Research On Full Bridge-Current Doubler Bidirectional DC/DC Converter Used In Fuel Cell Vehicles

Researching of Fuel cell vehicles have become a hot topic for its zero-emissions, however, fuel cells have the defects because of soft output characteristics, a super capacitor should be in parallel on the fuel cell to improve its output characteristics. Super capacitor has good characteristics in power per unit, charging-discharging speed and long cycling life,so it’s very suitable for vehicles. It can improve efficiency of energy utilization by supplying additional power when vehicle speeds up and recycling braking energy when vehicle brakes. For the voltage of super capacity changes greatly, which brings disadvantage influence to fuel cell vehicle’s motor drive. According to vehicle’s driving conditions, bi-directional DC/DC converter can solve above problem, and it can increase driving performance by optimizing motor control.After considering the technology performance of application in fuel cell vehicle and comparing characteristics of some bi-directional DC/DC conversion topologies, this thesis chooses full bridge-current doubler DC/DC conversion topology to achieve energy bi-directional conversion between super capacity and DC bus and designs circuit’s element parameters. By applying state space averaging method, this paper analyzes the work condition of the bi-directional DC/DC converter and relatively small signal model is set up. Then using PID compensator to improve stability of the system, MATLAB has been used to draw Bode diagram of open-loop transfer function before and after compensation. Generation of phase-shifted full bridge control signals is focused on and synchronous rectification signal modulation method of forward and reverse working mode is researched. The fourth chapter narrates the digital implementation of control system, including sampling circuit and software flow chat. TMS320F28335 made by Texas Instruments complete all the calculating work, such as voltage and current sampling, implement of digital PID control algorithm and PWM output waveform. F283X series DSP is more suitable for high demand areas for floating point arithmetic is increased to it based on the original series. The fifth chapter gives design of output and input filter of converter, including the selection of devices and calculation of parameters. Based on the theoretical calculation, a 400W experimental prototype was implemented. The experimental results show that the prototype can output stable voltage waveforms in both forward and reverse working mode with high energy transfer efficiency in certain load.