Fuzzy speed control in drive systems with voltage inverters and induction motors

The aim of this paper is the implementation and validation of a fuzzy logic speed controller, for a voltage inverter and asynchronous motor drive system. The fuzzy controller has an aperiodic response, and gives good speed regulation at high mechanical load changes. On the other hand, it gives a small stationary error, and the controller is instable at very low speed or high speed change. The speed controller input variables are the speed error and the speed error change, and the output variable is the frequency of the inverter output voltage. The inverter gating signals were obtained using the classical sinusoidal PWM modulation. The sinusoidal control voltages of the PWM modulator were obtained as a function of frequency (speed controller output). Changing the direction of rotation was obtained by imposing negative speed. As a result, the fuzzy controller outputs negative frequency which is evaluated by the PWM modulator changing the phase shift. The control system has only one control loop which is the speed control loop, so the current through the motor windings is not limited. Although, the current stress is low, even at time moments when the output frequency has a steep change or when the motor load is connected. The controller implementation and validation was accomplished on a comprehensive drive system built in the Matlab Simulink environment.