The cell-based class of Voltage Source Converter (VSC) topologies, including Modular Multilevel Converter (MMC), are being considerably employed through the power system to interconnect heterogeneous electrical systems. Their versatility to play with the converter topology is widely exploited to accommodate several terminals and ports according with the specific application. One of the most challenging, and fundamental, question to comprehend the behavior of each topology concerns the definition of the so-called degrees of freedom (DOFs). The topology-geometry of the converter circuit is strongly characterizing its intrinsic DOFs; however, it is not yet considered a methodology to assess them in a generalized approach. For instance, the well-known Clarke transformation, to achieve the electrical DOFs, is only valid for a star-based system topology. Therefore, topology changes might lead to different, and not evident, converter DOFs. With respect to this, the main purpose of the article is to present a systematic methodology, scalable to every cell-based converter topology, to assess their electrical DOFs and the inherent ports affinities. The method lies in the topology-graph Laplacian spectral analysis, which indicates the structural normal modes at the converter points of connections. The analysis is then validated experimentally.

$P$/$\omega $admittance modeling is one of effective techniques to analyze the low-frequency oscillation (LFO). However, existing modeling methods are typically developed for specific control strategies on a case-by-case basis, lacking a general framework. Such case-specific formulations limit the broader applicability of this model in power system studies. To address this limitation, a general$P$/$\omega $admittance modeling framework is proposed based on the equivalence of controlled source and impedance (ECSI). In the proposed framework, the VSC is modeled as a controlled frequency source, which is regulated by both active power and the frequency at the filter terminal, whereas the reactive power-voltage dynamics are modeled as an equivalent admittance in parallel with the line admittance. Such a modeling strategy enables the construction of$P$/$\omega $admittance models for VSCs with diversified controls, using a consistent and intuitive framework. Leveraging the model’s transparency, the LFO characteristics of various VSCs are identified. The case study of a multi-VSC system demonstrates that the proposed model can accurately reflect the interactions among control loops and reveals the characteristics of LFO caused by different controls of VSCs, providing a powerful tool for stability analysis and control design. Finally, comprehensive simulations under various scenarios are conducted to verify the accuracy of the proposed model.

This study presents a novel approach for diagnosing machine conditions using deep learning models applied to Gabor-transformed motor current signatures. The dataset comprised signals from five single-phase 2-HP induction motors with five fault conditions, each tested under five different loading conditions. These signals were transformed into 2D time-frequency plots using the Gabor Transform (GT), capturing essential frequency changes over time. A convolutional neural network (CNN) model was then employed to classify motor faults based on these plots. Methodologically, the CNN was trained and validated across various GT configurations, including different image resolutions and color modes. Performance was measured using a 10-fold stratified cross-validation. The results demonstrated significant improvements, with the best GT configuration achieving an average accuracy of 98.43%, substantially higher than the traditional LightGBM method's 93.20% accuracy. The study underscores the efficacy of combining GT with CNN for enhanced fault detection, providing a robust alternative to existing machine learning and deep learning methodologies,

The increasing use of power electronics converters to integrate renewable energy sources has been a subject of concern due to the resonance oscillatory phenomena caused by their interaction with poorly damped AC networks. Early studies are focused on assessing the controller influence of a single converter connected to simple networks, and they are no longer representative for existing systems. Lately, studies of multi-infeed grid-connected converters are of particular interest, and their main aim is to apply traditional criteria and identify their difficulties in the stability assessment. An extension of traditional criteria is commonly proposed as a result of these analysis, but they can be burdensome for large and complex power systems. The present work addresses this issue by proposing a simple criterion to assess the stability of large power systems with high-penetration of power converters. The criterion has its origin in the mode analysis and positive-net damping stability criteria, and it addresses the stability in the frequency domain by studying the eigenvalues magnitude and real component of dynamic models in the admittance matrix form. Its effectiveness is tested in two case studies developed in Matlab/Simulink which compare it with traditional criteria, proving its simplicity.

The number of high voltage direct current (HVDC) links continue to increase over the years, most of them, for offshore applications or bulk power transmission over long distances. The present paper evaluates the possible development of a direct current (dc) grid in Europe given the present, and future, HVDC links. Eight potential cases for the interconnection between close links are suggested as starting scenario for a multiterminal network. The need of a dc-dc converter and its special requirements are evaluated in function of suggested interconnections. As an example, a case study is chosen to evaluate the behavior of an interconnection between line commutated converter (LCC) and voltage source converter (VSC) link using a front-to-front (F2F) isolated converter.

In this paper, the steady-state behavior of the modular multilevel converter (MMC) is studied under balanced and unbalanced AC grid voltage conditions. The suggested mathematical model is derived combining the converter internal arm variables and both AC and DC grids variables. Moreover, the steady-state solution of the system can be achieved by setting the internal power balance within the converter. In order to verify the steady-state model, different types of AC fault conditions are imposed, and the output values are compared with the simulation results of an average model of the MMC circuit. The results show that the proposed analysis is in close agreement with the simulations for all conditions evaluated, validating the developed equations.