Transformerless hybrid power filter topologies derived from nine-switch inverter

One of the most important power quality issues is related to current harmonics generated by nonlinear loads such as diode and thyristor front-end rectifiers. The hybrid power filter (HPF) mixes low power rating active power filter (APF) with passive filters. Recently, some APF topologies based on dual converters configurations have been shown to be very attractive where it must deal with highly nonlinear loads. Based on this fact, the goal of this paper is to present two dual transformerless HPF configuration based on the nine-switch inverter. The first topology uses the nine-switch inverter itself and the second is a derivation of nine-switch inverter with reduced number of switches. Both alternatives use the same concept of having an inverter with two sets of three-phase outputs connected in series with two passive LC filters. Thus, it is expected that the presented solutions present an enhanced harmonic compensation capability respect to the state-of-art APF´s. Experimental results are presented for both HPF topologies in order to demonstrate the effectiveness of the proposed solutions.