The Questions That Follow The "Major Blackout"

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FAULHABER Drive Systems

Wuxi InfiMotion Technology Co., Ltd.

At the recently concluded PCIM in Nuremberg, the blackout in Spain and Portugal was a recurring topic. What happened there? Did it have to happen sooner or later? Can something like this happen to us as well? What should be learned from it? What will or should change?

The power outage in the two countries was of course an unpleasant event for everyone affected. Its cause has not yet been precisely clarified. Investigations are underway to analyze the sequence of events.

In the end, the question of cause and effect arises, and it is certainly necessary to take a critical and objective look at the current situation in the European interconnected grid.

A look at Technical Details

Part of the outage involved the shutdown of generators when the grid frequency left the allowable range. This protective mechanism is part of all power generators, regardless of whether generators with rotating masses are in motion or whether the electricity comes from solar cells.

The problematic scenario that can occur is that when a large generator fails, other generators actually need to step in. If this does not happen—or does not happen quickly enough—the grid frequency moves to levels outside the allowable range, and instead of contributing to stabilization, more generators drop out, thereby reinforcing the fault effect itself. Domino effect.

Owners of solar systems know this effect as well: if the grid fails, no yield is to be expected from their own photovoltaics despite the sun. The background is that most inverters require the grid and its voltage to synchronize with it.

One speaks of grid-following generators, which can only feed energy into an existing grid.

In contrast, there is the group of grid-forming or island-capable inverters. These generate their own so-called island grid in the event of a supply network failure. To protect the public grid and the people working on it, the private system is disconnected from the public grid and forms a self-sufficient island—hence the term island grid.

When the public grid is switched back on, synchronization occurs and the island is reconnected with the grid.

It depends on the local conditions which type of inverter is used in a wind or solar farm, but even in plants within the power range of several MW or even GW, grid-following systems are mostly used today.

The outage in Spain and Portugal will certainly stimulate discussion about whether large solar and wind farms should not only be grid-supportive but even grid-forming.

From the perspective of inverter technology and power electronics, this is not a problem—it could actually be changed via software. In most cases, even retrospectively as an upgrade.

The challenge lies in the communication between decentralized producers. The occurrence of so-called zombie grids, larger islands that supply themselves but do not inform the network operator, must be prevented. Among other things, they pose a danger to maintenance personnel because they keep lines and networks active that the operator assumes are switched off.

The "virtual power plant," which has been discussed more frequently, could be a solution here. In it, a multitude of decentralized, small producers represent a single centrally controlled system that is available to the grid operator like a large power plant.

Also helpful is the rapidly growing expansion of energy storage systems that can provide balancing power for grid stabilization at high speed.  (mr)