Robust low-cost control scheme of direct-drive gearless traction machine for elevators without a weight transducer

This paper proposes a novel low-cost control strategy of gearless traction permanent-magnet synchronous machines for direct-drive elevator applications. It can improve robustness of the weight-sensorless traction machine system installed with an ordinary incremental encoder. In order to improve the riding comfort for the passengers during brake releases, a novel starting torque compensation strategy without a weight transducer is presented. After analyzing the dynamic characteristics and the friction torque of the elevator traction system, two starting torque compensation methods based on the dichotomy and the staircase method are proposed for the weight-sensorless elevator applications. This way, electromagnetic torque can be generated to balance the load torque, and sliding can be prevented when the elevator brake releases during the starting operation. To achieve the current vector decoupling control for the traction machine installed with an incremental encoder, the initial rotor position estimation at standstill based on a hybrid signal injection method is adopted. First, a high-frequency oscillating sinusoidal voltage signal is injected to obtain the magnetic pole position. Then, two pulse voltage vectors are injected in the positive and negative directions to identify the magnet polarity. The experimental results demonstrate the feasibility of the proposed control strategy with an 11.7-kW traction machine.