Identification of mechanical properties in brushless permanent magnet motors by means of coil impedance measurement

In this paper we present a new vibroacoustic and electro-mechanical coupled lumped equivalent network, which accurately describes torsional vibration conditions of permanent magnet synchronous motors (PMSMs) in case of single-phase pulsating current excitation in conjunction with small angular displacement of the rotor. Our model contains both mechanical and electrical parameters of the motor and yields their dependence upon rotor position and explains vibroacoustical effect of cogging torque. We introduce an experimental technique for the measurement of quantities proportional to mechanical and electrical impedance of the motor, than we provide a method for curve fitting and parameter identification on the measured transfer functions. Finally we present a case study on the detection of possible faults when cementation of the rotor magnets is not satisfactory.