| 1. |
- Sabouri, Mohammad, et al.
(författare)
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Increasing the resiliency of power systems in presence of GPS spoofing attacks: A data-driven deep-learning algorithm
- 2023
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Ingår i: IET Generation, Transmission & Distribution. - : Institution of Engineering and Technology (IET). - 1751-8687 .- 1751-8695. ; 17:20, s. 4525-4540
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Tidskriftsartikel (refereegranskat)abstract
- The growing use of wireless technologies in power systems has raised concerns about cybersecurity, particularly regarding GPS spoofing attacks (GSAs). These attacks manipulate GPS data, leading to modifications in the phase angle of phasor measurement units (PMUs). In this paper, a Deep-learning GPS-Spoofing Counteraction (DLGSC) algorithm is proposed, utilizing PMU data for GSA detection and PMU data correction. The algorithm incorporates a recurrent neural network (RNN) and a set of long short-term memory (LSTM) units separately, for signal correction after attack detection. Unlike existing methods that struggle with simultaneous attacks or they are static methods, DLGSC tackles these challenges by leveraging deep learning techniques. By selecting appropriate features for GSA detection, DLGSC achieves accurate results. The algorithm is evaluated on standard IEEE 14-bus and IEEE 39-bus power systems, and its performance is compared to statistical, dynamic, and Deep Learning (DL) methods in the literature. Additionally, an experimental setup is designed to validate the algorithm in a laboratory environment. Results demonstrate the easy-implementable DLGSC algorithm's satisfactory real-time performance in various scenarios, such as load variations and noise, achieving over 98% accuracy. Notably, DLGSC is cable of detecting multiple GSAs on different PMUs.
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| 2. |
- Abdoshahi, Neda, et al.
(författare)
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On the energetics of the cubic-to-hexagonal transformations in TiAl plus Mo alloys
- 2022
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 240
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Tidskriftsartikel (refereegranskat)abstract
- Diffusionless transformations allow access to metastable phases and enrich the materials design portfolio. They are well suited for atomistic modeling; nonetheless, they are challenging when involving disordered systems or alloys with complex compositions. This work presents a comprehensive study of transforma-tion energetics between bcc and hcp ordered and disordered phases in the TiAl+Mo model alloy system. By employing two complementary techniques I. VASP-SQS, and II. EMTO-CPA, we can show that chemical disorder flattens the energy landscape but may introduce a small barrier. Unlike that, the energetics of ordered phases are barrier-less and hence would suggest a spontaneous transformation. Finally, we show that Mo stabilizes the bcc phases, leading to a barrier-less transformation hcp -+ bcc for both ordered and disordered states when Mo content exceeds ti 12 at.%.
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| 3. |
- Abdoshahi, Neda, et al.
(författare)
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Structural stability and mechanical properties of TiAl plus Mo alloys : A comprehensive ab initio study
- 2021
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 221, s. 117427-
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Tidskriftsartikel (refereegranskat)abstract
- Titanium aluminides are technologically important intermetallic alloys with also many curious properties interesting from a basic research point of view. When alloyed with Mo, several (meta)stable phases have been reported; their properties are, however, largely unknown due to the alloy processing (e.g. fast cooling) and/or non-existence as a single-phase material. Here we employ first principles calculations to study compositional trends in structural and mechanical properties. We could show that Mo increases the density of all studied phases, leads to their chemical destabilization with the exception of the ordered bcc /3o phase, increases their ductility, and enhances the elastic anisotropy. Discrepancies between two employed ab initio methods (special quasi-random structures vs. coherent potential approximation) in the case of the /3o and B19 phases are rationalized with significant local distortions which may eventually facilitate a spontaneous phase transformation. Predictions of ordering temperatures solely based on the configurational entropy do not yield values in the experimentally expected ranges.
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| 4. |
- Abolpour, Roozbeh, et al.
(författare)
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A New Power Flow Model With a Single Nonconvex Quadratic Constraint : The LMI Approach
- 2022
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Ingår i: IEEE Transactions on Power Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8950 .- 1558-0679. ; 37:2, s. 1218-1229
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we propose a new mathematical model for power flow problem based on the linear and nonlinear matrix inequality theory. We start with rectangular model of power flow (PF) problem and then reformulate it as a Bilinear Matrix Inequality (BMI) model. A Theorem is proved which is able to convert this BMI model to a Linear Matrix Inequality (LMI) model along with One Nonconvex Quadratic Constraint (ONQC). Our proposed LMI-ONQC model for PF problem has only one single nonconvex quadratic constraint irrespective of the network size, while in the rectangular and BMI models the number of nonconvex constraints grows as the network size grows. This interesting property leads to reduced complexity level in our LMI-ONQC model which in turn makes it easier to solve for finding a PF solution. The non-conservativeness, iterative LMI solvability, well-defined and easy-to-understand geometry and pathwise connectivity of feasibility region are other important properties of proposed LMI-ONQC model which are discussed in this paper. An illustrative two-bus example is carefully studied to show different properties of our LMI-ONQC model. We have also tested our LMI-ONQC model on 30 different power-system cases including four ill-conditioned systems and compared it with a group of existing approaches. The numerical results show the promising performance of our LMI-ONQC model and its solution algorithm to find a PF solution.
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| 5. |
- Abolpour, Roozbeh, et al.
(författare)
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Inside-Ellipsoid Outside-Sphere (IEOS) model for general bilinear feasibility problems : Feasibility analysis and solution algorithm
- 2023
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 147, s. 110738-
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with general bilinear feasibility problems. A nonlinear transformation is introduced that reformulates a general bilinear feasibility problem as a Linear Matrix Inequality (LMI) problem augmented with a single non-convex quadratic constraint. The single non-convex quadratic constraint has a regular concave constraint function. Due to the LMI part of this formulation, it is easier to analyze, and we prove that the solution space of this formulation is located inside several ellipsoids and outside a sphere. This leads to our proposed Inside-Ellipsoid and Outside-Sphere (IEOS) model for general bilinear feasibility problems. Then, the feasibility analysis of our proposed IEOS model is performed. The related necessary feasibility conditions and sufficient feasibility conditions are theoretically developed. Moreover, an iterative algorithm for solving our IEOS model is also proposed.Two applications including matrix-factorization problem in control systems and power-flow prob-lem in power systems are considered to evaluate the practicality of our proposed approach. Both problems are formulated as IEOS models. It is shown that our proposed model can provide more accurate solutions to these problems as compared to previous competing approaches in the relevant literature.
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| 6. |
- Abolpour, Roozbeh, et al.
(författare)
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Optimal frequency regulation in an uncertain islanded microgrid : A modified direct search algorithm
- 2022
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1416 .- 1752-1424. ; 16:4, s. 726-739
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a methodology for frequency regulation in a microgrid involving renewable energy sources (RES) using a dynamic controller, which is an output feedback controller (OFC). The parameters of OFC are tuned by searching the design space of the controller. Since the RES model is not exactly known, the uncertain model is derived and the OFC is considered for it. The goal of controller tuning is to find appropriate parameters of the controller such that the norm of frequency deviations, even in presence of uncertainties in the RES parameters is minimized. An algorithm based on searching the controller design space is suggested to find the suitable controller gains. The algorithm assumes the controller parameters lie in a convex space and searches the space systematically such that an appropriate solution is found. The method is proved mathematically and two theorems are mentioned, accordingly. Finally, a simulated model of a RES is utilized for algorithm evaluation and the results demonstrate the algorithm capability in optimal frequency regulation.
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| 7. |
- Dehghani, Mohammad, et al.
(författare)
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Stability and ordering of bcc and hcp TiAl plus Mo phases : An ab initio study
- 2022
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Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 205
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Tidskriftsartikel (refereegranskat)abstract
- Atomic ordering in bcc and hcp TiAl+Mo alloys near equiatomic TiAl composition is investigated by different ab initio tools. We show that small addition of Mo, about 5 at. %, is enough to make bcc alloys with more than 50 at. % of Ti stable with respect to the hcp alloys. Moreover, such alloying also leads to stabilizing the B2 ordered structure with respect to its B2(2) modification, which is the bcc-based ground state structure of binary TiAl. The site preference of Mo in the B2 and B19 ordered alloys is investigated by different methods: in the dilute limit, using the transfer energy formalism; in concentrated alloys, from the total energies of disordered and partially ordered alloys in the mean-field coherent potential approximation; and from Monte Carlo simulations. These methods produce consistent results for the B2 phase predicting a strong preference of Mo to Al sublattice. The site preference of Mo in the B19 phases varies from a weak preference for Al sites in the single impurity calculations to a quite strong preference for Ti sites in the mean-field approximation and finally to a strong Al preference in Monte Carlo simulations. Mo alloying dramatically increases the order-disorder transition temperatures in bcc and hcp Al-deficient Ti0.5Al0.5-xMox alloys.
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| 8. |
- Javanmardi, Hamidreza, et al.
(författare)
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A mesh-based partitioning algorithm for decreasing conservatism in solving bilinear matrix inequality problems
- 2023
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Ingår i: Optimal control applications & methods. - : Wiley. - 0143-2087 .- 1099-1514. ; 44:5, s. 2571-2594
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a mesh-based partitioning algorithm (MBPA) to solve bilinear matrix inequality (BMI) problems is proposed, where the main idea is to divide the solution space of a non-convex BMI problem into smaller parts in the form of Simplexes through meshing the space. In each simplex, only the concave part of BMI constraints is approximated by piecewise affine matrix (PAM), which eventually leads to a convex sub-problem. After that, the feasible solution can be easily obtained in each simplex through the linear matrix inequality (LMI) optimization. Although the proposed MBPA exploits PAM approximation, it relaxes several restrictive conditions used in other methods, so, it can be used as an effective approach for solving BMI problems. Various numerical examples on systems from COMPleib library to design static output feedback controller are provided to validate the proposed MBPA. Simulation results reveal the satisfactory performance of MBPA in several examined problems and provide acceptable performance compared to other existing BMI solution algorithms. Comparing the percentage of superiority of MBPA with some existing prominent BMI algorithms in several control problems including spectral abscissa optimization problems, (Figure presented.) and (Figure presented.) optimization problems for the closed-loop systems of COMPleib show that the proposed algorithm is more successful than the previous ones.
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| 9. |
- Javanmardi, H., et al.
(författare)
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BMI-Based Load Frequency Control in Microgrids Under False Data Injection Attacks
- 2021
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Ingår i: IEEE Systems Journal. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-8184 .- 1937-9234. ; , s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- In this article, the power fluctuation problem caused by adding renewable energy sources to microgrids (MGs) is addressed. These power fluctuations which can cause several adverse effects, including system instability, load shedding, and eventually blackouts are attenuated by designing a load frequency controller (LFC) to provide a constant and uniform frequency in different operation cases of MGs. This article designs a dynamic output feedback controller (DOFC) for LFC in MGs while considering the contraction observer for attack mitigation. We suggest a new formulation of the sufficient conditions for the DOFC design problem in the form of bilinear matrix inequalities (BMIs) and try to minimize the frequency deviation subject to load, solar, and wind energy changes. The proposed formulation effectively changes the problem to a new BMI model which can easily be divided into two problems, one is a convex optimization problem and the remained part is a quadratic matrix inequality problem which is linearized around the feasible solution of the linear matrix inequality part by a Taylor-like expansion. This leads to a more exact and less conservative solution as compared to the previous methods suggested in the literature. To illustrate the merits of the developed approach, numerical simulations on a sample ac–MG are carried out. Comparing norms of the frequency variations in the closed-loop system with multiple prominent methods in previous works, including ${{\bm{H}}_\infty },{\bm{\ \mu }}$, fuzzy type-1, and intelligent-PI, shows that our proposed method reduces the two and infinity norms of frequency fluctuations by 84% and 80%, respectively compared to the traditional ${{\bm{H}}_\infty }$ method which is the best among the analyzed approaches. This further verifies the efficacy of the designed DOFC in our article.
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