A constant-parameter equivalent-circuit model which neglects motorlosses is used to determine the effects of d-qreactances and open-circuit voltage on the power capability of salientpole permanent magnet motors in variable-speed-drive applications. It isshown that peak power capability over a range of speeds can be obtainedby proper control of the armature current magnitude and phase. Due tothe voltage constraint imposed at the motor terminals, the powercapability will fall to zero for most motor designs at a given highspeed. A simple relationship between the motor open-circuit voltage andthe direct axis reactance is derived to obtain motor designs that, evenwith this voltage constraint in place, extend their theoretical powercapability, neglecting losses, to infinite speed. All results arepresented in normalized curves using a per-unit system
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