Micro grid Design

Micro grid design for performance evaluation of micro grid system

The chosen model for the microgrid system in the research project is consists of 13.8kV, three feeder distribution system which is connected to a large network through a 69kV radial line. The 13.8 kV busbar of the three feeders are radially connected to the main grid through the transformer and a 69kV line.  The network at the end of the 69 kV line is represented by a 69 kV, 1000 MVA short circuit capacity bus. Combination of both linear and non linear loads are supplied through the three feeders of the subsystem. Both load 1 and load 2 are at feeder 1. Load 3 is at feeder 2. Whereas load 4 and load 5 are at feeder 3. DG1 is a 5.0-MVA conventional diesel-generator or a gas-turbine generator DG2 represents a fixed-speed wind-turbine set with rated capacity of 2.5-MVA which is interfaced through an synchronous generator (SG) equipped with excitation and governor control systems.

Project Methodology

Project flowchart

The designed micro grid model will be simulate under two circumstances which is during in grid connected mode and islanded mode. As for islanded mode there are two conditions that will be consider which are for unplanned switching event and preplanned switching event.

The designed  micro grid model will be simulate by using the Power System Computer Aided Design (PSCAD) software. 

PSCAD software 

PSCAD/EMTDC is an industry standard software for studying the transient behavior of electrical networks. EMTDC performs the electromagnetic transients calculations while PSCAD provides the graphical interface.PSCAD/EMTDC offers a large database of built-in components, and allows theuser to define his own models, either using other built-in components or coding a component in Fortran. Both methods are used during this study. Some components, like the electrical generators, are taken from the software library, while others, like the governors or the wind turbine aerodynamical model, are user-defined.

Islanded mode

Islanded mode is when the microgrid is disconnected with macro-grid. As usual, the micro grid operates in grid-connected mode, but when a fault occurs at the upstream grid, it should disconnect and shift into islanded operation mode. During islanding, the power balance between supply and demand does not match at the momentAs a result, the frequency of the microgrid will fluctuate, and  the system can experience a blackout unless there is an adequate power balance matching process. The control of  the energy storage system inverter responds in milliseconds. Otherwise, because of the nature of the control of some micro sources such as the diesel generator, gas engine, and fuel cell, these micro sources have a relatively slow response time

Distributed Generation

Distributed generation also called as the on-site generation, dispersed generation, embedded generation, decentralized generation, decentralized energy or distributed energy, generates electricity from many small energy sources. Distributed generation can be divided in two level; local level and the end point level. Local level generation is usually consists of renewable energy technologies that are site specific such as wind turbine, solar system, and geothermal energy production. These plants is smaller and less centralized compared than the traditional plant. For some customers, distributed generation can lower costs, improve reliability, reduce emissions, or expand their energy option. Distributed Generation may add redundancy that increases grid security even while powering emergency lighting or other critical systems.   

Wind Farm

Photovoltaic system

Mini hydro plant

MICRO GRID?

With continuous demand of electricity, most of the energy and utility service provider were seeking an alternative solution to generates electricity due to meet the demand of their end-users. Micro grid system is known as the alternative solution to generate the electricity but the question is how far is the performance and the reliability of the micro grid system in order to support the macro grid system. Before we go further in the micro grid. it is better to understand what a micro grid is; there are actually no single clear definition on what micro grid is but some experts were discussing microgrids in term of residential sized system while some of them discussing on campus and community wide systems.But what can be conclude that the microgrid is a system is a portion of power system which include one or more distributed generation (DG) units capable of operating either in parallel or independent from the main grids while providing continuous power to the loads.