Wu Mingli

Analysis of Low-Frequency Oscillation in Electric Railways Based on Small-Signal Modeling of Vehicle-Grid System in dq Frame

The line-side converter, which can represent an ac-dc-ac drive electric vehicle when analyzing the low-frequency oscillation in electric railways, is modeled in dq frame with the proposed single-phase dq-decomposition method. With this model, an underdamped mechanism of the vehicle-grid interaction is confirmed. Besides, a low-frequency stability prediction approach is presented, based on the dominant-pole analysis and verified by the simulation and the testing result. The proposed modeling method and prediction approach benefit in three aspects: It is more convenient to rebuild the model with a change of either the line-side converter controller or the system condition, much quicker to predict the low-frequency instability and more explicit to guide the modification of the controller software to damp the low-frequency oscillations.

The application of SVC for the power quality control of electric railways

Electric railways are pollution sources of power quality in the public power system. The low power factor and current harmonics caused by AC-DC locomotives have been difficult problems needed to be deal with for a long time in China. Some countermeasures have been taken by the railway authorities to improve the power qualities in recent years. This paper presents the performance of the SVC, which is a combination of passive filters and thyristor controlled reactor, based on the measured data of power qualities of An-ding traction substation of Beijing-Shanghai electrified railway. The different operational manners of the compensator are compared with the measured data of three-phase unbalance and total harmonic distortion. The SVC technique has shown a promising solution to the improvement of power quality of electric railways. The compensator topology and relevant parameters should be given enough attention in engineering application to obtain an optimal effect.

Windowed SHE-PWM of Interleaved Four-Quadrant Converters for Resonance Suppression in Traction Power Supply Systems

AC electric locomotives that use a number of interleaved four-quadrant converters generate high-frequency switching harmonics which may stimulate certain resonances in traction power supply systems (TPSSs). A windowed selective harmonic elimination pulse-width modulation (SHE-PWM) method is proposed to suppress such resonances. Owing to the windowed design and the precalculated solutions, the proposed method covers the wide potential resonant frequency range and addresses the resonant frequency variation while keeping the low switching frequency of the traction converters. The proposed windowed SHE-PWM is fully tested with a closed-loop controller in a simulation model with the TPSS and the ac electric locomotive. Comparative simulation results show that the windowed SHE-PWM is an effective alternative that overcomes the resonance suppression limitations of the conventional phase-shifted PWM (PS-PWM). The performance of proposed windowed SHE-PWM on an experimental equivalent resonant circuit is further evaluated and compared with PS-PWM. Both simulation and experimental results verify the effectiveness and feasibility of the proposed method.

The switching transient simulation of SVC used in electric railway traction substation

The power quality of electrified railway has become one of the close attentive questions of public electric power systems in China and abroad at present. One of the effective measures to improve the power quality of the electric railway is to install SVC (TCR+FC) equipment in the traction substations. This paper presents the analysis of switching transients of the reactive power compensator, which are important in the design of the compensator for the selection of the elements tension. The simulation model of the compensator is established with PSCAD to emulate the process of the switching transients. The different operational manners of the SVC are investigated in An-ding traction substation of Beijing-Shanghai electrified railway. The simulation has been validated by the comparisons of the computed results with the field measured data.

High speed EMU modeling based on the measured data

Based on a large amount of actual measured data on railway line, this paper presents a modeling method using curve-fitting and probabilistic density functions for a high speed EMU. This method better simulates the real world and can be used to build a rapid data exchange between the trains and the traction power system simulation.

Control strategy of symmetry compensation system of traction power supply system in phase

The paper presents an analysis for the control strategy of symmetry compensation system (SCS) of traction power supply system in phase (TPSSIP). The theory of traction power supply system in phase and three study conditions are classified. The method that conforms the capacity of symmetry compensation system is outlined. The control strategy of SCS is validated by simulation program.

A high performance control strategy for three-level NPC EMU converters

A high performance control strategy for a three-level neutral-point-clamped (NPC) converter employed in electric multiple units traction drive system is proposed in this paper. The strategy is based on a multiple frequency tuned quasi-proportional resonant (PR) controller for the AC current loop. A notch filter is used in the DC bus voltage loop to filter out the ripple affecting the controller. A feed-forward loop is included in the inner current control loop to deal with AC power supply disturbances. The impact of the quasi-PR controller parameters on its performance is investigated through frequency-domain analysis. The generation of the low-order harmonics of the line current caused by the DC-link voltage fluctuations is analyzed from the control point of view. Simulation results presented in the paper validate that the proposed control strategy provides a better current tracking performance and a lower current harmonic content when compared with other more conventional control strategies.

Physical Interpretation of Impedance Formulas for Conductors Enclosed in a Cylindrical Tunnel

Based on a comparison of earth models and conductor impedance equations, a physical interpretation of the self and mutual impedance for conductors enclosed in a cylindrical tunnel with peripherally infinite homogeneous earth is put forward. The inherent relations between Carsons formulas and Tylavskys formulas are revealed through a rigorous mathematical justification. A new concept of complex radius, which is similar with the complex depth, is introduced to explain the simplified approximate impedance expressions.

Study on traveling wave fault location device for electric railway catenary system based on DSP

This paper analyzed the current typical methods of the travelling wave fault location. The basic principles of the fault location device and part of its hardware realization were introduced based on the selected single-end scheme. The core processor used TMS320F2812, a DSP chip produced by TI company. Using wavelet analysis technique, an algorithm for the fault location of electric railway catenary system was developed through the extract of the signal module maximum from the collected signals.

Performance of the integrated grounding system of hefei-nanjing passenger dedicated railway

In order to ensure the human and equipment safety, the concept and the technique of the integrated grounding system has been introduced in high speed railway engineering in China. High running speed and dispatching density lead to large traction load currents in the power supply systems. Moreover, the high speed railway widely adopt non-ballasted track, which has a relative high rail leakage resistance to the ground. This can result in very high electric potential of the rail. The integrated grounding system uses two buried bare copper wires to connect together various grounding structures along the railway properly to guarantee equipotential states of different systems and equipments. Based on the immense measured data in the field of Hefei-Nanjing passenger dedicated line, the performance of the integrated grounding system is analyzed in this paper. Some further suggestions are also put forward to improve the electric characteristics of the integrated grounding systems used in railway design.