Journal of Energy Technologies and Policy www.iiste.org ISSN 2224-3232 (Paper) ISSN 2225-0573 (Online) Vol.1, No.4, 2011 8 Modeling Power Losses in Electric Vehicle BLDC Motor James Kuria 1* Pyung Hwang 2 1. Department of Mechanical Engineering, Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62000-00200, Nairobi, Kenya 2. School of Mechanical Engineering, Yeungnam University, Gyeongsan, 712-749, Republic of Korea * E-mail of the corresponding author: jkuria@eng.jkuat.ac.ke Abstract In order to design an efficient motor cooling system, it is important to accurately predict the power losses which are normally dissipated in form of heat. This study presents an analytical method for estimating bearing frictional losses and numerical method for estimating electromagnetic losses for an electric vehicle BLDC motor. The power losses obtained are used as heat sources when evaluating the thermal performance of the motor. The results showed that electromagnetic losses are dominant and contribute over 80% of all losses, while bearing losses contribute about 12% of the total electric motor. The results also showed that bearing losses increase significantly with increasing speed or load. Keywords: BLDC motor, bearing frictional losses, electromagnetic losses, joules losses, eddy current losses 1. Introduction Extensive research on electric vehicle motor system is currently being conducted to minimize overreliance on petroleum products and to curb emissions associated with climate change. When designing an electric motor, it is important to study the motor losses in order to find ways of improving motor efficiency and to design an efficient cooling system. Motor losses consist of electromagnetic and mechanical losses. The electromagnetic losses have been well understood since most electric motor designers have an electrical background. Kyoung-Jin et al (Ko et al., 2010), undertook a study to predict electromagnetic losses of a high speed permanent magnet synchronous motor using analytical and FEA. Coupled electromagnetic and thermal studies have been carried by various researchers (Driesen et al., 2002; Marignetti, 2007; Z. Makni, 2007; Dorell, 2008). In most of these studies, the effect of mechanical losses was neglected or expressed using a factor. However, to accurately predict the overall efficiency and total heat generated in a motor system, the mechanical losses, which include bearing and windage losses, have to be considered. This work aims at investigating the electromagnetic and mechanical power losses of a 1.2 kW brushless direct current (BLDC) permanent magnet motor. The specifications of the motor are shown in Table 1. The motor is to be used to power an electric vehicle compressor. 2. Bearing Frictional Losses Bearing friction losses consist of four main components (Hamrock & Anderson, 1983): 1. Hydrodynamic rolling force. 2. Sliding friction losses between the rolling elements and the races. 3. Sliding friction between the rolling elements and the separator/ cage. 4. Hysteresis losses. 2.1 Forces on Ball-Race Contacts