In a situation where fossil energy resources globally run short and the greenhouse effect increases, the interest in new technologies of energy conversion to reduce the demand of primary energy and emission of pollutants grows. The use of high temperature fuel cells like solid oxide fuel cells (SOFCs), especially in combination with gas turbines (GTs), promises remarkable room for improvement in the areas mentioned, compared to other state-of-the-art technologies. But design and handling of such complex plants require efficient control strategies to promote safe and reliable operation. The development of powerful control algorithms is based on an exact knowledge of the operating behavior, which can be obtained using dynamic system models. In this paper a nonlinear model with bulk parameters and 19 dynamic states is presented; the main assumptions and the underlying equations are given. The simulated system consists of a compressor, a SOFC, a turbine, a recuperator, an ejector with a diffusor, a reformer, and a load. Additionally, from the nonlinear model a linear one in state-space representation is derived at nominal conditions. The results of both models are compared. The agreement of the dynamic behavior and of steady state final values is satisfactory. Thus in future studies, methods of linear control theory could be used with the linear model to develop efficient control strategies.

This study analyses the feasibility of electric 3-wheeled motorcycle-taxis in Dar es Salaam from a technical and user oriented point of view on the power train. Based on the experiences and expectations of an interviewed group of drivers, two electric power train variants for 3-wheeled vehicles have been set up and compared. In order to calculate the vehicle energy demand, a simulation model has been set up. This model uses a drive cycle that has been generated for the specific location of Dar es Salaam using GPS tracks recorded during a field trip. Results contain the vehicle battery weight, energy demand and range for varied battery capacities. Finally, a possible power train variant is suggested.

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The purpose of the current work is to develop an appropriate control system for a solid oxide fuel cell/gas turbine hybrid system. The main focus lies on the usage of linear control theory for the parameterization of the controller structure. The studies are carried out with a control oriented simplified dynamic model of a 25 MWe hybrid system based on a conceptual design previously presented in literature. As a specific feature additional firing of the gas turbine combustor is used as an extra actuating variable offering several advantages. Foregoing necessary investigations deal with calculating the on- and off-design behavior of the sample system and with defining a reasonable part-load operating curve taking into account several constraints like efficiency, stack temperature, surge margin, etc. Also, preliminary studies of the transient open loop behavior are performed. They reveal that the input variables should be changed with specific care to avoid critical situations during load change. As a precondition for linear control theory a low-order linear model is deduced and validated. With consideration of the transient simulation results and of the properties of the linear model a proper control strategy is suggested, which consists of a proportional output feedback taking into account the multi-input-multi-output character of the system and three distributed proportional-integral controllers that define the requested load point onto the operating curve. Lastly, the controllers are parameterized based on linear control theory and verified.

The purpose of the current work is to analyze and also to verify the operating behavior of a solid oxide fuel cell/gas turbine (GT) hybrid system in order to derive necessary requirements for an appropriate control system. The studies are carried out with a control oriented simplified dynamic model of a 25 MWe hybrid system based on a conceptual design previously presented in literature. As a specific feature additional firing of the GT combustor is investigated. First the design point is defined. Then the off-design performance is presented in terms of characteristic performance maps. Based on operating map investigations an appropriate part-load operating curve is defined with considerations given to constraints (e.g., stack temperature or surge margin), efficiency, and operational flexibility. The load range goes from 40% part-load to 105% overload. To investigate the transient behavior five open loop simulations are carried out changing different model inputs, as well as all model inputs applying a 30% load change according to the operating curve. The simulated behavior reveals that the inputs should be changed with specific care to avoid critical situations during load change.