A Novel Strategy of Efficiency Control for a Linear Compressor System Driven by a PWM Inverter

Linear compressors with a free piston driven by a linear motor have attracted wide attention in cooling apparatuses such as refrigerators due to their high efficiency. The method of using triacs as a linear motor drive is not satisfactory for improving the efficiency of linear compressors. In this paper, the performance of linear compressors using a pulsewidth modulation inverter is investigated, with emphasis on the efficiency and power factor along with variations of both mechanical and electrical resonant frequencies. The strategy for improving the efficiency of the linear compressor is suggested by controlling the average value of the product of the piston stroke and motor current to 0. The performance of both the stroke and efficiency controls of the linear compressor is verified through experiments under various gas pressure conditions.