WIND ENERGY APPLICATIONS - Unicamplcv.fee.unicamp.br/images/BTSym-19/Papers/003.pdf · Wind turbines work by converting the kinetic energy in the wind into mechanical energy and then

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

[email protected]

²State University of Campinas, São Paulo, Brazil

[email protected]

[email protected]

[email protected]

[email protected]

²Fluminense Federal University (UFF), Rio de Janeiro, Brazil

[email protected]

²Annamalai University, Tamilnadu, India

[email protected]

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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