A Bi-Dictional DC-DC Converter for Elctrical Vehicle Driving System

Abstract

Skyrocketing fiiel prices and extensive use of fossil fuel for conventional vehicles which operate at lower eftiaency has created global environmental issues as well as econoniical issues. In a world where environment protection and e!;ergy conservation are growing concerns these problems have drawn attention towards more energy efficient technology in vehicle. Vehicles powered by electric power offers low emissions, higher efficiency, better control and an additional feature of Regenerative braking. An active parallel interface between battery and Ultracapacitor avoids the limitations of battery and this hybrid energy unit (Ultracapacitor + fiattery pack) provides high power as well as energy density capable of higher accelerations and decelerations. Usage of the Ultracapacitor will minimize the loss of energy, and minimal degradation of the main battery pack. This interface requires an electronically controlled DC-DC converter. In this paper a bidirectional buck-boost converter is selected, which would be capable of regenerative braking. The system uses a MOSFET Buck-Boost converter, which is connected to the Ultracapacitor bank at the Boost side, and the main battery at the Buck side. Energy transfer between source and load is more efficient with selected converter as compared to conventional two-switch bidirectional converter. Selected converter employs a variable frequency control algorithm for boost mode and fixed frequency PI control for buck mode. All the variables are calculated and accordingly the PWM switching pattern of the MOSFETs is generated. This scheme has variable switching frequency in continuous current mode operation and it minimize the Bus voltage ripples.