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Control system for distributed generation in low voltage network systems DOI:10.15199/48.2018.07.12

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Prosumer energy generation is becoming an increasingly important element of electric power systems. A novel feature of such installations is the option of equipping them with energy storage units [1]. In Poland, it is chiefly solar PV installations that are applied as micro-sources of energy. In 2016, total installed capacity in PV microinstallations connected to the network system exceeded 100 MW [2], which makes a fourfold increase as compared to the preceding year. It is forecasted that in the oncoming years the photovoltaic market will develop equally dynamically. Operation of PV sources is characterized by daily cycles of variable generation depending on the insolation conditions. The insolation level varies depending on the time of year and day and also on the actual weather conditions. A prosumer installation includes loads, whose operation is also of a variable character depending on a week day and the daily work and life routines of the inhabitants. Unfortunately, it often happens that characteristics of the generation and of the loads are not mutually correlated, which can cause problems for the network system where to the prosumer installations are connected [3]. The above makes a challenge for the distribution network operators (DNOs), who are responsible for proper operation of the network, because the LV grid changes from an one-source supply structure to a more complex system that includes many sources. It can bring about a change from the unidirectional to the bidirectional power flow and most of the presently operated grids are not adjusted to that [4]. Connection of distributed sources to the system involves changes in the load flow, voltage profile of the grid and voltage drop values, which consequently affects voltage values in individual nodes of the grid. Practical experience shows that it leads to exceeding of the allowed voltage values in those nodes. Another problem for the DNOs are such sources,[...]

Monitoring the impact of prosumer micro installations on the electrical parameters of low-voltage network systems DOI:10.15199/48.2019.02.12

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Introduction The development of distributed generation will lead to the emergence in the low-voltage network of phenomena occurring so far in higher voltage networks. Particularly important will be phenomena causing changes in power flows and deterioration of power quality parameters, which pose potential threats for devices connected to the network. In order to counteract them, it will be necessary to monitor the work of those parts of the network in which a large number of micro-sources with a relatively high power have been installed. Analysis of the LV (low-voltage) network operation requires in such a case the implementation of complicated, multi-variant simulations and analyses, e.g. voltage conditions in the LV network with various levels of saturation with microinstallations, different structure and load profile. The essence of the problem According to the relevant act [1], micro-installation is "a renewable energy installation with a total installed electrical power not exceeding 40 kW, connected to a power grid with a rated voltage lower than 110 kV or with a heat-generating power in the combination no greater than 120 kW". The connection of low-voltage power sources of this type to end users, according to another act [2], can take place in two ways: - on the basis of the notification, - by submitting an application for determining the terms of connection to the distribution network, The article focuses on the first of the above-mentioned ways of connecting micro-installations - based on the application. The development of micro-installations, especially photovoltaics, caused by a drop in their prices seems to be unavoidable. As a consequence, one should expect various technical problems, among which the most serious will probably be voltage impact [3, 4], resulting from the power flow from the point of connection of these sources towards the MV/LV (medium voltage/low-voltage) substations. It results from the[...]

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