Piezoelectric Wind Turbine Automation using radio frequency

Sanjay Srikanth Nekkanti, Suman Kalyan Biswas, Pritha Chowdhury

Abstract - The total wind power of the

atmosphere at any instance of time is estimated to

be 3.6 billion kilowatts [4]. Piezoelectric sensors

uniformly placed around the circumference of the

wind turbine mast can detect maximum wind

velocity direction. Movement of nacelle in the

direction of maximum wind velocity is attributed to

the movement of stepper motor. The power

generated from the wind turbine is stored in battery,

monitored by a potential detector. Piezoelectric

sensors placed on the rear side of propeller generate

electricity through back flow of air. The battery

power can be used efficiently along with an

overhead AC supply. The charge level of the battery

is conveyed using DTMF or AX.25 through radio

channel. The control station transmits a control

signal to make the transition from overhead AC to

DC supply once the optimum charge level is

attained. The charge declined is reported back to the

control station.

Keywords - Piezoelectric Sensors, Potential

detector, Radio channel, Wind velocity direction.

I. INTRODUCTION

Wind power systems use the energy in the wind and

with a wind turbine the energy is transferred to

mechanical power which in a generator is converted

to electrical power. The varying wind speed

introduces special considerations concerning grid

connections and integration into the whole power

system. Winds are movement of air masses in

relation to the ground surface. The winds are

caused by pressure forces and sometimes also by

the gravitation.

II. GENERAL DESCRIPTION AND DESIGN

A. Power from wind turbine

( )21

2P rρ π=

P = Power in the Wind (watts)

ρ = Density of the Air (kg/m3)

r = Radius of your swept area (m2)

v = Wind Velocity (m/s)

π = 3.14

Fig 1: Variation of Mean Wind Speed Round the

Year in INDIA (Chennai).

B. Piezoelectric sensor

Piezoelectric materials are excellent power

generation devices because of their ability to couple

mechanical and electrical properties. When a

piezoceramic transducer is stressed mechanically by

a force, its electrodes receive a charge that tends to

counteract the imposed strain. This charge may be

collected, stored and delivered to power electrical

circuits or processors [2]. For example, when an

electric field is applied to piezoelectric sensors a

strain is generated and the material is deformed.

Consequently, when a piezoelectric is strained it

produces an electric field, therefore piezoelectric

materials can convert ambient vibration into

electrical power. The charge generated by the

piezoelectric crystal is proportional to the applied

force, for instance in the x direction the charge is

1xQ d=Qx = charge at an instance in the x direction

d11 = proportionality constant

Fx = force applied

Because a crystal with deposited electrodes forms a

capacitor having capacitance C, the voltage V,

which develops across the electrodes is

11x xQ d FV

C C= =

V= voltage

C= capacitance

In turn, the capacitance can be represented through

the electrode surface area a, and the crystal

thickness l :

0k aC

l

ε=

ɛ0 = permittivity of free space

a = electrode surface area

l = crystal thickness

k = dielectric constant

Where ε0 is permittivity of free space and k is the

dielectric constant. Then the output voltage is

11 11

0

x xd F d F lV

C k aε= =

MPX2010 Compensated Pressure Sensor

The MPX2010 / MPXV2010G series Piezoelectric

pressure sensors provide a very accurate and linear

voltage output directly proportional to the applied

pressure. These sensors house a single monolithic

silicon die with the strain gauge.

SDX SERIES

Low Cost Compensated Pressure Sensors in DIP

Package FEATURES - 0 to 1 psi to 0 to 100 psi -

Temperature Compensation - Small Size - Low

Noise - High Impedance for Low Power

Applications

GENERAL DESCRIPTION

The SDX series sensors will provide a very cost

effective solution for pressure applications that

require small size plus performance. These

internally calibrated and temperature compensated

sensors give an accurate and stable output over a

0°C to 50°C temperature range. This series is

intended for use with non-corrosive, nonionic

working fluids such as air and dry gases. Devices

are available to measure absolute, differential and

gage pressures from 1 psi (SDX01) up to 100 psi

(SDX100). The Absolute devices have an internal

vacuum reference and an output voltage

proportional to absolute pressure. The output of the

bridge is ratiometric to the supply voltage and

operation from any D.C. supply voltage up to +20 V

is acceptable.

Fig 2: Pressure Sensors

C. Piezoelectric sensors on mast:

An anemometer comprises an array of 20

piezoelectric pressure sensors separated by 18

degrees [1]. The sensors are mounted on the circular

mast to face into a different wind direction.

Electrical means are used to address each of the

sensors for determining which of the sensors is

generating, within a given time period, the greatest

output voltage, thereby indicating the direction of

the wind during such time period. In one

arrangement, the amplitude of such greatest output

voltage is used, via a look-up table, to determine the

speed of the wind during such time period.

Fig 3: Arrangement of Sensors on the Mast

Fig 4: Piezoelectric sensor circuit for the detection

of the Maximum wind direction

D. Voltage Comparator

For comparison of the voltage output from all the

sensors 8051 Microcontrollers are used. It is

programmed to detect the maximum voltage output

from the sensors placed on the mast. The position of

the sensors is sent in as a trigger signal to the

stepper motor.

E. Stepper Motor:

The stepper motor is an electromagnetic device that

converts digital pulses into mechanical shaft

rotation. Advantages of stepper motors are low cost,

high reliability, high torque at low speeds and a

simple, rugged construction that operates in almost

any environment. It has no brushes or contacts.

Basically it’s a synchronous motor with the

magnetic field electronically switched to rotate the

armature magnet around. A stepper motor system

consists of three basic elements, often combined

with some type of user interface like host computer.

A stepper motor is placed inside the pole at the

bottom section. The shaft of the stepper motor is

welded perpendicularly to the nacelle. The

anemometer detecting the wind direction would

transmit a triggering pulse to the host computer.

The computer calculates the ample delay and is

programmed to shut down the supply once the

motor completes the required angular rotation. The

rotation of the stepper motor synchronizes the

rotation of the nacelle in the direction of maximum

wind.

The step angle can be as small as 0.72 deg or as

large as 90 deg. But the most common step sizes are

1.8 deg, 2.5 deg, 7.5 deg and 15 deg.

Fig 5: Overall Arrangement

F. Piezoelectric sensors on the rotor blades

Piezoelectric sensors inscribed on the rear side of

the rotor blades generates power to be stored in a

battery to drive the stepper motor and a transceiver

placed on the mast. The piezoelectric sensors are

connected in series to obtain a net high output

voltage. Each variation of a particular model of

sensor will produce a convenient 5 Volts signal.

The back flow of air applies pressure on the

piezoelectric sensors thereby generating electrical

power which can be coupled in series to get

maximum power output.

Fig 6: Considering the Nacelle Facing Towards the

positive Y-axis direction

TABLE I

Wind Utilization at Different Angles in Region 1

and 2

TABLE II

Back flow of Air in Region 3 and 4

** When the inclination of wind is more than 90

degrees then the effective wind utilization is zero

since there is back flow of air. Movement of the

nacelle in the direction of wind would facilitate full

utilization of wind velocity.

Fig 7: Wind Speed Utilization

Note:

The application of the concept enables optimum

utilization of wind energy in region 1 & region 2 and

facilitates full utilization in region 3 & region 4 where

wind energy was not utilized due to the back flow of air.

G. Potential Detector circuit

A potential detector circuit is connected to the

storage batteries to detect the charge of the battery.

Fig 8: Potential Detector Circuit

H. Control using a Radio Frequency

Optimization of the charge of the battery is done

using the telemetry data analysis from the potential

detector transceiver sent via radio frequency. The

charge level of the battery is received at the control

station for giving the appropriate commands using

DTMF or AX.25 for the power switching. The

telemetry data is digitally transmitted over air. The

digital signal is encoded using a base band encoder.

The transmission and interception of the digital data

is achieved through a specially designed antenna.

Detecting an optimum level of charge in the battery,

the control station transmits a control signal to make

the transition from overhead AC to DC supply of

the battery. The decline of charge in battery is

reported back to the control station enacting a vice-

versa action. The control over the power generation

and utilization gives an additional advantage of

power management in case of emergency.

Community radio services, internet services, audio

and video transmission can be used over the

digitally multiplexed channel.

Fig 9: 27 MHZ CB Transceiver

FEATURE:

1) High/Low transmit power selection.

2) Noise blanker function to eliminate the external

noise.

3) High gain low noise receiver.

4) Long communication distance.

The schematic block diagram shows the digital data

transmission path.

Fig 10: Digital Data Transmission

Fig 11: Transceiver block diagram

I. Social Impact

A small wind turbine of around 2 meters in size

generates 1.5 KW - 2.5 KW of power which is

sufficient to serve the power requirements of at least

two rural houses [6].

Power Requirements of each house:

Fan - 50 to 100 watts

Light Bulbs - 100 watts

Colour TV - 250 watts

Miscellaneous - 400 watts

Countries like India have a very long coastline of

7300km. Land breeze occurs in coastal areas during

the night when the ground is cooled faster than the

water. This causes the wind to flow from land

towards the sea. The land breeze is significantly

weaker than the sea breeze, about 1m/sec. The sea

breeze occurs in coastal areas during sunny weather

when the ground surface is heated faster than the

water, this causes a wind direction from water

towards the land. The wind speed at ground level

can be in the range of 5 – 10 m/sec [3]. The

maneuvering of the nacelle in the direction of

maximum wind velocity would facilitate us to

generate the maximum power. The same

communication channel can be digitally

multiplexed with community radio signals to impart

free education (school over air).

Fig 12: Basic Plan for a Small Home Wind Turbine

III. CONCLUSION

One survey of 11 major U.S transmission regions

found last year that applications to connect new

wind and solar generators came in aggregate to 250

gigawatts – that’s the equivalent of roughly 250

standard atomic power plants – while combined

natural gas, coal and nuclear applications came to

just 180 GW. Placement of 2 meters small windmill

over the roof tops of the rural houses would

eliminate the power crisis problem in rural and

remote areas.

REFERENCES

[1] Piezoelectric Wind Sensors, US patent-

4615214.

Publications:

[2] Velocity Controlled Piezoelectric

Switching Energy Harvesting Device

[ICREPQ’09 -Yuan-Ping , Dejan Vasic,

François Costa, Wen-Jong , C. K. Lee]

[3] Encyclopedia of Physical Science and

Technology (3RD Edition, Volume-17) pp

839.

[4] Britannica Learning Library 2006

[5] Whitakers world of facts 2009 (by

Russell Ash).

Websites:

[6] www.capcity.adelaide.sa.gov.au

[7] www.windpower.org