Digital Simulation Results Research Articles

Image encryption and decryption using fractional Fourier transform and radial Hilbert transform

A technique for image encryption using fractional Fourier transform (FRT) and radial Hilbert transform (RHT) is proposed. The spatial frequency spectrum of the image to be encrypted is first segregated into two parts/channels using RHT, and image subtraction technique. Each of these channels is encrypted independently using double random phase encoding in the FRT domain. The different fractional orders and random phase masks used during the process of encryption and decryption are the keys to enhance the security of the proposed system. The algorithms to implement the proposed encryption and decryption scheme are discussed, and results of digital simulation are presented.

Scanning Electrochemical Microscopy. 60. Quantitative Calibration of the SECM Substrate Generation/Tip Collection Mode and Its Use for the Study of the Oxygen Reduction Mechanism

The substrate generation/tip collection (SG/TC) mode of scanning electrochemical microscopy (SECM) coupled with linear voltammetry is proposed as a way to quantify reaction intermediates generated in the solution at small substrates (100 mum diameter). The collection efficiency (CE) for SG/TC mode depends on the collector tip radius (a), the tip/substrate distance (d), and the size of the insulating glass sheath surrounding the collector tip (RG). In this work, we present experimental and simulated calibration CE values for different SG/TC geometries. Results of digital simulations in axial 2-D symmetry with the tip approaching a planar substrate are shown and fit experimental results obtained using ferrocenemethanol as a redox mediator very well. This model assumes that the mediator reacts under stationary-state conditions and undergoes diffusion-controlled electron transfer without any heterogeneous or homogeneous kinetic complications. Empirical equations for all SG/TC geometries reported here are provided as a convenient way to predict the maximum CE value for any given distance within the calibration range. Hydrogen peroxide quantification during the oxygen reduction reaction (ORR) at a Hg on Au electrode in acid pH was carried out using the SG/TC mode of SECM to demonstrate the utility of this technique in determining the number of electrons transferred (n) in the ORR. The results (n = 2.12-2.19) clearly point out the predominance of the two-electron pathway over the four-electron pathway when ORR takes place at this electrode material. Therefore, this work presents a powerful alternative to the rotating ring-disk electrode (RRDE) as means of obtaining mechanistic information by calculating the number of electrons transferred during an electrochemical reaction.

Intelligent Fuzzy Optimal Active and Combinatorial Control System of Building Structures

The authors have already proposed an intelligent fuzzy optimal and active control system (IFOACS) and the effectiveness of IFOACS was proved using digital simulations and shaking table tests. However, the results show that the control effect of IFOACS becomes small in case of near-source region earthquakes. To improve control effects in case of near-source region earthquakes, a combinatorial control system (CCS), in which IFOACS is combined with a fuzzy active control system (FACS), is also proposed. In this paper, control rules in CCS are optimized using parameter-free genetic algorithms (PfGAs) considering limitations of an actuator such as maximal strokes and control forces. Effectiveness of proposed combinatorial control system (CCS) is verified and discussed based on results of digital simulations.

A novel control scheme for electric vehicle EV-drive

The paper presents a novel non-linear error-driven error-scaled multi-loop dynamic speed control scheme for electric vehicle EV-PMDC drives. The proposed controller is a dynamic self-adjusting regulator to ensure satisfactory reference speed tracking, minimum inrush PMDC-motor current and minimum impact on the limited battery source capacity. It handles the inherent non linearity in the EV-drive moment of inertia, frictional coefficient and load torques. The full four motor EV-drive is fed from a DC source battery with type-B DC-DC converter (chopper) – a pulse-width modulated strategy that is fully modulated, using the non-linear multi-loop dynamic error-driven control scheme. As a comparison, a classical PID scheme is also presented. Digital simulation results show the effectiveness of the non-linear multi-loop control strategy and its robustness to tolerate load non-linearities, especially in combined inertia, frictional coefficient and load torques.

Underpotential dissolution of metals under conditions of partial mass-transport control

Underpotential dissolution was studied over a wide range of concentrations, from complete diffusion control to surface control, assuming reversibility. Applicability of the Frumkin isotherm was assumed. Digital simulation was employed, showing the dependence of the parameters of the UPD, E peak, j peak and W 1/2 on the concentration and the sweep rate. A strong influence of the Frumkin parameter, f, on the parameters of the UPD was demonstrated. Anodic dissolution under diffusion control shows no dependence of E peak, j peak on c bulk, at constant sweep rate. In contrast, under pure surface control the peak current is independent of concentration and the peak potential changes with concentration following the Nernst equation. A dimensionless parameter P was used, to allow easy demarcation of the regions of diffusion, mixed and surface control. Empirical equations were obtained for the values of E peak, j peak and W 1/2 as a function of the experimental parameters, under conditions of pure diffusion control. The experimental system studied was lead on polycrystalline silver. The characteristic dissolution parameters of the UPD process were determined for a wide range of concentrations of PbCl 2 in 0.1 M HCl (1 × 10 −6 to 7 × 10 −3 M), scan rates of 10–50 mV/s and initial fractional surface coverage ranging from 0.1 to 1. In the range accessible experimentally, very good agreement with the results of digital simulation was found, for f = −2.05 ± 0.1. The formal potential for UPD formation was found to be E UPD ∘ ′ = - 293 mV vs . Ag / AgCl / 1 M HCl , which is 88 mV positive with respect to the formal potential for OPD deposition of lead in the same system.

An analytical method for predicting current harmonics produced by an ac/dc converter under unbalanced supply voltage

This paper proposes an analytical method for calculating both characteristic and uncharacteristic harmonic currents produced by a six-pulse AC/DC converter under unbalanced supply voltage. The method allows the mathematical relationship between the complex unbalance factor (i. e. ratio of negative-sequence voltage to positive-sequence voltage) and the resulting harmonic currents (magnitudes and phases) to be found. An approximate harmonic model derived from the analysis is also proposed. Comparisons between the basic analytical model, the approximate model and the digital simulation results are given to validate the analysis.

Color image encryption and decryption using fractional Fourier transform

We propose the encryption of color images using fractional Fourier transform (FRT). The image to be encrypted is first segregated into three color channels: red, green, and blue. Each of these channels is encrypted independently using double random phase encoding in the FRT domain. The different fractional orders and random phase masks used during the process of encryption and decryption are the keys to enhance the security of the proposed system. The algorithms to implement the proposed encryption and decryption scheme are discussed, and results of digital simulation are presented. The technique is shown to be a powerful one for colored text encryption. We also outline the implementation of the algorithm and examine its sensitiveness to changes in the fractional order during decryption.

APPLICATIONS OF POLE SHIFTING SELF TUNING SPEED GOVERNOR CONTROLLERS FOR MULTIMACHINE POWER SYSTEMS

Examination of the performance of fixed parameter controllers has resulted in the development of pole shifting strategies for speed governor control of multimachine power system. For a pole shifting controller design an input signal is incorporated in the self tuner. This input signal is of a composite output term of the terminal voltage and the rotor speed deviation of each generating unit. The control is based on a criterion which automatically generates a pole-shifting factor to shift the closed loop poles of the system towards the origin in the z domain without violating the control constraints. The pole-shifting factor is depicted on line at each sampling instant depending on the error measurements of the terminal voltage of each generating unit. The output of the pole shifting controller is fed in the summing point of the speed governor of each unit of the multimachine power system. Digital simulations of a 9 bus, 3 machine of a multimachine power system are performed and the comparisons of conventional governor control and self tuning control performances are presented. Nonlinear digital simulation results show the effectiveness of the proposed technique to damp out the oscillation and work effectively over a wide range of loading conditions.

Wavelet ANN Based Stator Ground Fault Protection Scheme for Turbo Generators

This article proposes a protection scheme for turbo generators to detect stator ground faults in particular closer to neutral. The scheme considers total generated voltage of the machine and makes use of wavelet multi-resolution analysis. A fault index is defined in terms of peak and valley values of the highest-level wavelet decomposition, which is compared with a threshold value to discriminate from other transients, like sudden unbalance, in load. To identify the faulty coil, an ANN employing back propagation algorithm is used with the lowest level wavelet coefficients as inputs. The results of digital simulation are presented for different fault impedances and fault locations.

EFFICIENT FUZZY LOGIC DESIGN TO IMPROVE DYNAMIC STABILITY OF LATERAL LANDING AUTOPILOT

In this paper, lateral beam guidance autopilot system has considered as an aerospace application. The construction and derivation of the equations of motion is considered and partial modification in internal construction of the autopilot has performed. Proposed efficient fuzzy logic and robust compensator control have applied to the lateral beam autopilot system to increase damping oscillation. Moreover, for comparisons the conventional optimal control has designed and evaluated. The robustness and convergence of the system due to the stability derivatives variations are studied. Efficient fuzzy logic control is preferred for this system where, it does not require the complex mathematics associated with conventional control techniques. The digital simulation results show the effectiveness of the proposed fuzzy logic and LQG controllers in terms of fast damping the oscillations, small settling time, and less over/under shoots.

Study of the oxidation of some catechols in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole by digital simulation of cyclic voltammograms

AbstractElectrochemical oxidation of catechol and its derivatives (1a–d) has been studied in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole (3) at various pHs. Some electrochemical techniques such as cyclic voltammetry using the diagnostic criteria derived by Nicholson and Shain for various electrode mechanisms and controlled‐potential coulometry were used. Results indicate the participation of catechols (1a–d) with 3 in an intramolecular cyclization reaction to form the corresponding 1,2,4‐triazino[5,4‐b]‐1,3,4‐thiadiazine derivatives. In various scan rates, based on an electron transfer–chemical reaction–electron transfer–chemical reaction mechanism, the observed homogeneous rate constants (kobs) for Michael addition reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results. The oxidation reaction mechanism of catechols (1a–d) in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole (3) was also studied. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 340–345, 2007

A nonlinear control for enhancing HVDC light transmission system stability

The purpose of this paper is to study the mathematical model and its control strategy of HVDC Light transmission system in order to enhance system stability. In this paper, the steady state mathematical model for the HVDC Light system is developed and the decoupled relationship between the controlling variables is proposed. An appropriate controller utilizing nonlinear control for HVDC Light system is proposed to maintain the dc link voltage and control the active and reactive power. The control is not complex. Basic functions of HVDC Light system can be realized. What is further, better performances are obtained when compared with a traditional control. The digital simulation results show that the proposed nonlinear control is effective to damp system oscillations and enhance system stability.

A new approach to identification of structural damping ratios

A new approach to identification of modal damping ratios from free vibration response of a linear structure with viscous damping is proposed in this paper. For a single degree of freedom (dof) system, the formulated relations among areas forming from time history of response are used to determine the damping ratio for the free decay vibration. Comparing with traditional logarithmic-decrement method, the approach in this paper has advantages such as stronger anti-noise ability, higher precision, better stability and convenience. For a multi-dof system, the free vibration response measured at one point on the structure is expressed in an analytical form at first, and then multiplied by e at . Giving the initial value, a can be obtained by Newton's dichotomy or golden section method while the product of the response and e at has equal vibration amplitudes after a period of time. Accordingly, the damping ratio for this mode can be determined. Repeating the above-mentioned process, all damping ratios for different modes can be obtained in the same way. Results of digital simulations and field tests for the Dongting Lake Cable-stayed Bridge in Yueyang show that the approach presented in this paper is effective and practical.

Electrochemical nitration of catechols: Kinetic study by digital simulation of cyclic voltammograms

Electrochemical nitration of catechols has been studied in the presence of nitrite ion as nucleophile in aqueous solution, by means of cyclic voltammetry and controlled-potential coulometry. The results indicate the participation of produced o -benzoquinones in Michael reaction with nitrite ion to form the corresponding nitrocatechols. Based on EC mechanism, the observed homogeneous rate constants of nitration reaction were estimated by comparing the experimental cyclic voltammograms with the digital simulated results.

Kinetic study of electrochemically induced Michael reactions of o‐benzoquinones with 2‐acetylcyclohexanone and 2‐acetylcyclopentanone

AbstractThe reaction of electrochemically generated o‐benzoquinones (2a‐f) as Michael acceptors with 2‐acetylcyclohexanone (ACH) and 2‐acetylcyclopentanone (ACP), as nucleophiles has been studied in various pHs using cyclic voltammetry. The results indicate that the participation of o‐benzoquinones (2a‐f) in the Michael reaction with acetylcyclohexanone (ACH) to form the corresponding catechol derivatives (4a‐f). Based on an EC mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results. Copyright © 2007 John Wiley & Sons, Ltd.

A Novel Method of Load Compensation Under Unbalanced and Distorted Voltages

In this paper, load compensation techniques under unbalanced and distorted voltages have been discussed. Two kinds of compensation methods are considered. In the first category, synchronous detection and modified equal current strategies are used under the unbalanced but sinusoidal source voltages. In the second method, load compensation based on instantaneous symmetrical component theory with positive sequence extraction is proposed and is shown to work under unbalanced and the non-sinusoidal source voltages. To support the proposed method, a 440 V (L-L) three-phase, four-wire distribution system is considered. The compensator is realized using a three-phase voltage source inverter (VSI) operated in the current control mode. Detailed digital simulation and experimental results are presented to validate the approach

Adaptive neuro-fuzzy controller of switched reluctance motor

This paper presents an application of adaptive neuro-fuzzy (ANFIS) control for switched reluctance motor (SRM) speed. The ANFIS has the advantages of expert knowledge of the fuzzy inference system and the learning capability of neural networks. An adaptive neuro-fuzzy controller of the motor speed is then designed and simulated. Digital simulation results show that the designed ANFIS speed controller realizes a good dynamic behaviour of the motor, a perfect speed tracking with no overshoot and a good rejection of impact loads disturbance. The results of applying the adaptive neuro-fuzzy controller to a SRM give better performance and high robustness than those obtained by the application of a conventional controller (PI).

Compact autonomous explosive-driven pulsed power system based on a capacitive energy storage charged by a high-voltage shock-wave ferromagnetic generator

A new concept for constructing compact autonomous pulsed power systems is presented. This concept utilizes a high-voltage explosive-driven shock-wave ferromagnetic generator (FMG) as a charging source for capacitive energy storage. It has been experimentally demonstrated that miniature FMGs (22–25cm3 in size and 84–95g in mass) developed for these experiments can be successfully used to charge capacitor banks. The FMGs, containing Nd2Fe14B energy-carrying elements, provided pulsed powers of 35–45kW in times ranging from 10to15μs. A methodology was developed for digital simulation of the operation of the transverse FMG. Experimental results that were obtained are in a good agreement with the results of digital simulations.

Nonlinear controller design of thyristor controlled series compensation for damping inter-area power oscillation

A design method of nonlinear controllers of thyristor controlled series compensation (TCSC) for damping inter-area power oscillation based on direct feedback linearization (DFL) is presented in this paper. To damp inter-area power oscillation of power systems, the power modulation action of the TCSC is illustrated firstly. Then the nonlinear model of a two-area power system with the TCSC control is constructed, and is linearized by the DFL. Finally, the design of the nonlinear optimal controller of the TCSC has been completed using the criterion of integration for time and absolute error (ITAE). The digital simulation results using NETOMAC program and detail models show that the presented controller of the TCSC can efficiently improve inter-area power oscillation damping of power systems.

A high-performance sensorless indirect stator flux orientation control of induction motor drive

A new method for the implementation of a sensorless indirect stator-flux-oriented control (ISFOC) of induction motor drives with stator resistance tuning is proposed in this paper. The proposed method for the estimation of speed and stator resistance is based only on measurement of stator currents. The error of the measured q-axis current from its reference value feeds the proportional plus integral (PI) controller, the output of which is the estimated slip frequency. It is subtracted from the synchronous angular frequency, which is obtained from the output integral plus proportional (IP) rotor speed controller, to have the estimated rotor speed. For current regulation, this paper proposes a conventional PI controller with feedforward compensation terms in the synchronous frame. Owing to its advantages, an IP controller is used for rotor speed regulation. Stator resistance updating is based on the measured and reference d-axis stator current of an induction motor on d-q frame synchronously rotating with the stator flux vector. Experimental results for a 3-kW induction motor are presented and analyzed by using a dSpace system with DS1102 controller board based on the digital signal processor (DSP) TMS320C31. Digital simulation and experimental results are presented to show the improvement in performance of the proposed method.