Online load torque compensator for single rolling piston compressor

A single rolling piston compressor (SPRC) is commonly applied to the low power room air-conditioning system because of the low cost. The SRPC has only one compression and discharge process per each mechanical rotation. During compression process of the refrigerants, the load torque is quite high. On the other hand, during discharge process, of the refrigerant from the compressor room, the load torque is low. This load torque variation makes speed ripple and induce severe vibration, which causes fatigue failures of pipes and compressor parts at low speed. To relieve the vibration, the compressor usually operates in the high speed range where the rotor and piston inertia reduce the vibration phenomenon. Or a predefined feed-forward load torque compensator is used at low speed to minimize the speed ripple and vibration. However, since the load torque variation varies depending on the temperature, pressure, and speed, the predefined load torque table, based on one operating condition, is not appropriate to all. In this paper, an on-line load torque observer for SRPC is proposed. The proposed method utilizes the speed ripple as load torque ripple factor. The speed ripple is transformed into frequency domain and compensates each frequency harmonic term in a feed-forward way independently. Experimental results are presented to verify the proposed method.