Development of a grid-tied parallel-serial full bridge fuel cell inverter controlling an unfavorable heater

This paper proposes a 1.0kW grid-tied inverter system for fuel cells. Since the fuel cells in this study have a variable output voltage range of 30~70V, the high DC link voltage is required to obtain a 220V ac voltage at the output of the system. For this, a DC-DC converter with a high conversion ratio should be required. However, the achievement of high conversion ratio in DC-DC converters generally causes a difficulty to increase the efficiency of the entire system. To solve this difficulty a parallel-serial full bridge mode inverter was proposed. The proposed inverter basically has a grid-tie performance and a control of an unfavorable heater. Without the heater control, the unexpected high input voltages may appears due to the slow response time of fuel cells to a rapid change of output power of the system. The validity of the performances for the proposed inverter has been proved through experiments for the 1.0kW grid-tied inverter system built.