General Purpose Microprocessor Modulator for a Wide Range of PWM Techniques for AC Motor Control

For a new concept of optimal digital controls for AC motor drives with PWM (pulse width modulation) inverters, a general purpose control system for generating the switching patterns had to be developed. This system shall be called modulator. On one hand it is designed to provide control signals based upon precalculated and preprogrammed switching angles dependent upon the desired inverter output voltage and frequency levels and based upon given opimization criteria. On the other hand, it is capable of superimposing deadband (on-off) current control. The latter feature is used as a safeguard against overcurrent and also for closely approximating a sinusoidal motor supply current. For realization of this modulator a microprocessor system has been developed and built up based upon the Intel 8085. The requirements stated above have made several new and unique solutions necessary which are briefly described in this paper.