Method and device for determining or suppressing a harmonic oscillation, contained in a measurement value, in the correct phase and with the correct amplitude, particularly in a direct AC converter for feeding an unbalanced load

摘要

In an actuator for a system of three measurement values, for which a reference variable (U*) with predetermined nominal frequency is predetermined, an actual-value vector (i) describing the measuring values (i1, i2, 13) is transformed by means of a first vector rotator (32') into a positive-sequence system circulating with the predetermined nominal frequency. The mean time values of the components of the transformed vector, formed by a filter (33') are transformed back into the space-fixed reference system by means of a second vector rotator (34'). This forms a quantity (i') containing the positive-sequence system fundamental contained in the measurement values in the correct phase and with the correct amplitude. In addition, the actual-value vector can also be transformed into the negative-sequence system, averaged and transformed back in order to determine the negative-sequence system fundamental (i''). When applied to the currents of a three-phase/three-phase direct AC converter, the addition of the two fundamentals supplies the fundamental current oscillation contained in each phase current with the zero crossings of which the anti-parallel rectifier bridges of the converter can be switched over. Including the negative-sequence system fundamental makes it possible additionally to obtain a correction variable which suppresses an unwanted negative-sequence system by being impressed on the reference variables. During the transformation of the actual-value vector into a positive-sequence system and negative-sequence system, rotating at triple frequency, the third harmonic can also be determined in order to obtain a correction variable for suppressing this harmonic. This makes it possible, in particular, to feed a high power from a three-phase system via a direct AC converter with connected balancing device into an alternating-current system without interfering system reactions, and the direct AC converter need only be dimensioned for a balanced active load. IMAGE