Starting and ultra low-speed control strategy for gearless traction permanent magnet synchronous machine

This paper proposes an improved control strategy of gearless traction permanent magnet synchronous machine installed with an incremental encoder for the direct-drive elevator applications. To achieve the accurate current vector decoupling control for the traction machine at starting operation, the initial rotor position estimation at standstill based on a hybrid signal injection method is present. Firstly, 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 the negative direction to identify the magnet polarity. On the basis of the traction machine state equations, a continuous speed observer is proposed adopting a full-order state observer. Therefore the continuous speed feedback information can be obtained according to the output signal from an ordinary incremental encoder. This way can make the traction machine drive achieve high-performance extra low-speed operation. The experimental results demonstrate the feasibility of the control strategy by an 11.7kW gearless elevator traction machine.