The use of microprocessors in the control of electric motors offer several advantages over traditional analog controllers. Probably the single most important advantage is the ability of the microprocessor to perform signal processing functions which previously required relatively complex analog circuitry. Moreover, a microprocessor based control system can be adapted to control different motors merely by reprogramming the microprocessor, without the need for extensive hardware modifications.
Microprocessor based A.C. motor control systems typically generate a group of PWM (pulse - width - modulated) waveforms for switching a group of motor driver switching elements (typically either thyristors or power transistors) to produce the motor driving waveforms. The number of PWM waveforms required depends on the number of phases supplied to the motor and the type of switching elements in the motor driver. In some instances, it is desirable to suppress certain harmonics in the PWM waveform to militate against undesirable effects on the motor. For example, in the control of three phase motors, multiples of the third harmonic (3rd, 6th, 9th, etc.) are often eliminated to reduce the heat generated by the motor.