Yufei Yue

Analysis and Comparison of Modular Railway Power Conditioner for High-Speed Railway Traction System

With the rapid development of modern electrified railway, negative-sequence current minimization is one of the most important considerations in the high-speed railway traction system. In the past, many multiple or multilevel topologies with high compensation capacity have been introduced for railway power conditioner (RPC). This paper presents a simplified quantitative comparison of five previous modular RPC topologies for negative sequence compensation in V/V and SCOTT traction systems, aiming for an optimal selection of the compensators. Performance criteria such as transformer requirement, voltage stress and current stress of a power switch, numbers of the power switches and capacitor are derived by analytical methods. Moreover, the numerical comparison of operating controllers is completed for modular RPCs. In addition, power losses of five modular RPCs are obtained by theoretical analysis, IPOSIM calculation as well as PSIM simulation. These calculations are validated via simulations results in PSIM. The main conclusion is that presented modular RPCs can be divided into general purpose RPC and special purpose RPC in terms of the behavior and efficiency. It is helpful to choose the appropriate topology for specific applications.

A circulating current suppressing method of MMC based STATCOM for negative-sequence compensation

As for the reactive power and negative sequence compensation caused by the unbalanced load, the modular multilevel converter based static synchronous compensator (MMC-STATCOM) is adopted and analyzed. To reduce the complexity of control system, the three-phase current error signal is transformed into αβ frame and proportional-resonant controller is adopted to implement the static current tracking. In order to reduce the operation performance of MMC-STATCOM, a system small-signal model is established and an efficient circulating current suppressing method is proposed. As the circulating current of each phase is controlled individually, this method can be widely applied in diverse MMCs. The simulation and experiment results have validated the feasibility of the proposed control method.