INTRODUCTION.

Electric motors are around us everywhere. Generators in power plants are connected to a three-phase power grid of alternating current (AC), pumps in your heating system, refrigerator and vacuum cleaner are connected to a single phase AC grid and switched on or off by means of a simple contactor. In cars a direct current (DC) battery is used to provide power to the starter motor, windshield wiper motors and other utilities. These motors run on direct current and in most cases they are activated by a relay switch without any control. [ABSTRACT FROM AUTHOR]