Active Distributed Power Systems Functional Structures for Real-Time Operation of Sustainable Energy Systems
Sammanfattning: Present power system will face great challenges in several areas depending on the market economy, extensive global integration and constant need for more electric power, which will force the system to operate much closer to its stability limits. Meeting these challenges may involve improving and complementing or even total restructuring of the power systems.New technologies are emerging such as renewable energy sources (RES) and power electronics, which in combination with information and automation will give opportunities to provide a number of services to the market. Market based operation may become a reality, where the management mechanism from contract to physical power transaction might get faster or even automated that could be an important advantage for renewable energy sources. Although, as several new generation units will be distributed and in same cases close to the consumption, local subsystems or distributed power systems would probably emerge to increase system reliability. Distributed power systems will function similarly to the present power system except for being down scaled and based on a high degree of automated functions. In such case the power system would in normal conditions still work similarly to present system where all distributed power systems are merged together. Only under special circumstances would affected distributed power systems disconnect, and later on, when appropriate, reconnect. In the meantime the individual distributed power system will run in ?stand-alone? mode.The thesis focus is related to real-time operation and control where a general information and functional structure for active distributed power systems has been studied. The structure is intended to provide future distributed power systems with a high degree in modularity, scalability, adaptability and autonomic behaviour enabling ?plug-and-produce?. Fundamental relations and principles are investigated as well as operation and strategy methods enabling autonomous operation of the systems. The basic solution is made by down-scaling the common centralized structure for operating a power system to several active distributed power systems that interact by well-defined hardware and software interfaces. In order to coordinate the system operation in real-time, a principal structure for distributed energy management system and information enabling market-based operation of renewable power sources is studied and adopted. Distributed functions for automated operation of various system configurations have been investigated to be able to automatically add and remove functionality due to changes in system configurations. The structure provides the means for condensing the necessary information for future needs on operation of new large RES (e.g. offshore wind power plants). The structure facilitates the expansion of new small RES (e.g. roof assembled solar power plants), where a new power unit is able to connect to an existing structure and then automatically adapt to the system. Well-defined system information and communication are necessary for the functioning of real-time operation. A part of the work includes studies on uniformed information and communication structures for different levels of communication, ranging from process- to market level communication. Although, most focus has been on the operational structure layer including several signals enabling the management of common generation units as well as intermittent power units such as RES.The information and functional structure is partly implemented in C++ modules and partly in the Dymola/Modelica simulation tool. Verifications are made both by simulation models and in a laboratory set-up. The verifications are performed for various system configurations where the simulation results agree with the experimental results.
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