An effective start-up algorithm for sensorless synchronous reluctance and IPM motor drives

In the last decade, interior permanent magnet and synchronous reluctance motors are receiving attention from both academic and industrial environments, that appreciate the considerable advantages in terms of cost reduction and power density. However, these motors call for more advanced control techniques, due to the rotor anisotropy and the nonlinearity of the magnetic circuit. Reliability and cost also push towards sensorless solutions. Often, the fundamental-frequency based techniques are preferred to the high frequency injection, for the noise and vibrations that the latter implies. Unfortunately, the former cannot work down to zero speed. The aim of this paper is the study and development of a simple and effective start-up technique for sensorless synchronous motor drives. Merged with fundamental-frequency based sensorless control, it yields a full-range ac drive that fits for many applications that do not require steady state operation at low/null speed. In particular, the paper paves the way for integrating the motor model in the start-up design, highlighting pitfalls of the standard methods and showing how to improve the transition to the closed-loop control.