A new soft switching direct converter for residential fuel cell power system

In this paper a new soft switching direct converter suitable for residential fuel cell system is discussed. The proposed system consists of two power stages which are soft switching full bridge dc/dc converter and three phase voltage source inverter without dc link capacitors. A new PWM strategy (with different placement of the zero-vector) for the 3 phase inverter is presented to supply split 120 V/240 V single phase ac voltage. The proposed dc/dc converter switching is synchronized with the inverter zero-vector: i.e. during the zero-vector interval of the inverter (during which the dc link current is also zero), the dc/dc converter commutation is initiated. This method of control is shown to result in zero current switching (ZCS), zero voltage switching (ZVS), lower EMI and higher efficiency over a wide operating range. Further, due to the absence of bulky dc link capacitors higher power density and lower cost can be achieved. The operating principle of the proposed soft switching direct converter is analyzed and design consideration for clamp circuit is discussed. Experimental results on 3 kVA direct converter prototype are provided to verify its feasibility.