 93% of it, is higher than AC induction motor. Loss is mainly in the stator, the motor is easy cooling; permanent magnet rotor element, wide speed range, flexible control, easy to achieve a variety of torque-speed characteristics of the special requirements, but also to maintain high efficiency over a wide range. More suitable for electric vehicle performance requirements.

2.4.2 Switched Reluctance Motor Control System

Switched reluctance motor has a highly non-linear characteristics, therefore, it is more complex drive system. Its control system comprises a power converter.

a. Power converter

Switched reluctance motor field winding, either by forward current or reverse current, the torque direction change, change of direction, each phase requires only a small capacity power switch, power converter circuit is relatively simple, not there will be direct access to a fault, good reliability, easy to implement soft-start system, and four-quadrant operation, it has a strong regenerative braking capacity. Three-phase AC induction motor than the cost of the inverter control system is lower.

b. Controller

The controller consists of a microprocessor, digital logic circuits and other components. The microprocessor according to the command input by the driver, while the position detector, the motor rotor position feedback of the current detector, analysis, processing, and make decisions in an instant, issuing a series of commands executed to control a switched reluctance motor adaptation run under different conditions of electric vehicles. The quality and flexibility to adjust controller performance, depending on the microprocessor software and hardware performance with the relationship.

c. Position detector

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

2.4.3 lack of Switched Reluctance Motor

Switched reluctance motor control system more complex than some of the other motor control system, the position detector is the key device of a switched reluctance motor, and its performance has a significant impact on the switched reluctance motor control operation. Because switched reluctance motors are doubly salient structure, inevitably torque ripple, noise is the main disadvantage of a switched reluctance motor. However, recent studies have shown that, using reasonable design, manufacturing and control technology, switched reluctance motor noise can be well suppressed. Further, since the switched reluctance motor output torque fluctuations, fluctuations in the DC current of the power converter is also larger, so the DC bus requires a large filter capacitor means

3 uses a variety of electric vehicle drive motor performance comparison

Electric vehicles in different historical periods using different electric is the use of the best and lower cost DC motor control performance. With the development of motor technology, manufacturing technology, power electronics and automatic control technology, the AC motor. Permanent magnet brushless DC motor and the switch reluctance motor exhibits superior performance than the DC motor, the electric car, these motors gradually replace the DC motor. Table 1 is a basic performance of the modern electric car motors used in various comparisons. Currently cross motive, permanent magnet motors and switched reluctance motors and their control means, the cost is still relatively high, after the mass production of these units and motor control means rapidly reduce the price, will be able to meet the requirements of economic efficiency, and electric vehicle lower prices.