Position sensor-less resonant frequency estimation method for linear compressor with assist springs

Higher efficiency for a linear motor should be achievable by adding assist springs and driving the motor at the resonant frequency, even if the efficiency of the motor itself is relatively lower than that of a rotational motor. When using a linear motor with assist springs in a sealed chamber such as a compressor, it is difficult to install a position sensor in such an environment; thus, position sensor-less resonant frequency control is essential. This paper proposes a drive control method that realizes resonant frequency driving without a position sensor. The resonant frequency is estimated on the basis of the detected motor phase current, and the position is estimated using only the fundamental component of the current after removing the offset of the detected current with a high-pass filter. Experimental results show that the proposed method can successfully track the resonant frequency dynamically without a position sensor.