Original Research Paper
Nonlinear System
A.R. Ghomi Taheri; F. Setoudeh; M. B. Tavakoli
Abstract
Background and Objectives: The Differential transform method (DTM) is used in the analysis of ordinary, partial, and high-order differential equations. Recently, the DTM is used in the nonlinear analysis of physical nonlinear dynamic systems. Methods: The DTM method is used to analyze and analytically ...
Read More
Background and Objectives: The Differential transform method (DTM) is used in the analysis of ordinary, partial, and high-order differential equations. Recently, the DTM is used in the nonlinear analysis of physical nonlinear dynamic systems. Methods: The DTM method is used to analyze and analytically solve the nonlinear mathematical model of bias current-controlled Colpitts oscillator with variable coefficients. Intervals of the validity of the proposed method are evaluated by using the fourth order Runge-Kutta method (RK4M). In this note, the Lyapunov exponent (LE) can be used to analyze the Colpitts oscillator. By using DTM, the LEs are calculated analytically with unknown parameters in a short interval of time t[0, 3 Sec]. Results: In this paper, intervals of the validity of the proposed method are evaluated using RK4M. In addition, LEs are calculated using analytical and numerical methods based on DTM technique and Wolf method, respectively. LEs of the proposed system are presented as a function of the control parameter to confirm the applied technique’s usefulness. Conclusion: By comparing these two methods, the proposed DTM analytical technique is relatively more precise. Simulation results confirmed the impact of different parameters on LEs with two different initial conditions. The results show good accuracy of the DTM in short time intervals t[0, 3 Sec]. Background and Objectives: The Differential transform method (DTM) is used in the analysis of ordinary, partial, and high-order differential equations. Recently, the DTM is used in the nonlinear analysis of physical nonlinear dynamic systems. Methods: The DTM method is used to analyze and analytically solve the nonlinear mathematical model of bias current-controlled Colpitts oscillator with variable coefficients. Intervals of the validity of the proposed method are evaluated by using the fourth order Runge-Kutta method (RK4M). In this note, the Lyapunov exponent (LE) can be used to analyze the Colpitts oscillator. By using DTM, the LEs are calculated analytically with unknown parameters in a short interval of time t[0, 3 Sec]. Results: In this paper, intervals of the validity of the proposed method are evaluated using RK4M. In addition, LEs are calculated using analytical and numerical methods based on DTM technique and Wolf method, respectively. LEs of the proposed system are presented as a function of the control parameter to confirm the applied technique’s usefulness. Conclusion: By comparing these two methods, the proposed DTM analytical technique is relatively more precise. Simulation results confirmed the impact of different parameters on LEs with two different initial conditions. The results show good accuracy of the DTM in short time intervals t[0, 3 Sec]. ======================================================================================================Copyrights©2021 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.======================================================================================================
Original Research Paper
Control
S. Khodakaramzadeh; M. Ayati; M. R. Haeri Yazdi
Abstract
Background and Objectives: Designing a terminal sliding mode observer (TSMO) in order to estimate the potential faults in a wind turbine with a doubly fed induction generator (DFIG) has been studied in previous research works. In this paper, a method for fault detection of a permanent magnet synchronous ...
Read More
Background and Objectives: Designing a terminal sliding mode observer (TSMO) in order to estimate the potential faults in a wind turbine with a doubly fed induction generator (DFIG) has been studied in previous research works. In this paper, a method for fault detection of a permanent magnet synchronous generator (PMSG) wind turbine using a TSMO is developed. Methods: The wind turbine (WT) dynamic model including, blades, drive train, PMSG, maximum power capture controller, and pitch controller is linearized around its equilibrium point and is simulated in MATLAB Simulink. A PID controller is designed for capturing the maximum power from wind. Also, a PI controller is designed in order to control the pitch angle. In this research, the blade imbalance fault (BIF), which is due to the difference between turbine blades’ mass distribution, is investigated. This fault may happen over time and causes rotor mass imbalance that leads to vibrations in the generator’s shaft rotating speed. A fault detection system (FDS) is proposed using a terminal sliding mode observer in order to diagnose the BIF. Results: Using the designed TSMO, the estimation errors of not only measured states but also unmeasured states converge to zero in finite time. This leads to the fast action of the FDS before a failure happens. Using the proposed FDS, the states and fault are estimated such that the estimation errors of states and the fault converge to zero in 0.035 seconds. Conclusion: The convergence of state estimation errors to zero in finite time, which is verified by simulation results, satisfies the authors’ expectation that using TSMO, the estimation errors of both output and non-output states converge to zero in finite time. ======================================================================================================Copyrights©2021 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.======================================================================================================
Original Research Paper
Analogue Integrated Circuits
F. Shakibaee; A. Bijari; S.H. Zahiri
Abstract
Background and Objectives: Comparators play a critical role in the analog to digital converters (ADCs) and digital to analog converters (DACs). So, different structures have been proposed to improve their performance. Power, delay, offset, and noise are the important factors that have significantly affect ...
Read More
Background and Objectives: Comparators play a critical role in the analog to digital converters (ADCs) and digital to analog converters (DACs). So, different structures have been proposed to improve their performance. Power, delay, offset, and noise are the important factors that have significantly affect the comparator’s performance. In low power applications, power consumption and delay are the critical concerns that should be minimized to obtain better performance. In this work, a low-power and high-speed comparator has been proposed, which is suitable for applications operating at a low power supply. Methods: Based on the conventional structure of the comparator, some modifications are implemented to achieve better performance in terms of power consumption and delay. Additionally, the proposed structure gives great performance when the difference of inputs is very small. To verify the proposed structure, it is designed and simulated in a 0.18 μm CMOS technology with a power supply of 1 V and sampling frequency of 2 MHz. Results: To draw a fair comparison, the conventional and proposed structure is simulated in equal circumstance. The size of transistors is designed with appropriate W/L ratios to achieve appropriate performance. The proposed structure not only reduces the power consumption by 44%, but also it decreases the delay by 9.1%. The power consumption of the proposed structure is around 0.12 µw. The total occupied area by the proposed structure is approximately 127.44 µm2. Conclusion: In this paper, we presented a delay analysis for the proposed dynamic comparator. Also, based on theoretical analyses, a new dynamic comparator consumes less power and operates faster compared with the conventional structure. The simulation results verify the theoretical analysis.
======================================================================================================Copyrights©2021 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.======================================================================================================
Original Research Paper
Microphone Array Processing
M. Kalantari
Abstract
Background and Objectives: One major problem in the minimum power distortionless response (MPDR) beamformer is the signal cancellation problem, i.e., the desired signal is canceled by the reflected signal, even though the distortionless response constraint is satisfied. Solving this problem is the objective ...
Read More
Background and Objectives: One major problem in the minimum power distortionless response (MPDR) beamformer is the signal cancellation problem, i.e., the desired signal is canceled by the reflected signal, even though the distortionless response constraint is satisfied. Solving this problem is the objective of this paper. Methods: It is well known that the signal cancellation problem can be avoided by minimizing the cross-spectrum matrix of noise, i.e., using the minimum variance distortionless response (MVDR) beamformer. But, in the case of disturbance signals which have correlation with the desired signal, estimation of this matrix is a challenging problem. In this paper we propose an approach for estimating the cross-spectrum matrix of noise signal from which we can solve the signal cancellation problem. Results: Simulation examples show that using the proposed method we can bypass the signal cancellation problem completely. Conclusion: A common belief is that in the case of a disturbance that is a reflected version of the desired signal, due to cohesive appearance and disappearance of both the disturbance and the desired signal, the estimation of cross-spectrum matrix of noise signal is typically not possible in practice. So, based on this common belief, we can’t use the MVDR beamformer in this case. In this paper, we show that this common belief is a fault. We propose a general approach for estimating the cross-spectrum matrix of noise signal that is applicable even in the case of correlated disturbances.
======================================================================================================Copyrights©2021 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.======================================================================================================
Original Research Paper
Recommender Systems
K. Vahidy Rodpysh; S. J. Mirabedini; T. Banirostam
Abstract
Background and Objectives: The main purpose of the recommender system is to estimate the user's desire and provide a list of items predicted using the appropriate information. Recommender systems offering suggestions items to users face the two challenges of cold start and sparse data. Methods: This ...
Read More
Background and Objectives: The main purpose of the recommender system is to estimate the user's desire and provide a list of items predicted using the appropriate information. Recommender systems offering suggestions items to users face the two challenges of cold start and sparse data. Methods: This paper aims to propose a novel method to overcome the cold start and sparse data challenges in recommender systems. Singular value decomposition is one of the most common methods to reduce sparse data in recommender systems by reducing dimensions. However, the basic singular value decomposition can only extract the feature vectors of users and items, potentially resulting in lower recommendation precision. Using similarity criteria between entities, in addition to being able to reduce cold start that can solve the problem of singular value decomposition through extracting more refined factor vectors. Besides, considering the context dimensions as the third dimension of the matrix requires the use of another flexible algorithm, such as tensor factorization offering a viable solution to minimize the sparse data challenge. We propose a novel method named TCSSVD. First, a two-level matrix is obtained through similarity criteria between the user and the item to reduce the cold start challenge. The second step, to reduce the challenge of sparse data, contextual information is used with the help of tensor in the two level singular value decomposition. Results: Two data sets IMDB and STS due to the exerting of users feature, items feature and contextual information to review the proposed method. In order to the accuracy of the prediction of the criterion RMSE with an accuracy of 95%. However, since the user's rating of the item is of particular importance in the recommender systems. The method TCSSVD compared to the methods tensor factorization, HOSVD, BPR, and CTLSVD are used evaluation measure Precision, Recall, F1-score, and NDCG. Conclusion: The findings indicate that the use of innovative similarity criteria to extract user attributes, items to reduce the cold start and the use of contextual information through the tensor in the TCSSVD in order to sparse data. The results contribute to improving the accuracy of the suggestions given to users in recommender systems. ======================================================================================================Copyrights©2021 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.======================================================================================================
Original Research Paper
Power Systems
M. Tolou Askari
Abstract
Background and Objectives: With the ever-increasing growth of electric loads, the need for generating electric power grows correspondingly. By considering the limitations of power generation, utilizing novel technologies has gained persistent momentum, one of which is deploying Phase-Shifting Transformers ...
Read More
Background and Objectives: With the ever-increasing growth of electric loads, the need for generating electric power grows correspondingly. By considering the limitations of power generation, utilizing novel technologies has gained persistent momentum, one of which is deploying Phase-Shifting Transformers (PSTs). Among the more important available relays for the transmission lines are Distance Relays. To this end, Distance Relays measure the voltage and current of the transmission line in its final installation location. On the other hand, the existence of Phase-Shifting Transformers on transmission lines alters the voltage and current signals at the relay location. This issue causes the impedance calculated by the relay to differ from its actual value at the fault location. As a result, the relay detects the fault location falsely, or in some cases does not recognize it at all. Methods: The effect of phase shifting transformer on the relay performance of the distances has been investigated in this study. Furthermore, the digital distance relays are modeled in a software environment and its validity is investigated through analytical relationships. Next, the efficacy of the transformer on distance protection is analytically studied. Finally, a new method has been proposed to improve distance relay performance. Results: Results from analysis and modelling shows that the effect of phase shifting transformers in relay-computed impedance has two faces, the first of which is related to the internal impedance of the transformer, while the other regards the serial voltage of the transformer. The latter face is much more influential than the former one. Conclusion: This fact renders the mere inner Impedance of phase-shifting transformer insufficient for using it to eliminate its effect. To this end, a method has been developed in which the voltages of both ends of the phase shifting transformer are measured by the PMUs and then sent to the facility for protecting power system after synchronization. There, this voltage is reduced from the voltage calculated by the relay, which renders the effect of the phase shifting transformer in the impedance calculated by the relay completely eliminated. ======================================================================================================Copyrights©2021 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.======================================================================================================
Original Research Paper
Nonlinear Control
A. Zakipour; N. Ghaffari; M. Salimi
Abstract
Background and Objectives: In this paper, a novel approach for regulation of the output current in the grid-connected three-level flying capacitor inverter is presented by using the sliding mode (SM) method. In the proposed method, it is possible to control the active and reactive components of the inverter ...
Read More
Background and Objectives: In this paper, a novel approach for regulation of the output current in the grid-connected three-level flying capacitor inverter is presented by using the sliding mode (SM) method. In the proposed method, it is possible to control the active and reactive components of the inverter output current independently, and therefore it can be employed for grid connection of the renewable energy resources or for harmonic and reactive power compensation of the local loads. The designed controller uses an external loop to control the voltage of the inverter DC link and has a constant switching frequency. The stability of the proposed method has also been proved by using the Lyapunov stability theory. The simulation results show that in different operating conditions, the proposed controller has a stable and robust response. Methods: Grid-connected three-level flying capacitor inverter is modeled by using averaged state space technique. Considering nonlinearity of the obtained model, an equivalent SM controller is developed for output current control of the multilevel grid connected inverter. To improve robustness and stability of the system against uncertainty of model parameters, a nonlinear component is added to the equivalent controller. Results: The proposed controller enjoys very fast dynamic response, so it can be employed in wide ranges of application e.g. reactive compensation and harmonic mitigation modes. In active power filtering operation, it is able to eliminate harmonic components of the grid from 20.61% to 1.34% which is compatible with IEEE and IEC standards. Conclusion: The stability of the proposed method has also been proved by using the Lyapunov stability theory. The simulation results show that in different operating conditions, the proposed controller has a stable and robust response.
======================================================================================================Copyrights©2021 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers.======================================================================================================
