Restart Strategy for Sensorless Control of Permanent Magnet Synchronous Motor in Flux-Weakening Region

In railway transportation applications, especially during the transition through neutral sections, it is necessary for the motors to restart at specific speeds. For permanent magnet synchronous motors (PMSMs) operating in the flux-weakening region, this presents a significant challenge with sensorless control strategies due to back electromotive force (BEMF) and the lack of position and speed information. This paper proposes a sensorless restart strategy that combines a single zero-voltage vector with a cascade extended state observer (CESO). During motor restart in the flux-weakening region, this method regulates the opening and closing of the contactor to mitigate the effects of uncontrolled rectification. The initial position and speed of the rotor are calculated using the current generated by a single zero-voltage vector, and fast convergence is achieved using a CESO to ensure the success of the restart process. The effectiveness of this method has been experimentally verified, demonstrating its potential to improve the reliability and efficiency of PMSMs in railway applications.