Simulation_of_Doubly_Fed_Induction_Generator_with_Wind_Turbine-libre.pdf

International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 2 Issue: 6 1683 – 1687

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1683 IJRITCC | June 2014, Available @ http://www.ijritcc.org

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Simulation of Doubly Fed Induction Generator with Wind Turbine

Ms Minakshi Devi

M.Tech-PS-student, Department of Electrical and Electronics Engg, AFSET (An Autonomous Institution)

Dhauj Faridabad Haryana Pin -121004 *Email ID: [email protected]

Mr. Ameenuddin Ahmad

Assistant Professor, Department of Electrical and Electronics Engg., AFSET (An Autonomous Institution)

Dhauj Faridabad Haryana Pin -121004 E mail ID: [email protected]

Abstract— The power generation from the renewable energy sources is in trend and is necessary as the conventional hydro-carbon fuels are limited in amount and demand of energy is increases. The recently work on renewable work is doing at flood level and everyone wants to increase efficiency and utilize these natural energy in abundant availability effectively for human development. The available renewable energy is solar, wind, bio-fuels, fuel cells. Wind energy has lesser cost and more clean as compare to other renewable energy sources. The variable speed double fed induction generator fixed-speed squirrel-cage induction generator has been proposed in the literature for wind turbine generation technology. The doubly fed induction-generator (DFIG) is used widely and accurately in with the wind turbine to produce electric energy since its flexibility - the direction and speed of winds may vary from location to location and time to time, the variable speed wind turbine technology offers inherent advantages over the fixed-speed one. The doubly feed induction generator control easily the variation of wind speed by injecting a compensating variable frequency current component in the rotor circuit with the help of the two back to back converters i.e. rotor side converter and grid side converter. This characteristic helps to facilitates both super as well as sub-synchronous operations of DFIG. This dissertation work is concerned with modeling and control of DFIG. The detailed mathematical model of the induction machines, DFIG and its converters and their control is reviewed. Using numerical differentiation of the SIMULINK models, lower order nominal representation of DFIG is obtained which is subsequently used for PID control design. The PID control is widely used control strategy in industry due to its simple design and robustness properties. The proposed results have been compared with the existing ones, with performance improvements. Keywords: Renewable Energy, Electric Energy, Converter, Induction Generator, Simulink, Direction, Time, Double Feed, __________________________________________________*****_________________________________________________

INTRODUCTION

1. INDUCTION MACHINES: The induction machine is widely used in variety of applications for converting the electrical power into mechanical one. Squirrel-cage Induction machine Wound rotor Induction machine The wound rotor type in the form of DFIG is widely used due to its better control and wide wind speed operations. 1.1 DYNAMIC d-q MODEL: The voltage equations of an induction machine can be represented in terms of the currents and the flux linkages in compact form as:

abcs s abcs abcs

abcr r abcr abcr

v r i p

v r i p

Where the quantities and their subscripts have usual meanings. 2. WIND TURBINE: The wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger.

FIG 1 WIND ENERGY CONVERSION INTO ELECTRIC ENERGY

2.1 Basic of Wind Turbine: - The mechanical power which is produced by the wind turbine is proportional to the cube of the wind speed i.e. Pm v3. Where Pm is the mechanical power of the wind and v is the velocity of the wind speed 2.2 COMPONENT OF WIND TURBINE 2.2.1 Drive Train and Aerodynamics: - The effect of the speed and pitch angle changes on the aerodynamic power during the grid faults, a simplified aerodynamic model is sufficient. For stability analysis, the drive train system must be approximated by the at least a two mass spring and damper model when the system response to heavy disturbance is analyzed Akhmatov. V. There is a flexible shaft through which the turbine and generator masses are connected. 2.2.2. Pitch Angle Control System:- PI control is used to realize the pitch angle, in Servo

mechanism model with time control servoT accounts for the

realistic response in the pitch angle control system. During the grid faults how fast the aerodynamic power can be reduced in order to prevent over speeding is decided by the rate –of change limit. 2.2.3. Wind Turbine Modeling:- for optimal operations of the wind turbine at different wind speeds, it must be operated at its maximum power coefficient

( optimumpC . =0.3-0.5i.e. at a constant tip speed ratio, for

operation around its maximum power coefficient. The Aerodynamic power generated by wind turbine is given as:-

Wind energy

Mechanical Energy

Electrical energy

http://en.wikipedia.org/wiki/Kinetic_energy

http://en.wikipedia.org/wiki/Mechanical_energy


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P aero = 0.5 A 3),( vCp

(3.1)

Here C P ( ), =c .)..( 6432

1

5

ceccc

i

c

i

(3.2)

1

35.0

.08.0

113 i

, and the coefficients c 1 to

c 6 are

c 1 =0.5176, c 2 =116, c 3 =0.4, c 4 =5, c 5 =21, c 6 =0.0068

&v

RT .

Tip ratio speed,

T Rotational speed of the rotor,

=pitch angle,

R= the radius of the area covered by the blades.

Fig 2. (a)With full-size converter ;( b) with doubly-fed induction generator Double fed induction motor The AC/DC/AC converter is divided into two components: The rotor side converter (Crotor) The grid side converter ( Cgrid). 1. Allows extracting maximum energy from the wind for

low wind speed

2. Converter required for DFIG can work on (25%-35%) of rated power. This is due to the reduced size of the rotor side converter.

Basic Principal of DFIG The basic principle used in DFIG is to interpose a frequency converter between the variable frequency induction generator ( it is mainly for injecting the current in the rotor circuitry for frequency compensation) and fixed frequency grid. The speed of machine can be controlled from either rotor side or stator side. Converter in both super and sub synchronous speed ranges. Since the slip power can flow in both directions i.e. to the rotor from the supply and from the supply to the rotor side

Fig 3. Basic diagram of doubly fed induction generator with converters The mechanical power and the stator electric power output are given as below

rmr TP

sems TP

the mechanical dynamical equations for the lossless generator are as

emmr TT

dt

dJ

In steady-state, the mechanical torque balances the electromagnetic torque acting on the machine and hence the relations are as

emm TT And rsm PPP it follows that:

smr PPP = Ssemrm sPTT

where srss /)( is defined as the slip of the

generator in per unit.


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Fig.4. Diagram of Working Doubly fed induction-generator wind-turbine A voltage source converter is used in DFIG for the following purposes: to control the rotor-side converter to control the grid-side converter to control the voltage of the DC link

DFIG

Rotor Side

Converter

Grid Side

Converter

VSC Control Circuitry

Common DC Link

G

R

I

DGear Train

Wind Turbine

Fig.5. General Schematics of DFIG and Wind Turbine along-with VSC Converters with common DC link SIMULATION AND RESPONSE OF THE DFIG SYSTEM A 2 MVA DFIG connected to the variable speed wind turbine and to the infinite bus through transformer, cable and

transmission line of the sample system taken was simulated in Matlab simulink. Initially the DFIG wind farm produces 1.8 MW. This active power, corresponds to the maximum mechanical turbine output for a 10m/s wind speed 1.95 MW minus electrical losses in generator. The corresponding turbine speed is 1.09 p.u of generator synchronous speed. The DC voltage is regulated at 1200 V and reactive power is kept at 0 Mvar. At t=0.02 s the positive-sequence voltage suddenly drops to 0.8 p.u. causing an oscillation on the DC bus voltage and on the DFIG output power. During the voltage sag the control system regulates DC voltage and reactive power at their set points (1200 V, 0 Mvar).

Detailed DFIG wind turbine diagram The schematics of the system is as shown in Fig. 5.1. For the simulation study, the detailed wind farm model available in the power system blockset has been adapted to incorporate the parameters of the sample system under study. Fig. 5.2 and Fig. 5.3 shown the DFIG subsection and block schematics of the grid side converter


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0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

time in sec

magnitude

Voltages at the DFIG terminals

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

time in sec

magnitude

Active power delivered of the DFIG CONCLUSION AND FUTURE SCOPE The supervisory PID-controller although improves the system response in comparison to the open-loop system but the number of oscillations are not removed completely. PI-controller designed in this work using the Static output feedback method not only improves the system response but also, reduce the percentage overshoot to zero. PI-controller using SOF method shows that the system settle down in lesser time as in the case when we use supervisory PID-controller. Table 5.1 clearly shows that the

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Simulation_of_Doubly_Fed_Induction_Generator_with_Wind_Turbine-libre.pdf