Identification of the magnetic model of permanent magnet synchronous machines using DC-biased low frequency AC signal injection

This paper proposes a simple testing procedure for accurate identification of the magnetic model of permanent magnet synchronous machines. The proposed method accounts for the magnetic saturation and the cross-saturation effects. The methods that are available from literature require a servomotor to drive the motor under identification at controlled constant speed and sometimes a torque sensor is mandatory. The proposed method can be applied with or without rotor locking and uses dc+ac injection strategy to identify the machine inductances to construct the magnetic model. The direct current sets the operating point while the superimposed ac component estimates the inductance at that particular point. Small ac signal is injected to ensure local linearity of the magnetic characteristic. Saturation effects are automatically accounted for by the dc bias and cross saturation effects are considered through maintaining a constant current along the cross-axis. The obtained magnetic model can be used for optimal control of the machine and for accurate torque estimation in vector controlled drives.