Real-time control system and entire control structure for a test bench for a MMC-based HVDC transmission system

High-voltage DC (HVDC) transmission lines offer highly efficient transport of electric energy. If applied to comparatively weak grids, self-commutated converters are the proper choice, because they allow stabilizing the grid in case of faults by injecting reactive power. However, proper control methods have to be applied - normal operation and the reaction to various fault conditions need careful analysis. For this purpose a scaled-down test bench for an HVDC system has been realised. Four modular multilevel-converters (MMCs) operate together, defining a multiterminal DC grid. The test bench provides a realistic environment to verify multiterminal operation and fault mitigation. For this purpose, a lot of signals have to be measured and transferred to the control. The control in turn has to provide many switching signals for the IGBT used. This paper presents layout and structure of the entire control and a modular control system that has been configured for the tasks of this HVDC-system test bench and includes first measurement results of controlled operation of the test bench.