Active filter for resonance reduction

A control unit (16) for an active filter (1) for reducing resonance in an electric system (2), the electric system (2) comprising a power source (20) distributing an alternating current (AC1) to an AC conductor (21) connected to a power consuming unit (22) for distributing the AC to the power consuming unit, the active filter (1) comprising a DC power source (10) and a DC conductor (15″;

• 3) connecting the DC power source (10) to the AC conductor (21), the control unit (16) comprising:
• a voltage measurement unit (17′) adapter to create a voltage signal on the basis of a measured voltage;
• a computing unit (17″) adapted to compute, using a biquadratic filter:
• a first compensating current on the basis of the voltage signal for reducing resonance in the electric system (2);
• and
• a switching system (17′″) placed between the DC power source (10) and the DC conductor (15″;
• 3) for creating the calculated first compensating current.