Environmental Engineering Reference
In-Depth Information
Sub-scripts: d, q
Direct, quadratic axis in synchronous reference frame
R, L, C
Resistance, inductance, capacitance
x
e
Stator electrical angular speed of PMSG
x
b
Base angular speed in rad/sec
x
r
Generator rotational speed of PMSG
L
s
Stator leakage inductance of PMSG
w
m
Exciter flux of PMSG
w
Flux leakage of PMSG
P
set
g
Set-value for active power of grid-side controller of VSC
Q
set
g
Set-value for reactive power of grid-side controller of VSC
Q
set
s
Set-value for reactive power of generator-side controller of
VSC
Sub-script: s
Stator quantity of PMSG and/or generator-side quantity of
generator-side controller of VSC
Sub-script: g
Grid-side quantity of grid-side controller of VSC
Sub-script: b
Base quantity for per-unit
Sub-script: filt
Filter quantity of RL-filter
Sub-script: dc
Dc-link quantity of VSC
k
p
;
k
i
Proportional and integral gain of PI controller
1.1 Introduction
Variable-speed power generation enables the operation of the turbine at its max-
imum power coefficient over a wide range of wind speeds, obtaining a larger
energy capture from the wind with a power converter which allows variable-speed
operation. One of the problems associated with variable-speed wind systems today
is the presence of the gearbox coupling the wind turbine (WT) to the generator.
This mechanical element suffers from considerable faults and increases mainte-
nance expenses. To improve reliability of the WT and reduce maintenance
expenses the gearbox should be eliminated.
Megawatt (MW) class wind turbines equipped with a permanent-magnetic
synchronous generator (PMSG) have been announced by Siemens Power Gener-
ation and GE Energy. In this concept, the PMSG can be directly driven or can have
smaller gearboxes or even gearless and is connected to the ac power grid through
the power converter. Use of the power converter is essential because it allows the
linkage of the generator operating at variable speed to the ac power grid at a fixed
electrical frequency. The converter rating must be similar to or even larger than the
rated power of the generator. Permanent-magnet excitation allows to use a smaller
pole pitch than do conventional generators, so these machines can be designed to
rotate at rated speeds of 20-200 rpm, depending on the generator rated power [
1
].
