모드 변경 회로를 이용한 고효율 권선 계자형 동기 전동기 설계

Abstract

A motor that uses a rare-earth permanent magnet (PM) usually has a high power density and can operate at a high speed by using flux weakening control, which can reduce the flux of the PM. For this reason, small and large PM motors are currently widely used. The price of the rare-earth PM, however, has risen and has become unstable. China, which produces over 90% of the rare-earth PMs in the world, regulates its production and trade as part of its rare-earth industry development plan and rare-earth industry development policy. Therefore, other countries have no choice but to depend on China for such rare-earth PMs. Consequently, it is important to develop an electric machine that can minimize the use of rare-earth PMs or that does not use rare-earth PMs at all. Wound field synchronous motor (WFSM) is a representative rare-earth free motor and has the advantages of a wide operation range and of having the ability to control the field and armature currents without using a PM. For this reason, WFSM has received much attention from various industries as an alternative for the existing rare-earth PM motors. With regard to the saliency characteristics and nonlinearity of WFSM, it was found that it has difficulty reducing the field current and operating effectively at a high speed due to the saturation of the induced voltage. In this paper, these limitations of WFSM are analyzed, and a new design method that can improve the efficiency and drive characteristics of WFSM in a high-speed region is proposed. First, the coil of the motor teeth was divided into coil 1 and coil 2, and dual winding was done. Coil 1 and coil 2 were then connected to the switching circuit. The connected circuits were connected to the inverter to drive the motor. The two coils are connected in series when driving at a low speed and high torque, and can enable driving by enhancing the series turn per phase. The series turn per phase can be lowered by connecting the two coils parallel to each other or turning off one coil at the time of driving at a high speed. Lowering the inductance, armature phase resistance, and induced voltage can reduce the phase angle of the current and can improve the efficiency when driving at a high speed. The performance of the motor was analyzed through a simulation and an experiment, by applying the proposed design method to WFSM, and the effect of the proposed method was verified.