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Stability analysis and experimental evaluation of a control strategy for islanded operation of distributed generation units
, Article IEEJ Transactions on Industry Applications ; Volume 131, Issue 8 , 2011 , Pages 1013-1022 ; 09136339 (ISSN) ; Karimi, H ; Iravani, R ; Sharif University of Technology
2011
Abstract
This paper presents stability analysis of a distributed generation (DG) controller (1), in an islanded mode, based on the Mapping Theorem and the Zero Exclusion Condition, and validates the results based on a laboratory scale experimental setup. The DG unit is interfaced to the host system through a voltage-sourced converter (VSC). The control strategy regulates the load voltage at the desired value in the islanded mode, despite uncertainties in the load parameters. The frequency of the island is controlled in an open loop manner by an internal oscillator. The experimental results show that the controller provides robust voltage control for a wide range of load parameters, and even maintains...
Passive Islanding Detection for Distributed Generation Using Decision Tree Algorithm
, M.Sc. Thesis Sharif University of Technology ; Abbaspour Tehrani Fard, Ali (Supervisor) ; Ranjbar, Ali Mohammad (Supervisor)
Abstract
The integration of renewable energy sources introduces several issues including islanding operation. Therefore, Islanding phenomenon should be detected by a fast and reliable islanding detection method. In this thesis an intelligent-based approach is proposed to detect islanding state for Photovoltaic (PV) and Doubly Fed Induction Generator (DFIG) units. Decision tree classification algorithm is chosen as weak classifier and by Adaptive Boosting (AdaBoost), detection accuracy is improved. 16 features are employed to construct feature vectors. Because of intermittency of renewable electricity generation, different states for PV and DFIG generation are assumed. Probable events are simulated...
A Novel Islanding Detection Method For Micro Grids
, M.Sc. Thesis Sharif University of Technology ; Vakilian, Mehdi (Supervisor)
Abstract
There is an increasing trend nowadays toward Distributed Generation (DGs). DG poses positive and negative side effects for both utility and customers. Reduction of system expansion costs, decreasing power loss and reliability enhancement are some benefits of DGs. Connecting DGs to the distribution system can lead to some troublesome issues. Anti-islanding protection is one of these issues. Islanding is the situation in which a distribution system becomes electrically isolated from the remainder of the power system, yet continues to be energized by DG connected to it. Traditionally, a distribution system doesn’t have any active power generating source in it and it doesn’t get power in case...
Load Shedding in Microgrids to preserve System Stability In The Islanded Operation Mode
, M.Sc. Thesis Sharif University of Technology ; Parniani, Mustafa (Supervisor)
Abstract
In the near future, it is expected that the microgrids become widespreed due to issues such as reliability, increased penetration of renewable energy sources and distributed generation, environmental concerns and shortage of fossil fuels. Different control methods have been suggested to regulate the frequency and voltage of the system so that these quantities remain in their permissible range upon islanding and in the islanded operation mode. However, in emergency conditions, such as shortage of generated power compared to the load of microgrid, frequency or voltage reduction occures due to imbalance. In this situation, it is invitable to shed extra load to maintain the stability and...
Integrated Control and Power Sharing of Distributed Generators in Islanded and Grid-Connected Microgrids
, M.Sc. Thesis Sharif University of Technology ; Parniani, Mostafa (Supervisor)
Abstract
Distributed generation (DG) technologies have achieved an intense progress during the last years. One of the appropriate ways to enter a DG system in the electrical network is through the use of microgrids. Because the majority of DG units are connected to the grid with power electronic converters, specific control strategies have been developed for these converters. Control strategies of DGs in microgrid differ in the grid-connected and the islanded states of operation. Changing the control modes from one state to another requires a reliable islanding detection method, and results in unwanted transients. It is, therefore, desirable to devise an integrated control approach for both states....
Robust Control of an Islanded Microgrid Consisting of Parallel Connection of Multiple DG Units
, M.Sc. Thesis Sharif University of Technology ; Karimi, Houshang (Supervisor)
Abstract
A robust decentralized control strategy for the islanded operation of a microgrid is proposed in this thesis. The microgrid consists of the parallel connection of several electronically-coupled distributed generation (DG) units. All DG units are connected to a point of common coupling (PCC) where a passive load is also connected. It is shown that the islanded microgrid can be modeled by an interconnected composite system comprising equal number of subsystems (to the DGs). Moreover, it is shown that the overall islanded microgrid can be controlled by only the local controllers about the individual subsystems. In this case, one of the DGs, referred to as the Master DG, is responsible for...
Stability analysis and experimental validation of a control strategy for autonomous operation of distributed generation units
, Article 2010 International Power Electronics Conference - ECCE Asia -, IPEC 2010, 21 June 2010 through 24 June 2010 ; June , 2010 , Pages 464-471 ; 9781424453955 (ISBN) ; Karimi, H ; Iravani, R ; IEEJ ; Sharif University of Technology
2010
Abstract
This paper presents stability analysis of a distributed generation (DG) controller [1], in an islanded mode, based on the Mapping Theorem and the Zero Exclusion Condition, and validates the results based on a laboratory scale experimental setup. The DG unit is interfaced to the host system through a voltage-sourced converter (VSC). The control strategy regulates the load voltage at the desired value in the islanded mode, despite uncertainties in the load parameters. The frequency of the island is controlled in an open loop manner by an internal oscillator. The experimental results show that the controller provides robust voltage control for a wide range of load parameters, and even maintains...
Voltage and FrequencyC Ontrol of an Electronically-Coupled Distributed Generation Unit
, M.Sc. Thesis Sharif University of Technology ; Karimi, Houshang (Supervisor) ; Nobakhti, Amin (Supervisor)
Abstract
The use of distributed generation (DG) units provides several advantages for the utility distribution grid. Mostly power electronics converter is used as an interface to connect a DG unit to a utility grid. A DG unit normally operates in a grid-connected mode. In this mode, the host grid dominantly dictates the voltage amplitude and frequency of the local load at the point of common coupling (PCC) and the DG unit controls its real/reactive power components. Separation of the DG unit and its dedicated load from the host grid is called islanding. Subsequent to the formation of an island, due to the lack of control over the voltage magnitude and frequency, the islanded DG system becomes...
Robust decentralized control for islanded operation of two radially connected DG systems
, Article 2010 IEEE International Symposium on Industrial Electronics, ISIE 2010, Bari, 4 July 2010 through 7 July 2010 ; July , 2010 , Pages 2272-2277 ; 9781424463916 (ISBN) ; Karimi, H ; Karimi Ghartemani, M ; The Institute of Electrical and Electronics Engineers (IEEE); IEEE Industrial Electronics Society (IES); IEEE Control Systems Society (CSS); Society of Instrument and Control Engineers (SICE-Japan); Politecnico di Bari ; Sharif University of Technology
2010
Abstract
A decentralized servomechanism controller for islanded (autonomous) operation of radial connection of two distributed generation (DG) units is proposed in this paper. Each DG unit utilizes a voltage-sourced converter (VSC) for interface to its dedicated load. The DG units and the loads are to operate in the islanded mode of operation. Each DG unit regulates the voltage of its dedicated load in a decentralized manner. In this paper, it is first shown that the radial connection of two DG units in the islanded mode constitutes an interconnected composite system consisting of two subsystems. Moreover, the paper shows that the overall islanded system can be controlled by the local controllers,...
Multivariable servomechanism controller for autonomous operation of a distributed generation unit: design and performance evaluation
, Article IEEE Transactions on Power Systems ; Volume 25, Issue 2 , 2010 , Pages 853-865 ; 08858950 (ISSN) ; Davison, E. J ; Iravani, R ; Sharif University of Technology
Abstract
A linear time-invariant (LTI) robust servomechanism controller for islanded (autonomous) operation of a distributed generation (DG) unit and its local load is proposed. The DG unit utilizes a voltage-sourced converter (VSC) as the interface medium. The controller design is obtained by introducing a new optimal controller design procedure, in conjunction with a proposed non-conservative robustness constraint. The proposed controller utilizes 1) an internal oscillator for frequency control and 2) a robust servomechanism controller (RSC) to regulate the island voltage. Despite uncertainty of the load parameters, the proposed controller guarantees robust stability and pre-specified performance...
A new control strategy for a multi-bus MV microgrid under unbalanced conditions
, Article IEEE Transactions on Power Systems ; Volume 27, Issue 4 , 2012 , Pages 2225-2232 ; 08858950 (ISSN) ; Karimi, H ; Mokhtari, H ; Sharif University of Technology
2012
Abstract
This paper proposes a new control strategy for the islanded operation of a multi-bus medium voltage (MV) microgrid. The microgrid consists of several dispatchable electronically-coupled distributed generation (DG) units. Each DG unit supplies a local load which can be unbalanced due to the inclusion of single-phase loads. The proposed control strategy of each DG comprises a proportional resonance (PR) controller with an adjustable resonance frequency, a droop control strategy, and a negative-sequence impedance controller (NSIC). The PR and droop controllers are, respectively, used to regulate the load voltage and share the average power components among the DG units. The NSIC is used to...