Increased electrification is a key factor if we are to phase out our dependence on fossil energy. This, of course, requires more electricity production. But the electricity grids are also facing major challenges when growing volumes of wind power are expected to fill the grids - at the same time as electricity consumers are increasingly turning into electricity producers.
To be able to handle large amounts of renewable electricity production in the power grid in the future, it is not only necessary to expand the capacity of the grid, but the technical innovation is also just as necessary. This applies both within the high-voltage transmission network and at the lower voltage levels that are closest to the regular electricity customers.
Two different research groups at the Department of Electrical Engineering at Chalmers are handling these problems, which thus arise in diametrically opposite places in the electrical system.
Electric Power Engineering finds methods
For Massimo Bongiorno, Professor of Electric Power Engineering, and his collaborators, the goal is to find methods to maintain the overall stability of the power system.
Why is it endangered? Well, you could say that what has been the core of the system until now – the classic synchronous generators – is shrinking.
“It is not the case that the core will completely disappear - for example, the hydroelectric generators will remain. But the share of electricity produced from coal, natural gas and nuclear power is decreasing. Instead, we see a sharp increase in wind power and, in a global perspective, solar power, he explains”.
This development means that the beneficial and stabilising effects that the synchronous machines have on the electricity grid are gradually eroded. This involves, among other things, providing so-called turning mass. At the same time, the use of various types of power electronic converters to feed in and extract power from the high-voltage network is increasing.
“Our task is therefore to provide wind power with the same good properties that the synchronous machines have traditionally stood for. Which is quite possible, provided it is controlled well, and the right tools are in place”, says Massimo Bongiorno.
System must quickly support
An example of what such a system must be able to do is to be able to quickly support frequency maintenance should a major fault occur in the network. Or to add active or reactive power, when required.
A few years ago, when the project started, the research world talked about creating "virtual synchronous machines". The idea was then to use power electronics and advanced control systems to make large wind farms fully behave in the same way as a large synchronous generator. Nowadays, the concept has been refined and the original concept abandoned.
“Now it is instead grid forming windfarms that everyone is talking about. This means combining a wind farm with an energy storage, which can consist of batteries or supercapacitors. For this, you have a converter that behaves as a controllable voltage source”, explains Massimo Bongiorno.
“This means that you could, for example, use a wind farm to start up a part of the grid that is down. This is what lies in the concept of grid forming, the ability to build an electricity grid from scratch. And today's wind farms cannot handle that”.
The research team at Chalmers works closely with Hitachi Energy (formerly ABB's grid division), which is a partner in the project. Statliga Svenska Kraftnät, which is responsible for the main grid and for the stability of the entire electricity system, is another important partner.
“It takes time before the results of this kind of research come out in practical application. One reason is that once it does, it must not go wrong. And it must last for many years”, notes Massimo Bongiorno.
In a different part of the electricity grid, changes are also taking place that require new solutions. It concerns the local electricity networks, typically at the voltage level below 10 kilovolts. It is here that the great mass of connections to the electricity grid are located – small industries, commerce, residential areas, and individual households.
Traditionally, these grid connections have only consumed electricity, but conditions are now changing rapidly. More and more electricity customers are also becoming prosumers (i.e., both consumers and producers of electricity) with local production from solar energy. This means that the power flows can periodically change direction, e.g., from lower voltage levels to higher and vice versa.
Associate Professor Anh Tuan Le at the Department of Electrical explains:
“One of the problems is that the local electricity grid companies today use the SCADA systems (Supervisory Control and Data Acquisition) that have limited real-time monitoring (observability) and control capabilities at the low voltage grid where the end-users are connected”.
Anh Tuan Le has been the coordinator of a recently concluded pan-European research project, UNITED GRID, with the task of improving the power grid companies' monitoring and control over the distribution grids.
A toolbox will complement existing systems
This has resulted in a "toolbox" that should be able to complement existing control systems, regardless of supplier. One of the tools, developed at Chalmers, will help companies deal with local congestion in the electricity grid.
“It is not only the growing production from the solar panels which increases the need for control and management, the consumption has also become more dynamic. Heat pumps are becoming more and more common, and we are getting new types of loads, such as charging electric vehicles”, emphasises Anh Tuan Le.
He adds that local battery storage is also expected to become more common in the coming years, which creates opportunities, while also making the peripheral power grids even more complex.
An example of problems that can arise locally in the distribution networks are increased voltage levels when the production from solar cells on the roofs of houses is high while the demand is low, something that can also lead to connected equipment being overloaded. A related problem is a highly fluctuating voltage during the day when the sun goes in and out of clouds.
“Our objective is to add more intelligence and controllability to the existing control systems. To some extent it is about automatic functions, in part it is about giving the electricity network companies greater opportunities to actively control their networks”, says Anh Tuan Le.
The toolbox that UNITED GRID has developed requires several new sensors in the electricity grid, but it is not about any big investments, according to him.
- We are aware of the expectations society has of the electricity grid companies' operations. Their equipment must be simple and robust. And cheap of course.
There is still some testing and validation to be done before the proposed toolbox is ready to launch on the market, but the interest from the target audience is palpable, according to Anh Tuan Le.
“Some companies may not see that they have any problems today, but many realise that the need will come in the foreseeable future”.
He adds that a local solar forecasting system developed within UNITED GRID has been tested by a French grid company, SOREA, participating in the project. And as for the "congestion tool" from the researchers at Chalmers, it has already been included as a new function in their control platform (Codex Smart Edge) marketed by the French IT partner Atos Worldgrid.
“Compared to much other research and development that we do at Chalmers, it can be said that UNITED GRID has produced a number of key exploitable results which have strong commercialisation potentials”, Says Anh Tuan Le.
Text: Sandra Tavakoli
Scientific articles
Transmission Line Protection Using Dynamic State Estimation and Advanced Sensors: Experimental Validation
Dynamic state estimation based transmission line protection scheme: Performance evaluation with different fault types and conditions
For more information, contact:
Massimo Bongiorno, Professor at the Department of Electrical Engineering, Chalmers Technical University
massimo.bongiorno@chalmers.se
+46317721631
Anh Tuan Le, Associate Professor at the Department of Electrical Engineering, Chalmers Technical University
tuan.le@chalmers.se
+46317723832