A microprocessor-controlled PWM inverter.

Abstract

The a.c. machine, and in particular the cage-type induction motor, processor several distinct advantages when compared with the d.c. machine. The a.c. motor has however traditionally been considered suitable only for constant speed applications, and for a long time, d.c. motors proved unrivalled in the industry for adjustable speed applications. In the early nineteen-sixties, solid-state inverters, employing the then recently developed thyristor as switching element, were introduced by actable contributors. This resulted in the realisation of a practical and efficient, stale variable- voltage, variable frequency drive for the speed control of three-phase a.c.-motors. In spite of the many advantages of a.c. machines, the cost of the converters and the complexity of the control required, were impeding the widspread application of a.c. drives in comparison with d.c. driver. The research and development efforts, in recent years have been focused mainly in these directions. The cost of control electronic has been substantially reduced by the advent of LSI technology. The microcomputer implementation of the control system not only provides simplification of hardware and improvement of reliability, but permits performance optimisation of the control system not only provides simplifications of hardware and improvement of reliability, but permits performance optimisation of the drive which would not be possible by convectional hardwired control. The availability of power MOSFET devices, with their high switching speeds and very low gate power requirements, has brought about the possibility of simpler, less costly, and improved design of the drive circuity. [ .... ]