A High Precision Efficiency Model of Electric Vehicle Power System for Efficiency Optimization

A precise integral efficiency model is the key to studying the efficiency optimization problem of electric vehicle power systems (EVPS). In this paper, a high-precision efficiency model of EVPS, which consists of lithium battery and permanent magnet synchronous motor is established. Firstly, based on the battery mathematical model, its efficiency map in terms of current and state of charge (SOC) is built under different temperature conditions. Furthermore, its efficiency model is established by the polynomial fitting method. Secondly, the dq-axis equivalent circuit model is used to build its theoretical efficiency map regarding torque and speed, which is also fitted to a polynomial efficiency model. In addition, two growth factors are introduced to respectively describe its different features in high and low torque ranges. Finally, the two efficiency models of battery and motor are combined to compose an integral efficiency model of the EVPS. Simulation results show that the proposed model in this paper achieves high calculation accuracy, and its maximum absolute error is limited within 2.0%.