Active filter for resonance reduction

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

• a DC power source;
• a DC conductor that connects the DC power source to the first AC conductor;
• a switching system placed between the DC power source and the first AC conductor, the switching system being configured to create a compensating current based on a received control signal,
• a voltage measurement unit adapted to measure a voltage of the first AC conductor and create a voltage signal on the basis of the measured voltage;
• and
• a computing unit adapted to (i) receive the voltage signal, (ii) sample the received voltage signal with a frequency exceeding 100 kSa/s, and (iii) compute the control signal on the basis of the sampled received voltage signal.

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

• measuring a voltage of an AC conductor supplying energy from an AC power source to a power consuming unit at a point between the AC conductor and a capacitor adapted to lead frequencies other than a utility frequency of the electric system to ground;
• sampling the measured voltage with a frequency exceeding 100 kSa/s;
• and
• computing a control signal for a switching system of the active filter on the basis of the sampled measured voltage, for creating a compensating current configured to suppress resonance in the electric system using the active filter.

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

• measuring a first voltage of a first AC conductor, a second voltage of a second AC conductor and a third voltage of a third AC conductor, the second and third voltage having a voltage offset in relation to the first voltage of the first AC conductor of substantially 120° and 240° respectively;
• creating a first voltage signal on the basis of the first measured voltage, a second voltage signal on the basis of the second measured voltage and a third voltage signal on the basis of the third measured voltage;
• sampling the first, second and third voltage signals with a frequency exceeding 100 kSa/s;
• and
• computing a control signal for a switching system of the active filter on the basis of the sampled first, second and third voltage signals, for creating a compensating current configured to suppress resonance in the electric system using the active filter.