Maximum Efficiency Operation of Vector-Controlled Synchronous Reluctance Motors Considering Cross-Magnetic Saturation

Abstract

The direct and quadrature axes inductances of flux barrier type Synchronous Reluctance Motors (SynRM) change depending on the magnitude of both direct and quadrature axes currents under the influence of the cross-magnetic saturation. This paper presents a maximum efficiency operation method of SynRMs with cross-magnetic saturation. An improved approximate equation that accurately expresses the inductance variation caused by cross-magnetic saturation is utilized for calculating the Maximum Efficiency Operation Current (MEOC, i.e., the d-axis current at maximum efficiency) at each load point. A vector control system in which the steady-state driving efficiency is maximized by selecting a d-axis current command from the obtained MEOC is shown. By considering cross-magnetic saturation the proposed method not only maximizes the efficiency but also improves the torque control accuracy. The validity of this method is demonstrated with calculated and measured results of on-load characteristics.