An automatic efficiency optimizer for fractional-horsepower appliance motors

It is a known fact that when an AC motor operates below its rated load, its efficiency can be improved by reducing the supply voltage to an appropriate level. This paper proposes an automatic voltage controller that optimizes the efficiency of fractional-horsepower motors when operating under variable load conditions. The scheme is based on perturbing the supply voltage (by controlling the firing delay angle of a triac) and observing the power drawn by the motor, and the process is repeated until minimum power is reached - thus referring to it as a Minimum Power Point Tracker (MPPT). Due to the simple convex property of the motor power-voltage curve for a given mechanical load, the method always reaches the optimal solution even under severe waveform distortion. The proposed method is validated by laboratory tests on fractional horsepower motors of major home appliances.