Abstract
Proper converter design can allow solid oxide fuel cells operated as distributed generators to mutually benefit both the load and the electric utility during steady-state conditions, but dynamic load variations still present challenges. Unlike standard synchronous generators, fuel cells lack rotating inertia and their output power ramp rate is limited by design. Two strategies are herein investigated to mitigate the impact of a large load perturbation on the electric utility grid: 1) external use of ultracapacitor electrical storage connected through a DC-DC converter and 2) internal reduction of steady-state fuel utilization in the fuel cell to enable faster response to output power perturbations. Both strategies successfully eliminate the impact of a load perturbation on the utility grid. The external ultracapacitor strategy requires more capital investment while the internal fuel utilization strategy requires higher fuel use. This success implies that there is substantial flexibility for designing load-following fuel cell systems that are model citizens.
Highlights
T HE UNITED STATES is moving toward an increasingly electrified society
This paper investigates possible methods for improving gridconnected fuel cell dynamic performance during load perturbations
A physically based solid oxide fuel cell (SOFC) model was previously developed in MATLAB/SIMULINK using a modeling methodology that was validated with experimental data from a 220 kW SOFC-MTG hybrid system in [22], dynamic single-cell transients in [23], and integrated simple-cycle SOFC systems in [24]
Summary
T HE UNITED STATES is moving toward an increasingly electrified society. The portion of U.S total energy use for electricity production grew from 27% in 1974 to 36% in 1989, and is projected to reach 46% by 2010 [1]. If the stack has sufficient fuel available when the power demand is increased, it will be able to increase output more quickly than if it must wait for more fuel This is the main principle of the utilization-based control strategy: deliver excess fuel to the stack at all times to facilitate faster response to load perturbations. Note that this strategy may require more steady-state fuel use and lower system efficiency unless it is only applied during periods when large power demand increases are expected (e.g., when building air conditioning equipment is turned on in the morning). The two strategies explored are: 1) using ultracapacitors for storing electrical energy and 2) reducing the steady-state SOFC fuel utilization Both methods are found to produce model citizen behavior of the grid-connected SOFC system
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