Patent ID: 9728962
Date: 2017-08-08
CPC Classifications: H02J,H02M

Claim:
1. An apparatus for filtering harmonics in a power transmitting contact line of a railway, the apparatus comprising: a multilevel converter having one single phase leg, the phase leg comprising switching cells, each switching cell comprising semi-conductor switches arranged to selectively provide a connection to a corresponding energy storage element, wherein the multilevel converter includes a controller provided to control switching of each switching cell, wherein the phase leg is configured in two parallel branches of cascaded switching cells, the two parallel branches being interconnected in a closed circuit, and the controller is provided to monitor a content of the harmonics in the contact line, and is adapted to filter the monitored harmonics by adapting the switching of the switching cells to absorb the harmonics, and wherein the controller is adapted to create a circulating current in the two parallel branches of the phase leg and adapted to modify the circulating current in the two parallel branches to transfer energy between the corresponding energy storage elements of at least two switching cells, upon detecting, during monitoring voltage levels of each of the corresponding energy storage elements, that at least one monitored voltage level deviates.