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 article proposes a novel restart strategy based on continuous short-circuit current for a wide speed range. In particular, 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.