Design And Control Of High Gain DC/DC Converters For Fuel Cells

With the increasingly serious problems such as environmental pollution and energy crisis,fuel cell vehicles have gradually become a research hotspot in the field of new energy vehicles.Due to the slow dynamic response of the fuel cell and the large voltage variation range,it is not able to better meet the requirements of the whole vehicle.It is usually necessary to use a DC-DC converter to achieve voltage decoupling and power control.In this dissertation,by comparing the different DC-DC converter topologies of fuel cell vehicles,the double-tube boost converter is chosen as the main topology of the high-gain DCDC converter for fuel cells.At the same time,an improved high gain DCDC converter topology is proposed.From the aspects of the working principle,circuit model and control method of the converter,the related research work on the selected DC-DC converter is carried out.Firstly,this dissertation investigates and analyzes the existing fuel cell DC/DC converter topology and finds that the isolated DC/DC topology cannot be applied to fuel cell vehicles due to its large size and low specific power.DC/DC converter topology is characterized by the number of devices,boost ratio,inductor capacitance and switching tube and diode stress.This dissertation chooses double-tube boost converter as the main topology of DC/DC converter for fuel cell.Through the detailed description of its working principle,the equivalent circuit and state equation under different working modes are given.Secondly,the classic PI algorithm is chosen to design the controller by comparing the advantages and disadvantages of different control methods.The state space averaging method is used to model the double-tube boost converter topology,and the closed-loop transfer function of the system is obtained.Based on this,a single closed-loop control system based on voltage feedback and a double closed loop based on voltage and current feedback are established.And analyze the stability of the system.Aiming at the problem that the double-tube converter is susceptible to input voltage disturbance under stable operating conditions,the input voltage based feed forward control method is adopted,which can effectively improve the dynamic characteristics of the system.Then,the circuit design of the dual-tube boost converter used is carried out.By analyzing the working state of the circuit,the component types of the main circuit are determined.A voltage detection circuit based on linear optocoupler and a current detection circuit based on Hall current sensor is designed to isolate the main circuit and the control circuit.A multi-level driving circuit based on photoelectric isolation is designed to realize fast turn-off of the MOSFET;an overcurrent protection circuit for switching tube current detection is designed to prevent the switch tube from being damaged due to excessive current.At the same time,the programming of the dual-tube boost converter system based on DSP is carried out.Finally,for the research topology and control method,the simulation model is built in simulink and simscape,and the effectiveness of single closed loop control,double closed loop control and feedforward control is verified.The experimental prototype was built and the prototype was debugged.The experimental results are basically consistent with the simulation,which shows that the dual-tube boost converter can meet the requirements of the fuel cell system for the converter.