Effects of short-time power outages and open phase failures on IPMSM sensorless rotor position estimation

Sensorless motor drives are claimed to be more reliable than their sensored counterparts, as they avoid electromechanical sensors, additional wires and circuitries. However, the assertion is true only in normal operations. In fact, if on one hand the elimination of electromechanical, and electronic devices increases the drive reliability as a small number of parts subjected to possible faults are present, a sensorless algorithm needs some extra signals to reconstruct the rotor position. Line voltage drops, inverter failures or other disturbances, which, in general, do not affect the behavior of a conventional position sensor, can heavily perturb these extra signals, decreasing reliability. The robustness of sensorless control techniques in abnormal working conditions has been very little investigated in the past. In the paper an experimental analysis regarding the consistence of the estimation techniques is presented, in case of loss of a motor phase, or utility line disturbances. Focusing on Interior Permanent Magnet Synchronous Motor (IPMSM) drives, two main classes of sensorless angular position estimation approaches have been considered: Model-based and HF injection based techniques. Comments on the behavior of these two classes of sensorless approaches are added.