Harmonic resonances in traction power supply systems (TPSSs) have attracted great attention due to their potentially destructive impact on the safe and stable operation of railways. Based on operation data acquired from Chinese railways, this paper presents a comprehensive review of this issue considering both academic and engineering requirements. Analysing actual incidents, the general patterns and effects of TPSS resonances are derived. The relation between the TPSS and the locomotive is illustrated by circuit models. Relevant methods for modeling locomotives and TPSSs are discussed. Both advanced resonance analysis methods giving general influence factors and a simplified resonance analysis explaining resonance features in a practical manner are discussed. Multiple ground-based and on-board solutions for resonance elimination are presented. At last, pre-identifying resonances in actual systems is investigated for addressing the open topic of resonance prevention.

AC electric locomotives that use a number of interleaved four-quadrant converters generate high-frequency switching harmonics which may stimulate certain resonances in traction power supply systems (TPSSs). A windowed selective harmonic elimination pulse-width modulation (SHE-PWM) method is proposed to suppress such resonances. Owing to the windowed design and the precalculated solutions, the proposed method covers the wide potential resonant frequency range and addresses the resonant frequency variation while keeping the low switching frequency of the traction converters. The proposed windowed SHE-PWM is fully tested with a closed-loop controller in a simulation model with the TPSS and the ac electric locomotive. Comparative simulation results show that the windowed SHE-PWM is an effective alternative that overcomes the resonance suppression limitations of the conventional phase-shifted PWM (PS-PWM). The performance of proposed windowed SHE-PWM on an experimental equivalent resonant circuit is further evaluated and compared with PS-PWM. Both simulation and experimental results verify the effectiveness and feasibility of the proposed method.

As high-speed railways develop rapidly worldwide, the problems of neutral section and power quality are becoming increasingly prominent. These problems affect the normal operation of the power grid and the electric locomotives. The co-phase power supply schemes were proposed by researchers, which can solve these problems well. Among them, the MMC-based scheme (MMC-5 L) is a representative one. The existing scheme, when applied to the auto-transformer (AT)-fed system which is usually adopted by high-speed railways, needs to install an auto-transformer on the output side. To eliminate the auto-transformer and to obtain the more suitable and superior co-phase power supply schemes to AT-fed system, two improved schemes are proposed in this paper based on the novel MMC-based scheme (MMC-6 L) we proposed before. While establishing the mathematical model, creating the control system, and carrying out simulation verification of the proposed schemes, the proposed schemes are compared with MMC-6 L and MMC-5 L in terms of topological characteristics, control system complexity, power loss, and functionality. The results show that while the proposed schemes can fulfill the functions of the co-phase power supply scheme well like the MMC-5 L and MMC-6 L, they are more suitable and superior for the AT-fed system in terms of control system complexity and power loss. Among them, MMC-5L1CB performs best in power loss, and MMC-4L2CB performs best in control system complexity.

This article presents a model predictive sliding control (MPSC) strategy with the dynamic reference tracking for cascaded H-bridge (CHB) multilevel converters. The nonlinear predicted sliding mode control (PSMC) and linear model predictive control (MPC) are combined as a two-level cascaded control structure. The proposed approach aims to get rid of time-consuming tuning to reach the good performance in the presence of uncertainties and disturbances, such as proportional–integral (PI). The MPC scheme is designed to predict the future optimal current and voltage vectors with a designed cost function. The high-level PSMC algorithm is proposed for the dynamic current reference with less chattering problems. The stability of the proposed strategy is analyzed with the Lyapunov direct method. The design principle of the system parameters is introduced with a step-by-step tuning procedure. With the proposed method, the response time can be reduced from 60 to 30 ms during the start-up conditions in the simulation tests. The overshoot of the cell voltages can be eliminated with low-harmonics current and dc-link voltage targets tracking. The validity and effectiveness of the proposed method are implemented by the experimental tests on a laboratory two-cell CHB converter. Compared with the PI-based MPC approach, the current total harmonic distortion (THD) can be reduced and the dc-side performance, including overshoot/undershoot and response speed, can be improved.

Accidents related with high‐order harmonic resonance seriously threaten the safety and stable operation of traction power supply systems (TPSSs). Generally, the resonant frequency of a TPSS, which is the crucial information for resonance suppression, cannot be accurately obtained through model‐based methods due to the TPSS complexity. This study proposes a direct measuring method that harmonic currents at different frequencies and amplitudes are injected into the TPSS by a harmonic generator (HG). Then, the resonant frequency can be identified by measuring the harmonic response. The HG based on a single‐phase cascaded H‐bridge converter and its control algorithms are developed. Both simulations on a railway system model and experimental results on an equivalent resonant circuit are carried out to validate the feasibility and effectiveness of the proposed method.

The rapid development of railway electrification has led to signaling relay malfunctions and locomotive urgent braking accidents caused by unbalanced traction harmonic current (UTHC), which seriously threaten transit safety. This paper presents a comprehensive study with a mechanism-modeling-solution approach that addresses the practical issue of UTHC interference in signaling systems and provides theoretical support for further research, relying on an actual case. Based on the mechanism analysis of UTHC interfering with the on-board and ground signaling terminals, UTHC and its induced harmonic electromotive force on both terminals are accurately modeled. The proposal and evaluation of solutions are supported by mathematical analysis of the relationship between traction-side current and signaling-side induced electromotive force. A low active loss passive filter with high filtering effect was designed and connected to the traction network for the actual case, effectively addressing the high-frequency harmonic resonance risk in traction power supply systems and the harmonic interference issue in signaling systems. Field tests validate the feasibility and effectiveness of this solution. Accounting for cost constraints, guidelines for reducing current unbalance between two rails or avoiding choke transformer core saturation are developed based on a comprehensive sensitivity analysis of traction current unbalance coefficient and signaling equipment parameters.