POWER ELECTRONICS

Instructor: Eng. Jalal Al Roumy

The Islamic University of GazaFaculty of EngineeringElectrical Engineering Department

الرحمن الله بسمالرحيم

EELE 5450 — Summer 2012

Lecture 15

Chapter six

DC Choppers and DC motor ControlVarious methods are available for obtaining a variable dc voltage from a constant dc source.

There is a demand for changing from one dc voltage to another.

Some of the more important practical applications include power converters or armature voltage control of dc motors, converting low or high battery source voltage to levels which best match practical load requirements, and controlling dc power for a wide variety of industrial processes.

Chapter six

DC Choppers and DC motor Control

The thyristor converter offers greater efficiently, faster response, lower maintenance, smaller size, and for many applications, lower cost than motor-generator sets or gas tube approaches.

In thyristor-type dc-to-dc converters, commutating circuits are required similar to those used in many inverters.

Chapter six

SCR Voltage Choppers

Control of a dc motor’s speed by an SCR voltage chopper is required where the supply is dc (as from a battery) or the ac voltage has already been rectified to a dc voltage.

Chapter six

SCR Voltage Choppers

Vout could be varied by the following methods:1. Ton may be varied while T is held constant (PWM).2. Ton may be kept constant while T is varied (freq. modulation).3. Combined pulse-width and frequency modulation.

Chapter six

A Free-Wheeling Diode DC Motor Drive Using the Jones Chopper

This circuit is frequently referred to as a chopper circuit.

Chapter six

A Free-Wheeling Diode DC Motor Drive Using the Jones Chopper

End of Lecture