Efficient modular multilevel converter based on active-forcedcommutated hybrid packed u-cells for HV networks

High-voltage DC (HVDC) converter topologies have been more desirable in the off-shore wind energy applications to increase the efficiency and reduce the losses. In this context, the paper presents a modified structure for modular multilevel voltage source converter (VSC) topology where the conduction and switching losses can be significantly reduced. As the conduction losses of the semiconductor devices affect the total efficiency of such systems, replacing part of the Insulated Gate Bipolar Transistor (IGBT) devices with thyristors in the conduction path of the proposed topology can reduce the total losses in the normal operation. Thus, both IGBTs and thyristors are implemented in a hybrid configuration. In this configuration, the IGBT devices are responsible for voltage/current transitions between the positive and negative parts of the waveforms while the thyristor devices are responsible for conducting the currents in the other constant polarity regions. MATLAB simulations and scaled-down experiments show that the modified structure can reduce the total losses of the HVDC converter significantly.