Improving sound quality of reciprocating compressor using random PWM

Recently, it has become more common to apply inverter systems to household electrical appliances in order to reduce their power consumption and acoustic noise through low speed operation, and to make their function more comfortable for human beings. For the inverter systems, however, it is highly required to reduce undesirable electromagnetic noise and psychoacoustic noise generated by PWM for variable speed operation. In this paper, the electromagnetic noise for deterministic PWM and random PWM methods applied to reciprocating compressors driven by brushless DC motors was analyzed. It was verified through experiments that applying random PWM reduced the appliance electromagnetic noise and improved the sound quality.