Σε κάθε Σύστημα Ηλεκτρικής Ενέργειας η ηλεκτρική ισχύς έχει δύο συνιστώσες: Την ενεργό, η οποία σχετίζεται με το παραγόμενο έργο και την άεργο, η οποία δε σχετίζεται με την παραγωγή έργου, αλλά συνεισφέρει σε απώλειες και πτώση τάσεως. Για να αποφύγουμε αυτά τα αρνητικά, στοχεύουμε στη μείωση της αέργου ισχύος, επιτυγχάνοντας έτσι βελτίωση του συντελεστή ισχύος. Με την πάροδο του χρόνου, τα επίπεδα αρμονικών τάσεων και ρευμάτων αυξάνονται συνεχώς, δημιουργώντας έντονα προβλήματα στα Συστήματα Ηλεκτρικής Ενέργειας. Λαμβάνοντας υπ’ όψιν στην ανάλυση ροής ισχύος ενός κυκλώματος την επίδραση των ανώτερων αρμονικών τάσης και ρεύματος, η βελτίωση του συντελεστή ισχύος γίνεται πολύπλοκη διαδικασία, ειδικά στην περίπτωση μη ιδανικής πηγής (μη μηδενική εσωτερική σύνθετη αντίσταση). Σκοπός της διπλωματικής εργασίας είναι η αναζήτηση τεχνικών περιορισμού της αέργου ισχύος, αφού πρώτα συσχετισθεί με τις ανώτερες αρμονικές τάσεως και ρεύματος. Γενικά, το πρόβλημα περιγράφεται και αναλύεται με διάφορες θεωρίες ισχύος και λύνεται με την τοποθέτηση κυκλωμάτων που επιτυγχάνουν αντιστάθμιση της αέργου ισχύος. Αρχικά αναφέρεται η περίπτωση βελτίωσης του συντελεστή ισχύος θεωρώντας ιδανική πηγή (μηδενική εσωτερική σύνθετη αντίσταση) με ημιτονοειδή τάση εξόδου και γραμμικό φορτίο. Σε αυτή την απλή περίπτωση, ένας πυκνωτής είναι ικανός να αντισταθμίσει πλήρως την καταναλούμενη από το φορτίο άεργο ισχύ. Στη συνέχεια εξετάζονται τα περιθώρια βελτίωσης του συντελεστή ισχύος σε συστήματα με: • Ιδανική, μη ημιτονοειδή πηγή τροφοδοσίας και γραμμικό φορτίο • Μη ιδανική, μη ημιτονοειδή πηγή τροφοδοσίας και γραμμικό φορτίο Στην πρώτη περίπτωση, η τοποθέτηση απλά ενός πυκνωτή παράλληλα προς το φορτίο μπορεί να βελτιώσει το συντελεστή ισχύος του φορτίου μέχρι ενός σημείου, ο οποίος λαμβάνει εν γένει τιμές μικρότερες της μονάδας. Υπάρχει δυνατότητα βελτίωσης του συντελεστή ισχύος μέχρι και τη μονάδα, χρησιμοποιώντας έναν πιο πολύπλοκο αντισταθμιστή. Στην πρώτη αυτή περίπτωση, η τιμή του αντισταθμιστή μπορεί να βρεθεί και αναλυτικά, ενώ στη δεύτερη περίπτωση η τιμή του πυκνωτή αντιστάθμισης υπολογίζεται μόνο με τη βοήθεια ενός επαναληπτικού αλγορίθμου. / In any power system electrical power has two components: active, which is related to the work done and reactive, which is not associated with the production of work, but contribute to losses and voltage drop. To avoid these negative, we aim to reduce reactive power, thus improving the power factor. Over time, the levels of harmonic voltages and currents are growing, creating severe problems in power systems. Considering the power flow analysis of a circuit the influence of higher harmonic voltage and current, improving the power factor is a complex process, especially in the case of non-ideal source (non-zero internal impedance). The purpose of this thesis is to find mitigation techniques reactive power, after having been associated with higher voltage and current harmonics. Generally, the problem is described and analyzed with various theories of power and is solved by placing circuits achieve reactive power compensation. Initially, the case for improving the power factor assuming ideal source (zero internal impedance) with sinusoidal output voltage and linear load. In this simple case, a capacitor is able to compensate fully consumed by the load reactive power. Then examine the scope for improving the power factor systems: • Ideal, non-sinusoidal power and linear load • Not ideal, non-sinusoidal power and linear load In the first case, the simple placement of a capacitor in parallel to the load can improve the power factor of the load up to a point, which generally takes values ​​smaller unit. Is it possible to improve the power factor up to the unit, using a more complex equalizer. In the first case, the value of the compensator can be found analytically, while in the second case the value of the compensation capacitor is calculated only using an iterative algorithm.

This Master of Applied Science thesis presents a single phase grid connected DC/AC inverter with reactive power (VAR) control for residential photovoltaic (PV) applications. The inverter, utilizing the voltage sourced inverter (VSI) configuration, allows the local residential PV generation to actively supply reactive power to the utility grid. A low complexity grid synchronization method was introduced to generate the parallel and orthogonal components of the grid voltage in a highly computationally efficient manner in order to create a synchronized current reference to the current control loop. In addition, the inverter is able to use a small long life film type capacitor on the DC-link by utilizing a notch filter on the voltage control loop. Simulations were performed on PSCAD/EMTDC platform and a prototype was also developed in the lab to prove the effectiveness of the controllers and the grid synchronization method.

This Master of Applied Science thesis presents a single phase grid connected DC/AC inverter with reactive power (VAR) control for residential photovoltaic (PV) applications. The inverter, utilizing the voltage sourced inverter (VSI) configuration, allows the local residential PV generation to actively supply reactive power to the utility grid. A low complexity grid synchronization method was introduced to generate the parallel and orthogonal components of the grid voltage in a highly computationally efficient manner in order to create a synchronized current reference to the current control loop. In addition, the inverter is able to use a small long life film type capacitor on the DC-link by utilizing a notch filter on the voltage control loop. Simulations were performed on PSCAD/EMTDC platform and a prototype was also developed in the lab to prove the effectiveness of the controllers and the grid synchronization method.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 122-124). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 122-124). Also available on the Internet.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [70]-74).

Thesis (M.E.)--University of Canterbury, 2006. / Typescript (photocopy). "March 2006." Includes bibliographical references (p. 171-179). Also available via the World Wide Web.

[pt] Este trabalho faz um estudo de várias metodologias de partição de custos em ambientes competitivos, com o objetivo de se propor algoritmos para a repartição do custo de suporte de reativo entre os diversos acessantes. Entre as várias metodologias estudadas, como por exemplo Nucleolus, Principio da Decomposição e Valor de Shapley, será verificado que o método de Aumann-Shapley é o mais adequado à repartição do custo de suporte de reativo, já que é baseada em custos marginais, bastante compatíveis com um ambiente econômico competitivo. Técnicas de otimização são de extrema importância para aplicação da metodologia de Aumann-Shapley, porque fornecem os multiplicadores de lagrange necessários ao cálculo dos custos marginais de potencia reativa, que são utilizados na repartição de custos de Aumann-Shapley. Neste sentido, é apresentado um algoritmo de pontos interiores, através do qual também se obtém o custo total de suporte reativo. Dois algoritmos para a repartição do custo de suporte de reativo serão então apresentados, um para aplicação ao caso determinístico e outro para o caso estocástico, de modo a se considerar s ocorrência de contingências na rede elétrica. A metodologia proposta é ilustrada em estudos utilizando- se dois sistemas teste: um de 24 barras e outro de 1653 barras. / [en] This work presents the study of some cost allocation methodologies in a competitive framework and proposes algorithms to reactive cost allocation among transmission consumers. Among the studied methodologies, e.g. Nucleolus, Decomposition Principle and Shapley Value, the Aumann-Shapley methodology will be shown to be the most adequate in sharing the cost of reactive support, due to its basis in marginal cost compatible with and economic competitive framework. Optimization techniques are very important to Aumann- Shapley methodology application, because the supplied Lagrange multipliers are extremely important to the evaluation of reactive power marginal cost, carried out in Aumann-Shapley cost allocation. Besides that, an interior point algorithm will be presented, which is used to obtain Lagrange multipliers and to determine the reactive support total cost. Afterwards, two algorithms will be presented to reactive power support cost allocation, one to be applied in a deterministic case and the other to a stochastic case, where contingencies in a electric network are taken into account. The proposed method is illustrated in studies with two electric test systems: one composed by 24 buses and other by 1653 buses.

M.Ing. / This study covers the problem of a periodic distortion and it's electronic compensation. The description and definition of power transfer in a single-phase electrical network is investigated. The various techniques for achieving optimal power transfer are then derived. From this the principle of the compensation of reactive power in an electrical power network is derived using the definition of power transfer. In order to evaluate and illustrate this principle a system configuration, consisting of a controlled source of reactive power is used. Due to the complexity of the system it was initially decided that a computer simulation would serve as an analytical aid. This provides the opportunity to conduct a thorough investigation into the functioning of the proposed compensator. Using the knowledge thus gained. an experimental system was developed. The simulated system is compared to practically obtained results in an experimentally developed compensator in order to evaluate the accuracy and reliability of the simulation. The study then concentrates on the characterization of the two systems as applied in the compensation of reactive power. This analysis also contributes to the identification of deficiencies in the system. The study then concludes with a critical evaluation of the work and suggestions for improvement. This includes the optimization of the total system and the application in industrial power networks.

Due to the increasing integration of renewable energy generations, the overvoltage and overload issues in transmission networks have become more significant, and they may occur at various locations. To mitigate the overvoltage issues, traditional solutions which often consider the installation of reactive power compensators such as shunt reactors, SVC, STATCOM may not be cost-effective. To mitigate the overload issues, traditional methods using direct or price-based demand control will affect customers’ electrical experience in that they are inconvenienced greatly. This thesis discusses the flexible tap changing techniques that utilise existing parallel transformers in distribution networks to provide reactive power absorption and demand response services for transmission systems. Among them, the tap stagger technique operates parallel transformers in small different tap positions, i.e. staggered taps, to result in more reactive power absorption from upstream networks. In addition, the tap changing technique changes voltages in the range of statutory limits through the adjustment of tap positions in order to change network demands without directly affecting customers. The aggregated reactive power absorption or demand response from many pairs of parallel transformers in distribution networks could be sufficient to provide VAr or demand support to transmission networks. Network capability studies have been carried out in OpenDSS simulation software to investigate the VAr absorption capability by using tap staggering technique and the demand reduction capability by using tap changing technique. The studies are based on two UK HV distribution networks (132-33kV) with 11 and 28 primary substations (33/11 or 6.6 kV) respectively, and the techniques are applied to parallel transformers in primary substations. Based on the results of the two networks, the capabilities of the whole ENW and the UK distribution networks have been estimated respectively by using linear estimation method. In addition, the VAr absorption capability of the tap stagger technique has been validated by using site trial data. The results show an average VAr absorption capability of 0.89MVAr for a primary substation, 315MVAr for ENW networks and about 2500MVAr for the UK at stagger level 4 and show an average demand reduction capability of 3.1% of the original demand at tap down level 3. The results of capability studies together with the validations results confirm that the flexible tap changing techniques are able to provide transmission networks with effective VAr support and demand response services. To assess network VAr absorption and demand response capability more precisely, this thesis also proposes an online load profile estimation method to estimate the load profiles of the network more accurately if not all substations in the network are monitored. The method uses Peak Load Share values, Euclidean Distance, and some load measurements to estimate load profiles. The method has been validated and compared with a traditional aggregation-based method. The results show an average estimation error of 13% ~ 23% in different conditions using the proposed method, and show an average estimation error reduction from about 47% (using the traditional method) to about 13% (using the proposed method). The results indicate that the developed method has a considerable improvement on the accuracy of load profile estimation.