Apparent power (i.e., the total amount of power flowing in an AC grid) is made up of two components: active power (P) and reactive power (Q).

Active power is the useful energy delivered to electrical consumers, while reactive power is essential for maintaining voltage by sustaining the electromagnetic fields required for energy transfer.

Why voltage stability matters

Voltage stability refers to the ability of a power system to maintain acceptable voltage levels under normal conditions and after disturbances. If voltage deviates too far from its nominal value, issues can arise, including:

• Cascading failures, potentially leading to widespread blackouts
• Equipment malfunction or damage due to undervoltage or overvoltage
• Increased losses and reduced system efficiency

In extreme cases, insufficient reactive power support can lead to voltage collapse, where voltage drops uncontrollably across a region.

The advantages of modern power electronics

Modern power electronics have become a cornerstone for maintaining voltage stability in today’s evolving electric grids. Their role is becoming even more critical as renewable generation is increasingly developed in geographically remote areas far from major load centers.

Power electronic converters enable grid operators to:

• Inject or absorb reactive power dynamically, responding almost instantaneously to system needs.
• Regulate terminal voltage through high-speed control loops.
• Maintain voltage stability during disturbances.

Grid-following vs. grid-forming control

Crucially, a converter’s contribution to voltage stability in a grid is determined by whether it operates in grid-following or grid-forming control mode.