Control of a Wind Driven Doubly Fed Induction Generator During Grid Faults

Master's Thesis from the year 2013 in the subject Engineering - Power Engineering, grade: none, , course: Electrical engineering (Renewable energy), language: English, abstract: Wind electrical power systems are recently getting lot of attention, because

they are cost competitive, environmental clean and safe renewable power

source, as compared with fossil fuel and nuclear power generation. A special

type of induction generator, called a doubly fed induction generator (DFIG),

is used extensively for high-power wind applications. They are used more

and more in wind turbine applications due to ease controllability, high

energy efficiency and improved power quality.

This thesis aims to develop a method of a field orientation scheme for

control both the active and reactive powers of a DFIG driven by a wind

turbine.The proposed control system consists of a wind turbine that drives a

DFIG connected to the utility grid through AC-DC-AC link. The main

control objective is to regulate the dc link voltage for operation at maximum

available wind power.This is achieved by controlling the and axes

components of voltages and currents for both rotor side and line side

converters using PI controllers. The complete dynamic model of the

proposed system is described in detail. Computer simulations have been

carried out in order to validate the effectiveness of the proposed system

during the variation of wind speed. The results prove that , better overall

performances are achieved, quick recover from wind speed disturbances in

addition to good tracking ability.

Generally, any abnormalities associated with grid asymmetrical faults are

going to affect the system performance considerably. During grid faults,

unbalanced currents cause negative effects like overheating problems and

mechanical stress due to high torque pulsations that can damage the rotor shaft, gearbox or blade assembly. Therefore, the dynamic model of the

DFIG, driven by a wind turbine during grid faults has been analyzed and

developed using the method of symmetrical components. The dynamic

performance of the DFIG during unbalanced grid conditions is analyzed and

described in detail using digital simulations.

A novel fault ride-through (FRT) capability is proposed (i.e. the ability of

the power system to remain connected to the grid during faults) with suitable

control strategy in this thesis. In this scheme, the input mechanical energy of

the wind turbine during grid faults is stored and utilized at the moment of

fault clearance, instead of being dissipated in the resistors of the crowbar

circuit as in the existing FRT schemes. [...]