Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy A new strategy of efficiency enhancement for traction systems in electric vehicles Xiaofeng Ding a , Hong Guo a , Rui Xiong b, ⁎ , Feida Chen a , Donghuai Zhang a , Chris Gerada c a School of Automation Science and Electrical Engineering, BeiHang University, Beijing 100191, China b National Engineering Laboratory for Electric Vehicles, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China c Department of Electrical and Electronic Engineering, The University of Nottingham, Nottingham NG72RD, UK HIGHLIGHTS • A novel efficiency enhancement strategy for traction system was proposed. • The proposed method supplies a fast search of the optimal variable (direct-axis current i d ). • The maximum increment of the efficiency for the overall inverter-motor system was 2.7%. • The saving of battery consumption is more than 9% due to the proposed strategy. • The proposed method has been validated by the experimental test. ARTICLE INFO Keywords: Electric vehicles (EVs) Overall efficiency Inverter-motor Loss model Golden section search ABSTRACT The inverter-motor drive system is the main traction force in electric vehicles (EVs). The overall efficiency of inverter-motor will directly determine the energy consumption of EVs. In this paper, aiming at improving the overall efficiency of inverter-motor, a novel methodology is proposed. Firstly, the iron loss, copper loss and stray loss of motor, as well as the devices’ conduction loss and switching loss in inverter are modeled. Afterwards, based on previous loss model strategy and gold section search strategy, a novel hybrid efficiency-optimization control strategy is proposed. The proposed method combines each benefit in loss-model and gold section search, and can realize high efficiency operation of the inverter-motor system in large power range. Additionally, the proposed method manifests faster search speed and better accuracy compared to conventional methods. Experiment results validated the effectiveness of the proposed hybrid control strategy. Meanwhile, the impact of the efficiency improvement on the driving cycle is further investigated through Advanced Vehicle Simulator (ADVISOR) simulations. 1. Introduction Due to the depletion of fossil fuels and the severe environmental pollution, electric vehicles (EVs) are considered one of the alternatives to traditional internal combustion engine vehicles [1–3]. Compared with other motors, permanent magnet synchronous motors (PMSM) have advantages of smaller size, higher efficiency, higher output torque, etc. Hence, PMSM combined with inverter is preferred as traction system usually in the EVs [4]. With batteries as power sources, its energy is limited. Therefore, the efficiency of traction system is of vital importance [5–9]. As mentioned in [10], the fuel economy can be improved by 5% if the conventional traction systems were replaced with the higher efficiency one. Similar improvements are discussed in another study [11]: the fuel economies of HEV and PHEV are improved by 14.7% and 18.1% respectively. Motors are also widely adopted in the other industrial applications, such as ventilation, machine tool, air conditioning systems, etc. Around $3–5 billion could be saved by adopting more efficient motor systems in the US [12]. Recently motor efficiencies have been improved greatly by novel materials, optimal designs and loss minimization controls, etc. Previously, different methods are proposed to improve the effi- ciency of motors [13–20]. In the motor design stage, optimal design and novel materials have been adopted to high efficiency electric machines [13]. After the motor is designed, manufactured and implemented in the drive system, the system’sefficiency can be further enhanced through loss minimization algorithms (LMAs) [14–20]. The LMAs are http://dx.doi.org/10.1016/j.apenergy.2017.08.051 Received 2 May 2017; Received in revised form 1 July 2017; Accepted 9 August 2017 ⁎ Corresponding author at: Department of Vehicle Engineering, School of Mechanical Engineering, Beijing Institute of Technology, No. 5 South Zhongguancun Street, Haidian District, Beijing 100081, China. Tel./fax.: +86 10 6891 4070. E-mail addresses: dingxiaofeng@buaa.edu.cn (X. Ding), rxiong@bit.edu.cn, rxiong6@gmail.com (R. Xiong), Chris.Gerada@nottingham.ac.uk (C. Gerada). Applied Energy 205 (2017) 880–891 0306-2619/ © 2017 Elsevier Ltd. All rights reserved. MARK