Research On The Topology Theory And Control Technonogy Of Isolated Boost Full Bridge DC-DC Converter

Aimed to develop auxiliary power system used in Fuel Cell Electric Vehicle(FCEV) for generous purpose, this paper takes Isolated Boost Full BridgeConverter (IBFBC) as the research object. Some new ways to solve IBFBC'sinhere disadvantages is proposed based on thorough investigation of thedeveloped and up to date IBFBC studies. The IBFBC topology, start-up problem,leakage induct problem of isolated transformer and magnetic reset problem ofinput induct are the basic issues in IBFBC problems, as is the research target. Several isolated boost converters are analyzed for the application of lowinput voltage, high output voltage, and high power of an auxiliary power systemin FCEV, and IBFBC is proposed to solve above problems. This paper analysesthe fundamental dc operation principles and small signal model of IBFBC inthe first time, which offers the theoretical basis of its main circuit andcontrol strategy design and application. The reason of input current inrush during start-up is clarified in theory.Two kinds of novel soft start-up schemes of IBFBC based on digital signalprocessor (DSP) are proposed, which modified the main circuit and propose anew pulse width modulated (PWM) control timing. As a result, the IBFBC realizedsoft start-up successfully. The reason of high voltage spike of the power switches caused by theleakage induct of the isolated transformer is analyzed, and the active clampscheme is adopted, which can solve the problem effectively. A novel softswitching control way is proposed. Through modifying the PWM wave, the activeclamp switching and all the power switching of the full bridge realize thezero voltage turn on. This paper analyzes magnetic reset problem of the input inductor. Whenthe converter stops normally, a novel soft-stop scheme is proposed. Theconverter works from boost mode to buck mode, and the energy stored in theinput induct releases gradually until to stop. If the converter stopssuddenly owing to the failure, fly-back winding magnetic reset scheme isadopted. The input induct is designed as a fly-back converter, and when theconverter stop suddenly, the induct energy releases from the fly-backwinding to the output end, thus the converter is protected from beingdestroyed.The design method of the key components of the main circuit is given.And also the main control circuit based on the DSP-TMS320F2407, the controlprogram based on DSP and the logic dispose program based CPLD are designed.A set of 5KW IBFBC with the input voltage 24VDC and output voltage 300VDCis developed. Overall experiment performances verify theoretical analysisand simulation results.In conclusion, this dissertation focuses on the most important aspectsof the IBFBC, and provides the system theory to converter design and analysis,which are validated in the project applications.