Modeling And Control Of DC-DC Converter For Fuel Cell Vehicles

DC-DC converter is a key part ina fuelcellvehicle powertrain.High voltage ratio,large current,and small ripple are required for this kind of DC-DC converter as a consequence of the developing requirements of fuel cell and powertrain.Aiming at these demands,modeling,control,and application of interleaved dual BOOST converter are focused on in this thesis.Firstly,ideal model and real nonlinear model with lossesconsidered are established.Issues such assteady voltage,steady current,losses,and efficiency of the converterare analyzed base on the model.Parameters such as phase number,switching frequency,switching sequence,and equivalent serial resistances in the real model are studied,which can influence the performance of the converter greatly.The steady state characteristics and circuit parameters are closely related to the operating cases of output power and duty cycle of the converter.Secondly,input-current control mode is proposed to regulate the output power of fuel cell.And input-current,output-current,input-voltage,and output-voltage control mode are proposed for protection of the converter in failure.Besides,three algorithmssuch as PI,sliding mode,and feed-forwardcontrol are designed and the stability of the control system is ensured globallyunder general conditions,of which the duty cycle is constrained to avoid some extreme condition.Thirdly,characteristics of the converter such as ripple,switching sequence,and frequency are studied with simulation model based on MATLAB/SIMULINK in both time and frequency domain.Steady and dynamic performances of the control system such as current sharing,steady accuracy and dynamic response are also analyzed.Lastly,experimental platform for the converter is built and prototypeof the converter is designed.Experimental validation of performance in steady and dynamic state,power regulation state,and failure protection state is carried out on both laboratory and real vehicle.The results show that interleaved dual BOOST converter is able to satisfy the increase demand of fuel cell vehicle powertrain.The input-current control algorithm proposed in this thesis can regulate the output power of fuel cellstably and efficiently,and share current of the inductors averagely.The combination of the fourcontrol modes and three control lawsis good for the improvement of performance and protection of the converter.This research can be a support for applications of interleaved dual BOOST converterto vehicles and has benefits for performance enhancement of fuel cell vehicles.