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124 DAMPING CONTROLLER DESIGN FOR WIND FARMS BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS
Zahra Rahimkhani
INTRODUCTION
Large interconnected ac systems have many well-known
advantages. However, larger interconnected ac systems
also increase the system complexity from the operation
point of view, and might adversely decrease the system
reliability.Steady state stability, lack of reactive power
supply, voltage stability, electromechanical oscillations
and transient stabilityare common problems that can
happen in power systemsexpanded and transmit large
amount of power over long distance transmission lines.
Increasing power system complexity gives rise to low
frequency oscillations in the range of 0.2–3.0 Hz. If not
well damped, these oscillations may keep growing in
magnitude until loss of synchronism results, (Hsu et al
1988 Shayeghi et al 2009, Zhang et al 2011).
In order to damp these power system oscillations
and increase system oscillations stability, the installa-
tion of power system stabilizer (PSS) is both economi-
cal and effective.However, PSSs may adversely affect
voltage pro le, may result in leading power factor, and
may not be able to suppress oscillations resulting from
severe disturbances, especially those three-phase faults
which may occur at the generator terminals(Banaei et
al (2010).Flexible AC transmission systems devices,such
as Static VAR Compensators (SVC), Thyristor Control
Series Compensators (TCSC), Static Synchronous Com-
pensators (STATCOM), and Uni ed Power Flow Control-
ler (UPFC),are one of the recent propositions to allevi-
ate such situations by controlling the power ow along
the transmission lines and improving power oscillations
damping(Banaei et al 2010, Shayeghi et al 2011).
The renewable energy systems and specially wind
energy have been attracted due to the increasing con-
cern about CO2 emissions. Wind power is rapidly
increasing its presence in the power generation mix
as one of the most promising renewable power source
(WWEA (2011) (Ackermann (2005). For many countries
wind power has already become an important electric-
ity source, e.g., Denmark, Portugal, Spain and Germany.
Due to this increment in wind power generation share,
power systems stability and reliability may be affected
(WWEA 2011 Tsili et al 2008). The characteristics of
wind farms are substantially different from conventional
power plants, such as hydraulic, nuclear or thermal
(WWEA 2011 (Ackermann 2005). These facts have led
to the establishment of grid codes regarding wind farm
connection, and their integration in the grid (Hamdan
1999 MinisteriodeIndustriaTurismoyComercio 2006).
According to these codes wind farms must comply with
requirements including voltage sag ride through capa-
bility (Gomis-Bellmunt et al 2008), frequency regulation
(Chen Blaajberg et al (2009), and active and reactive
power regulation (ChenBlaajberg et al (2009).
In the future more wind farm contribution will be
required by the system operators. The capability to damp
power system oscillations will play an important role.
There is a draft of the new Spanish grid code for wind
power in which reference as already been made to inertia
emulation and power oscillation damping (Gomis-Bell-
munt et al (2008) (Chen,Blaajberg et al (2009).Different
methods to select the best feedback signal to damp power
oscillations have been discussed in (Hamdan (1999), but
the case for WPPs has not been yet well covered. Recent
research focuses on the best input–output signal pairs
coupling based controllability and observability analy-
ses such using singula value decomposition(SVD) (Li
et al (2012).
Also a lead lag based QPSO controller is designed to
damp low frequency oscillations. It is well known that
traditional lead-lag damping controller structure is pre-
ferred by the power system utilities because of the ease of
on-line tuning and also lack of assurance of the stability
by some adaptive or variable structure methods (Panda
et al(2008) (H Shayeghi et al (2009). Having several local
optimum parameters for a lead-lag controller, using of
traditional optimization approach is not suitable for
such a problem. Thus, the heuristic methods as solution
for nding global optimization are developed (Panda et
al (2010) (Panda S (2009).Particle swarm optimization
(PSO) is a novel population based metaheuristic, which
utilize the swarm intelligence generated by the coopera-
tion and competition between the particle in a swarm
and has emerged as a useful tool for engineering optimi-
zation (Shayeghi et al 2008).This new approach features
many advantages; it is simple, exible, fast and can be
coded in few lines. Also, its storage requirement is mini-
mal. However, the main disadvantage is that the PSO
algorithm is not guaranteed to be global convergent. In
order to overcome this drawback and improve optimiza-
tion synthesis, in this paper, a quantum-behaved PSO
technique is proposed for optimal tuning of wind tur-
bine based damping controller for enhancing of power
systems low frequency oscillations damping.
In this paper a novel approach is presented to model
power system supplied by wind turbine namely
Phillips-
Heffronmodel based d-q algorithm in order to studying
system dynamical stability.In addition, a block diagram
representation is formed to analyze the systemstability
characteristics.Also, singular value decomposition (SVD)
is used to choose damping control signal which has most
effect on damping the electromechanical (EM) mode
oscillations. A very powerful tool commonly used for
this purpose is Popov-Belevitch_Hautus(PBH) which can
be used to evaluate the EM mode controllability of the
PSS and the different inputs of system.A single machine
in nite bus (SMIB) system equipped with a PSS and a
wind turbine as a negative load. The problem of damp-