A Case Study of Hybrid Filter Applications in Power Transmission Systems

Problems related to harmonic propagation in transmission systems have been noticed in the last years. 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 overcurrents. One of the possible solutions to solve the problem of high harmonic levels would be the use of pure active filters. However, this alternative may be very expensive due to the high power of the transmission systems. This paper relates to a comparative study on 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 the quality factor of the filter when the passive filters work under its nominal current. The second one consists of an active filter in parallel with passive filters, compensating all eventual overcurrent in these. Simulation results with the two proposed topologies present the efficiency of, and the differences between, the hybrid filters in power transmission systems