International Journal of Industrial Electronics and Electrical Engineering, ISSN: 2347-6982
Volume-2, Issue-10, Oct.-2014
DIFFERENT ASPECTS OF USE OF POWER ELECTRONICS WITH
WIND ENERGY CONVERSION SYSTEMS-STATE OF ART
1
1
ASHUTOSH KASHIV, 2H.K. VERMA, 3PRAGYA NEMA
Asstt Prof., Electrical and Electronics Engineering, Oriental University, Indore, (M.P.) India
2
Professor, Electrical and Electronics Engineering, S.G.S.I.T.S. Indore, (M.P.) India
3
Professor, Electrical and Electronics Engineering, L.N.C.T. Indore, (M.P.) India
E-mail: ashutosh.kashiv@gmail.com, vermaharishgs@gmail.com, pra3sam@yahoo.co.in
Abstract- Wind energy is freely available in all over the world and its generation is increasing day by day. The Wind Energy
Conversion Systems (WECS) are dynamic and non linear power generation systems. For controlling and conditioning of
output power from wind energy farm, the Power Electronics (PE) equipments are very essential part of wind energy
conversion systems. Here this paper presents the state of art of using different PE equipment application in different WECS.
Keywords- Power Electronics (PE) Devices, Wind Energy Converter Systems (WECS)
I.
Table 1 Renewable electricity generation capacities
by different energy source, 2011-2040 (in Giga
Watts)
INTRODUCTION
Increase in Population, invention of new machines
and improvement of living standards will obviously
result ever increase in demand of electrical energy.
World energy demand will expand by 56% between
2010 and 2040.
Indian Wind Energy Association has forecasted that,
the ‘on-shore’ potential for utilization of wind energy
for electricity generation is of the order of 65,000
MW. The potential of total energy is much higher
than the exhausted.
On 31st Oct 2013 installed wind power generation
capacity in India was 19933.68 MW spread across
Tamil Nadu (7154 M W) , Gujarat (3,093MW),
Maharashtra (2976MW), Karnataka (2113MW),
Rajasthan (2355MW), Madhya Pradesh (386MW)
Andhra
Pradesh
(435MW),
Kerala (35.1W),
Orissa (2MW) West Bengal (1.1MW) and other states
(3.20 MW).
Renew
able
Source
20
11
20
15
20
20
20
25
20
30
20
35
20
40
MSW/
LFG
3.8
0
3.8
9
3.8
9
3.8
9
3.8
9
3.8
9
3.8
9
Hydro
power
78.
20
78.
09
78.
66
79.
27
79.
43
79.
96
80.
64
Geothe
rmal
Bioma
ss
2.3
8
7.2
9
45.
88
4.5
2
2.7
0
8.6
7
58.
76
19.
24
3.6
3
9.6
9
59.
68
22.
35
4.3
4
10.
45
60.
54
24.
22
5.7
0
11.
19
62.
35
27.
09
6.6
0
12.
32
70.
37
34.
73
7.4
6
13.
88
88.
35
50.
96
Wind
Solar
Table 1 shows wind systems will have the biggest
share in the renewable energy sector and will be the
most promising renewable energy sources for
generation of electricity.
It is estimated that 6,000 MW of additional wind
power capacity will be installed in India by the end of
2014 .Wind power accounts for 8.5% of India's total
installed power capacity, and it generates 1.6% of the
country's power. In terms of wind power installed
capacity, India is ranked 5th in the World. Today
India is one of the major contributors in the global
wind energy market.
This growth of wind power generation will definitely
affect the operations and controlling of the power
system networks. Despite the stochastic nature of the
wind, grid reliability has to be guaranteed. The
operating performance of wind electric generators has
considerable stress on the quality of electric power
and reliability in the performance of power systems.
Wind systems will have the biggest share in the
renewable energy sector and will be the most
promising renewable energy source for generation of
electricity. Electricity generation from wind systems
will increase from 45.88 GW in 2011 to 88.35 GW in
2040 worldwide.
The present day variable speed wind turbines follow
the point to extract the maximum power.
This is enabled by variable speed operation and the
power electronic module interfacing the turbine and
the grid. A next section of the paper defines the need
of power electronics in different WECS.
World Renewable Energy Generation data by
different renewable energy sources for the duration
2011 year to 2040 is given in the Table 1.
Different aspects of use of Power Electronics with Wind Energy Conversion Systems-State of Art
58
International Journal of Industrial Electronics and Electrical Engineering, ISSN: 2347-6982
II.
Volume-2, Issue-10, Oct.-2014
DIFFERENT TYPES OF WIND ENERGY
CONVERSION SYSTEMS
On the basis of generator used and configurations
WECS can be categorized into four types. They are
described below:
First type of WECS mainly consists of a Squirrel
Cage Induction Generator (SCIG) popularly known
as Danish concept. In this WECS Squirrel Cage
Induction Generator (SCIG) directly connected to the
grid through a transformer.
The Induction machine requires VARs to operate.
This configuration needs a reactive power
compensator to reduce the reactive power demand.
The major limitation of this concept is it does not
support any speed control.
Fig 1 Block Diagram of Wind Energy Conversion System with
Power Electronics
Type 1 WECS does not require any PE converter.
This system needs the compensation of reactive
power. FACTS devices such as STATCOM can be
used for this purpose.
Second type of WECS uses a Wound Rotor Induction
Generator (WRIG) containing slip rings. It is a
limited Variable speed (typically 0-10%) controlled
wind turbine with variable rotor resistance, known as
OptiSlip.
Third type of WECS uses a doubly fed induction
generator (DFIG) and requires a wound-rotor design.
The stator of the DFIG is connected directly to the
grid and the rotor winding is connected via slip rings
to a Converter.
Fig. 2 Type 1 WECS consisting of squirrel cage Induction
Generator
The main drawbacks of this concept are: It does not
support any speed control, so unable to give optimum
power output. Its mechanical construction should be
able to withstand high mechanical stress caused by
wind gusts.
It is a variable speed controlled wind turbine with a
wound rotor induction generator (WRIG) and partial
power scale frequency converter (30% of nominal
generator power) on the rotor circuit.
The variable speed DFIG is highly efficient. It is
designed to get maximum energy from the wind, and
It provides electricity at a constant frequency,
irrespective of the wind speed. Main drawbacks of
this WECS are the use of slip-rings and the protection
schemes and controllability in the case of faults.
Forth type of WECS can use the wound rotor
synchronous generator (WRSG) or permanent magnet
synchronous generator (PMSG). The stator windings
are connected to the grid through a full-scale power
converter. This configuration corresponds to the full
variable speed controlled wind turbine. Applications
of Power Electronics in the above mentioned four
WECS is explained in the subsequent section of the
paper.
III.
Type 2 configuration, shown in figure 4, corresponds
to the limited variable speed controlled wind turbine
with variable rotor resistance. It uses a wound rotor
induction generator (WRIG).
Fig. 3 Type 2 WECS consisting of WR Induction Generator
having variable speed using rotor resistance control
NEED OF POWER ELECTRONICS
CONVERTERS AND DEVICES IN
DIFFERENT WECS
A controlled resistance is connected in series with the
rotor winding of the generator. Size of this resistance
defines the range of the variable speed (0-10% above
synchronous speed). A capacitor bank compensates
the reactive power. Soft Starters are used to provide
Smooth grid connection. An extra resistance is added
in the rotor circuit, which can be controlled by power
electronics. Thus, the total rotor resistance is
The power electronic (PE) converters play a vital role
in modern WECS. Block Diagram of a General
WECS with Power Electronics control is shown in
the Figure 1.
Different aspects of use of Power Electronics with Wind Energy Conversion Systems-State of Art
59
International Journal of Industrial Electronics and Electrical Engineering, ISSN: 2347-6982
controllable and the slip and thus the power output in
the system are controlled. The dynamic speed control
range depends on the size of the variable rotor
resistance. Type 3 configuration is known as the
doubly-fed induction generator (DFIG) WECS. It is a
variable speed controlled wind turbine with a wound
rotor induction generator (WRIG) and partial power
scale frequency converter (rating 30% of nominal
generator power) on the rotor circuit. The
configuration is shown in Fig 4.
Volume-2, Issue-10, Oct.-2014
The important challenges for the PE converter and its
control strategy in a variable speed WECS are:

Attain maximum power transfer from the
wind, as the wind speed varies, by controlling the
turbine rotor speed, and

Change the resulting variable-frequency and
variable-magnitude AC output from the electrical
generator into a constant-frequency and constantmagnitude supply which can be fed into an electrical
grid.
IV.
REVIEW OF THE PAST WORK
RELATED TO POWER ELECTRONICS
IN WECS
There are several issues related to the use of PE
devices and converters in WECS. Extensive
researches have been made in this field. Review of
the works related to Power Electronics in WECS has
been done in this section.
Fig. 4 Type 3 WECS consisting of doubly fed Induction
Generator
The stator is connected to grid directly. The rotor
frequency is controlled by a partial-scale power
converter it results the controlling of the rotor speed.
The speed range (generally ±30% of synchronous
speed) is defined by the power rating of this partialscale frequency converter. Converter is also used to
provide the reactive power compensation and a
smooth grid connection. The rotor speed control
range is higher compared to the WRIG type WECS.
The Frequency converter of small size makes this
arrangement more economical. In this WECS the
power electronics converters makes the wind turbine
to behave like a dynamic power source to the grid.
Drawbacks of this system are the use of slip-rings and
the protection and controllability in the situation of
grid faults.
S. Bisoyi et. al. explained the various converter
topologies for SCIG, DFIG and PMSG WECS.
Bidirectional power flow is needed in the SCIG
WECS for reactive power support from the grid. The
use of back to back PWM converter with suitable
controllers has been suggested for SCIG system by
researchers in. Applications of Fuzzy logic controller
and PI type Fuzzy controller for PWM in SCIG have
been mentioned in.
Static Kramer drive system, back to back PWM
converter, Resonant DC link converter, Matrix
converter topologies are used for DFIG WECS.
Fuzzy logic, sliding mode control technique can be
applied in Static Kramer drive system for high
efficiency and torque oscillation smoothing.
Limitations of the system are firing and commutation
problem with the rotor side converter and harmonic
distortion by the grid side converter system. Pulse
width modulation (PWM) voltage source converter
(VSC) is used in DFIG system. Eguchi et. al.
proposed vector current control of PWM VSC.
Applications of Matrix converter have been explained
in. Thyristor supply side inverter, Hard switching
supply side inverter, intermediate DC/DC converter
stage, back to back PWM converter topologies are
used in PMSG system.
Type 4 WECS consisting of direct drive synchronous
generator. In this configuration variation of speed
with full scale power conversion is performed by the
generator connected to the grid through a power
converter as shown in Fig. 5. The stator winding of
the generator is connected to the grid through a fullscale power converter. The reactive power
compensation and a smooth grid connection for the
entire speed range are performed by frequency
converter. The generator can be asynchronous
generator, electrically excited synchronous generator
(WRSG), or permanent magnet excited type (PMSG).
Recently, the squirrel-cage induction generator has
also started to be used for this configuration due to
the advancement in the power electronics.
The introduction of power transistors provides the
possibility of implementing four-quadrant operations
by anti-parallel connection of two two-quadrant
switches. Switch commutation problem in it produces
over-current due to short circuiting of the ac sources,
over-voltage spikes or due to open circuiting the
inductive loads that can destroy the power
semiconductor. Safe commutation has been achieved
by the development of several multi-step
commutation strategies. Reliability is one of the
biggest concerns regarding wind turbines. The power
electronic converter is one of the weak points of the
It is worth mentioning that use of PE converter is
dependent on the configuration of WECS.
Fig. 5 Type 4 WECS consisting of Variable Speed
Wind Turbine with Synchronous Generator
Different aspects of use of Power Electronics with Wind Energy Conversion Systems-State of Art
60
International Journal of Industrial Electronics and Electrical Engineering, ISSN: 2347-6982
electrical system in context with reliability issues.
The most frequent failure causes are the Component
failures (more than 35%). Malfunctioning of the
control system occurs more than 25 % times.
Failures due to other impacts such as breakdown of
voltage or storm only appear approximately 19 % in
sum. According to a survey based on 200 products
from 80 companies failures in the converter are 30 %
due to capacitors, 26 % due to PCBs, 21 % due to
semiconductors, and 13 % due to solder. An industry
based survey mentioned in reports that Power
Electronics devices are the most fragile component of
the converter with a share of 40 % followed by
capacitors with a share of 26 % and the gate drives
with a share of 24%. The power semiconductors as
well as the DC link capacitors are weak points in the
converter and both together may be responsible for
more than half of all failures in power electronic
converters. The power electronic converter only takes
a small proportion of the overall costs of a wind
turbine on the one hand, but it causes high financial
losses in case of a fault, when operation of the turbine
is interrupted. Extensive researches have been made
in the field of reliability of Power Electronic Devices.
Volume-2, Issue-10, Oct.-2014
switching frequency, which is limited by losses in the
power electronic devices, tends to reduce as the
power ratings of the devices and the converters
increase. This means that high power 2-level
converters could have disproportionally large filters.
Alterative converter topologies, which can help
reduce the size of the filter, have been the subject of
recent research. O. Bouhali et al. proposed Multilevel converters including neutral point clamped and
cascaded converter. Multi-level converters have the
advantage of reducing the voltage step changes, and
hence size and the cost of the main filter inductor for
given current ripple, at the expense of increased
complexity and cost of the power electronics and
control components. A practical high power multilevel converter may use a relatively low switching
frequency device with a voltage rating greater than
necessary to meet the current rating requirement.
Other possible converter topologies, which are worth
investigating, include current source converters and
matrix converters. The matrix converter is
particularly appealing when the power source is AC,
e.g. high frequency turbine generator or variable
frequency wind turbine generator. Using a matrix
converter, the cost of the AC/DC conversion stage
and the requirement for a DC link capacitor or
inductor could be saved. Combinations of the above
converters may be also possible, e.g. an interleaved
multi-level converter or an interleaved matrix
converter, perhaps with soft switching.
A high availability is yielded by a long MTBF and a
short MTTR. The high technical availability of
today’s onshore wind turbines of approximately 9599 % is particularly a result of a frequent service and
fast repair in case of a fault.
The introduction of new switching devices playing an
important role in the development of higher power
converters for wind turbines with increased reliability
and efficiency. The main choices are IGBT modules,
IGBT press pack, and IGCT press pack. The presspack technology leads to an increase in reliability,
higher power density and better cooling capability at
the price of a higher cost compared to power
modules. Press-pack IGCT supports the development
of MV converters and are already state of the art in
high-power electric drives but not yet widely adopted
in the wind turbine industry because of cost issues.
Apart from the matrix converters there are also other
three suggested topologies, namely the tandem
converter, the multilevel converter and the resonant
converter. The NCC topology is the most efficient
followed by the multi level and the tandem converter.
Z-source inverter based wind power conversion
systems are relatively new. Applications of Z-source
Converter based wind power conversion systems are
explained in.
Z source converters are highly
controllable, provides wide range of speeds, short
circuit protection.
The increasing use of power from renewable sources
has made it necessary for the sources to behave, as
much as possible, like conventional power plants in
terms of supporting the network voltage and
frequency with good power quality.
R. Manavalan
et al. in their paper proposed a new power
conditioning scheme for DFIG-based WECS that uses
a 3-phase diode rectifier followed by a boost
regulator as grid side converter and a multilevel
neutral point clamped (NPC) inverter to supply
variable frequency voltage to the rotor.
CONCLUSIONS
Different types of WECS are used and PE plays a
vital role in them. Several problems and issues related
to use of power electronics persists. Use of PE in
WECS affects the quality of output power, stability,
reliability, size and cost of WECS. Several advanced
switching devices and converters such as Z source
converter, matrix converter, multi level converter etc.
have been suggested. As a result of rapid
developments in power electronics, semiconductor
devices are gaining higher current and voltage
ratings, less power losses, higher reliability, as well
as lower prices per kVA therefore, PE converters are
The size and cost of the filter are very significant
factor. Filter size can be reduced by either increasing
the switching frequency of the converter or reducing
the converter voltage step changes. However the
Different aspects of use of Power Electronics with Wind Energy Conversion Systems-State of Art
61
International Journal of Industrial Electronics and Electrical Engineering, ISSN: 2347-6982
becoming more attractive in improving the
performance of wind turbine generation systems.
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