In 2011 the Danish government presented a new energy strategy for the horizon of 2050, with the aim of becoming independent of all fossil fuels and therefore 100 pct. based on renewable energy. DTU researchers are helping to realise this goal by predicting future faults in the energy system caused by the absence of power plants to regulate current and frequency.
The transition towards a greener energy system has been top of the agenda for the past couple of years. Scientists have proved that not only will we run out of fossil fuels in the future, but also that the use of them is harmful to the earth and its atmosphere. Alternative solutions are therefore in demand.
SCAPP (Synchronous Condensers APPlication in Low Inertia Systems) is the name of a project managed by Center for Electric Power and Energy (CEE) at DTU Electrical Engineering. In collaboration with Siemens Denmark the project studies how to apply and control synchronous compensators optimally to replace the role of the conventional power plants - ensuring a reliable and sufficient renewable-energy-based power system.
Power plant substitute
With more renewable energy in the power system and less use of fossil-based power plants, the requirements of stability in the electricity system makes synchronous compensators relevant as they can counteract fluctuations of frequency and voltage in the grid. The word synchronous refers to the fact that the speed of rotation of the compensator shaft corresponds to the frequency of the electricity grid. In the event of a decrease or increase in the frequency and voltage level of the grid, the device itself will counteract the change.
The compensator is therefore a relevant substitute for our current power plants that mainly consists of synchronous generators. However, the role and benefit of synchronous compensators are not yet fully realized by the power engineering worldwide. Therefore, the SCAPP project sets out to study the effect of synchronous condensers in a renewable rich energy system, by looking at the control, protection, design and allocation of synchronous compensators.
Realistic real-time tests
In order to explore the role and potential of the compensators in future renewable energy grids, it is essential to test the system stability under different scenarios of generation combinations. Halfway through its duration (2014-2018) SCAPP now has developed a solid and accurate model of the Danish power system, which has been validated by the industry. They also have developed a model of the power electronics control. With these models in store, they are ready for hardware-in-the-loop testing of the power system and compensator.
"With this loop we can test a variety of things. We can test different system scenarios and we can test different controls and protections of the condensers and power systems"
CEE Associate Professor, Guangya Yang
The model of the power system runs through a real time digital simulator (RTDS), which provides a fast, reliable and accurate simulation of the system. This simulation is connected to the actual control and protection systems of a condenser that will react on the signals passed from the simulation. These reactions are then passed back to the simulated power system. This way, the researchers at DTU has created a loop, where the control and protection system used by the condensers can be tested in a realistic platform of future challenges.
“With this loop we can test a variety of things. We can test different system scenarios and we can test different controls and protections of the condensers and power systems,” Associate Professor Guangya Yang explains.
Future challenges
With the modelling work in place the researchers can now focus on testing and validating existing control and protection solutions with different levels of penetration of renewable energy – as well as future scenarios. The testing of different both current and future scenarios makes it possible to seek out the best solutions for the future renewable integration.
Testing and demonstrations of the system have already shown some challenges in the current system operation which must be improved before minimising the assistance from power plants.
Researchers at DTU continue to present and test different scenarios to clarify more future challenges by answering questions like: “What can happen to the protective relays?”, “Will it be able to detect faults in the system?” and “What can we do to help it detect faults and make the right reaction based on the definition of these faults?”, which are some of the questions that must be considered before closing power plants in order to prevent power system shutdowns.
Lead in the field
The findings of the SCAPP project will be beneficial for both the Danish industry and government. The partner, Siemens Denmark, will be able to optimise their control systems and protection devices to ensure a stable current and a reliable system. Also, they will have obtained more general knowledge about installing compensators, which will help promote sales in other countries.
Furthermore, the findings will help the Danish government to safely guide the transition from power plants to renewables - and thereby to reach the goal of 100 pct. renewable energy supply.
By identifying the requirements for synchronous condensers in the future, Siemens Denmark and DTU researchers are ensuring that Denmark maintains a leading position in the integration of renewable energy.