A novel technique for detection and analysis of hunting in line-start IPM motors using stator current signature

A line-start interior permanent magnet (LSIPM) motor is an induction-start synchronous motor. LSIPM motors are subjected to inherent hunting phenomena. Applications such as reciprocating pumps and compressors create periodic load torque variations; inducing hunting in the system. Hunting introduces torsional vibration in the motor drive system. This paper presents a novel technique using the stator current signature to detect hunting for LSIPM motors. Wavelet packet decomposition is applied to analyze the stator current signals for identifying the electrical signatures of hunting. Experimental investigations have been carried out for a 3-phase 4-pole 208V, 1HP LSIPM motor in order to validate the performance of the proposed method under various operating conditions. A 3-phase full bridge IGBT inverter drive is used to operate the motor at variable command frequencies. Based on experimental results, the proposed technique can successfully identify the hunting phenomenon without a vibration/position sensor. It can be applied for LSIPM motors operated by either fixed frequency direct supply or power electronics based variable speed drives.