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In electric vehicles driven by an AC motor，it is not possible to directly connect this type of motor to the continuous voltage source that the battery constitutes.It is necessary to interpose between the energy source and the traction motor（s）a conversion（called an inverter）which transforms electrical DC current into electrical AC current and which makes it possible to carry out the control of the motor torque and the speed regulation of the vehicle both in the traction mode and in the braking mode.

Continuous-to-alternate conversion can be produced in multiple ways but the characteristics of road vehicles and the rationalization of industrial solutions have resulted in favoring an inverter structure with six bidirectional switches constituted by the association of an IGBT and a diode assembled in anti-parallel and controlled according to a standard PWM function.This type of assembly makes it possible to associate a voltage source（like a battery）and a receiver of the power controlled in current（asynchronous motor，synchronous motor wound or with permanent magnet）.It should be noted that in a PWM inverter，the output voltage is a succession of voltage pulses（square pulses of voltage）of variable width so that the average value of the fundamental of this wave is sinusoidal over the period of stamping.The moments of switches'shutdown and opening are generally given in real-time by means of appropriate control electronics.

This control method has two important advantages:

—it pushes the output voltage harmonics back towards the high frequencies，which facilitates voltage filtering；

—it makes it possible to vary the value of the fundamental output voltage.

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.It should be noted that in a PWM inverter，the output voltage is a succession of voltage pulses（square pulses of voltage）of variable width so that the average value of the fundamental of this wave is sinusoidal over the period of stamping.需要明确的是，在PWM逆变器中，输出电压是一系列不等宽的脉冲电压（矩形脉冲电压），但在一个周期内该波形的均值变化与正弦波等效。

Exercises（练习）

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

（1）An inverter is a converter of DC current to alternative current.

（2）asynchronous motor

（3）voltage filtering

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

（3）在交流电动机驱动的电动汽车上，电动机是不能与电池组成的电源直接相连的。