LVRT Control Strategy of DFIG Based Wind Turbines Combined the Active and Passive Protections

Abstract

Due to its advantages, Doubly Fed Induction Generator (DFIG) is the most used generator in the wind power area. However, the DFIG provides electrical power at a constant frequency even if the rotor speed varies, also it allows a better capture of wind energy. Although the DFIG has a high sensitivity regarding the electrical faults, which brings up many challenges in terms of compliance: Power provider and electrical operator (in terms of production continuity and quality of energy). Actually, the grid connection requirements impose strict rules to respect for Low Voltage Ride Through (LVRT) and grid support capabilities following the Grid Code (GC). Therefore, it’s crucial for wind turbines (WT) to propose an advanced control. In fact, when detecting voltage dips, WTs must stay connected to the grid to provide the required reactive power in order to have a safe and reliable operation. The objective of this article is to propose a new LVRT strategy able to keep WTs connected to the grid despite severe voltage dips. The principle of this strategy is to make a connection between the level of dips and the optimal solution to overcome the fault. For this reason, the proposed strategy is based on the combination of two solutions (an active and a passive method): The first aims to improve the control strategy to mitigate the over-current at low voltage dips. The second is applied for severe voltage dips using protection circuits: Series Dynamic Braking Resistor (SDBR) and DC-Chopper.

LVRT control strategy of DFIG based wind turbines combined the active and passive protections