On the Influence of Insertion Index Calculation on MMCs for HVDC Applications and their Control Systems

Abstract:
Performance analysis of Modular Multilevel Converters and their control systems is presented in this paper. It is shown that the insertion index calculation (IIC) as part of the modulation scheme of the converter influences the quality of the control systems. Depending on whether the voltage ripples in the submodule capacitors are considered or not for the IIC, oscillations can be present in the AC- and DC-side control loops. Three types of calculation methods together with two control schemes are taken into account. For the investigations a simulation model based on the Continuous Model of the MMC and a discrete switching model are used, that are implemented in PSCAD/EMTDC. Analysis of power frequency coupling on a MMC HVDC link operated in parallel to HVAC systems gives some further insights into the topic.