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.

The traction load of a high-speed railway (HSR) may cause significant voltage fluctuations in the traction power supply system and the utility grid. To evaluate power quality, modeling traction load is an urgent need as well as a fundamental work. This paper aims to build a probabilistic model to describe the pattern of traction load changing with time. It is very challenging due to the randomness of train behavior. This paper first investigates the stochastic process of traction load and points out that the size and frequency of load fluctuation respectively rely on the slope and length of rail ramp. Based on this, train power (TP) and headway (TH) are set as two basic components of the probabilistic model, where TP and TH are described by a normal distribution and an exponential distribution, respectively. In addition, a sliding time-window method is developed for generating time-dependent load samples. The proposed method has low complexity, as well as can consider the randomness, giving more realistic simulation results. It can be used to forecast traction load for a planning railway or to establish a measurement-based model for an operating railway. A case study is performed for parameter identification and model verification, and the rapid voltage change (RVC) caused by HSR loads has been evaluated in different operation scenarios.

Measurements of (inter)harmonic impedances of the traction power supply system (TPSS) play important roles in the validation of TPSS modeling, suppression of resonances, stability analysis of locomotives converters, etc. A harmonic generator (HG) and its construction are proposed in this article to directly measure the impedance of TPSSs. Compared to other experimental setups, the HG can emit a fully controlled single-tone (inter)harmonic current at the high voltage level in a wide frequency range, i.e., at least covering 150-3750 Hz. Field tests have been carried out in the actual 2 × 25 kV railway considering the influence of locations and lengths that are scarcely presented in existing literatures. Both the implementation process and test waveforms have verified the effectiveness and feasibility of the HG. The test results, which denotes that locations do not change the resonant frequency while railway lengths will shift resonant frequencies distinctly, can be a basis for developing techniques aimed to improve the power quality.

For electric vehicle (EV) charging coordination, relaxation and approximation methods are usually employed to improve scheduling efficiency in solving integer linear programming (ILP) problems. Nevertheless, they have a few inherent flaws, such as frequent charging interruption and large deviation in final SOC. Based on the recursive method, this paper proposes a search-swapping algorithm (SSA) for optimal approximation. It leverages the non-aftereffect property of charging scheduling to approximate the optimal solution as well as uses single recursion instead of multiple recursion to reduce computation cost from exponential time to polynomial time. Compared with the conventional algorithms, it has much higher efficiency, less charging interruption, and better final SOC uniformity. Furthermore, a single-round interactive protocol is designed for hierarchical coordinated framework to achieve power dispatch. Numerous simulations show that the SSA has outstanding efficiency and satisfactory optimality.

To investigate the harmonic resonance in electric railways, determination of the traction network impedance using a utility instrument is an important and challenging task. This article presents a novel industrial test device which can directly measure the impedance of the actual traction network which is the power source of the railway. The structure arrangement and the parameter design are accomplished to meet the requirements for high-voltage level and strong anti-electromagnetic interference capability. Following this, frequency-dependent impedance measurement is implemented through the injection of controlled harmonic currents using the cascaded H-bridge converters. Furthermore, the power flow analysis is carried out to demonstrate that this device does not need any additional power source and can generate harmonic power. In a new-built railway, this device has been adopted to conduct the on-site test of the traction network impedance. Then, the multi-conductor simulation model is established for the purpose of mutual verification between the field test result and simulation result. Furthermore, the on-site test results can be applied to determine the resonance frequency before a nenw-built line is put into use so that any harmonic resonance can be avoided by taking effective measures in advance.