An active filter is a power-quality device that measures waveform distortion and then injects a compensating current or voltage in real time. Instead of relying on fixed tuned components, it adapts to changing harmonic content, load conditions, and network impedance. That makes it useful where non-linear equipment, converters, or rapidly varying loads create distortion that would be hard to clean up with passive filtering alone.
In cyber-physical infrastructure, active filters matter because clean power is part of system reliability. If harmonic distortion is left unchecked, sensitive equipment can misbehave, overheat, or trip. In practice, active filters appear in industrial plants, converter stations, and other grid-connected systems as a control layer that stabilizes power quality. From a security perspective, their sensors and controllers are important trust points: if measurement data or control logic is corrupted, the filter can compensate incorrectly and make the electrical problem worse instead of better.