SIMULATION OF DOUBLY FED INDUCTION GENERATOR IN SMALL HYDRO

Abstract

Small hydro energy conversion systems are used all over the world for the supply of clean and renewable energy, with virtually no emissions and quick startup time. Small hydropower is still a preferred option in many areas. Some areas are still unable to effectively make use of some cheaper turbine options, like reversible pumps. Since they must operate at a fixed speed for a given supplied head of water in order to effectively transfer energy from water turbine to the generator. Variable Speed Constant Frequency (VSCF) systems using power electronics and Doubly Fed Induction Generators (DFIG) are able to solve this problem. The concept has been used in larger (over I MW) wind turbines for many years with greater success, and has slowly become accepted into hydroelectric systems. Recently; they are effectively used to electrify the remote and rural areas where grid electricity not available. This dissertation work cover, a variety of VSCF systems and various simulation models for DFIG used in grid-connected small hydro generation are discussed. A wide literature review of earlier studied carried out on DFIG with hydro application is also included. Using MATLAB/SIMULINK tool a detail model of DFIG with hydro turbine is developed and simulated for find out its suitability in hydro. One of the most recent rotor side-control schemes of DFIG using vector control is also discussed. In this method bi-directional AC-AC converter is used in the rotor circuit to control the current injected into it. Due to the bi-directional nature of converter, it can be used to feed the rotor power back to the grid, resulting that it reduces rotor power losses and it supply power to the grid at super-synchronous speed. Vector control techniques can also be applied to control rotor currents to achieve fast and decoupled control of the generator. The DFIG is controlled in order to get the steady state. The main advantage of the DFIG technology with power electronic converters is its ability to generate or absorb reactive power, thus eliminating the need for installing capacitor banks as in the case of squirrel-cage induction generators. Therefore DFIG may become a suitable option for small hydro power.