Power and temperature control of fluctuating biomass gas fueled solid oxide fuel cell and micro gas turbine hybrid system

This paper addresses how the power and temperature are controlled in a biomass gas fueled solid oxide fuel cell (SOFC) and micro gas turbine (MGT) hybrid system. A SOFC and MGT dynamic model are developed and used to simulate the hybrid system performance operating on biomass gas. The transient behavior of both the SOFC and MGT are discussed in detail.An unstable power output is observed when the system is fed biomass gas. This instability is due to the fluctuation of gas composition in the fuel. A specially designed fuel controller succeeded not only in allowing the hybrid system to follow a step change of power demand from 32 to 35 kW, but also stably maintained the system power output at 35 kW. In addition to power control, fuel cell temperature is controlled by introduction and use of a bypass valve around the recuperator. By releasing excess heat to the exhaust, the bypass valve provided the control means to avoid the self-exciting behavior of system temperature and stabilized the temperature of SOFC at 850 °C.