Common mode filter device and electrical equipment

A common mode filter device adapted for being connected between an electrical AC network and an electrical apparatus, said common mode filter device comprising:

• a first electrical connection dedicated for connecting an earth terminal of the AC network to a common terminal of the electrical apparatus;
• at least two second electrical connections each for connecting a respective phase terminal of the AC network to a respective power terminal of the electrical apparatus;
• at least one damping circuit, said damping circuit comprising a damping resistor and a damping capacitor which are serially connected;
• and
• separately for each second electrical connection:
• two LC-filters arranged serially, each LC-filter comprising a separate capacitor connected between said second electrical connection and the first electrical connection, and each LC-filter also comprising a separate common mode inductor arranged in said second electrical connection upstream of the capacitor of the same LC-filter, relative to a direction from the AC network to the apparatus, wherein
• the common mode filter device further comprises two transformers and a current control circuit,
• a secondary winding of a first one of the transformers being arranged for producing a detection voltage representative of a common mode current existing in the second electrical connections,
• the current control circuit being arranged for sensing the detection voltage and for generating a control current in a primary winding of a second one of the transformers,
• the common mode inductor of the LC-filter closest to the electrical apparatus for each second electrical connection being a respective secondary winding of the second transformer, so as to generate a compensation current in said common mode inductor of the LC-filter closest to the electrical apparatus of each second electrical connection,
• the second transformer further comprises another winding connected in closed loop with the damping resistor and the damping capacitor, and the damping resistor and damping capacitor are selected so that a resonance effect of at least one of the LC-filters on an insertion loss function relative to the common mode filter device is reduced or suppressed, and
• in that the current control circuit and both transformers are adapted so that the compensation currents compensate at least partially for the common mode current which is transmitted into the second electrical connections by the electrical apparatus from the power terminals.