Novel Speed and Rotor Position Estimation Strategy Using a Dual Observer for Low-Resolution Position Sensors

Recently, high-performance ac motor drive technologies, including field-oriented control (FOC), have been widely used in home appliance products such as direct-drive drum washing machines. In low-cost ac machine drive systems, speed or position sensors with high resolution are not available due to high costs. Instead, 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. In addition to the low resolution of the sensor, its accuracy is poor due to mechanical errors and signal processing. The inaccurate and delayed position information degrades the performance of current regulation and also increases torque ripples, which is the source of mechanical vibration and acoustic noise. In order to overcome this hardware problem, this study proposes a software technique based on a novel dual observer and a position sensor offset compensation strategy. The dual observer can estimate the rotor speed and position without time delay or bumps. Also, with the compensation algorithm for position sensor offset, the misaligned synchronous reference frame $d$- and $q$-axis can be corrected. Experimental results verify the effectiveness of the proposed method.