ABSTRACT
This chapter provides the basic principles of direct current (DC) and alternating current (AC) induction machines. Many industrial applications require the provision of a variable-speed rotary drive for their operation. The most common form of DC variable-speed drive is that based on the control of armature voltage using a fully-controlled or half-controlled. The chapter examines their operation in the motoring, generating and braking modes. It addresses the principles of variable-speed drives as applied to both DC and AC induction machines. The chapter also examines the control of drives based on both machine types. It provides some applications of variable speed drives. The chapter deals with briefly other types of electric motor. Cycloconverters are generally used with synchronous machines to provide a low speed, high power drive. Such drives offer high levels of efficiency with good control over a restricted speed range, typically from near zero speed to around one-third or one-half of the synchronous speed set by the supply frequency.
