Method of Estimating the Stroke of LPMSM Driven by PWM Inverter in a Linear Compressor

Linear compressors with a free piston driven by a linear motor have widely attention in cooling apparatuses such as refrigerators due to their high efficiency. The stroke of piston in a linear compressor driven by LPMSM can be obtained from integrating the EMF of LPMSM, but it may be saturated due to dc components in measured motor voltage and current. The method for estimating the piston stroke by using both the high-pass filter and dc offset compensation is suggested. The attenuation and dc offset of stoke are investigated according to a variation of cut-off frequency of high-pass filter. Through the experiments with 16-bit DSP, it can be seen that the piston stroke is nearly sinusoidal waveform without any dc offset at transient state as well as at steady-state condition.