Decentralizad Reactive Power Sharing and Frequency Restoration in Islanded Microgrid

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Decentralizad Reactive Power Sharing and Frequency Restoration in Islanded Microgrid

ارائه دهنده: Provider: Mohsen adinevand

اساتید راهنما: Supervisors: Dr Mohammad Hasan Moradi

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: دکتر علیرضا حاتمی - دکتر مجید غنی ئی زارچ

زمان و تاریخ ارائه: Time and date of presentation: 14 march 2021

مکان ارائه: Place of presentation:

چکیده: Abstract: the reduction in the use of fossil fuels and the preservation of these valuable reservoirs for future generations, which will reduce greenhouse gas emissions and reduce environmental problems, is one of the most important concern today in the world. in the field of electricity generation to reduce the emissions of these gases in recent years, the use of renewable energy sources has received much attention. The microgrid concept (MG) is considered as the best solution to integrate renewable energy sources into power systems, which is expected to receive substantial electrical power through renewable energy sources and distributed generation units.the most important components of microgrids are distributed generation (DGs), storage devices , local loads, and control systems. Microgrids can operate in either networked mode or as an island.The operation of microgrids in islanding mode has many advantages such as power quality improvement, increasing reliability and supply of load demand for distribution network and consumers, so the performance of microgrids in islanding mode and issues related to its control is very important. In islanding mode, the management task of DGs to supply active and reactive load regulating the bus voltage and microgrid frequency is the responsibility of the control system, which is carried out using two overall centralized control and decentralized control methods. One of the most popular decentralized control methods is the droop control method. the main idea of which is to imitate the governor behavior of synchronous generators in power systems. In this method, load distribution between DGs is done without the use of telecommunication lines and using local signals. In addition to its many advantages, the droop control method also has some disadvantages. this dissertation intends to investigate the main problems, namely the lack of proper reactive power distribution between DGs and microgrid frequency change, which are major problems for the drop control method and in recent years in various articles have proposed solutions to these problems, and in this dissertation DGs are first controlled based on the common drop method (in which the drop characteristics are such that the DGs' share of the load is proportional to their nominal power).Then , a decentralized method is presented which is a more powerful droop control method which has improved the process of power distribution between distributed generation units by creating a transient coupling between the active and reactive power droop control of each units .In this method, through two separate processes, firstly, it distributes reactive power between DGs correctly and with high accuracy, and secondly, it returns the microgrid frequency to its nominal value. The proposed method, in order to do this properly, requires synchronization between the DGs so that the processes start simultaneously on all the DGs, which is synchronized using the wavelet transform. Then, inspired by conventional synchronous generators, virtual damping is proposed to reduce the frequency fluctuations in the MGs. Then, it is shown that the conventional frequency recovery method enters the offset to the phase angle, which contrasts with the exact power distribution. For this purpose, a new control method, based on phase angle feedback, for instantaneous frequency recovery is proposed along with a new method for adaptive adjustment of feedback coefficients to maintain accurate active power sharing. According to the theoretical analysis and simulation results presented in this dissertation, it is determined that the proposed method restricts frequency fluctuations, improves frequency deviations, and improves the dynamic stability margin of the island microgrid, while ensuring the accurately active power sharing between the DGs. The low frequency oscillations of the conventional P - F droop loop are also attenuated by the modified drop control. Keywords: renewable energy resource, microgrid, distributed generation units, Decentralized control, droop control, frequency restoration, reactive power sharing, wavelet transform

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