Partial Compensation Control in Co-phase Traction Power for Device Rating Reduction

Single-phase traction transformers are widely used in traction power supply systems due to their characteristics such as low cost and simple structure. Railway power conditioners (RPCs) could increase the loading capacity of the substations and improve the supply quality. In this paper, a Railway Hybrid Quality Conditioner (Railway HPQC) is applied to reduce reactive power, relieve system unbalance, and suppress harmonics. The operational voltage of the Railway HPQC is much lower than conventional RPC. A method named partial compensation was used to reduce current rating of the RPC, in which the compensating currents are expressed as a function of power factor target at the grid side. When this method is used in the HPRC, the operational voltage varies with the compensating currents over a wide range. A comprehensive design procedure is developed, so that both current and voltage ratings of the Railway HPQC are reduced with partial compensation. A reduction of more than 50% is achieved by compensating the power factor at the grid side to 0.95 instead of to unity. The control block diagram for the Railway HPQC with partial compensation is presented. The design and control of the Railway HPQC are validated by simulation and experimental results.