The Effect of the Harmonic Content Generated by AC/DC Modular Multilevel Converters on HVDC Cable Systems

With the increasing penetration of renewable and decentralized energy sources into the power grid, an extended use of DC voltages is expected on both distribution and transmission levels. Generation of DC voltages by means of voltage source converters is associated with a wide spectrum of harmonic distortions at converter terminals, both on the ac and on the dc sides. This can lead to partial discharges in power cables, which deteriorate insulation material thus weakening its performance and reducing cable life-time. In the previously published paper, the effect of harmonic distortion on appearance of partial discharges in cable insulation was evaluated. Here, the study related to the PD behavior has been made focusing on the influence of multilevel converter parameters such as the number of submodules and the switching frequency chosen to generate different voltage stresses. In addition, effects of using a function generator for producing desired waveform instead of the dSPACE board as in the previous work, are highlighted. In particular, it is shown implementation of the former made it possible utilizing the Pry-Cam synchronization and thus the realization of the PD pattern.