The Research Of Topologies Of High Efficiency & High Power Density Converters

Higher power density and higher efficiency are the eternal pursuit of switching converter.In order to pursue higher efficiency at high frequencies,soft switching of power devices is a necessary means.At present,the main soft switching topologies are phase shifting and resonant topologies.However,the ZVSs of lagging-leg switches in phase-shift topologies are difficult to achieve;In LLC resonant topologies,the higher frequency requires larger magnetizing current which limits the efficiency;Traditional two-stage LLC resonant topologies cannot achieve soft switching of all power devices.In view of the above problems,this thesis proposes five new topologies with shared leg technology based on the application requirements of different power levels.Then,this thesis analyzes and studies the working principles and characteristics of these topologies.Finally,the characteristics of the five topologies are verified and compared by experiments.The experimental results show that the efficiency and switching frequency of these five topologies are greatly improved compared with the other topologies.The main innovations are as follows:(1)In order to solve the problem that the ZVSs of lagging-leg switches in PSFB are difficult to realize,a PSTB topology consisting of all leading-legs is proposed.With shared leg technology,all three bridge legs in three full-bridges are leading-legs and lagging-legs at the same time.The primary switches can achieve soft switching quickly within full load range.The test results are as follows:the switching frequency of the PSTB converter is 300kHz,the peak efficiency is 90.4%without the use of synchronous rectification,3%higher than similar topology at same conditions.(2)In order to broaden the voltage regulation range of the PSTB,a PSDB and a PSSB topology with different conversion ranges are proposed.These two topologies replace some of the transformers in the PSTB topology with inductors,and the output voltage is regulated by the phase shift between the bridge legs.The prototype test results are as follows:the switching frequency of the PSDB and PSSB converter is 300kHz,the peak efficiencies of them are 94.7%and 93.8%without the use of synchronous rectification.(3)In order to improve the switching frequency of the PSTB topology,a PSTB ZVZCS topology is proposed.The topology removes three output inductors based on the PSTB topology,allowing transformers to operate in DCM mode,thereby enabling soft switching of the secondary-side rectifying devices.The prototype test are as follows:the switching frequency of the PSTB ZVZCS converter is 1MHz,the power density is 843W/in~3,the peak efficiency is 96.6%,about 1%higher than similar topology at same conditions.(4)Aiming at the problem that the soft switching of the two-stage LLC converter is difficult to realize,a ZVS buck-boost LLC cascaded topology is proposed.The topology can utilize the forward and negative currents of the pre-stage inductor to achieve ZVS of all switches,and effectively reduce the required magnetizing current.The prototype test results are as follows:the switching frequency of the ZVS buck-boost LLC cascaded converter is 1MHz,the power density is 414W/in~3,the peak efficiency is 95.6%,3%higher than similar topology at same conditions.Basing on shared leg technology,these five topologies have high power density and can realize ZVS easily.Since the transformers work in DCM,PSTB,PSDB and PSSB are more suitable for occasions where the power level is higher and the system's conduction loss is more sensitive.Since the secondary-side diodes can realize ZCS,PSTB ZVZCS and ZVS buck-boost LLC cascaded topology are more suitable for high frequency and high power density applications which are more sensitive to switching losses.PSDB,PSSB and ZVS buck-boost LLC cascaded topology sacrifice a portion of efficiency and power density to be more suitable for applications with wide conversion range.