A Novel Restart Strategy for Sensorless Rail Traction PMSM Drive with Continuous Short-circuit Current

In rail traction, rotating restart is a common operational condition. For permanent magnet synchronous motors (PMSMs), obtaining accurate speed and rotor position prior to restart is crucial. In sensorless control system, the short-circuit current method is the most commonly used approach to obtain the initial position and speed. However, due to strict limitations on short-circuit time and interval time, this method is limited to a narrower speed range. This paper proposes a novel restart strategy based on continuous short-circuit current for wide speed range. Especially, it can handle the case that the amplitude of back electromotive force (EMF) exceeds the direct current (DC) bus voltage. Taking stator resistance into account, a mathematical derivation of the short-circuit current is performed. Using the continuous short-circuit current and a phase-locked loop (PLL), the initial motor speed and position are estimated. Furthermore, by applying the test zero-voltage pulses (ZVPs), the initial speed range is determined. The effectiveness of the proposed method is verified by simulation and experimental results.