fuzzy logic control of a variable speed, varieble pitch wind turbine.pdf

7/27/2019 Fuzzy Logic Control of a Variable Speed, Varieble Pitch Wind Turbine.pdf

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FUZZY LOGIC CONTROL OF A VARIABLE SPEED, VARIABLE PITCH WIND

TURBEVE

M. Perales, J. Ptrez , F. Barrero, J. L. Mora, E. GalvBn, J . M. Carrasco, L.G. Franquelo.

D. de la Cruz", L. Fernandez", A. Zazo"

Grupo dc Tecn ologia E lec trh ica , Departamento de Ingeneiria Electronica.ES1 de la Universidad de Sevilla.

Avda. Cam ino de 10s Descubrimentos S/N, 4 I092 SEVILLA.

e-mail: [email protected]

(*) Desarrollos Eolicos S. A.

Avda. de la Buhaira S/N. S E V IL L A

Tlf: 4937000.

Tlf: 4487368, Fax: 4463 153.

e-mail: [email protected]

Abstract

I r i t h i s p q i er i s n sxstenr irserl to ei'nlirate n i ~ r r i nb le

speed ntrd pitch nngle wirrd nirbiiie 6) f i r zzy logic

tecliniques i s described. A firzzy logic corrtrol hos been

p ro p o sed b a sed or1 the speed iviird estinintioir irr order

to ge t r?ioxiniurri p o w e r mid strrbility of the system. A

l l k W p r o t o ty p e system rrsirrg 111'0 inverte r corinecred 6yn DC-Link cnpncitor /ins beeir used: thefirst orie worksns n coritrolled rectifier Biiplenierrtiirg vector control

n i id the secotid one /inridles the power- iriyected bit0 the

utility grid. Experirneiiml result of n I IK W gerierotor

will b e s1ioiv11.

I. Introduction

Many horizontal axes, grid-connected, medium to

large scale wind turbines are regulated by pitch control

and most o f wind turbines so far built have practically

consta nt speed, since they use an AC generator, directly

connected to the distribution grid, which determines i t s

speed of rotation.

Inthe last years, variable speed control has beenadded to pitch-angle controlled design in order to

improve the performance of the system ([11-[41).

Variable speed operation of a wind turbine has

important advantages versus constant speed ones. The

reduction of electric power fluctuations by changes in

kinetic energy of the rotor, the potential reduction of

stress loads on the blades and the mechanical

transmissions and the possibility to tune the turbine to

local conditions by adjusting thc control parameters are

main advantages of va riable speed win d turbine. O n the

other hand, variable speed control i s normally used with

fix pitch angle and very few works using both controls

have been reported.

Objective for variable speed control system are

sumarized by the following general goals: to regulate

and smooth the power generated, to maximize the

energy capture, to alleviate the transient loads

throughout the wind turbine, unity power factor in the

line side with no harmonics current injection, to reduce

the machine roto r flux at light load red ucing core losses.

Objectives for the pitch--angle control are similar

to the variable speed ones but only can be match a

maximum i n energy capture, which w ill be minor than

variable speed. I f pitch angle control i s used together

wit h variable velocity, better performances are obtained.

For example, to permit the starting blades angle to differ

from the operation blade pitch angle, hence allowing

easier starting and optimum running, power and speed

can be limited through ro tor pitc h regulation.

11. Control Strategies

In order to control the induction generator, two

inverter connected by a DC --L ink capacitor have been

used. The first one works as a controlled rectifier and

the second one handles the power in,jected into the

0-7803-5735-3/99/$10.0001999 IEEE 614

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mailto:[email protected]



utility grid (lig ure I ).

divided in three parts: induction generator control,

power injected into the u t i l i t y grid control and fuzzy

power control.

The control ol the induction generator can he A. Induction Generator Control Block.

This control is based on the well known indirect

vector method. The rotor speed is added to slip speed toohtain the synchronous speed on the reference frames.

P u h l i c G r i d

3 8 0 V

t ine

.....................

......................

Figure 1. Variable speed Power circuit.

In that relerence frame, the torque and flux control

components, Id ,and I , , . respectively. in those axes. A

Space Vector technique is used to control the induction

generator current. This current control has been

implemented in a static Ieference liame. The control

block diagram is represented i n

can he perlornied controlling the stator current ... ........

I~

Figure 3. Public Grid current injection Block Diagram.

B. Control of the Power Injected to the

Public Grid.

The DC-link capacitor voltage must he controlled to

maintain a constant reference voltage. This is performed,

injecting i n the public grid the active power delivered by

the induction generator. The control block diagram is

represented in Figure 3. A space vector technique is also

used to control the current injected into the utility grid. In[his case, th e current has heen implemented in a

stationary reference frame.

Figure 2. Indirect Vector Control Method Block Diagram.

C. Fuzzy Power Control Block:

The power control block implements different

615



i-3 In this control i t i s very important to use an anti-

window reset (the integral term i s reseted during the

transitions to other cont rol zone).

Controllerf, Constant power control.

This action i s only taken into account in a region

Gcnrmio

Figure 4. Fuzzy and vector Control.

con trol policies de pending on ro tor speed and generates a

current torque control action I # l ,roportional to the

machine torque.

I n th is case, several low l ~ v e legulators are used.

Such con trol loops are:Controller f , :Zero power control.

The control action is:

Controllerf? Maximum power control.

This i s a more complex controller. We calculate the

optimal velocity for niaxiiiiuin power capture. The

commanded velocity,wuc,, , is obtained using a model of

the wind turbine in order to estimate the wind speed. I t is

well known that rotor speed Iiiust be proportional to tlie

wind speed in a niaxitiiuni o f the power captured. The

ratio for both speeds i s defined like /z = -, where R

is the turbine radius, w , i s th e turbine rotor speed

and V, K is the win d speed. Fo r the wind turbine used in the

experiments the optimal value forL is I",,,,,= 4.7

Finally, the commanded generator speed can be obtained

by the follow ing expression:

= 0 .

Rw,

Vt r

Where p i s the ratio o f generator speed and turbine

rotor speed and the wind speed, v , r , i s obtained from a

static inverse model of the wind turbine which uses the

torque and the rotor speed as input.

The control action, IiI2s t l i e output o f the speed

control and i t can hc obtained hy a PI controller:

below 1500 rpm. I n this region the output is calculated by

the following expression:

Over 1500 rpm, the flux component, I,, wi l l he

changed in a similar form.

Controllerf, Maximum speed control.

Actually this controller is a limiter. The action,I,,

,

force to the speed to decrease. I o , i s calculate in this form:

I o , = -K , IW

Each control loop listed before is responsible for

maintaining i t s set point, and the output o f each controller,

I,, , yz o z , q l il l be differenl for each other.

To combine all control policies, a fuzzy logic based

control, similar to the controller proposed by Sugeno and

Takagi [7],has been presented in this paper. The fuzzy

system acts as a supervisor which combines all outputs

actions, depending on the rotor speed,bVr. The

mem bership functions fo r ro tor speed are shownin

Figure5 .

Mernbeiship functions for Veloci ty

1 SMALL MEDIUM LARGE VERY LARGE

(I .....................................................

w,=0.?0-.. ..................... ..;.. I

.........................

12Sq 1750

wr= I580

WI-00

Figure 5. Membership function for rotor Velocity.

Rule based inference process and defuzzy fication are

listed in Figure 6.

616



If WI is SMALL. then I., is 1 ;

If W r is MEDIUM. then

If W r i s LARGE. ihrn 1, i s .I t

is 1:

I If W r i s V E R Y LARGE. tlirn I. , is 1, I .

Figure 6. Inference and defuzzytication process.

III.Experimenta1 results

Figure 7 shows power and control systems of the

test-rig used to evaluate the proposed control. In that

figure, two subsystems can be found: the DC motor and

th e AC generator control. The DC motor is used to

emulate the wind turbine and is controlled by a

commercial full bridge rectifier impleniented by

thyristors, with a control system based on a

microcomputer.

.. ~ ~~ ~

Figure 7. Power control system implementation in the testrig.

In Figure I is shown the power control system

implementation. There are two subsystems: The DC motor

subsystem and the AC generator suhsystem.

The overall system is governed by a personal

computer, which includes the control board based on a

DSP and the software used to eniulate the wind turbine.

A photograph of the test rig used i n the experiments

is shown in.

. . .c,+.' . - 1...

Figure 8. Photography oi the test rig.

Tlie DC motor is torque controlled in order to

emulate the wind turhine including the pitch control,

large inertia term and mechanics oscillations.

Figure 9 shows oscillograms of the injected current

in the public grid i n ooininal condition and the generator( . I I I T ? " t ~

Figure 9.Current injected into the public grid (channel I )

an d the generator current (channel 2) in nominal cond itions(IS00 pin 380 V) . Channel I IOMdiv. channel 2 SA/div and

IOmddiv.

i n order to evaluate the overall system, a wind data

tile between 6 an d l 4 d s has been used, which is showni n Figure IO . Using this waveform, we can get easily th e

transitions between zones.

617



Figure IO . Wind waveform used i n the experiments.

In Figure I I is sliown the evolution of the generator

during the experiments. The upper graph shows the

generator speed and below i t can he observed the tip

speed ratio (1.

! : : : - = =$ 500

'0 5 10 15 20 21 30 35 40 45 50Tlempo IS ,

Figure 11.Generator Rotor Spezd (upper graph) and ti pspeed ratio measured (continuous line) lip speed ratio estimated

(dashed line).

The optimal value /i is 4.7 ond the wind turbine is

force to work with that value during the test. It ca n be

observed a good estiiiiiltion.

1V.Conclusion.s

A control system based on a DSP has been used in

this paper in order to cvaluate $omc control policies for

wind-energy conversion systems. The generator control

has been implementcd using a vecior control niethod. Th e

different control policies, niilxmiuiii power capture and

snioth torque depending o n the wind speed have been

implemented by a new furzy controller which combines

al l these factors and calculates the current torque

reference. An inverse model of the wind turbine has been

used to estiniate the wind speed and to obtain the optimalspeed reference. Experimental results have been shown

confirming the validity o f the proposed co ntrol method.

ACKNOWLEDGMENT

This work has been supported by the First User

Program (FUSE) included in the ES PR IT project, entitled

"DSP-Based control for variable speed wind turbine"

experiment number 2063, CICYT (TAP-960371) and

Desarrollos Edlicos S . A.

Bibliography

[ I ] R . David Richardson and Gerald M. McNerney, "WindEnergy Systems", Pruccefliiig qf IEEE. VOL. 81, NO. 3. March

1993.

[2]. M. Godoy Simoes, Bimal K . Bose. "Fuzzy Logic BasedIntelligent control of a Variable Speed Cage Machine Wind

Generation System". IEEE, 1995.

[3]. Torbjonrn Thiringer and Jan Linders. "Control by Rotor

Speed of a Foxed--Pitch Wind Turbine Operating i n a Wide

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"Comparison of Energy Capture and S tructural linplcinentationsof Various Policies of Controlling Wind Turbines". Wind

Energy: Teclriiology ond l,,i/~leiiieiiruriuii (Amsterdam

EWECPI).[SI. Donald S. Zinger. Eduard Muljadi. "Annualized WindEnergy Improvement Using Variable Speeds". IEEE

Trmrsocrions 0,s 1,rdirsn:v App l im r i om , VOL. 33. NO. 6, Nov-

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[ 6 ] .F. Barrero, J.L. Mora, M.Perales, A . Marchante, E.Galvin,J.M Carrasco. A. Torralba and L.G. Franquelo. " A Test-Rig toevaluate a Wind Turbine Generation Control System based onD S P . EPE'97. Trondheim, Norway. pp. 2.642-2.64s.

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fuzzy logic control of a variable speed, varieble pitch wind turbine.pdf

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