Patent ID: 8908398
Filing Date: 2014-12-09
Classification: H02M

Abstract:
1. A method for operating a converter circuit, wherein the converter circuit includes a converter unit having a multiplicity of controllable power semiconductor switches, and includes a transformer, which has at least one winding set with a primary winding and a secondary winding, the converter unit being connected, on an AC voltage side, to the primary winding of the respective winding set, wherein the method comprises: a) monitoring a magnitude of the magnetic flux of each winding set with respect to a threshold value, and determining the polarity of the magnetic flux of each corresponding winding set, respectively; b) applying an adjustable negative DC voltage from the converter unit to the respective winding set when the magnitude of the magnetic flux through the respective winding set exceeds the threshold value and the polarity of the magnetic flux through the respective winding set is positive; c) applying an adjustable positive DC voltage from the converter unit to the respective winding set when the magnitude of the magnetic flux through the respective winding set exceeds the threshold value and the polarity of the magnetic flux through the respective winding set is negative; d) repeating steps a) to c) until the magnitude of the magnetic flux through the respective winding set undershoots the threshold value; e) after the magnitude of the magnetic flux through the respective winding set has undershot the threshold value and when the polarity of the magnetic flux through the respective winding set is positive, applying the adjustable negative DC voltage from the converter unit to the primary winding of the respective winding set until a voltage/time integral of the applied negative DC voltage is less than or equal to a predefinable negative flux value; and f) after the magnitude of the magnetic flux through the respective winding set has undershot the threshold value and when the polarity of the magnetic flux through the respective winding set is negative, applying the adjustable positive DC voltage from the converter unit to the primary winding of the respective winding set until a voltage/time integral of the applied positive DC voltage is greater than or equal to a predefinable positive flux value.