Optimal PWM controller for an inverter driven induction motor

The characteristics of inverter-driven AC-drives mostly depend on the chosen controllers and the inverter output voltage synthesis. The paper analyses previous techniques, and derives a digital current controller in field coordinates, in which pulse width modulates the inverter output voltage. The modulator produces good results under steady-state and transient conditions. It is applicable with fast transistors or GTO inverters without any modification. Besides the high efficiency at low switching frequencies, the modulator responds very quickly to large changes in the drive functioning conditions. The modulator is simple to construct and can easily be realized on a single chip microprocessor. It reacts faster than the prediction PWM which is realised on faster signal processors. The average switching frequency of the proposed modulator is, at equal current harmonic contents, lower than that of any other current controller PWM except online prediction optimisation controllers.