Transcript Slide 1

PROPORTIONAL CONTROLLER BASED GRID
CONNECTED WIND SYSTEMS
By
B.SIVAPRASAD
K.P.REGHU
EEE, SXCCE
V.MINISH
Under the guidance of
Mr. D.R.BINU BEN JOSE
SENIOR LECTURER, EEE DEPT, SXCCE
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ABSTRACT
This project presents the simulation of a closed loop scheme for interfacing wind driven
Permanent Magnet (PM) alternator with utility grid through a line commutated inverter.
A proportional controller can be used in conjunction with certain block sets from
MATLAB/SIMULINK for generating appropriate firing pulses for the SCRs in the inverter.
The control objective is to extract maximum power from the wind energy system and to transfer
this power to the utility. This is achieved by controlling the firing angle delay of the inverter.
The complete closed loop scheme will be modeled and simulated in MATLAB/ SIMULINK
environment and the simulation results will be presented
It has the advantage of having permanent gear ratio (PGR) which avoids unnecessary wear and
tear of gear tooth instead of variable gear ratio (VGR) where frequent maintenance and
replacement of gear is required.
The alternator output will normally be of variable voltage and variable frequency (VVVF). The
power at VVVF will be converted to DC and interfaced with the grid using line commutated
inverter.
This project also investigates the harmonics of the line current and the use of passive filter for the
minimization of grid current harmonics.
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INTRODUCTION
In our project we use permanent magnet alternator whose output is a variable voltage variable
frequency, which is first rectified using a diode bridge and the DC power is then transferred to the
utility at its own voltage and frequency using a line commutated inverter.
This project investigates a simple maximum power point tracking system for variable speed wind
turbines.
The control uses a closed loop circuit which will fire the thyristors at the maximum power
operating point.
The closed loop system is developed using a simple proportional controller, which convert the
power delivered to the grid into corresponding firing angle using which the inverter is fired.
With increase in the speed, the PM generator output will increase, the corresponding firing angle
decreases and thereby the power delivered to the grid increases.
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Block schematic diagram of the closed loop scheme
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CLOSED LOOP SCHEME
Directly interfacing the wind energy system to the utility gives rise to problems of voltage
fluctuations, flickering and generation of sub-harmonics/harmonics associated with the pulsating
torque.
Since, the reactive power consumed by a controlled rectifier is a function of the firing delay angle,
there is a limit on the maximum value of the firing delay angle.
This constraint will limit the operating speed range of the wind driven permanent magnet
alternator, since, once the firing delay angle reaches its upper limit there is no control on the dc
link voltage.
Hence, the input voltage to the rectifier has to be restricted by limiting the maximum speed of the
wind turbine mechanically. This will prevent complete utilization of available wind energy.
The problems are overcome by using an uncontrolled diode bridge rectifier and a line
commutated inverter.
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MAXIMUM POWER TRACKING CONTROLLER
The control objective is to track and extract maximum power from the WES and to transfer this
power to the utility grid.
To achieve this maximum power tracking controller is implemented using a proportional controller.
The power transferred over the DC link can be related to the maximum power output (Pmax) of
the WES by the conversion efficiency of the generator and the rectifier.
The maximum power output of the WES is a function of the wind velocity (Vw) and the tip speed
ratio λ.
The maximum power output of the permanent magnet alternator at different (Vw) is computed.
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OPEN LOOP SIMULATION OF A GRID CONNECTED PM
ALTERNATOR DRIVEN BY WIND TURBINE
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REAL AND REACTIVE POWER OF OPEN LOOP SCHEME
REAL POWER
REACTIVE POWER
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RECTIFIER OUTPUT OF OPEN LOOP SCHEME
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GRID VOLTAGE AND CURRENT OF OPEN LOOP SCHEME
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CLOSED LOOP SIMULATION OF A GRID CONNECTED
PM ALTERNATOR DRIVEN BY WIND TURBINE
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FILTER CIRCUIT
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SIMULATION OF MULTIPLIER AND SIGNAL
CONDITIONING CIRCUIT
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REAL AND REACTIVE POWER OF THE CLOSED LOOP SCHEME
WITHOUT FILTER
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WITH FILTER
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GRID VOLTAGE AND CURRENT OF CLOSED LOOP SCHEME
WITHOUT FILTER
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GRID VOLTAGE AND CURRENT OF CLOSED LOOP SCHEME
WITH FILTER
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RMS GRID CURRENT
WITH FILTER
WITHOUT FILTER
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RECTIFIER OUTPUT OF CLOSED LOOP SCHEME
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AVERAGE POWER OUTPUT OF RECTIFIER
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HARMONIC CURRENT WAVEFORMS WITH FILTER
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FIRING PULSE VARIATION OF PULSE GENERATOR
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VARIATION OF FIRING ANGLE OF PULSE GENERATOR
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REAL POWER VS TURBINE TORQUE
Input Power
Output power
Firing angle
2
347
330.5
169.6
2.5
439
420.2
169.5
3
533
510.2
169.3
3.5
629.2
602.1
169.2
4
747.5
714.7
169.1
4.5
827.2
789.1
169
5
932.4
886.2
168.8
5.5
1037
982.9
168.7
6
1143
1081
168.6
6.5
1253
1183
168.5
7
1369
1285
168.3
7.5
1483
1388
168.2
8
1600
1495
168.1
8.5
1731
1604
167.9
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CLOSED SCHEME CHARECTERISTICS
REAL POWER (W)
Torque
2000
1800
1600
1400
1200
1000
800
600
400
200
0
INPUT POWER (W)
OUTPUT POWER
(W)
2 2 3 3 4 4 5 5 6 6 7 7 8 8
TURBINE OUTPUT TORQUE
(Nm)
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CONCLUSION
PM Alternator is used so wind energy available can be utilized
to the maximum level.
Maximum power tracking is possible for all particular wind
speed by using Proportional Controller.
With increase in the speed, the PM generator output will
increase, the corresponding firing angle decreases and thereby the
power delivered to the grid increases.
Passive filter is used for the minimization of grid current
harmonics.
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REFERENCES
R.M.Hilloowala ,A.M. Sharaf, ‘A Utility Interactive Wind Energy Conversion scheme with an
Asynchronous DC link using a Supplementary Control loop’, IEEE Transactions on Energy
Conversion,Vol.9,No.3,September 1994.
Salman K. Salman and Anita L.J. Teo ‘Windmill Modeling Consideration and Factors
Influencing the Stability of a Grid- Connected Wind Power-Based Embedded Generator’, IEEE
Transactions On Power Systems, Vol. 18, No. 2, May 2003.
D.Watson, J.Arrilaga and T.Densen “Controlled dc power supply from wind driven self excited
induction machines”, IEEE proc. Vol.126, No.12, pp. 1246-48,1979.
G.L.Johnson, “Wind Energy Systems”, Prentice Hall Inc., Englewood Cliffs, NewJercy,1985.
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THANK YOU
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