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.

Assessing the Applicability of Vertical Transportation in Power System Inertial Support

Abstract: Displacement of conventional generation with inverter-fed renewable generation hampers power system stability due to a decrease in rotating masses and spinning reserves. This reduction in inertial response capability requires more advanced power system design and innovations in frequency control technology and related power system balancing markets. This paper investigates the potential of applying vertical transportation devices to provide the system with virtual inertia to maintain the frequency quality. The study focuses on the Nordic power system and considers the demand response from both elevators and escalators. The results indicate that vertical transportation is able to contribute to the frequency support with little impact on the aggregate travel time of passengers. However, the capability is limited during the most likely periods of low system inertia, which, in the Nordic power system, occur during summer nights.

Multi-Objective Allocation of EV Charging Stations and RESs in Distribution Systems Considering Advanced Control Schemes

Abstract: Renewable energy sources (RESs) and electric vehicle charging stations (EVCSs) have been extensively incorporated into distribution systems. Due to the stochastic nature of RES generation and electric vehicles (EVs), risky operational challenges might impact the grid. Therefore, this paper proposes a multi-objective planning framework to optimally allocate EVCSs in conjunction with RESs. Specifically, the proposed RESs and EVCSs planning framework considers three sub-objectives to be minimized, i.e., voltage deviations, energy losses, and EVs owners’dissatisfaction. Further, active power curtailment of RESs is precluded while considering the diverse operational constraints of the grid, RESs, and EVCSs. To provide further benefits, advanced control schemes of the interconnecting RES inverters, grid-to-vehicle (G2V), and vehicle-to-grid (V2G) schemes are considered in the proposed framework. A two-level approach is developed to solve this holistic framework with competing sub-functions to obtain the Pareto-optimal solutions. The outer optimization level precisely optimizes the RES locations and sizes, along with the optimal places of the EVCS. On the other hand, the inner level determines the optimal EVCS charging considering stochastic EV power, RES inverter reactive power, and the time-of-use energy tariff. The proposed framework has been tested on the 69-bus distribution system. The simulation results reveal the efficacy of the proposed RES and EVCS planning framework. The total voltage deviation and energy losses achieved by the proposed framework are reduced by 96% and 74%, respectively, with respect to the uncontrolled charging of EVs, while the owners’ satisfactions are met.

Optimization-Based Distribution System Reliability Evaluation: An Enhanced MILP Model

Abstract: Standard mathematical-programming-based models have attracted considerable attention for optimizing distribution system planning and operation due to their salient advantages. More specifically, mixed-integer linear programming (MILP) has proven very effective in modeling such problems. The availability of optimization software for efficiently solving MILP problems with guaranteed convergence to optimality while providing a measure of the distance to the optimal solution has made MILP models more popular. Although a plethora of efficient MILP formulations have been proposed for planning and operating studies of distribution grids, incorporating reliability into such models is still challenging. Recently, several innovative techniques have been proposed in the literature for optimization-based reliability evaluation of distribution networks. However, either oversimplifications or high computation costs are featured, thereby limiting the applicability of such approaches in practical problems. To overcome this issue, this paper presents an enhanced MILP model for distribution system reliability evaluation. The proposed model boosts the computational effectiveness without sacrificing solution accuracy. Numerical experience with the proposed model demonstrates its superior performance over the state of the art.

Microgrid Stability Analysis Considering Current State-Feedback

Abstract: A converter-based microgrid including several distributed generations (DG) and energy storage systems (ESS) embodies a small power system consisting of several synchronous machines and loads. The stability issue and the coordination between generating units is an essential challenge, either in island or in grid-connected microgrids. The instability of individual DGs cause the microgrid instability as a whole. So, the individual unit stability and the microgrid stability both must be ensured simultaneously. The state feedback concept which is considered in control of converters has a substantial effect on the converter stability and microgrid stability, subsequently. This study will introduce a small-signal model for the microgrid including converter-based DGs and loads considering the previous studies in this field. A phase locked loop (PLL) is required for the control strategy. The effect of current state feedback is scrutinized and analyzed in this study as the main contribution. The effectiveness of the proposed control strategy to enhance the microgrid stability using chosen state feedback is examined through simulation studies. The simulation results ensure that the microgrid stability using the proposed control method and state-feedback is strengthened.

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.