The surge in the cost of fuels can be accounted as a major trigger which leads to the advent of hybrid vehicles. The hybrid electric vehicles are in the reckoning to address the dangers of the exponential increase in contamination of air and global warming associated with greenhouse gases. A vehicle that is a combination of reversible storage devices like batteries and main energy sources (oil or gas) [1]. A HEV emanates reduced emission from its IC engine when compared to a pure petrol car of the same size. In the context of Hybrid Electric Vehicle, the DC-DC power converters are the electronic devices that condition the source voltage of one level to the output voltage of another level of different DC voltage based on the application provided for the electric vehicle for charging and discharging modes. The need for these power converters arises from the different voltage ratings of the hardware equipment being used. These converters acting importance due to the fact that they are efficient, easy to design and cost effective in the Hybrid electric vehicle application. The paper presents the modelling, design and simulation of buck converter the bidirectional converter based on the transmission line of powertrain of electric vehicle application. The aim is to obtain from a stable input voltage to the output voltage which is lower with high frequency and minimum ripple with specified fixed frequency in the buck operation. In bidirectional converter, the voltage stepdown is required while charging the battery while step up is needed while providing power to the motor from the battery. The design of the above-mentioned converters is performed using the standard method present in the literature. The simulation is done on PowerSim 8.0. The waveforms for the voltage and current for inductor, capacitor and the diode is also obtained. It is found that the simulation results of the voltages are in close agreement with the analytical calculations. © 2019 IOP Publishing Ltd. All rights reserved.