edgeFLEX starts a series of monthly insights of the project from the perspective of the project partners. Enjoy reading them.
Today: University of Bologna
What does a supermarket have in common with the trial in Italy?
Would you trust a supermarket using scales which provide results with variations of plus minus 100 g? Well, I may say yes if every time the scale error is in my favour. However, there is no need of experts to conclude that there is something wrong in those scales, or better, that those scales are inappropriate for the purpose.
The same concept can be extended – and it is applied everyday – to the electrical grid. The main difference is what we are measuring. We are not dealing with grams of tomatoes or litres of milk; instead, we are measuring voltages (V) and currents (A). These two quantities are then used to compute more complex ones like synchrophasors, powers, energies, etc. Another significant analogy with the supermarket is that we pay tomatoes as well as energy after the scale or the energy meter measured them. That is why it is crucial to perform accurate measurements.
That is the starting point of the Italian trial. Several commercial and prototype edge devices have been installed in the distribution network to achieve some important goals. First, a more observed network facilitates the distribution system operators work of controlling and managing it. Second, the capabilities of such edge devices trigger a variety of novel functions/algorithm like the voltage and frequency control, or the inertia estimation. Of course, these algorithms succeed only if the inputs they require can be trusted. Therefore, the trial exploits very accurate voltage and current sensors (imagine a scale that measures variations of 0.1 g).
In the specific case of the trial, the voltage control is implemented in the monitored portion of grid. Briefly, the voltage control takes hundred/thousands of “pictures” of the grid every second to assess its healthy. Afterwards, the voltage control algorithm can apply countermeasures to adjust the voltage in the “unhealthy” nodes. This smart control is possible if the voltage control algorithm has been given active access to the electrical assets of the grid. For example, renewable energy sources are connected/disconnected to increase/reduce the voltage of one or more nodes.
At the status of the trial, the biggest success has been to correctly integrate the commercial and prototype equipment with the existing one. Consider that system operators have really complex electrical and communication infrastructure, that typically is not built to accept new devices. Overcoming compatibility and communication issues is the perfect starting point of successful trial that will be completed in the following weeks.
Today: RWTH Rheinisch-Westfälisch Technische Hochschule Aachen
The new role of VPP foreseen in edgeFLEX of the Virtual Power Plant (VPP) requires the integration of grid automation solutions to support the System Operators in the management of the electrical grid. Since the beginning of the project it was clear that edgeFLEX required the investigation and the implementation of all the different aspects that characterize the grid automation system. These four aspects are: measure, estimation, control and simulation.
To perform any action on the grid, data must be acquired via measurement devices and sent to the servers that collect the set of data. Within the framework of edgeFLEX, the RWTH Aachen University has developed the edgePMU, to perform accurate and synchronized phasor measurements by collecting data on a low-cost device and performing processing in the edge cloud.
Consequently, power and frequency measurement data can be used to estimate the inertia of the system, providing hints for the Transmission System Operators (TSO) to assess the robustness of the grid.
Moreover, the collected measurements and estimated data can also be used for calculating the required control actions for the electrical grid.
Within the context of edgeFLEX, voltage control algorithms have been developed to manage the distributed generators installed in the distribution grid for maintaining the voltage within the technical limits.
All these three elements of the circle are meant to be applied in real grids, however, to test the algorithms and the communication interfaces, the real system is normally substituted with a simulated environment, which also allows the DSOs to perform critical tests on it.
The development of all these aspects also brought with it some challenges. The installation of edgePMUs in the grid, for example, required understanding sensors and monitoring systems of the field trials. The control and estimation algorithms also needed a correct interface with the rest of the platform. Working on these challenges has helped RWTH increase its knowledge on aspects of devices deployment and integration with cloud platforms.
As a result, RWTH has been able to install and start collecting grid data from the field trials in Germany and Italy. Moreover, tests in a simulated environment have proven the ability of the control algorithms to be interfaced with edgePMU and use the measurements to calculate the correct set-points for the simulated grid.
Edoardo De Din, Gianluca Lipari, Jonas Baude und Diala Nouti
An inspirational story from the lockdown
The legend tells that Newton formulated the gravitational theory in 1665-66 after watching an apple fall. It is not a legend but probably less known that this discovery happened when Newton was at home, in Lincolnshire, as the University of Cambridge closed because of a bubonic plague epidemic. Newton himself described the two years he spent on lockdown as "the prime of my age for invention." With the due proportion and without any presumption of having discovered any fundamental principle of physics, I can now say that the two years that I spent mostly at home during the COVID19 pandemic has been an intense period of learning and discoveries for me too.
Staying at home, I did not have to commute to go to work and no students and colleagues were dropping by my office. And, as a consequence, there was much more free time. I dedicated this time to read, mostly mathematical books. Among these, the classical book “Differential Geometry” by J. J. Stoker. I was, at that time (end of 2020, beginning of 2021), elaborating on the definition of frequency and have just completed the paper “Complex Frequency” that was eventually published after two tough rounds of reviews on the IEEE Transactions on Power Systems.
When I started reading the book by Stoker, I was surprised to find a similarity between the formula of the curvature of a space curve and the expression of instantaneous frequency of an electric voltage in rectangular coordinates. The two expressions are, in fact, very similar except for the fact that the formula of the curvature uses the speed and acceleration of the position of a trajectory and has the unit of the inverse of a length, whereas the instantaneous frequency uses the voltage and its first-time derivative and has the unit of a frequency. For a while the similarity wandered in my mind just as an interesting oddity, but void of any implication.
It is not rare to find similar mathematical expressions in completely different disciplines. These similarities, in most cases, do not mean there is any actual link between the disciplines. Yet, the two formulas of curvature and instantaneous frequency were coming back to my mind suggesting that they were in effect linked through some deep bond. One day, thinking of Faraday’s law, which states that the voltage is the time derivative of the magnetic flux, I realized that, if the flux is associated to a trajectory, then the voltage is a speed. And that was it.
Prof Federico Milano
Representation of a trajectory of a generalised magnetic flux in a three-phase abc space. The tangent vector at any point P of the trajectory is the voltage v(t), and the normal vector is the derivative of the voltage with respect to the arc length v ̇(t) divided by the curvature κ(t). The local frequency of the voltage is given by w(t) = |v(t)| κ(t).
Trajectory of a voltage with time varying frequency in the three-phase abc space.
This simple assumption led to find that the “geometric frequency” of a voltage is in effect its curvature multiplied by the voltage magnitude. This fact has several implications. First, it generalises the concept of instantaneous frequency and solves the paradoxes to which the definition of this quantity leads. Second, it allows splitting the time derivative of the voltage into two terms: a translation and a rotation, which are useful for control applications. Third, it allows to generalize the Park transform, which is arguably the most important coordinate transformation utilised in power system dynamic analysis and control. Fourth, it provides the tools to design novel, simple, yet effective frequency and voltage controllers. Of course, this “discovery” does not have the depth and the tremendous impact of Newton’s gravitational theory. It is nevertheless a beautiful finding with several interesting applications. And it is comforting to think that this finding was given raise by the long quiet days during the various lockdowns and that not everything was bad about the pandemic.
- F. Milano, Complex Frequency, IEEE Transactions on Power Systems, vol. 37, no. 2, pp. 1230-1240, March 2022. arXiv: 2105.07769 DOI: 10.1109/TPWRS.2021.3107501
- F. Milano, A Geometrical Interpretation of Frequency, IEEE Transactions on Power Systems, vol. 37, no. 1, pp. 816-819, January 2022. arXiv: 2105.07762 DOI: 10.1109/TPWRS.2021.3108915
- F. Milano, G. Tzounas, I. Dassios, T. Kërçi, Applications of the Frenet Frame to Electric Circuits, IEEE Transactions on Circuits and Systems I: Regular Papers, vol. 69, no. 4, pp. 1668-1680, April 2022. arXiv: 2112.03633 DOI: 10.1109/TCSI.2021.3133948
- W. Zhong, G. Tzounas, F. Milano, Improving the Power System Dynamic Response through a Combined Voltage-Frequency Control of Distributed Energy Resources, IEEE Transactions on Power Systems, accepted in January 2022, in press. DOI: 10.1109/TPWRS.2022.3148243
- F. Sanniti, G. Tzounas, R. Benato, F. Milano, Curvature-Based Control for Low-Inertia Systems, IEEE Transactions on Power Systems, accepted in June 2022, in press. DOI: 10.1109/TPWRS.2022.3184189
- F. Milano, G. Tzounas, I. Dassios, M. A. A. Murad, T. Kërçi, Using Differential Geometry to Revisit the Paradoxes of the Instantaneous Frequency, IEEE Open Access Journal of Power and Energy, accepted in June 2022, in press. arXiv: 2206.12091
- F. Milano, The Frenet Frame as a Generalization of the Park Transform, submitted to the IEEE Transactions on Power Systems, under review. arXiv: 2206.09209
How 5G can better support power operators
With the dramatic growth of renewables, now is the time to revise the Virtual Power Plant (VPP) concept and this is the challenge edgeFLEX addresses. VPPs need to support not only the promotion of intermittent Renewable Energy Sources (RES) but also the integration of all Distributed Energy Resources (DER) into the full scope of grid operations. Such a leap is enabled by the new edgeFLEX architecture for VPPs in which communications, supported by 5G, correspond to multiple layers of dynamics, pave the way for a fully renewable energy system.
We are happy that we are currently planning a demonstration for an edgeFLEX stand at the EuCNC and 6G Summit conference in Grenoble in June! EuCNC will be our first edgeFLEX stand at a conference as the project started in April 2020 during the Covid-19 lock-downs. Despite everyone working from home and no face-to-face meetings being possible, the relationships between the project partners developed very well based on our many virtual meetings. We lightened up the isolated environment of the project partners with chocolates and tea packages sent directly to the homes of all project participants based in many different European countries!
On the stand at EuCNC, we plan to demonstrate results of our work in the project, such as those of our 5G latency tests. By runing laboratory tests in live 5G networks in Aachen, Germany, we investigated how 5G can support the edgeFLEX services. Additionally, we had the opportunity to try out the brand-new testbed for the new 5G feature Ultra-Reliable Low-Latency Communication (URLLC) which will provide even lower latency and higher reliability than currently available 5G versions.
Exposing 5G capabilities to vertical sector applications is a hot topic at the moment, and we in Ericsson were lucky to be able to investigate this topic for the power network domain and define the benefits and use cases for the exposed capabilities. In edgeFLEX, we are showing newly developed 5G enhancements providing VPP operators with the possibility to work together with Distribution System Operators (DSOs) enabling better monitoring and control and faster stabilisation of the power grid. The secure and reliable data exchange between the assets of VPP operators and the services of DSOs can be enabled by exposing 5G capabilities through new exposure capability interfaces. These interfaces can help VPPs and DSO’s to integrate 5G more easily and quickly in their existing infrastructure reducing their monitoring, control, and trading challenges. Thus, 5G will not only be able to support the existing needs of the power operators, additionally it will also enable new business cases in the coming years for the sector actors in the power domain!