A microcontroller-based soft-starter for residential air-conditioners: harmonic analysis

Purpose - The purpose of this paper is to reduce the inrush current and dip in voltage for energy-saving purposes in relation to residential air-conditioning systems. Design/methodology/approach - The paper focuses on the experimental harmonic investigation of a window-type residential AC unit line current under time-based soft-starting control strategy. The control strategy assumes that only source voltage and current measurements are available. The soft-starter is based on power electronic devices controlled through a firing signal generated by a programmed microcontroller during the first 500 ms. Findings - The harmonic content shows the effect of the soft-starter in exciting high-frequency components of the line current. Harmonics investigations show that the high frequencies - even or odd multiples - of the fundamental line frequency are all excited by the soft-starter approach. Some of these frequencies may harm the life cycle of the air-conditioner. Research limitations/implications - The real data harmonic analysis shows that the adopted approach excites the entire frequency spectrum of the signal. A better monitoring of the harmonics is required. A closed loop adaptive soft-starting control may perform much better than a time-based soft-starting strategy. Originality/value - The paper assesses the power quality related to time-based soft-starting strategy of a residential air-conditioning system to reduce the inrush current and the dip in voltage, both with a serious effect on energy savings, especially when the AC load is around 65 per cent of the total power demand load.