The impedance-based stability analysis of single-phase voltage source converters (VSCs) emphasizes the precise impedance modeling. Considering the complexity of dq-frame impedance modeling and measurement, this paper proposes a mirror-frequency impedance modeling and measurement approach of single-phase VSCs in the stationary frame based on harmonic linearization. First, the mirror-frequency definition is put forward and the dynamics of the second-order generalized phase-locked loop considering the mirror-frequency effects is validated by simulations. Next, the impedance model considering the mirror-frequency effects and dc-link voltage control loops is compared with the conventional one-dimension impedance model, and a mirror-frequency impedance measurement method is presented, which are verified by experiments on the hardware in the loop platform. The results indicate that the mirror-frequency impedance model considering the dc-link voltage control are more accurate and better captures the cross-coupling dynamics of VSCs. Finally, the different bandwidths of dc-link voltage control loops and different capacitances are designed to study the impacts of dc-link voltage control loops and ripples on impedance. The experiments and impedance-based analysis illustrate that the wider bandwidth of dc-link voltage control loops or the less capacitance with high dc-link voltage ripple will expand the frequency range of negative impedance in the low frequency.

Electric means of transportation have seen a rapid expansion partly due to flexibility to commuters and carbon emission reduction. However, transportation electrification is creating severe power quality problems in the utility grid. A single-phase voltage-source traction converter (VSTC) plays a vital role in high-speed train operation. However, it is partly blamed for injecting instability into the vehicle-grid coupling systems (VGCSs). Therefore, understanding the function of VSTC and complying with various grid codes and technical standards for VGCSs is essential. Furthermore, grid-connected VSTC must comply with strict safety standards, such as IEEE Std. 519 and IEEE Std. 16. However, with hundreds or thousands of literature available, it is difficult to choose an effective control method that meets all the requirements. Consequently, to illustrate a clear picture of the development of effective control strategies, this work review recent control techniques, mainly for harmonics rejection and low-frequency oscillation suppression. Factors affecting grid stability and control performance are first identified and discussed in detail. Then, effective control methods to alleviate the disturbance are elaborated. Moreover, future trends on control strategies for VSTCs considering the recent advancements of artificial intelligence are extensively discussed.

To eliminate the low-frequency oscillation (LFO) phenomenon in the vehicle-grid system of high-speed railways, a single-phase cascaded H-bridge multilevel active power filter (APF) directly accessed to the 27.5-kV traction network is proposed in this article, which can provide the dynamic reactive and interharmonic compensation. To explore the mechanism of APF on LFO suppression, the dq-frame impedance model of vehicle-grid system with APF is established first. The impact of the second-order generalized integrator model and the duty ratio model on the impedance accuracy is discussed in detail. Then, based on the generalized Nyquist stability criterion and system power consumption criterion, the stability of vehicle-grid system and its sensitivity to parameters in different cases are compared. The results indicate that the proposed APF can significantly improve the low-frequency stability of vehicle-grid system and owns much better performance than the STATCOM proposed in previous literatures. Finally, the time-domain simulations in MATLAB and the experiments on the controller hardware in the loop platform are implemented, which further validate the accuracy of theoretical analysis and the superior performance of APF in LFO elimination.

Modulating the traction converters produces current harmonics at the switching frequencies and their multiples. These harmonics should be minimized to meet the network specifications. The LC ‐trapped filters, tuned to these frequencies, can easily meet this requirement, but the existing applicable trap filters have not been studied with the traditional traction system topologies. Thus, this paper presents a trapped LCL filter with an LC resonator on the converter side, called a fully integrated T‐LCL filter, for the traction power supply system. The model and analysis reported in this research demonstrate that the presented filter has several advantages, which can be summarized by: reducing the size by winding many coils through magnetic integration, attenuating the switching frequency and its multiple harmonics that reduce the current total harmonic distortion, assuring durability against the filter parameters differences, and preserving system stability under transient conditions. The proposed filter can become a promising trap filter based on these advantages. Simulation models of an ac/dc single‐phase traction rectifier with the proposed filter were created and tested in MATLAB/Simulink, verifying its superiority. Finally, the filter is validated by performing hardware‐in‐the‐loop experiments.

At the end of October 2022, Elon Musk concluded his acquisition of Twitter. In the weeks and months before that, several questions were publicly discussed that were not only of interest to the platform's future buyers, but also of high relevance to the Computational Social Science research community. For example, how many active users does the platform have? What percentage of accounts on the site are bots? And, what are the dominating topics and sub-topical spheres on the platform? In a globally coordinated effort of 80 scholars to shed light on these questions, and to offer a dataset that will equip other researchers to do the same, we have collected all 375 million tweets published within a 24-hour time period starting on September 21, 2022. To the best of our knowledge, this is the first complete 24-hour Twitter dataset that is available for the research community. With it, the present work aims to accomplish two goals. First, we seek to answer the aforementioned questions and provide descriptive metrics about Twitter that can serve as references for other researchers. Second, we create a baseline dataset for future research that can be used to study the potential impact of the platform's ownership change.

The traction network voltage low-frequency oscillation (LFO) in high-speed railways easily leads to the traction blockade of electric multiple units (EMUs), which seriously affects the normal operation of high-speed railway. A passivity-based control (PBC) strategy for single-phase EMUs rectifier is proposed in this paper. First, for single-phase EMUs rectifier, the Euler-Lagrange (EL) mathematical model in dq frame is built, which can realize the decoupling of active and reactive power. Second, according to the unique characteristics of the rectifier, it is proven that the rectifier is strictly passive, which is the premise of PBC controller design. Third, using the deduced EL mathematical model and the passivity of rectifier, the PBC controller for the single-phase rectifier of EMUs is designed with the damping injecting method. Next, compared with dq current control and interconnection and damping assignment passivity-based control (IDA-PBC), it can be verified that the PBC controller has better dynamic and static characteristics, and can significantly suppress the voltage LFO of traction network. In these strategies listed in this paper, using the PBC, the single-phase rectifier input current has minimal total harmonic distortion, and the DC-link voltage has minimal oscillation. Finally, the dSPACE semi-physical experiment platform of cascade system of EMUs and traction network is built. Simulation results are validated by the dSPACE semi-physical experiments, which can be indicated that the PBC has the better inhibitory effect for LFO as compared with IDA-PBC and dq current control in single-phase EMUs rectifier.