Efficiency improvement of induction servos in both transient and steady states with fuzzy logic controllers

The purpose of this paper is to improve motor efficiency for a three-phase induction servo system with unity input power factor in both transient and steady states. In steady-state, the rotor flux can be regulated and rapidly converge to optimum efficiency point by the proposed scheme with first fuzzy logic controller. While turning into transient-state, the second fuzzy logic controller is utilized to determine the reduced recovering flux rather than the rated flux for energy saving and convergence acceleration. A new method for flux regulation is also proposed to shorten the delay time of speed response caused by adopting the flux level other than the rated value during the transient-state. The proposed scheme is evaluated with a 1.5-kW three-phase induction motor. The experimental results show that the input power can be quickly reduced from 80 W to 40 W in the steady-state at 1000 rpm. An input energy saving of 65 J can be obtained from using the reduced flux recovery during the transient interval of 15 seconds when motor speed is changed from 500 to 1000 rpm. By the proposed scheme, the input energy saving increases to 150 J under the same conditions and the speed response has not been deteriorated.