Rotor Angle Estimation Error Compensation Algorithm Based on Extended Back-EMF Sensorless for Low-Speed Operation in Washing Machines

When a motor operates in a washing machine, the laundry and water contribute to the load torque. The characteristics of the load torque vary with the operating speed due to changes in the centrifugal force. The typical speed of the washing cycle is around 50rpm, and at such low speeds, the centrifugal force is relatively weak. As a result, the laundry does not fully adhere to the inner wall of the drum, causing irregular movements and rapid load torque variations. This paper proposes an algorithm to compensate for sensorless angle estimation errors caused by abrupt load torque fluctuations during low-speed operation in washing machines. A speed compensation term reflecting the load torque variations is formulated and integrated into the existing extended back-EMF based sensorless algorithm. Experiments are conducted using a 48-pole surface-mounted permanent magnet synchro-nous motor (SPMSM) for washing machines under low-speed conditions. The experimental results show that the proposed control system with the speed compensation term significantly enhances control stability and accuracy, even under conditions of rapid load torque variations during low-speed operation.