Transformer-coupling Combined Full-bridge Converter And Its Soft Switching Techniques

Due to the high conversion efficiency and high power density,the equipment based on power electronic is increasing rapidly in the conversion of electrical energy applications.DC-DC converters,which have been widely adopted in industry,aerospace,transportation and renewable energy applications,are important part of power electronic equipment.As the development of power electronic technology,the types of DC-DC converters are becoming more rich and the suitable DC-DC topology can be selected based on the electrical specifications.However,the common topologies cannot be applied in some special applications.Many novel DC-DC topologies are proposed to extend the applied range of power electronic.A systematic research on the composing laws and internal relations of DC-DC converters contributes to the theory formation of topology derivation.Based on the analysis of fundamental DC-DC topologies,this thesis proposes a transformer-coupling basic cell(TCBC)to generate some novel derivative topologies.The TCBC is introduced into the full-bridge converter to extend the soft-switching range.Compared with the traditional phase-shifted full-bridge(PSFB)converter,the proposed converters can achieve wide range of soft-switching,low current ripple and high conversion efficiency.By analyzing the structure of switching mode power supplies,a single port cell with inductor,capacitor and switch is proposed.Buck,Boost and Buck-Boost converters can be rebuilt based on the proposed cell.Two basic cells are connected through a capacitor and four topologies are obtained,which correspond to Buck-Boost,Cuk,Sepic and Zeta,respectively.By adding a winding to the inductor,a TCBC with dual port is obtained.The topology families can be obtained by combining the TCBC with the basic converters.The novel converters satisfy the requirements in some special applications.The construction of TCBC in the isolated full-bridge converter is researched.In the primary side,the full-bridge converter is constructed by four switches,which generates four TCBCs.Considering the main transformer,five power output ports can be achieved.By adopting the method of permutation and combination,all the connection styles are analyzed and optimised.The combined converter contains more than one output power port and multilevel rectified voltage can be obtained,which is helpful to reduce the filter inductance and voltage stress of rectifier diodes.This thesis focuses on the combined full-bridge converter with dual port and proposes a novel zero-voltage zero-current switching(ZVZCS)full-bridge converter.The leading-leg switches operate with ZVS while the lagging-leg switches operate with ZCS.The ZVZCS converter can achieve a wide range of soft-switching and low current ripple.The combined full-bridge converter based on adaptive-energy-storage(AES)full-bridge converter is also researched.Compared with the traditional PSFB converter,the AES converter overcomes problems of narrow ZVS range,secondary voltage oscillation and duty-cycle loss.However,the conventional AES converter exists circulating current,which causes more conduction loss.Based on the combined method,some improved AES converters are proposed.In the improved converters,the energy from primary side can be transferred to the secondary side during freewheeling interval.Both the current ripple of filter inductor and the voltage stress of rectifier diode are reduced.Compared with the conventional AES converter,the improved converter can obtain a wider ZVS range,lower current ripple and higher conversion efficiency.The detailed theory analysis and experimental results are presented in this thesis.Finally,the common problems in the proposed combined full-bridge converter are analyzed and the corresponding solutions are also introduced in this thesis.In order to transfer the power continually,the combined converter contains two power output ports,which leads to the narrowed voltage gain.In this thesis,the voltage gain of combined converter is extended by changing the driver sequence of switches.The soft switching operation in the proposed converter is obtained by using the energy stored in the leakage inductance to discharge the junction capacitances.The switches may lose the soft switching characteristic at light loads.By analyzing the ZVS commutation process,it is noted that the difference between magnetizing current and the reflected output current can be used to discharge the capacitances.For the combined full-bridge converter,the light load current is benefit to achieve the soft switching characteristic.