The process of electric multiple units (EMUs) passing long downhill sections is inevitable in the construction of mountain railways. Moreover, huge regenerative braking energy (RBE) will be sent back to the traction network, threatening voltage safety. Due to the lack of accurate vehicle-grid integrated models considering slope parameters in studying the RBE, this article proposes a modeling scheme, taking China railway high-speed 3 (CRH3) EMUs as an example. First, based on the extended dual pulsewidth modulation (PWM) mathematical model, the quantitative formula for calculating the motor braking power of the CRH3 EMUs is established. Moreover, the slope parameters are introduced into the vehicle-grid model via force analysis and regenerative braking power calculation. Then, by substituting the calculated results into the extended dual PWM mathematical model, the target instruction parameters are solved. Next, the accurate electrical characteristics, including catenary voltage, electromagnetic torque, and converter voltage, are simulated to evaluate the voltage safety. Finally, by comparing the simulation and semi-physical experiment results with the experimental data from the Chengdu to Chongqing railway line, the feasibility, validity, and accuracy of the model are verified.

The direct-quadrature (DQ) model, mirror-frequency impedance (MFI) model, and harmonic state-space (HSS) model are three main modeling methods for single-phase power electronic converter systems. These models are established under three different frameworks: the dq-frame, the mirror-frequency frame, and the extended harmonic domain frame. The purpose of this article is to demonstrate how to create a unified modeling framework and to provide an unambiguous relationship between the impedances in these three domains. The unified model framework facilitates flexible and scalable modeling by making different models to be easily interconnected with other systems. In addition, to simplify the stability analysis and impedance measurement process, the three modeling methods are reduced to first-order single-input and single-output (SISO) equivalent models, respectively, based on the model reduction technique. Finally, the impedance measurement and stability analysis results of electric multiple units (EMUs) accessed vehicle-grid system demonstrate the accuracy of the conversion and SISO equivalence technique.

Dynamic compensators, such as active power filter (APF) and static synchronous compensator (STATCOM), can be used to mitigate the low-frequency oscillations (LFO) in high-speed railway vehicle-grid systems. However, the small-signal impedances of APF and STATCOM are affected by that of vehicles, which makes it challenging to characterize the impedance of these devices directly and ensure stable operation. The traditional stability analysis is based on terminal impedances of source and load subsystems, which does not always provide sufficient insight into LFO suppression. In this article, a novel idea based on $dq$ -frame admittance decomposition is proposed to investigate the impact of APF and STATCOM on the system stability. The proposed approach is demonstrated in simulation and experimental results. It is shown that the control paths of the APF and STATCOM for measuring the vehicle current introduce their coupling with the vehicle. The resulting coupling admittance of these devices plays a significant role in the load admittance reshaping and determining their ability to enhance the system stability and suppress the LFO.

Abnormal vibration can lead to frequent maintenance requirements of electric locomotives. Many factors contribute to the vibration, and the influence mechanism of pulsating torque generated by interharmonics in the traction drive system (TDS) is not clear at present. In this paper, an electromechanical coupling model is developed to investigate the influence of harmonics and interharmonics in the electric TDS on the vibration of key locomotive components. Firstly, this paper attempts to analyze the generation mechanisms of interharmonics and their resulting pulsating torque in electric TDS and derives the formulas for calculating interharmonics and pulsating torque frequencies. Then, an electromechanical coupling model is established based on the electric TDS and the multibody dynamics, and the influence of pulsating torque caused by interharmonics on the vibration of the locomotive key components is discussed in detail. It is observed that the locomotive vibrations, especially the longitudinal and vertical vibrations of bogies and wheels, can be significantly influenced by the pulsating torque. It is noticeable that the frequencies of the vibrations are consistent with those of pulsating torque, which proves that electrical parameters can affect the vibrations of key locomotive components. The research of this paper provides a new idea for restraining locomotive vibration.

Accurately characterizing wheel polygonal wear (PW) is critical for evaluating the operation status of vehicle-rail systems. While prior research has predominantly focused on employing a two-dimensional wheel profiles, it has overlooked the combined effects of circumferential and lateral wear. Furthermore, although there is evidence suggesting that interharmonics can influence wheel wear, existing studies have not thoroughly explored this aspect. Therefore, this paper examines the evolution characteristics of three-dimensional (3D) PW under the influence of interharmonics from the perspective of electromechanical coupling. Initially, an evolution model for 3D wheel PW is developed, integrating an electromechanical coupling model, a 3D wheel profile model, and the USFD wear function. Subsequently, 3D distribution characteristics of PW under multiple operating conditions are analyzed. The results reveal significant differences in the order and depth of PW across different lateral positions. Specially, on curved tracks, the order of PW is presented in distinct groupings. The dominant polygon of the locomotive running (70 km/h) on a straight track is 200 mm, attributed to ࣬5ƒ-7ƒ ₀ ࣬ interharmonic effect, whereas on the curved track, it is 316 mm, attributed to P2 resonance. Moreover, as the curve radius increases, the ratio between PW depth of 316 and 200 mm significantly decrease.