Computer Control Of A PWM Induction Machine Drive System

The aim of this paper is to study and realize a universal control scheme for a pulse width modulated drive system using the capability of digital computation in real time. Two micro-processor-systems and additional digital and analog circuits are implemented in order to fulfill that control scheme. The system speed would be dynamically changed for a wide range, starting from stand still up to twice the nominal speed in the field weakening range. Also at the same time, the maximum source voltages and currents are fully used. The implementation of the circuit to produce the firing pattern for the pulse width modulated inverter depends on voltage signals corresponding to the phase voltage instead of phase currents in order to eliminate the torque and field errors which will occur at high frequencies due to the inequality of the sinusoidal desired and actual currents. The control system is tested using a 2.5 KW squirrel cage motor and the obtained results prove that the system is stable and suitable to be implemented in industrial applications.