Bidirectional Isolated Dc-Dc Converter for Fuel Cells and Supercapacitors Hybrid System

Abstract: In future, electrical power systems for electrical vehicles may employ hybrid energy sources, such as fuel cells and super capacitors. The fuel cells (FCs) and super capacitors (SCs) as an environmentally renewable energy system has been applied in many such fields, as hybrid electric vehicle and uninterruptible power supply (UPS) systems. The available power generated from a fuel cell (FC) may not be sufficient to meet sustained load demands, mainly during peak demand or transient conditions. During these conditions, supercapacitor (SC) bank can supply a large amount of power. The combined use of FC and SC has the potential for better energy efficiency, reducing the cost of FC technology, and improved fuel usage. Here, a bidirectional isolated dc–dc converter for fuel cells and the supercapacitor hybrid energy system is being controlled by phase-shift angle and duty cycle method. The dc-dc converter acts as a multiport device. The converter has three modes of operation (1) Boost mode (2) SC power mode (3) SC recharge mode. All switches are controlled by phase shifted PWM signals with a variable duty cycle. Zero voltage switching (ZVS) is achieved by the parasitic capacitance of the switches. For the simulation, MATLAB/Simulink is used. Here the operation principle of the proposed converter is being described and the waveforms for various stages of operation are analyzed.

Keywords: Bidirectional dc–dc converter, fuel cell, supercapacitor.