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When the control parameters and operating conditions remain unchanged, it is usually believed that the admittance characteristic of grid-connected inverter is time-invariant. However, considering the effect of frequency-coupling, an abnormal phenomenon is observed in the admittance measurement of the grid-connected inverter: the phase of the off-diagonal elements Y12 and Y21 in the admittance matrix is always changed with time, which presents a time-varying admittance characteristic. To explore this phenomenon, the theoretical analyses based on the traditional frequency-coupling admittance measurement method are made. Because the initial phase of the signal cannot be obtained from Fast Fourier Transform (FFT) in experiments and the disturbance frequency and coupling frequency are different, the phase difference between the two frequency components changes with time. However, the influence is not considered in the traditional frequency-coupling admittance measurement method, which makes the measurement results exhibit the confusing time-varying characteristic. The phenomenon is defined as pseudotime-varying admittance characteristic in this letter. To accurately measure the admittance characteristic of the grid-connected inverter, a frequency-coupling admittance measurement method based on phase correction is proposed, which corrects the phase of disturbance frequency components and coupling frequency components. Finally, the effectiveness of the proposed measurement method is verified by experiments.

In this study, a humanoid prototype of 2-DOF (degrees of freedom) lower limb exoskeleton is introduced to evaluate the wearable comfortable effect between person and exoskeleton. To improve the detection accuracy of the human-robot interaction torque, a BPNN (backpropagation neural networks) is proposed to estimate this interaction force and to compensate for the measurement error of the 3D-force/torque sensor. Meanwhile, the backstepping controller is designed to realize the exoskeleton's passive position control, which means that the person passively adapts to the exoskeleton. On the other hand, a variable admittance controller is used to implement the exoskeleton's active follow-up control, which means that the person's motion is motivated by his/her intention and the exoskeleton control tries best to improve the human-robot wearable comfortable performance. To improve the wearable comfortable effect, serval regular gait tasks with different admittance parameters and step frequencies are statistically performed to obtain the optimal admittance control parameters. Finally, the BPNN compensation algorithm and two controllers are verified by the experimental exoskeleton prototype with human-robot cooperative motion.

High-energy neutral and charged Drell--Yan differential cross-section measurements are powerful probes of quark-lepton contact interactions that produce growing-with-energy effects. This paper provides theoretical predictions of the new physics effects at the Next-to-Leading order in QCD and including one-loop EW corrections at the single-logarithm accuracy. The predictions are obtained from SM Monte Carlo simulations through analytic reweighting. This eliminates the need of performing a scan on the new physics parameter space, enabling the global exploration of all the relevant interactions. Furthermore, our strategy produces consistently showered events to be employed for a direct comparison of the new physics predictions with the data, or to validate the unfolding procedure than underlies the cross-section measurements. Two particularly relevant interactions, associated with the W and Y parameters of EW precision tests, are selected for illustration. Projections are presented for the sensitivity of the LHC and of the HL-LHC measurements. The impact on the sensitivity of several sources of uncertainties is quantified., 32 page, 10 figures, 3 tables; v2: several plots have been updated to fix a problem in the code, the overall discussion has been slightly improved, and few typos have been corrected; v3: typos corrected, preprint added

This paper presents an analytical model for intrinsic short-circuit admittance (Y) parameters of DH-DD-TM-SG MOSFET. Y parameters have been modeled using different small-signal equivalent circuit parameter which is used to find the Scattering parameters. These Y parameters have further been employed for computing S-parameters. These parameters are further used to investigate the microwave performance parameters of the proposed device. The Unilateral Power Gain and the maximum oscillation frequency is determined to evaluatethe microwave performance. The proposed device shows a higher cut-off frequency (f_T) and maximum oscillation frequency as to TM-SG MOSFET. The proposed device exhibits a 4.2% improvement in U_T 2.81% in G_ms and 6.9% improvement in G_MTPG as compared to TMSG. The analytical result of DH-DD-TM-SG MOSFET is in accordance with the simulated results.

The convergence of the iterative harmonic analysis (IHA) of networks with nonlinear loads can be improved if the Gauss algorithm is replaced by the modular decoupled Newton solution (M-DNS). The core of the M-DNS is the harmonically coupled admittance matrix (HCAM) of each nonlinear load. HCAM of high-power converters has received special attention. However, the HCAM of single-phase uncontrolled rectifiers (SPUR) with capacitive smoothing has only been developed under certain simplifications for the SPUR. A reference model for the SPUR is extensively accepted and a detailed analytical procedure (DAP) is the fastest way to obtain the steady state of the SPUR. The main object of this paper is to present a HCAM for the reference model of SPUR with capacitive smoothing. This HCAM is directly derived from a DAP for the converter. Convergence properties of the IHA with this HCAM are studied.

This paper presents a dq power flow based energy storage control system for reliable and stable operation of a renewable power generation based microgrid system. The control objectives are storing the excess energy from the microgrid into the storage unit or supplying energy deficit from the storage unit to the microgrid to achieve power equity between the generation and load, and regulation of voltage and frequency during stand-alone microgrid operation. Whereas during grid-connected microgrid operation, the control objective is to ensure storing energy in the storage unit and exchange power between the microgrid and the utility grid. The proposed controller is developed for inverter interface energy storages using dq power flow. The dq power flow is formulated using bus voltage components and the bus admittance matrix in dq frame. The dq power flow in the developed controller generates command (reference) active and reactive powers for the inverter interfaced storage unit connected to the microgrid buses. In addition, the implemented current controller of the inverter assures such command powers exchange between the storage unit and the microgrid. The developed dq power flow based storage unit (DQPFSU) control system is tested under various operating conditions for both in grid-connected and stand-alone microgrid operation. The test results of the developed DQPFSU controller illustrates satisfactory performance in generating fast control actions to ensure reliable and stable microgrid operation under various changing conditions. Moreover, the validity of such control actions has examined from the frequency response and bus voltages of the case study microgrid under various tested operational conditions.

The standard power-mismatch Newton method is still frequently used for computing load flow due to its simplicity and generality. In this paper, a matrix-based generalization for the usual power flow equations to an arbitrary number of phases is derived. The proposed equations enable computing power injections and the Jacobian matrix in terms of submatrices that compose the network admittance matrix. Besides the more compact representation, another advantage of the proposed generalization is execution time reduction compared to the standard scalar formulation. Simulations are carried out to demonstrate the time reduction achieved via the proposed equations.

This paper presents an algorithm for solving the AC basic power flow based on some enrichments provided in the bus admittance matrix methods findable in the literature. In particular, the interpretation of the slack bus generator as a current source rather than a voltage one and its inclusion inside an "all-inclusive" admittance matrix allows obtaining strong performances of the algorithm. In fact, this method gives both a well conditioning of the admittance matrix and the reduction of matrix partitioning for each iteration. As a result, a greater precision of the solution, a shorter execution time compared to classical commercial methods, a decreasing number of iterations and optimal convergence properties are obtained. Eventually, in order to show the efficiency of the method, real and fictious networks are tested, by comparing its results and performances with robust open source/commercial software packages that use well-known methods (i.e. Newton-Raphson and Fast Decoupled Load Flow methods).

Muscle weakness is the primary impairment causing mobility difficulty among stroke survivors. Millions of people are unable to live normally because of mobility difficulty every year. Strength training is an effective method to improve lower extremity ability but is limited by the shortage of medical staff. Thus, this paper proposes a robot-assisted active training (RAAT) by an adaptive admittance control scheme with virtual reality interaction (AACVRI). AACVRI consists of a stiffness variable admittance controller, an adaptive controller, and virtual reality (VR) interactions. In order to provide human-robot reality interactions corresponding to virtual scenes, an admittance control law with variable stiffness term was developed to define the mechanics property of the end effector. The adaptive controller improves tracking performances by compensating interaction forces and dynamics model deviations. A virtual training environment including action following, event feedback, and competition mechanism is utilized for improving boring training experience and engaging users to maintain active state in cycling training. To verify controller performances and the feasibility of RAAT, experiments were conducted with eight subjects. Admittance control provides desired variable interactions along the trajectory. The robot responds to different virtual events by changing admittance parameters according to trigger feedbacks. Adaptive control ensures tracking errors at a low level. Subjects were maintained in active state during this strength training. Their physiological signals significantly increased, and interaction forces were at a high level. RAAT is a feasible approach for lower limb strength training, and users can independently complete high-quality active strength training under RAAT.

Power flow (PF) flexibility in the multi-terminal HVDC (MT-HVDC) grids is a thought-provoking issue. It leads to employing the active DC power flow controller (DC-PFC)s. Hence, this paper examines the static average model (AM) and power injection model (PIM) of an interline DC-PFC (IDC-PFC). It is to provide a suitable base for DC PF studies and easy embedding of the DC-PFCs into MT-HVDC grids’ PF equations. In this regard, this paper proposes a new DC PF solver (DC-PFS) for the IDC-PFC compensated MT-HVDC grids within the well-accepted Newton-Raphson (NR) framework. It requires a few modifications in the main structure of the system's Jacobin (J) matrix compared to the uncompensated MT-HVDC grid. Also, the system's admittance matrix and its symmetry are preserved. In the proposed concept, the IDC-PFC cooperates with other MT-HVDC grid's state variables to satisfy the predetermined control objective(s). Furthermore, this paper proposes a new solution procedure (SP) to handle various system's limitations during the processes of solving the DC PF problem. Meanwhile, there is no need to modify the related J matrix. The effective and accurate performance of the IDC-PFC's models, as well as presented NR-based DC-PFS and SP, are verified by performing several simulations on the 8-bus CIGRE MT-HVDC grid.

© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works 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.

Accurate and efficient electromagnetic transient (EMT) simulation of various types of solid-state transformers (SST) is extremely time-consuming due to the complex module structure, flexible topology connections, large number of electrical nodes and simulation time-steps limited in the range of micro-seconds. Therefore, it is urgent to develop the EMT equivalent modelling and fast simulation of SSTs for system level studies. Taking the modular multilevel converter (MMC) based SST as an example, this paper proposes an accelerated EMT model which focuses on the equivalence of the dual active bridge (DAB) based high-frequency link (HFL) in the SST. Compared with the existing algorithms, two critical factors of the proposed method that contribute the most to the efficiency improvement are the preprocessing of the nodal admittance equation and the conversion of the short-circuit admittance parameters. The proposed model is verified in PSCAD/EMTDC by comparing it with the detailed EMT model. The results show that the accelerated model is one to two orders of magnitude faster than the detailed model without sacrificing the accuracy. The experiment validation also confirms the validity of the proposed model.

In this paper, we present an improved high frequency small-signal distributed model for SiGe HBTs under forward-active mode based on the transmission line theory. The distributed nature of the transistor structure is taken into account in the proposed model. The single SiGe HBT is considered to be a cascade of many infinitesimal transistors, connected with the intrinsic base resistance. The closed-form solutions of admittance parameters for the distributed model are derived by solving the transmission line equation. With reasonable approximation and simplification, the model parameters are then directly extracted based on the nonlinear rational function fitting. The new improved distributed model and parameter extraction technique are validated with a $1\times 1.2\times 30\,\,\mu \text{m}^{2}$ SiGe HBT from 100 MHz to 20.89 GHz. The simulated $S$ -parameters in the proposed transmission line model are in close agreement with the measured data, and the frequency characteristics of the transistors are well predicted.

The current stage of world energy development is characterized by the creation of powerful, territorially unified energy systems under free market conditions as well as renewable energy integration. Such transactions challenge networks’ configurations and their operating modes. Electric power system (EPS) static stability could be considered one of the primary targets in this regard. The aim of this study was to evaluate the undergoing and expected modernization of the Latvian EPS in terms of static stability in a regional scale-based case study. In order to define static stability, a method based on a bus admittance matrix was proposed. A simplified Latvian EPS model was developed and assessed for the following three modes: past (2017), current (2020), and planned (2025), taking into account the Baltic States’ planned development scenarios including large wind farm integration. The evaluation of computation results provided an opportunity to visually inspect changes in the EPS’ sensitive elements such as lines and nodes. As a result, positive changes were observed (decrease of several weak points) for the planned mode (2025) as compared to the past mode (2017) under the considered modernization scenario. The detailed analysis and results are presented in the article.

This paper is focused on the investigation of self-oscillation regimes associated with very simple structure of lambda diode. This building block is constructed by using coupled generalized bipolar transistors. In the stage of mathematical modeling, each transistor is considered as two-port de-scribed by full admittance matrix with scalar polynomial forward trans-conductance and linear backward trans-conductance. Thorough numerical analysis including routines of dynamical flow quantification indicate the existence of self-excited dense strange attractors. Plots showing first two Lyapunov exponents as functions of adjustable parameters, signal entropy calculated from gen-erated time sequence, sensitivity analysis, and other results are provided in this paper. By the construction of a flow-equivalent chaotic oscillator, robustness and long-time geometrical sta-bility of the generated chaotic attractors is documented by the experimental measurement, namely by showing captured oscilloscope screenshots. Tento článek je zaměřen na výzkum vlastních oscilačních režimů v rámci velmi jednoduché struktury lambda diody. Tento stavební blok je zkonstruován s využitím zobecněných bipolárních tranzistorů. V etapě matematického modelování je každý z tranzistorů uvažován jako dvojbran popsaný plnou admitanční maticí se skalárními polynomiálními dopřednými transkonduktancemi a lineárními zpětnými transkonduktancemi. Detailní numerická analýza zahrnující procedury pro kvantifikaci dynamického chování dokazují existenci hustých podivných atraktorů. Grafy ukazující první dva největší Ljapunovské exponenty jako funkce variabilních parametrů systému, entropie generovaných signálů vypočtená z časových posloupností, citlivostní analýza a další výsledky jsou uvedeny v tomto článku. Robustnost a dlouhodobá geometrická stabilita generovaných chaotických atraktorů je dokumentována konstrukcí dynamicky ekvivalentního chaotického oscilátoru, jeho experimentálním ověřením, konkrétně zachycenými snímky obrazovky osciloskopu.

This paper presents and briefly discusses recent observations of dynamics associated with isolated generalized bipolar transistor cells. A mathematical model of this simple system is considered on the highest level of abstraction such that it comprises many different network topologies. The key property of the analyzed structure is its bias point since the transistor is modeled via two-port admittance parameters. A necessary but not sufficient condition for the evolution of autonomous complex behavior is the nonlinear bilateral nature of the transistor with arbitrary reason that causes this effect. It is proved both by numerical analysis and experimental measurement that chaotic motion is miscellaneous, robust, and it is neither numerical artifact nor long transient motion. Tento článek prezentuje a stručně diskutuje poznatky z nedávného pozorování dynamiky izolované buňky zobecněného bipolárního tranzistoru. Matematický model tohoto jednoduchého systému je uvažován na nejvyšším stupni abstrakce, takže jej zahrnuje mnoho různých obvodových struktur. Klíčovou vlastností analyzované struktury je pracovní bod, protože tranzistor je modelován dvojbranovými admitančními parametry. Nezbytnou, ale nikoliv postačující podmínkou evoluce autonomního komplexního chování je nelineární obousměrná povaha tranzistoru, přičemž není podstatná příčina této povahy. Numerickou i experimentální analýzou je ukázáno, že chaotické chování je rozličné, robustní, a nejedná se ani o numerický artefakt, ani dlouhý přechodný děj.

Weak grids are gaining considerable attention since power generation resources are remote from constant power loads (CPLs), which results in low-frequency/harmonic oscillation. Meanwhile, due to the play, and plug demand of modern power system, the line inductance of weak grids often changes, which is also regarded as the variation regarding short circuit ratio (SCR). Based on this, the conventional impedance-based stability operation point assessment approaches should be expanded into stability domain assessment approach considering the line inductance variation. Therefore, the stability-oriented line inductance stability domain assessment approach for weak grids with CPLs is proposed in this paper. Firstly, the source impedance matrix of weak grid, and load admittance matrix of CPLs are separately built. Secondly, an improved stability forbidden domain criterion is proposed through related mapping transformation process, which has lower conservatism than two previous improved stability criteria. Thirdly, the improved stability forbidden domain criterion is switched into the condition that the intermediate matrices are Hurwitz. Meanwhile, the line inductance stability domain is directly obtained through these intermediate matrices, and guardian map theory. Finally, the simulation, and experiment results illustrate that the proposed approach has less conservatism, and high efficiency. This work was supported by National Key Research, and Development Program of China under Grant 2018YFA0702200.

The use of photovoltaic reactive power and energy storage active power can solve the problems of voltage violation, network loss, and three-phase unbalance caused by photovoltaic connection to low-voltage distribution networks. However, the three-phase four-wire structure of the low-voltage distribution network brings difficulties to power flow calculation. In order to achieve photovoltaic utilization through optimal power flow, a photovoltaic-energy storage collaborative control method for low-voltage distribution networks based on the optimal power flow of a three-phase four-wire system is proposed. Considering the amplitude and phase angle of voltage and current, a three-phase four-wire node admittance matrix was used to establish the network topology of the low-voltage distribution network. Also, to minimize the network loss, the three-phase unbalance and voltage deviation. a multi-objective optimization model based on three-phase four-wire network topology was established considering the voltage constraints, reverse power flow constraints and neutral line current constraints. Through improving the node admittance matrix and model convexity, the complexity of solving the problem is reduced. The CPLEX algorithm package was used to solve the problem. Based on a 21-bus three-phase four-wire low-voltage distribution network, a 24-h multi-period simulation was undertaken to verify the feasibility and effectiveness of the proposed scheme.

A large number of nonlinear loads have an impact on the stable operation of the power system. To solve this problem, this article proposes a nonlinear load harmonic prediction method based on the architecture of Power Distribution Internet of Things. Firstly, this method integrates the characteristics of edge computing technology and Power Distribution Internet of Things technology and proposes a Power Distribution Internet of Things framework applied to nonlinear load harmonic prediction, which provides top-level design for subsequent harmonic prediction methods of Power Distribution Internet of Things; then, considering the electrical characteristics of the typical nonlinear load, the mathematical model of nonlinear load data is constructed based on the harmonic coupling admittance matrix model on the edge side. At the same time, a nonlinear load harmonic prediction model based on dynamic time warping and long-term and short-term memory network (DTW-LSTM) is established in the cloud computing center to realize high accuracy and high real-time prediction and analysis of nonlinear load harmonics. Finally, the simulation results based on the general data set show that the MAE evaluation index of the proposed method is less than 5% in the experimental group, which shows good generalization ability, and has some advantages over the current method in operation efficiency.

This paper develops a small-signal impedance model of modular multilevel converters (MMCs) using harmonic state-space (HSS) method and studies the stability in a multiple converter scenario. In order to simplify analysis on the coupling characteristics between different frequencies in MMCs, the proposed model is developed in the positive-negative-zero (PN0) sequence-frame, where the zero-sequence current in three-phase three-wire system is directly set to zero without introducing complicated method. A simple 2 by 2 admittance matrix in PN0-frame is extracted from the MMC small-signal model for ease of system stability analysis. Using the developed impedance model, the multi-infeed interaction factor (MIIF) measure is adopted to analyze the most significant interactions for multi-infeed converter systems to be prioritized. Different outer-loop controllers are adopted and compared in the analysis to illustrate the effect of different control modes on converter impedance and system stability. Analytical studies and time-domain simulation results are provided to validate the proposed model and stability analysis.

This paper proposes a subsynchronous resonance (SSR) mode analysis method for the converter-based power system. In the system, the converters are modeled as multiple-input multiple-output admittance matrices, which essentially are two-port networks. Thus, the system including the grid impedances can be modeled as the connections of two-port networks, where the SSR mode can be identified by applying the impedance-based stability analysis method. To further distinguish the contributions of converter control dynamics to the SSR mode, the nodal admittance matrix is systematically obtained by applying the graph theory. Then, the modal impedances of the system can be derived and analyzed with the participation factors of each bus and the eigenvalue sensitivities to the specific entry in admittance matrix, which enable to quantify the contributions of network components to the SSR mode, and the theoretical analysis is validated by a case study.

Lower-limb exoskeletons as walking assistive devices have been intensively investigated in recent decades. In these studies, intention detection and performance evaluation are important topics. In our previous studies, we proposed a disturbance observer (DOB)-based torque estimation algorithm and an admittance control law to shape the admittance of the human-exoskeleton system (HES) and comply with the user&rsquo, s walking intention. These algorithms have been experimentally verified under the condition of no ground reaction force (GRF) in our previous studies. In this paper, we devised and integrated with the exoskeleton control system a sensing and communication module on each foot to measure and compensate for GRF. Rigorous theoretical analysis was performed and the sufficient conditions for the robust stability of the closed-loop system were derived. Then, we conducted level ground assistive walking repeatedly with different test subjects and exhaustive combinations of admittance parameters. In addition, we proposed two tractable and physically insightful performance indices called normalized energy consumption index (NECI) and walking distance in a fixed period of time to quantitatively evaluate the performance for different admittance parameters. We also compared the energy consumption for users walking with and without the exoskeleton. The results show that the proposed admittance control law reduces the energy consumption of the user during level ground walking.

This paper presents a method to calculate the bistatic response of an elastic object immersed in a fluid using its structural Green's function (in vacuo structural admittance matrix), calculated by placing the object in a spatially random noise field in air. The field separation technique and equivalent source method are used to reconstruct pressure and velocity fields at the object's surface from pressure measurements recorded on two conformal holographic surfaces surrounding the object. Accurate reconstruction of the surface velocity requires subtraction of the rigid body response computed using a finite element approach. The velocity and pressure fields on the surface lead to the extraction of the in vacuo structural admittance matrix of the elastic object, which is manipulated to yield the farfield bistatic response for a fluid-loaded target for several angles of incidence. This method allows the computation of the scattering properties of an elastic object using exclusive information calculated on its surface (no knowledge of the internal structure required). A numerical experiment involving a cylindrical shell with hemispherical caps is presented, and its bistatic response in water shows excellent agreement with a finite element solution.

[EN] Permittivity is a useful tool to characterize the composition and quality of many geomaterials. In general, the non-resonant permittivity measurement methods exhibit a higher degree of uncertainty than their resonant counterparts. In resonant measurements, the reduction in uncertainty comes typically with a loss in broadband. This article describes the theory, design, and application of multipoint coaxial reentrant resonant cavities applied to low-loss geomaterials at different temperatures. Specifically, a full-wave method based on circuit analysis is developed and applied for a circular corrugated waveguide. Moreover, the mode-matching method is applied to calculate the generalized admittance matrix (GAM). Two multipoint cavities and software were built and validated. The first cavity has five resonant frequencies, between 170 MHz and 2.3 GHz, and the second has four resonant frequencies, between 1.3 and 8.6 GHz. Thus, this method allows for ¿broadband-resonant¿ measurements. The permittivity values of liquid hydrocarbons, powdered kerogen, and pyrite are shown.

In this paper, we investigate the stability properties of inverter-based microgrids by establishing the possible presence of the so-called critical clusters - groups of inverters with their control settings being close to the stability boundary. For this, we consider the spectrum of the weighted admittance matrix of the network and show that its distinct eigenvalues correspond to inverter clusters, whose structure can be revealed by the corresponding eigenvector. We show that the maximum eigenvalue of the weighted admittance matrix corresponds to the cluster, closest to stability boundary. We also establish, that there exists a boundary on the value of this eigenvalue, that corresponds to the stability of the overall system. Thus, we make it possible to certify the stability of the system and find the groups of inverters in which control settings are closest to the stability boundary., Accepted for the PSCC conference

The increasing focus on the active participation of low-voltage (LV) active distribution networks (DNs) in electricity markets requires the real-time optimal control of these DNs. To achieve this goal, a cheap semi-definite programming (SDP)-based optimal power flow (OPF) model for active neutral-equipped DNs, hosting both wye- and delta-connected loads, is proposed in this paper, aiming at overcoming the high computational requirement of the primal SDP-based OPF model. The coupled power injections between conductors are explicitly represented for each conductor by utilizing the network admittance matrix-based approach. Furthermore, three novel propositions (P1, P2 and P3) are proposed for the modelling of the constant current component of ZIP end-users in the context of the proposed OPF model. Moreover, the impact of the voltage-angle deviation on the exactness of the P1- and P2-based models is discussed. Simulations are carried out on several LV active DNs for various parameters of ZIP end-users, and the quality of the proposed OPF model is verified through the %optimality gap, power mismatch, voltage violation and root-mean-square error criteria. It is successfully shown that the proposed OPF model provides an optimal and feasible solution for all load types (wye, delta, mixed wye-delta) under a large range of ZIP load parameters. Furthermore, among the three propositions, the P3-based OPF model appears to be the most accurate in terms of determining an optimal and feasible solution. Finally, the reduced computational time of the cheap conic model allows its real-time implementation for medium- and large-sized DNs for which the primal multi-phase SDP-based model is practically difficulty to realize.

We present a detailed study of the effect of gate-oxide-related defects (traps) on the small-signal radio frequency (RF) response of III-V nanowire MOSFETs and find that the effects are clearly identifiable in the measured admittance parameters and in important design parameters such as h 21 (forward current gain) and MSG (maximum stable gain). We include the identified effects in a small-signal model alongside results from previous investigations of III-V RF MOSFETs and thus provide a comprehensive physical small-signal RF model for this type of transistor, which accurately describes the measured admittance parameters and gains. We verify the physical basis of the model assumptions by calculating the oxide defect density from the measured admittances.

This paper presents a comparison of computational time required to build the admittance matrix of five test systems (ranging from 200 to 70,000 nodes) considering two formation approaches: element-by-element and matrix approach. The algorithms have been implemented in MATLAB ™ and tested in four multi-core platforms. Implementations include sparse and dense matrix representation and parallel/non-parallel computing. Results show the matrix approach considering sparse representation and parallel computing is the best approach in computing time.

The artificial material single-layer (AMSL) method, recently proposed to model solid conductive shields in finite-element solvers without using a fine discretization, is here extended to model multilayer shields. First, the admittance matrix of a multilayer shield is analytically derived by the transmission line (TL) theory. Then, considering that the field through conductive shields propagates normally to the shield surface, the TL admittance matrix is equated to that of a 1-D finite element to extract the physical constants of a homogenized artificial material. These constants are adopted to model the multilayer shield region in the finite-element method (FEM) calculations by using only one layer of finite elements in the direction of the field propagation. By the AMSL-FEM, the field propagation through the multilayer shield is accurately modeled taking into account the skin effect and avoiding the fine discretization of the shield.