Valentina Zaccaria

Pressurized SOFC Hybrid Systems: Control System Study and Experimental Verification

In this paper, two different advanced control approaches for a pressurized solid oxide fuel cell (SOFC) hybrid system are investigated and compared against traditional proportional integral derivative (PID). Both advanced control methods use model predictive control (MPC): in the first case, the MPC has direct access to the plant manipulated variables, in the second case, the MPC operates on the setpoints of PIDs which control the plant. In the second approach, the idea is to use MPC at the highest level of the plant control system to optimize the performance of bottoming PIDs, retaining system stability and operator confidence. Two MIMO (multi-input multi-output) controllers were obtained: fuel cell power and cathode inlet temperature are the controlled variables; fuel cell bypass flow, current and fuel mass flow rate (the utilization factor kept constant) are the manipulated variables. The two advanced control methods were tested and compared against the conventional PID approach using a SOFC hybrid system model. Then, the MPC controller was implemented in the hybrid system emulator test rig developed by the thermochemical power group (TPG) at the University of Genoa. Experimental tests were carried out to compare MPC against classic PID method: load following tests were carried out. Ramping the fuel cell load from 100% to 80% and back, keeping constant the target of the cathode inlet temperature, the MPC controller was able to reduce the mismatch between the actual and the target values of the cathode inlet temperature from 7 K maximum of the PID controller to 3 K maximum, showing more stable behavior in general.

Fuel Cell Temperature Control With a Precombustor in SOFC Gas Turbine Hybrids During Load Changes

The use of high temperature fuel cells, such as Solid Oxide Fuel Cells (SOFCs), for power generation is considered a very efficient and clean solution to conservation of energy resources. When the ...

A Real-Time Degradation Model for Hardware in the Loop Simulation of Fuel Cell Gas Turbine Hybrid Systems

The theoretical efficiencies of gas turbine fuel cell hybrid systems make them an ideal technology for the future. Hybrid systems focus on maximizing the utilization of existing energy technologies by combining them. However, one pervasive limitation that prevents the commercialization of such systems is the relatively short lifetime of fuel cells, which is due in part to several degradation mechanisms. In order to improve the lifetime of hybrid systems and to examine long-term stability, a study was conducted to analyze the effects of electrochemical degradation in a solid oxide fuel cell (SOFC) model.The SOFC model was developed for hardware-in-the-loop simulation with the constraint of real-time operation for coupling with turbomachinery and other system components. To minimize the computational burden, algebraic functions were fit to empirical relationships between degradation and key process variables: current density, fuel utilization, and temperature.Previous simulations showed that the coupling of gas turbines and SOFCs could reduce the impact of degradation as a result of lower fuel utilization and more flexible current demands. To improve the analytical capability of the model, degradation was incorporated on a distributed basis to identify localized effects and more accurately assess potential failure mechanisms. For syngas fueled systems, the results showed that current density shifted to underutilized sections of the fuel cell as degradation progressed. Over-all, the time to failure was increased, but the temperature difference along cell was increased to unacceptable levels, which could not be determined from the previous approach.Copyright

Gas turbine advanced power systems to improve solid oxide fuel cell economic viability

Coupling a solid oxide fuel cell (SOFC) with a gas turbineprovides a substantial increment in system efficiency comparedto the separate technologies, which can potentiallyintroduce economic benefit ...

Advanced Control for Clusters of SOFC/Gas Turbine Hybrid Systems

The use of model predictive control (MPC) in advanced power systems can be advantageous in controlling highly coupled variables and optimizing system operations. Solid oxide fuel cell/gas turbine ( ...

Advanced Control for Clusters of SOFC/GT Hybrid Systems

The use of model predictive control (MPC) in advanced power systems can be advantageous in controlling highly coupled variables and optimizing system operations. Solid oxide fuel cell/ gas turbine (SOFC/GT) hybrids are an example where advanced control techniques can be effectively applied. For example, to manage load distribution among several identical generation units characterized by different temperature distributions due to different degradation paths of the fuel cell stacks. When implementing a MPC, a critical aspect is the trade-off between model accuracy and simplicity, the latter related to a fast computational time. In this work, a hybrid physical and numerical approach was used to reduce the number of states necessary to describe such complex target system. The reduced number of states in the model and the simple framework allow real-time performance and potential extension to a wide range of power plants for industrial application, at the expense of accuracy losses, discussed in the paper.Copyright

Ambient Temperature Impact on Pressurized SOFC Hybrid Systems

In this paper advanced control strategies based on Model Predictive Control (MPC) method are compared against a traditional PID controller in a Gas Turbine Pressurized SOFC hybrid system.A model of the integrated mGT-SOFC hybrid system has been developed to analyze the impact of ambient temperature changes on system performance and dynamic behaviour. Four different MIMO controllers (multi input multi output) based on a linearized system model have been implemented in order to control fuel cell temperature and power with different ambient temperatures. Fuel cell temperature is regulated by manipulating the cell by-pass mass flow, while power is regulated by changing the fuel cell electrical current and fuel mass flow (the fuel utilization factor is kept constant). Load following simulations have been carried out as follows: the same load ramp from 100% to 80% of fuel cell power and back has been set and studied under three different ambient conditions, 263K, 288K and 313K (−10°C, 15°C and 40°C).MPC demonstrated superior performance over the two distributed PID controls, thanks to the better setpoint tracking on the cell temperature, which is particularly evident when the ambient temperature deviates from the nominal condition. This is mainly explained by the capability of MPC in including the effects of non-linearities of the real system.Copyright