IMPROVEMENT OF LVRT CAPABILITY BY COMBINING-SWITCH TYPE FAULT CURRENT LIMITER AND SUPER CAPACITOR FOR DFIG BASED WIND TURBINES

Background: An improved Low Voltage Ride Through (LVRT) control approach for a Doubly Fed Induction Generator (DFIG) based Wind Energy Conversion System (WECS) is offered in this paper. DFIG is sensitive to grid voltage variation; hence it requires reactive power support to overcome this drawback for safe and stable operation of power grid. The DFIG is interfaced to the AC network through a Grid Side Converter (GSC) and a Rotor Side Converter (RSC) to facilitate the variable speed operation of the wind turbine. When compared with pitch angle control, rotor side converter and grid side converter is simple and permits rotor speed to increase further than the prescribed value. Grid side converter (GSC) control diminishes the DC link instability and Rotor Side Converter (RSC) control reduces the transient current during the period of fault. The benefit of energy storage, which helps to improve the LVRT, is also applied. Methods: The Switch Type Fault Current Limiter (STFCL) and Super Capacitor (SC) are the two essential proposed methods used in this system. The STFCL excellently decreases the over current in the rotor side throughout the fault. Since the Fault Current Limiting Inductors are located in series with the stator to limit the rotor over current throughout the fault. On the other hand SC improves the system stability. It has huge power concentration to balance the system power. Results: The viability of the proposed method is established by the experimental results on a 1.5 MW DFIG system using MATLAB/SIMULINK software. From the above methods, the design of energy storage and STFCL with control on RSC and GSC the rotor voltage, current, real and reactive power remains within the safe working limit throughout the period of fault. This control works for both symmetrical and asymmetrical fault. Conclusions: The proposed control technique enables DFIG to carry on the power production during fault and offer the reactive power support to the grid. With this scheme, rotor current and voltage waveforms are enhanced. The torque oscillation is reduced and successfully suppressed the transient rotor current.