New algorithms ensure grid stability with renewable generators

22.04.2025

Source: E & M powernews

Large power plants currently ensure a stable alternating current cycle in the European electricity grid. Researchers at ETH Zurich have also developed such clock generators for PV and wind power.

Europe is to be supplied with renewable energy. The expansion of wind and solar power capacities and the provision of sufficient electricity in winter are just two of the challenges that arise. Another is maintaining the alternating current frequency of 50 Hertz in the grid. The electricity flows one hundredth of a second in one direction and one hundredth of a second in the other. The generators of the large power plants currently set this clock, they are synchronized with each other via the grid.

Electronically controlled inverters are required for renewable generators such as wind power and photovoltaics. This is because wind and solar power plants produce direct current that only flows in one direction. This must be converted into alternating current via inverters. Today's inverters are geared to the rhythm of the grid and feed their electricity in synchronously. If there are fewer and fewer coal and nuclear power plants in the grid in the future, new clock generators will be needed.

This will require grid-forming inverters that actively help to keep the cycle stable. Until now, engineers had no viable solution for how such grid-forming inverters can continue to work in the event of a short circuit or a voltage dip in the power grid and at the same time be protected against overload. The group led by Florian Dörfler, Professor of Complex Control Systems at ETH Zurich, has developed a solution.

Radical protection mechanism

In today's inverters, a protective mechanism ensures that they disconnect from the grid in the event of a grid fault. This protection is necessary, as the inverter would attempt to compensate for the missing voltage in the event of a severe voltage dip in the power grid by supplying a high current to the grid. This would overload it and irreparably damage it within milliseconds.

With new algorithms for intelligent control, Dörfler's group has now succeeded in continuing to operate the grid-forming inverters even in the event of a grid fault. This means that there is no longer any need for a rigorous shutdown. This means that a wind power or photovoltaic system can remain connected to the grid even in the event of a grid fault, continue to supply electricity and thus help to stabilize the grid frequency. The system can thus take on the role that is currently played by traditional large-scale power plants.

The inverter controller continuously measures the grid parameters and adapts the inverter to them in real time via a feedback loop. ETH Zurich has filed a patent application for its new algorithms.

Master's theses in industry

The brilliant idea came from one of Dörfler's Master's students, who is now doing his doctorate at ETH. Maitraya Desai realized that the best way to deal with grid faults is to treat the grid voltage and the frequency of the alternating current independently of each other. In the event of a grid fault, it is difficult to maintain the voltage. The new control algorithm therefore concentrates on the clock frequency and attempts to keep it stable in the grid under all circumstances. The control algorithm limits the current to prevent the inverter from being overloaded, while allowing the voltage to fluctuate freely.

"We and others have been researching this area for 15 years," says Dörfler. The new algorithms contribute to the stability of the power grid, reduce the risk of blackouts and pave the way from large centralized power plants to a decentralized, flexible system of smaller power plants that supply renewable energy. This could make them a key component of the energy transition, concluded the head of research.

The original publication on grid-forming inverters is available online.

Author: Susanne Harmsen