고조파 철손을 고려한 농형 유도전동기의 고조파 등가회로

Abstract

Recently, electric power steering (EPS) has become an increasingly popular alternative to hydraulic power steering (HPS) because of advancements in electrical machines and control electronics. EPS offer several advantages over conventional HPS, such as improved fuel economy, and ability to provide assistance even when the engine is off. These benefits result in significant energy savings. The interior permanent magnet synchronous motor (IPMSM) is the most commonly used type of motor in electric and hybrid vehicles owing to its high power density and high efficiency. However, the unstable price of rare-earth magnets has restricted the use of motors requiring such magnets. An induction motor (IM), which does not require rare-earth magnets, has a relatively simple motor structure and low manufacturing costs. As a result, studies are focusing on the characteristic of IMs with a view to them replacing PM motor. It is essential to consider the saturation of the core when designing a motor for automotive applications, because automotive electric motors face many size limitations. The most convenient method for analyzing the characteristics of a squirrel cage IM is finite element analysis (FEA). This method, however, requires much computational time and a large memory capacity. Additionally, the estimation of the motor characteristics is limited because the FEA can not consider the core loss. To improve the reliability of the characteristic analysis, a new method that can resolve these problems is required. Thus, a new equivalent circuit that considers the saturation of the core and the harmonics of core loss is required. Consequently, to reliably determine the characteristics of an IM, this paper presents a modified space harmonic equivalent circuit that considers the harmonics of the core loss resistance. Then, the flux density in the core is calculated using the magnetic circuit of the motor, to reflect the saturation of each core. Finally, an input current wave considering the harmonics and saturation is calculated. The reliability of the harmonic equivalent circuit is verified. The characteristics of the motor analyzed by the classical equivalent circuit (fundamental wave) are compared with the performance calculated by the proposed harmonic equivalent circuit analysis. Additionally, the experimental apparatus and a fabricated IM are described, and the validity of this study is assessed by testing the IM in EPS.