Institutional Repository
Technical University of Crete
Technical University of Crete
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| URI: | http://purl.tuc.gr/dl/dias/680B0BB8-7C31-4532-B448-1F1F6FD035C7 | ||
| Year | 2024 | ||
| Type of Item | Diploma Work | ||
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| Bibliographic Citation | Stefanos Kosmopoulos, "Optimization of reactive power flow by DC/AC photovoltaic (PV) inverters into the electrical grid", Diploma Work, School of Electrical and Computer Engineering, Technical University of Crete, Chania, Greece, 2024 https://doi.org/10.26233/heallink.tuc.101793 | ||
| Appears in Collections |
A significant consequence of the rapid cost reduction in photovoltaic (PV) systems is their continuously increasing installed capacity in recent years. This growth is transforming the operation of low-voltage networks, as power flow becomes bidirectional. High penetration levels of photovoltaic electricity generation can lead to several critical operational challenges for the electrical grid, such as power quality degradation due to voltage drops or transient overvoltages. The presence of photovoltaic DC/AC converters capable of reactive power control facilitates voltage regulation under challenging transient conditions, significantly contributing to energy loss reduction, improved grid stability and reliability, as well as economic benefits for both electricity providers and consumers.The objective of this thesis is to study specific control methods for DC/AC converters in PV Distributed Generation (DG) units connected to the electrical grid. These methods aim to enable the seamless integration of PV systems into low-voltage networks and maximize their contribution to grid voltage regulation. A detailed simulation of their operation was performed using Matlab/Simulink. As part of the simulations, a generalized model of a low-voltage network with electricity generation from ten PV systems was developed. The main goal was to investigate the potential for grid voltage regulation through reactive power control provided by photovoltaic DC/AC converters. A dynamic model of a large distributed photovoltaic installation with a total capacity of 100 kWp was developed. Reactive power control by PV converters was implemented using the Q(U) Control technique, which regulates voltage by adjusting the reactive power injected into or absorbed from the grid based on the locally measured voltage at the converter terminals. The multiple operating points of reactive power are determined by a predefined Q-U characteristic programmed into the power converters. This control method can operate autonomously, allowing for increased PV penetration levels in the distribution network while minimizing voltage rise incidents. Additionally, controlling the reactive power exchange by each DC/AC PV converter provides a tool for minimizing thermal losses in transmission line circuits. This thesis also presents the implementation and development of a control system in Matlab/Simulink to optimize reactive power flow under realistic conditions across various energy production scenarios. The approach is based on designing a series of actions that optimally adjust the sensitivity of reactive power control according to voltage fluctuations at the point of connection of PV power systems to the electrical grid. Analysis of the simulation results shows that this voltage regulation method, within the framework of the simulated configuration, aligns with the theoretical analysis conducted beforehand.
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