Operation Of Transmission Grid Research Articles

Auction Design for Local Reserve Energy Markets

In this paper we develop an auction mechanism that is designed for a local energy market. It aims to enable regionally or virtually restricted trading of ancillary services, which enhances the position of the balance group responsible party beyond that of simple accounting. Furthermore, it makes local market participants somewhat more independent from the transmission grid operator, but at the same time provides incentives for investments in distributed generation technologies. A wider spread of these technologies can help to save CO2 emissions, while at the same time a part of them can also be used to counter the fluctuations of energy from volatile renewable sources, such as wind and solar power. Because of their relatively high margins and small share in total production, ancillary services are well-suited for a remuneration scheme. Participants in the auction are, thus, private households, which imposes specific design characteristics on the auction. Most importantly, it needs to be transparent and easy to understand, as homeowners will typically not have the insights of a professional trader as well as lack a similar position and motivation. Also, the confinement to a single balance group, i.e. a local market, means that especially in the beginning of the trading only a small number of bidders can be expected. Therefore, competition will initially be limited, so that the auction design needs to be adapted accordingly. In order to test the performance of the proposed auction market design under varying information policies, a simple agent-based simulation program has been developed. We find that the theoretical predictions hold and that competition quickly leads to price convergence.

European Project to Improve Models of Geomagnetically Induced Currents

Geomagnetically induced currents (GICs) from solar storms pose a risk to the operation of power transmission grids in Europe and across the globe. The European Risk from Geomagnetically Induced Currents (EURISGIC) project, which began in March 2011 and is supported by the Seventh Framework Programme of the European Union, seeks to mitigate this natural hazard by developing European capabilities for GIC forecasting and warning. Recent well-recognized GIC events were the province-wide blackout in Quebec, Canada, in March 1989 and the blackout in the city of Malmö, in southern Sweden, during the Halloween storm of October 2003. The progressive integration of interconnected and geographically wide power transmission grids is obviously increasing the GIC risk. Hence, there is a need for greater scientific understanding of phenomena in the solar-terrestrial environment that lead to GICs and for the development of systems that facilitate GIC modeling, forecasting, and mitigation. Within the EURISGIC project the flow of GICs throughout the European grid for hypothetical and real events will be simulated using improved grid network models and conductivity models for the continent. The project will produce the first Europe-wide real-time prototype forecast service of GICs in high-voltage power systems, based on in situ solar wind observations by the Advanced Composition Explorer (ACE) spacecraft, empirical modeling, and comprehensive simulations of Earth's magnetosphere. Moreover, on the basis of long-term geomagnetic recordings, EURISGIC will derive the first map of the statistical risk of large GICs throughout Europe. Of special interest is a search for untapped data sources for the solar storm of September 1859, famously observed by British astronomer Richard Carrington, which is often referred to as the most intense geomagnetic storm ever recorded. The project aims to assist European scientists as they strive for 30- to 60-minute lead time forecasts of GIC events. There is presently only one European magnetohydrodynamic code for global simulations of the solar wind-magnetosphere interaction, namely, Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4), developed at the Finnish Meteorological Institute. During EURISGIC, GUMICS-4 will be upgraded to be able to produce real-time GIC forecasts. For this development, EURISGIC will obtain valuable contributions from the U.S. expertise gained from NASA's Solar Shield project (http://ccmc.gsfc.nasa.gov/Solar_Shield/). The U.S. and European codes will run in parallel to produce GIC forecasts in Europe, and they will also stimulate further improvements in simulations. Calculation of GICs in a given power grid is a straightforward problem, which has been considered in several previous national studies, for example, in Finland, Sweden, and the United Kingdom. The key problem is to determine the geoelectric field that drives GICs in power grids. This electric field can be calculated from the measured magnetic field using models of the Earth's conductivity. A special challenge for EURISGIC is to compile a simplified conductivity map of Europe that enables efficient computation of Europe's electric field. When the geoelectric field is known, calculation of GICs in a power grid is reduced to a simple direct current (DC) mathematical problem. In combination, early warning forecasts, risk maps, and worst-case-scenario assessments provided by EURISGIC will contribute to mitigating the risks that GICs represent, thereby avoiding destruction of transformers and enhancing the protection of critical infrastructure in Europe and elsewhere in the world. The project began in March 2011 and will last until February 2014. The Finnish Meteorological Institute is the coordinator, with Ari Viljanen as the coordinating person. Other European Union partners come from Hungary, Sweden, and the United Kingdom. In addition, Russia and the United States belong to the consortium, ensuring the best global GIC expertise within the team. An external group of advisors representing power engineering, education, and space weather services will provide independent reviewing and suggestions to help the consortium reach its ambitious goals. EURISGIC is funded by the Seventh Framework Programme of the European Union (Project 260330). The EURISGIC Web site is http://www.eurisgic.eu. The following are members of the consortium, with their representatives given in parentheses: Finnish Meteorological Institute, Finland (Ari Viljanen); British Geological Survey/Natural Environment Research Council, United Kingdom (Alan Thomson); NeuroSpace, Sweden (Magnus Wik); Swedish Institute of Space Physics, Sweden (Peter Wintoft); Geodetic and Geophysical Research Institute, Hungary (Viktor Wesztergom); Polar Geophysical Institute, Russia (Yaroslav Sakharov); and Catholic University of America, United States (Antti Pulkkinen). Ari Viljanen is a senior scientist at the Finnish Meteorological Institute, in Helsinki, Finland. E-mail: [email protected]

Dynamic modelling and control of fully rated converter wind turbines

Today, many countries are integrating large amount of wind energy into the grid and many more are expected to follow. The expected increase of wind energy integration is therefore a concern particularly to transmission grid operators. Based on the past experience, some of the relevant concerns when connecting significant amount of wind energy into the existing grid are: fault ride through requirement to keep wind turbines on the grid during faults and wind turbines have to provide ancillary services like voltage and frequency control with particular regard to island operation. While there are still a number of wind turbines based on fixed speed induction generators (FSIG) currently running, majority of wind turbines that are planned to be erected are of variable speed configurations. The reason for this is that FSIG are not capable of addressing the concern mentioned above. Thus, existing researches in wind turbines are now widely directed into variable speed configurations. This is because apart from optimum energy capture and reduction of mechanical stress, preference of these types is also due to the fact that it can support the network such as its reactive power and frequency regulation. Variable wind turbines are doubly fed induction generator wind turbines and full converters wind turbines which are based on synchronous or induction generators. This paper describes the steady state and dynamic models and control strategies of wind turbine generators. The dynamic models are presented in the dq frame of reference. Different control strategies in the generator side converter and in the grid side converter for fault ride through requirement and active power/frequency and reactive/voltage control are presented for variable speed wind turbines.