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RISS 인기검색어
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- 저자 : Ajami, Ali (검색결과 15 건)
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A. Jami,P. S. Heyns 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.9
Nonstationary flow conditions can introduce complexities and nonlinear characteristics to pumping systems. This paper presents comparative studies of impeller fault detection techniques combined with artificial neural networks (ANNs) to propose the most appropriate diagnosis system. An experimental study, including seven impeller conditions, is performed to further explore the phenomena. Statistical parameters, frequency peaks, and wavelet packet energy present data feature sets, and a three-layer back-propagation ANN is used for fault recognition. The verification of the results proves that the detectability of the wavelet packet transform (WPT)-ANN model is considerably improved by using the energy of the decomposed vibration from WPT. This model can save computational time and provide superior diagnostic information. This study provides two key contributions. First, the feasibility and effectiveness of common monitoring techniques are compared. Second, the results demonstrate the accuracy of the proposed models for impellers operating under variable working conditions, which has not been previously addressed in the literature.
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Ajami, Ali,Aghajani, Gh.,Pourmahmood, M. The Korean Institute of Electrical Engineers 2010 Journal of Electrical Engineering & Technology Vol.5 No.2
This paper describes a new stochastic heuristic algorithm in engineering problem optimization especially in power system applications. An improved particle swarm optimization (PSO) called adaptive particle swarm optimization (APSO), mixed with simulated annealing (SA), is introduced and referred to as APSO-SA. This algorithm uses a novel PSO algorithm (APSO) to increase the convergence rate and incorporate the ability of SA to avoid being trapped in a local optimum. The APSO-SA algorithm efficiency is verified using some benchmark functions. This paper presents the application of APSO-SA to find the optimal location, type and size of flexible AC transmission system devices. Two types of FACTS devices, the thyristor controlled series capacitor (TCSC) and the static VAR compensator (SVC), are considered. The main objectives of the presented method are increasing the voltage stability index and over load factor, decreasing the cost of investment and total real power losses in the power system. In this regard, two cases are considered: single-type devices (same type of FACTS devices) and multi-type devices (combination of TCSC, SVC). Using the proposed method, the locations, type and sizes of FACTS devices are obtained to reach the optimal objective function. The APSO-SA is used to solve the above non.linear programming optimization problem for better accuracy and fast convergence and its results are compared with results of conventional PSO. The presented method expands the search space, improves performance and accelerates to the speed convergence, in comparison with the conventional PSO algorithm. The optimization results are compared with the standard PSO method. This comparison confirms the efficiency and validity of the proposed method. The proposed approach is examined and tested on IEEE 14 bus systems by MATLAB software. Numerical results demonstrate that the APSO-SA is fast and has a much lower computational cost.
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Ajami, Ali,Mokhberdoran, Ataollah,Oskuee, Mohammad Reza Jannati The Korean Institute of Electrical Engineers 2013 Journal of Electrical Engineering & Technology Vol.8 No.6
Nowadays multilevel inverters are developing generally due to reduced voltage stress on power switches and low total harmonic distortion (THD) in output voltage. However, for increasing the output voltage levels the number of circuit devices are increased and it results in increasing the cost of converter. In this paper, a novel multilevel inverter is proposed. The suggested topology uses less number of power switches and related gate drive circuits to generate the same level in output voltage with comparison to traditional cascaded multilevel inverter. With the proposed topology all levels in output voltage can be realized. As an illustration, a symmetric 13-level and asymmetric 29-level proposed inverters have been simulated and implemented. The total peak inverse (PIV) and power losses of presented inverter are calculated and compared with conventional cascaded multilevel inverter. The presented analyses show that the power losses in the suggested multilevel inverter are less than the traditional inverters. Presented simulation and experimental results demonstrate the feasibility and applicability of the proposed inverter to obtain the maximum number of levels with less number of switches.
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Advanced Cascade Multilevel Converter with Reduction in Number of Components
Ajami, Ali,Oskuee, Mohammad Reza Jannati,Mokhberdoran, Ataollah,Khosroshahi, Mahdi Toupchi The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.1
In this paper a novel converter structure based on cascade converter family is presented. The suggested multilevel advanced cascade converter has benefits such as reduction in number of switches and power losses. Comparison depict that proposed topology has the least number of IGBTs among all multilevel cascade type converters which have been introduced recently. This characteristic causes low cost and small installation area for suggested converter. The number of on state switches in current path is less than conventional topologies and so the output voltage drop and power losses are decreased. Symmetric and asymmetric modes are analyzed and compared with conventional multilevel cascade converter. Simulation and experimental results are presented to illustrate validity, good performance and effectiveness of the proposed configuration. The suggested converter can be applied in medium/high voltage and PV applications.
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Ali Ajami,Gh. Aghajani,M. Pourmahmood 대한전기학회 2010 Journal of Electrical Engineering & Technology Vol.5 No.2
This paper describes a new stochastic heuristic algorithm in engineering problem optimization especially in power system applications. An improved particle swarm optimization (PSO) called adaptive particle swarm optimization (APSO), mixed with simulated annealing (SA), is introduced and referred to as APSO-SA. This algorithm uses a novel PSO algorithm (APSO) to increase the convergence rate and incorporate the ability of SA to avoid being trapped in a local optimum. The APSO-SA algorithm efficiency is verified using some benchmark functions. This paper presents the application of APSO-SA to find the optimal location, type and size of flexible AC transmission system devices. Two types of FACTS devices, the thyristor controlled series capacitor (TCSC) and the static VAR compensator (SVC), are considered. The main objectives of the presented method are increasing the voltage stability index and over load factor, decreasing the cost of investment and total real power losses in the power system. In this regard, two cases are considered: single-type devices (same type of FACTS devices) and multi-type devices (combination of TCSC, SVC). Using the proposed method, the locations, type and sizes of FACTS devices are obtained to reach the optimal objective function. The APSO-SA is used to solve the above non?linear programming optimization problem for better accuracy and fast convergence and its results are compared with results of conventional PSO. The presented method expands the search space, improves performance and accelerates to the speed convergence, in comparison with the conventional PSO algorithm. The optimization results are compared with the standard PSO method. This comparison confirms the efficiency and validity of the proposed method. The proposed approach is examined and tested on IEEE 14 bus systems by MATLAB software. Numerical results demonstrate that the APSO-SA is fast and has a much lower computational cost.
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Advanced Cascade Multilevel Converter with Reduction in Number of Components
Ali Ajami,Mohammad Reza Jannati Oskuee,Ataollah Mokhberdoran,Mahdi Toupchi Khosroshahi 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.1
In this paper a novel converter structure based on cascade converter family is presented. The suggested multilevel advanced cascade converter has benefits such as reduction in number of switches and power losses. Comparison depict that proposed topology has the least number of IGBTs among all multilevel cascade type converters which have been introduced recently. This characteristic causes low cost and small installation area for suggested converter. The number of on state switches in current path is less than conventional topologies and so the output voltage drop and power losses are decreased. Symmetric and asymmetric modes are analyzed and compared with conventional multilevel cascade converter. Simulation and experimental results are presented to illustrate validity, good performance and effectiveness of the proposed configuration. The suggested converter can be applied in medium/high voltage and PV applications.
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Modeling and State Feedback Controller for Current Source Inverter Based STATCOM
A. Ajami,M.Younesi 제어로봇시스템학회 2008 제어로봇시스템학회 국제학술대회 논문집 Vol.2008 No.10
The static synchronous compensator (STATCOM) is increasingly popular in power system application. In general, power factor and stability of the utility system can be improved by STATCOM. Specifically, STATCOM can regulate the voltage of connection point and compensate the power factors of equipment serviced by that node. The dynamic performance of STATCOM is critical to these performance and stability function. STATCOM is a multi input and multi output system (MIMO), which can be presented by a mathematic model. In this paper, an optimal linear quadratic regulator (LQR) design is presented for transient dynamic performance of current-source converter based STATCOM.
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Ali Ajami,Ataollah Mokhberdoran,Mohammad Reza Jannati Oskuee 대한전기학회 2013 Journal of Electrical Engineering & Technology Vol.8 No.6
Nowadays multilevel inverters are developing generally due to reduced voltage stress on power switches and low total harmonic distortion (THD) in output voltage. However, for increasing the output voltage levels the number of circuit devices are increased and it results in increasing the cost of converter. In this paper, a novel multilevel inverter is proposed. The suggested topology uses less number of power switches and related gate drive circuits to generate the same level in output voltage with comparison to traditional cascaded multilevel inverter. With the proposed topology all levels in output voltage can be realized. As an illustration, a symmetric 13-level and asymmetric 29-level proposed inverters have been simulated and implemented. The total peak inverse (PIV) and power losses of presented inverter are calculated and compared with conventional cascaded multilevel inverter. The presented analyses show that the power losses in the suggested multilevel inverter are less than the traditional inverters. Presented simulation and experimental results demonstrate the feasibility and applicability of the proposed inverter to obtain the maximum number of levels with less number of switches.
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