Efficient Control of Active Transformers for Increasing the PV Hosting Capacity of LV Grids

The increased penetration of grid-connected photovoltaic (PV) systems in low-voltage (LV) grids creates concerns about overvoltage in these grids. The proposed methods to prevent overvoltage, such as reactive power absorption by PV inverters and active power management of customers, focus on decreasing the voltage rise along LV feeders, and the potential of active medium-voltage to low-voltage (MV/LV) transformers for overvoltage prevention has not been thoroughly investigated. This paper presents the application of active MV/LV transformers for increasing the PV hosting capacity of LV grids. The potential interferences between the operation of active transformers and the reactive power absorption by PV inverters are investigated, and a voltage droop control approach is proposed for the efficient control of these transformers during high PV generation periods. The proposed method can potentially increase the PV hosting capacity of the grid, while eliminating the need for a complex and centralized controller. The voltages of specific locations or the grid state estimations provide adequate data for adjustments of the droop parameters. The simulations and field test results associated with the implementation of the proposed method to a newly developed active LV grid with high PV penetration in Felsberg, Germany, confirm the efficiency of the proposed method

Power quality and electromagnetic compatibility: special report, session 2

The scope of Session 2 (S2) has been defined as follows by the Session Advisory Group and the Technical Committee: Power Quality (PQ), with the more general concept of electromagnetic compatibility (EMC) and with some related safety problems in electricity distribution systems. Special focus is put on voltage continuity (supply reliability, problem of outages) and voltage quality (voltage level, flicker, unbalance, harmonics). This session will also look at electromagnetic compatibility (mains frequency to 150 kHz), electromagnetic interferences and electric and magnetic fields issues. Also addressed in this session are electrical safety and immunity concerns (lightning issues, step, touch and transferred voltages). The aim of this special report is to present a synthesis of the present concerns in PQ&EMC, based on all selected papers of session 2 and related papers from other sessions, (152 papers in total). The report is divided in the following 4 blocks: Block 1: Electric and Magnetic Fields, EMC, Earthing systems Block 2: Harmonics Block 3: Voltage Variation Block 4: Power Quality Monitoring Two Round Tables will be organised: - Power quality and EMC in the Future Grid (CIGRE/CIRED WG C4.24, RT 13) - Reliability Benchmarking - why we should do it? What should be done in future? (RT 15

PRZEGLĄD METOD REGULACJI NAPIĘCIA W SIECIACH ELEKTROENERGETYCZNYCH NISKIEGO NAPIĘCIA Z DUŻYM UDZIAŁEM GENERACJI ROZPROSZONEJ

Deterioration of voltage conditions is one of the frequent consequences of connecting an increasing number of photovoltaic sources to the low-voltage (LV) power grid. Under adverse conditions, i.e. low energy consumption and high insolation, microgeneration can cause voltage surges that violate acceptable limits. Research shows that the increase in voltage is the main limitation for connecting new energy microsources to the LV network and forces the reconstruction of the network. An alternative to costly modernizations can be the implementation of appropriate strategies for controlling network operation to maintain the voltage at the required level. The article presents an overview of the methods and concepts of voltage control in a low-voltage network developed so far to mitigate the undesirable phenomenon of voltage boosting. The focus was mainly on local methods—not requiring communication infrastructure—as best suited to the conditions of Polish distribution networks. Gathering the results of many tests and simulations carried out in different conditions and on different models allowed for the formulation of general conclusions and can be a starting point for further research on a control method that can be widely used in the national power system.Jedną z częstych konsekwencji przyłączania do sieci elektroenergetycznej niskiego napięcia (nn) coraz większej liczby źródeł fotowoltaicznych jest pogorszenie warunków napięciowych. W niesprzyjających warunkach – przy niskim poborze energii i wysokim nasłonecznieniu – mikrogeneracja może powodować podskoki napięcia przekraczające dopuszczalne granice. Badania pokazują, że wzrost napięcia stanowi podstawowe ograniczenie dla przyłączania nowych mikroźródeł energii do sieci nn i wymusza przebudowę sieci. Alternatywą dla kosztownych modernizacji może być wdrożenie odpowiednich strategii sterowania pracą sieci pozwalających utrzymać napięcie na wymaganym poziomie. W artykule zaprezentowano przegląd opracowanych dotychczas metod i koncepcji regulacji napięcia w sieci nn mających na celu opanowanie niepożądanego zjawiska podbicia napięcia. Skupiono się głównie na metodach lokalnych – nie wymagających do prawidłowego działania infrastruktury komunikacyjnej – jako najlepiej przystosowanych do warunków polskich sieci dystrybucyjnych. Zebranie wyników badań i symulacji, przeprowadzonych przy różnych założeniach i na różnych modelach, pozwoliło na sformułowanie ogólnych wniosków i może stanowić punkt wyjścia do dalszych badań nad metodą sterowania mogącą znaleźć szerokie zastosowanie w krajowym systemie elektroenergetycznym

Optimal planning of distribution grids considering active power curtailment and reactive power control

In this paper, a new planning methodology is proposed for existing distribution grids, considering both passive and active network measures. The method is designed to be tractable for large grids of any type, e.g., meshed or radial. It can be used as a decision-making tool by distribution system operators which need to decide whether to invest in new hardware, such as new lines and transformers, or to initiate control measures influencing the operational costs. In this paper, active power curtailment and reactive power control are taken into account as measures to prevent unacceptable voltage rises as well as element overloads, as these allow postponing network investments. A low-voltage, meshed grid with 27 nodes is used to demonstrate the proposed scheme. In this particular case, the results show that by using control measures, an active distribution system operator can defer investments and operate the existing infrastructure more efficiently. The methodology is able to account for variations in operational and investment costs coming from regulatory influences to provide an insight to the most cost-efficient decision