A comparative analysis of cascaded-multilevel hybrid filters applied in power transmission systems

Passive filters, commonly used to attenuate non-characteristic harmonics in High Voltage Direct Current (HVDC) systems, stay at risk of disconnection from the system due to overcurrent problems. A possible solution to solve the problems involving high harmonic levels would be the use of pure active filters. However, this alternative is unpractical due to the high power of the transmission systems. This paper proposes two different topologies of hybrid filters to damp harmonic resonance in power transmission systems. The first one combines a small-rated active filter in series with passive filters, limiting overcurrents, when existent, or improving its own quality factor. The second one consists of an active filter in parallel with passive filters, which compensates all eventual overcurrent in the system bus. Both topologies utilizes the state of the art in very high power semiconductors and multilevel power converters. Simulation results present a comparative analysis, highlighting the efficiency of, and the differences between, the two proposed hybrid filters.