Comparative Study on Low Voltage Ride Through Techniques for Double Fed Induction Generator in Wind Energy Conversion System Under Fault Conditions

Abstract

Due to the technological advancement of wind turbines (WTs) from fixed to variable speed, wind energy is now becoming one of the most accessible and exploitable types of renewable energy. Large wind power stations frequently use Double Fed Induction Generator (DFIG) based Wind Energy Conversion Systems (WECSs). DFIG has several advantages, including a lower rated power converter, lower costs, lower losses, improved efficiency, variable speed operation, and independent active and reactive power control capabilities. However, connecting this wind farm to the current grid poses significant power system difficulties. This is due to DFIG's vulnerability to grid faults such as voltage dip. This fault causes the flow of excess current across both the stator and the rotor terminals, which may consequently lead to some serious damage of the generator, power converters, and also DC Link capacitor. However, in spite of all of this, the current Grid Code (GC) requires the system to stay connected to the grid during this fault condition and support it in retaining its nominal voltage. This capacity of the system is also known as Low Voltage Ride Through (LVRT) capacity. For the system to archive such capacity, some appropriate protection mechanisms or controlling strategies must be utilized. Therefore, in this thesis, the crowbar protection technique and the Adaptive Neuro Fuzzy Inference System (ANFIS) controller are employed. Furthermore, the performance of the system while employing the PI controller, crowbar protection technique, and ANFIS controller is analyzed and compared under grid fault conditions, i.e., a voltage dip with a magnitude of 0.1pu (worst case) using MATLAB/Simulink 2021a software and based on actual data obtained from Adama II wind farm. The settling time of ANFIS for controlling the rotor currents in d and q axes (idr and iqr) and DC link voltage is 3.6 seconds, 3.57 seconds, and 3.4 seconds, respectively. On the other hand, the settling times of the PI controller for the controlling the rotor currents in d and q axis and the DC link voltage are 4 seconds, 3.91 seconds, and 45.2 seconds, respectively, while the crowbar protection technique's settling times are 4, 6, and 4.9 seconds, respectively. According to these simulation results, the ANFIS controller provided the best performance of the three strategies since it allowed both the rotor currents and the DC link voltage to return to their steady state values faster than the remaining two techniques.