الفهرس | Only 14 pages are availabe for public view |
Abstract Recently, microgrid applications are become widely utilized because of its features, where it is a local interconnection between distributed generators (DGs) and loads. Distributed generators can be renewable energy sources (RES), conventional sources, or both types. Microgrid can offer many benefits such as losses reduction during energy transfer from generation unit to load, reduction in the amount of harmful gases, and enhancement the system reliability. However, microgrids with dominant renewable resources face many challenges such as deteriorating the power quality in terms of voltage and frequency. In the thesis, frequency variation will be studied in detail, where it occurs because of sudden changes in load or climatic changes that cause a temporary mismatch between generation and load. The change in frequency depends on the microgrid grid inertia. A low inertia operation leads to increase rate-of-change-of-frequency (ROCOF), and low frequency nadir in a very short time. Such situations can lead to tripping of frequency relays (causing under-frequency load shedding) and, in the worst case, may lead to cascaded outages. In the first microgrid, a proposed technique is applied to a microgrid containing a wind turbine and thermal power plant to overcome the decoupling problem. The inherent inertia of the wind turbine that is in the rotating masses is used to store/release energy from/into the system during transient periods through speed control. In the second microgrid, a microgrid consists of a PV plant and a thermal power plant, there is no inertia in the PV plant because of the absence of the rotating mass. In the thesis, the super-capacitor is integrated with the DC bus of the grid interface inverter of the PV system, and voltage control based on frequency deviation to imitate the synchronous generator inertia is applied. In the third microgrid, a microgrid has a wind turbine, a PV plant, and a thermal power plant, a control scheme is proposed which boosts the cooperation of wind and PV generation systems to support the microgrid frequency response concurrently. . |