Parameters and performance of a high-field permanent-magnet synchronous motor for variable-frequency operation

The paper studies the application of conventional two-axis machine theory to the performance analysis of modern permanent-magnet synchronous motors. A representative motor with radially-oriented samarium-cobalt magnets in a rotor of interior type is considered as an example. Full performance data are measured for the full 360° range of load angles at various supply frequencies. Performance computations using constant motor parameters show significant discrepancies when compared with measurements, particularly at low supply frequency. Detailed determinations of parameter values reveal an important variation of quadrature-axis reactance as a function of quadrature-axis current, owing to magnetic saturation on this axis. When this variation is included within the analysis, together with temperature variation of stator resistance, excellent correlation is shown in all respects.