Since the beginning of railway electrification, power quality has been a main problem in railway networks because of their special characteristics. Many ways of power quality improvement have been investigated and applied to ac and dc traction systems through railway electrification history. This paper presents a perspective on power quality issues through railway electrification development and investigates the necessity of power quality and system requirements for appropriate power quality. Compensation strategies are classified and compared. This aims to provide a comprehensive perspective of the power quality issue in railway power/distribution networks for researchers and engineers working on railway electrification. Less than 100 research articles are referenced for researchers to obtain good background information.

Power Quality Issues in Railway Electrification: A Comprehensive Perspective

With the development of high-speed and high-power electrified railway, power quality of traction power grid becomes more serious. In order to achieve three-phase balance of traction power grid, a modular multilevel converter (MMC)-based railway traction power conditioner (RTPC) is studied, which is characterized by modular multilevel cascaded structure. The RTPC consists of four H-Bridge links and output filter inductors, which can be connected to 27.5-kV traction feeders in co-phase supply system directly. This conditioner can be used for different kinds of traction system, especially suited to Scott traction system. According to the analysis of equivalent electrical model and power balance of RTPC, a hierarchical control strategy is put forward aiming to balance the submodule capacitor voltages, which ensures the safety and stability of system. Finally, the structure and its control strategy are verified by the simulation and experiment effectively.

A Railway Traction Power Conditioner Using Modular Multilevel Converter and Its Control Strategy for High-Speed Railway System

An advanced cophase traction power supply system is proposed to solve the power quality problems of the traditional traction power supply system, such as unbalance, reactive power, and harmonics to three-phase industrial grid. The three-phase to single-phase converter-based substation is adopted in this system, which can transfer active power from three-phase grid to single-phase catenary and compensate reactive power and harmonics of the locomotives. One catenary section could be utilized in the advanced cophase system instead of the multiple split sections in traditional system. The neutral sections and problems caused by them in traditional system could be avoided. In this paper, the characteristics of the advanced cophase system and the automatic current-sharing control algorithm of three-phase to single-phase converter are studied and analyzed. The simulation and experimental results verify the viability and effectiveness of the proposed system.

Advanced Cophase Traction Power Supply System Based on Three-Phase to Single-Phase Converter

In order to bring railway static power conditioner (RPC) into full play in suppressing negative sequence current in the V/v traction power supply system, the reason of negative sequence current and compensation mechanism were analyzed, and the mathematical model with minimum negative sequence current under the constraint of voltage fluctuation, power factor, device capacity, transformer winding capacity, and energy conservation was set up. For solving the small-scale multidimensional nonlinear and constrained optimization problem, an intelligent algorithm based on sequential quadratic programming (SQP) method is proposed through a comparative analysis of existing optimization algorithms and the traditional analytical method. The proposed algorithm is capable to complete an optimizing computation process in several milliseconds with the precision of 0.1 A, and its computational efficiency and precision can meet the needs for real-time control of RPC. A self-adaption real-time optimization computing platform was built in combination with detectable analogue quantities of traction power supply system and RPC, including catenary network voltages, feeder currents, and compensation currents. Simulation and engineering experimentation results are provided to illustrate that the model and its computation are effective and feasible.

Negative Sequence Current Optimizing Control Based on Railway Static Power Conditioner in V/v Traction Power Supply 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.

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

Unbalance and reactive power currents of electric railway will result in poor power quality of three-phase industrial power grid. A co-phase traction power supply system is introduced in this paper to solve these problems by adopting single-phase ac-dc-ac converter. The converter is connected between two secondary windings of traction transformer with abilities of active power transmission and reactive power compensation. Because of the power conversion, the co-phase supply system can utilize single-phase feeding connection scheme instead of traditional two-phase feeding scheme. An actual 10 MVA/27.5 kV co-phase system with impedance-matching balance transformer is designed, developed, and tested. Its real-time detection, control, and distribution algorithms with field programmable gate array-based implementation are introduced. Some test running results validate the performance of the digital controller and demonstrate the feasibility of the proposed co-phase power supply system.

Digital Detection, Control, and Distribution System for Co-Phase Traction Power Supply Application

The invention provides an MMC (Multi Media Card) based single-phase-three-phase conversion system containing a capacitor bridge arm. The MMC based single-phase-three-phase conversion system containing the capacitor bridge arm is formed by connecting a single-phase two-bridge-arm converter and a three-phase three-bridge-arm convertor by a back to back manner; the system is mainly used for transmitting active power from a single-phase power supply for power traction to a three-phase motor; a capacitor bridge arm is combined with a MMC bridge arm, so that the system cost can be greatly reduced; the capacitor bridge arm is formed by connecting two same capacitor sets in series, and each capacitor set is formed by connecting DC energy storing capacitors of the same specification in series and in parallel; the MMC bridge arm is formed by connecting two sets of same MMC chains in series, and each MMC chain is formed by connecting one inductor L with p power modules with the same structure in series, wherein the power modules are of single-phase half-bridge structures, and each power module comprises an IGBT half bridge and a DC energy storing capacitor. The system is applicable to harmonic wave and reactive power compensation and is also applicable to the variable voltage, variable frequency and variable phase and other places; the system is advanced and reliable in technology and easy to be carried out.

MMC (Multi Media Card) based single-phase-three-phase conversion system containing capacitor bridge arm

The utility model relates to an MMC (modular multilevel converter) based single-phase to three-phase conversion system comprising a capacitor bridge arm, which is formed by connecting a single-phase two-bridge-arm converter and a three-phase three-bridge-arm converter back to back and mainly applied to active power transmission from a single-phase power supply to a three-phase motor in electric traction. The capacitor bridge arm is combined with MMC bridge arms, thereby reducing the system cost to the maximum degree. The capacitor bridge arm is formed by connecting two sets of identical capacitor banks in series, and each capacitor bank is formed by DC energy storage capacitors with the same specifications in a series-parallel connection mode. Each MMC bridge arm is formed by connecting two sets of identical MMC chains in series, each MMC chain is formed by connecting an inductor and p power modules with the same structure in series, and each power module is of a single-phase half-bridge structure and composed of an IGBT half-bridge and a DC energy storage capacitor. The system provided by the utility model can compensate harmonic waves and the reactive power, and is also applicable to occasions of voltage transformation, frequency conversion, phase conversion and the like. The MMC based single-phase to three-phase conversion system comprising the capacitor bridge arm is advanced in technology, reliable and easy to implement.

Lu Ke

Papers

Digital Detection, Control, and Distribution System for Co-Phase Traction Power Supply Application

MMC (Multi Media Card) based single-phase-three-phase conversion system containing capacitor bridge arm

MMC (modular multilevel converter) based single-phase to three-phase conversion system comprising capacitor bridge arm