Reasearch In Three-phase DC/DC Converter Based On PWM

As the development of distribution generation technology and the increasement of equipmentsupplied with DC electricity, DC mirco-grid (DC MG) has been one of the research hotspots. Undi-rectional and bi-directional DC/DC converters occupy most of the power conversion units in DC MG.Therefore it’s very meaningful to research DC/DC converter with high power density, high efficiency,high reliability and low cost for excellent performance of DC MG. With the increasement of highpower equipments, traditional single-phase DC/DC converter faces the problem of high current stressof devices including magnectic and semiconductor devices. Three-phase DC/DC converter can de-crease the current stress. This paper focuses on three-phase DC/DC converter in DC MG.Firstly, an asymmetrical PWM current-tripler recitifier three-phase full-bridge (CTRTPFB)DC/DC converter with Y-Δ connected transformer is proposed. The converter is applied between highvoltage bus360VDC and low voltage bus48VDC in DC MG. The operating principle is analyzed de-taily and the difference of ZVS achievement between upper switches and lower switches of the bridgeleg is discussed. Compared with CTRTPFB converter with Δ-Δ connected transformer and phase-shiftfull-bridge converter, the converter proposed shows advantages in decreasing current stress and largerload range of ZVS.Secondly, a novel PWM control stragety is proposed for CTRTPFB converter in order toachieve bi-directional operation and expand effective duty range. Besides, the new PWM stragetyincrease voltage conversion ratio to decrease transformer turns ratio resulting smaller leakage induc-tance.Thus the converter is preferred for high voltage conversion ratio conditions such as thebi-directional converter between the high voltage bus and energy storage unit in DC MG. Controlledby the new control stragety, the converter operates in two modes. The component stress and lossanalysis of two operation modes are compared detaily to give the design principle.Lastly, a2kW prototype was established for both asymmetrical and novel PWM control strategyfor the CTRTPFB converter respectively.The experiment results shows that: all power switchesachieve ZVS and the output current ripple is decreases largely with traditional asymmetrical PWM;the converter can achieve bi-directional operation and increase one time voltage conversion ratio.