In Hybrid Electric Vehicles (HEV), one of the most important phenomenon which has effect on the vehicle performance is certainly quality of power and power flow in the system. A good power quality in the system can be provided by decreased fluctuation in power flow and a longer life-time of the battery utilized in the electric subsystem of the vehicle. In this paper, we utilize a parallel-series type HEV simulation which is developed in Matlab/Simulink environment. In such type of HEVs, there are different operation modes. When switching between those operation modes, undesired power flow fluctuations occur. In order to smooth the power flow fluctuations and decrease the charge/recharge cycle times of battery, proposed Electric Double Layer Capacitor (EDLC) is developed and connected to battery pack in parallel in the simulation system. The impact of EDLC on the HEV performance can be seen clearly.