Battery and Powertrain Sizing for L7e-CU Type Electric Vehicle

Abstract The aim of this paper is to present the workflow of battery sizing for electric L-7 type vehicle. The “Worldwide harmonized Light vehicles Test Procedure” (WLTP) as a global standard to determine the vehicle energy usage is used as a vehicle speed profile and acceleration limitations. As per legislation the electric L7-type vehicle speed is limited to 90 km/h having electric motor with 15 kW nominal power. Accordingly to these limitations the “Worldwide harmonized Light vehicles Test Cycles” WLTC class 2 (Figure 1) is used by involving all three test cycles (low, middle and high). Firstly the vehicle characteristics are defined containing: vehicle/kerb mass, battery mass, passengers mass, cargo mass, wheel dimensions, frontal area, wind drag coefficient, frictional coefficient, aerodynamic resistance, tire resistance force, wind speed and air density in function of temperature. Figure 1. WLTC class 2 driving cycle. The vehicle dynamic model is used to calculate the total wheels torque (Figure 2) and electric motor shaft power (Figure 3) accordingly to vehicle characteristics and applied WLTC class 2 driving cycle speed profile. Figure 2: Total wheels shaft torque accordingly to vehicle specifications. Figure 3: Electric motor shaft power accordingly to vehicle specifications. The electric power train is usually composed of gearbox with its ratio and efficiency. These have to be included in the analysis to correctly define the electric motor torque-speed and power-speed characteristics as well as energy flow and total energy consumption. To properly asses the total energy consumption (Figure 4) the electric motor and frequency inverter efficiency maps are included. Figure 4. Energy profile during one WLTC class 2 driving cycle accordingly to vehicle characteristics. Based on the upper described calculations the battery sizing workflow for L-7 type electric vehicle will be presented in full paper. Many different charging aspects will be involved to additionally optimize and maximize the usage of total energy capacity of the vehicle battery. References 1. https://unece.org/DAM/trans/doc/2014/wp29/ECE-TRANS-WP29-2014-027e.pdf