Resonant Frequency Tracking Control for a Linear Compressor with Assist Springs

This paper proposes a drive control method for a linear compressor driven by a linear motor. Generally, the efficiency of a linear motor itself is relatively lower than that of a rotational motor. However, higher efficiency should be achievable by adding assist springs and driving at the resonant frequency. We have developed a novel resonant frequency estimation method that calculates the phase difference between a supplied voltage and a mover position. Since the phase difference changes according to the drive frequency with respect to the resonant frequency, our method calculates the phase difference by using the arctangent of a Fourier coefficient, which controls the drive frequency to keep the phase difference at 90°. Experimental results show that the proposed method can successfully track to the resonant frequency dynamically even if the mechanical condition is changed.