5.3.3　Choppers

Text（课文）

1.Definition

A chopper is a current converter which makes it possible from a DC voltage source（at constant voltage value）to adjust and control voltages and currents，different from the input values and adapted to the necessary needs to supply various receivers（motors，batteries，etc）.

2.Description

In its basic version，an electronic chopper is composed:

of a controllable switch（IGBT，MOSFET，GTO，etc.）；

of a freewheel diode；

of passive components，coils and capacitors，which provide the functions of filtering input and output chopper currents.The mass and volume of these components depend for a large part on the operating frequency of the power switch；

of the controlled device.

3.Usage of choppers in electric vehicles

In an electric vehicle choppers have two essential applications:

firstly，they are essential in the supply of propulsion motors when these are DC motors；

secondly，they are necessary to adapt the main battery voltage to that of the electronic auxiliaries and 12V network used（sensors，regulators，etc.）.

The use of a chopper indeed makes it possible to maintain the motor current with the desired value while ensuring the progressive adjustment of the motor voltage without notable loss.The chopper allows us to regulate the torque and the speed of the motor and thus of the vehicle in traction but also during electric braking.This braking can be energy recovery，rheostatic or combined—i.e.associated with electric braking and a part of mechanical braking.Of course，specific provisions must be taken to carry out the necessary controls and protections，for example the use of a filter situated between the battery and the chopper itself to ensure the decoupling of the voltage source consisting of the battery and the traction 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.A chopper is a current converter which makes it possible from a DC voltage source（at constant voltage value）to adjust and control voltages and currents，different from the input values and adapted to the necessary needs to supply various receivers（motors，batteries，etc）.斩波器是将电压值固定的直流电，转换为电压值可变可调的直流电源的装置，输出的电压不同于输入电压并且可以适应各接收器的所需电压（电动机、电池等）。

Exercises（练习）

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

（1）They are essential in the supply of propulsion motors when these are DC motors.

（2）The chopper allows us to regulate the torque and the speed of the motor and thus of the vehicle in traction but also during electric braking.

（3）energy recovery

（4）power switch

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

（1）斩波器

（2）续流二极管

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

What is the chopper？

Reading material（阅读材料）

Indeed，we cannot consider the brutal connection of a DC motor on fixed-voltage energy source batteries for example—for two reasons:

no adjustment of the motor torque or speed would be possible；

the direct electric motor supply would be destructive from both an electric（overcurrent）and a mechanics（overtorque），point of view.

The use of a current chopper located between the energy source and the DC motor makes it possible to solve these two constraints and it brings significant progress with respect to the startingup processes:insertion of a variable resistor in series between the source and the motor.