An advanced combined co-phase traction power supply system is proposed by combining a single-phase traction transformer and an active power flow controller (PFC) in an electrified railway. In the new system, the power quality problems caused by single-phase traction load are solved in the grid side and continuous power can be provided to electric trains without neutral sections in the traction side. The mathematic model of the new system is built by power transformation analysis. The compensation currents of the PFC are calculated based on the power balance principle. According to the power quality standard in China, the optimised partial compensation algorithm is presented to replace the existing full compensation one. Moreover, the capacity of the PFC adopting the proposed algorithm is much less than those in the previous studies with the same outcome. The validity of the compensation algorithm and the control method are demonstrated by the simulation results and the effectiveness of the proposed system is verified by the case studies.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-gtd.2015.0513

Modelling and performance analysis of advanced combined co-phase traction power supply system in electrified railway

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.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2013.0396

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

Wavelet transform has received great attention in power community in the last years, because are better suited for the analysis of certain types of transient waveforms than the other transforms approach. This paper presents a descriptive overview of the wavelet transform applications in power systems. The main publications carried out in this field have been analyzed and classified by areas. A list of 116 references is also provided.

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An overview of wavelet transforms application in power systems

Single-phase traction transformers are widely used in traction power supply systems due to their characteristics such as a low cost and a simple structure. Railway power conditioners (RPCs) could increase the loading capacity of substations and improve the supply quality. In this paper, a hybrid RPC (HRPC) is applied to reduce reactive power, relieve system unbalance, and suppress harmonics. The operational voltage of the HRPC is much lower than that of a conventional RPC. A method named partial compensation was used to reduce the current rating of the RPC, in which the compensating currents are expressed as a function of the power factor target at the grid side. When this method is used in the HPRC, the operational voltage varies with the compensating currents over a wide range. A comprehensive design procedure is proposed so that both the current and voltage ratings of the HRPC are reduced with partial compensation. A reduction of more than 50% is achieved by compensating the power factor at the grid side to 0.95 instead of to unity. The control block diagram for the HRPC with partial compensation is presented. The design and control of the HRPC are validated by simulation and experimental results.

Hybrid Railway Power Conditioner With Partial Compensation for Converter Rating Reduction

With the rapid development of high-speed and heavy-load electrified railway, the peak impact and the regenerative braking energy content of traction load become increasingly significant, which has become an important problem affecting the construction and operation benefits of electrified railway. On the basis of comprehensively solving the power quality problems of electrified railway, a multi-application strategy based on the railway static power conditioner (RPC) with the energy storage system (ESS) is proposed in this paper to improve the economic benefits of the traction system. Through the implementation of the peak clipping and the recuperation and utilization of regenerative braking energy of traction load with the guidance of such strategy, the comprehensive economic benefits of the traction system can be improved. By analyzing the mathematical relationship between the comprehensive economic benefits and the parameters such as peak clipping rate and regenerative braking energy utilization rate of the system, an optimization model with the goal of maximizing the comprehensive economic benefits is established. Therefore, the optimal configuration capacity of the ESS is obtained. Finally, the experiments are carried out in MATLAB. The results show that, with the multi-application strategy, the peak load clipping and the recuperation and utilization of regenerative braking energy can be simultaneously realized. It is also demonstrated that the comprehensive economic benefits and environmental benefits can be improved while improving energy efficiency.

Multi-Application Strategy Based on Railway Static Power Conditioner With Energy Storage System

High-speed electrified railway traction load will affect the power quality. To satisfy the request of rapid speed and high density traffic, the large and impactive traction power is necessary for trains running on the high-speed electrified railway. The traction load call for a power system with strong power supply capability, and its effects on power quality of the power system should not be ignored. A 220kV single-phase traction power supply system for the Wuhan-Guangzhou highspeed electrified railway section is introduced. On the basis of the traction power supply system's actual operation situation, the impact performance of traction load and imbalance characteristic of load current are analyzed, and the ability of traction power supply system to withstand the traction load is also briefly evaluated. By installing power quality monitoring system in the substation supplying traction load directly, the actual operation data of this traction power supply system is obtained. The voltage and current characteristics is analyzed, and the effects of traction load on the power quality are evaluated using the related power quality indicators. The research shows that the most outstanding factor worsening power quality is the unbalance three phase current. Because the regional power network is always operating at a bus-splitting mode, the way integrating the single-phase traction transformers into different phases of the power grid to balance the system's three-phase load can not achieve the desired result. The program and operation scheme for high-speed electrified railway power supply system introduced in this paper has a significance of being referenced and promoted, it can satisfy the reliability requirements of power grid operating and quality requirements of power supply.

Research for the effects of high-speed electrified railway traction load on power quality

The frequency property of wavelet transformation (WT) has been studied in depth in this paper with comparison to the discrete Fourier transform (DFT). The band overlapping and frequency leakage among different scales of WT is discussed. Several new wavelet functions with compact-supported property in frequency domain are constructed. A general process for selecting proper wavelet function according to practical requirements is proposed. A novel WT based method is developed to detect generator inner faults. Comparing with the DFT method, the WT based signal analysis requires no frequency tracking and is not affected by frequency deviation. No leakage of frequency occurs with the new method applied. Simulation results prove the feasibility and advantages of the new method presented by the paper.

A novel method for large turbine generator protection based on wavelet transformation

According to the requirements of high reliability for power supply, it is necessary to monitor on some specific or selected power equipment with high quality in a specific period, which then resulting in some new requirements for automation systems. Under this background, a unified data platform, based on the common device model and the network topology, for power systems is built through integrating the information of equipment and operation from EMS, DMS, GIS and the automation systems in stadiums. The topology models of both the transmission system and the distribution networks are merged, and the data sources and maintenance for all the automation systems could be unified on this platform. Some new advanced applications, e.g. power tracing in the whole network and comprehensive system security assessment, could also be developed based on it. Furthermore, high data quality for automation systems and superior information display is available for specific application requirements based on this platform, and a customizable power automation system, which could better response to the requirements of the customers with high reliability in power supply, could be developed by flexible cutting and focusing on the concerned information and functions. The research in this paper has been applied to the supervisory system for the Guangzhou power system during the 16th Asian Games, which illuminates the high theoretical and practical value of the integrated platform.

Customizable power automation system based on an integrated data platform

Along with the widely application of microcomputer protections,the electromagnetic interference problems of protection devices and circuits has aroused more and more interests.The common electromagnetic interference in power systems is analyzed and the interference sources,coupling approaches and the suppress ways are discussed as well.Two electromagnetic interference cases in field are analyzed.The corresponding suggestion is also presented with theoretical analysis and engineering application value.

Wu Guopei

Papers

Research for the effects of high-speed electrified railway traction load on power quality

A novel method for large turbine generator protection based on wavelet transformation

Customizable power automation system based on an integrated data platform

Analysis of the electromagnetic interference of protection device