Research Articles
Control
Omid Moradi; Saeed Abazari; Nima Mahdian
Abstract
This paper proposes a nonlinear model by an optimal stabilizing controller for weak/islanded grids using a unified power quality conditioner (UPQC). The UPQC can be employed to stabilize a grid-tie inverter (GTI) or a synchronous generator (SG) with minimum control effort. The idea that GTI behavior ...
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This paper proposes a nonlinear model by an optimal stabilizing controller for weak/islanded grids using a unified power quality conditioner (UPQC). The UPQC can be employed to stabilize a grid-tie inverter (GTI) or a synchronous generator (SG) with minimum control effort. The idea that GTI behavior is like the synchronous generator is implemented in this study. The research aims at using an advanced controller to reduce oscillations and achieve stability in a micro-grid. Here, the robust sliding mode controller-based UPFC is employed to design an optimal grid stabilizer. The paper considers variations in UPQC terminal voltage during the transient period of the system, unlike other articles that assume it to be constant. The performance of the proposed algorithm is evaluated by two benchmark networks. The paper presents a comparative study of transient stability in a micro-grid system under different loads. Simulation results reflect the robustness of the proposed sliding mode controller for oscillation reduction in comparison with the Lyapunov-based nonlinear optimal controller and PI controller. In addition, results show the effectiveness of the proposed nonlinear controller in controlling both GTI and SG in the micro-grid system.
Research Articles
Power systems
Zahra Moravej; Seyed Mahmood Mortazavi; Mojtaba Mohseni
Abstract
IIn this paper, an efficient method to detect and discriminate mechanical defects of transformer winding based on extracting the winding frequency responses using outlier data detection and ensemble algorithms ,which in total constitutes an efficient hybrid method has been proposed. First, the frequency ...
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IIn this paper, an efficient method to detect and discriminate mechanical defects of transformer winding based on extracting the winding frequency responses using outlier data detection and ensemble algorithms ,which in total constitutes an efficient hybrid method has been proposed. First, the frequency response of the high voltage winding of a real model of transformer (1.6 MVA) was extracted in different condition and arranged as primary data. Then, due to the high standard deviation of the characteristics and the weight of the outlier samples above the threshold of 1.1, the Local Outlier Factor (LOF) method was used to clean the samples. Finally, data mining algorithms have been used to detect and distinguish mechanical defects. Based on the results, the decision tree bagging ensemble method reported the best accuracy compared to other techniques and improved the accuracy of the decision tree with total accuracy of 92.68% by LOF. These results also showed that all methods improved accuracy by LOF. Therefore, it can be claimed that the proposed method has the ability to discriminate the mechanical defects of the transformer winding with appropriate accuracy.
Research Articles
Power systems
Mohammadreza Noori; Seyed Ghodratollah Seifossadat; Alireza Safarian
Abstract
In this paper, a novel selective DC fault detector approach based on the adaptive cumulative sum method (ACUSUM) is suggested for the protection of high voltage direct current (HVDC) transmission lines. Using a communication channel, the proposed method detects DC fault occurrence as well as determining ...
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In this paper, a novel selective DC fault detector approach based on the adaptive cumulative sum method (ACUSUM) is suggested for the protection of high voltage direct current (HVDC) transmission lines. Using a communication channel, the proposed method detects DC fault occurrence as well as determining faulty line at a multi-terminal HVDC (MT-HVDC) transmission system; the whole in less than 2ms. The suggested approach works in the time domain and employs the ACUSUM method as a mathematical tool for detecting abrupt variation at the magnitude of lines current for fault detection. Simulation results confirm the selectivity of the proposed algorithm at different DC fault situations which enhances the reliability of the power system. Besides the low sampling rate, the ACUSUM calculation burden is very low and its implementation needs no special or complicated hardware. Rather than appropriate speed, adaptivity, independence from system parameters, robustness against fault resistance, fault distance and noise are significant advantages of the proposed algorithm in comparison with other methods. adaptivity, independency from system parameters, robustness against fault resistance, fault distance and noise are significant advantages of the proposed algorithm in comparison with other methods.
Research Articles
Optimization
Seyed Mehdi Shafiof; Javad Askari Marnani; Maryam Shamssolary
Abstract
This article aims to introduce a modern numerical method based on the hybrid functions, consisting of the Bernoulli polynomials and Block-Pulse functions. An indirect approach is proposed for solving the fractional optimal control problems (FOCPs). Firstly, the two-point boundary value problem (TPBVP) ...
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This article aims to introduce a modern numerical method based on the hybrid functions, consisting of the Bernoulli polynomials and Block-Pulse functions. An indirect approach is proposed for solving the fractional optimal control problems (FOCPs). Firstly, the two-point boundary value problem (TPBVP) is calculated for a class of FOCPs, including integer-fractional derivatives, leading to a system of fractional differential equations (FDEs), which have the left and right-sided Caputo fractional derivatives (CFD). Therefore, a new approach is proposing to achieve the left Riemann-Liouville fractional integral (LRLFI) and right Riemann-Liouville fractional integral (RRLFI) operators for Bernoulli hybrid functions. Then, hybrid functions approximation, LRLFI, and RRLFI operators, and the collocation method are used to solve the TPBVP. The error bounds for the hybrid function and LRLFI and RRLFI operators are also presented. Moreover, the convergence of the proposed method is proved. Finally, the simplicity and accuracy of the method are illustrated using some numerical examples.
Research Articles
Communication
Hadi Esmaeeli; Mehdi Rezaei
Abstract
Videos directly captured from a computer or smartphone screen have certain characteristics that differentiate them from camera-captured (CC) ones. These videos are called screen content (SC) videos whose specific encoder has been introduced as a new extension of the HEVC standard called screen content ...
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Videos directly captured from a computer or smartphone screen have certain characteristics that differentiate them from camera-captured (CC) ones. These videos are called screen content (SC) videos whose specific encoder has been introduced as a new extension of the HEVC standard called screen content coding (SCC). Most screen content applications are real-time with low delay requiring an accurate rate control. The difference in the characteristics and use of special coding tools such as palette mode, intra block copy, and adaptive color transform in this standard, have affected the mechanism of bit rate generation and control. This paper presents methods and criteria to evaluate the controllability of the bit rate of SC videos and compare it with that of CC counterparts. Furthermore, the requirements of SC video rate control are studied. The experimental results indicate that the bit rate of SC videos is much less controllable than the conventional ones so that the conventional rate-distortion models and bit rate control algorithms are not effective in coding the SC videos.
Research Articles
Optimization
Elham Khoshbakht Sangcar; Farhad Namdari; Mysam Doostizadeh
Abstract
This paper studies the reciprocal impact of distribution network protection and reconfiguration of active Nowadays, with increasing energy consumption in distribution networks and the demand of consumers to buy highly reliable power, it is of high importance to establish adapt between protection and ...
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This paper studies the reciprocal impact of distribution network protection and reconfiguration of active Nowadays, with increasing energy consumption in distribution networks and the demand of consumers to buy highly reliable power, it is of high importance to establish adapt between protection and operation of the power system. distribution system. Accordingly, a distribution network reconfiguration is carried out to find the optimal switching operations in an economic way. Since the switching operations will change network topology as well as short circuit level of buses, the protection coordination may be invalid. To address this issue, constraints of the coordination of protection relays and fuses is being formulated and added to the reconfiguration problem. Moreover, the nonlinear equations of the problem are linearized and are transformed the reconfiguration problem into Mixed-Integer Linear Programming (MILP) one to achieve the global optimal solution. The proposed method has been implemented on 33 bus distribution network. The results clearly show effectiveness of the active and reactive power management in an intelligent distribution network considering protection concepts.
Research Articles
Control
Majid Akbarian; Naser Pariz
Abstract
Lyapunov's theorem is the basic criteria to establish the stability properties of the nonlinear dynamical systems. In this method, it is a necessity to find the positive definite functions with negative definite or negative semi-definite derivative. These functions that named Lyapunov functions, form ...
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Lyapunov's theorem is the basic criteria to establish the stability properties of the nonlinear dynamical systems. In this method, it is a necessity to find the positive definite functions with negative definite or negative semi-definite derivative. These functions that named Lyapunov functions, form the core of this criterion. The existence of the Lyapunov functions for asymptotically stable equilibrium points is guaranteed by converse Lyapunov theorems. On the other hand, for the cases where the equilibrium point is stable in the sense of Lyapunov, converse Lyapunov theorems only ensure non-smooth Lyapunov functions. In this paper, it is proved that there exist some autonomous nonlinear systems with stable equilibrium points that despite stability don’t admit convex Lyapunov functions. In addition, it is also shown that there exist some nonlinear systems that despite the fact that they are stable at the origin, but do not admit smooth Lyapunov functions in the form of V(x) or V(t,x) even locally. Finally, a class of non-autonomous dynamical systems with uniform stable equilibrium points, is introduced. It is also proven that this class do not admit any continuous Lyapunov functions in the form of V(x) to establish stability.
Research Articles
Power systems
Masoud Maleki Rizi; Saeed Abazari; Nima Mahdian
Abstract
This paper presents enhancement of power system dynamic stability while equipped with both unified power flow controller and doubly fed induction generator by using LMI technique. We have used all UPFC (Unified Power Flow Controller) main basic PI controllers and its POD (Power Oscillation Damping) supplementary ...
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This paper presents enhancement of power system dynamic stability while equipped with both unified power flow controller and doubly fed induction generator by using LMI technique. We have used all UPFC (Unified Power Flow Controller) main basic PI controllers and its POD (Power Oscillation Damping) supplementary controller. More complete model of DFIG (Doubly Fed Induction Generator) and both RSC (Rotor Side Converter) and GSC (Grid Side Converter) dynamics with their controllers have considered too. These two devices controllers have simultaneously co-ordinate and optimized with compromising between their control variables parameters. PSO (Particle Swarm Optimization) algorithm has used to optimize an objective function based on Eigen values and damping ratio to reach to best parameters and variables of controllers of both of UPFC and DFIG. LMI (Linear Matrix Inequality) have applied to whole system linearized model to reach to optimally modified eigenvalues. Within steady state and dynamic study we considered practical line thermal capacity and UPFC power rating too. Simulation results in 39-bus 10-machine Ne-England power systems ilustrate the capability of applied method. The results demonstrated that coordinated control of these two devices beside using LMI tend to more damping of system modes oscillation and more stability in power system.
Research Articles
Control
Aylar Khooshehmehri; Saeed Nasrollahi; Morteza Aliyari
Abstract
In this paper, a model predictive control approach based on a generic particle filter is proposed to synchronize two Josephson junction models with different parameters. For this purpose, an appropriate objective function is defined to assess the particles within the state space. This objective function ...
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In this paper, a model predictive control approach based on a generic particle filter is proposed to synchronize two Josephson junction models with different parameters. For this purpose, an appropriate objective function is defined to assess the particles within the state space. This objective function minimizes simultaneously the tracking error, control effort, and control smoothness. The dynamic optimization problem is solved using a generic particle filter. Here, Josephson junction is described with Resistive Capacitive Inductive Shunted Josephson model, and the synchronization is obtained using the slave–master technique. Moreover, to verify the implementation capability of the proposed algorithm, a processor in loop experiment is performed. The results show that the open-loop system, without the controller, has a chaotic behavior. Numerical simulations are conducted to assess the performance of the proposed algorithm. The results show that the proposed approach can be implemented in a real-time application. Also, the performance of the suggested controller is compared with the proportional integral derivative controller and sliding mode controller.
Research Articles
Power systems
Hojatolah Makvandi; Mahmood Joorabian; Hassan Barati
Abstract
The present study introduces a new extensive-area ANFIS (Adaptive Neuro-Fuzzy Interface System)-based method to detect wide area instability and control the time of controlled islanding execution within power systems. The ANFIS parameters are optimized by the PSO method to increase the method’s ...
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The present study introduces a new extensive-area ANFIS (Adaptive Neuro-Fuzzy Interface System)-based method to detect wide area instability and control the time of controlled islanding execution within power systems. The ANFIS parameters are optimized by the PSO method to increase the method’s accuracy at various disturbances and loading circumstances. In addition, to take various stability margins within the areas into account, a novel parallel ANFIS network (P-ANFIS) is implemented in which a distinct ANFIS is allocated for every nearby area. Extended off-line studies are performed to train ANFIS to respond in real-time accurately based on the selected wide area input signals. These parameters are monitored continuously through a wide area measurement system (WAMS) and the proposed P-ANFIS starts to assess the stability between related areas in real-time in the case of potentially unstable oscillations. Once an unstable oscillation is detected, the islanding command is transmitted to perform the controlled islanding scheme. The suggested technique is used in an IEEE 39 bus power system and its performance is demonstrated at different disturbances in terms of both speed and accuracy. It is found that the suggested ANFIS-based technique can determine islanding requirement and its time of execution properly at different disturbances.
