Matti Lehtonen

Bio: Matti Lehtonen is an academic researcher from Aalto University. The author has contributed to research in topics: Fault (power engineering) & Electric power system. The author has an hindex of 40, co-authored 694 publications receiving 8559 citations. Previous affiliations of Matti Lehtonen include Razi University & New York University.

Review on the PV Hosting Capacity in Distribution Networks

Abstract: The increasing penetration of Photovoltaic (PV) generation results in challenges regarding network operation, management and planning. Correspondingly, Distribution Network Operators (DNOs) are in the need of totally new understanding. The establishment of comprehensive standards for maximum PV integration into the network, without adversely impacting the normal operating conditions, is also needed. This review article provides an extensive review of the Hosting Capacity (HC) definitions based on different references and estimated HC with actual figures in different geographical areas and network conditions. Moreover, a comprehensive review of limiting factors and improvement methods for HC is presented along with voltage rise limits of different countries under PV integration. Peak load is the major reference used for HC definition and the prime limiting constraint for PV HC is the voltage violations. However, the varying definitions in different references lead to the conclusion that, neither the reference values nor the limiting factors are unique values and HC can alter depending on the reference, network conditions, topology, location, and PV deployment scenario.

Impacts of automatic control systems of loop restoration scheme on the distribution system reliability

Abstract: Loop restoration scheme (LRS) is a special feeder automation (FA) scheme, which is used by utilities to improve distribution system reliability. The LRS is controlled and managed by its automatic control system (ACS). The impacts on distribution system reliability indices of implementing LRS mainly depend on the type of its ACS. Two common types of ACS of LRS are presented and used in this study. Successful operation of ACS is dependent on the protection and automatic control functions of switching devices of LRS. Different failure modes of these switching devices can therefore affect the procedure of ACS in fault detecting, isolating and service restoration. The impacts of failure of protection and automatic control functions of switching devices and fuse of lateral distributors on reliability indices are illustrated. The worth of implementing LRS and its ACS type is represented by the reduction in expected customer interruption cost. A distribution test system is utilised to examine the impacts of two common types of ACS of LRS on the distribution system reliability. Selecting the type of ACS of LRS by utilities relies on the desired level of load-point and system reliability improvement. This study aims to quantitatively assess the impacts of two common types of ACS of LRS on the distribution system reliability.

Equipment sensitivity to voltage sags-test results for contactors, PCs and gas discharge lamps

Abstract: Voltage sag tolerance levels were measured for samples of three equipment categories sensitive to sags: contactors, PCs and gas discharge lamps. An up-to-date voltage waveform generator was used to produce and repeat the events as necessary. Remaining voltage and sag duration were the test variables. For contactors also the effect of point-on-wave of sag initiation was studied. The results were rather well convergent with earlier studies by other institutes. This justifies more generalized conclusions on performance of these device categories as well as more statistical approach to the issue. This kind of typical equipment sensitivity data is needed as a library for the future sag assessment methods.

Short-Term Forecasting of Heat Demand of Buildings for Efficient and Optimal Energy Management Based on Integrated Machine Learning Models

Abstract: The increasing growth in the energy demand calls for robust actions to design and optimize energy-related assets for efficient and economic energy supply and demand within a smart grid setup. This article proposes a novel integrated machine learning (ML) technique to forecast the heat demand of buildings in a district heating system. The proposed short-term (24h-ahead) heat demand forecasting model is based on the integration of empirical mode decomposition (EMD), imperialistic competitive algorithm (ICA), and support vector machine (SVM). The proposed model also embeds an ML-based feature selection (FS) technique combining binary genetic algorithm and Gaussian process regression to obtain the most important and nonredundant variables that can constitute the input predictor subset to the forecasting model. The model is developed using a two-year (2015–2016) hourly dataset of actual district heat demand obtained from various buildings in the Otaniemi area of Espoo, Finland. Several variables from different domains such as seasonality (calendar), weather, occupancy, and heat demand are used to construct the initial feature space for FS process. Short-term forecasting models are also implemented using the Persistence approach as a reference and other eight ML approaches: artificial neural network (ANN), genetic algorithm combined with ANN (GA-ANN), ICA-ANN, SVM, GA-SVM, ICA-SVM, EMD-GA-ANN, and EMD-ICA-ANN. The performance of the proposed EMD-ICA-SVM-based forecasting model is tested using an out-of-sample one-year (2017) hourly dataset of district heat consumption of various building types. Comparative analysis of the forecasting performance of the models was performed. The obtained results demonstrate that the devised model forecasts the heat demand with improved performance evaluated using various accuracy metrics. Moreover, the devised model achieves outperformed forecasting accuracy enhancement, compared to the other nine evaluated models.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

World energy outlook

Abstract: This chapter discusses leading problems linked to energy that the world is now confronting and to propose some ideas concerning possible solutions. Oil deserves special attention among all energy sources. Since the beginning of 1981, it has merely been continuing and enhancing the downward movement in consumption and prices caused by excessive rises, especially for light crudes such as those from Africa, and the slowing down of worldwide economic growth. Densely-populated oil-producing countries need to produce to live, to pay for their food and their equipment. If the economic growth of the industrialized countries were to be 4%, even if investment in the rational use of energy were pushed to the limit and the development of nonpetroleum energy sources were also pursued actively, it would be extremely difficult to prevent a sharp rise in prices. It is evident that it is absolutely necessary to pursue actively the development of coal, natural gas, and nuclear power if a physical shortage of energy is not to block economic growth.