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The integration of multiterminal hybrid HVDC grids connecting LCC- and VSC-based networks faces several technical challenges such as DC fault isolation, ensuring multi-vendor interoperability, managing high DC voltage levels, and facilitating high-speed power reversal without interruptions. The two-stage DC-DC converter emerges as a key solution to address these challenges. By implementing the modular multilevel converter (MMC) structure, the converter's basic topology includes half-bridge sub-modules on the VSC side and full-bridge sub-modules on the LCC side. However, while this topology has been discussed in the literature, its connection to an LCC-based network with controlled current magnitude lacks detailed analysis regarding operational challenges, control strategies under various scenarios, and design considerations. This paper fills this gap by providing comprehensive mathematical analysis, design insights, and control strategies for the modular DC-DC converter to regulate DC voltage on the LCC-HVDC side. Additionally, the proposed control scheme minimizes the interfacing inductor between the two bridges, ensuring uninterrupted power flow during reversal and effective handling of DC faults. Validation through Control-Hardware-in-the-Loop testing across diverse operational and fault scenarios, along with a comparative analysis of different converters, further strengthens the findings. © 2017 Elsevier Inc. All rights reserved. [ABSTRACT FROM AUTHOR]

The paper proposes an ameliorated methodology to minimize the effect of charge injection over a wide input common-mode range. Instead of a conventional single dummy switch compensation [1] , the multi-dummy switches are proposed and employed to eradicate the injected charge on to the sampling capacitor. A detailed methodology is presented to compensate the charge injection in a MOS switch. The closed-form equations are derived mathematically to substantiate the proposed technique. For the proof-of-concept, a track-and-hold (T/H) stage has been simulated in 0. 18 μ m CMOS technology with the proposed technique for a 10-bit resolution. The proposed technique based T/H stage exhibits the spurious free dynamic range (SFDR) of 62.6 dB, effective number of bits (ENOB) of 9.36, peak input-referred third-order intercept point (IIP3) of 13.02 dBm and an input-referred 1 dB compression point (P 1dB) of 3.8 dBm at 1.074 MHz input frequency, sampled at 100 MSa/s. The performance of the proposed method is compared with the existing single dummy switch compensation method where our technique shows 88.8% compensation in minimizing the charge injection error and 272% improvement in dynamic linearity. Moreover, the presented technique quantifies 9 × improvement in mean percentage error (MPE) when simulated across the various process corners and rail-to-rail input common-mode voltage. • The paper presents a multi-dummy switch technique to minimize the charge injection error in a MOS switch. • Mathematical analysis has been carried out to validate the concept. • A design methodology is proposed to limit the charge injection error within ±0.5 LSB for 10-bit track-and-hold circuit. • The presented method is compared with existing single dummy switch compensation technique and the results depict 272% improvement in dynamic linearity. • The proposed method provides 9X improvement in the mean percentage error over the existing method. • The design is simulated in CMOS 180 nm technology and the post-layout simulation results are reported in the paper. [ABSTRACT FROM AUTHOR]

• According to the comparative small-signal analysis of GCC adopting PLL and RPS, it is demonstrated that the current information introduced by the RPS is equivalent to adding a positive real part to its open-loop transfer function, which improves the stability of the GCC system. • Based on the admittance model developed in this paper, it is revealed that RPS can effectively reduce the negative resistance area and reduce the frequency coupling effect. Then the stability of GCC in a weak grid is improved. However, the specific mechanistic analysis cannot be easily carried out on the unified admittance model. • Finally, a SISO model is derived to intuitively visualize the mechanism of instability for GCC adopting PLL in a weak grid, which can be attributed to the gain spike and phase jump. RPS with a lower-order structure can effectively avoid the above two shortcomings, which achieves the same dynamic performance as PLL. For grid-connected converters (GCC), the synchronization unit (SU) is indispensable for the vector current control (VCC). Usually, the phase-locked loop (PLL) is employed as SU. However, PLL could introduce negative resistance contributing to potential instability issues. Thus, the second-order generalized integrator PLL (SOGI-PLL) and the reactive power-based synchronization method (RPS) are proposed to enhance the stability. Nevertheless, the intrinsic reason why RPS enhances stability is not clear. Therefore, a detailed comparative analysis among PLL, SOGI-PLL, and RPS is presented in this paper to reveal the mechanism of this stability enhancement. Firstly, an admittance model is derived to analyze the differences between these three synchronization methods. However, it is not intuitive enough to explain the detailed mechanism. Then, a SISO model containing the current controller, physical circuit, and synchronization unit is developed, which is established on the relationship between power and angle. According to this SISO model, it is revealed that the presence of the gain spike introduced by PLL and SOGI-PLL leads to instability. RPS avoids these issues due to its introducing current information for phase margin enhancement and its lower-order structure. Finally, the validity of the mathematical analysis and derived models are verified by experimental results. [ABSTRACT FROM AUTHOR]

• A new DC-hub is proposed for interconnection of VSC-based HVDC ports based on thyristor device. • Zero-reactive power control across the common AC link is proposed to achieve reduced RMS current. • Comprehensive mathematical analysis is illustrated for circuit design parameters for the DC-Hub under study. • Transformation from Sinusoidal to Quasi-Trapezoidal to accommodate the utilization of thyristor based DC-Hub. • Small scale hardware setup is built to test the proposed DC-Hub under different healthy and unhealthy scenarios of power flow. The promising features of HVDC technology have led to the possibility of numerous renewable resources integration and enormous DC grids interconnection. In spite of the obstacles, these interconnections encounter such as the necessity to block DC faults, achieving isolation between different schemes, the ability to maintain power flow throughout different power flow profiles, and the interfacing with various infrastructures, the DC-Hub arises to overcome these interconnection obstacles being the excellent approach to enhance the DC grid capabilities. This paper proposes a new monolithic modular thyristor-based multilevel converter, which serves as the fundamental building block of the DC-Hub, offering advantages such as lower switch count, bidirectional power flow, and DC fault blocking capability. Moreover, a control algorithm, for zero reactive power circulation in the DC-Hub, is introduced. The proposed algorithm successfully mitigates the circulation of reactive power throughout the entire range of power flow. A comprehensive mathematical analysis, optimum design of converter parameters, and the proposed control technique, which suppress the circulating reactive power at full range of power flow, are illustrated. Finally, simulation modelling and hardware test rig are established to validate the claims of the DC-Hub at different normal and faulty scenarios. [ABSTRACT FROM AUTHOR]

Multiphysics processes are common in nature and can occur in conjuction with intense strains. When strain softening is also present, the original uniform strain distribution is lost and strain localization occurs. In a classical continuum strain localization happens on a mathematical plane (i.e shear band of zero thickness). This leads to mesh dependent numerical analyses, in which strain localizes on the smallest mesh length. In this paper we investigate under which conditions multiphysics processes regularize the problem of strain localization. We study, for the first time, the influence of all the different coupling terms present in the original coupled multiphysics balance equations on the strain localization profile. We also consider the influence of viscosity and inertia effects. We show that the multiphysics processes do not always lead to mesh independent results. Furthermore, our rigorous mathematical analysis provides bounds for the different coupling parameters, for which multiphysics processes lead to strain regularization and mesh independent numerical results. Finally, we corroborate our mathematical findings, applying them to a numerical example of a coupled hydro-mechanical system of a fault under shear. [Display omitted] • The hypothesis that multiphysics couplings alleviate mesh dependence is tested. • All mechanisms of the multiphysics coupling are considered. • The influence of viscosity and inertia is investigated. • Bounds are given for the different coupling parameters for strain regularization. • A numerical example of the hydro-mechanical system of a fault under shear is shown. [ABSTRACT FROM AUTHOR]

The aim of this study is to develop new and efficient theories for handling complex and unreliable data in real-world scenarios. The proposed approach integrates two distinct theories: the Bipolar Complex Fuzzy Set (BCFS) and the Soft Set (SS), resulting in a novel and superior method compared to existing solutions. Furthermore, the value of big data analytics cannot be overstated as it provides businesses with the opportunity to use their data to find areas for development and progress. To gain insights from raw data, it must first be collected and organized. Data modeling represents these large, complex data sets in a visual format, such as a chart or diagram. However, the visualization process often results in uncertainties and inaccuracies, highlighting the need for a more robust approach to data analysis. To address this issue, this paper introduces the concept of Bipolar Complex Fuzzy Soft Relations (BCFSRs), a fuzzy decision-making method within a complex bipolar fuzzy environment that can have the advantages of both a Bipolar Complex fuzzy relation and a soft relation at the same time. In BCFSRs, an element can have degrees of membership in both the positive and negative directions, reflecting a more nuanced and versatile representation of uncertainty or ambiguity. These mathematical ideas are explained through the Cartesian product of two Bipolar Complex Fuzzy Soft Sets (BCFSSs) and serve to simplify the decision-making process by presenting the BCFSSs in a clear and concise manner. The inventive notion of the BCFSRs elucidates the combined positive and negative effects of anything with parameterization. To support organizations in making data-driven choices and obtain insights for strategic planning and inventiveness, the analysis of big data is essential in several industries, including financial services, marketing, and medical treatment, among others. To choose the optimal big data analytics for efficient operation, this research presents modeling methodologies based on BCFSRs, including the formulation and analysis of scoring functions. The validity of the proposed work is demonstrated through a comparison study with existing methods, providing valuable insights for effective data analysis. • Bipolar Complex fuzzy and soft sets are presented. • Introduced novel, and effective ideas to manage complex, unreliable data. • Presents modeling methodologies based on Bipolar Complex fuzzy soft information. • Conducted a comparative study of existing techniques. [ABSTRACT FROM AUTHOR]

The holes are very easy to appear delamination and burr during CFRP drilling. The tool geometry has a great impact on the hole making. In this paper, according to the principle of bionics and structural features, a novel bionic drill bit was designed. The mathematical model of the lower incisor teeth occlusal movement was established. The cutting mechanism of the bamboo rat lower incisor on PW-CFRP material was studied. It was found that the curvature of the contour curves of the front cutter faces were constantly changing, which was conducive to the removal of chips. The curvature change of the contour curve of the rear cutter surface is small and the curve is relatively smooth, which is conducive to reducing friction. The mathematical modeling analysis was carried out on the feeding process of bamboo rats, and the mathematical relationship between the bite radius R and the cutting angle θ was obtained. The optimal cutting angle θ = 10° and the corresponding biting radius R = 40 mm were obtained by finite element simulation. The surface cutting quality of bamboo rat's lower incisors is better than that of ordinary cutting tools. The novel bionic tool can effectively reduce the burr and delamination of the exit layer. [ABSTRACT FROM AUTHOR]

In this paper, we propose a simple approach to the construction of a general class of L -stable explicit second-order one-step methods for solving stiff problems. These methods are nonlinear and derive from a novel approximation for the right-hand side functions of differential equations inspired by the nonstandard finite difference methodology introduced by Mickens. Through rigorous mathematical analysis, it is proved that the proposed numerical methods are not only explicit and L -stable, but also convergent of order two. Therefore, they are suitable and efficient to solve stiff problems. The proposed numerical methods generalize and improve a nonstandard explicit integration scheme for initial value problems formulated by Ramos (2007). Moreover, the present approach can be extended to construct A -stable and L -stable high-order explicit one-step methods for differential equations. Finally, the theoretical findings and advantages of the developed numerical methods are supported and illustrated by a series of numerical experiments in which stiff problems are considered. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a novel model that simulates the spread of the monkeypox virus. The new model takes into account the effect of the interaction between the human and rodent population along with some realistic factors that have not been introduced before such as imperfect vaccination and nonlinear incidence rates. Moreover, the human population is further divided into low-risk and high-risk groups to better reflect recent observations. To understand the dynamics of the new model, the existence, uniqueness, and continuous dependence on initial conditions, as well as its positivity and boundedness of the model are investigated in detail. The obtained solution is proved to be positive and has bounded behavior. Furthermore, the reproduction number R 0 for the proposed system is computed and detailed bifurcation analysis is performed to reveal major qualitative changes in the model's dynamics. In addition, we investigate the influence of key parameters on the basic reproduction number. We also explore and analyze the stability of equilibrium points in the space of parameters. The new findings reveal that the virus is more frequently witnessed among the high-risk group, which may provide some restrictions to stop the spread through social limitations. To validate our theoretical results, we conduct numerical simulations, which provide insights into the behavior of the model under different conditions. The new findings aim in developing preventive control measures to suppress the spread of the virus and to develop effective strategies for controlling and preventing outbreaks, ultimately protecting public health and minimizing the impact of the disease. [ABSTRACT FROM AUTHOR]

• A correct formulation of average Nusselt number for the case of linearly heated wall is derived. • Thermal balance analysis provides the verification of the correct formulation. • Comparison of the existing and the correct formulation is included. The comment below addresses an inaccurate formulation in the calculation of the Nusselt number for linear heating as presented in the paper titled "Steady natural convection flows in a square cavity with linearly heated side wall(s)" by M. Sathiyamoorthy, T. Basak, S. Roy, and I. Pop, Int. J. Heat Mass Transfer 50 (2007) 766–775. Consequently, this analysis provides a mathematical reformulation for the local and mean Nusselt numbers of a linearly heated side wall. It regenerates a few quantitative results for a specific case solely intended for comparative purposes. [ABSTRACT FROM AUTHOR]

• An active mitigating control approach is proposed to reduce torsional and edgewise vibrations in the PMSG-based WTs on the basis of a high fidelity dynamic model for the drivetrain and blade structures. • In the proposed approach, an auxiliary damping term, based on the difference between the blade and hub speeds, is added into the original electromagnetic torque, when the mechanical-structural modes are excited. • The needed variables for implementing the damping control term are estimated by a novel robust method based on the sliding-mode observer. • The efficiency of the proposed mitigating approach is evaluated by mathematical analyses and simulation results under several case studies. Fatigue loads associated with torsional and blade-edgewise vibrations are recognized as major reasons of large scale wind turbine failures. This paper presents an active mitigating control approach to reduce torsional and edgewise vibrations in the PMSG-based wind turbine. Due to the interactions of both vibrations, the active control is designed based on the expanded dynamic model of the mechanical-structural flexibilities. In this way, the blades are modeled as flexible cantilever beams, and thus, in the drive-train model the dynamics of the blades are considered. The control input to suppress the vibrations is achieved by the power electronic converters through adding an axillary term proportional to the speed difference between the blade and hub into the power control loop. This term manipulates the generator torque to counteract the unwanted vibrations. The needed drive-train and mechanical variables for making the auxiliary term are estimated by a novel robust method based on the sliding-mode observer. Using mathematical analyses and simulation results, it is shown that the proposed active mitigating approach well alleviates the fatigue loads of the torsional and edgewise modes even under severe changes in the drive-train stiffness coefficients. Thus, the proposed sensorless control approach is an appropriate remedy action for alleviation of WT fatigue loads even under parameters uncertainties. [ABSTRACT FROM AUTHOR]