The document discusses different types of generators used in wind turbines, including synchronous generators, induction generators, and doubly fed induction generators. It focuses on the benefits of using direct-drive permanent magnet generators, which eliminate the need for a gearbox and have higher reliability, lower maintenance costs, and lower power losses compared to other wind turbine systems. Larger wind turbines up to 20 MW in capacity are also discussed.

1. P R E P A R E D B Y : -
S O N U K U M A R B A I R W A
CONVERTER CONTROL IN
WIND TURBINE

2. Introduction
 Wind power generation system normally consists of wind
turbine, generator and grid interface converters if
applicable, among which the generator is one of the core
components. In the development of wind power
generation techniques, synchronous generator, induction
generator and doubly fed induction generator have been
employed to convert wind power to electrical power.
 Wind turbines usually rotate at a speed of 30-50
rev/min, and generators should rotate at a speed of
1000-1500 rev/min, so as to interface with power
systems.

3.  Hence, a gearbox should be connected between a wind
turbine and a generator and it requires regular
maintenance, which also causes unpleasant noise, and
increases the loss of wind power generation. In order
to overcome these problems, the wind power
generation with Direct-Drive Permanent Magnet
Generator without gearbox was developed. The
permanent magnet generator driven directly by the
wind turbine is a multi-pole and low speed generator.
Different types of Direct-Drive Permanent Magnet
Generators were developed for wind power generation,
such as axial-flux machine and radial-flux machine.

4. Way to control of energy generation
 Among which, WT with doubly fed induction
generator (DFIG) with the features of low investment
and flexible control becomes the dominant type of
WT installed in the wind farm .
 The stator of a DFIG is normally connected to a
power grid directly, and its rotor winding is fed back
from the terminal of the stator by controlled voltage
source converters.
 The converters only supply the exciting current of
DFIG, hence the capacity is fairly low, say 20%-25%
of the DFIG rated capacity approximately.

5.  The fed back converters are based on insulated gate bipolar
transistors (IGBT), such that the control of the DFIG is
flexible, and the controllers have significant effect on the
dynamic characteristic of the WT with DFIG .
 It is known that the wind turbine with the capacity of about
2MW usually rotates at a speed of 10-20 rpm, and the
generator should rotate at a speed of 1000- 1500 rev/min, so
as to be interfaced to the power grid.
 Hence, the gearbox should be used to interface the WT and
the generator.
 The gearbox demands regular maintenance, causes
unpleasant noise, and increases the power loss of the WT
system

6.  In order to overcome these technical challenges of the
WT system involving gearbox, the permanent magnet
generator (PMG), which is a multi-pole and low speed
generator, is employed in the WT system to convert the
wind power into electric power.
 The PMG is driven directly by the WT, and the gearbox
is eliminated .
 Compared with the other types of WT systems, the WT
with direct drive permanent magnet generator (DDPMG)
has the advantages of higher reliability, lower cost for the
maintenance and lower power loss in the WT system.

7.  With the development of wind turbine technologies,
the size and capacity of wind turbines becomes
bigger and bigger.
 For instance, now the largest wind turbine of its next
generation dedicated offshore wind farms can ensure
the lowest possible cost of energy, has a capacity of 7
MW, and a rotor diameter of 164 meters .
 According to a report from the EU-funded project ,
20 MW wind turbines are feasible.