Design of a wind power generation system using a permanent magnet synchronous machine, a boost regulator and a transformer less step down circuit

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 01 | Jan-2014, Available @ http://www.ijret.org 49
DESIGN OF A WIND POWER GENERATION SYSTEM USING A
PERMANENT MAGNET SYNCHRONOUS MACHINE, A BOOST
REGULATOR AND A TRANSFORMER-LESS STEP DOWN CIRCUIT
Sameer Ahmed Khan Mojlish
Lecturer, Department of Electrical & Electronic Engineering, Independent University, Bangladesh (IUB),
Abstract
This paper presents a wind power system using a Permanent Magnet Synchronous Machine (PMSM). The whole system consists of a
wind turbine, a permanent magnet synchronous machine, a three phase diode rectifier, a boost converter, a transformer-less step down
circuit, an H-bridge inverter and a T-LCL filter. The 3-phase AC output from the PMSM is sent to the 3-phase diode rectifier for
conversion to DC and a boost regulator is used to step-up this DC voltage to the desired level. This step-upped DC voltage is then
converted into AC output by the H-Bridge inverter. The switching technique of the proposed inverter consists of a combination of
Sinusoidal Pulse Width Modulation (SPWM) and a square wave along with grid synchronization conditions. As the suggested method
is entirely transformer-less, it significantly reduces Total Harmonic Distortion (THD) to less than 0.1% and minimizes its size. The T-
LCL Immittance Converter not only reduces the harmonics of the inverter output but also provides a nearly constant output current
thereby stabilizing the system. The system setup and the simulation results were obtained using the PSIM software.
Keywords: Wind Turbine, Permanent Magnet Synchronous Machine, Boost Converter, Step- down Circuit, T-LCL
Immittance Converter, Inverter
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1. INTRODUCTION
The changing world climate is a serious threat to our planet.
The global warming phenomenon, driven by the emission of
carbon dioxide (CO2) from the use of fossil fuels is slowly
killing our planet. Moreover, the cost of fossil fuel is also
increasing day by day and its sources are gradually becoming
exhausted [7]. As a result, the cost of the utilization of the
renewable energy systems is on the decreasing trend making
them ideal for use in power generation systems. Of the many
renewable energy resources such as solar, wind, biomass, tidal
etc. solar and wind energy systems are most commonly used.
Wind energy can be used for generating large amounts of
power. Wind energy systems are particularly useful in remote
areas where grid connection is not accessible or not feasible.
In those places, the wind power generation systems can be
used for meeting the consumer load demands in a cost-
effective manner. In conventional wind energy systems,
transformers are used to step-down grid voltages. But
transformers are bulky and costly equipment and also
contribute to the Total Harmonic Distortion (THD) of the
inverter output [4]. Hence, in this paper a transformer-less
wind generation topology has been proposed.
The block diagram for the proposed wind power system is
shown in Fig1. The design includes 1) a 3–phase permanent
magnet synchronous machine which has 3-phase windings on
the stator and a permanent magnet on the rotor [2-4]; 2)a
three-phase diode rectifier to convert AC output from the
PMSM to DC output;3) a boost converter to step up this DC
output to the desired level. 4) an H-bridge inverter for
converting the DC output of the boost converter into AC
output; 5) a T-LCL Immittance converter to suppress the
harmonics of the inverter output and produce a pure sinusoidal
wave and 6) a transformer-less step down circuit to produce
the gate pulses of the inverter using a combination of SPWM
and square wave.

__________________________________________________________________________________________
Fig-1: Block diagram of Wind PowerGeneration System
2. WIND TURBINE
When moving air exerts force on the propeller like blades
around a rotor of the wind turbines, electricity is generated.
The rotor is connected to a low speed shaft which in turn is
connected via gearbox to a high speed shaft. The gear box is
responsible for increasing the rotational speed from 10-60 rpm
to 1200-1800 rpm. The high speed shaft is connected to a
generator which is then used for generating electricity [6].
The mechanical power [1] from the wind turbine is given by:
Pm=
1
2
ρACp(λ, β)vw
3
………….. (1)
Where ρ=air density, A= rotor swept area, Cp(λ, β)=power
coefficient function, λ =tip speed ratio, β=pitch angle,
vw=wind speed.
The efficiency of the wind turbine to convert wind energy into
mechanical energy is given by Cp, which is dependent on
λand β. The tip speed ratio, λ, is the ratio of the turbine
angular speed to the wind speed as shown in Eq.(2).
Maximum power can be obtained for different wind speeds by
controlling the rotational speed. The pitch angle, β, is the
angle in which the turbine blades are aligned with respect to
its longitudinal axis.
λ =
Rωb
vw
………………………… (2)
Where R= turbine radius and ωb=angular rotational speed.
3. PROPOSED DESIGN
The design and the performance of the proposed wind power
generation system were performed using the PSIM simulation
software. The input was taken by means of the built-in wind
turbine block of the software. It was then connected to the
generator via the gear box and the electrical-mechanical
interface. The various sections of the whole system are
discussed in details below.
3.1 Permanent Magnet Synchronous Machine
The generator used for the design was a 3-phase permanent
magnet synchronous machine (or permanent magnet
synchronous generator)[2]. A 3-phase permanent magnet
synchronous machine has 3-phase windings on the stator and
permanent magnet on the rotor as shown in Fig-.2, where a,b
and c are the stator winding terminals, n is the neutral point
and the shaft node is used for establishing connection with the
high speed mechanical shaft. The back emf of the machine is
sinusoidal.
Fig-2: Permanent Magnet Synchronous Machine
3.2 Three-phase Diode Bridge Rectifier
The variable frequency sinusoidal voltages produced by the
generator cannot be used for establishing connection with the
grid. First, they need to be rectified into DC and then
converted into AC voltages of desired frequency and
amplitude.The rectification is done by a 3-phase diode bridge
rectifier as shown in Fig-3.
Fig-3: Three phase Diode Bridge Rectifier
3.3 Step-up Boost Converter
The output of the rectifier is then converted into 312V DC by
means of a boost converter [8], as shown in Fig-4. The boost
converter’s output should be 312V since it is the input of the
inverter, the output of which should be the same as the grid
voltage (312V peak or 220V rms) in Bangladesh. The output
voltage of the boost converter is given by:
Vout =
Vin
1−D
…………. (3)

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Where Vout=average output voltage, Vin=input voltage and
D=duty cycle.
Fig-4: Boost Converter for stepping up voltage to required
level
The design parameters of the boost converter are given in
Table 1.
Table -1: Design of Boost Converter
Symbol Actual meaning Value
Vin Given input voltage 250V
Vout Desired average output
voltage
312V
fs Switching frequency of
converter
20KHz
IL,max Maximum inductor
current
7.33A
∆iL Estimated inductor ripple
current(1.75% of IL,max)
0.128A
∆Vout Desired output voltage
ripple(0.021% of output
voltage)
65mV
Iout Maximum output current 4.3A
The inductor value is selected using the following equation [8]
 
outsL
inoutin
V×f×I
VVV
=L

So,
  19.36mH≈
31220000.128
250312250
××
×
=L

The capacitor value is selected using the following equation
[8]
C outs
out
V×f
D×I

So,
0.656mF≈
0.06520000
0.1984.3
×
×
=C
3.4 Transformer-less Step down Circuit
The step down operation is performed using a voltage divider
as shown in Fig-5.
Fig-5: Voltage divider Circuit
Using voltage divider equation, [8]
 
 
R2+R1
v×R2
=v in
out
Setting
    100kΩ7.07V312V =R1;=v;=v outin and
solving for R2, we get R2=2.32KΩ.
3.5 Inverter and Inverter Switching Circuit
The H-Bridge DC-AC inverter has two parallel MOSFET
gates. This is shown in Fig-6. A combination of analog and
digital circuits is used to produce the gating pulses of the
MOSFETs.
Fig-6: H-Bridge Inverter
In conventional inverters only one type of switching technique
is used. But this proposed design instead uses a combination
of SPWM and square wave to reduce the switching loss by
reducing the switching frequency. Fig-7 shows the proposed
switching circuit of the inverter. The sine wave is sampled
from the grid by using a transformer-less voltage divider

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circuit which steps down the voltage from 220V (rms) to
5V(rms).The sine wave sampled is used to generate the
SPWM signal thus ensuring that the output voltage from the
inverter will have the same frequency as the grid [5]. After
sampling, the sine wave is rectified with a precision rectifier,
the output of which is shown in Fig-8.
Fig-7: Control Circuit of the Inverter
Fig-8: Rectified sine wave
In addition, a high frequency triangle wave of 10 KHz is used.
Then the two signals are passed through a comparator to
produce the SPWM signal as shown in Fig-9. A square wave
signal is used as the line frequency (50 Hz for Bangladesh)
and is in phase with the SPWM as shown in Fig-10.The square
wave is passed through a NOT gate to produce a signal that is
180 degree out of phase with the original signal.
Fig-9: SPWM signal
Fig-10: Square wave signals
The inverter requires four switching signals since it has four
MOSFETs. To produce the four signals, an AND operation is
performed between two sets of square wave signals and the
SPWM signal. The four sets of switching signals can be
categorized in two groups. The first group contains MOSFETs
Q1 and Q4 while the second group contains MOSFETs Q2
and Q3. The gate pulses for switching of MOSFETs are
illustrated in Figs 11 and 12 respectively. When Q4 is ON, Q1
is switched ON with the SPWM signal and both Q2 and Q3
are OFF. This produces a positive voltage at the inverter
output. When Q3 is ON, Q2 is switched ON with the SPWM
signal and Q1 and Q4 are both OFF. This produces a negative
voltage at the inverter output.
Fig-11: Switching signal from control circuit for MOSFETs
(Q1 and Q4)
Fig-12: Switching signal from control circuit for MOSFETs
(Q2 and Q3)

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3.6 Filter Circuit
To eliminate harmonics from the inverter output, a filter circuit
is employed. In conventional inverters, LC filter is used but
this design employs a T-LCL Immitance Converter. The filter
circuit consists of two inductors L1 and L2 and a capacitor C in
the shape of a T as shown in Fig-13.
Fig-13: T-LCL Filter
From the derivation of the equation of the output current of the
filter, I2 is found as [4]:
)4.....(]1[
0
2
0
1
2
QZ
Z
Z
V
I 
Where V1 is the input voltage, Z2 is the load impedance and Q
is the quality factor,
 5..........
r
ωL
=Q
With ω=2 π f as the angular frequency, r is the internal
resistance of the inductor and Z0 is the characteristic
impedance determined by L and C,
C
L
=Z0 ……. (6)
When r is negligible or zero, the quality factor becomes
infinity. Under this condition,
 7........
0
1
2
Z
V
I 
From eq. (7), it is observed that the output of the T-LCL filter
is independent of load. Therefore this filter is capable of not
only reducing harmonics but is also helpful in providing a
constant current to the load.
The values of L and C of T-LCL filter (considering
Butterworth type) is calculated using the cut-off frequency
condition of low pass filters, i.e.
 8........
2π
1
0
Cf
=Z
c
Where Z0 is the characteristic impedance given by Eq. (6).
Assuming Z0 as 30Ω and choosing fc=50Hz, we get the values
of L and C using Eqs. (6) and (8),
0.106mF≈
30502
1
××π×
=C
And L=C
2
0Z =0.106 95.4mH≈3010 23
×× 
4. POWER TRANSMITTING
The real power supplied by the inverter is given by [2]
Real Power
   
sin
Z
V×V
=P
t
gridinv
,
Where,
Zt= Linking line impedance
Vinv= Output voltage of inverter
Vgrid= Grid voltage
ϕ= Angle between Vinv and Vgrid.
From the above equation, it is clear that maximum real power
can be transmitted into the grid for ϕ=90 degrees. Since the
voltage angle of the inverter must lead grid voltage angle to
transmit power into grid, the sampled sine wave from the grid
is passed through a phase shifter circuit to make the leading
adjustments. As mentioned earlier, to send maximum power
into the grid, the leading angle must be 90 degrees. But in
practice, due to stability reasons the angle is kept somewhat
less than 90 degrees. [5]
5. SIMULATION RESULTS
The PSIM simulation results are provided in this section. the
simulation results are given at the nominal speed of 12m/s to
generate maximum power.
Fig-14 shows the output voltages of the permanent magnet
synchronous generator. The frequency of the distorted
sinusoidal waves is 20 Hz and hence the need for the rectifier
arises for converting it into DC voltage and then the
conversion of DC to 50Hz(grid frequency) AC voltage.

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Fig-14: Output phase voltages of Synchronous generator
Fig-15 shows the DC output of the rectifier which is 250V.
Fig-16 shows the output of the Boost converter which steps up
250V to the desired 312V.
Fig-15: The DC output voltage of the Rectifier
Fig-16: The DC output voltage of the Boost Converter
Fig.-17 shows the AC output voltage waveform in the absence
of any filter. The waveform is non-sinusoidal and contains lots
of harmonics. To eliminate these harmonics, a low pass T-LCL
filter is employed at the output of the inverter which produces
a pure, sinusoidal voltage.
After filtering, we obtained a pure sinusoidal voltage of
frequency 50Hz and of rms value 220V as shown in Fig-18.
Fig-17: Output voltage without filtering in PSIM.
Fig-18: Output voltage after filtering in PSIM
Since this waveform has an amplitude of 312V (220V rms)
and a frequency of 50 Hz, this output can be used for sending
real power to the grid. The Total Harmonic Distortion (THD)
of this inverter output is 0.01% which is much less than the
IEEE 519 Standard.
CONCLUSIONS
In this paper, the design of a wind power generation system
using a permanent magnet synchronous machine along with a
boost regulator and a transformer-less Step down circuit has
been presented. The PSIM simulation results show that a
220V, 50Hz output voltage can be obtained using the
particular set-up. The total harmonic distortion (THD) was
found to be 0.01% which is much lower than the IEEE 519
standard. Thus the proposed wind power generation system
can be used for sending power to the grid.
In future, the simulation results would be expanded and
variable wind speeds would be taken into account.
REFERENCES
[1]. H. Bakshai and Jain P.K, “A hybrid wind-solar energy
system: A new rectifier topology”, Applied Power Electronics
Conference and Exposition (APEC), 25th Annual IEEE, 21-25
Feb, 2010.

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[2]. Ali M. Eltamaly, “Modeling of wind turbine driving
permanent magnet generator with maximum power point
tracking system”. King Saud University, Vol.19, eng.. Sci.(2),
Riyadh(1427H/2007).
[3]. M.E.Topal and l.T.Ergene. “Designing a Wind Turbine
with Permanent Magnet Synchronous Machine”. IU-JEEE,
vol. 11(1), 2011.
[4]. “PSIM User Manual”.
http://paginas.fe.up.pt/~electro2/labs/psim-manual.pdf.
[5]. T.K.Kwang and S. Masri, “Single phase grid tie inverter
for photovoltaic application,” Proc. IEEE Sustainable
Utilization and Development in Engineering and Technology
Conf, November 2010.
[6]. S.B. Afzal, M.M. Shabab and M.A.Razzak, “A combined
Π- and T-type Immitance converter for constant current
applications”, Proc. IEEE International Conference on
Informatics, electronics and vision (ICIEV), May 2013,
Dhaka, Bangladesh
[7]. “Running on Renewables”.
http://www.pspb.org/e21/lessonplan_detail.php
[8].M.H.Rashid, Power Electronics, Circuits, Devices and
Applications, 3rd ed, New Delhi: Prentice-Hall of India
private limited, 2007
BIOGRAPHIE:
Sameer Ahmed Khan Mojlish completed
B.Sc. in Electrical and Electronic
Engineering (EEE) from Bangladesh
University of Engineering and Technology
(BUET) in 2009 and M.Sc. in Electrical and
Computer Engineering from Purdue University, USA in 2012.
He has been working as a Lecturer in the Department of
Electrical and Electronic Engineering f Independent
University, Bangladesh (IUB) since September 2012. His
research interest includes power systems, power electronics
and renewable energy.

Design of a wind power generation system using a permanent magnet synchronous machine, a boost regulator and a transformer less step down circuit

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Design of a wind power generation system using a permanent magnet synchronous machine, a boost regulator and a transformer less step down circuit