Design of a microprocessor based current-hysteresis controller

A microprocessor based three-phase independent current-hysteresis controller driving a voltage source inverter is designed for controlling speed of an induction machine. The controller forces the machine current to follow current reference which is regulated, concerning frequency and magnitude, in order to keep rotor speed under control. The assembly routine is executed quickly, so that the hysteresis band can be narrow. Thus, the current approaches an ideal sinusoidal waveform with low high-harmonic content. In addition, the speed control loop succeeds in machine control while keeping the airgap flux constant and, as a result of this, breakdown torque constant. Cooperation of the above control loops is achieved without using interrupts