A team at ETH Zurich has patented a new algorithm for grid-forming inverters that keeps frequencies stable while protecting the devices from damage. Its novelty relies on considering frequency, voltage, and current separately.
From pv magazine Germany
A research team from Swiss research institute ETH Zurich has created a new algorithm for operating inverters in a grid-forming mode.
The patented algorithm operates the inverter as a voltage source. This is important when short circuits and voltage drops significantly complicate grid operation.
Until now, power plants in which a steam turbine drives a generator have set and maintained the grid frequency. These include, in particular, nuclear, coal-fired, and gas-fired power plants. Since such power plants are no longer to be used in the future, alternatives must be created through new operating modes for inverters in photovoltaic systems, battery storage systems, and wind turbines.
Such inverters must become a voltage source or clock generator. However, this behavior is difficult to implement, especially during faults. In the event of a sudden voltage drop in the grid, for example, the inverters, unless otherwise controlled, would attempt to maintain their performance level by feeding correspondingly more power into the grid, which would destroy the electronics. For this reason, in the event of a fault, inverters shut down to protect themselves.
With this in mind, a team led by Florian Dörfler, Professor of Complex Control Systems at ETH Zurich, succeeded in designing an algorithm that keeps the frequency stable without damaging the device. Dörfler’s doctoral student, Maitraya Desai, realized that in the event of grid faults, the grid voltage and the frequency of the alternating current should be treated independently of each other.
The control algorithm proposed algorithm follows this principle and attempts to keep the frequency stable under all circumstances. In doing so, the algorithm limits the current and allows the voltage to fluctuate freely.
The team has already tested the algorithm in a computer simulation. Since the control algorithm is software, the team has also been able to test the system on a test system in the laboratory. Building a new test environment was not necessary.
In the next step, Dörfler and his team plan to work with companies to implement the control algorithm in practice and introduce it into new software products.
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