Publication

Abstract : Today, the most of the industries use variable frequency drives (VFDs) on a large scale. This paper presents a method for implementation of a rule-based fuzzy logic controller (FLC) for a constant speed operation of a three-phase induction motor (IM). The control strategy is based on keeping the voltage–frequency (V/f) ratio constant. A simulation study is done on a 10 HP (7.5 kW), 400 V, 50 Hz, and 1440 rpm three-phase squirrel cage IM. The system consists of a three-phase diode rectifier feeding a three-phase PWM inverter with a dc link capacitor. The inverter is switched at fundamental frequency as dictated by a fuzzy logic controller block. Actual speed of the motor and variation of speed error is the two inputs to the fuzzy logic controller block, and variation of frequency is available as the output of this block. This variation in frequency is added to the preceding sample frequency of the inverter to obtain the current fundamental frequency of the inverter. The V/f block determines the fundamental voltage magnitude of the motor corresponding to the current frequency. The same control algorithm is implemented using a PI controller. A complete simulation in closed loop of the model is carried out and the machine was found to be running at the set speed. The performance of fuzzy logic-based control is seen to be superior compared to that with a conventional PI controller.