Microprocessor based pulse width modulated inverter

Abstract

Microprocessor control of variable voltage and variable frequency inverter drivers has many advantages over conventional analogue techniques; such as improved reliability, manufacture, maintanence and servicing, and increased control flexibility. In addition that, precise timing and suffcient harmonic elimination can be obtained. It also results from a reduction in the complex control circuitry since it is replaced by microprocessor software. As conventional method, a desired sinousodial wave is modulated with a carrier triangular wave, however it has essentialy some defects such as: (a) insufficient tolerance of temperature fluctuations. (b) when the two waves are not synchronised, a short pulse can occur and causes commutation failure. (c) if a precise control is desired, circuits become much complex, as a result, it increases cost substaintially. (d) analogue method can do nothing for harmonic minimization. The digital control can solve these problems, in addition posseses the following advantages. (a) since data are calculated beforehand, the output waveform has high quality, for exam.ple of harmonic suppression. (b) it is easy to add new functions or to modify them since they are under the software control of the microprocessor. In this thesis, a software based pulse vlidth modulated (PWM) inverter drive eystem is presented. Emphasis is placed on minimization of the hardware requirements. An additional critarion is that an efficient program structure is used in order to minimize the computation time required; hence increasing the operational speed considerably.