System for Controlling a Wind Turbine

Corneliu Buzduga

Stefan cel Mare University, 13 University, Suceava, Romania

Keywords: Wind Turbine, Power Generator, Positioning System, Transmission System, Sensors.

Abstract: This paper presents the improving operating principle of a wind turbine actually achieving an optimum control

of the rotation speed. This control consists in limiting the speed of rotation to a permissible maximum value

based on the peripheral speed determined by tests of resistance of the materials from which the blades are

made. Constructively, the whole mechanism is built from a set of interconnected functional blocks such as:

the positioning system, the shaft-hub-shaft assembly, the transmission system, the blade step change system

and, last but not least, the generator.

1 INTRODUCTION

Since the weather conditions are not constant, with

slow or sudden variations in both direction and

intensity of the air currents, the optimum operating

point of the generator suffers permanent changes, the

generator must continually adapt to environmental

conditions (U.S. Energy Information Administration,

2013). Optimal position detection and adaptation go

to a smart microprocessor-based system. This,

according to predefined instructions, will have to

interpret the data from various sensors and perform

wind turbine operation corrections so that a maximum

output is reported consistently at the given wind

speed and safe operation of the whole assembly. The

electricity produced by this wind turbine is stored in

the batteries as a reserve or consumed directly (World

Energy Council, 2010).

In operation, an important aspect is the height

regime at which the turbine will be installed, known

as the dynamics of the air currents differ at altitude,

thus a height between 10 ÷ 15 meters of the tower is

an economically suitable choice and aesthetically,

framing the entire system in the landscape, but also

places the turbine in an area of turbulent air flows due

to both neighbouring constructions and tree

vegetation. Another determinant factor that

influences the efficiency of the turbine is its location,

which often proves to be less favourable and,

compared to the airflow maps of its direction and

intensity, determines that the installation of a wind

turbine be considered less profitable (Wagner, 2017).

Electricity is directly proportional to both the

rotor speed of the generator and the mechanical

power of the propeller shaft. The two parameters are

dependent on each other in the sense that the

mechanical power at the shaft is determined by the

structural characteristics of the blades (dimensions

and aerodynamics) and the maximum speed of

rotation under safe conditions is determined by the

diameter of the turbine. In order to eliminate this

inconvenience, the solution addressed was the use of

an oversized turbine, thus ensuring at the same wind

speed a greater mechanical power on the turbine

shaft. With this solution we succeeded in changing

the operating point, the target being the production of

electricity at wind speeds starting at 3,5 ÷ 4 m/s, but

at the same time this solution radically changes the

dynamics of operation at high speeds, which,

although rare manifestation, the likelihood of

occurrence during violent storms jeopardizes the

integrity of the system. Under this consideration, in

addition to the production of electricity, which is the

main aspect to be pursued, the consideration should

also be given to the protection systems of the entire

device so that its operation can be safely carried out

regardless of the weather conditions to which it is

subjected (Jianbo and Qunyi Liu, 2017).

The protective systems must ensure continuous

adaptation of the turbine to environmental conditions,

and be able to react to all factors that can disrupt

proper operation. Although it is a more sophisticated

implementation method, the electronic control

solution brings several advantages such as continuous

adaptation according to a calculation algorithm,

Buzduga, C.

System for Controlling a Wind Turbine.

DOI: 10.5220/0007827502190225

In Proceedings of the 8th International Conference on Smart Cities and Green ICT Systems (SMARTGREENS 2019), pages 219-225

ISBN: 978-989-758-373-5

219

remote control and monitoring of operating

parameters (Suaad, 2013)

2 SYSTEM SETUP

2.1 The System Components

a. THE ROTOR

The rotor or propeller consists of three movable

blades around the longitudinal axes assembled on a

supporting hub and represents the active element that

transforms the kinetic energy of the wind into

mechanical energy available on its own shaft, which

rotates when the air currents is present and the turbine

are aligned in their direction. The mobility of blades

around their own axis is useful and necessary at the

same time to change the angle of attack, known as

pitch, in this way controlling the speed of rotation

until it keeps the rotor at constant speed regardless of

the wind speed.

A particular case is the passing of the blades in a

flag step, in this way the propeller can be dynamically

broken as a further protection during storms.

Figure 1: The hub and the mechanical interconnection

system of the blades.

b. THE ORIENTATION SYSTEM

The orientation system is designed to position the

nacelle, making a 360 degree rotation around the axis

of the tower (vertically to the ground plane). The

positioning is carried out by a universal DC motor,

with a built-in speed reducer, controlled by the

microcontroller, which has as reference the position

of a wind direction sensor, called weathervane.

Depending on the weather conditions, the nacelle is

oriented with the rotor in the wind direction, over a

minimum operating threshold, always aiming at

correcting the position.

Figure 2: The orientation system, drive motor and chassis.

As the construction number has been reduced as

much as possible, the guidance system also has a

secondary supporting role, being the link between the

pillar and the support frame of all mechanical and

electrical components.

c. THE TRANSMISSION SYSTEM

The transmission system is designed to drive the

rotation movement taken from the main shaft and

deliver it to the generator. By comparison, the

behaviour of the transmission is similar to a gearbox

of a car, but operating in the sense of increasing the

rotation, with a continuous transmission ratio of 1: 1.4

to 1: 4.7, respectively the amplification follows a

straight slope between the intervals minimum and

maximum, there being no thresholds that can cause

vibrations in the pillar when switching gears.

The transmission ratio is changed electrically by

means of a universal DC motor controlled by the

microcontroller, which monitors the incoming and

outgoing speeds during operation of the system. In

order not to force the rotor and eventually premature

shutdown of the turbine, changing the ratio of the

transmission to the amplification direction will be

performed only after the propeller has reached a

minimum threshold of 400 rpm, at which point the

input shaft speed will remain at an approximate

threshold constant. If the wind speed decreases in

intensity and the turbine output decreases, the

transmission gradually returns to the minimum

threshold, with the condition that the propeller does

not fall below 400 rpm and the transmission has a

positive gain ratio.

d. THE POWER GENERATOR

The power generator that supplies the turbine is the

result of changing a synchronous motor in the sense

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that parameters such as winding conductor material

and section have been changed, the number of coils

and the number of paths. With the modifications we

have made, we have been looking for a large voltage

(about 120 V DC) and a low load current to be cut so

that the winding and transport losses are as low as

possible. By construction, the generator is a three-

phase Y-connection with the permanent magnet rotor

of the ferrous material outdoors, also acting as

cooling fan, and on the inside the stator with 36

notches distributed equally to the three electric phases

(Archer and Jacobson, 2012).

Figure 3: The power generator – left: assembly, centre:

rotor and right: stator.

e. THE ELECTRONIC CONTROL AND

COMMAND MODULE

The operating principle is based on the block diagram

of Figure 4.

Figure 4: The block diagram; operating principle.

Running the entire system at rest has the following

steps:

Step 1: The air currents are not present or their

intensity is too low to justify starting the turbine. As

a result of operating tests, the lower limit threshold at

which it was set as starting point is 2.5 m/s, the wind

speed sufficient to start and accelerate the rotor.

Below this minimum threshold, although the rotor is

in motion, the energy collected at the generator

terminals is insignificant, resulting only in idle

operation (John and Julia, 2015).

Step 2: Once the minimum wind speed is

exceeded, the turbine switches to two-stage

operation:

- detecting the wind direction and the aligning

wedge to appropriate position. A particular aspect

is that the platform is given a degree of freedom

of ± 5 ° geometric to the actual direction, thus

avoiding the scenario in which the position

correction is continually attempted during

turbulent air streams. This is more likely to be the

case that, as soon as the nacelle has moved in one

direction for correct alignment, at the smallest

deviation of the steering sensor, the positioning

motor is restarted for a new adjustment, after

which the cycle resume.

- checking and adjusting if necessary the blade step.

As a result of the operating tests, in addition to the

two positions, respectively the working position

and the flag step corresponding to the heads of the

race, it was also required to declare an

intermediate step, which I called a standby

position. The insertion of this intermediate

position produces a positive contribution at the

moment of the rotor start, and after the main shaft

exceeds 60 rpm, corresponding to the propeller,

the blades are switched to the working position

where acceleration to the maximum required by

the conditions forecasts.

Step 3: After the start, the turbine is only allowed

to operate with wind direction correction, monitoring

the input and output speed of the transmission block

until the propeller reaches a set speed of 400 rpm.

From this point the transmission ratio starts to change

in the direction of the increase or decrease as the case

may be, the modification being made gradually and

without the propeller decreasing its speed below the

set limit. In the case of wind gusts that can cause

sudden accelerating, the speed will be automatically

controlled, limited to 450 rpm, by a centrifugal

mechanical system. The wind turbine will be left to

operate in this way as long as the wind speed does not

exceed an alert threshold of 12 m/s (Jacobson and

Archer, 2012).

Step 4: Is a procedure to protect the turbine from

any possible storms. Once the warning threshold of

12 m/s is exceeded for more than 60 seconds, the

blade step will be changed to reduce aerodynamic

performance, being switched to the standby position

where the turbine will continue to operate but the

System for Controlling a Wind Turbine

221

propeller speed will be reduced. In the same way, if a

15 m/s alert threshold is exceeded, the propeller will

pass the flap, the tube will enter dynamic braking

where this time the air currents will block the rotation

of the propeller until it stops completely (Bie and

Zhang, 2012).

The engine control system is built around a

microcontroller that, according to initial instructions,

has the task of modifying or correcting the current

status of the entire system. We can say about the

microcontroller that its functions are divided into two

main categories, namely the command function that

uses the output signals, the final result being the

motors' operation as the case may be, and the

monitoring function which, by means of some sensors

and transducers, interprets the operating parameters.

The monitoring function pursues:

- direction and speed of the wind;

- aligning the platform in the direction of the air

currents;

- propeller and generator shaft speed;

- operating parameters of the generator: voltage,

current, temperature;

- maintaining self-regulation systems at work

intervals (race limits).

2.2 The Sensors Used in System Design

a. THE WIND SENSOR

For wind speed monitoring, a digital unit

incorporating the anemometer and weathervane was

used on the market under the name of TX20 SENZOR

model developed by La Crosse Technology Ltd.

Figure 5: The wind sensor.

The sensor will transmit the data every 2 seconds

as long as pin 3, DTR, is connected to GND. The data

chart contains 41 bits divided into 6 data sections. The

transmission is for 49.2 ms, the duration of one bit

being 1.2 ms.

b. THE POSITION SENSOR

The role of this sensor is to align the propeller in the

wind direction. It is also a wind sensor, i.e. a

weathervane, but in which the output signal is

analogous, used in a particular way in that the

mounting base is movable to the ground. The

Weathervane is mounted on the platform body, which

in turn is movable around the axis of the tower. In the

correct alignment position, the mobile element must

be aligned halfway through the time the sensor can

detect wind direction deviations. A deviation in either

direction from this position will detect what triggers

the rotation of the platform as well as the base of the

sensor, the mobile element being maintained in the

wind position. In this way, the weathervane returns to

the correct position by turning the nacelle off. The

phenomenon is repeated whenever position

corrections are needed. The type of sensor used is a

weathervane, known as wind wane model NRG #

200P.

Figure 6: The weathervane NRG model # 200P.

The mobile element of the weathervane operates

an internal potentiometer in a complete rotation of

360 degrees and can be deflected by winds at speeds

of 1 m/s.

The potentiometer has an internal resistance of 10

KΩ and can be directly supplied to a voltage in the

range of 1 ÷ 15V DC, the output signal being a

voltage proportional to the wind direction. From

constructive limitations and because a degree of

freedom of 360 degrees is desired, for an interval

between 8 ÷ 10 geometric degrees the sensor output

is null, in this area the potentiometer cursor does not

have a conductive film continuity. This is an

impediment if the output signal is to be interpreted

directly by a microprocessor; in the possibility that

the potentiometer cursor would be in the area called

dead band, the output signal is missing, which may

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cause operating errors. Although the probability of

error is small, the dead band has a range of

approximately 8 ÷ 10 geometric degrees, which

means 2.75% of the measurement range, they must be

eliminated or reduced as much as possible (Al-

Muhaini and Heydt, 2013).

c. THE SPEED SENSORS

Changing the transmission ratio and the variable pitch

of the propeller is determined by the rotation speed of

the propeller shaft and the generator. In this respect,

the speeds of the two shafts must be monitored

throughout the turbine operating mode. There are

several types of sensors specifically developed to

determine the speed of rotation of the trees, among

them, those with the longest use being non-contact

sensors. According to the output signal type, the

sensors can be classified into capacitive, inductive or

Hall Effect sensors. For slow speed shafts, rotation

speed detection sometimes uses reed relays, but the

blades of the contact are subject to premature aging

due to the large number of triggers to which it is

subjected. The types of sensors used are produced by

Honeywell under the SS411P encoding.

To trigger the sensor we used permanent magnets,

four of which are fixed to a disc mounted on the shaft

for which the speed is determined. Magnets are fixed

to the disk table at equal distances with alternating

poles. During rotation of the shaft and the magnets,

they will enter the sensor trigger area, the output

signal becoming a rectangular signal that will have

two periods during a complete rotation. The

frequency of the output signal is directly proportional

to the rotation speed of the shaft, so its mathematical

computation can be determined by the formula:



(1)

where f is the signal frequency and n is the speed

Figure 7: The propeller shaft switch disk.

Similarly, the rotation movement of the drive

motor of the transmission mechanism is detected,

indicating that this time the sensor is of the unipolar

type and on the disk mounted on the shaft are

diametrically opposed on the circumference only two

magnets with the same pole magnetically pointing

towards the sensor. Thus, every half-turn is sensed by

a low level of the output signal.

The same model of the unipolar Hall sensor, in the

same configuration, is used to detect positions where

the blades are in the position we named above the

standby position and the alignment of the platform to

a reference point. For the interpretation of output

signals, it should be noted that they are at a low level

when they are at points of interest and at a high level

in the rest (Conti and Rizzo, 2015).

d. THE TEMPERATURE SENSOR

Over a long period of operation, the internal

temperature of the generator may reach critical values

that may result in its destruction. To avoid possible

damage or troubleshooting due to a high temperature

regime, it is preferable to switch the temperature

generator above the threshold. Thus, the stator

temperature should be monitored throughout the

operation.

Figure 8: The temperature sensor. Model DS18B20.

Variants of temperature-sensitive elements that

are compatible with the microcontroller and without

the need for complex processing of signal processing

are the thermistor, analogue sensor LM35 or

DS18B20 digital sensor, the latter being the one to be

used. The main advantage is that for communication

with the microprocessor, data transmission from the

device is done on a single wire (and mass, GND).

e. THE CURRENT SENSOR

Electrically operated mechanisms have an average

degree of complexity, and for undesirable reasons,

malfunctions may occur, resulting in an increase in

engine current absorbed above the normal operating

range. These situations would be likely to cause

blockage, defeat limiters or a high degree of wear on

the engine. Maintaining under voltage at currents well

above normal operating limits would cause excessive

engine heating leading to irreparable damage, and

other elements in the supply circuit may be affected.

Elimination of these possible situations is

accomplished by monitoring the current in the motor

circuits, in this sense, by introducing a current sensor

into the circuit. For easy deployment, we used a

System for Controlling a Wind Turbine

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sensor model built on an integrated circuit developed

by Allegro MicroSystems, under ACS712 encoding.

It is an SMD small integrated circuit in the SOIC8

capsule, the current detection being based on the

linear Hall Effect. The sensor is invasive, requiring

interruption of a supply line, and can detect current in

both AC and DC circuits.

Figure 9: The current sensor. Model ACS712.

f. THE VOLTAGE SENSOR

For complete monitoring of the entire system, it is

necessary to interpret the electrical parameters of the

generator. If the implementation of the output current

detection function is somewhat considered to be easy,

with different variants of inversion or non-invasive

AC sensors, measuring output voltage of the

generator with a microcontroller imposes certain

restrictions precisely because of the operation. The

output voltage is a variable signal in both amplitude

and fecundity, the maximum values being considered

dangerous to be detected directly. Thus, during

operation, when weather conditions allow, at the

terminals of the three-phase generator, for current

configuration of connections, weights can be

recorded in the range 0 ÷ 90 V AC with frequencies

proportional to the voltage in the range 0 ÷ 400 Hz.

The maximum possible voltage is high enough to

reach values considered dangerous, which is why

indirect measurement is recommended to determine

its value. Due to the variable frequency, it is not

possible to use a low voltage transformer to obtain a

low level signal so that it can be processed by the

microcontroller, the frequency variation limits cause

them to malfunction, being well above tolerances.

The voltage collected from the generator

terminals is rectified and filtered, then applied to a

resistive divider dimensioned so that for the

maximum possible applied value, the divider's mean

point does not exceed the 12 V DC threshold.

However, there is a possibility that, due to the lack of

a consumer, the tension will increase much, even

beyond the limit. To avoid damaging the circuit

caused by an accidental voltage, even if there is an

increase above the 12V level, it will be stabilized by

a Zenner diode.

Taking into account the fact that, in order to be

interpreted by the microcontroller, the input signal

can be a DC voltage, for detecting the voltage level of

the generator we proposed and implemented the

following scheme:

Figure 10: The voltage sensor. Electronical scheme.

The method has the advantage of galvanic

separation of power circuits from signal circuits and

prevents the destruction of the microcontroller if the

turbine enters the operating mode in the absence of

the supply voltage of the microcontroller by

introducing external voltages on the signal port.

g. THE MICROCONTROLLER

The Arduino Mega 2560 development board has 54

digital input / output pins (of which 14 can be used as

PWM outputs), 4 UART serial ports, 16 analog

inputs, a USB connection, a 16 MHz quartz crystal

oscillator, a power jack and a reset button.

The 54 digital pins can be used as outputs or

inputs with the digitalRead (), digitalWrite () and

pinMode () functions. These digital pins use the

digital signal in which the 0 logic is represented by

the absence of voltage and 1 logic having the voltage

level of 5V. Analog pins provide a resolution of 10

bits meaning 1024 different values. These pins

measure voltages between 0V and 5V.

Arduino Mega 2560 has facilities for

communication with a computer, other

microcontrollers or other Arduino cards. The Arduino

software includes a serial monitoring that allows

simple textual data to be received or sent to the

development board.

The microcontroller is programmed to take data

from the sensors to display them using the LCD

module. As an example, see figure 11.

Figure 11: Display data taken from sensors.

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3 CONCLUSIONS

The system was tested under real conditions with

good results for initial tests under laboratory

conditions. At the same time, a second electronic

module was developed to complement the system, its

functions being communication, the data taken being

processed and displayed on a display. The results are

promising, so we can consider the test period ended

after the entire system is tested under realistic

conditions in a time frame that includes both a cold

season and a warm season.

The wind turbine will be used to provide the

electricity needed for a home or small production hall.

REFERENCES

U.S. Energy Information Administration. Web. 29 May

2013, http://www.eia.gov/

World Energy Council. 2010 Survey of Energy Resources,

London, UK.

Wagner, H.-J., 2017. Introduction to wind energy systems,

The European Physical Journal Conferences, 148,

pp.1-16.

Jianbo Y., Qunyi Liu, Xin Li, and Xiandan Cui., 2017.

Overview of Wind Power in China: Status and Future,

Sustainability, 9, 1454.

Suaad J., 2013. Environmental Impacts of Wind Energy,

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Archer C.L. and Jacobson M.Z. 2005. Evaluation of global

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John O. D., Julia R. G., Jeffrey R. K., Parviz M., and Jifeng

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