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

An active power compensator (APC) based on single-phase back-to-back power converter is proposed in this paper to solve problems of power quality of electric railway power supply system. This system adopts a single-phase feeding connection, which is called cophase power supply scheme. In this scheme, APC connects the balance transformer between feeding phase for power supply and another phase for compensation. It has some characteristics, such as active power balancing, reactive power compensating, and harmonics filtering. In order to achieve these characteristics, the control scheme requires seven combination models. In this paper, a multifunctional control algorithm is proposed to realize every conceivable model. A cophase system with APC based on field programmable gate array (FPGA) and YNvd balance transformer is also designed and evaluated. The experimental results obtained from this prototype illustrate that the compensating ability is extremely high in steady-state and dynamic responses, and the power quality of a substation with distorted loads can be improved integrally.

Single-Phase Back-To-Back Converter for Active Power Balancing, Reactive Power Compensation, and Harmonic Filtering in Traction Power System

This paper presents an easy and a robust sensor fault detection and isolation (FDI) and fault tolerant control (FTC) of a single phase PWM rectifier for electrical railway traction application. Catenary current sensor and dc link voltage sensor failures are considered. The FDI method is based on observers and residual generation. The different FDI algorithm steps allow a good detection and isolation of the sensor fault and identify the faulty sensor. The reconfiguration strategy consists of two steps with open loop control and closed loop control working. Simulation results are presented to illustrate the good performance of the FTC procedure. Experimental results are also presented to show the effectiveness of the proposed FDI and FTC algorithms and good performances of the rectifier after the reconfiguration.

State Observer-Based Sensor Fault Detection and Isolation, and Fault Tolerant Control of a Single-Phase PWM Rectifier for Electric Railway Traction

With the fast proliferation of single-phase distributed generation (DG) units and loads integrated into residential microgrids, independent power sharing per phase and full use of the energy generated by DGs have become crucial. To address these issues, this paper proposes a hybrid microgrid architecture and its power management strategy. In this microgrid structure, a power sharing unit (PSU), composed of three single-phase back-to-back (SPBTB) converters, is proposed to be installed at the point of common coupling. The aim of the PSU is mainly to realize the power exchange and coordinated control of load power sharing among phases, as well as to allow full utilization of the energy generated by DGs. Meanwhile, the method combining the modified adaptive backstepping-sliding mode control approach and droop control is also proposed to design the SPBTB system controllers. With the application of the proposed PSU and its power management strategy, the loads among different phases can be properly supplied and the energy can be fully utilized, as well as obtaining better load sharing. Simulation and experimental results are provided to demonstrate the validity of the proposed hybrid microgrid structure and control.

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Hybrid Three-Phase/Single-Phase Microgrid Architecture With Power Management Capabilities

This paper proposes a frequency adaptive phase-locked loop (PLL) for use in single-phase systems. The main objective is to obtain a reliable synchronization signal even in polluted grids, where the fundamental frequency is contaminated with harmonics, or present variations in phase, amplitude, and/or frequency. The proposed PLL is based on the concept of a variable sampling period technique, already implemented in a three-phase digital synchronization method proposed by the authors. This single-phase method allows us to automatically adjust the sampling frequency to be an integer multiple of the line frequency. In this case, the phase error is calculated just by one multiplication, thereby reducing implementation. A sliding Goertzel transform-based filter is also used in the loop to reject the undesired effects of this phase error detector and line disturbances, such as harmonics. To stabilize the loop, a controller that maximizes the bandwidth with an acceptable transient is introduced. The characteristics of the proposed single-phase PLL are described and the experimental results obtained from a DSP implementation are presented. A set of comparative simulations between the proposed PLL and some single-phase PLL described in the literature are conducted to validate the method. The advantages of the proposed system over other methods analyzed are also dealt with. The robustness of the system is verified by the experimental tests conducted as well as by the harmonic filtering properties. The system is also characterized by its simple architecture, which allows us to provide a high dynamic response with a very much reduced number of calculations.

Frequency Adaptive PLL for Polluted Single-Phase Grids

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

This paper presents a new method for automatic monitoring of noisy power quality, which is based on the Hilbert transform (HT) and the proposed slip-singular value decomposition (SVD)-based noise-suppression algorithm. The proposed method first employs the fast Fourier transform (FFT)-based low-pass filter and HT to obtain the instantaneous fundamental amplitude and the FFT sequence of the signal. Second, the slip-SVD-based noise-suppression algorithm and threshold filtering are used to extract cleaned singular value characteristic waveform of the high-frequency signal. Through judging the instantaneous fundamental amplitude, cleaned singular value characteristic waveform, and the FFT sequence, the presence of disturbances including single and combined disturbances can be easily detected by the proposed method. To demonstrate the effectiveness of the proposed method, extensive tests are conducted on the diverse simulation disturbances and the actual data obtained from the practical power systems of China. The test results show that the proposed method has the advantages such as low false detection rate, good noise tolerance capability, short computational time, fewer parameters, practicability, and compatibility in comparison with the traditional disturbance detection methods. Besides, the proposed method can provide some important features such as amplitude, duration, and frequency for classification. Such advantages make the proposed method to be a good choice for real-time applications.

A New Method With Hilbert Transform and Slip-SVD-Based Noise-Suppression Algorithm for Noisy Power Quality Monitoring

Short-term wind speed syntheses correcting forecasting model and its application

The traction power supply system of electric railway has the disadvantages of heavy unbalanced three phase, large harmonics and reactive power, needing neutral section insulator in every supply sector, which conditions the improvement of high speed and heavy-haul railway. New cophase traction power supply system can solve these problems radically. In this paper, connection type of traction transformer and the optimum matching topology of comprehensive power flow controller (CPFC) are discussed based on the mathematic model. The cophase direct and AT power supply models are set up, and the properties are analyzed. The control modes and operating performance of system are demonstrated, and the modes can be switched according to system status. Compared with the existing system, the economy of new cophase traction power supply system is evaluated. These studies have great significance on the design and application of new cophase traction power supply system.

Qunzhan Li

Papers

Single-Phase Back-To-Back Converter for Active Power Balancing, Reactive Power Compensation, and Harmonic Filtering in Traction Power System

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

A New Method With Hilbert Transform and Slip-SVD-Based Noise-Suppression Algorithm for Noisy Power Quality Monitoring

Short-term wind speed syntheses correcting forecasting model and its application

Optimized Design and Performance Evaluation of New Cophase Traction Power Supply System