Patent ID: 8193889

Claim:
A filter appliance for a multiphase electrical converter device, the filter appliance comprising: at least three first electrical terminals for receiving alternating voltages produced by the multiphase electrical converter device, at least three second electrical terminals for electrically connecting to an external electrical system, at least three main current coils, each of the main current coils being formed of foil conductor and being electrically connected between one of the first electrical terminals and one of the second electrical terminal, shielding coils, and a magnetic core structure made of magnetically amplifying material and comprising legs each of which being surrounded by one of the main current coils and at least one of the shielding coils, wherein each of the main current coils is provided with at least one of the shielding coils and first ends of the shielding coils are electrically connected to a third electrical terminal of the filter appliance, each of the shielding coils being formed of foil conductor that is alongside and a distance apart from the foil conductor of the corresponding main current coil so as to form a capacitive shield between successive turns of the corresponding main current coil, the main current coils are mutually adjacent so that magnetic axes of the main current coils are separate, and a cross section of each leg is dimensioned to cover less than 75% of a cross section of a space surrounded by one or more of the main current coils and one or more of the shielding coils surrounding that leg so as to provide, for magnetic flux, an additional path parallel to that leg.