| 1. |
- Stotsky, Alexander, 1960
(författare)
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Accuracy Improvement in Least-Squares Estimation with Harmonic Regressor: New Preconditioning and Correction Methods
- 2015
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Ingår i: Proceedings of the IEEE Conference on Decision and Control. - 2576-2370 .- 0743-1546. - 9781479978861 ; 54rd IEEE Conference on Decision and Control,CDC 2015, s. 4035-4040
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Konferensbidrag (refereegranskat)abstract
- Numerical aspects of least squares estimation have not been sufficiently studied in the literature. In particular, information matrix has a large condition number for systems with harmonic regressor in the initial steps of RLS (Recursive Least Squares) estimation. A large condition number indicates invertibility problems and necessitates the development of new algorithms with improved accuracy of estimation. Symmetric and positive definite information matrix is presented in a block diagonal form in this paper using transformation, which involves the Schur complement. Block diagonal sub-matrices have significantly smaller condition numbers and therefore can be easily inverted, forming a preconditioner for a large scale system. High order algorithms with controllable accuracy are used for solving least squares estimation problem. The second part of the paper is devoted to the performance improvement in classical RLS algorithm, which represents a feedforward estimation procedure with error accumulation. Two correction feedback terms originated from combined high order algorithms are introduced for performance improvement in classical RLS algorithms. Simulation results show significant performance improvement of modified algorithm compared to classical RLS algorithm in the presence of roundoff errors.
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| 2. |
- Stotsky, Alexander, 1960
(författare)
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Combined high-order algorithms in robust least-squares estimation with harmonic regressor and strictly diagonally dominant information matrix
- 2015
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Ingår i: Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering. - : SAGE Publications. - 2041-3041 .- 0959-6518. ; 229:2, s. 184-190
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Tidskriftsartikel (refereegranskat)abstract
- This article describes new high-order algorithms in the least-squares problem with harmonic regressor and strictly diagonally dominant information matrix. Estimation accuracy and the number of steps to achieve this accuracy are controllable in these algorithms. Simplified forms of the high-order matrix inversion algorithms and the high-order algorithms of direct calculation of the parameter vector are found. The algorithms are presented as recursive procedures driven by estimation errors multiplied by the gain matrices, which can be seen as preconditioners. A simple and recursive (with respect to order) algorithm for update of the gain matrix, which is associated with Neumann series, is found. It is shown that the limiting form of the algorithm (algorithm of infinite order) provides perfect estimation. A new form of the gain matrix is also a basis for unification method of high-order algorithms. New combined and fast convergent high-order algorithms of recursive matrix inversion and algorithms of direct calculation of the parameter vector are presented. The stability of algorithms is proved and explicit transient bound on estimation error is calculated. New algorithms are simple, fast and robust with respect to round-off error accumulation.
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| 3. |
- Stotsky, Alexander, 1960
(författare)
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Frequency Regulation in Smart Microgrids Based on Load Estimation
- 2018
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Ingår i: Journal of Control, Automation and Electrical Systems. - : Springer Science and Business Media LLC. - 2195-3880 .- 2195-3899. ; 29:4, s. 525-533
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Tidskriftsartikel (refereegranskat)abstract
- The desired frequency is maintained in Smart Microgrid (SMG) when the generated power matches the grid load. Variability of wind power and fluctuations of the load are the main obstacles for performance improvement of frequency regulation in SMG. Active Power Control (APC) services provided by wind power generators is one of the main sources for performance improvement in frequency regulation. New coordinated APC architecture, which involves simultaneous speed and pitch control actions delivers desired power to the grid despite significant variations of the wind power. A tool-kit with discrete-time input estimation algorithms, which estimate input quantity using output measurements is presented. Unmeasurable load fluctuations are estimated with input estimation method using measurements of grid frequency deviation. Desired power for APC is driven by estimated and a priori known loads. This observer-based control method reduces the risk of overshoots and oscillations in frequency regulation loop compared to PID controllers driven directly by the frequency deviation. The stability of the closed loop frequency control system is proved, and simulation results show that observer-based control architecture provides significant improvement of the frequency regulation in SMG.
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| 4. |
- Stotsky, Alexander, 1960
(författare)
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Grid Frequency Estimation Using Multiple Model with Harmonic Regressor: Robustness Enhancement with Stepwise Splitting Method
- 2017
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Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 50:1, s. 12817-12822
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Konferensbidrag (refereegranskat)abstract
- Reduction of inertia in electricity networks due to high penetration level of renewable energy sources will require wind turbines to participate in frequency regulation via Active Power Control. The performance of frequency regulation and protection system depends strongly on the performance of network frequency estimation. Fast frequency variations and uncertainties associated with unknown harmonics and measurement noise in the network signals are the main obstacles to performance improvement of frequency estimation with classical zero crossing method, which is widely used in industry. The same uncertainties introduce challenges in model based frequency estimation. These challenges are addressed in this paper within the framework of multiple model with harmonic regressor. Additional challenges associated with computational complexity of matrix inversion algorithms and accuracy of inversion of ill-conditioned matrices in the multiple model are also discussed in the paper. New high order algorithms with reduced computational complexity are presented. Instability mechanism is discovered in Newton-Schulz and Neumann matrix inversion techniques in finite precision implementation environment. A new stepwise splitting method is proposed for elimination of instability and for performance improvement of matrix inversion algorithms in the multiple model. All the results are confirmed by simulations.
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| 5. |
- Stotsky, Alexander, 1960
(författare)
-
High order algorithms in robust least-squares estimation with SDD information matrix: Redesign, simplification and unification
- 2015
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Ingår i: Proceedings of the IEEE Conference on Decision and Control. - 2576-2370 .- 0743-1546. ; 2015-February, s. 271-276
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Konferensbidrag (refereegranskat)abstract
- This paper describes new high order algorithms in the least-squares problem with harmonic regressor and SDD (Strictly Diagonally Dominant) information matrix. Estimation accuracy and the number of steps to achieve this accuracy are controllable in these algorithms. Simplified forms of the high order matrix inversion algorithms and the high order algorithms of direct calculation of the parameter vector are found. The algorithms are presented as recursive procedures driven by estimation errors multiplied by the gain matrices, which can be seen as preconditioners. A simple and recursive (with respect to order) algorithm for update of the gain matrix, which is associated with Neumann series is found. It is shown that the limiting form of the algorithm (algorithm of infinite order) provides perfect estimation. A new form of the gain matrix is also a basis for unification method of high order algorithms. New combined and fast convergent high order algorithms of recursive matrix inversion and algorithms of direct calculation of the parameter vector are presented. The stability of algorithms is proved and explicit transient bound on estimation error is calculated. New algorithms are simple, fast and robust with respect to round-off error accumulation.
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| 6. |
- Stotsky, Alexander, 1960
(författare)
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Modified Flipped Classroom Model in Chalmers Professional Education
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper is the final report for the project inthe course ’Blended Learning and Digital Media in HigherEducation’ given by Elisabeth Saalman and Thommy Eriksson.This paper proposes new implementation-ready concept ofvideo education in the wind energy area for Chalmers Professional Education. Modified Flipped Classroom Model with video feedback is proposed in this paper as a new pedagogical concept. The model allows video education without skilled Instructor in the classroom and includes a number of components:1) video lecture in wind energy, 2) quizzes, 3) discussions and 4)video summary of the discussions and 5) video feedback from skilled Instructor.Video Lecture ’Lesson on Wind Turbine Control’ was developedwithin this project, recorded in Camtasia and supplied with the ’Guide’ and ’Slides’.
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| 7. |
- Stotsky, Alexander, 1960
(författare)
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Modified SOLO Taxonomy Model for Constructive Alignment in Automatic Control & Signal Processing Education
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Controls is the engineering field that deals withmodeling, regulation and performance assessment of dynamicsystems so that they behave according to the desired specifications.Signal processing is the area, which develops methodsfor processing of sensory data in different areas.Achievements in applied mathematics, new sensors and actuator technologies, developments of new IT tools and software create new opportunities in control and signal processing engineering.This in turn implies new challenges and developments in control and signal processing education.New modified SOLO (Structure of the Observed LearningOutcome) Taxonomy model is developed for automatic controland signal processing education. New model provides a simple, reliable and robust concept, which is well associated with the method of constructive alignment for five levels of understanding.The model is applied for constructive alignment of basiccourse in automatic control and to mini-lesson in digital signal processing.
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| 8. |
- Stotsky, Alexander, 1960
(författare)
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Nonlinear speed and yaw control for wind turbine powered vessels
- 2016
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Ingår i: Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering. - 2041-3041 .- 0959-6518. ; 230:3, s. 255-265
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Tidskriftsartikel (refereegranskat)abstract
- The application of conventional wind turbines on board a vessel creates a number of new challenges for turbine control systems. Thrust force is used in marine applications as an additional control variable for propulsion of the vessel.Variability of the wind speed and wind direction, together with the yaw rate and range constraints, impose strong requirements on the turbine control system. A new projection algorithm that projects the turbine thrust force on the heading direction of vessel is proposed in this paper for controlling propulsion. Variations in the wind direction and wind speed are counteracted via turbine yaw angle, making the turbine thrust force always aligned with the heading direction of the vessel. The conventional Kv2 speed controller is modified for varying yaw offset and a combined algorithm for simultaneous control of the turbine speed and thrust force is proposed. Stability of the Kw^2 speed controller for varying yaw offset is proved via the Lyapunov method. The controller also takes into account the constraints on the yaw rate and minimizes the turbine gyroscopic effects via a proper choice of the virtual upper bound of the input voltage of the yaw motor. All of the results are illustrated by simulations using measurement data acquired from the Hönö turbine.
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| 9. |
- Stotsky, Alexander, 1960
(författare)
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Towards accurate estimation of fast varying frequency in future electricity networks: The transition from model-free methods to model-based approach
- 2016
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Ingår i: Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering. - : SAGE Publications. - 2041-3041 .- 0959-6518. ; 230:10, s. 1164-1175
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Tidskriftsartikel (refereegranskat)abstract
- Accurate estimation of fast varying fundamental frequency in the presence of harmonics and noise will be required for effective frequency regulation in future electricity networks with high penetration level of renewable energy sources. Two new algorithms for network frequency tracking are proposed. The first algorithm represents a robust modification of classical zero crossing method, which is widely used in industry. The second algorithm is a multiple model algorithm based on the systems with harmonic regressor. Algorithm allows complete reconstruction of the frequency content of the signal, using information about the upper bound of the number of harmonics only. Moreover, new family of high-order algorithms together with new stepwise splitting method are proposed for parameter calculation in systems with harmonic regressor for the accuracy improvement. Statistical methods are introduced for comparison of two new algorithms to classical zero crossing algorithm. The modified algorithm provides significant improvement compared to the classical algorithm, and the algorithm with harmonic regressor provides further improvement of the statistical performance indexes with respect to the modified algorithm.
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