This paper proposes a smooth transition method from I–f starting control to back electromotive force (EMF)-based sensorless control in an interior permanent magnet synchronous motor (IPMSM). In the low-speed region, the back EMF is too small for accurate estimation. Thus, current-frequency (I–f) control is widely used for motor start-up. In conventional methods, the transition from I–f control to back-EMF-based sensorless control leads to large current ripple due to the mismatch of operating points. Therefore, this paper presents a method that matches the operating point at the transition, enabling the IPMSM to operate precisely at the maximum torque per ampere (MTPA) point. The proposed method uses the current vector and the angle error between (I–f) control and Back-EMF sensorless; therefore, it does not require mechanical parameters that are generally unknown, such as the inertia (J) and viscous friction coefficient (B). In addition, since this method performs the control transition while the motor is accelerating, it enables a robust and rapid transition. The validity of the proposed method is verified through simulation result.
