Field Weakening in Buried Permanent Magnet AC Motor Drives

The usual uncoupled d-q model of salient pole synchronous machines (Park's Model) may be insufficient for accurate modelling of buried magnet permanent magnet machines. This paper shows that the addition of a nonbilateral coupling between the direct and quadrature axis equivalent circuits greatly improves the steady state model. The cross coupling reactance has important implications in improving operation in the constant horsepower mode. In particular, it is demonstrated that the cross coupling term acts to reduce the effective internal voltage so that some field weakening can be achieved. The results should be useful in permanent magnet machine design for variable speed drive applications.