الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
As the essential component of the smart grid systems, a microgrid utilises local distributed generation constituents, energy reserve modules, with local loads to construct a smaller low, or medium, voltage power system. In general, a microgrid can function in two modes: the grid-connected mode and the islanded mode. As of late, hierarchical control for islanded microgrid systems has been proposed as a standard to describe their function and setup. It splits the control organization into three tiers, namely, primary, secondary, and tertiary. The primary control is built on every local distributed generation controller in a decentralized way. While in the secondary layer, the frequency and voltage recovery control as well as the power quality improvement is involved. In the tertiary control, economic dispatch and power flow optimization issues are involved which relies on being connected to the grid. Both the secondary and tertiary control are generally realized in a centralized mean. And so, disadvantages occur such as high computation and communication cost, weak fault tolerance aptitude, absence of plug-and-play abilities, and so on. In order to overpower these drawbacks, distributed control followed by decentralised control are employed to improve performance.
Firstly, this study presents an overcurrent protection strategy to maintain the operation of Distributed Generator (DG) units under Model Predictive Control (MPC) with primary and secondary levels of control for a faulted autonomous AC microgrid. Primary layer involves a Finite Control Set-MPC (FCS-MPC) for reference voltage tracing and droop control with Proportional-Integral (PI) control for power sharing between DGs. Space Vector Modulation switching gate signals are generated. Unscented Kalman Filter-based estimator with MPC-based Voltage control and a communication-less event time-dependent protocol for frequency control are proposed for voltage restoration along with frequency supervision as secondary control stage in islanded DGs operation. The performance under faults of proposed controller is compared with that under conventional hierarchical control and MPC unmodified control.
Secondly, the employment of a novel hybrid metaheuristics optimization technique to improve and stabilize voltage secondary layer of control being applied on fractional-order Fuzzy Proportional-Integral-Derivative controllers in case of a faulted autonomous three-phase AC microgrid. As of frequency control part, a Proportional-Integral-Derivative controller is used. The under-study islanded microgrid comprises of multiple distribution generation units connected with impedance lines along with local loads. The fractional-order Fuzzy Proportional-Integral-Derivative controller is considered to have superior performance than conventional ones despite the increase in the number of tunable parameters. And so, a Hybrid Water Cycle and Moth Flame optimization algorithm is considered to reach optimum solution for the applied decentralized controllers. The performance of the controller is compared through varying optimization techniques and changing controller type.
The proposed control strategies can return both voltage and frequency to their corresponding reference values while preserving precise power sharing, under a suitable local stability condition. And so, under the mentioned new strategies, the AC islanded microgrid operation stability is enhanced.