Browsing by Author "Lehtonen, Matti, Prof., Aalto University, Department of Electrical Engineering and Automation, Finland"

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  • Domestic Space Heating Load Management in Smart Grid - Potential Benefits and Realization
    (2016) Ali, Mubbashir
     School of Electrical Engineering | Doctoral dissertation (article-based)
    In future power systems, intermittent renewable generation sources are expected to have a considerable segment in the total generation assortment. Given the inconsistency and unpredictability of intermittent renewable energy sources, the fast growing integration of intermittent renewable generation could negatively affect the operations of power system. Since demand response (DR) is a flexible load shaping tool, it is viewed as a practicle solution to enhance the overall system efficiency in future smart grids. The overall objective of this dissertation is to evaluate the possible advantages of responsive domestic heating, ventilation, and air conditioning (HVAC) loads for DR applications and the development of practical frameworks to realize them. Due to its considerable share in energy consumption profile and operational flexibility, the DR treatment is restricted to the HVAC load. The DR applications include the minimization of customer energy cost and increased utilization of intermittent generation while taking into account customers' thermal comfort. The goal of this dissertation is divided into three major tasks so as to describe the DR benefits for various applications. A comprehensive assessment of HVAC DR potential for up/down ramping is suggested in the first task. The second task proposes generic frameworks for HVAC load management that are directed towards minimizing customer energy payments while taking customer's preferences into consideration. Finally, the last task establishes tools for increased utilization of wind generation by optimally managing the cyclic operation of responsive HVAC loads. To accomplish this dissertation objective, simulations are conducted using the proposed frameworks for Finnish systems. The following significant deductions are indicated in the results. The flexibility to unleash DR for up/down ramping is affected by the heat demand requirements, while upward DR is strongly limited by HVAC power ramping capability and allowed thermal comfort limits. Furthermore, utilization of DR will greatly shrink customer energy payments which mainly depends on the permissible indoor temperature deviation. The monetary savings are value added when DR is jointly activated in both energy and balancing market using the proposed model. Additionally, it is revealed that joint optimization of DR and RTTR will attain greater utilization of wind generation in distribution networks as weighed against DR activation alone. The developed models can be utilized by power system operators and stake holders to enhance the system operation. Consequently, the developed tools will help to achieve a better understanding of HVAC DR potential and advantages and will act as support to maximize the DR enrolment at the end user level.
  • Flexible Loads in Smart Grids - Charging Solutions for Electric Vehicles and Storage Space Heating
    (2016) Malik, Farhan Hameed
     School of Electrical Engineering | Doctoral dissertation (article-based)
    Renewable generation sources provide emission free power production, however their intermittent nature requires more elasticity on the demand side. Matching the demand and supply with more intermittent renewable sources in the system is challenging due to their variable generation. A bulk storage media for electrical energy and a big share of time shiftable load could help solve the problem to a great extent in increasing the utilization of network resources and achieving the optimal usage of energy. Large storage could offer a worthy cushion to house fluctuations on both the generation and consumption sides. Shifting the time of use for flexible loads could offer cost savings to the end customer and support the network in dealing with critical situations. Electric Vehicles (EVs) and Storage Space Heating (SSH) have a great potential as a flexible load and storage media. For instance, EVs could draw extra power from the power grid in off-peak hours or with the excessive production from renewables. It could supply power back to the power grid in peak hours or if generation from the renewables is dropped. If penetration of EVs increase rapidly, then fulfilling their charging needs in every scenario with the existing power network and market mechanism would be challenging. The development of intelligent charging infrastructure for EVs to charge them as optimally as possible both in terms of charging cost and time is a subject of concern. Along with EVs, space heating load contributes a big share in the overall load of a household. SSH has an abundant potential as a flexible load for grid support in energy balance management. Intelligent charging control of Heat Storage (HS) could assist the grid in mitigating fluctuations on both the consumption and generation sides. This study considers the charging solutions for EVs and SSH. The main focus of this work is to suggest charging solutions for EVs for fulfilling their charging needs in every scenario. This research investigates the impact of different power tariffs on charging profiles under various simulation scenarios, to propose a demand bidding framework for rescheduling of charging and make a feasibility study on uncontrolled fast charging of EVs on highways. This thesis is a slight addition in the field of power systems engineering, especially in charging solutions for EVs and SSH in energy balance management. Elementary advantage is the customer participation in energy market. Cost effective use of energy and power network resources could be achieved. Fluctuations due to intermittent renewable generation could be mitigated. Network capacity utilization and possible expansion of the grid with the increased EV penetration is identified. 
  • Methods for Damping Inter-Area Oscillations in the Nordic Power System
    (2017) Elenius, Stefan
     School of Electrical Engineering | Doctoral dissertation (monograph)
    In the Nordic power system the damping of low frequency inter-area oscillations sets limits on the transfer capability when power is transferred from Finland to the other Nordic countries over AC transmission lines. In this thesis the damping of inter-area oscillations in the Nordic system has been studied, with the emphasis on the Finnish part of the system. A full scale system model of the Nordic system has been used in the studies. Two different software packages have been used that can handle large power system models. For non-linear simulations the PSS/E software has been used, and for linear-analysis the software package PacDyn. A new method based on long-distance frequency responses has been introduced for controllability assessment. With this method an approximation of the relative variation in controllability factor magnitudes can be obtained by comparing the frequency responses of transfer functions over long distances. Another new method that is based on linear feedback over long distances has been introduced to verify the effects on damping and to show the correlation to results from computations with long-distance frequency responses. The advantage of these two methods is that they can be used with both non-linear and linear system models. Long-distance frequency response computations, combined with computations of damping using feedback over long distances, has proven to be a methodology that gives the same information about controllability as computation of controllability factors with linear analysis software. For practical purposes, the long-distance frequency response computations alone may give sufficient information about the controllability of the inter-area modes. A third new method that is based on synthesized feedback over long distances was introduced to be used with the non-linear system model. The effects on damping with HVDC power modulation, controlled shunt compensation (SVC), controlled series compensation (TCSC), and power system stabilizers of generators were studied with linear analysis. The results from the linear analysis were compared to results obtained with the non-linear model. A good agreement was found. It was further discovered that there is a strong correlation between the rate of change of phase angles in the frequency response of the transfer function for bus voltage control and damping from SVC operating in bus voltage control.
  • Novel Methods for Arcing Fault Detection and Location in Power Distribution Systems
    (2017) Zoko Ble, Frank
     School of Electrical Engineering | Doctoral dissertation (article-based)
    Conventional power system protection functions mainly deal with currents and voltages associated with faults and most protection devices monitor current, voltage, or impedance against critical setting values. However, in many arc fault conditions of earlier stage, the arc associated current amount is under the setting of relays, and subsequently the arc continues to burn undetected. Power arc generates electromagnetic signals. Radiation producing power arcs can originate from different sources and causes, like due to tree leaning on energized conductors, downed conductor or broken insulators. This thesis first investigates the characteristics of these electromagnetic signals and then examines algorithms for arc fault location using laboratory produced arcs. Using strategically placed antennas the electric arc electromagnetic (EM) radiation can be detected at remote distance and, to some extent, the arc source location can also be determined. This work investigates feasibility of detecting and locating the actual arc source point in 3D Cartesian plane through the multiple radiation detection and location methods. In this study the following six different arcing fault detection and location methods are compared in pinpointing electric arc electromagnetic (EM) sources in power systems: cross-correlation method (XCORR), first peak of arrival method (FPA), leading edge of first arrival peak method (LEFAP), energy attenuation method (ENERGY) or inverse square method, angle of arrival method (AoA), and wavelet analysis (WAVELET). It is evident that the interpretation of the results based on these six methods depends to some extent on statistical methods; therefore, the methods undergo statistical analysis evaluation in order to determine a suitable power arc location algorithm which can be used in real field measurements. Specifically, analysis of variance (ANOVA) and multiple linear regressions (MLR) are applied for statistical estimation and for comparison of the results with the actual source point. The results show that it is feasible for the six methods, using the radiated signals from arcing fault, to detect and locate the arcing source with a reasonable accuracy. The cross-correlation among these proposed methods shows a better potential in clarifying the electric arc source position when compared with other algorithms.
  • Reliability aspects of network planning for meshed subtransmission networks
    (2015) de Oliveira e Sousa, Bruno Jorge
     School of Electrical Engineering | Doctoral dissertation (article-based)
    As the intermediate part of the power system connecting transmission and distribution systems, the subtransmission networks incorporate a great number of intrinsic features. Despite their ambiguous role, sometimes being treated as distribution or as transmission, the subtransmission networks have a clear and direct effect on power quality issues for end-customers. Therefore, they must be handled and appropriately modeled, because of their particularities and operational practices.  This thesis proposes modifications to the generic network cost function which is adjusted to the subtransmission networks. These modifications are located in the outage cost component, in the inclusion of the voltage sag cost component, and in the network assessment of two-dimensional time-related scenarios. More particularly, this work is focused on urban meshed topology with underground cable and overhead line connections. This type of network is well represented by the typical 110-kV Nordic subtransmission network which constitutes a realistic example in cold countries.  Furthermore, this thesis develops four modules that complement the subtransmission network assessment algorithm. The Reliability Module assesses networks in a block-layer structure from the perspective of the delivery point. The Voltage Sag Module determines the voltage sag distribution function and its severity coefficients. The Network Cost Module compiles statistical data and results from the previous modules to estimate the total network cost over a project period. As an ancillary tool, the Sensitivity Module identifies zones of low reliability within the tested network and suggests remedial actions. The results show that this sort of subtransmission network with short and medium-length lines contains large voltage sag and outage costs. For instance, overhead networks are susceptible to meteorological phenomena, thus producing high rates of failures, interruptions and voltage sags. Conversely, underground networks are virtually immune to these, consequently resulting in an extremely low number of interruptions and voltage sags. Despite the aggregated investments, the gradual replacement of overhead networks with underground networks would most likely yield several operational benefits, including reinforcement of grid resilience and reliability, as well as supporting power quality to end-customers.