Patent ID: 7411802

Claim:
A method of converting a direct current voltage of a source of direct current voltage into an alternating current voltage at a frequency through a bridge circuit comprising four switching elements (V 1 -V 4 ) and four free-wheeling elements (D 1 -D 4 ), said four switching elements (V 1 , V 2 , V 3 and V 4 ) being gated in such a way, that one corresponding switching element (V 1 , V 3 ) of a first bridge half is gated at at a mains frequency and one corresponding switching element (V 2 , V 4 ) of a second bridge half is gated at a high clock rate, a direct current voltage circuit, an alternating current voltage circuit and a plurality of free-wheeling phases being provided, characterized in that the alternating current voltage circuit is decoupled from the direct current voltage circuit during the free-wheeling phases by means of the switching element (V 2 ) or (V 4 ) and an additional switching element (V 5 ) disposed in the direct current voltage circuit which defines a commutation circuit, a free-wheeling current flowing through one of said free-wheeling elements (D 1 , D 3 ) of the first bridge half in said bridge circuit when in the decoupled state, in that the four switching elements (V 1 -V 4 ) of the bridge circuit are asymmetrically gated in such a manner that a respective one of the switching elements (V 1 and V 3 ) of the first bridge half is gated at a mains frequency, while a respective one of the switching elements (V 2 and V 4 ) of the second bridge half is clocked at the clock rate, in that the additional switching element (V 5 ) located in the direct current voltage circuit is clocked only in synchronism with a clocked switching element (V 2 ) during one half wave of the mains frequency whilst it is clocked only in synchronism with another one of the switching elements (V 4 ) during the other half wave of the mains frequency, in that the switching elements (V 1 -V 4 ) are connected to a free wheeling element (D 1 -D 4 ) whereby a free-wheeling current is flowing through one of the free-wheeling elements (D 1 or D 3 ) connected to the first bridge half in the bridge circuit in the decoupled state, and in that harmonics are reduced in the alternating current voltage circuit through at least one reactor.