The stability of the electricity grids is of central importance for society and the economy. One topic that has now moved into the focus of grid operators is temporary overvoltage events in the grid, the significance of which is only starting to be recognized. These can occur, for example, as a consequence of a short-circuit in the grid if this has led to a loss of supply power or to load shedding, i.e. to the disconnection of individual generators and consumers. The existing risk due to overvoltages is not new, but the problem can be complicated by the increasing decentralization of the power supply. How critical overvoltages are and how frequently they actually occur has not yet been sufficiently clarified. In order to be prepared in time, however, the first national and international grid connection guidelines now demand that large-scale consumers and generation plants of all kinds connected to the power grid are able to withstand overvoltages – conventional power plants are just as affected by this as combined heat and power plants, photovoltaic plants or wind turbines.
The overvoltage requirements specified in these guidelines are based on assumptions and estimates. Until now, however, there has been no comprehensive analysis of the technical causes of critical large-scale overvoltages in the power grid. At the same time, grid operators and producers of generation plants need a clear concept of what requirements need to be developed. In order to improve the competitiveness of German plant manufacturers, certainty must be created here. Therefore, the research project “OVRTuere (Over Voltage Ride Through – Temporary Overvoltages and Derived Rules for Efficient and Safe Grid Operation)” was launched in November 2018. The project is financed by the Federal Ministry for Economic Affairs and Energy (BMWi) under the funding priority "Grids for the Power Supply of the Future" within the German Government's 6th energy research program. As Fraunhofer ISE, we have been responsible for project management in a joint project with the companies M.P.E. GmbH, FGH GmbH, FGH e.V., and Autarsys GmbH.
In order to secure and improve the stability of the electricity grid and ultimately make the grids fit for the use of 100% renewable energies, concrete milestones are needed. These will be developed together with the project partners involved:
- First, the extent, magnitude and relevance of overvoltages need to be better understood. The engineering firm M.P.E. GmbH, which specializes in the integration of renewable energies into the grid, and the non-profit research association FGH e.V. (Research Association for Electrical Equipment and Power Electronics) identify and analyze grid situations that lead to temporary overvoltages in transmission and distribution grids. Subsequently, various measures for dealing with overvoltages will be investigated. Special attention is paid to battery converters, since with common products, overvoltage on the mains side can lead to uncontrolled feedbacks into the battery, which can result in the destruction of the devices. This is particularly relevant since battery systems connected to the power grid via converters will play a key role in the energy system of the future in the course of storage integration. Fraunhofer ISE and Autarsys GmbH (manufacturer of battery storage systems) are developing and testing a demonstrator for overvoltage-proof battery converters
- M.P.E. GmbH and FGH e.V. define suitable and cost-optimized requirements for overvoltage resistance for the generation plants and consumers
- Fraunhofer ISE and FGH GmbH, the spin-off of the FGH e.V. responsible for the development of test systems, will focus on the following further areas: Various test facilities for temporary overvoltages are to be developed and investigated. The purpose of these test facilities is to test the overvoltage behavior of generating plants
- Various generation plants such as photovoltaic inverters, wind turbines and battery converters are tested with these overvoltage test devices and their overvoltage behavior is improved. Fraunhofer ISE and FGH GmbH are responsible for this