Abstract: In order to formulate the optimal energy allocation strategy, the energy flow of a plug-in hybrid electric vehicle in different operation conditions are analyzed. The related parameters of the energy transfer between vehicle components including temperature, pressure, torque, rotating speed and flow rate at low-SOC states are measured by tests, the energy distribution of vehicle is calculated and analyzed, and the energy flow and energy recovery rate under new European driving cycle (NEDC) and worldwide harmonized light vehicles test cycle (WLTC) are compared. The results show that when battery SOC is low, the average fuel consumption of engine under WLTC cycle is about 1.6 times of that under NEDC cycle and the most energy consumed in vehicle driving under both cycles comes from engine. In addition, the energy consumed in driving under WLTC cycle is less than that under NEDC cycle with a difference smaller than 1%, while the energy recovery rate under WLTC cycle is lower than that under NEDC cycle with a little more difference of 2.31%

Key words: plug-in hybrid electric vehicle, energy flow, NEDC, WLTC