Calculation of harmonics at the connection point of a modular multilevel HVDC converter

Abstract:
The noticeable growth of the renewable electricity generation leads to an increased application of self-commutated converters instead of line commutated converters in the energy transmission matrix. As a consequence, these new converters will play a significant role for the stability of the whole grid. Therefore deterministic calculation methods are required to perform harmonic and stability analysis of the system in a reasonable way. This paper shows a method to describe the behaviour of HVDC PLUS modular multilevel converters by means of harmonic impedances, leading to linear time invariant control models. These harmonic impedances are used to calculate the harmonic voltages which appear at the point of common coupling (PCC) as a result of the background harmonics and harmonics which are introduced by the converter itself. This work outlines the influence of several factors like modulation index, on-state voltages of applied semiconductors, switching frequency and interlocking times.