Back-to-Back HVDC Modular Multilevel Converter for Transient Voltage Dip Mitigation in Passive Networks

For nuclear research laboratories like CERN, where the exceptionally high power quality conditions are required, the immunity against transient voltage dips is of vital importance. By using the traditional HVDC modular multilevel converter in a back-to-back configuration with properly dimensioned submodule capacitors, voltage dips can be mitigated instantaneously, improving power quality of the network. The dimensioning of the capacitors is shown as one of the key elements of this paper. Firstly, the actual voltage dips statistics recorded at CERN are presented and described. Then, the traditional capacitor submodules dimensioning method is presented and compared to the proposed energy design rule. To validate the energy dimensioning and the mitigation performance, a detailed Simulink model of a 220MVA HVDC modular multilevel converter is described and the main results are presented. The paper concludes with the main conclusions of this study and the future works.