PREDICTION OF ANNUAL ENERGY PRODUCTION FROM PV STRING UNDER MISMATCH CONDITION DUE TO LONG-TERM DEGRADATION

Reduction of long-term degradation effects represents a long-time challenge in photovoltaic (PV) manufacturing industry. Modelling of long-term degradation types and their impact on maximum power of PV systems have been analysed in this article. Brief guidelines for PV cell-based modelling of PV systems have been illustrated. Special study case, PV string consisting of 12 PV modules, has been modelled in order to determine degradation and mismatch power losses. Modified methodology for prediction of annual energy production from PV string, based on horizontal irradiation and ambient temperature experimental measurements at the location of Belgrade, has been developed. Coefficient named “degradation factor” has been introduced to include and validate degradation power losses. Economic considerations have indicated evident money income reduction, as a consequence of lower annual energy production related to long-term degradation

Тransverse differential protection of double circuit overhead lines

Dvostruki nadzemni vodovi (DNV) se često projektuju i grade u elektroenergetskim sistemima (EES) sa osnovnim ciljem povećanja kapaciteta i pouzdanosti prenosa električne energije. Najčešće povezuju dva aktivna visokonaponska dijela EES-a, ali se mogu pronaći i u radijalno napajanim mrežama industrijskih nivoa napona, za šta je karakterističan primjer napajanje udaljenih industrijskih zona i rudnika u razvijenim državama. Zbog postojanja dva paralelna sistema vodova na zajedničkim stubovima duž iste trase, aktivne su elektromagnetske sprege šest provodnika, što značajno komplikuje realizaciju osjetljive i selektivne relejne zaštite u odnosu na standardne slučajeve relejne zaštite jednostrukih nadzemnih vodova. Od relejne zaštite DNV-a očekuje se selektivnost u pogledu razlikovanja kvarova unutar i izvan štićene dionice, lociranja na kom od dva paralelna voda se nalazi kvar i određivanja faza koje su obuhvaćene petljom kvara. U okviru ove doktorske disertacije analizirani su postojeći i razvijeni novi algoritmi u cilju poboljšanja osjetljivosti i obezbjeđivanja selektivnosti usmjerene poprečne diferencijalne zaštite DNV-a. Kao preduslov za kvalitetan istraživački proces, na početku je definisan precizan matematički model DNV-a, praćen odgovarajućom softverskom implementacijom i detaljnom metodologijom proračuna podužnih električnih parametara. Potom je data i komparativna analiza uticaja različitih transpozicija provodnika DNV-a na signale struja u asimetričnim režimima rada. Nakon formiranja i implementacije modela DNV-a, razvijen je interaktivni simulator rada relejne zaštite primjenom softverskog paketa MATLAB, u svrhu detaljnog simulacionog ispitivanja postojećih i novorazvijenih algoritama. U prvom koraku istraživačkog procesa analizirani su i detaljno ispitivani tradicionalni koncepti relejne zaštite DNV-a. Putem odgovarajuće komparativne analize utvrđene su prednosti i mane koncepta poprečne diferencijalne zaštite u odnosu na koncept distantne zaštite. Drugi korak istraživačkog procesa je posvećen analizi i ispitivanju posebne klase algoritama poprečne diferencijalne zaštite koji u svom radu ne koriste naponske signale. Za slučaj dvostrano napajanog DNV-a, vršeno je ispitivanje i data je komparativna analiza rezultata rada dva najpoznatija algoritma poprečne diferencijalne zaštite, zasnovana na priraštajima strujnih signala. U trećem koraku istraživanja predložen je novi algoritam zasnovan na promjeni faznih uglova strujnih signala za usmjerenu poprečnu diferencijalnu zaštitu radijalnog DNV-a. Osnovni cilj razvoja novog algoritma je zasnovan na pretpostavci da je moguće poboljšati osjetljivost usmjerene poprečne diferencijalne zaštite za slučaj radijalnog DNV-a, u odnosu na postojeće algoritme koji u svom radu koriste samo signale struja. Zatim je za slučaj radijalnog DNV-a vršeno novo ispitivanje i data je komparativna analiza rezultata rada postojećeg poznatog algoritma zasnovanog na priraštajima strujnih signala i predloženog novog algoritma zasnovanog na promjeni faznih uglova strujnih signala.Double circuit lines (DCL) are often designed and used in the power systems with the main goal of improving the capacity and reliability of the power transmission. They usually connect two high-voltage active networks, but also can be found in industry-level voltage radial networks in developed countries with typical application of supplying power to remote industrial areas and mines. Due to the existence of two parallel lines on the same transmission towers, along the same route, electromagnetic couplings of six conductors significantly complicate realization of the sensitive and selective relay protection systems when compared to relay protection systems for typical transmission lines consisting of three conductors. Relay protection of DCL is expected to be selective in the distinction of the faults inside and outside of the protection zone, as well as in the distinction of the faulted and healthy line, and it is additionally required for protection to detect which phases are faulted. Within this thesis, the existing and new algorithms are developed in order to improve sensitivity and ensure selectivity of the transverse differential protection of DCL. A precise mathematical model of DCL is initially defined as a precondition for quality research process, which is followed by the corresponding software implementation and detailed methodology of longitudinal electrical parameters calculation. Then the comparative analysis of the impact of different transpositions of DCL conductors on current signals in unbalanced operation mode is presented. After defining and implementing DCL model, an interactive simulator of relay protection is developed using a software package MATLAB with the main goal of enabling detailed simulation analysis of the existing and newly created algorithms. Traditional concepts of DCL relay protection operation are analysed and tested in the first step of the research process. The advantages and drawbacks of transverse differential protection concept are determined and compared with those corresponding to distance protection concept. The second step of the research process includes the analysis and testing of the special algorithms for transverse differential protection that do not require the voltage signals for operation. For the case of doubly-fed DCL, two selected algorithms based on increments of current signals are tested and the comparative analysis of the obtained results is given. In the third step of the research process a new algorithm, based on the changes of phase angles of current signals, is proposed for protection of radial DCL. The main goal behind the development of the new algorithm is based on the assumption that is possible to additionally improve sensitivity of directional transverse differential protection in the case of radial DCL, when compared to existing algorithms using only current signals for operation. Then the new testing is performed in the case of radial DCL in order to compare the existing well-known algorithm based on increments of current signals with newly proposed algorithm based on the changes of phase angles of current signals

Near Real-Time Distributed State Estimation via AI/ML-Empowered 5G Networks

Fifth-Generation (5G) networks have a potential to accelerate power system transition to a flexible, softwarized, data-driven, and intelligent grid. With their evolving support for Machine Learning (ML)/Artificial Intelligence (AI) functions, 5G networks are expected to enable novel data-centric Smart Grid (SG) services. In this paper, we explore how data-driven SG services could be integrated with ML/AI-enabled 5G networks in a symbiotic relationship. We focus on the State Estimation (SE) function as a key element of the energy management system and focus on two main questions. Firstly, in a tutorial fashion, we present an overview on how distributed SE can be integrated with the elements of the 5G core network and radio access network architecture. Secondly, we present and compare two powerful distributed SE methods based on: i) graphical models and belief propagation, and ii) graph neural networks. We discuss their performance and capability to support a near real-time distributed SE via 5G network, taking into account communication delays