Title : Low Voltage Ride-Through Enhancement
of Doubly Fed Induction Generator Using a Dynamic Voltage Restorer
Author : Eman Saad Hamid El-Hawatt
Collection : Ph.D. Electric
Abstract:
In
recent years, the total capacity of wind generation connected to the power
system has been increased significantly due to its low environmental cost and
low installation cost compared with other renewable energy. With the rapid
increase in penetration of wind power in electric power systems, wind power
systems may cause problems to system operation, such as voltage variations,
grid voltage unbalance, and grid instability. Wind farms can no longer be
considered as a simple energy source. Now they must have an operational
behavior with several control tasks similar to those of conventional power
plants. One of these control tasks, especially with doubly-fed induction
generator DFIGs, is the fault ride-through capability.FRT is to keep connection
of the wind power generator to the power system when power system disturbance
(e.g. voltage sag and swell, over and under frequency etc.) occurs. In FRT, the
case of voltage sag is called Low Voltage Ride-Through (LVRT). However, sudden
voltage sag may cause unstable generator operation due to an unbalance between
input power (mechanical) and output power (electrical). In order to achieve the
LVRT, the stabilization of the generator and voltage recovery are needed This
thesis presents LVRT method for DFIG wind turbine to protect the power
converters and ride-through grid faults during grid voltage dips without
disconnecting of the turbine from the grid. This limits the high rotor current
and the high voltage across the DC bus. Finally the work presents a (LVRT)
capability enhancement strategy of a (DFIG) using a dynamic voltage restorer
(DVR). The performance of the DVR depends on its controller. The PI, PID, Fuzzy
and adaptive PI using Fuzzy controller for the DVR is proposed to enhance
>the LVRT capability and fulfill the grid codes without disconnecting the
turbine from the grid at symmetrical grid sag voltage & unsymmetrical
(single phase sag voltage) used fuzzy controller. Simulation results using
Matlab are presented for a 1.5 MW DFIG with a DVR system to validate the
effectiveness of the proposed control technique.
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