Development of Strategies for Fault Ride Through Capability Improvement of a Grid Connected DFIG based Wind Energy Conversion System

Now-a-days, the growing demand of electricity and the scarcity of fossil fuels, encourage to generate electricity from never ending renewable energy resources such as wind, solar etc., Wind energy has become one of the most important and promising sources of renewable energy. Today the wind power capacity of the world is approximately 539,291 MW at the end of 2017 and around 52,552 MW of capacity was added in the year 2017 only. The rapid increase in wind farms and production of wind energy facilitates the interconnection of Wind Turbine Generation System (WTGS) with the grid for uninterruptable power supply. With increased penetration of wind power into electrical grids, Variable Speed Induction Generators are largely preferred for its dynamic features. Out of these, Doubly Fed Induction Generator (DFIG) is one which has various advantages such as providing four quadrant operation, unit power factor and maintained reactive power. But a grid connected system is always subjected to various load conditions and grid faults such as short circuits adversely affecting the continuous power supply. Hence to maintain all the appropriate operating conditions, the power system operators has decided some grid code requirements (GCR) out of which the Fault Ride Through (FRT) capability improvement is one. FRT is defined as the ability of the wind generator to stay connected to the grid in short periods of voltage dip caused by any disturbances. Various methods are there to improve the FRT capability of a DFIG system. It may be achieved through implementation of different devices such as crowbar protection (CB), active crowbar protection (ACB_P), Dynamic voltage restorers (DVRs), STATCOMs and Superconducting Fault Current Limiters (SFCLs). Some improved control technologies for the converters of the DFIGs are also there through whose application FRT capability can be improved without any external hardware circuit. Here in this work, CB, ACB_P, DVR and SFCL are implemented separately with a 1.5 MW grid connected DFIG system and the dynamic responses of the DFIG is studied during fault conditions. Finally by implementing sophisticated control techniques such as second order sliding mode (SOSM) control and Higher Order Sliding Mode Control (HOSM) methods, the back to back converter of the DFIG is operated to achieve effective FRT capability