As wind farms penetration in power systems has now becoming an increasing source of energy, and thus progressively conventional power plants are replaced or operated at lower limits, the respective power system operators are concern about the stability and reliability of their power systems. Theref...
Course Project: Participation by wind farms in transient stability and small-
signal stability of power systems
Candidate
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I hereby declare this is my own unaided work, submitted in partial fulfillment for the degree in
Master of Engineering in Electrical
,ELEN7013 Project: Participation by wind farms in transient stability and small-signal stability of
power systems.
Table of Contents
1 INTRODUCTION..............................................................................................................................3
2 POWER SYSTEM STABILITY CHALLENGES..............................................................................3
3 WIND FARM TECHNOLOGIES......................................................................................................4
3.1 Double Fed Induction Generator (DFIG).....................................................................................4
3.2 Full Converter Synchronous Generator........................................................................................5
4 TRANSIENT STABILITY AND SMALL-SIGNAL STABILITY OF POWER SYSTEMS.............6
4.1 Methodology................................................................................................................................6
4.1.1 Modal Analysis.....................................................................................................................7
4.1.2 Participation Factors.............................................................................................................8
4.1.3 Power System Oscillations....................................................................................................9
4.2 Application of Case Studies.........................................................................................................9
4.2.1 Wind Farm Operated at Constant Power.............................................................................11
4.2.2 Wind Farm Operated at Power Tracking.............................................................................12
4.2.3 Wind Farm Operated at Speed Tracking.............................................................................13
4.2.4 Impact of Tie-Line Power Flow..........................................................................................15
4.2.5 Impact of Transmission Line...............................................................................................16
5 CONCLUSIONS..............................................................................................................................17
6 REFERENCES.................................................................................................................................19
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, ELEN7013 Project: Participation by wind farms in transient stability and small-signal stability of
power systems.
1 INTRODUCTION
Electric power systems are often described as consisting of generation, transmission and distribution.
Generation usually consists of synchronous generators which produce electricity, which is achieved
by prime movers converting thermal energy or pressure to rotating mechanical energy, which is in
turn converted into electrical energy by the generator. The transmission system connects major
generators and distribution systems together by means of transmission line. Voltages are transformed
from generator voltages up to higher transmission voltage levels, and then steeped down for loads in
distribution system.
Traditionally, only synchronous generators were used to generate power driven by steam, gas or
running water turbines and their characteristics and controllability of both generator and prime movers
are well understood and facilitated to their full potential. With such conventional power plants the
voltage and frequency of large interconnected AC power systems can be controlled and held stable in
steady state as well as in transient operating conditions. Thus re-establishing of stable conditions after
a transient fault, i.e. recovering the grid voltage and damping power system oscillations caused by the
fault.
As wind farms penetration in power systems has now becoming an increasing source of energy, and
thus progressively conventional power plants are replaced or operated at lower limits, the respective
power system operators are concern about the stability and reliability of their power systems.
Therefore, progressively power system operators issue a revised grid connection requirements
specifically made for wind turbines and wind farms.
Until recently, wind turbines were treated by and large as embedded generators, which were not to
contribute to power system control and hence wind turbines were not required to actively control
voltage or frequency. In addition, wind turbines were required to disconnect from the grid when
abnormal operating conditions occurred. However, if wind farms substitute conventional power
plants, it also has to take over the power system control (amongst this, is to ride through transient
disturbances in power system i.e. generation must not be lost due to temporary excursions in voltage
or frequency) and stabilisation tasks which the substituted conventional power plants were carrying
out.
A transient short circuit fault is a very common disturbance in a power system. It suppresses the grid
voltage and upsets the rotating machines in the vicinity of the fault, causing the speeds of these
machines and the power flows in the network to oscillate. Such sub-synchronous system oscillations
have to be damped to avoid the system to be unstable and traditionally, such oscillations are damped
by conventional power plants with synchronous generators which are equipped with power system
stabilisers [1].
This project involves a study to determine what positive or negative effect the presence of wind farms
has in transient stability behaviour of power systems containing conventional synchronous generators
and whether wind farms can contribute positive damping when small-signal oscillations occur, taking
into consideration Doubly Fed Induction Generators (DFIGs) and Fully Rated Converters.
2 POWER SYSTEM STABILITY CHALLENGES
Power system stability can be classified into three categories [2]:
a) Rotor angle stability refers to the ability of synchronous machines in an interconnected power
system to remain in synchronism after being subjected to a disturbance. Instability may result
in the form of increasing angular swings of some generators, leading to their loss of
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