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Title: Enhanced control and protection for inverter dominated microgrids
Author: Li, Xinyao
ISNI:       0000 0004 5355 4875
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2014
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Implementation of distributed energy resources (DER) has the potential to lower the carbon oxygen emissions, reduce the power distribution losses and improve the overall system operation. Despite the numerous advantages brought by these small-scale DERs, effective protection and control of such systems are still unsolved challenges. The distribution system is increasingly being confronted with congestion and voltage problems, which limits further penetration of DERs. Numerous studies have been conducted to analyse these challenges and provide recommendations or guidance for protection and control in the past few years. There is also a lot of effort to develop an advanced regime for integration of large amounts of DERs, such as the "microgrid". Microgrids are designed to provide control and protection of a cluster of DERs, storage units and loads in a way that can coordinate with the conventional utility grid operation with little conflict. As flexible as it is, a microgrid is connec ted to the utility grid behaving as a controllable entity in normal operation, and can be disconnected from the grid to present itself as a power island in emergency, e.g. system black-out. Since most of the DERs are interfaced with inverters, this thesis is dedicated to provide in-depth investigation of protection and control within inverter dominated microgrids. The thesis provides two main valuable contributions. Firstly, an enhanced control scheme for a microgrid consisting of multi inverter interfaced generators (IIG) is developed and compared to the conventional droop based decentralized control. The proposed control scheme is particularly designed for systems with IIGs interconnected via relatively long cable lengths (several kilo metres). It also allows switchless mode transition between islanded operation and grid-connected operation, which reduces the transient voltage and current oscillations, and enhances the transient behaviour of the IIGs. Compared to the conventional droop based decentralized control, the proposed control scheme has better operational stability and is immune to different lengths and R/X ratios of connecting cables. The proposed control also brings better voltage regulation and has a larger power output capacity. Secondly, a new travelling wave based protection scheme is developed which involves modification of an application friendly signal processing technique - Mathematical Morphology. The impact of distance to fault, fault inception angle and fault impedance is analysed and quantified. The thesis proposes a systematic protection solution which is proved to be immune to the changes of system topology, modes of operation and load conditions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available