System Integration of Distributed Energy Resources

Besides their primary product – electricity – large central power stations supply socalled ancillary services that are necessary to maintain a secure and stable operation state of the electric power system. As the need for electricity from these units is being displaced by renewable energy sources, this project aims at investigating how the ancillary services can be provided by others in the system, e.g. small generation units, and flexible demand. The goal is a power system, where all units – small and large, producers and consumers – to the largest possible extent contribute to optimal system operation. It is therefore investigated in this project how ancillary services can be provided by alternatives to central power stations, and to what extent these can be integrated in the system by means of market-based methods. Particular emphasis is put on automatic solutions, which is particularly relevant for small units, including the ICT solutions that can facilitate the integration. Specifically, the international standard "IEC 61850-7-420 Communications systems for Distributed Energy Resources" is considered as a possible brick in the solution. This standard has undergone continuous development, and this project has actively contributed to its further development and improvements. Different types of integration methods are investigated in the project. Some are based on local measurement and control, e.g. by measuring the grid frequency, whereas others are based on direct remote control or market participation. In this connection it is considered how aggregation of many units into one logical entity, can make it possible for these units to provide ancillary services. As part of the investigations, operational, physical and thermodynamic models for e.g. micro-CHP and different types of flexible demand have been established. These models can be used for future investigations as well. A mixture of empirical and analytical methods have been used when defining the models and their parameters. The project concludes that distributed energy resources, including flexible demand, can contribute significantly to optimal system operation by supplying ancillary services. Furthermore, the project shows concrete examples of possible, technical solutions to exploit this potential. In the project, information infrastructures and control methods to realize the various concepts have been designed, implemented, and tested, including e.g. microcontroller systems for price- or frequency-responsive devices. Looking ahead, demonstration projects in near future will hopefully be able to strengthen the confidence in the investigated control concepts. The experience gained, and the technical solutions developed in this PhD project can be utilized in such demonstration projects, and in a longer timescale contribute to forming the basis for further increase in the renewable energy sources penetration in the power system.