"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 5, Special Issue 1, April 2015)
Second International Conference on Advanced Developments in Engineering and Technology (ICADET-15), INDIA.
Control of Wind Energy by Using Buck-Boost Converter
Anshul Mittal1, Khushboo Arora2
1
HRIT Engineering College
ABES Institute of Technology
2
Abstract-- Wind energy is one of the most emerging
technologies in the vast field of renewable energy.
Eventually there have been much advancement in wind
technology but the technological advancements are still
needed for wind power control for different loading
conditions. Therefore simulation of these conditions on
software is essential.
In this paper, a model of PMSG based wind turbine
followed by power electronic circuits, such as rectifier,
chopper & inverters then finally feeding to 3-phase load has
been developed. The power is controlled with the help of
Buck-Boost Converter connected across the dc link to keep
constant voltage supply at output side. The simulation is
carried on MATLAB/SIMULINK.
Keywords: Permanent magnet synchronous generator,
Hybrid System, buck-boost converter.
I. INTRODUCTION
Due to environmental concerns caused by excessive
exploitation of conventional resources, now the focus is
diverted to non-renewable resources especially solar &
wind as these are environmentally clean and eco-friendly.
In the beginning, wind power generation was
negligible as compared to conventional plants due to lack
of sophisticated wind turbine (WT) technology but now
with the development of new technologies; there has
been an exponential growth in the wind power.
In the recent decade, Wind energy generation is been
increased up to a remarkable milestone in gross power
generation around the globe. The total installation of
wind power capacity reaches to 305.4 GW around the
world with 14107 wind farms. India has grown its
installation up to 20.15 GW at the end of year 2013[1].
The total wind farms are grown to 443 in India.
The advancements in this area of have unfolded many
technological barriers in order to commercialize this
technology. Also today there are number of options
available for selection for wind power installation set up,
one of the famous set up is Permanent magnet
synchronous generator (PMSG) based wind turbine
system. The ac power produced can be controlled by
power electronic circuits in accordance to load
application, such circuits may be ac voltage controller,
rectifiers and for dc powered loads chopper are mostly
employed. In this model generated power is converted to
dc by rectifier then fed to buck boost chopper.
The buck boost chopper controlled by PWM technique
produces variable dc output voltage. This is the main
circuit in the model which controls power. Further
variable dc power is fed to ac load by MOSFET inverter.
II. W IND T ECHNOLOGY
Turbine blades are aerodynamically optimized to
capture the maximum power from the wind in normal
operation with a wind speed in the range of about 3 to 15
m/s. In order to avoid damage to the turbine at a high
wind speed of approximately 15 to 25 m/s, aerodynamic
power control of the turbine is required [2].
Power in air flow :Pair= 0.5ρA ν3
Where Pair is power in air flow,
ρ is air density, Kg/ m3
ν is velocity of wind. (m/s)
A is area swept by blade. (m2)
Fig.2.1 Power speed variation of wind energy system.
Power Coefficient: CP = P wind turbine /Pair
Where, Pwind turbine is power of wind turbine.
Tip speed ratio :λ= ω r / ν
Where,ω= rotational speed of rotor. (Radian/sec)
r = blade length (m)
ν = upwind speed (m/s)
Beta limit: the turbine can never extract more than 59.3%
of power of air (Pair). Also CP ranges from 25 to 40 %.
CP&λ are dimensionless and so can be used to describe
the performance of any size of wind turbine rotor. Also
maximum power coefficient is only achieved at a single
wind speed[3]. Hence one argument for operating a wind
turbine at variable rotation speed is that it is possible to
operate at maximum CP over a range of wind speeds.
Lord Krishna College of Engineering (An ISO 9001:2008 Certified Institute) Ghaziabad, Uttar Pradesh, INDIA.
Page 293
"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 5, Special Issue 1, April 2015)
Second International Conference on Advanced Developments in Engineering and Technology (ICADET-15), INDIA.
III. PMSG CONFIGURATION
Fig 3.1 Full Capacity converter configuration for wind energy
system.
The performance of the wind energy systems can be
greatly enhanced with the use of full capacity power
convertor. Fig.3.1 shows such a system in which the
generator is connected to grid via a full-capacity
convertor system. Squirrel cage induction generators,
wound rotor synchronous generators, and permanent
magnet synchronous generators (PMSG) have all found
application in this type of configuration with a power
ratio up to several megawatts. The power rating of the
convertor is normally the same as that of the generator.
With the use of the power convertor, the generator is
fully decoupled from the grid, and can operate in full
speed range. This also enables the system to perform
reactive power compensation and smooth the grid
connection[6]. The main drawback is a more complex
system with increased costs.
It is noted that the wind energy system can operate
without the need for a gearbox if a low speed
synchronous generator with a large no of poles is used.
The elimination of the gearbox includes the efficiency of
the system and reduces initial costs and maintenance[7].
However a low speed generator has a substantial larger
diameter to accommodate the larger no. of poles on the
perimeter, which may lead to an increase in generator
and installation costs. Some of the most common
convertor topologies used for this type of WECS include
two-level voltage source convertor in back to back
configuration, diode bridge rectifier plus DC-DC boost
stage and convertor in back to back conversion.
IV. B UCK B OOST CONVERTERS
A non-inverting buck-boost converter is essentially a
cascaded combination of a buck converter followed by a
boost converter, where a single inductor-capacitor is used
for both. As the name implies, this converter does not
invert the polarities of the output voltage in relation to
the polarities of the input.
This converter requires the use of two active switches
and is designed by combining a buck converter and boost
converter design in the same topology. Due to this design
this converter can work as Buck-only, Boost-only or
Buck-Boost converter.
The input voltage source is connected in parallel with
diode
, MOSFET Switch-2 load capacitor, C as
indicated in Figure 4.1. MOSFET Switch-1 is connected
between the input voltage source and diode
. The
inductor is connected between
and MOSFET Switch2, while
is connected between MOSFET Switch-2 and
the output or load capacitor[4].
Fig 4.1Two switch non-inverting buck-boost converter
(1) Operation of Non-Inverting Buck-Boost Converter:
In this topology the converter will be operated either
in buck mode or boost mode depending upon the load
condition. In buck-only mode, MOSFET Switch-1, with
the diode
. MOSFET Switch-2 is turned OFF and
diode D2 is always ON. MOSFET Switch-1 and
form
the buck switching leg. Figure 4.2. shows the converter
operating at buck mode.
Fig 4.2 Converter operating at buck mode
When the converter is operated at boost mode then, the
MOSFET Switch-1 remains close. In boost-only mode
MOSFET Switch-2 is used as a switch and
acts as the
diode in the boost regulator. MOSFET Switch-1 is
always ON and is turned OFF. MOSFET Switch-2 and
form the boost switching leg. Figure 4.3. shows the
circuit diagram of the buck- boost converter operating at
boost mode.
Fig 4.3 Converter operating at boost mode
Lord Krishna College of Engineering (An ISO 9001:2008 Certified Institute) Ghaziabad, Uttar Pradesh, INDIA.
Page 294
"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 5, Special Issue 1, April 2015)
Second International Conference on Advanced Developments in Engineering and Technology (ICADET-15), INDIA.
In buck-boost mode the MOSFET Switch-1 and
MOSFET Switch-2 are simultaneously ON during the
switching cycle or ON time, while
and
are
simultaneously ON during the opposite switching cycle
or OFF time. This means that when MOSFET Switch-1
and MOSFET Switch-2 are turned ON, the inductor is
getting charged, so
and
are turned OFF. Vice versa
when ,
are ON, the inductor is charging the load
capacitor, so MOSFET Switch-1 and MOSFET Switch-2
are turned OFF.
(3) Flow Chart of PWM Controlling
During the various wind speed, the wind variation
occurs during this operation. To control the wind
variation, it needs a controlling method to become a
steady state operation, for this controlling[5], A PWM
controlling method is used in this thesis.
A PWM controlling method controls the two switches
of buck-boost converter. This controlling method shows
by a flow chart in this thesis as-
(2) Design of Non-Inverting Buck-Boost Converter:
The design of non-inverting buck-boost converter is
same as the inverting buck-boost converter. The
converter is designed considering the data below,
= Output voltage = 17.2V
= Diode forward drop = 0.525V
= Minimum input voltage=12V
= Average output current = 2.37A
f= switching frequency=20 KHz
The calculation starts with the calculation of duty
cycle.
The duty cycle can be calculated as:
D=
[27]
So duty cycle, D = 0.6
Ripple Current in the inductor:
Fig.4.4 Flow Chart of PWM Controlling
In this model, a controlling technique is used which
control the wind power. It is represented by a flow chart
as shown in fig. 4.4, from above flow chart, the values of
, &
are to be compared. If the value of
is
less than
than it will go for buck mode but if Vref is
greater than
than it will go for boost mode. We can
see this process in single flow chart in fig. 4.5& fig. 4.6.
i) Buck Mode-
Where,
= Average Inductor current =
= 1A
The inductor of the converter can be found as
L=
=
So L=317 µH. This is the minimum inductor value for
the converter. We choose 600 µH as inductance. The
output capacitance can be found from the following
equation.
Considering, Δ
= Output ripple voltage = 0.2 V,
= 355uF.
For this experiment we choose L=600µH and
C=470µF.
Fig 4.5 Buck Mode Condition
Lord Krishna College of Engineering (An ISO 9001:2008 Certified Institute) Ghaziabad, Uttar Pradesh, INDIA.
Page 295
"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 5, Special Issue 1, April 2015)
Second International Conference on Advanced Developments in Engineering and Technology (ICADET-15), INDIA.
In this Buck mode condition, the values of ,
,
will be compared. If the value of
than it will compare with triangular carrier wave to
generate PWM for pulse-1of mosfet-1(mosfet-2 keeps off
during this time).
ii) Boost Mode-
The simulation of above mentioned circuit topology
has been carried out in MATLAB/ Simulink environment
for performance analysis. The figure 5.1 shows the
Simulink model of PMSG feeding a resistive load
through a Buck-Boost converter. The Buck-Boost
converter employs PWM controlling technique for
providing the three phase balanced output voltage and
frequency with fixed dc or inverter output.
Fig. 5.1 MATLAB Simulation model
Fig.4.6 Boost Mode Condition
(4) PWM Controlling Model
After the represent of both buck & boost modes, a
practically model is designed by taking some blocks as
triangular pulse, PI controller, relational operator & a
constant block which are so combined as shown in fig.
4.7.
Fig 4.7 PWM Controller
From fig. 4.7, it represents two modes (buck & boost).
If input voltage is high, it will subtract output voltage
from reference voltage and pass to the relational operator
& finally go for buck-boost modes. If the value of
constant is 1 than it shows buck mode. If the value of
constant is 0, it shows boost mode condition.
V. MODELING & S IMULATION
Permanent Magnet Synchronous Generator (PMSG) is
fed from a wind turbine. In the wind turbine, wind energy
is converted into mechanical energy which energizes the
generator to produce electrical energy. This generator has
three phase distributed winding on the stator and
permanent magnet pole on the rotor. In this case voltage
and current are supplied through stator winding. The
power filter (Rf,Lf ,Cf) located at the input of the
converter mitigates the high-frequency components of
the Rectifier input currents, generating almost sinusoidal
source currents and avoiding the generation of over
voltages and also employed to smoothen out the voltage
and current waveform.
Scope 1 is attached to measure speed of rotor in rad/s.
Also Scope 1 displays the graph of stator current in phase
A and electromagnetic torque. Three phase stator
voltages and currents are displayed by scope 2. The
phase voltage and current of the stator is observed from
the scope 3 and 4, respectively. The output of three-phase
generator is fed to the Buck-Boost Converter. The output
of PMSG is AC and the Buck-Boost convertor is a DC to
DC convertor. Scope 5 is attached to measure the
converter controlled dc output and also display input of
the converter. Output current of converter output, 3-phase
inverter output voltage and inverter output voltage are
observed from the Scope 6,7,8 respectively.
A PMSG has been used to provide the variable voltage
and variable frequency at its output and the output of the
PMSG is fed to the Buck-Boost converter for
improvement in its performance in terms of smoothing or
constant output.
Lord Krishna College of Engineering (An ISO 9001:2008 Certified Institute) Ghaziabad, Uttar Pradesh, INDIA.
Page 296
"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 5, Special Issue 1, April 2015)
Second International Conference on Advanced Developments in Engineering and Technology (ICADET-15), INDIA.
VI. RESULTS & D ISCUSSIONS
Fig. 6.6 Buck-Boost Input Current
Fig.6.1Wind Speed 10 m/s
Fig. 6.7 Buck-Boost Output Voltage
Fig. 6.2 Rotor Speed
Fig. 6.8 Buck-Boost Output Current
Fig. 6.3 Load Torque & Electromagnetic Torque
Fig. 6.9 Three Phase Inverter Voltage & Current
Fig. 6.4 PMSG Active & Reactive Power
Fig. 6.10 Inverter Active & Reactive Power
Fig. 6.5 Three Phase PMSG Voltage & Current
Lord Krishna College of Engineering (An ISO 9001:2008 Certified Institute) Ghaziabad, Uttar Pradesh, INDIA.
Page 297
"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 5, Special Issue 1, April 2015)
Second International Conference on Advanced Developments in Engineering and Technology (ICADET-15), INDIA.
Table:1
Analyzed values at different wind speed.
S. No.
1
Parameters
Constant of PWM
(Buck-boost )
2
wind speed(m/s)
3
time run of model (sec.)
4
load torque (N-m)
5
6
7
8
9
Electromagnetic- Torque
(N-m)
rotor speed (rad/sec)
active power
(Watt)
reactive power
(VAR)
voltage o/p of pmsg and i/p of
rectifier (line-line)
220
220
220
220
10
12
15
15
1
1
1
2
31.2
31.8
33.5
34.1
28-36
29 - 35
30-36
31-37
149
154
164
175.7
4750
5000
5500
6100
-257
-300
-380
-442
1060
1100
1140
1200
5.5
5.5
5.7
5.7
350625
450 614
470720
470750
2 to -4
2 to -4
1.6 to 4.3
1.6 to 4.3
215.2
215.2
215.7
215.7
5.25 8.25
5.25 8.25
5.25 8.25
5.25 8.25
(Volts)
10
current o/p of pmsg and i/p of
rectifier
(Amps)
11
voltage o/p of rectfier and i/p of
buck boost
(Volts)
12
current o/p of rectfier and i/p of
buck boost
(Amps)
13
voltage o/p of buck boost and
i/p of inverter
(Volts)
14
current o/p of buck boost and
i/p of inverter
(Amps)
15
voltage o/p of inverter i/p to 3
phase load(Amps)
205
205
205
205
16
current o/p of inverter i/p to 3
phase load(Amps)
6.2
6.2
6.2
6.2
1500
1500
1500
1500
860
860
860
860
17
18
active power to load
(Watt)
reactive power to load
(VAR)
Lord Krishna College of Engineering (An ISO 9001:2008 Certified Institute) Ghaziabad, Uttar Pradesh, INDIA.
Page 298
"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 5, Special Issue 1, April 2015)
Second International Conference on Advanced Developments in Engineering and Technology (ICADET-15), INDIA.
Fig. 6.11Graph of DC voltage output of buck boost when Vref.
Constant is 400
Buck-Boost Output Voltage
600
500
400
> Voltage
As the wind speed increases, the overall system
working conditions become faster & operating electrical
power, voltage/ current parameters increases accordingly.
The model is subjected to run for 1 second in most of
cases considered here. But within 1 second the system
has reached almost steady state & at this steady state the
magnitudes of system parameters are observed.
As observing the table, PMSG output power increased
with increment in wind speed, torque produced by
machine also increases. Further PMSG output voltage
increases accordingly as 1060 for 10 m/sec; 1100 for 12
m/sec; 1140 m/sec for 15 m/sec. In the same
correspondingly current is controlled. This power passed
through rectifier, the peak value of rectifier output
voltage increases significantly as 625 to 720 for 10 to 15
m/s of wind speed respectively.
The dc voltage is fed to buck boost converter, this
controls dc voltage at output, the PWM firing pulse
generator is employed for controlling dc power. The
model is subjected to constant reference voltage
magnitude (Vref) of 220 in PWM block for the results
stated in above table. Conceptually if this ON time of
buck boost (in terms of reference voltage in model) is
increased/varied the dc output of buck boost can be
increased / varied. The duty cycle of the buck boost
converter is increased in order to increase charging time
of inductor. As the charging time of inductor would be
high, the output voltage peak would be high. Further the
output voltage of dc buck boost is fed to 3 phase load via
inverter. The variation of Vref and buck boost output
voltage is shown in table as:-
300
200
100
0
0
0.1
0.2
0.3
0.4
0.5
> Time
0.6
0.7
0.8
0.9
1
Fig. 6.12Graph of DC voltage output of buck boost when Vref.
Constant is 600
DC voltage (y-axis) vs Vref Constant
(x-axis)
500
400
Table 2:
Variation of voltage.
300
S.
No.
1
Vref. Constant (in
PWM Block)
150
DC Voltage Output (buck
boost O/P)
220 Volts
2
450
220 Volts
3
600
422 Volts
voltage
200
100
0
0
500
1000
Fig 6.13Graph between DC voltage output of buck boost and Vref.
Constant (in PWM Block)
Lord Krishna College of Engineering (An ISO 9001:2008 Certified Institute) Ghaziabad, Uttar Pradesh, INDIA.
Page 299
"Sharpening Skills.....
Serving Nation"
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459 (Online), Volume 5, Special Issue 1, April 2015)
Second International Conference on Advanced Developments in Engineering and Technology (ICADET-15), INDIA.
In this way the output voltage of the buck boost is
controlled. Accordingly the power fed to 3 phase is
varied as per need of load.
[2]
[3]
VII. CONCLUSION
Constant dc voltage is found to be improved by the use
of the PWM controlling techniques in the Buck-Boost
Converter switches incorporated in the WECS. The
output dc voltage can be controlled for the values
between 150-450 V and output Voltage of inverter could
be constant automatically. In this way the dc or ac output
is improved if WECS output is not constant.
REFERENCES
[1]
Available: http:/www.thewindpower.net
[4]
[5]
[6]
[7]
Bin wu, Yongqiang Lang, NavidZargari, Samir Kouro, “Power
conversion and wind energy system”, pp17, 144-148, IEEE press,
john wiley publication 2011
olimpoanaya-lara, Nick Jenkins, JanakaEkanayake, Phil
Cartwright, Mike Hughes “Wind energy generation modelling and
control”, pp 10-14, john wiley publication 2009.
M. H. Rashid, Power Electronics: Circuits, Devices and
Applications (3rd Edition), Prentice Hall, 2003.
N. Mohan, T. M. Undeland, W. P. Robbins, Power Electronics:
Converters, Applications, and Design, 3rd Bk&Cdr edition,
Wiley, 2002.
GierasJ.F. and Mitchell, W.I., 1892. “Permanent Magnet Motor
Technology. Design and Application”, Marcel Dikker, New York.
Vergauwe, J., Martinez, A. and Ribas, A., 2006. “Optimization of
a Wind Turbine Using Permanent Magnet Synchronous Generator
(PMSG)”,
Proceedings
ICREP,
http://www.icrepq.com/icrepq06/214-vergauwe.pdf.
Lord Krishna College of Engineering (An ISO 9001:2008 Certified Institute) Ghaziabad, Uttar Pradesh, INDIA.
Page 300