A new traction power supply system supplied by the Scott 3rd port and its partial compensation with current decomposition

To solve the reactive power and negative-sequence problems in electrified railways, this paper presents a novel railway power supply system, which synthesizes two secondary-side voltage ports of the Scott transformer to form the 3rd voltage port supplying the traction loads. The system can simultaneously ensure satisfactory power quality for the grids and cancel the neutral section out of the traction substation. The configuration and operation principle of the system are first explained, and a comparison with two other traction power supply systems is conducted. To reduce the operation currents and compensation capacity, a partial compensation strategy based on current decomposition is proposed. Compared with other strategies, the proposed strategy is characterized by a more intuitive physical mechanism and concise expressions, and hence has the advantage of smaller calculation and flexible application. On control, the reference detection based on this strategy is also explored to generate compensation currents instantaneously. In this paper, the mathematical relationships between the power quality indices and current components are established. And the capacity reduction analysis with partial compensation is given in detail. Both the simulation and experimental results are presented to show the feasibility and effectiveness of the proposed system and the strategy.