Research On Low-voltage Ride-through And Dynamic Equivalence Of Doubly-fed Induction Generators

Bulk wind power integration influences security and stability of power systems. Aftershort-circuit fault, Wind Turbine Generators (WTGs) keeping integration provide reactiveand active support to the power grid beneficial to fault recovery process. However, largevoltage drop will increase currents of the stator and rotor, voltage of the DC link voltage,and damage the Back-to-Back. The rotor speed increases, and the mechanical transfer shaftmay fatigue. The disintegration of the wind farms is possibly followed by major blackouts.So it is necessary to study the Low-Voltage Ride-Through (LVRT) capability of the WTGs.With tremendous wind power capacity, simulation speed and memory requirements toWTGs are insufficient to meet the requirements of dynamic analysis and control.This dissertation focuses on the LVRT technology and dynamic equivalence of theDoubly-Fed Induction Generators (DFIGs). The main works are given as following.Firstly, based on to the dynamic model of the DFIG, the stator and rotor currents, andthe reactive output of the DFIG with the rotor crowbar resistance (RCR), with the statorseries resistance (SSR), or with both, are derived to quantify the advantages anddisadvantages of the first two LVRT strategies.Secondly, coordination strategy for the SSR and the RCR is newly proposed. Bysetting the criterions of switch-in and out currents of the SSR and the rotor crowbar, theirswitch sequence is coordinated. While guaranteeing LVRT capability, the proposedalgorithm reduces duration of the DFIG integrated to the system as ordinary inductiongenerator, decreases the var absorption from the grid, and reduces fluctuation of theelectromagnetic torque.Finally, the K-means clustering algorithm is applied to classify the WTGs. The DFIGsare clustered with the wind speeds and their parameters. The DFIGs belonging to the samecluster are aggregated by the capacity weighted method. Effect of the dynamic equivalenceis verified with different wind speeds and fault modes.