General Principle Of Active Filtering - ABB PQFA Instruction Manual

Distorted networks may also cause generators malfunctions.
Overall it may be concluded that an excessive amount of harmonics leads to a
premature ageing of the electrical installation. This is an important motivation
for taking action against harmonics.
3.2.

General principle of active filtering

The active filter measures the harmonic currents and generates actively a
harmonic current spectrum in opposite phase to the measured distorting
harmonic current. The original harmonics are thereby cancelled. The principle
is shown in figure 3.2.
Supply
Figure 3.2. Principle of active filtering
The control of the active filter in combination with the active generation of the
compensating current allows for a concept that may not be overloaded.
Harmonic currents exceeding the capacity of the active filter will remain on the
network, but the filter will operate and eliminate all harmonic currents up to its
capacity.
The principle of active filter showing currents and spectra is clarified in Figure
3.3.
Fundamental only
1 . 3 1 . 3
0 360 0
- 1 . 3 - 1 . 3
Asea Brown Boveri Jumet S.A.
PQFA Instructions Manual
i
distortion
Load
i
compensation
PQFA
1 . 3
3 6 0 0
- 1 . 3
360
8