A New Bumpless Rotor-Flux Position Estimation Scheme for Vector-Controlled Washing Machine

Abstract

For a washing machine, permanent-magnet (PM) motors are commonly used due to their superior efficiency, high torque-to-volume ratio, and so on. PM motor driving system with vector control scheme requires rotor-flux position information. Hall-effect position sensors are often used for that purpose because their volume is small and is cost effective compared with other types of position sensor such as an encoder, even though they have low resolution of position information. Generally, two low-resolution hall-effect sensors are employed to provide rotor flux position for cost reduction purpose and it means four resolutions per one electrical 360° rotation. The detected rotor-flux position by hall sensor signals is manipulated to change linearly by interpolation method. However, because of electrical and mechanical nonuniformity associated with hall sensors, the calculated or estimated position is not linearly changed. In other words, there exist bumps at the point where hall signal occurs even at the constant speed operation and it degrades control performance. To solve this problem, this paper proposes a novel scheme for bumpless position estimation. In addition, the proposed reduced-order observer does not use mechanical parameters such as inertia. The validity and effectiveness of the proposed algorithm are verified by experiments on a top-load washing machine vector-controlled with two Hall-effect sensors.