OPTIMAL CONTROL SCHEME FOR SINGLE PHASE INDUCTION MOTOR

Abstract

The recent increase in electricity prices and the usage of single-phase induction motors
(SPIMs) provide a stimulus for focused research on energy-efficient optimization of SPIM
load such as air-conditioners and refrigerators. Variable speed control of SPIM provides a
promising way forward to reduce its power consumption. However, during variable speed
operation under the popular constant V/f method, SPIM is required to operate at non-rated
conditions. The operation of SPIM at non-rated conditions disturbs its symmetrical and
balanced operation, thus degrading its efficiency. Moreover, soft-starting of SPIM at non-
rated conditions is also challenging due to the resulting reduction in starting-torque. In this
article, after a detailed analysis of SPIM energy-efficiency, an improved sensor-less optimal
speed control strategy is developed to enable the symmetrical and balanced operation of
SPIM at all the operating points over the entire speed-range to improve its performance. A
novel algorithm, termed as the phase-shift algorithm, is also devised for efficient
implementation of the proposed optimal speed control strategy. In addition, a unique
framework for efficient soft-starting of SPIM at very low frequencies is also developed. The
simulation-based results of the motor operated through the proposed phase-shift algorithm
validate the energy-saving potential of the proposed control strategy.