A New Hybrid Multilevel DC–AC Converter With Reduced Energy Storage Requirement and Power Losses for HVDC Applications

A dc-ac converter for voltage-source converter (VSC)-HVdc technology has a significant influence on the performance of the entire power transmission system. This paper introduces a new dc-ac converter composed of submodules and series insulated-gate bipolar transistor (IGBT) switches. The basic idea of this hybrid solution is to shape the ac voltage by submodules but, per half cycle, reconnect them to different electrical points by IGBT switches. This concept can help to reduce the quantities of submodules, thereby reducing the energy storage requirement significantly. Another advantage is that the IGBT switches can be soft switched by utilizing the high controllability of the submodules. This brings extra benefit of power losses reduction. In this paper, the operating principle of this hybrid converter is explained. Its performances are also presented in detail and compared with those popular VSC dc-ac converters. The feasibility of the new concept is also verified by simulation and experimental results.