Power electronics

Abstract

POWER ELECTRONICS is the name given nowadays to the study of circuits and systems using solid-state devices to control electrical power. Though power devices such as SCRs became common in high-voltage traction motors as long as thirty years ago, it is only in the last ten years that the marriage of microprocessors and power devices has brought about a revolution in the control of electrical power. This revolution is especially noteworthy in electric motor drives. We have seen that speed control of AC motors was not easy from a supply of fixed frequency, and that DC motors were preferred when a large range of speeds was required. Power electronics has removed that restriction by making it possible to operate AC and DC machines over a large range of speeds by varying the frequency or the voltage, or both, of its supply. In essence the methods are

• 1. AC(f₁, V₁) → converter → AC(f₂, V₂)

• 2. AC(f₁, V₁) → rectifier → DC → converter → AC(f₂, V₂)

There is no space here to go into the details of control circuitry but some of the essentials of power electronics can be discussed, starting with the three-phase bridge rectifier.