Small Signal Stability Issues of Emerging Distribution Networks with High Penetration of Distributed Generations

Sudarshan Dahal (2012). Small Signal Stability Issues of Emerging Distribution Networks with High Penetration of Distributed Generations PhD Thesis, School of Information Technol and Elec Engineering, The University of Queensland.

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Author Sudarshan Dahal
Thesis Title Small Signal Stability Issues of Emerging Distribution Networks with High Penetration of Distributed Generations
School, Centre or Institute School of Information Technol and Elec Engineering
Institution The University of Queensland
Publication date 2012-01
Thesis type PhD Thesis
Supervisor Prof. Tapan Kumar Saha
Dr. Mithulananthan Nadarajah
Total pages 276
Total colour pages 36
Total black and white pages 240
Language eng
Subjects 0906 Electrical and Electronic Engineering
Abstract/Summary Present distribution networks are changing into smarter, reliable and more flexible networks utilizing latest developments on power generation, storage and communication technologies. The changes have been brought about by integration of renewable energy resources, modern controllers, advanced communications and metering infrastructures. As a result, there are a number of dynamic devices operating in a closer proximity in small geographical areas of distribution networks. Moreover, there are increased chances of interactions among dynamic components within the distribution networks. Such interactions can lead to instabilities. Instability issues must be addressed to accommodate higher penetration of renewable energy resources and increasing network efficiency. This thesis attempts to address one of the major instability issues, i.e. small signal stability. Small signal stability can be a limiting condition for synchronized operation of generators and the power transfer capability of emerging distribution systems. Instability of this type results into system oscillations causing unwanted operation of protective devices leading to the system collapse. The objectives of this research are assessment and enhancement of small signal stability issues of emerging distribution networks with high penetration of distributed generators (DG units). This research basically covers issues on modelling, stability analysis and control system design. The studies are made on two test distribution networks, i.e. a 16- bus radial network and a 43-bus industrial mesh network. In order to achieve these objectives the following studies are accomplished in this research: - An investigation is made on small signal stability of a renewable energy based medium voltage electricity distribution system. The influence of different kinds of generators on small signal stability is discussed. Similarly, the influence of varying penetration of renewable energy on state participation and modal sensitivity is observed. Also, influence of shunt compensator placement on small signal stability is investigated. - Techniques for ranking of loads for assessing load impact on small signal stability have been discussed. Evaluation of dynamic loading margin as indicated by Hopf bifurcation is discussed. The influence of composite load modelling on modal damping and dynamic loading margin of the system has been investigated. - Control methodologies for enhanced small signal stability of distribution network are investigated. The opportunities for controlling network components such as a capacitor bank or a load have been explained. Similarly, discussions are made on installing a damping controller at a distributed generator such as photovoltaic or wind generator. Similarly, design of a coordinated controller tuned by multiple DG units is presented. The results show that emerging distribution can oscillate with unique frequency of oscillations. Oscillatory modes are sensitive to the variations of generator outputs. Damping ratios of the oscillations are affected by shunt compensators and load characteristics. Oscillatory modes with lower damping ratio can be critical to the system stability. Suitable control methodology must be applied to enhance damping ratio of critical modes. Damping ratio can be enhanced by an auxiliary controller installed at a selected capacitor bank or a selected load. Similarly, such a damping controller can be installed at a DG unit such as a photovoltaic or a variable speed wind generator. Moreover, multiple DG units can be controlled by a coordinated controller to enhance damping ratio of critical modes. Coordinated controller is tuned by multiple DG units so that it operates even if some of the DG units are out of operation. The contributions made by the thesis can be useful to network service providers as well as DG unit owners for better stability performance in emerging distribution networks.
Keyword damping controller
distributed generations
modal interactions
small signl stability
Additional Notes 76, 81-85, 89-92, 100, 104-109, 113, 129-130, 133-135, 147-150, 152-153, 156-161, 167

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Created: Thu, 14 Jun 2012, 11:53:55 EST by Sudarshan Dahal on behalf of Library - Information Access Service