Investigation of six-pulse three-phase converters in unsymmetrical operation

Power converters operated in unsymmetrical three-phase electrical systems will generally work asymmetrically. This introduces disadvantages for the operation of the electrical power system, such as non-characteristic harmonics in voltage and current. In this paper, a method is presented to control the behavior of electrical equipment based on line-commutated current converters using unsymmetrical firing angles. Thereby the operation of the essentially non-linear system is described as sectional continuous linear problem. For its solution an approach with differential equations in the range of space-phasors is used. On the basis of a six-pulse line-commutated current converter it is shown to be possible to optimize the unsymmetrical operation with respect to certain quality criteria.