Study on Reducing Cogging Torque of Interior PM Motor for Agricultural Electric Vehicle

Abstract –This paper proposes a new design of rotor shape of Interior Permanent Magnet Synchronous Motor (IPMSM) used for agricultural electric vehicle (AEV). The distribution of the residual magnetic flux density at the air gap is modified by rotor surface shape and V-type magnet angle. As a result, cogging torque and physical characteristic have been improved, and back electromotive force (back-EMF) of the suggested model has been improved to be closest to sine wave form compared to initial model. The validity of the proposed rotor shape optimization is confirmed by the manufactured IPM rotor core and measured the performance of the cogging torque. Keywords: AEV ,c ogin t rque IP MS 1. Introduction Agriculture contributes 9% to the global warming problems according to a report by the Intergovernmental Panel on Climate Chang (IPCC). It was found the agriculture accounts for about 3% of total emitted carbon dioxide in world. In order to reduce the emission of carbon dioxide from agricultural vehicles and to help protect the global the global climate, it is essential that agricultural electric vehicle (AEV) is developed [1]. Accordingly, many countries, especially the advanced countries, show the trend of moving to electric operating system even for agricultural use. Even in the midst of active research and development in electric operating system for such high-demand products as automobiles, we find a conspicuous lack of research and development of agricultural electric vehicles. At the same time, given the steady increase of oil price in the international market and the possibility of technological monopoly by a few advanced countries, it is imperative to put our effort in the development of high-efficiency operating motors, the core of operating system for the electric vehicles [2]. Due to the nature of agricultural farm machinery Electric vehicles driving in the natural space, so the smooth operation in harsh environmental conditions, so be capable of driving motors must satisfy both the durability and reliability and are installed in confined spaces, high efficiency and small size and light weight are essential demand. To meet these requirements permanent magnet synchronous motor is mainly used. Depending on the structure of the rotor permanent magnet synchronous motors Surface Permanent Magnet (SPM) and Interior Permanent Magnet (IPM) IPM motor which can be divided into high-speed operation utilizing reluctance torque can be easily and have the advantage of driving is a trend that is being widely applied to the motor. Especially, interior permanent-magnet synchronous motors (IPMSMs) with potential high efficiency, high power factor, high power density and excellent flux weakening capability is one of the best choices for the electric vehicle (EV) propulsion system [2]. However, the IPM motor has a feature of large cogging torque by the difference caused by unbalanced magnetic reluctance because of the shape of stator and rotor. As cogging torque could cause the vibration and noise of the motor, it is essential to design to reduce the cogging torque [3]-[6]. In this paper, a new rotor shape design of IPM motor for reducing cogging torque is suggested where the distribution of the residual magnetic flux density at the air gap is modified by rotor surface shape and V-type magnet angle. The finite-element analysis (FEA) is applied for the optimal shape design of rotor surface shape and V-type magnet angle, because the IPM motor has an extreme saturation in rotor core. This paper shows the validity of the proposed rotor shape optimization, the manufactured IPM rotor core and the performance of the cogging torque.