Soft Switching and High Frequency Isolation

Multi-phase soft-switching high-frequency isolated DC-DC converter is proposed for power conversion in modular stacked HVDC power transmission and distribution system. Input-series output-parallel connection of current-fed full-bridge DC-DC converter modules is proposed to increase voltage blocking capability at the input and decrease current ripple at the output. Basic powerelectronic building block is zero-current switching (ZCS) fullbridge phase-shift PWM DC-DC converter. Phase shift between switches in each leg of the converter is adjusted to control power flow while phase shift between gate signals of individual phases is selected according to the number of phases in order to minimize ripple of the output voltage.

Converter analysis is carried out to develop a simple equivalent boost converter model of the three-phase soft-switching converter suitable for system-level analysis and simulation. Strategies are developed to ensure fast detection of faults and continued operation of the converter in the case of fault in one phase module. To verify the proposed system design and analysis, experimental results on scaled-down laboratory prototype are presented for a three-phase ZCS DC-DC converter.