Power converters operated in unsymmetrical three-phase elec-trical systems will generally work asymmetrically. This intro-duces disadvantages for the operation of the electrical power system, like non-characteristic harmonics. In the case of con-trollable power converters, such as thyristor converters, it is possible to operate the converter with asymmetrical firing an-gles. This offers the opportunity to react on the system’s unbal-ance optimizing the asymmetrical operation of the converter to lower the disadvantages. In this paper, a method is presented to calculate the behaviour of electrical equipment based on line-commutated current con-verters. 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. It is shown to be possible to optimize the unsymmetrical operation with respect to certain quality criteria by using unsymmetrical firing angles.