Causes of increase in the terminal voltage of a permanent-magnet-assisted salient-pole synchronous machine

Permanent-magnet-assisted salient-pole synchronous machines (PMa-SMs) have the ability to increase the terminal voltages as compared with conventional salient-pole synchronous machines. This paper investigates the main cause of the voltage increase under no-load conditions. The rotor and the stator flux components produced by permanent magnets (PMs) in a PMa-SM are computed by linear finite element analysis with frozen permeability. The results show that most of the flux produced by the PMs remains in the rotor unless the field current is very large. Therefore the main cause of the voltage increase is reduction of magnetic saturation in the rotor field poles.