Active filter for resonance reduction

An active filter for reducing resonance in an electric system, the electric system comprising a power source distributing an alternating current to an AC conductor, a power consuming unit connected to the AC conductor and receiving the alternating current from the AC conductor and the active filter comprising:

• a DC power source;
• a DC conductor connecting the DC power source to the AC conductor;
• and
• a control unit comprising:
• a voltage measurement unit adapter to create a voltage signal on the basis of a measured voltage;
• a computing unit 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, wherein the biquadratic filter has a sample frequency exceeding 100 kSa/s;
• and
• a switching system placed between the DC power source and the DC conductor for creating the computed first compensating current.

A method of suppressing resonance in an electric system comprising an active filter, the method comprising:

• measuring a voltage of a conductor supplying energy from an AC source to an energy consuming unit,
• creating a voltage signal on the basis of the measured voltage,
• computing, using a biquadratic filter, a compensating current on the basis of the voltage signal, wherein the biquadratic filter has a sample frequency exceeding 100 kSa/s, and
• creating a control signal for controlling a switching system to create the compensating current by means of pulse width modulation.