Modeling and Model-based Analysis of a Solid Oxide Fuel Cell Thermal-Electrical Management System with an Air Bypass Valve

Abstract

For stand-alone solid oxide fuel cell (SOFC) power systems without grid connection, delivering demanded power, maintaining system temperature constraints, and achieving high system efficiency are the key design objectives. A typical SOFC system consists of an SOFC stack and a blower, a heat exchanger, an exhaust-burner as the primary components in its balance of the plant. In this work, a novel SOFC system design with an air bypass valve and a target operating range of 1 to 5kW is considered. A system dynamic model, which captures the spatial electrical and thermal distributions of stack, is developed and optimal operating points to maintain the maximum steady state system efficiency are explored while enforcing four constraints on temperature and temperature gradient. Furthermore, the effects of the control variables, namely the bypass valve opening ratio (BP), voltage (U), fuel utilization (FU), and air excess ratio (AR) in improving system performance and expanding feasible operating range are quantified. In addition, the open-loop optimal operation strategy is obtained. The analysis demonstrates that the design of the stand-alone SOFC system is feasible and the bypass valve plays an important role in improving the overall system performance and operation ability.