Environmental Engineering Reference
In-Depth Information
b
Pitch angle
k
Tip speed ratio
x
w
Turbine angular speed
P, Q
Active and reactive power for the induction generator
i
ds
;
i
qs
Stator currents in d-q axes
u
ds
;
u
qs
Stator voltages in d-q axes
L
Inductor of the grid side filter
R
Resistance of the grid side filter
C
DC-link capacitor
i
d
;
i
q
d- and q-axis current components of the converter
s
d
;
s
q
d- and q-axis switching control signals
e
d
;
e
q
d- and q-axis voltage component of the three-phase supply
x
Angular frequency of the power source
P
ac
;
P
dc
Active power of AC and DC sides
3.1 Introduction
Renewable energy is an important sustainable energy in the world. It comes from
natural resources, such as wind, solar, rain, tides, biomass, and geothermal heat.
Up to now, as an essential part of low emissions energy in a lot of countries,
renewable energy has been an important to the national energy security, and
played a significant role in reducing carbon emissions.
Wind energy is a large and important renewable energy source, and widely used in
the world and has become a reliable and competitive means for electric power
generation. Total global wind power capacity is near 198 gigawatts (GW) in 2010 [
1
].
Wind energy conversion system (WECS) is an apparatus for converting the
kinetic energy available in the wind to mechanical energy that can be used to
operate an electrical generator for producing electricity. A typical WECS includes
a wind turbine, a generator, interconnection apparatus, and control systems.
Generators for wind turbines generally include the following types: synchronous,
permanent magnet synchronous, doubly-fed induction, and induction generators.
For small-to-medium power wind turbines, permanent-magnet and squirrel-cage
induction generators are often used because of their reliability and low cost.
Induction, permanent magnet synchronous, and wound field synchronous gener-
ators are currently used in various high-power wind turbines [
2
].
A lot of control methods for WECS have been proposed in literatures. A wind
speed sensorless neural network (NN) based maximum power point tracking
(MPPT) control algorithm for variable-speed WECS is proposed in [
3
]. The power
regulation of variable-speed WECS was studied in [
4
]. A sliding-mode control
(SMC) strategy was proposed to assure the system stability and impose the ideally
designed feedback control solution in spite of model uncertainties. A second-order
sliding-mode control (2-SMC) scheme
for a wind turbine-driven doubly-fed
