Search

Copyright of Petroleum Refinery Engineering is the property of Petroleum Refinery Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract This paper recommends new design for non-isolated semi-quadratic buck/boost converter with two similar structure that includes the following features: (a) the continuous input current has made it reasonable for PV solar applications and reduced the value of the capacitors in the input filter reducing the input ripple as well as EMI problems; (b) the topology is simple, and consists of a few numbers of components; (c) the semiconductor-based components have lower current/voltage stresses in comparison with the recently recommended designs; (d) semi-quadratic voltage gain is D (2 − D) / (1 − D)2; (e) 94.6 percent from the theoretical relations and 91.8 percent from the experimental for the output power of 72W, the duty of 54.2 percent, and output voltage of 72 V are the efficiency values in boost mode; (f) 89.3 percent from the theoretical relations and 87.2 percent from the experimental for the output power of 15W, the duty of 25.8 percent, and output voltage of 15 V are the efficiency values in buck mode. One structure is the continuous output current and negative output polarity, and other structure is positive output polarity. The recommended topologies have been studied in both ideal and non-ideal modes. The continuous current mode (CCM) is the suggested mode for the proposed converters. Moreover, the requirements of CCM have been discussed. The various kinds of comparisons have been held for voltage gain, efficiency, and structural details, and the advantages of the suggested design have been presented. A small-signal analysis has been completed, and the suitable compensator has been planned. Finally, PLECS simulation results have been associated with the design considerations.

This paper recommends new design for non-isolated semi-quadratic buck/boost converter with two similar structure that includes the following features: (a) the continuous input current has made it reasonable for PV solar applications and reduced the value of the capacitors in the input filter reducing the input ripple as well as EMI problems; (b) the topology is simple, and consists of a few numbers of components; (c) the semiconductor-based components have lower current/voltage stresses in comparison with the recently recommended designs; (d) semi-quadratic voltage gain is D (2 − D) / (1 − D)2; (e) 94.6 percent from the theoretical relations and 91.8 percent from the experimental for the output power of 72W, the duty of 54.2 percent, and output voltage of 72 V are the efficiency values in boost mode; (f) 89.3 percent from the theoretical relations and 87.2 percent from the experimental for the output power of 15W, the duty of 25.8 percent, and output voltage of 15 V are the efficiency values in buck mode. One structure is the continuous output current and negative output polarity, and other structure is positive output polarity. The recommended topologies have been studied in both ideal and non-ideal modes. The continuous current mode (CCM) is the suggested mode for the proposed converters. Moreover, the requirements of CCM have been discussed. The various kinds of comparisons have been held for voltage gain, efficiency, and structural details, and the advantages of the suggested design have been presented. A small-signal analysis has been completed, and the suitable compensator has been planned. Finally, PLECS simulation results have been associated with the design considerations. [ABSTRACT FROM AUTHOR]

Summary: Most of the existing adaptive filter algorithms pay more attention to improving performance while ignoring the computational complexity and the impact of the impulsive environment. When encountering the impulsive noise environments, the performance of traditional nonlinear adaptive filter may be significantly reduced and usually needs high computational cost. Therefore, this article proposes a hyperbolic tangent Leclerc robust nonlinear adaptive filter based on the low complexity decomposable Volterra model (HTLNAF‐DVM). The filter is implemented by imposing a rank‐one structure on the full Volterra model to get a product of linear filters, and employs a hyperbolic tangent Leclerc function as a robust norm to effectively improve the robustness against the impulsive noise. In addition, we give the theoretical analyses of the steady‐state mean‐square performance of the proposed HTLNAF‐DVM. Finally, the simulation results prove that the proposed HTLNAF‐DVM algorithm has better performance than the existing algorithms and fit well with the theory. [ABSTRACT FROM AUTHOR]

Until now, various studies have been conducted on the drag coefficient of pickup trucks, but little research has been conducted on the effect of the front overhang length and roof design on the drag coefficient. In this study, the flow characteristics and drag coefficients of 54 models with different front overhang lengths, roof angles, and angular positions were compared using a computational fluid dynamics code to reduce the drag coefficient of an eco-friendly pickup truck. Reducing the aerodynamic drag of electric vehicles can improve battery utilization and improve the overall performance of the powertrain, so it is important to analyze and optimize geometric design steps to improve drag reduction strategies. The three-dimensional steady-state analysis model used in this study was verified by comparing the model results with experimental values reported in previous studies. In addition, the impacts of four factors on the drag coefficient were analyzed to develop an optimal design that takes into account smaller and better characteristics. The drag coefficient was reduced by 10.3% compared to that of the base model. Based on the numerical analysis of all models to be applied to pickup truck design, a correlation of the drag coefficient with the shape was proposed, showing a low error range of +1.9% to −1.74%. [ABSTRACT FROM AUTHOR]

• The take-over ability of drivers is assessed by visual characteristic indicators, physiological characteristic indicators, vehicle control indicators and take-over behavioral indicators. • Both text-based user manual and behavioral spectrum-based training methods are proposed to improve take-over ability. • The behavioral spectrum-based training group showed superior performance. • Drivers' take-over ability reached stability after undergoing 14 take-over operations. • These results could contribute to the safety of human–machine codriving vehicles and the design of future driver training systems. During human–machine codriving, drivers need to take over the vehicle when a take-over request (TOR) appears. If drivers have not received relevant training before driving, they may be unable to complete the take-over within the limited time, or the stability of subsequent vehicle control may be insufficient, which can lead to accidents. In this study, two types of take-over ability improvement methods are proposed. Participants were recruited and randomly divided into a control group (n = 15, no take-over training) and two experimental groups (n = 15, text-based training; n = 15, behavioral spectrum-based training). One-way ANOVA or the Kruskal–Wallis test and post hoc contrasts were used to analyze the differences in data indicators between the three groups of drivers after 20 take-over operations, and another method was proposed to validate the efficiency of the take-over operations on the stability of take-over ability. The results show that compared with the control group, both experimental groups demonstrated a significant improvement in take-over ability, with the behavioral spectrum-based training group exhibiting better take-over performance than the text-based training group. Moreover, after 14 take-over operations, drivers' take-over ability in the behavioral spectrum-based training group stabilized. The findings of this study can contribute to the safety of human–machine codriving vehicles and the design of future driver training systems. [ABSTRACT FROM AUTHOR]

We consider multiclass make-to-stock production/inventory systems in which the manager makes three decisions, including pricing, outsourcing, and scheduling, to maximize the long-run average profit. For a sequence of systems in the heavy-traffic regime, with linear or strictly convex holding/waiting cost functions, we propose a sequence of policies and establish its asymptotic optimality. Our proof combines the lower bound approach and a thorough steady-state analysis of the systems. We also establish general results on the existence and tightness of the stationary distributions of the state processes under a more general family of policies. Funding: X. Gao's research is supported in part by the Hong Kong Research Grants Council [Grants 14201520, 14201421, and 14212522]. J. Huang's research is supported in part by the Hong Kong Research Grants Council [Grants 14500819 and 14505820] and the National Natural Science Foundation of China [Grant 72222023]. [ABSTRACT FROM AUTHOR]

This paper discusses an alternative and Simulation Program with Integrated Circuit Emphasis (SPICE)‐compatible solution for the steady‐state simulation of power distribution networks. It introduces two alternative auxiliary subcircuits that allow to efficiently simulate the network in any simulation tool for circuit analysis. This feature introduces remarkable benefits in terms of simplicity and generality, since it avoids the need for any iterative method, thus bridging the gap between classical industry‐standard and general‐purpose simulators based on circuital equations, such as SPICE, and dedicated tools for the load flow analysis of power systems. The approach is first demonstrated based on a simple illustrative example, for which the performance in terms of accuracy and efficiency is discussed and then applied to the standard IEEE 33‐node power distribution benchmark. [ABSTRACT FROM AUTHOR]

We study response time, a key performance characteristic of queueing mechanisms. The studied model incorporates both active and passive queue management, arbitrary service time distribution, as well as a complex model of arrivals. Therefore, the obtained formulas can be used to calculate the response time of many real queueing mechanisms with different features, by parameterizing adequately the general model considered here. The paper consists of two parts. In the first, mathematical part, we derive the distribution function for the response time, its density, and the mean value. This is done by constructing two systems of integral equations, for the distribution function and the mean value, respectively, and solving these systems with transform techniques. All the characteristics are derived both in the time-dependent and steady-state cases. In the second part, we present numerical values of the response time for a few system parameterizations and point out several of its properties, some rather counterintuitive. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In recent years, distributed adaptive processing has received much attention from both theoretical and practical aspects. One of the efficient cooperation structures in distributed adaptive processing is the diffusion strategy, which provides a platform for the cooperation of nodes that run an adaptive algorithm, such as the least mean-squares (LMS) algorithm. Despite the studies that have been done on the diffusion-based LMS algorithm, the effect of deficient length on such structures has been overlooked. Accordingly, in this paper, we study the steady-state performance of the deficient length diffusion LMS algorithm. The results of this study show, in particular, that setting the tap length below its actual value leads to drastic degradation of the steady-state excess mean-square error (EMSE) and mean-square deviation (MSD) in diffusion adaptive networks. Furthermore, unlike the full-length case, where the steady-state MSD and EMSE decrease significantly with the step size reduction, this study shows that in the deficient-length scenario, there are no significant improvements in the steady-state performance by reducing the step size. Therefore, according to this study, the tap length plays a key role in diffusion adaptive networks since the performance deterioration due to deficient selection of tap length could not be compensated by an adjustment in the step size. Experiments exhibit a very good match between simulations and theory. [ABSTRACT FROM AUTHOR]

A methodology for the steady state analysis of self-excited induction generators (SEIGs) is proposed employing an approach using simple co-ordinate geometry. The equivalent circuit of the SEIG is taken and its three complex admittances, Y̅1, Y̅2 and Y̅3, are considered. Using the nodal analysis of the circuit and considering the nature of the parameters involved for ensuring self-excitation of the induction machine, it is shown that a triangle can be obtained by plotting Y̅1, Y̅2 and Y̅3 in the complex plane. Utilizing the well-known properties of the triangle, in a few steps, a simple equation is derived for the per unit (pu) speed, in terms of pu frequency, real part of Y̅1 and rotor resistance. This, consequently, leads to another simple expression for the calculation of the magnetizing reactance and further processing of the performance analysis of SEIG. Thus, this proposed method does not require advanced techniques or complex calculations. The analytical results arrived at are compared with those calculated using the popularly adopted genetic algorithm technique and recently evolved binary search method and also with the values obtained experimentally on a 3-phase, 3.75 kW, 230 V delta-connected induction machine run as an SEIG. A very close agreement is seen between these three sets of results. [ABSTRACT FROM AUTHOR]

Modern production processes frequently require steady-state analysis of continuous dynamic systems. Traditional numerical approaches, however, fall short in efficiency when tasked with addressing large-scale or dynamic problems. To tackle the inverse problem inherent in stability analysis, this study presents an innovative approach by integrating a combined excitation function into the foundational zeroing neural network (ZNN) model. This integration constrains the ZNN model, evolving it into an enhanced EZNN model specifically designed for solving the inverse of dynamic complex matrices. Additionally, this paper conducts a rigorous theoretical analysis of the robust performance of the EZNN model when excited by the combined function, both in the presence and absence of noise interference. The model solution process is promoted by using a class of high-dimensional continuous dynamic systems as an example, and numerical simulation experiments are used for validation. Considering the dynamic system satisfying {A(t)=(4+sin(2t) 4-cos(2t) 5+sin(2t))C(t)=(cos(t)sin(t)-cos(t)-sin(t)cos(t)sin(t))b(t)=4+cos(4t),d(t)=(cos(2t),cos(2t))T\left\{ \matrix{ A(t) = \left( {4 + \sin (2t)\quad 4 - \cos (2t)\quad 5 + \sin (2t)} \right) \hfill \cr C(t) = \left( {\matrix{{\cos (t)} & {\sin (t)} & { - \cos (t)} \cr { - \sin (t)} & {\cos (t)} & {\sin (t)} \cr } } \right) \hfill \cr b(t) = 4 + \cos (4t),d(t) = {(\cos (2t),\cos (2t))^T} \hfill \cr} \right. , the error E1(x(t),t) obtained by the EZNN model with combinatorial function excitation always remains negative or tends rapidly to 0. The x (t) obtained by the model converges rapidly to an exact solution of the system. Through the discussion of parametric conditions, it is also found that increasing the value of parameter γ increases the rate of convergence of the ZNN model.

Until now, various studies have been conducted on the drag coefficient of pickup trucks, but little research has been conducted on the effect of the front overhang length and roof design on the drag coefficient. In this study, the flow characteristics and drag coefficients of 54 models with different front overhang lengths, roof angles, and angular positions were compared using a computational fluid dynamics code to reduce the drag coefficient of an eco-friendly pickup truck. Reducing the aerodynamic drag of electric vehicles can improve battery utilization and improve the overall performance of the powertrain, so it is important to analyze and optimize geometric design steps to improve drag reduction strategies. The three-dimensional steady-state analysis model used in this study was verified by comparing the model results with experimental values reported in previous studies. In addition, the impacts of four factors on the drag coefficient were analyzed to develop an optimal design that takes into account smaller and better characteristics. The drag coefficient was reduced by 10.3% compared to that of the base model. Based on the numerical analysis of all models to be applied to pickup truck design, a correlation of the drag coefficient with the shape was proposed, showing a low error range of +1.9% to −1.74%.

This study presents a method to directly calculate the stator current Fourier spectra in double-cage induction motors to diagnose faults in rotor cages. A circuit model is developed for this purpose, allowing the modelling of any asymmetry in the outer and inner rotor cages. The model extends the conventional model of a cage motor by considering the higher space harmonics generated by the stator windings. The asymmetry of the cages is modelled by growing the resistance of any of the rotor bars. This results in various model equations, to be solved by looking for diagnostic signals. Motor current signature analysis is typically used to diagnose cage motors based on the Fourier spectra of the stator currents during steady-state operation. This study determines these spectra for double cage motors using the harmonic balance method, omitting the transient calculations. The calculation results confirmed the sensitivity of the stator current Fourier spectra as a diagnostic signal to distinguish faults in the outer and inner cages.

The identification and analysis of harmonics, frequency, and transient events are essential today. It is necessary to have available data relating to harmonics, frequency, and transient events to understand power systems and their proper control and analysis. Power quality monitoring is the first step in identifying power quality disturbances and reducing them and, as a result, improving the performance of the power system. In this paper, while presenting different methods for measuring these quantities, we have made some corrections to them. These reforms have been obtained through the analysis of power network signals. Finally, we introduce a new monitoring system capable of measuring harmonics, frequency, and transient events in the network. In addition, these values are provided for online and offline calculations of harmonics, frequency, and transient events. In this paper, two new and practical methods of the "algebraic method" are used to calculate network harmonics and wavelet transform to calculate transient modes in the network. Furthermore, the proposed monitoring system is able to reduce the amount of data-storage memory. The results of the simulations performed in this article show the superiority of using the new method presented for online and offline monitoring of power quality in electric power systems. [ABSTRACT FROM AUTHOR]

This paper presents a novel three-phase star-connected stand-alone asynchronous generator (SAG) with only two capacitors, connected in series with two stator phase windings, for supplying power to single-phase resistive load. This new scheme has excellent voltage regulation (less than 1.7%) due to the presence of these two series capacitors and does not require any separate voltage regulating device making it very simple and cheaper. The symmetrical component theory has been used to form a simplified equivalent circuit of the scheme. Graph theory has been applied to the equivalent circuit to simplify the process of obtaining two non-linear higher-order equations which are solved using the binary search algorithm (BSA) to obtain the values of per unit frequency and magnetizing reactance. Accordingly, using the magnetization characteristics of the machine and the performance equations, the steady-state performance of the SAG has been obtained. To investigate the behavior of the SAG under transient conditions, such as voltage build-up, load switching and load perturbation, a dynamic model of the generator scheme has been developed on the basis of d-q axes theory in stationary reference frame including the effect of main and cross flux saturation. The simulated results have been validated through experimentation using an induction machine rated as 2 hp, 4-pole, 415 V, 3.5 A, 3-phase, 1440 rpm, 50 Hz. The simulated results closely agree with the experimental results, indicating the efficacy of the proposed approach. This can be a promising single-phase power generation scheme for supplying power in remote rural areas. [ABSTRACT FROM AUTHOR]

Abstract Turbines are generally oversimplified in conventional algorithms for steady‐state analysis of hydropower plant (HPP) networks. Moreover, conventional algorithms are hardly suitable for serial HPPs. In this paper, a modified global gradient algorithm (MGGA) is developed by extending turbine models and optimizing turbine interpolation. First, the nonlinear model of turbines is established with the proposed variable resistance factor and added to the global matrix. Then turbine unit quantity interpolation is proposed to compute the turbine operating parameters. Finally, turbine links and pipes can be iterated synchronously, and the global matrix is solved using the Newton–Raphson method. Characteristics of MGGA are evaluated by employing two test HPPs, including rapidity of convergence, computational stability of turbine, and applicability for serial HPPs. The results show that: (a) The iterative numbers of the MGGA are 0.72 and 4.98 times on average less than that of CA1 and CA2 for the accuracy of 10−6 in 400 operating conditions, even though MGGA has an obvious hysteretic nature; (b) Only MGGA can successfully calculate the extreme cases that large head losses in HPP networks; (c) Although fixed head nodes are not present between turbine links, such as serial HPPs, MGGA still works.

Recently the grid-following inverter-based power generation systems (IBPGSs) dominate over synchronous generators (SGs) in load sharing in some areas of power grids in many countries worldwide. The trend of increasing penetration of IBPGSs to grid results in decreasing number of SGs in operation. This can result in a slowly decreasing system inertia which results in fast dynamics during transient conditions, that may lead to failures of phase-locked loops (PLLs), which are widely used in grid-following IBPGSs. Consequently, the grid-following IBPGS-dominated grids are facing stability issues in their operations. To support these grid-following IBPGSs for their stable operations, a stable grid-forming IBPGS is required that can operate as SGs. In this paper, a grid-forming controller is designed for IBPGSs that can enable IBPGSs to mimic SGs and work as grid-forming inverters that operate like SGs to maintain the grid dynamics suitable for the stable operation of the IBPGSs. For this purpose, a detailed mathematical model of the SG and its associated controller has been used with the proposed grid-forming controller. From the steady-state and transient dynamics, a mathematical relationship between the inertia support from the grid-forming controller and an SG has been developed to control the inverter in the grid-forming IBPGS. The performance of the grid-forming IBPGS during steady-state and transients due to load change, fault, and grid-isolation has been compared with the SG. The simulation results have validated the effectiveness of the proposed controller and grid-forming IBPGSs to help control the voltage and frequency of the IBPGS-dominated power systems.

We study response time, a key performance characteristic of queueing mechanisms. The studied model incorporates both active and passive queue management, arbitrary service time distribution, as well as a complex model of arrivals. Therefore, the obtained formulas can be used to calculate the response time of many real queueing mechanisms with different features, by parameterizing adequately the general model considered here. The paper consists of two parts. In the first, mathematical part, we derive the distribution function for the response time, its density, and the mean value. This is done by constructing two systems of integral equations, for the distribution function and the mean value, respectively, and solving these systems with transform techniques. All the characteristics are derived both in the time-dependent and steady-state cases. In the second part, we present numerical values of the response time for a few system parameterizations and point out several of its properties, some rather counterintuitive.

This study presents a method to directly calculate the stator current Fourier spectra in double-cage induction motors to diagnose faults in rotor cages. A circuit model is developed for this purpose, allowing the modelling of any asymmetry in the outer and inner rotor cages. The model extends the conventional model of a cage motor by considering the higher space harmonics generated by the stator windings. The asymmetry of the cages is modelled by growing the resistance of any of the rotor bars. This results in various model equations, to be solved by looking for diagnostic signals. Motor current signature analysis is typically used to diagnose cage motors based on the Fourier spectra of the stator currents during steady-state operation. This study determines these spectra for double cage motors using the harmonic balance method, omitting the transient calculations. The calculation results confirmed the sensitivity of the stator current Fourier spectra as a diagnostic signal to distinguish faults in the outer and inner cages. [ABSTRACT FROM AUTHOR]

Turbines are generally oversimplified in conventional algorithms for steady‐state analysis of hydropower plant (HPP) networks. Moreover, conventional algorithms are hardly suitable for serial HPPs. In this paper, a modified global gradient algorithm (MGGA) is developed by extending turbine models and optimizing turbine interpolation. First, the nonlinear model of turbines is established with the proposed variable resistance factor and added to the global matrix. Then turbine unit quantity interpolation is proposed to compute the turbine operating parameters. Finally, turbine links and pipes can be iterated synchronously, and the global matrix is solved using the Newton–Raphson method. Characteristics of MGGA are evaluated by employing two test HPPs, including rapidity of convergence, computational stability of turbine, and applicability for serial HPPs. The results show that: (a) The iterative numbers of the MGGA are 0.72 and 4.98 times on average less than that of CA1 and CA2 for the accuracy of 10−6 in 400 operating conditions, even though MGGA has an obvious hysteretic nature; (b) Only MGGA can successfully calculate the extreme cases that large head losses in HPP networks; (c) Although fixed head nodes are not present between turbine links, such as serial HPPs, MGGA still works. [ABSTRACT FROM AUTHOR]

The Least Mean Square (LMS) algorithm has a slow convergence rate as it is dependent on the eigenvalue spread of the input correlation matrix. In this research, we solved this problem by introducing a novel adaptive filtering algorithm for complex domain signal processing based on q-derivative. The proposed algorithm is based on Wirtinger calculus and is called as q- Complex Least Mean Square (q-CLMS) algorithm. The proposed algorithm could be considered as an extension of the q-LMS algorithm for the complex domain. Transient and steady-state analyses of the proposed q-CLMS algorithm are performed and exact analytical expressions for mean analysis, mean square error (MSE), excess mean square error (EMSE), mean square deviation (MSD) and misadjustment are presented. Extensive experiments have been conducted and a good match between the simulation results and theoretical findings is reported. The proposed q-CLMS algorithm is also explored for whitening applications with satisfactory performance. A modification of the proposed q-CLMS algorithm called Enhanced q-CLMS (Eq-CLMS) is also proposed. The Eq-CLMS algorithm eliminates the need for a pre-coded value of the q-parameter thereby automatically adapting to the best value. Extensive experiments are performed on system identification and channel equalization tasks and the proposed algorithm is shown to outperform several benchmark and state-of-the-art approaches namely Complex Least Mean Square (CLMS), Normalized Complex Least Mean Square (NCLMS), Variable Step Size Complex Least Mean Square (VSS-CLMS), Complex FLMS (CFLMS) and Fractional-ordered-CLMS (FoCLMS) algorithms. [ABSTRACT FROM AUTHOR]

The distributed estimation performance of multitask diffusion affine projection (AP) algorithm (MD-APA) will be greatly reduced under the impulsive noise interference. To overcome this defect, a robust MD-APA is derived by using M-estimate function (MD-APM) to resist the impulsive noise interference. The mean performance, mean square performance and steady-state performance of MD-APM algorithm are studied, and the convergence range of the step-size and the theoretical steady-state MSD are obtained. In addition, the computational complexity of MD-APM algorithm is analyzed in detail. Simulation experiments show that the proposed MD-APM algorithm has better estimation performance compared with MD-APA and MD-APSA under the impulsive noise interference, and its theoretical steady-state mean square deviation (MSD) can provide accurate prediction. [ABSTRACT FROM AUTHOR]

Doubly fed induction machines (DFIMs) are less commonly used as motors in the industry. DFIMs are more commonly designed as doubly fed induction generators (DFIGs) and used as variable speed generators in wind turbines. In this paper, a large‐scale DFIM is studied in steady‐state operation. In this study, using the steady‐state models and equivalent circuits, a comprehensive analysis of the DFIM performance in motor operation mode is performed. Using the simulation results, the behaviour of the motor in all three synchronous, super‐synchronous, and sub‐synchronous modes is analyzed and evaluated in detail. Adjusting and controlling the rotor voltage in DFIMs is very essential. Therefore, a simple method for optimally adjusting the amplitude and angle of the rotor voltage in steady state is proposed for three different optimization scenarios that maximize output power, efficiency, and power factor, respectively. The results show that by properly determining the rotor voltage, the DFIM can perform optimally in a wide range of speed variations. [ABSTRACT FROM AUTHOR]

In this paper, a steady-state model of an LLC resonant half-bridge converter with internal loss resistance is proposed, in order to maximize power conversion efficiency, and steady-state characteristic equations of DC voltage gain and input impedance are derived for the optimal design of the converter. First, to confirm the validity of the steady-state characteristic equation and the optimal design process, a prototype converter with a maximum output of 2 kW was designed. Through comparison of simulation, calculation, and experimental results obtained from the prototype test, it is shown that the calculation results proposed in this paper were closer to the experimental results than the calculation results obtained under the lossless condition. In addition, the relationship between the switching frequency and the load current of the prototype was compared, in order to determine the operating range of the switching frequency, which is important in the converter design stage. In this case, it was confirmed that the calculated value reflecting the internal loss showed a close result. In conclusion, we confirm the usefulness of the analysis results reflecting the internal loss resistance proposed in this paper and the optimal design process. [ABSTRACT FROM AUTHOR]

The quantum calculus provides an extra degree of freedom to search the local and global minima by inducing a q-parameter. Motivated by this fact, a quantum calculus-based noisy links incremental least mean squares (NL-qILMS) algorithm is proposed. Moreover, for the proposed NL-qILMS, we also devised various time-varying techniques for the selection of the optimal q-parameter to improve the performance. Furthermore, the closed-form solutions for the steady-state mean square deviation, excess mean square deviation and mean square error are derived. The analytical results are validated through simulation. Finally, extensive simulations have been done to evaluate the performance of the proposed algorithm for various choices of optimal q-values. [ABSTRACT FROM AUTHOR]

In distributed wireless networks, the adaptation process depends on the information being shared between various nodes. The global minimum, is therefore, likely to be affected when the information shared between the nodes gets corrupted. This could happen due to several reasons namely link failure, noisy environment and erroneous data etc. In this research, we propose a computationally efficient robust incremental least mean square (RILMS) algorithm to resolve the aforementioned issues. Essentially, a fusion step is introduced in the framework of the incremental least mean square (ILMS). Prior to adaptation at a node, the information shared by the neighbouring node is fused with the temporally preceding information of the node using an efficient combiner. An adaptive fusion strategy is proposed resulting in dynamic weight assignment for the fusion step. Closed form expression for the steady-state excess mean square error (EMSE) is derived and the performance of the proposed algorithm is evaluated for the noisy link environments and compared to the existing algorithms. Extensive experiments show the efficacy of the proposed approach compared to the contemporary methods. The proposed algorithm is found to be robust against the link failure and local node divergence problems. The improved performance of the proposed RILMS algorithm comes with a significant reduction in computational complexity compared to the convex combination based ILMS (CILMS) approach.

A new multitask incremental least mean-square (MILMS) algorithm using orthonormal codes is developed. In the multitask topology, nodes belong to different clusters, with each cluster performing its own ILMS estimation. The closed-form expressions of both the theoretical transient and steady-state mean squared deviation (MSD) are derived. The proposed MILMS algorithm is further reinforced by two combination strategies, referred to here as the combine-then-adapt (CTA), and adapt-then-combine (ATC), giving rise to two new improved algorithms, the CTA-MILMS and ATC-MILMS that substantially improve the MSD. Two further variants of these two improved algorithms are also developed based on the combination of the variable step size (VSS) and discrete cosine transform (DCT) techniques, leading to the two combined algorithms, termed here as CTA-VSSMILMS and ATC-VSSMILMS, respectively. Analysis of the first and second moments of the step size, under the transient and steady-state conditions, is also included. The problem of agent localization is solved using the MILMS algorithm by deploying a fixed number of anchors with known positions that surround agents with unknown positions. Extensive experiments were carried out to show the excellent match between the theoretical transient and steady-state expressions and their corresponding empirical results in terms of MSD performance. Moreover, we show that both the ATC-VSSMILMS and CTA-VSSMILMS algorithms improve the accuracy and computational speed of the MSD results of the proposed MILMS algorithm, thanks to the VSS-induced reduction of the number of needed steps and the DCT-induced data compression effect. • Development of the novel MILMS method in its two versions that both enjoy a superior performance. • Theoretical derivation of novel closed-form expressions in transient and steady-state analyses. • Development of four new variants of the main MILMS algorithm to enhance performance. • Extending the aforementioned analyses to the application of agent localization. • Development of MILMS algorithm and its variant using local normal codes without orthogonality. [ABSTRACT FROM AUTHOR]

The dynamic analysis of a power law-based functionally graded (FG) rotor-bearing system with induced porosities for non-uniform porosity distributions has been performed using the finite element method. A novel porous rotor element considering the effects of transverse shear deformation, gyroscopic moments, translational and rotational inertial has been developed for non-uniform porosity distributions based on the Timoshenko beam theory. Material properties are graded based on the power law along the radial direction of the FG shaft. The nonlinear temperature distribution law has been considered in conjunction with the power law to vary the temperature across the cross-section of the FG shaft. Material is graded in such a way that the stainless steel is comprised at the core of the FG shaft and the outer periphery of the FG shaft is made of Zirconia. The steady-state and transient time and frequency responses of a thermally loaded porous FG rotor-bearing system have been computed for both types of uneven porosity distribution using the Houbolt time marching technique and Fast Fourier Transform, respectively. The free vibration analysis has also been performed on the porous FG rotor-bearing system for various parameters such as power law index, the volume fraction of porosity and porosity distribution under different thermal gradients. The reduction of critical speed with increased amplitude is observed from the steady-state and transient frequency responses with an increase in volume fraction of porosity and temperature gradients

We propose a normalized least mean squares algorithm with variable step size. Unlike other solutions, it has low computational cost, only three parameters that are simple to choose, and its steady-state performance can be easily predicted. Simulations show a competitive performance in comparison with other solutions, and validate our theoretical analysis. [ABSTRACT FROM AUTHOR]

When it comes to designing a mini-submarine, the most important questions are what it should look like to achieve the purpose for which it was built and what propulsion force is required to operate it at expected parameters. This paper aims to answer some of these questions using a numerical analysis designed to optimize the body shape using the Ansys CFX software package. The mini-submarine understudy is research one and it is equipped with eight thrusters. The optimization aims to choose an optimal body shape between the frame type which is the simplest, cheapest, easiest to execute and offers easy access to all components, and the closed hull type which is more compact has lower hydrodynamic resistance, but is difficult to execute, is expensive and difficult to access inside for interventions and inspection. The cases of study are incompressible turbulent flow for a complete submerged body, distinguished by the complexity of the form and the conditions under which the computation must be performed. The simulation will be done at several speeds, according to the known power of the thrusters in steady-state conditions. The results will be compared whit measuring data, analyzed, and presented comparatively base on hydrodynamic resistance and speed, but will be discussed the other criteria as well. [ABSTRACT FROM AUTHOR]

The intermittent nature of wind generation makes essential the development of new tools to support the security assessment of electrical power systems (EPS) with this type of alternative energy source. In this context, the static security region (SSR) is a powerful tool that allows the steady-state security assessment of a EPS through visual inspections. The nomograms enable to carry out a fast analysis of the possible generation scenarios that a system can assume without violating its security limits. Therefore, the mains objective of this paper is to include a new security limit in the SSR, to complement the security assessment. This new limit is associated with intermittent generation sources, such as wind farms. For that purpose, an algorithm for the automatic construction of SSR is presented, where this new security limit was incorporated. The proposed methodology is applied to the well-known New England test system. The results presented validate and indicate the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

With theincreased penetration of renewable sources, power gridsare becoming stressed due to fluctuating generation. To alleviate stress from inconsistent sources, utilities employ energy storage systems alongside renewable sources and rely on dispatching synchronous generators. However, optimal dispatch of such devices is limited by traditional AC optimal power flow methods that do not account for time-dependent constraints, such as the state of charge of energy storage systems and generator ramping constraints. Multi-period optimal power flow is proposed as a large non-convex non-linear problem to optimally dispatch and control generators and energy storage elements across multiple time periods. In this paper, we introduce a scalable, robust framework to solve multi-period optimal power flow using a differential dynamic programming scheme that makes it capable of scaling to large systems containing energy storage devices. We demonstrate the efficacy of this solution by optimizing the SyntheticUSA testcase over a set of time periods. A robust homotopy method is applied to achieve fast simulation times that can be parallelized for further improvements. [ABSTRACT FROM AUTHOR]

Modulation ratio is an important index for power converters, which is related to the circuit parameter selection, converter transformer taps changing, control scheme design, etc. Nevertheless, the modulation ratio in modular multilevel converters (MMC) has not been well studied yet, and in most cases, it is used by referring to the modulation ratio of two-level converters. However, considering the particular features of MMCs, whether the modulation ratio can likewise be applied for MMCs is required to be studied. This article found that there are three problems lying in the modulation ratio of MMCs; as a result, the modulation ratio cannot always accurately reflect the modulation characteristics of MMCs. The study concluded that, in evaluating the overmodulation risk of MMCs, the modulation ratio is only accurate in the situation where the circulating current suppression controller is adopted in the control scheme. Using modulation ratio as the substitution of the amplitude of fundamental modulation signal can introduce large errors (from −15.63% to 12.74% in case studies), except when the MMC mainly outputs/consumes the active power. Finally, the analyses and conclusions are verified by the Zhangbei HVDC project based on the RT-Lab platform and by the 5 kVA/400 V downscaled MMC prototype. [ABSTRACT FROM AUTHOR]

Distributed narrowband active noise control (NANC) systems using diffusion filtered-x least mean square (FxLMS) algorithm can effectively suppress the low-frequency periodic noise generated by rotating machinery. The computational burden is dispersed among the nodes over the acoustic sensor networks. The frequency of the reference signal is usually identified by a non-acoustic sensor in a NANC system. However, the frequency of the reference signal will be different from the primary noise frequency due to inevitable aging and fatigue accumulation and the control performance of NANC degrades considerably. This phenomenon is referred to as frequency mismatch (FM). In this letter, we analyze the performance degradation of the diffusion FxLMS algorithm due to FM in an NANC system. A theoretical model of the diffusion FxLMS algorithm in the presence of FM is derived based on the equivalent transfer function approach. Extensive simulations are performed to confirm the validity of the theoretical analysis. [ABSTRACT FROM AUTHOR]

In this article, we propose steady-state modeling of dc–dc converters driven by multiple pulsewidth modulation (PWM) signals. The proposed dc–dc converter modeling uses a switched state-space framework, and the switching signal discontinuities are represented by a Fourier series to obtain the average model. The advantage of the proposed modeling is that it is not dependent on the dc–dc converter topology, and the dimension of the state-space model does not increase with the number of storage devices. Additionally, the duty cycle and phase displacements among the driving PWM signals can be arbitrary and systematically modeled. The effectiveness of the proposed modeling is supported by simulation and experimental results. [ABSTRACT FROM AUTHOR]

In designing Molten Salt Reactors, implementing passive safety systems that rely on natural circulation phenomena can be an attractive proposal to remove decay heat from the core. In this type of reactor, when the active cooling system fails, the fuel-coolant salt flows by natural circulation in the presence of Internal Heat Generation due to the fuel dissolved and mixed within the coolant salt. Adopting a Natural Circulation Loop for the dissipation of the heat generated can be an attractive safety system, but it is affected by some undesired phenomena regarding flow mass rate oscillation, which influences the heat transfer efficiency and local temperature. In particular, it is necessary to understand the influence of the Natural Circulation loop on the internal stability of the reactor. The purpose of the DYNASTY-eDYNASTY facility (DYnamics of NAtural circulation for molten SalT internallY heated), built at Politecnico di Milano, is to investigate the dynamical effects manifesting in a Coupled Natural Circulation Loops and to get insights about the phenomenology which can result relevant for the study of accidental scenarios in Molten Salt Reactors, simulating the natural circulation in the reactor and the Natural Circulation Loop of the passive safety system. This paper, starting from the one-dimensional model of the DYNASTY-eDYNASTY facility, develops a in-house code for the computation of the steady states and a Stability Map for the stability analysis of the Coupled Natural Circulation Loops. Verification of the results has been carried out by comparing the outcomes derived from the MODELICA model of the DYNASTY-eDYNASTY facility adopting the DYMOLA® environment. The steady-state model can predict the results of the DYMOLA® simulations with acceptable accordance, and the verification of the Stability Map with DYMOLA® simulations highlighted a good prediction of the model developed for the stability analysis. [ABSTRACT FROM AUTHOR]

Increasing penetration of power electronics is changing the understanding of modern power systems. In particular, current saturation of converters leads to multiple equilibrium points for both normal and short-circuit conditions. This paper aims to identify equilibrium points in power systems with penetration of power electronics. First, a steady-state model of power systems considering the power electronics operation is presented. Then, a general methodology is developed to obtain equilibrium points including all possible combinations of converter current saturation states. A system of equations is defined for each combination and is solved considering the possibility to have single or multiple solutions. This methodology is suitable for steady-state analysis in normal operation and during short-circuit scenarios. Test systems with Voltage Source Converters are used to validate the presented methodology.

This work proposes positive- and negative-sequence equivalent circuits of grid-forming inverters for steady-state analysis. The proposed models are especially attractive for performing long-duration voltage regulation analysis and short-circuit studies involving grid-forming inverters. Our proposed equivalent circuit models are based on the inverter’s voltage and current control loops in the $\alpha \beta $ and dq frames. For this reason, they operate according to prescribed control functions and specified impedances (i.e., filter impedance, current limiter block, virtual admittance block, and PI/PR controller block). The equivalent circuit model accuracy is validated by comparing system steady-state voltage and current responses obtained by detailed time-domain models in PSCAD/EMTDC to those by the equivalent circuit models implemented in steady-state load flow program (e.g., OpenDSS). Two distinct control structures implemented in the $\alpha \beta $ and dq frames are used for the validation. Single line-to-ground and line-to-line-to-ground faults are simulated in a small islanded microgrid as well as the IEEE 34-node test feeder. Fault impedances varying from 0 to 5 ohms are simulated. We show that the equivalent models precisely replicate the steady-state response of the detailed time-domain models.

This paper introduces the concept of inductors asymmetric input voltage to derive a new high voltage gain converter. The proposed converter has continuous input, positive output, and high-power density features suitable for renewable energy applications. The operating principle, steady-state performance, practical voltage gain, small-signal analysis, and efficiency of the converter are presented in this work. A comprehensive comparison is made with the high voltage gain converters available in literature in terms of component count, voltage gain, effectiveness index, voltage and current stress on the power devices, per unit switching device rating, and other features like output polarity and availability of common ground. The proposed topology possesses a higher effectiveness index and lower switching device power rating (SDP), resulting in a good form factor. To validate the performance of the proposed converter, the experiments are conducted on the 150 W laboratory prototype, and corresponding results are presented in this work.