Novel speed and rotor position estimation strategy using a dual observer for low resolution position sensors

Recently, high performance AC motor drive technologies including a field oriented control (FOC) are widely used in home appliance products such as a direct- drive drum washing machine. In home appliance, speed or position sensors with high resolution are prohibitive due to the cost problems. Usually, a low resolution sensor is installed to calculate the speed and rotor position. In the FOC, however, accurate rotor angle information is essential for high performance torque control. On top of the low resolution of the sensor, the accuracy of the sensor is poor due to mechanical errors of sensor itself and installation. The inaccurate and delayed position information degrades the performance of current regulation and also increases torque ripples, which is the source of vibration and acoustic noise. In order to overcome the hardware problems, this paper proposes a software technique using a novel dual observer and position sensor offset compensation strategy. The dual observer can estimate the rotor speed and position without any time delay and bumps with the compensation algorithm for the position sensor offset by adjusting the misaligned synchronous reference frame d and q-axis. Experimental results verify the effectiveness of the proposed method.