Abstract
Based on the benchmark solid oxide fuel cell (SOFC) dynamic model for power system studies and the analysis of the SOFC operating conditions, the nonlinear programming (NLP) optimization method was used to determine the maximum electrical efficiency of the grid-connected SOFC subject to the constraints of fuel utilization factor, stack temperature and output active power. The optimal operating conditions of the grid-connected SOFC were obtained by solving the NLP problem considering the power consumed by the air compressor. With the optimal operating conditions of the SOFC for the maximum efficiency operation obtained at different active power output levels, a hierarchical load tracking control scheme for the grid-connected SOFC was proposed to realize the maximum electrical efficiency operation with the stack temperature bounded. The hierarchical control scheme consists of a fast active power control and a slower stack temperature control. The active power control was developed by using a decentralized control method. The efficiency of the proposed hierarchical control scheme was demonstrated by case studies using the benchmark SOFC dynamic model.
Highlights
It is a trend to replace conventional power plants with the more environmentally-friendly distributed generators (DG) in order to reduce the greenhouse gas (GHG) emission from the power sector
High temperature reaction heat produced during the energy conversion process in the fuel cell (FC) stack permits an solid oxide fuel cell (SOFC) generator to be coupled with a gas turbine to form a combined heat and power (CHP) system, which can reach a higher efficiency of up to 80% [3,4]
The open-loop poles of the SOFC are analyzed to study the dynamic response of the SOFC and a hierarchical control scheme for the SOFC is proposed based on the dynamic response analysis
Summary
It is a trend to replace conventional power plants with the more environmentally-friendly distributed generators (DG) in order to reduce the greenhouse gas (GHG) emission from the power sector. Most of the 1-D models are used for the stand-alone SOFC analysis It was reported in [16] that the SOFC stack terminal voltage and temperature will reach a steady state value after a few seconds and tens of minutes respectively under the constant fuel utilization factor control scheme when the stack current has a step change. 0-D SOFC models have been widely used for load tracking studies under both stand-alone and grid-connected conditions [21,22,23] Such a lumped-parameter model can emulate the FC operations with acceptable accuracy only if certain strict assumptions are met, e.g., the fuel utilization factor is constant [11]. The paper presents a maximum electrical efficiency load-tracking control scheme for the grid-connected SOFC in order to improve the operation performance. (4) The cell stack is well-insulated and the energy losses caused by radiation, convection and conduction are negligible
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