| 1. Introduction | | | | generator has some drawbacks, as it requires reactive |
| The micro grid system is as shown in the Fig.1.The | | | | power to improve the voltage regulation. In addition to |
| recent concept of micro grid system is to group a | | | | this induction generator used in micro hydel scheme, |
| cluster of loads and parallel DG system within a certain | | | | converts all available mechanical energy into electrical |
| local area. In remote areas when two or more DGs | | | | energy to eliminate the controller for the turbine. |
| are interconnected formed micro grid system. Micro | | | | 3. Micro Hydel Units |
| grid system can operate in both the grid connected | | | | Controller on turbine side is avoided to make the |
| mode or islanding modes. | | | | system simple and cost effective. Thus, whenever the |
| Proper operation of these modes requires the | | | | consumer load is reduced, the surplus generated |
| implementation of high performance power flow | | | | energy from induction generator must be dumped |
| control and voltage regulation algorithms [1,2]. | | | | somewhere else so as to maintain constant voltage |
| Fig. 1. Micro grid System | | | | and frequency in the system. These drawbacks can |
| Three critical components play major roles in the | | | | be overcome by using an electronic load controller and |
| proper operation of micro grid in both modes [3]. They | | | | VAR compensator. Already many different types of |
| are | | | | electronic load controller exist for the stand-alone |
| · Local micro source controller | | | | system. When several induction generators involve in a |
| · System optimizer | | | | micro grid system, reactive power compensation |
| · Distribution protection | | | | required by these generator become more significant |
| 2. Plant Design | | | | and high performance power flow control and voltage |
| Micro source controller is an important component of | | | | regulation algorithms are required. |
| the micro grid system. It provides a basic control of | | | | Fig.2 Micro Hydel units for stand alone |
| real and reactive power using droop characteristics. All | | | | System |
| the sources are connected to the point of common | | | | On the other hand consumer load is fluctuating and |
| coupling (PCC) after dc voltage sources are | | | | varies continuously. This type of load can be named |
| converted to an acceptable ac sources using voltage | | | | as uncontrolled load. Whenever micro grid system is |
| source inverter (fig.1). Energy manager provides the | | | | operating in an islanding mode the unbalanced surplus |
| system optimization. Energy manager uses the | | | | electrical energy must be dumped to maintain the input |
| information on local load needs, power quality | | | | essentially constant. This can be achieving by using |
| requirement, demand side management request etc to | | | | load controller, which diverts the surplus energy to |
| determine the amount of power that micro grid should | | | | dump load placed parallel to uncontrolled load. |
| draw from the main grid. Based on the information it | | | | References |
| receives, some of its key functions are to provide the | | | | [1] S. S. Murthy, R. Jose, and B. Singh, "Experience in the |
| individual power and voltage set points for each micro | | | | development of microhydel grid independent power |
| source controller, provides logic and control for islanding | | | | generation scheme using induction generators for |
| and reconnecting the micro grid during events. | | | | Indian conditions," presented at TENCON '98. 1998 IEEE |
| Protection is necessary in the event of fault in the | | | | Region 10 International Conference on Global |
| micro grid system. If the fault occurs in the main grid | | | | Connectivity in Energy, Computer, Communication and |
| then it should be isolated from the main grid as rapidly | | | | Control, 1998. |
| as possible. If the fault occurs within the micro grid | | | | [2] Y. Li, D. M. Vilathgamuwa, and P. C. Loh, "Design, |
| system the protection coordinate should isolated the | | | | analysis, and realtime testing of a controller for multibus |
| smallest possible section of the feeder to eliminate the | | | | microgrid system," Power Electronics, IEEE |
| fault. | | | | Transactions on, vol. 19, pp. 1195-1204, 2004. |
| Induction motor is used as an induction generator when | | | | [3] R. H. Lasseter, "MicroGrids," presented at Power |
| electricity is generated from micro hydel units (fig. 2) or | | | | Engineering Society Winter Meeting, 2002. IEEE, 2002. |
| from wind turbines. Induction generators have many | | | | [4] B.Palle,M.G.Simoes, “Dynamic Simulation and |
| advantages over synchronous generator such as | | | | Analysis of Parallel Self-Excited Induction Generators |
| ruggedness, less maintenance requirements, absence | | | | for Islanded Wind Farm Systems,” Industry |
| of dc excitation and inherent short circuit protection | | | | Applications, IEEE |
| when working as a stand alone low cost energy | | | | Transactions on, vol. 41, pp. 1099-1105, 2005. |
| conversion schemes. On the other hand an induction | | | | |