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WIND ENERGY APPLICATIONS
Thiagarajan Y¹, Yuzo Iano², Vania V.Estrela², Gabriel Gomes de Oliveira², Ana Carolina², Reinaldo
Padilha² and R.Ashokkumar²
¹Sri Venkateshwaraa college of Engineering and Technology, Puducherry, India
²State University of Campinas, São Paulo, Brazil
²Fluminense Federal University (UFF), Rio de Janeiro, Brazil
²Annamalai University, Tamilnadu, India
Abstract- The utilization of renewable energy for electric power production is an
antique method .Nowadays, due to the tremendous increase in fossil fuels prices and
the environmental problems caused due to the burning of fossil fuels made scientist
and researchers to focus on renewable energy sources because they are
inexhaustible, clean and they can be used in a decentralized way. For example, the
wind generators are in position to supply more electric energy for stand alone and
grid connected applications .This research work focuses on a new design, for
extraction of maximum power using Variable Speed Wind Turbines (VSWTs) by
developing an optimal control method for VSWT. Here the output of VSWT coupled
with Permanent magnet synchronous generator (PMSG) is first converted to fixed
DC using a chopper. Later dc output from the chopper is then inverted to obtain AC
power using PWM technique for effective power flow.
Keywords - Variable Speed Wind Turbines (VSWTs), maximum power point
tracking (MPPT), Permanent magnet synchronous generator (PMSG), Direct current
(DC), Alternating current (AC), Pulse width modulation (PWM), Horizontal Axis
Wind Turbine (HAWT), Distributed Generation (DG).
1. INTRODUCTION
Global warming has been attributed to the increase of the atmospheric gases concentration
produced by the burn of fossil fuel. Many factors such as exhausting of fossil-fuel
resources, energy security concerns, and global warming, increase the need for renewable
energy. Electric power generation using non-conventional sources is receiving
considerable attention throughout the world due to the exhaustion of fossil fuels and
environmental issue. Their main advantages are pollution free and inexhaustibility while
the main drawbacks are the cost and uncontrollability. Wind is one of the most abundant
energy sources, which can be harnessed by wind turbines and converted to electricity by
generators. The wind power mainly depends on geographic and weather conditions that
vary from time-to-time. Three factors have made wind power generation cost-competitive,
they are:
i. the state incentives,
ii. the wind industry that has improved the aerodynamic efficiency of the wind
turbine,
iii. the evolution of power semiconductors and new control methodology for the
variable-speed wind turbine, that allows the optimization of wind turbine
performance.
Wind energy is pollution free, clean, cost competitive and an infinitely sustainable form
of energy. It does not produce greenhouse gases or toxic radioactive waste. Wind energy
is the kinetic energy present in moving air. Wind energy is the fastest growing source of
renewable energy in the world which could be tapped easily. The power from the wind
can be obtained by allowing it to blow fast moving wings that exert a torque on the rotor.
The bladed rotor is the most important and most visible part of the wind turbine.
Depending upon the blade positions, wind turbines can be classified into two.
1) Based on the axis of rotation:
Vertical Axis Wind Turbine (VAWT)
Horizontal Axis Wind Turbine (HAWT)
2) Based on the speed of operation:
Constant speed
Variable speed
2. DEVELOPMENT
The rotor turns a shaft which transfers the motion into the nacelle (the large housing at the
top of a wind turbine tower). Inside the nacelle, the slowly rotating shaft enters a gearbox
that significantly increases the rotational shaft speed. The output (high-speed) shaft is
connected to a generator that converts the rotational movement into electricity at medium
voltage (a few hundred volts). Power generation using wind energy is possible in two
ways, viz. constant speed operation and variable speed operation using power electronic
converters. Variable speed power generation for a wind turbine is attractive because
maximum efficiency can be achieved at all wind velocities.
2. 1 Maximum Power Point Tracking of Wind Energy Conversion System.
Increased demand for electricity and scarcity of fossil fuel that is used to generate
electricity, leads to the development of Distributed Generation (DG) to satisfy local
demand. Renewable energy sources play a significant role. This content focuses on
bringing out constant electricity using Variable Speed Wind Turbines (VSWTs) by
developing an optimal control method for VSWT.VSWT coupled with permanent magnet
synchronous generator (PMSG), and the output is first converted to fixed DC using a
chopper. The dc output from the chopper is then inverted to obtain AC using PWM
technique.
2.1.1 Mathematical Model of Wind Turbine
Wind turbines work by converting the kinetic energy in the wind into mechanical energy
and then to electrical energy by using power converters. The energy available for
conversion mainly depends on the wind speed and the swept area of the turbine.
The kinetic energy of the wind in motion is,
(2.1)
The rate of change in energy gives power in the wind:
(2.2)
Then mass flow rate is given as,
(2.3)
Substituting Eqn (2.3) in equation (2.2), we get,
(2.4)
Power coefficient is,
(2.5)
Where Cp<1
From Equation (2.4) and Equation (2.5), the output power of the wind is obtained,
Where A=πR2
(2.6)
Cp may be expressed as the function of , which is the Ratio of blade tip speed to wind
speed and it is related to rotor blade pitch angle β. The theoretical upper limit of power
coefficient is 0.59 according to Betz limit.
(2.7)
The wind turbine torque on the shaft is calculated from the power:
By tip speed ratio formula, we get,
Torque coefficient - defined as the ratio of power coefficient to the tip speed ratio.
(2.8)
2.1.2 Control Strategy for Maximum Power Point Tracking
Although the wind speed varies with time, the wind turbine can be optimized to run at
near peak power production for various wind speeds. Forgetting optimized output,
different control methods are used. Following is the proposed control strategy. The wind
turbine can deliver Maximum power when the rotor speed varies with the wind speed
operating at maximum power coefficient (Cp). MPPT control is an active research area to
extract the maximum possible power from the available wind power. The maximum
power point tracking from the wind turbine is obtained by measuring the DC voltage of
the three-phase diode bridge rectifier and power of wind turbine by controlling the duty
cycle of the DC-DC boost chopper. There is a general relation between power and voltage
as shown in Fig 5.1, where it is a similar relation between the mechanical energy and rotor
speed of the PMSG. To reduce the error and number of the control block, the controller is
developed with two inputs. This control generates an appropriate duty cycle to the boost
chopper, resulting in maximum output power. From Fig 3.1 it is observed that at any wind
speed value there is one point of maximum power at a specific amount of DC voltage.
There is a linear relationship between the rotor speed of the PMSG and the DC voltage.
By changing the duty ratio of the chopper the operating point can be shifted from one
curve to another with changing wind speed.
Figure.2.1 Power -Voltage curve
As indicated in fig.3.1, the power-voltage curve is divided into two regions:
1) Positive-region (located on the right side of MPP).
2) Negative region (located on the left side of MPP).
The control actions are summarized in Table.2.1.
Table.2.1. Control actions for various operating points
Table 2.1, gives the control of the proposed MPPT technique.
As the wind speed changes and so as the voltage varies, the control of boost chopper
varies periodically and aims at tracking the optimum operating point. By sensing the
output power of the turbine and output voltage of rectifier the duty ratio of the boost
chopper is varied according to the control strategy proposed.
2.1.3. Flow Chart for Maximum Power Point Tracking
P
+
+
-
-
V
+
-
+
-
Region
I
II
II
I
D
-
+
+
-
Figure.2.2. Control Flow Chart.
START
INITIALISE D AND ∆D
SENSE V (K) AND P (K)
∆P = P (K+1) – P (K)
∆V = V (K+1) –V (K)
∆P>0
∆V>0 ∆V>0
D - ∆D D + ∆D D + ∆D D - ∆D
∆P=0
D TO CHOPPER
RETURN
K=K+1
YES
NO
YES
YES
NO
NO NO YES
2.1.4 Algorithm for Maximum Power Point Tracking
The MPPT algorithm includes several steps; thus it can be summarized as below:
1. First since the DC voltage at the rectifier and power of wind turbine.
2. Then since the DC voltage at the rectifier and power of wind turbine (K+1)the iteration.
3. Compare the previous wind turbine power, voltage value with modern wind turbine
power, voltage by using the formulae:
∆P=P(K+1)-P(K)
∆V=V(K+1)-V(K)
4. Check whether ∆P>0 or ∆P<0.based on the following four condition Duty ratio of the
boost chopper is increased or decreased.
1. If ∆P>0 and ∆V> 0, then D=D-∆D
2. If ∆P>0 and ∆V<0, then D=D+∆D
3. If ∆P<0 and ∆V<0, then D=D-∆D
4. If ∆P<0 and ∆V> 0, then D=D+∆D
5. Repeat the 3-5 until ∆P =0.
2.2. Simulated Model for Wind Energy Conversion System 2.2.1 Matlab Model
Figure.2.3 MATLAB/SIMULINKModel for Wind Turbine
Fig. 2.3 shows the simulation model of the wind turbine. The inputs to the wind turbine
are wind velocity, clock pulse, the angular velocity of the turbine, the angular velocity of
the generator and the stator voltage. The outputs of the wind turbine are the angular
velocity of the turbine, the angular velocity of the generator, stator voltage, Lambda,
power coefficient, torque, and power.
Figure.2.4 MATLAB/SIMULINK Model for PMSG
Fig. 2.4 shows the MATLAB/SIMULINK model of Permanent Magnet Synchronous
Generator. SIMULINK model of PMSG is simulated for different values of wind speeds,
and the performance of the Permanent Magnet generator is analyzed.
Figure. 2.5 MATLAB/SIMULINK model for WECS
The Fig.2.5 shows the Simulation model of Wind Energy Conversion System. This model
consists of a wind turbine, Permanent Magnet Synchronous Generator, boost chopper,
inverter blocks. This model is simulated for various wind velocities. The inputs to the
wind turbine are wind velocity, clock pulse, the angular velocity of the turbine, the
angular velocity of the generator and the stator voltage. The outputs of the wind turbine
are the angular velocity of the turbine, the angular velocity of the generator, stator voltage,
Lambda, power coefficient, torque, and power.
Figure. 2.6 MATLAB/SIMULINK model for overall system
Fig. 2.6 shows the overall Simulation model of Wind Electric System. This model
consists of a wind turbine, Permanent Magnet Generator, boost chopper, inverter and
control blocks. The output of the controller is duty cycle, d. It is fed into the boost
chopper. This model is simulated for various wind velocities and analysis is done. The
inputs to the wind turbine are wind velocity, clock pulse, the angular velocity of the
turbine, the angular velocity of the generator and the stator voltage. The outputs of the
wind turbine are the angular velocity of the turbine, the angular velocity of the generator,
stator voltage, Lambda, power coefficient, torque, and power.
3. RESULTS AND DISCUSSIONS
3.1 Power- speed characteristics
Figure. 3.1 Power-Speed Characteristics of the wind turbine.
The Fig.3.1 shows the Power-Speed characteristics of the wind turbine. For example for a
wind velocity of 11 m/sec the equal power and speed values are 1241 Watt and 31 rpm
respectively. Similarly, for various wind velocities, the Power-Speed characteristics are
obtained.
POWER Vs SPEED
0
500
1000
1500
2000
2500
3000
3500
-20 0 20 40 60 80
SPEED
PO
WE
R
6
7
8
9
11
12
13
14
15
mpp
3.2. PMSG Output Waveform
Figure. 3.2 PMSG Output Waveform.
The Fig.3.2 shows the PMSG output waveform. For example for a wind
The velocity of 10 m/sec the peak to peak voltage is 78 V. If wind velocity increases,
PMSG voltage also increases.
Figure: 3.3 Rectifier Output Voltage.
The Fig.3.3 shows the output of diode rectifier for a wind velocity of 10 m/s. This unit
converts the input AC voltage into equivalent DC. The rectifier output is fed to boost
chopper, where we implement control to get constant voltage and peak power.
3.3 Inverter Output Voltage
Fig. 3.4 Inverter Output Voltage.
Fig 3.4 shows the inverter output voltage. This unit converts the input DC voltage into
equivalent AC. The inverter is Sinusoidal Pulse Width Modulated inverter (SPWM). The
PWM pulses for the six switches of the inverter are generated by comparing three-phase
sinusoidal reference wave with a triangular carrier wave.
3.5. Maximum power points tracked
Fig. 3.5 Maximum Power point tracking waveform for Various Wind Speeds.
3.4 Applications
Earlier the applications of wind energy were less due to the cost and variations of wind.
However, recent improvements in technology reduce the cost by increasing the efficiency
of WECS. So Variable Speed WECS finds various applications. Some of them were
mentioned below:
WATER PUMPING SYSTEM
The livelihood and well-being of people, animals, and crops depends on a reliable, cost-
effective supply of water. Small wind turbines have been used to pump water from wells
for centuries.
STAND-ALONE SYSTEMS FOR HOME AND BUSINESS
Wind power along with Solar panel provides nominal power to homes and businesses that
are remote from an established grid. The applications for electricity in households include
heating, cooling, and lighting.
A system with grid-connected can provide power to a community center, primary health
centers or schools. In the health center, it serves in the storage of vaccines and radio
communication for emergency calls. A Grid system for a school can provide power for
computers and educational television, video, and radio.
Industrial applications
• Used in Telecommunications
• Activation of Radar
• Pipeline control
• Navigational Aids
• Cathodic protection
• Weather stations/seismic monitoring
• Air-traffic control
The variable-speed wind energy conversion system using a permanent magnet
synchronous generator has been discussed, and the optimal control in the duty cycle of the
chopper was proposed. The optimum power of wind turbine and the rectifier output
voltage is used as the reference for MPPT control. Also, MPPT control is achieved
without a wind speed sensor. The control algorithm is made simple from other existing
algorithms by voltage and power as a reference. The proposed method is advantageous in
the way that it does not need any information about wind velocity or optimal power
characteristic of the wind generator.
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