Digital Simulation Results Research Articles

Enhancing the Performance of Pre-Charging Strategy of a Modular Multilevel Static Synchronous Compensator

This paper presents an improvement in an energizing strategy for a three-phase four-wire modular multilevel converter connected to an electric network as a static synchronous compensator. The new procedure comprises three stages. During the first stage, two thyristors control the current drained from the grid in order to charge the capacitors of the submodules of the positive and negative arms of two phases of the converter. After that, the energy stored in these capacitors is shared with the others submodule capacitors by firing the semiconductor switches of the converter in a strategic way. In addition of limiting the current drained from the grid during all the energizing procedure, the proposed strategy does not produce overvoltage at the converter dc terminals. The results of digital simulations are presented to validate the mathematical analysis and to demonstrate the performance of the proposed energizing strategy.

A new approach to extract reference currents for multilevel shunt active filter in three phase systems

<span lang="EN-US">In this article, we present a new study of technique to extract reference currents for three-level shunt active filter controlling by fuzzy logic. The APFs is realized using three phase voltage and the carrier-based PWM strategy. A new technique for identifying reference currents will be developed. It is based on concordia method using multi-variable filter, and makes the total or selective extraction harmonic currents of references, and by consequence making their compensations, total or selective. The results of digital simulation in the Matlab-Simulink environment of a system of power to thyristor outputs on an inductive load show well the effectiveness of this new technique of extraction of the harmonics of reference.</span><p> </p>

Evolving Fuzzy Models for Prosthetic Hand Myoelectric-Based Control

This article applies an incremental online identification algorithm to develop a set of evolving fuzzy models (FMs) that characterize the nonlinear finger dynamics of the human hand for the myoelectric (ME)-based control of a prosthetic hand. The FM inputs are the ME signals obtained from eight ME sensors and past inputs and/or outputs. The FM outputs are the finger angles, considered here as the midcarpal joint angles, to ensure their control. The best evolving FMs that characterize each of the five fingers are described with the results validated on real data. Simple second-order linear models are next given to enable the cost-effective controller design. Five separate control loops are proposed, with proportional-integral (PI) controllers separately tuned by a frequency-domain approach. Simple PI-fuzzy controllers are designed starting with the linear PI controllers to ensure the control system performance improvement. The evolving FMs are used to simulate accurately the behavior of the human hand. Digital simulation results are included to show the effectiveness of the PI-fuzzy controllers and the performance improvement in comparison to the initial PI ones.

An Improved Impedance Measurement Method for Grid-Connected Inverter Systems Considering the Background Harmonics and Frequency Deviation

The impedance of inverter and grid is to determine the stability of grid-connected inverter systems. Therefore, it is of great importance to obtain accurate grid impedance and inverter impedance. However, the previous studies on impedance measurement are easily subject to background harmonics and grid frequency deviation, which brings to nonunique identification and inaccurate extraction of current or voltage perturbations. In this article, an improved impedance measurement method is investigated for the grid-connected inverter systems. First, a novel selection principle of frequency for injected perturbation is proposed to avoid the impact of background harmonics on impedance measurement. Moreover, a two-stage series multiple-complex coefficient filter (TSMCCF) is also proposed to accurately extract these perturbations considering system may subject to harmonics and grid frequency deviation. Compared with the conventional MCCF, the proposed TSMCCF improves the dynamic performance and accuracy of impedance measurement without increasing the complexity. It is worth noting that the proposed method is not affected by background harmonics and grid frequency deviation, and could be applied in both three-phase and single-phase systems for impedance measurement. To validate the effectiveness and feasibility of the proposed impedance measurement method, real-time digital simulation results are presented based on the RT-LAB platform.

Photovoltaic-Wind and Hybrid Energy Storage Integrated Multisource Converter Configuration-Based Grid-Interactive Microgrid

In this article, a new dc–dc multisource converter configuration-based grid-interactive microgrid consisting of photovoltaic (PV), wind, and hybrid energy storage (HES) is proposed. Control structure along with power sharing scheme to operate the system under various operating modes, such as: 1) grid-connected mode; 2) islanded mode; 3) state of charge of battery ( $SoC_{b}$ ) less than or greater than specified limits; and 4) operating renewable sources (PV and wind) at maximum power point, is presented. The detailed analysis, modeling, and design of the proposed configuration and control structure are presented. The key highlights of the proposed configuration are: 1) low component count; 2) voltage boosting, voltage regulation of supercapacitor and power-sharing among the battery and supercapacitor are inherent; and 3) simple control structure with a reduced number of sensors. Supercapacitor-battery-based HES is interfaced which effectively handle the power fluctuations due to the wind, PV, and sudden load disturbances. Integration of supercapacitor to respond to high-frequency fluctuations increases the lifetime of battery storage and reduces the sizing of the storage unit. The proposed system is verified through digital simulation and experimental results.

Control algorithm for DSTATCOM to compensate consumer-generated negative and zero sequence voltage unbalance

This paper presents a control algorithm, based on consumer-generated voltage imbalance assessment, for a distribution static synchronous compensator (DSTATCOM). The proposed algorithm quantifies, in the time-domain, the parcels of voltage unbalance due to the supplier (utility) and consumer using measurements of the instantaneous voltages and currents at the point of common coupling. Small-signals models are derived and used to design the controllers for the DSTATCOM in order to compensate for the negative and zero sequence voltages caused by the consumer. These controllers are designed in the synchronous reference frame, with two inner current loops and two outer voltage loops for each compensated sequence, to ensure the DSTATCOM tracks the reference voltages generated by the unbalance assessment algorithm. Digital simulation results obtained with an unbalanced distribution network are used to validate the proposed methodology. Through the comparison of the results obtained with and without the proposed unbalance assessment algorithm it is possible to conclude that the capacity of the compensator can be significantly reduced when only the unbalanced voltage parcel caused by the load is compensated.

Modeling and Control Design of an Autonomous Hybrid Wind/Energy Storage Generation Unit

The purpose of the present paper is to investigate a controller design and simulations of autonomous hybrid wind turbine system with variable-speed permanent magnet synchronous generator (PMSG) and a system for storing energy. The proposed system is mainly composed of a wind turbine drives permanent magnet synchronous generator, uncontrolled rectifier, DC/DC converter, DC/AC inverter and static loads. Furthermore, the mathematical model of the studied sub-systems and two control loops are considered. The first one is the controller which needed to preserve the DC-link voltage fixed at its desired value. The second one is the controller which needed to regulate the charge/discharge modes of the storage battery. The suggested hybrid wind/energy storage power generation model is considered and analyzed in case of without controller firstly. Then, the considered hybrid wind/energy storage power generation unit with the proposed controller is examined through a step change in wind speed. Digital simulation results show that the power desired by the linked loads may be successfully supplied and transported by the presented hybrid wind turbine and energy storage power generation system based on proportional-integral-derivative (PID) controller. Also, the emulation results show that there a good foretelling of the electrical variable waveforms and good achievement in case of the presented controller emulated with the case of without controller as maintaining the load voltage fixed at its reference values

Power Quality Assessment and Event Detection in Distribution Network With Wind Energy Penetration Using Stockwell Transform and Fuzzy Clustering

Power quality (PQ) is a vital issue in the present power systems integrated with large renewable energy sources since more power electronics devices are incorporated in the system. This article proposes a novel method for assessing PQ associated with wind energy integration. This method is effective to recognize PQ issues in power systems with high penetration of wind energy with a low computational burden. Furthermore, it detects different operational issues in the distribution network. Stockwell transform (S-transform) is utilized to decompose the voltage signal and calculate the S-matrix. To assess the PQ, a plot is developed from this matrix. The features of this matrix such as mean, standard deviation, and maximum deviation are further utilized for detecting the operational issues such as wind speed variation, islanding, synchronization, and outage of the wind generation by using clustering with fuzzy C-means. A modified IEEE 13-bus test system is utilized to validate the proposed method, which is also supported by hardware and real-time digital simulator results. The quality of power is graded with the help of a proposed PQ index under various operational events with different levels of wind energy penetration. The proposed method is effective for the identification and grading of different operational events in terms of PQ and recognizing a wide range of PQ issues with a high share of wind energy. The performance of the proposed scheme is established by comparing its results with other approaches.

Seismic Behavior Analysis of Damaged Steel Fiber‐Reinforced High‐Strength Concrete Frame Joints Strengthened by FRP

In this paper, the seismic behavior of fiber‐reinforced polymer (FRP) strengthened and unstrengthened steel fiber‐reinforced high‐strength concrete frame joints under low cyclic loading was tested. Then, the nonlinear finite element program was used to simulate the seismic behavior of FRP strengthened and unstrengthened steel fiber‐reinforced high‐strength concrete frame joints under low cyclic repeated load. The influence of FRP bond direction on the seismic behavior of steel fiber‐reinforced high‐strength concrete frame joints was studied. Through the comparison of the test values and numerical simulation values of the hysteretic curve, skeleton curve, energy dissipation capacity, displacement ductility, bearing capacity degradation, stiffness degradation, and other performance indexes of frame joints, the rule was obtained. The results showed that the 45° bonding direction of carbon fiber cloth is better than the 0° bonding direction, and the digital simulation results are in good agreement with the test results. Therefore, the constitutive model, element, end constraint, and loading method used in the finite element numerical simulation of this paper were reasonable, which can provide reference for the similar research in the future.

Experimental Validation of Solar Photovoltaic-Based Unified Power Quality Conditioner with Modified Power Angle Control Scheme

Abstract This article proposes a modified Power Angle Control (PAC) strategy for a Unified Power Quality Conditioner (UPQC) with Distributed Generation (DG) for the viable interconnection of a Solar Photovoltaic (SPV) system into the network. The UPQC is composed of both shunt and series Active Power Filters (APFs). Shunt and series APFs are the standout among the best custom power devices, which gives compensation to current- and voltage-based unsettling influences distinctly. In the SPV-interconnected UPQC, the shunt APF supplies power from DG to the associated load, apart from providing a reactive power request, which prompts an expansion in the Volt-Ampere (VA) burden after its rating. The PAC scheme intends the successful use of series and shunt APFs through the sharing of reactive power to decrease the VA burden on shunt APF. The PAC strategy depends on an enhanced Synchronous Reference Frame that is equipped with a Second-Order Generalized Integrator–based Phase Locked Loop, which has simple calculations, is vibrant, and utilizes existing estimations of the SPV-incorporated UPQC. The execution of the proposed SPV-incorporated UPQC is examined with the presence of nonlinear and reactive burdens. The dynamic performance of the SPV-UPQC is checked under the grid disturbances, for example, voltage sag, swell, varying load, and change in sunlight-based light. The viability of the proposed control strategy is assessed through the digital simulation and equipment exploratory model results.

A Compensation Strategy Based on Consumer's Voltage Unbalance Assessment for a Distribution Static Synchronous Compensator

This paper presents a new control algorithm for a distribution static synchronous compensator (DSTATCOM) based on consumer's voltage unbalance assessment. The proposed controller quantifies, in real time, the parcels of voltage unbalances due to the supplier (utility) and consumer by using local measurements of voltages and currents. The compensator mathematical model is used to derive small signal models in such a way to design controllers to compensate for the negative sequence voltage caused by a consumer. Two inner control loops, designed in synchronous reference frame, assure the DSTATCOM tracks the reference signals generated by the voltage controllers. Digital simulation results obtained with an unbalanced distribution network are used to validate the proposed methodology. The comparison of the results shows that the capacity of the compensator can be significantly reduced when only the unbalanced voltage portion caused by the load is compensated.

P.397 Differences in facial emotion recognition and mental state facial recognition in a population with schizophrenia

This paper proposes a novel energizing strategy for a three-phase modular multilevel converter connected to the electric network as static synchronous compensator. The energizing system is comprised of two thyristors and its controller. A comprehensive mathematical model is developed for each energizing stage. Based on the models, a control law is designed in order to compute the thyristors firing angle. This is performed in such a way that the maximum value of the energizing current drained from the grid is limited. First, during the positive half-cycle of the mains voltage, the current flows through two arms of the modular converter charging its DC capacitors. In the following half-cycles, the pre-charged capacitors transfer part of their stored energy to the other arms capacitors. The process is repeated until the total DC voltage of the modular converter reaches the grid voltage peak value. Digital simulation results are presented to validate the proposed methodology.

Coupling well hydrodynamic tests data with results of digital simulation for better identification of reservoir properties

In the study the existing approaches for stabilization time estimation are given and compared with the results of hydrodynamic simulation. A deviation from an assumed ellipsoid shape of drainage area has been observed for a horizontal well based on the simulation results. Then this geometrical definite form was taken into account in the gas influx equation. On its basis the time period of pseudo-steady state was estimated. As a result, stabilized horizontal gas well tests are considered to be not effective as the time period is too long when pseudo-steady state is reached and it’s impossible to carry out the test in reality. However, it is suggested to continue a well test for a reduced period by adapting well tests on the model and matching simulation output with gauge measurements.

Electrochemical synthesis of a new phosphonium betaine. Kinetic evaluation and antibacterial susceptibility

Cyclic voltammetry, controlled-potential coulometry, chronoamperometry, chronocoulometry and chronopotentiometry methods were used for the electrochemical study of 1-acetyl-4-(4-hydroxyphenyl)piperazine (APIP) in the presence of triphenylphosphine (TPP) as a nucleophile. The data show that electrochemically generated APIPox can serve as a Michael acceptor for nucleophilic attack by TPP to yield a new phosphonium betaine (APTP). In this work, we prepared a new product in good yield and purity by reaction of TPP with APIPox in an undivided cell equipped with carbon anode. Based on an EC mechanism, the observed homogeneous rate constant (kobs) of the Michael addition reaction of APIPox with TPP were estimated by comparing the experimental cyclic voltammograms with the digital simulated results. Furthermore, electrochemical oxidation of APIP has been studied both experimentally and theoretically to provide insight into the influence of natural charge and thermodynamic stability parameters on the type of chemical reaction which follows APIPox. In addition, the synthesized compound was evaluated for in vitro antibacterial.

Second Order Sliding Mode Control of the Output Voltage of an Alternative Power Source in a Single-Phase Grid

The object of the study is an alternative power source of sinusoidal voltage, consisting of a PWM bridge frequency converter, a single-phase linear output transformer with an additional output LC-filter, which is connected to a non-autonomous grid. An additional inductance is inserted into the primary winding of the transformer to reduce current ripples. The mathematical model of this system, which is described by ordinary differential equations, is constructed. Usual assumptions are used that the system of equations is linear, and the current of the magnetization of the transformer can be neglected. Therefore, a transition to a simplified circuit for replacing a single-phase transformer is possible. The synthesis of the control law by means of the forced introduction of the traditional sliding mode for minimizing the influence of perturbations on the source output voltage is carried out. Conditions of the existence of a sliding mode with the use of the known method of equivalent control are obtained. In the formation of a sliding surface, a sliding mode of the second order was used, which made it possible to reduce the number of quantities of electric variables that require direct measurement. The proposed strategy allows achieving more robustness, acceptable steady state error, exponential convergence, and good matching of the output voltage of the source for the autonomous consumer network. This strategy eliminates the need to use an accurate current sensor, which reduces the cost of the frequency converter and facilitates practical implementation. The features of the functioning of an alternative energy source with this type of sliding mode in a system with real parameters of electric circuits are investigated. The comparisons are presented as simulations among conventional sliding mode (first order) control and second order sliding mode in a sliding surface at different test conditions, such as stationary state, grid voltage perturbations and output load disturbances. The results of digital simulation are presented. Simulation was performed taking into account the constraints inherent in the real object of power electronics and influencing the possibility of technical implementation of the developed control strategy. In the mode of minimum dissipation there is a very slight deterioration of the spectral composition of the voltage, which can be neglected. The possibility of reducing the effect of load changes on the form of the output voltage has been considered, taking into account the constraints specific to real systems, and has been verified using digital simulation. Ref. 14, fig. 4

Evaluating seepage radius of tight oil reservoir using digital core modeling approach

The main development method of tight oil was depletion development. It is determined that the seepage radius of tight reservoir is crucial to the layout and prediction development of tight oil development. Since the pore throat level of tight reservoirs was frequently nanoscale, the reservoir pressure propagation velocity was even faster than conventional medium high permeability. The fracture system in the tight oil reservoir, which is the main flow channel of oil flow to the direction of wellbore, is more sensitive to the sharp change in reservoir pressure. Hence, the stress-sensitive absolute permeability of the reservoir near the wellbore will fluctuate significantly during the depletion development phase, rather than a constant value. At present, the numerical simulation and graph method, which are commonly utilized in the regression and prediction of the depletion-developing seepage radius. Both do not consider the stress sensitivity phenomenon which caused by nanoscale pores of tight oil and the change of the permeability in the model. As a result, the prediction is not accurate and the model needs to be modified. Meanwhile, the percolation parameters at the scale of the tight oil permeability cannot be accurately obtained in using conventional experimental methods owing to the limitations of the accuracy of the experimental instruments. In this paper, the test of fluid permeability under overburden was carried out to verify the stress sensitivity of the tight core. The microscopic mechanism of nanoscale pore-throat stress sensitivity in tight reservoirs was analyzed from the perspective of tight reservoir mineral composition and nanopore characteristics by using Quantitative Evaluation of Minerals by Scanning Electron Microscopy (Qemscan) and MAPS micro-image splicing technology. Nanoscale pore network model was established with nano-CT scanning and the digital core seepage simulation of tight core was figured out. The accuracy of the digital core seepage simulation method was verified in comparison with the indoor over pressure liquid permeability test. The conventional reservoir model was modified by using the digital core seepage simulation result, and the new model has a high degree of confidence in predicting the tight oil seepage radius.

A novel energizing strategy for a grid-connected modular multilevel converter operating as static synchronous compensator

This paper proposes a novel energizing strategy for a three-phase modular multilevel converter connected to the electric network as static synchronous compensator. The energizing system is comprised of two thyristors and its controller. A comprehensive mathematical model is developed for each energizing stage. Based on the models, a control law is designed in order to compute the thyristors firing angle. This is performed in such a way that the maximum value of the energizing current drained from the grid is limited. First, during the positive half-cycle of the mains voltage, the current flows through two arms of the modular converter charging its DC capacitors. In the following half-cycles, the pre-charged capacitors transfer part of their stored energy to the other arms capacitors. The process is repeated until the total DC voltage of the modular converter reaches the grid voltage peak value. Digital simulation results are presented to validate the proposed methodology.

Small current ground fault location method based on Hilbert transform

A new method for small current grounding system single-phase-to grounding fault location used transient component and Hilbert transform is proposed. The feeder terminal unit detects zero-mode current and line voltage signals, First, perform the Hilbert transform on the transient line voltage, Then multiply the line voltage after the Hilbert transform with the zero-mode current, defined the product as fault direction parameter. The FA master determines the line segment where the fault point is located based on the characteristics of the opposite polarity of the front and rear direction parameters of the fault point. The results of digital simulation prove that the proposed method has certain feasibility.

Digital beamform simulation in anechoic chamber

The results of digital beamform simulation, principles of processing and use of the obtained experimental data are presented. Methods were developed and an experimental setup was created for full- scale modeling and measurement of the characteristics of digital antenna systems with spatio-temporal signal processing at the Scientific and Production Center for Radio Information Metrology of the Moscow Aviation Institute (SPC RIM MAI).

Interface algorithm development for PHIL simulations of MMC‐HVDC devices via real‐time impedance matching

Power hardware-in-the-loop (PHIL) simulation combines the advantages of digital and physical simulations, which is an effective method to study and analyse modular multi-level-converter-based high-voltage direct current (MMC-HVDC) technology. For the damping impedance method (DIM) interface algorithm, a real-time impedance matching method is proposed to improve the stability and accuracy of the PHIL simulation system. The equivalent impedance between the power interface and the MMC converter station is calculated according to the voltage difference and current between them, and the equivalent impedance parameters of MMC, in both de-blocking and blocking modes, are obtained by the Thevenin equivalent models; then the information of the hardware under test impedance is used to update the DIM interface algorithm. In addition, a compensation control method for interface delay is used to reduce the system error. The excellent performance of stability and accuracy is verified by digital simulation results, which show that the proposed DIM interface algorithm is able to keep the PHIL simulation system stable under different kinds of disturbances and the maximum relative error of the active power <1.2%.