Changes in the distribution grid
The German power generation structure changes from a central to a decentralized one. New decentralized generation units at distribution grid level will take over tasks of conventional power plants. Therefore the impact of distribution systems to ensure overall system stability will increase. In some regions of Germany there is already more energy production than consumption. It happens that the local distribution grid is not able to transport the produced energy to other regions and thus has to be expanded. The reason for this is that distribution grids were initially built to distribute the energy from large conventional power plants to end consumers and not for “collecting” energy from decentral generation units.
An increasing number of battery storage units and electric vehicles will further complicate the grid-management. Uncoordinated charging processes as well as swarm effects can lead to peak loads and can be the reason for the necessity of grid expansion, too.
Ensuring the sustainability and affordability of the German “Energiewende” (energy transition) while maintaining a high quality of supply reliability requires a suitable coordination of decentral energy systems. In order to overcome these challenges an overall concept is developed and tested by the publicly funded project “Grid-Control”.
The research Project has started in July 2015 and will prospectively run until end of 2018. The objective is a techno-economical system approach covering as well role specific solutions. One part of the approach is the intelligent market- and grid-oriented coordination of controllable loads and battery storage units.
The project consortium
We are a consortium of nine partners from industry and research. The project coordinator Netze BW GmbH is the biggest distribution system operator for energy, gas and water in the German federal state Baden-Württemberg.
We take up the results of previous projects, bring the approaches and outcome together and continue the further development.
The project is part of the funding initiative “Zukunftsfähige Stromnetze” (Sustainable Grids) of the German Federal Ministry for Economic Affairs and Energy.
Next to Netze BW GmbH as the consortium leader, the following partners from industry and research institutions are involved: ads-tec GmbH, Fichtner IT Consulting AG, FZI Research Center for Information Technology, Karlsruhe Institute for Technology (KIT), Landis+Gyr GmbH, PREdistribuce a.s., Seven2one Informationssysteme GmbH and University of Stuttgart.
Seven focus topics
We are working on concepts and system solution in seven different topics
- Probabilistic grid planning
- Power flow control
- Coordinated voltage management
- Power flow prognosis
- Congestion management
- State estimation
- Short circuit power and spinning reserve
The integration of the different approaches and system solutions in an overall concept creates an additional value by using synergy effects. At first, we define the functions and interfaces of the system solutions. After that, we develop the hard- and software components and integrate them as test components in test environments. The concepts and system solutions are tested and evaluated in laboratory tests (KIT) and field tests (Netze BW GmbH).
In the following, further insight into the individual focus topics is given.
Probabilistic grid planning
The distribution grid operator constructs new power lines based on the expected maximum power consumption or power infeed. This approach can lead to an inefficient grid expansion if the whole grid capacity is only needed a few hours a year. Furthermore, controllable loads and battery storage units may change the peak loads in a way that the maximum simultaneous power consumption is higher than expected. To enhance the grid resource efficiency we develop probabilistic grid planning methods (MV and LV). The application of flexibility options (Grid Traffic Light Concept) and innovative grid components are considered. This enables the comparison of cost efficiency of new grid operation concepts vs. conventional planning methods.
Power flow control
Distribution grids will enhance to wide area power plants. Two control methods are developed in an decentralized automation system, the Regional Energy Management System (REMS).: Power-flow reduction with a fixed delta (aggregated feed-in management) and Power-flow control with a fixed set point at a reference node; similar to the active power control of conventional power plants. This approach enables the distribution system operator to guarantee a reliable grid operation with increased complexity and a growing number of small decentral generation units in the future.
Power flow prognosis
Due to the increasing direct marketing of renewable energy and the increasing use of flexibilities by market participants it will be almost impossible to predict the grid state without any knowledge of the market. Therefore an integrated process between the market participants and the DSO is developed, enabling the generation of power flow forecasts in MV/LV grids.
Coordinated voltage management
A prioritization and coordination of multiple voltage control actions is developed in order to conduct an optimized voltage management. This function is part of the decentral automation system (Regional Energy Management System).
Proactive congestion management via Gris Traffic Light Concept
Based on the power flow prognosis an approach for a proactive congestion management by a Grid Traffic Light Concept is developed. This requires a cooperation between distribution system operator, the energy market participants (e.g. aggregators) and the prosumers. The concept applied assumes that the DSO provides constraints for the market actions by means of non-discriminatory quota (yellow Grid Traffic Light phase) or opportunity ranges (green Grid Traffic Light phase). Market participants may act freely within the provided restrictions and may optimize among themselves e.g. by trading quota or flexibilities. The DSO does not act as a market participant and does not specify precise requirements for individual units. To calculate the capacity constraints a Grid Load Management System (GLMS) is developed. Besides congestion management in the green and yellow phase, the grid state is monitored by the Regional Energy Management System (REMS). On the basis of real time measurements (1 minute frequency) the REMS executes emergency measures (e.g. curtailing the feed-in of PV-systems) in case of a red Grid Traffic Light phase.
In the future it will be necessary to monitor the power flows in the middle and low voltage grids to be able to execute emergency measures in case of congestion. A state estimator is developed to allow a reliable and precise determination of the grid state with a minimum amount of sensor systems. In the grid-control field test a state estimator for a MV and LV grid will be implemented and validated.
Short circuit power and spinning reserve
Due to the shut down of conventional power plants the amount of short circuit power and spinning reserve decreases. A hybrid energy storage system is developed and integrated in the laboratory environment. This residential building laboratory enables to investigate the facilitation of providing spinning reserve and short-circuit power by decentralized generation units.
The system solutions
To handle the role specific requirements, the developed system components are assigned to the DSO, the market participants and the prosumers.
The following components are assigned to the DSO:
– Regional Energy Management System (REMS)
– Grid Load Management System (GLMS)
The REMS monitors the grid, executes emergency measures including a coordinated voltage management and supports new power flow control methods. It acts on a decentral level below the Scada System and communicates with decentral energy systems on the prosumer side (e.g. battery storage units, PV-systems) and measurement units as well as controllable assets (e.g. controllable substation transformers).
The market participants operate a Flexibility Management System (FMS) which supports the marked and grid oriented optimization of available flexibilities.
Next to the prospective smart meter infrastructure a Building Energy Management System (GEMS) and Grid Control Units (GCU) are utilized to control the diverse decentral systems at prosumer side. The GEMS takes over the energy optimization within the building and provides flexibilities to the Flexibility Management System of its market participant. For grid operation purposes the GCU enables the REMS to take over the control of the individual decentral system or unit (e.g. red Grid Traffic Light phase).
Freiamt is a rural MV-grid-section where the maximum generation below a feeder of a switching substation is more than three times higher than the maximum load. These
conditions form an environment to test the grid of the future in today’s grid operation.
The system components are tested and evaluated for about 12 months in collaboration with 30 end consumers. 30 local secondary substations are equipped with measuring (MV/LV) and communication technologies. Furthermore, battery storage units (three domestic units for prosumers and one neighborhood storage unit with 120 kWh), a controllable MV/LV transformer and a charging point for electric vehicles are part of the test environment. All controllable decentral energy systems are connected to the REMS via Grid Control Units. The battery storage units as well as the charging station are used for evaluating the Traffic Light concept and therefore are also equipped with Building Energy Management Systems (GEMS).
The aim of the tests is to proof the feasibility and to evaluate the developed concepts and system solutions.
If you have any further question, don’t hesitate to contact the project coordinator Katharina Volk (k.volk(at)netze-bw.de).