A Novel Estimation Method of Sensorless Initial Rotor Position for Surface-mounted PMLSM

The detection of the initial position for a sensorless surface-mounted permanent magnet linear synchronous motor (PMLSM) is difficult because it has no salience. The purpose of this work is the development of an estimation method of initial position for surface-mounted PMLSM without a position sensor. The principle of the estimation is based on low frequency voltage injection. The amplitude and phase of the voltage is controllable. When a rotating voltage vector is injected to the motor at standstill, there is a microinching when the voltage phase is line to the direct axis of the motor. Then the current will decrease due to the back electromotive force (EMF). The initial mover position is identified by this change. The method can be performed without motor parameters and the additional hardware. Simulations and experiments show that the initial mover position can be estimated at standstill by using the optimal voltage vector, and that the PMLSM can start smoothly.