This paper proposes a smooth pulse number transition technique of synchronized pulse width modulation (PWM) for an interior permanent magnet synchronous motor (IPMSM) sensorless control. Conventional sensorless control based on back electromotive force (EMF) has the problem that the current and voltage used as inputs to the back EMF observer are transformed using one sampling delayed estimated position. This results in time delay in current and voltage estimation, and discontinuity problems in frame transformation because the control period changes rapidly at the pulse number transition of synchronized PWM. The proposed technique analyzes and compensates for the time delay effects in terms of discrete time on the input and output terms of the back EMF observer. Additionally, by analyzing the process of calculating the estimated position, an estimation technique is introduced considering the rapidly varying control period at the pulse number transition point. Therefore, the proposed technique can overcome the problem of current surge at the pulse number transition point. The validity of this paper is verified by experimental results.
