Analysis and Improvements in the Key Performance Aspects of Grid Connected Microgrids

Yellapragada, Venkata Pavan Kumar and Bhimasingu, Ravikumar (2018) Analysis and Improvements in the Key Performance Aspects of Grid Connected Microgrids. PhD thesis, Indian Institute of Technology, Hyderabad.

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Abstract

The microgrids are low-to-medium voltage distribution systems, which constitutes an interconnection of renewable or alternative energy sources (e.g., solar photovoltaics, wind power, fuel-cells, diesel generators, etc.), energy storage units (batteries, supercapacitors, electric vehicles, etc.), flexible loads, suitable power conversion devices, and control units. The fashion in which all these constituents are interconnected is called as an “architecture” for the microgrid. The microgrid can operate as a single entity in island mode of operation or in parallel with electric utility grid in grid-connected mode of operation. Grid-connected mode of operation is usually preferred to ensure continuous and reliable supply to the local loads. However, the microgrid should exhibit stable responses to operate in grid-connected mode, unless, it can disturb the other generators connected in parallel to it. The fruitful operation of the microgrid depends on four key aspects such as (i) intermittent nature of the energy sources due to their environmental dependency, (ii) suitable architecture selection to interconnect all the constituents, (iii) design of suitable power conversion devices, (iv) design of effective controllers. In literature, the renewable energy intermittency was addressed by considering hybrid energy source (combination of different sources instead of the single type of source) and usage of energy storage units, so that the stored energy can be used in contingencies. Similarly, three physical architectures such as central DC bus architecture, central AC bus architecture, and hybrid (AC-DC) coupled architecture (whose selection impacts the number of power converters required, power conversion efficiency and quality) were developed based on the type of major power flow (AC or DC) in the system. Moreover, various network architectures were developed by IEEE-1547, ISA-95, NIST-Grid 3.0, and IEC-61850 standard groups (whose selection impacts the communication reliability) in view of providing a hierarchical arrangement of system constituents and as well external participants in modern-day microgrids.

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