Power-Transmission via an MMC-based HVDC System for the Rededication of Existing AC-Lines

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. At high voltages of e.g. 400 kV, modular multilevel converters (MMC) fulfill all requirements. For testing all relevant aspects of a multiterminal HVDC-transmission system, a scaled-down test bench has been realized. Four MMCs define the multiterminal DC system. With regard to practical demands, no explicit communication between the control systems is allowed for stable operation of the transmission system. This paper gives an overview of the test bench and then concentrates on the bidirectional power flow of the HVDC System in a bipolar configuration.