Improvement of the Constant-Power Speed Range of Surface-Permanent Magnet Machine Using Winding Switching

Abstract

In this study, a cumulative/differential winding switching method is proposed for the extended constant power operation (CPO) of a surface-permanent magnet (SPM) machine. In this method, the three-phase winding of the machine is divided into two equal sub-phase sets, and field weakening is realized by switching the interconnections between the sets. The field-weakening ratio depends on the shift angle between the two sub-phase sets. Hence, it is possible to adjust this angle to obtain a constant power speed range (CPSR). The dependence of the CPO possibility of the proposed winding switching method on the shift angle is analyzed. The analytical requirement for the CPO is formulated, and an algorithm for choosing an optimal winding layout is proposed. The winding switching method is then implemented on a four-pole 24-slotted surface-permanent magnet synchronous machine, and the stator winding is changed according to the CPO requirement. The finite element modeling and experimental results verify the extension of the CPSR to four per unit (pu), using the proposed winding switching method with a suitable shift angle. Hence, this method is suitable for constant-power applications, such as traction and electric vehicles.