M.H. Nehrir

Power Management of a Stand-Alone Wind/Photovoltaic/Fuel Cell Energy System

This paper proposes an AC-linked hybrid wind/photovoltaic (PV)/fuel cell (FC) alternative energy system for stand-alone applications. Wind and PV are the primary power sources of the system, and an FC-electrolyzer combination is used as a backup and a long-term storage system. An overall power management strategy is designed for the proposed system to manage power flows among the different energy sources and the storage unit in the system. A simulation model for the hybrid energy system has been developed using MATLAB/Simulink. The system performance under different scenarios has been verified by carrying out simulation studies using a practical load demand profile and real weather data.

Dynamic models and model validation for PEM fuel cells using electrical circuits

This paper presents the development of dynamic models for proton exchange membrane (PEM) fuel cells using electrical circuits. The models have been implemented in MATLAB/SIMULINK and PSPICE environments. Both the double-layer charging effect and the thermodynamic characteristic inside the fuel cell are included in the models. The model responses obtained at steady-state and transient conditions are validated by experimental data measured from an Avista Labs SR-12 500-W PEM fuel-cell stack. The models could be used in PEM fuel-cell control related studies.

Generation unit sizing and cost analysis for stand-alone wind, photovoltaic, and hybrid wind/PV systems

This paper presents the results of investigations on the application of wind, photovoltaic (PV), and hybrid wind/PV power generating systems for utilization as stand-alone systems. A simple numerical algorithm has been developed for generation unit sizing. It has been used to determine the optimum generation capacity and storage needed for a stand-alone, wind, PV, and hybrid wind/PV system for an experimental site in a remote area in Montana with a typical residential load. Generation and storage units for each system are properly sized in order to meet the annual load and minimize the total annual cost to the customer. In addition, an economic analysis has been performed for the above three scenarios and is used to justify the use of renewable energy versus constructing a line extension from the nearest existing power line to supply the load with conventional power. Annual average hourly values for load, wind speed, and insolation have been used.

Control of PEM fuel cell distributed generation systems

This paper presents modeling, controller design, and simulation study of a proton exchange membrane fuel cell (PEMFC) distributed generation (DG) system. The overall configuration of the PEMFC DG system is given, dynamic models for the PEMFC power plant and its power electronic interfacing are briefly described, and controller design methodologies for the power conditioning units to control the power flow from the fuel cell power plant to the utility grid are presented. A MATLAB/Simulink simulation model is developed for the PEMFC DG system by combining the individual component models and the controllers designed for the power conditioning units. Simulation results are given to show the overall system performance including load-following and fault-handling capability of the system.

A Physically Based Dynamic Model for Solid Oxide Fuel Cells

This paper presents a physically based dynamic model for tubular solid oxide fuel cells (SOFCs) based on the electrochemical and thermodynamic characteristics inside SOFC. The diffusion, material conservation, electrochemical, and thermodynamic equations are used to develop the SOFC model. The effect of temperature on the steady-state (V-I and P-I) characteristics of the SOFC model has been studied, and the model responses have been obtained for constant fuel flow as well as for constant fuel utilization operating modes. The dynamic characteristics of the model are investigated in small, medium, and large timescales, from milliseconds to minutes. The model has been implemented in MATLAB/Simulink and used to investigate the distributed generation applications of SOFCs.

Optimal unit sizing for a hybrid wind/photovoltaic generating system

Abstract The application of a hybrid wind/photovoltaic (PV) power generating system for utilization as a stand-alone or a network connected system is investigated. The optimum combination of wind and PV generation coupled with battery storage for a stand-alone system has been obtained for a hypothetical site in Montana. Generation and storage units for the hybrid system are properly sized in order to meet the annual load and minimize the total annual cost to the customer. The optimal solutions are found by a numerical study using the hourly load demand for a typical residential home in the Northwestern US. Hourly wind speed and approximate solar radiation data have been used.

Load Transient Mitigation for Stand-Alone Fuel Cell Power Generation Systems

Summary form only given. A load transient mitigation technique is proposed in this paper for stand-alone fuel cell-battery power systems. The technique can be used not only to improve the output power quality of the overall system, but also to mitigate or eliminate the electrical feedback stresses upon fuel cells caused by load transients. As a result, the durability of fuel cell can also be improved. System analysis and controller design procedure for the proposed technique are given in the paper. Simulation studies have been carried out for proton exchange membrane fuel cell (PEMFC) and solid oxide fuel cell (SOFC) based power systems. Simulation results show the effectiveness of the proposed technique in preventing load transients to affect fuel cell performance.

Unit sizing of stand-alone hybrid wind/PV/fuel cell power generation systems

An economic evaluation of a hybrid wind/photovoltaic/fuel cell generation system for a typical home in the Pacific Northwest is performed. In this configuration the combination of a fuel cell stack, an electrolyzer, and a hydrogen storage tank is used for the energy storage system. This system is compared to a traditional hybrid energy system with battery storage. A computer program has been developed to size system components in order to match the load of the site in the most cost effective way. A cost of electricity and an overall system cost are also calculated for each configuration. The study was performed using a graphical user interface programmed in MATLAB.

Development of a Monte Carlo based aggregate model for residential electric water heater loads

A model for a residential electric water heater load is developed using an energy flow analysis of the water heater tank. An aggregate model for residential electric water heater loads is then developed using a rejection type Monte Carlo simulation technique. The resultant aggregate model is then used to assess the effectiveness of several demand-side management strategies using the water heater load profile presented in a previous analysis.

Towards real-time microgrid power management using computational intelligence methods

Microgrids are an emerging technology which promises to achieve many simultaneous goals for power system stakeholders, from generator to consumer. The microgrid framework offers a means to capitalize on diverse energy sources in a decentralized way, while reducing the burden on the utility grid by generating power close to the consumer. As a critical component to enabling power system diversity and flexibility, microgrids encompass distributed generators and load centers with the capability of operating islanded from or interconnected to the macrogrid. To make microgrids viable, new and innovative techniques are required for managing microgrid operations given its multi-objective, multi-constraint decision environment. In this article, two example computational intelligence methods, particle swarm optimization (PSO) and ant colony optimization (ACO), for application to the microgrid power management problem are introduced. A mathematical framework for multi-objective optimization is presented, as well as a discussion of the advantages of intelligent methods over traditional computational techniques for optimization. Finally, a three-generator microgrid with an ACO-based power management algorithm is demonstrated and results are shown.