OPERATION & MANAGEMENT OF MICROGRID USING BACK TO BACK CONNECTED VOLTAGE SOURCE CONVERTERS WITH THE UTILITY MAINS

Abstract

Grid Coupled distributed generation Systems (DGs) are gaining wide popularity and acceptance these days. There is a need for faster and reliable systems for operation particularly when dealing with grid connected distributed generation systems (DGs). But most of the state-of-the-art systems are not so cost-efficient, faster and reliable. The objective of this project is to develop a new, highly efficient and cost-effective algorithm for the distributed generation (DG) interface for grid interactive applications. This thesis proposed a solution for arrangement of electrical power, generated by distributed generators (DG), catering to local loads as well as the grid. The interface design is capable of accomplishing the following tasks: (a) the generated power is feed to the local as well as main grid through the back to back voltage source converters (VSCs). (b) In case of generated active power being more than the local load, the difference is fed to the grid, and when it is less than the local load, additional power is drawn from the grid. (c) Islanding of the system for its protection in case of absence of the grid. (d) Load Scheduling. In case the grid gets disconnected from distributed generation systems (DGs), the proposed system detects this condition quite easily. At the time of grid disconnection, if the power fed by the DG is insufficient, then the load is scheduled according to the need and supply. At the time of reconnection to grid, the voltage source converters are synchronized and allow transferring with in short time. The DGs are made to operate in the islanding mode even after the grid is detected and is synchronized with the grid first. After the synchronization is complete, the operation is successfully transferred from islanding to normal mode. A combination of the above two techniques (normal operation and islanding operation) with the option of selecting the one suiting and fulfilling the need accordingly at the particular time can be highly cost-efficient, fast and reliable. The work presented in thesis deals with issues related to formation of microgrid, its operation and solution to the difficulties faced by such integration with main grid. The MATLAB modeling and simulation of operation of micro grid under both grids connected and islanding mode is discussed in different chapters. The grid connected mode address to load sharing, reactive power compensation and other power quality issues, whereas, the islanded mode has been shown to deal with islanding detection, isolation from the main grid, intentional scheduling of the load and reconnection of the main grid to the microgrid. The simulation result presented in the thesis depicts performance of the proposed control method under dynamic perturbation on microgrid and grid side.