5.1.2　Classification of Electric Motors

Text（课文）

Differing from the industrial applications of motors，the motors used in EVs and HEVs usually require frequent starts and stops；high rates of acceleration/deceleration；high torque and low-speed hill climbing；low torque and high-speed cruising，and a very wide speed range of operation.The motor drives for EVs and HEVs can be classified into two main groups，namely the commutator motors and commutatorless motors，as illustrated in Figure 5.2.

Figure 5.2　Classification of electric motor drives for EV and HEV applications

1.DC Motors

Text（课文）

Commutator motors mainly are the traditional DC motors，which include series excited，shunt excited，compound excited，separately excited，and permanent magnets（PMs）excited motors.DC motors need commutators and brushes to feed current into the armature，thus making them less reliable and unsuitable for maintenance-free operation and high speed.In addition，winding-excited DC motors have low specific power density.Nevertheless，because of their mature technology and simple control，DC motor drives have been prominent in electric propulsion systems.

New words and expressions（单词和短语）

1.New words（单词）

2.Expressions（短语）

Notes to the text（难点解析）

★1.Nevertheless，because of their mature technology and simple control，DC motor drives have been prominent in electric propulsion systems.然而，由于技术成熟和控制简单，直流电动机驱动一直在电驱动系统中有着突出的地位。

Exercises（练习）

◆1.Translate the following passages（expressions）into Chinese（英译汉）

（1）commutator motors

（2）series excited

◆2.Translate the following passages（expressions）into English（汉译英）

（1）并励

（2）永磁（PM）励磁

（3）复励

（4）他励

◆3.Directions:Answer the following questions briefly according to the text

What can DC motor be classified？

2.Induction Motors

Text（课文）

Technological developments have recently pushed commutatorless electric motors into a new era.Advantages include higher efficiency，higher power density，and lower operating cost.They are also more reliable and maintenance-free compared to commutator DC motors；thus，commutatorless electric motors have now become more attractive.

Induction motors are widely accepted as a commutatorless motor type for EV and HEV propulsion.This is because of their low cost，high reliability and maintenance-free operation.However，conventional control of induction motors such as variable-voltage variable-frequency cannot provide the desired performance.With the advent of the power electronics and microcomputer era，the principle of field-oriented control（FOC）or vector control of induction motors has been accepted to overcome their control complexity due to their nonlinearity.However，these EV and HEV motors using FOC still suffer from low efficiency at light loads and limited constant-power operating range.

New words and expressions（单词和短语）

1.New words（单词）

2.Expressions（短语）

Notes to the text（难点解析）

★1.Vector control of induction motors has been accepted to overcome their control complexity due to their nonlinearity.矢量控制原理已被用来克服由于异步电动机非线性带来的控制难度。

Exercises（练习）

◆1.Translate the following passages（expressions）into Chinese（英译汉）

（1）Induction motors are widely accepted as a commutatorless motor type for EV and HEV propulsion.

（2）They have been accepted as having great potential to compete with induction motors for EV and HEV applications

（3）maintenance-free

◆2.Translate the following passages（expressions）into English（汉译英）

（1）异步电动机

（2）变压变频

3.PM Synchronous Motors

Text（课文）

By replacing the field winding of conventional synchronous motors with PMs，PM synchronous motors can eliminate conventional brushes，slip rings，and field copper losses.Actually，these PM synchronous motors are also called PM brushless AC motors，or sinusoidal-fed PM brushless motors，because of their sinusoidal AC current and brushless configuration.Since these motors are essentially synchronous motors，they can run from a sinusoidal or pulsed waveform modulation supply（PWM supply）without electronic commutation.These motors are generally simple and inexpensive，but with relatively low output power.Similar to induction motors，these PM synchronous motors usually use FOC for high-performance applications.Because of their inherently high power density and high efficiency，they have been accepted as having great potential to compete with induction motors for EV and HEV applications.Figure 5.3 shows the Leroy-Somer Synchronous Motor.

Figure 5.3　Leroy-Somer Synchronous Motor

New words and expressions（单词和短语）

1.New words（单词）

2.Expressions（短语）

Notes to the text（难点解析）

★1.PM synchronous motors can eliminate conventional brushes，slip rings，and field copper losses.永磁同步电动机可排除传统的电刷、集电环以及励磁绕组的铜耗。

Exercises（练习）

◆1.Translate the following passages（expressions）into Chinese（英译汉）

（1）field winding

（2）synchronous motors

★2.Translate the following passages（expressions）into English（汉译英）

（1）铜耗

（2）正弦交变电流

Reading material（阅读材料）

When PMs are mounted on the rotor surface，they behave as nonsalient synchronous motors because the permeability of PMs is similar to that of air.By burying those PMs inside the magnetic circuit of the rotor，the saliency causes an additional reluctance torque，which leads to facilitating a wider speed range at constant power operation.On the other hand，by abandoning the field winding or PMs while purposely making use of the rotor saliency，synchronous reluctance motors are generated.

4.PM Brushless DC（BLDC）Motors

Text（课文）

By virtually inverting the stator and rotor of PM DC motors（commutator），PM brushless DC（BLDC）motors are generated.It should be noted that the term“DC”may be misleading，since it does not refer to a DC current motor.Actually，these motors are fed by rectangular AC current and hence are also rectangular-fed PM brushless motors.The most obvious advantage of these motors is the removal of brushes.Another advantage is the ability to produce a large torque because of the rectangular interaction between current and flux.Moreover，the brushless configuration allows more cross-sectional area for the armature windings.Since the conduction of heat through the frame is improved，an increase in electric loading causes higher power density.Different from PM synchronous motors，these PM BLDC motors generally operate with shaft position sensors.

New words and expressions（单词和短语）

1.New words（单词）

2.Expressions（短语）

Notes to the text（难点解析）

★1.By virtually inverting the stator and rotor of PM DC motors（commutator），PM brushless DC（BLDC）motors are generated.实际上，通过转换永磁直流电动机（有刷电动机）定子和转子的位置，就可得到永磁无刷直流电动机（BLDC）。

Exercises（练习）

◆1.Translate the following passages（expressions）into Chinese（英译汉）

（1）These PM BLDC motors generally operate with shaft position sensors.

（2）PM brushless motors

（3）armature windings

◆2.Translate the following passages（expressions）into English（汉译英）

（1）转轴位置检测器

（2）定子和转子

5.Switched Reluctance Motors（SRMs）

Text（课文）

Switched reluctance motors（SRMs）have been recognized to have considerable potential for EV and HEV applications.Basically，they are direct derivatives of single-stack variable-reluctance stepping motors.SRMs have the definite advantages of simple construction，low manufacturing cost and outstanding torque-speed characteristics for EV and HEV applications.Although they possess simplicity in construction，this does not imply any simplicity of their design and control.Because of the heavy saturation of pole tips and the fringe effect of pole and slots，their design and control are difficult and subtle.Traditionally，SRMs operate with shaft sensors to detect the relative position of the rotor to the stator.These sensors are usually vulnerable to mechanical shock and sensitive to temperature and dust.Therefore，the presence of the position sensor reduces the reliability of SRMs and constrains some applications.Recently，sensorless technologies have been developed in the Power Electronics and Motor Drive Laboratory—again，at Texas A＆M University.These technologies can ensure smooth operation from zero speed to maximum speed.

New words and expressions（单词和短语）

1.New words（单词）

2.Expressions（短语）

Notes to the text（难点解析）

★1.These sensors are usually vulnerable to mechanical shock and sensitive to temperature and dust.这些检测器通常容易因机械振动而受损，并对温度和尘埃敏感。

Exercises（练习）

◆1.Translate the following passages（expressions）into Chinese（英译汉）

（1）Therefore，the presence of the position sensor reduces the reliability of SRMs and constrains some applications.

（2）outstanding torque-speed characteristics

◆2.Translate the following passages（expressions）into English（汉译英）

（1）无位置检测器技术

（2）开关磁阻电动机

Reading material（阅读材料）

For a purely electric vehicle application，the permanent magnets solution is preferred for many reasons:output in the electric vehicle use area，compactness，mass and noise level.

On the other hand，for a general-purpose use（alternator starter，pure hybrid and electric）and since the cost criterion becomes the determining parameter，the choice of the switch reluctance motor seems relevant compared to the synchronous and asynchronous solutions because of the lower manufacturing cost of the motor and the lowest cost of power electronics，taking into account the weaker control currents for this type of motor.

However，the use of this very promising technology requires two main challenges:

control of noises and vibrations；

reduction of the torque ripple.

Table 5.1 is the comparison of electric motor technologies.

Table 5.1　Comparison of electric motor technologies
（Power 30 kW，Voltage DC200 V，Battery Torque 150 N·m）