This paper presents an impedance-based model to systematically investigate the interaction performance of multiple trains and traction network interaction system, aiming to evaluate the serious phenomena, including low-frequency oscillation (LFO), harmonic resonance and resonance instability. The train-network interaction mechanism is therefore studied and one presents a detailed coupling model for investigating the three interactive phenomena and their characteristics, influential factors, analysis methods and possible mitigation schemes. In the Part I of the two-part paper, the measured waveforms of such three phenomena are firstly characterized to indicate their features and principles. An interactive model of the train-traction network system for investigating the three problems is then presented. In order to reveal the interaction mechanism, the all-frequency impedance behaviors of the electric trains and traction network are equally modeled. In which, an impedance-based input behavior of the train is fully investigated with considering available controllers and their parameters in DQ-domain. While, the entire traction network, including traction transformer, catenary, supply lines, is represented in a frequency-domain nodal matrix. Furthermore, the impedance-frequency responses of both electric train and traction network are measured and validated through frequency scan method. Finally, a generalized train-network simulation and experimental systems are proposed for verifying the theoretical results of the two-part paper.

Harmonic distortion and harmonic resonance problems have been widely concerned and reported in railway electrification systems (RESs) due to the harmonic injection from the nonlinear electric train, especially high-speed/high-capacity/large-power trains. This paper presents an overview of the harmonic and resonance problems in the RES, including harmonic problem composition, harmonic modeling, available influential factors assessment, harmonic resonance, and associated suppression methods. The harmonic problem mainly consists of the background harmonics brought from the utility system, resonance-region harmonics interacted by capacitive and inductive network elements, and characteristic harmonics generated from the switching process of the onboard power conversion system. The mathematical modeling and analysis methods are introduced, including frequency scanning analysis, S-domain analysis, resonance mode analysis, and modal sensitivity analysis. Available influential factors/parameters have been fully investigated against above-mentioned harmonic problems. Finally, different harmonic suppression methods have been compared and summarized in this paper.

This paper proposes an energy storage system (ESS) for recycling the regenerative braking energy in the high-speed railway. In this case, a supercapacitor-based storage system is integrated at the DC bus of the back to back converter that is connected to the two power phases of the traction power system (TPS). In order to ensure the suitability of the ESS in the TPS, the operation modes are classified by considering the load conditions of the TPS and the state-of-charge limit of the supercapacitor. Then, a master-slave control strategy with a central controller is proposed. In which, the central controller realizes the flexible management for all operation modes, by means of the state machine logic. Meanwhile, the master-slave control serves for coordinating the operation of the multiple converters according to the commands from the central controller. Finally, the capabilities of the proposed ESS are validated by sufficient experiments under different operation modes and the simulation based on the field data.

Safety enhancement for lithium-ion batteries (LIBs) has received a lot of attention from academic and industrial fields. However, there is a lack of overview from the perspective of the application power electronics (PEs) in the systems. This article gives an overview of PE-based safety enhancement technologies for LIBs, mainly focusing on battery management. It introduces the latest advances in battery protection, balancing, monitoring, and lifetime improvement, all based on PE technologies. Detailed discussion and future research opportunities are given. This article aims to provide a reference for PE researchers who want to make some efforts in LIB safety.

The wide adoption of a new type of electric trains results in multiple frequency-scale instability problems, such as low-frequency oscillation (LFO), harmonic resonance and harmonic instability. Among them, LFO has been commonly reported at electric railway depots with multiple energized electric trains. This phenomenon occurs at rail depots around the whole world, thus attracting widespread research attention. LFOs cause adverse ef-fects on the system stability and protection infrastructure of both the traction network and electric trains. This paper presents a comprehensive review of LFOs that consider both academic theoretical analysis and industrial engineering requirements. A unified mathematical model of the traction network and electric train is derived with a view to revealing the mechanism and factors that induce LFOs when these two systems interact. The study also draws deep insights from results of experimental measurements and industrial mitigation schemes already implemented in Chinese railway systems. A variety of mitigation techniques and recommendations based on theoretical principles and practical constraints are presented.

Regenerative braking energy (RBE) utilization plays a vital role in improving the energy efficiency of electrified railways. To date, various power flow control-based solutions have been developed to recycle the RBE for utilization within railway power systems (RPSs). In this paper, an overview of the state-of-the-art power flow control-based solutions for RBE utilization in AC electrified railways is presented. It provides a technical analysis of four primary power flow control-based solutions for RBE utilization, including power sharing-based, energy feedback-based, energy storage-based, and composite solutions. The critical architectures of power flow conditioners for each solution are analyzed in depth. Meanwhile, the power flow control strategies for these solutions are reviewed from the perspectives of power flow management and converter control. From the industrial point of view, the critical challenges associated with fault protection, economy, and environmental impact are discussed. In addition, future trends are comprehensively elaborated from internal and extended improvements. This comprehensive review provides an insightful understanding of the technology readiness, constraints, and perspectives regarding the power flow control-based RBE utilization in electrified railways, contributing to bridging the gaps between academic research and industry implementation.