Sensorless vector control suitable for position-dependent load torque applications

An applicative sensorless vector control with an additional current loop has been developed. The proposed method is suitable for applications such as compressors and pumps that have position-dependent load torque properties because the basic concepts of the proposed method keep motor phase current constant. That is to say, the proposed controller reduces peak current and suppresses rotor speed fluctuation simultaneously by keeping the motor torque constant over one rotation. The additional current loop consists of a periodic component extraction function applying a simplified Fourier transform algorithm and controls the extracted fundamental component of a periodic load torque using the q-axis current controller. Simulation results show detailed behaviors of additional current loop and their effectiveness. Moreover, the effects of the proposed method were clarified by results of an experiment in which a refrigerator equipped with a reciprocating compressor was used as an actual verification application.