Direct Multivariable Control for Modular Multilevel Converters

Modular multilevel converters (MMCs) have enabled new and demanding applications for power electronics in the high voltage/high power range. In these applications, very fast and tight control of all variables of the MMC is of prime importance. This article presents a new multivariable control (MVC) concept, which enables independent and extremely fast control of all essential variables. For each variable, a tolerance band can be specified, which is strictly met even under unexpected severe transients and disturbances. The minimized dead times achieved by the control are more than one order of magnitude smaller than the state of the art. The MVC has been implemented based on FPGA-hardware and digital signal processing of the measured values. Experimental results of the control performance and the robustness against parameter variation are presented, using a down scaled MMC with 96 submodules. These results include the analysis of steady-state operation, dynamic performance, and fault scenarios.