Shibin Gao

Potential Harmonic Resonance Impacts of PV Inverter Filters on Distribution Systems

This paper presents a clarification study to identify the potential resonance phenomenon between photovoltaic (PV) inverters and the distribution system. LCL and LC filters are widely applied in PV inverters to mitigate high-order harmonic components generated by PV inverters. There is a possibility that these filters will excite harmonic resonance by interacting with the system impedance. The mechanism of this phenomenon is investigated here by mathematical analysis and measurement. The results indicate that the resonance can be attenuated if the damping resistance, such as damping resistor and residential linear loads, is large enough. Alternatively, three sets of field tests are conducted in the laboratory to verify and clarify the potential harmonic resonance and its factors. Furthermore, a full case of an actual North American distribution system with PV installations is also studied. The results indicate that the harmonic resonance caused by the PV filter is almost attenuated and cannot cause serious problems. At the same time, the filter may have some advantages in mitigating harmonics. Finally, to complete this paper, other sustainable energy resources with voltage-source converters (VSCs) are compared.

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

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.

Passive Filter Design for China High-Speed Railway With Considering Harmonic Resonance and Characteristic Harmonics

In order to make high-speed trains (HSTs) lighter and more reliable, LC or LCL high-pass filters, which are widely adopted to mitigate high-order harmonics, are not installed in most of China HSTs. Therefore, the harmonic problem is a concern, because of the significant adverse impacts it has on the tractive drive system of the train and power quality of the utility system. The harmful harmonic distortions in high-speed railways (HSRs) are mainly caused by harmonic resonance and massive characteristic harmonics emission. This paper presents the results of harmonic assessment and harmonic filter design for a typical HSR line in China. Harmonic penetration analysis (HPA) is implemented and carried out to determine the harmonic distorted types for a wide range of possible train-operating conditions in a timetable. Both statistical field test and numerical calculation are used in passive filter design for HSRs. A C-type filter is designed here to address these typical harmonic distortions. The studies will be validated by detailed simulations based on the train timetable by counting the 95% index of the 24-h profile of harmonic results.

Power-Quality Impact Assessment for High-Speed Railway Associated With High-Speed Trains Using Train Timetable—Part I: Methodology and Modeling

The proliferation of the voltage-source converter-based high-speed trains has resulted in significant distortions in voltage and current waveforms in both traction power supply system and the utility system. The dynamic behaviors of the high-speed trains (HSTs) make the assessment of such power-quality (PQ) problems quite difficult. There is an urgent need for techniques that can quantify the collective PQ impacts of modern trains during a 24-h period. Dynamic behavior modeling of the modern trains during the operating duty period between two station stops is studied here for PQ assessment. The 24-h profiles of the train timetable and rail infrastructure are entered to compute the information, including train positions, speeds, power consumptions, etc. Moreover, six sets of the measurement-based Norton-equivalent model under different operations are implemented to represent the dynamic harmonic behaviors of the train. In addition, the systemic modeling of the utility system, traction lines, and Scott-connection transformer is also described. After comparing the results of calculations and measurements, the proposed model is ideally effective for analyzing the consequences of HSTs dynamic behavior and system topology that are involved in fundamental power flow and harmonic power flow in order to evaluate the comprehensive PQ impacts in a companion paper.

An Extended Habedank’s Equation-Based EMTP Model of Pantograph Arcing Considering Pantograph-Catenary Interactions and Train Speeds

Pantograph arcing is a more and more common and prominent phenomenon in ac-electrified railway systems, especially with the increase of pantograph-catenary (PAC) interaction and train speed. In order to address this issue, an extended Habedanks equation-based model, by means of the Electromagnetic Transients Program (EMTP), is presented to obtain equivalent modeling for pantograph arcing studies considering train speeds in this paper. First, the pantograph arcing phenomenon is investigated, such as transient mechanisms and influencing factors. Second, based on the features of existing and emerging pantograph arcing, Habedanks arc equations are further derived and studied by improving voltage gradient and power dissipation. Next, due to the relationship among voltage gradient, power dissipation, and arc length, the maximum detachment interval law between pantograph and contact wire is obtained by establishing the finite-element model for PAC interaction, and the ultimate extended Habedanks equation-based EMTP model of pantograph arcing considering different train speeds is acquired. Then, the related model parameters are discussed and determined. Finally, based on the China Beijing-Yizhuang HSR line model in EMTP, the arc characteristic differences considering loads under different parameter values are compared and analyzed. The comparison results illustrate that the proposed model can be feasible to determine and reveal the pantograph arcing characteristics and influences in the HSR system as well as the PAC contact loss problems.

Power-Quality Impact Assessment for High-Speed Railway Associated With High-Speed Trains Using Train Timetable—Part II: Verifications, Estimations and Applications

This paper investigates the voltage profiles and harmonic impacts of high-speed trains on the traction power-supply system (TPSS) and primary utility system. Power-quality (PQ) assessment has become not only a computing tool for TPSS design and planning, but also an indispensable technique for utilities to estimate the accurate PQ impacts from the railway systems. Therefore, to achieve comprehensive PQ assessment in TPSS, a dynamic fundamental/harmonic power-flow (DF/HPF) method is developed in a companion paper, while further application of the technique is described in this paper. The fundamental and harmonic results calculated in a 24-h period, such as loading levels, voltage profiles, unbalance, power loss, and harmonic distortions have been computed. In addition, the statistical measured background harmonics of the utility system are represented by Weibull function and considered in the harmonic evaluation. The unbalance and harmonic impacts are investigated and checked with national standards in this paper. The proposed method can be effective for excavating and predicting the potential serious PQ problems existing in the TPSS by using a train timetable.

Modal Frequency Sensitivity Analysis and Application Using Complex Nodal Matrix

Modal impedance sensitivity and modal frequency sensitivity are two important characteristics of resonance modal analysis. Modal sensitivity is to calculate the sensitivity of a resonance mode against the parameters of network components. The eigendecomposition of a real matrix transformed from a complex matrix not only increases the dimension of nodal admittance matrix, but also creates two equal resonance frequencies in different modes. In this letter, a modal frequency sensitivity analysis using original complex nodal matrix (CMFS) is presented. The results obtained by this method are compared with those by realistic modal frequency sensitivity (RMFS) and the simulation verifies that this method possesses higher accuracy and applicability than that of RMFS. CMFS can determine each no-coupling resonance mode and investigate frequency sensitivity with respect to network component parameters. In addition, Newtons method is introduced to the shift of resonance frequency cooperating with the CMFS.

Harmonic Resonance Evaluation for Hub Traction Substation Consisting of Multiple High-Speed Railways

In many hub traction power-supply systems (TPSSs), the 27.5 kV busbars in the traction substation (TSS) have supplied several railway lines in a local area for reducing the number of TSSs. However, the multiple railway lines connected to the busbar may affect the resonance behaviors of the entire system. It is therefore necessary to investigate the resonance behaviors under such hub TPSS conditions since the harmonic current collection of all railway lines will aggravate the resonance problem. Thus, resonance-mode assessment and its sensitivity method is adopted for investigating the resonance behaviors of hub TPSS affected by different numbers of connected lines, lengths of supply lines, system capacities, etc. The numerical results of modal sensitivity indices are compared to investigate and quantify the harmonic resonance issue caused by multiple electrical railway lines. In addition, the resonance frequency-shift technique and modal impedance sensitivity index-based method are also employed to mitigate the critical harmonic resonances. The results illustrate that it is effective to analyze resonance issues by adopting the harmonic model and modal methods in this paper. The two types of resonance behaviors (i.e., primary resonance and resonance band) caused from the hub TPSS have been fully investigated, and the resulting harmonic distortion of hub TPSS is suppressed.

Research and Analysis of Transient Process of Locomotive Passing Neutral Section Based on Habedank Arc Model

Over-voltages frequently happen when locomotive passes the neutral section via articulated phase insulator, which is aggravated by arcing phenomenon. In this paper, Habedank arc model built in MATLAB/SIMULINK is introduced into the process of locomotive passing the neutral section. The electrical transient process is analyzed in different conditions considering and not considering the arc model and compared to the statistical results of over-voltage tests. The simulation results show that generation of over-voltages is related to the phase angle of A-phase contact line, the voltage phase angle difference between contact lines of A- and B-phases and the time of locomotive getting into and out of the neutral section, a certain rule is presented. The arc model built in this paper can describe the arcing phenomenon well when locomotive passing the neutral section, and the simulation results of over-voltage are consistent with the theoretical analysis.

Train–Network Interactions and Stability Evaluation in High-Speed Railways–Part I: Phenomena and Modeling

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 harmonic 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 Part I of the two-part paper, the measured waveforms of such three phenomena are first characterized to indicate their features and principles. A unified framework of the train–traction network system for investigating the three problems is then presented. In order to reveal the interaction mechanism, 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. 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 system are conducted for verifying the theoretical results of the two-part paper.