Sensorless Commissioning of Synchronous Reluctance Machines Augmented with High Frequency Voltage Injection

This paper deals with the self-commissioning of synchronous reluctance motors. Previous work has demonstrated that the motor flux maps can be accurately identified at standstill by exciting the machine with square-wave voltage pulses of large amplitude, of the same order of the machine nominal voltage. This was made without the need of rotor locking and without using position sensors. The knowledge of the d and q axes position was obtained by a preliminary sensorless commissioning and then used for directing the d and q voltage pulses accordingly, in open-loop fashion. At free shaft, the position tends to oscillate under such alternated excitation, introducing position error and thus inaccuracy. For high values of the torque current component the rotor can even start spinning suddenly, thus stopping the identification. The loss of control impedes of identification of the flux maps above a certain limit, at least in the q direction. In the past, polynomial fitting was used to extrapolate the flux map in the missing parts of the dq current domain, with good results. In this paper, the rotor position is closed-loop estimated during the motor commissioning, so to counteract the occurrence of sudden spin and extend the explored current area in the q direction. An additional pulsating voltage, also of the square-wave type, is superimposed to the main excitation voltage, and the position is tracked through current demodulation. In this way, the area explored in the dq current plane is substantially extended, if compared to previous method. The proposed approach is verified through experimental results on one synchronous reluctance motor prototype.