Permanent magnet synchronous motors (PMSMs) are expected to be downsized traction motors for railway vehicle, because the efficiency of PMSM is higher than that of induction motors.Rotor angle is usually measured by rotational position sensor, such as encoders or resolvers, for precise current (torque) control according to the rotational angle. Position sensorless control, which requires no encoder, is discussed to be applied, because railway vehicle traction systems require higher reliability.To reduce switching loss, an inverter for railway vehicle traction stops its switching at coasting condition after acceleration. Therefore, starting procedure at coasting condition is technical issues to be solved for rotational sensorless control system of PMSM for railway vehicle traction application. Instantaneous initial rotor position and speed estimation, right after gate start, are very essential for restarting operation of inverters. The current information is easily used for the estimation of initial rotor position and speed, because inverters for railway vehicle traction are equipped with current sensors.Restart methods employing only current sensors have been reported. The methods estimate initial rotor speed and position by three phase short circuited current vector by inverter arms on. The methods are premised on a speed of 150 Hz or less and a current control period of 300 µs or less in general purpose inverters Fig. 1. The experimental result of proposed method application. However, the maximum rotor speed of PMSMs for railway vehicle traction is approximately 300 Hz and the current control period of inverters for railway vehicle traction is 500 µs or more. Therefore, the methods are not available for railway vehicle traction system unless arranged.To cope with this problem, we propose a novel estimation method of the initial rotor speed. The proposed method estimates the initial speed by the derivative of each phase angle of the current vector at three short circuited periods.The proposed estimation method is verified by experiments using a 4-pole, 2 kW, 2100 rpm mini model test prototype.The figure 1 shows results of the inverter restart at 300 rpm, at 1000 rpm, at 1800 rpm, at 2100 rpm, respectively. Where, V DC is inverter input DC voltage, i d and i q are respectively d and q axis currents, i m is motor current vector amplitude, i u is U-phase current, E m is inverter output voltage reference, T m is motor torque, N real is actual rotor speed and N est is estimated rotor speed.The test result of Fig. 1 shows that the proposed method estimates initial rotor position and speed at high accuracy in full speed range and enables applications with higher maximum rotor speed and longer current control period to restart stably. This paper confirms that the proposed method contribute to increase the reliability of PMSM traction systems for railway vehicle.-3 -