Control design of an atmospheric solid oxide fuel cell/gas turbine hybrid system: Variable versus fixed speed gas turbine operation

Abstract

This study is focused on a hybrid fuel cell/gas turbine (FC/GT) system with an atmospheric pressure solid oxide fuel cell (SOFC). The impact of the gas turbine rotational speed on dynamic performance and controllability of a hybrid system is investigated. The transient response of the FC/GT system to perturbations in the power demand has been investigated. Two operational strategies of gas turbines are compared: (1) fixed speed operation, and (2) variable speed operation. For both operation strategies, a wide range of power production is numerically simulated. The results show that variable speed operation is superior for the FC/GT hybrid configuration studied. Variable speed operation allows a 50% turn down in power with no additional balance of plant equipment required. The system efficiency is maintained above 66% for variable speed operation compared to 53% for fixed speed operation with auxiliary combustion.

Novel solid oxide fuel cell system controller for rapid load following

“…The model is nonlinear based on transport and conservation principles. The modeling methodology used has been verified experimentally and utilized for controls development in previous work [2][3][4][5][6][7][8][9]. Since the focus of the paper is controls, the physical dynamic model is only briefly presented in Appendix A.…”

“…a. Fuel and air temperatures at the entrance to the fuel cell stack should be maintained to within 200 K of the fuel cell operating temperature [6,7,10,14,15]. b. Endothermic cooling caused by fuel reformation reactions at the fuel cell anode inlet should be minimized.…”

Experimental and theoretical evidence for control requirements in solid oxide fuel cell gas turbine hybrid systems

“…In the SOFC/GT hybrid system, the fuel cell high temperature SOFC exhaust drives a gas turbine, providing air flow and pressurizing the SOFC while driving an electric generator that produces additional electrical power. As a result, SOFC/GT hybrid systems have demonstrated efficiencies above 50% [5,18] and studies have shown the possibility for electrical conversion above 70% [4,19] when operating on natural gas and above 60% in an integrated coal gasification plant [6,19]. Higher efficiency reduces CO 2 emissions while separated fuel and air flows in the SOFC allow system designs for CO 2 sequestration with minimal performance cost [16,20,21].…”

“…Similar SOFC technology development programs have been rapidly advancing SOFC technology in Europe and Japan [22,23]. At the system design level both prototypes and mathematical modeling have developed multiple system designs and control strategies [8,19,[24][25][26][27]. The current work seeks to illustrate the fidelity of the hybrid system modeling methodology developed at the National Fuel Cell Research Center [10,18,24,28,29] and draw attention to critical system sensitivities caused by fluctuations in temperature, electrochemical current, and fuel composition variations.…”

Networked control of Distributed Energy Resources: Application to solid oxide fuel cells

“…Over the past decade, several efforts have been made towards the development and implementation of control strategies for DERs (e.g., [3], [4], [5], [6], [7], [8]). Important contributions in this direction include the use of conventional and model-based feedback control algorithms to regulate various types of grid-connected DERs in order to enhance power system stability (e.g., [9], [10], [11], [12]), mitigate power quality problems (e.g., [13]) and improve the continuity of electricity supply (e.g., [14]), as well as the development of various distributed control and coordination architectures using multi-agent based control approaches (e.g., [15], [16], [17], [18]).…”