Modelling and control of a railway power conditioner in co-phase traction power system under partial compensation

Co-phase traction power supply system provides continuous power to traction loads without neutral sections. In order to reduce system unbalance, compensate reactive power and harmonics, a railway power conditioner (RPC) operates together with traction transformer in each substation. In the past study, the RPC is designed to achieve three-phase balance and unity power factor (PF) at the grid side. As a result, its rating is high. According to the power quality tariff plan in China, the penalty for reactive power can be avoided if the PF is higher than 0.9. In this study, a grid-side PF of 0.9 is achieved via different control approaches after analysis. Among these approaches, the rating of the RPC in the worst case is more than twice that in the best case. Hence, selection of a suitable control parameter is necessary. The minimum rating of the RPC is achieved by setting the power angle of phases A and B lagging and the power angle of phase C leading under partial compensation. The rating of the RPC is reduced to 70% by setting PF to 0.95 instead of 1. Simulation and experimental results are provided to show the validity of the modelling, design and control method.