Virtual power plants and digital twins are key weapons in the battle to stabilise the electricity grid in the age of renewables, argues Berhard Loher, segment manager, excitation, ABB Energy Industries.
In the rapidly evolving energy landscape, one characterised by a surge in demand for power and an increasingly complex, fragmented electricity network fed by renewables, power grid operators are turning to virtualisation to manage supply and demand, minimise wastage and ensure grid stability.
Why is electricity supply and demand changing?
The traditional, centralized model of electricity generation, whereby constant and reliable power from large fossil fuel and nuclear power plants is matched to established demand, thus avoiding frequency fluctuations, is being phased out in favour of clean energy such as wind and solar PV.
At the same time, rapid electrification driven by electric vehicles, heating, cooling, data centres and emerging industries means demand for electricity is becoming increasingly distributed and erratic.
The traditional model of power generation used the energy contained in large rotating mass systems to ensure grid stability. Without the back up of grid-level energy storage, renewables do not provide constant power, so this must be stored for when the sun doesn’t shine and the wind doesn’t blow.
The necessity of utilizing the maximum amount of renewable power when available results in strong fluctuations in the generated power in the grid at any one time, increasing the chance of disruptive events such as fast rate of change of frequency (RoCoF), fault-ride through and power oscillations.
In response, transmission system operators (TSOs) have established stringent new grid codes, the rules to which all players that connect power-generating assets to the power network must comply.
The onus is therefore on utilities, aggregators and power grid operators to not only continue to integrate renewable energy into the electricity network, but also to legislate for unpredictable demand. Virtualisation can help companies meet these dual challenges and ensure grid stability.
What is virtualization?
When we talk about virtualization, we firstly mean ‘digital twins’, control system digital simulation models that are fed with data on the real-time status and working condition of power plant assets.
Digital twins are validated through site measurements or components certifications, and are used in two ways: firstly, TSOs use these digital models of systems to perform simulations that ensure grid stability and to plan for future investments designed to strengthen the network at its weak points.
Second, digital twins are employed by operators to demonstrate to authorities that their equipment is compliant with grid code requirements during commissioning and operation, and can counteract events that cause network instability. This is especially important in countries with strict grid codes, such as Germany, which released the first grid code VDE-AR-N 4110 and VDE-AR-N 4120 standards.
ABB grid code compliance solutions provide utilities with faster grid connection and optimization of their power plant operations. Studies using software, such as ABB’s SMTS 3.0, PowerFactory and MATLAB/Simulink, based on validated excitation system simulation models ensure fast allowance to connect to the grid, avoiding penalties and difficult technical communication with grid authorities.
In addition, ABB UNITROL Excitation systems enable synchronous generators to rapidly absorb and inject reactive power in order to counteract voltage fluctuations. UNITROL also provides Advanced Power System Stabilizer (PSS) functions that enable synchronous generators to effectively damp inter-area oscillation modes without jeopardizing the reaction of the system to RoCoF events.
Another concept that relies on virtualization is a virtual power plant (VPP). Comprising hundreds of smaller physical plants, VPPs aggregate the optimum load profile of each to ensure power is supplied to the grid in the most efficient and cost-effective way, thus matching supply to demand profiles.
Virtualization will become increasingly important as the energy grid decentralises, and supply and demand continue to fluctuate. At present, the grid code compliance process is carried out on-site every 2–5 years. In the future, it may take place every week, with the excitation system performing auto tuning remotely. The ultimate vision is for a digital twin to simulate operations continuously.
Digitally recreating key systems can also improve asset monitoring and maintenance, providing the dual benefit of creating a stable electricity supply alongside positively impacting the bottom line.
VPPs in action in Germany
ABB is helping VPP operator and power trader Next Kraftwerke meet the strict grid code compliance requirements in its native Germany, one of several VPP projects ABB is involved in around the world.
Using ABB Ability OPTIMAX plant optimization software, Next Kraftwerke is now able to pool the output of hundreds of small and medium-sized renewable energy plants in a single VPP. The system gathers valuable data on both plant production and grid balancing, performs real-time optimization calculations, and determines production schedules for each plant in order to maintain grid stability.
If an imbalance occurs, the TSO instructs Next Kraftwerke to increase or reduce output immediately or within minutes. The command is received and acted on in real time by the OPTIMAX® solution.
The VPP has the scale and flexibility to participate in the country’s lucrative ancillary services market. Since the installation of OPTIMAX® in 2012, Next Kraftwerke has grown rapidly and can comfortably meet its own power demand while simultaneously providing energy services to the wider economy.
The project is a compelling example of how VPPs are being used to manage and optimise the supply of electricity in the new age of renewables, achieving flexibility and scale, and ensuring grid stability.
