Speed control for BLDCM driver using repetitive control

This paper proposes a sensorless speed control method for brushless direct current motor (BLDCM) found in compressors of refrigeration and air conditioning systems. The proposed sensorless control is comprised of a repetitive plug-in controller that operates with variable sampling frequency, where the sampling instants are determined from the zero crossing point (ZCP) of the back-electromotive force (BEMF). The ZCP of the BEMF is obtained by a least squares method which improves the determination of the next phase commutation instant as well as the speed estimation. As a result, it is possible to track speed reference and reject periodic load torque disturbances caused by the compressor. Finally a comparison with a conventional speed control system reveals the good performance of the proposed controller where the first and second harmonic from the load torque disturbance are attenuated significantly.