IRJET- Simulation of a Doubly Fed Induction Generator based Wind Energy Conversion System using MATLAB

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 119
Simulation of a Doubly Fed Induction Generator based Wind Energy
Conversion System using MATLAB
Sreejith S1, Vijina K2
1PG Scholar, Dept. of Electrical and Electronics Engineering, Sree Buddha College of Engineering, Pattoor,
Kerala, India
2Asst.Professor, Dept. of Electrical and Electronics Engineering, Sree Buddha College of Engineering, Pattoor,
Kerala, India
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Abstract - Doubly fedinductiongeneratorsarewideemployed
in wind energy conversion system because of its low device
price, simplicity, and improved potency etc. The doubly fed
induction generator stator coil windings are directly
connected to the grid whereas the rotor windings are
connected to the grid via power electronic converters. The
field oriented control is often used for doubly fed induction
generator. The modelling of doubly fed induction machine is
also presented and different output waveforms are analyzed.
Key Words: Doubly fed induction generator, wind
turbine, field oriented control, wind energy conversion
system, power electronic converters
1. INTRODUCTION
Nowadays the wind energy plays a vital within the world as
a result of its environmental friendliness and availability.
The wind turbines utilized in wind energy conversion
system (WECS) are mainly constant speed and variable
speed. Among them variable speed turbine is more energy
efficient since the wind speed is variable in nature. Squirrel
cage induction generator (SCIG), doubly fed induction
generator (DFIG) and permanent magnet synchronous
generator (PMSG) are the 3 sorts of generator used for wind
energy conversion system, among thisDFIGismosttypically
used for WECS as a result of its advantages like improved
efficiency, active and reactive power management, reduced
losses, reduced convertor price and ability of power factor
correction..
In DFIG primarily based wind energy conversionsystem, the
stator windings of DFIG is directly connected to the grid
whereas the rotor windings are connected to the grid via
power electronic devices like rotor and grid side converters.
DC link capacitor connected between rotor and grid side
device act as DC voltagesupply.Theconverters [1] employed
in DFIG primarily based WECS need only a fraction of the
generated output power so the converters are designed to
transfer 30% of the total power. The active and reactive
power from stator to grid of the turbine is controlled by
rotor side converter [2]-[4]. The grid side converters
controls the dc link voltage and permits the device to
generate or absorb reactive power [5]-[6].InDFIGthestator
and rotor can offer power so it's referred to as doubly fed.
Field oriented control (FOC) or vector control is usually
utilized in doubly fed induction generator controls because
of its ability of controlling the motor speed more efficiently.
Field oriented control conjointly provides the flexibility of
controlling the active and reactive power of the generator
one by one. Currently, there are commonly two sorts of field
oriented control in DFIGs, they are stator voltage and stator
flux oriented control, respectively. The stator flux oriented
control is wide utilized in the DFIGcontrol designs [7]within
which the q-axis current element is employed for active
power management and also the d-axis elementisemployed
for reactive power management. Whereas for the stator
voltage oriented control, the case is on the contrary, the d-
axis element is employed for active power management and
also the q-axis current element is employed for reactive
power management.
2. DOUBLY FED INDUCTION GENERATOR
The doubly fed induction generator basic block diagram is
shown in Fig. 1. In this the stator windings is directly
connected to the grid whereas the rotor windings are
connected to the grid via power electronics converters such
as rotor side and grid side converter.
Fig -1: Doubly Fed Induction Generator
Mathematical modelling equations of DFIG is given below,
Stator and rotor voltage equations are,

Where Vds, Vqs, Vdr and Vqr are the stator and rotor d axis
voltages and q axis voltages respectively.RsandRrarestator
and rotor resistance respectively.
ωe is the angular speed and ωr is the rotor speed. ids, iqs,idr,
and iqr are the stator and rotor d axis currents and q axis
currents respectively. Fds, Fqs, Fdr and Fqr are the flux
linkages.
Flux linkage expressions are,
Where Fmd and Fmq are the mutual flux linkages of d axis
and q axis respectively.
Torque equation,
Fig -2: MATLAB model of DFIG
Fig -3: dq model of OEWIM
3. PROPOSED SYSTEM
3.1 Floating Capacitor Bridge inverter
The topology by using floating capacitor dual inverter has
been analyzed for various applications [8].The capacitor
floats with regard to the earth’s potential that's neitherofthe
two terminals are grounded.Thecapacitorareoftenusedasa
Nursing energy storage componenttomakealowerorhigher
voltage power supply. They often offer reactive power to a
machineand can be used forcompensating any voltagedrop.
Fig -4: Conventional OEWIM topology
The proposed topology is to manage the voltage across the
floating capacitor by implementing correct switching states
thereby reducing the necessity of isolation transformer as
shown in fig 4. The figure shows the traditional open end
winding induction motor. One end of the machine is
connected to a transformer to realize thedesiredoutputthat
will increase the weight, cost etc. This disadvantage can be
overcome by using the proposed scheme that replaces the
transformer with a floating capacitor bridge.

Fig -5: Block diagram of proposed topology
The figure shows an OEWIM and dual inverters with only a
single dc source at the primary side and the second
converter is connected to a floating capacitor bank.
3.2 Modulation Strategy
The modulation strategy used to control the voltage across
the floating capacitor is by space vector pulse width
modulation technique (SVPWM). The space vector pulse
width modulationisa veryadvancedPWMmethodologythat
is best appropriately used for three phase inverters. This
strategy switches each of the inverters equally to get the
specified output. This strategy has special switching
sequences and can produce the output with less harmonic
distortion and also provide additional economical use of
supply voltage than the pulse width modulation techniques.
The main objectivesofthemodulationschemeembrace wide
linear modulation range, less switching lossesandharmonic
distortion, easy implementation and fewer process
calculations.
3.3 Operating principle
The floating capacitor bridge can be charged and discharged
by considering the proper switching states. The different
switching combinations obtained from the space vector of
dual inverters, there will be discharging, charging and
neutral conditions for the floating capacitor.
Fig -6: Modes of Operation
Consider an example of state(74) where 7 (1 1 1) represents
the top three switches and 4 (0 1 1) represents the switching
states of the top threeswitchesoffloatingcapacitor.Fromthe
figure the first mode shows the charging of capacitor, where
the current flows from positive to negative terminal of the
floating capacitor. The second mode are the zero states,
therefore no impact on floating capacitor’s voltage. The third
mode shows that current flows from negative to positive
terminal which results in the discharging of capacitor.
4. SIMULATION RESULTS
The following graphs shows the simulation resultsof doubly
fed induction generator modelling in MATLAB. Fig 7 shows
the input voltage waveform of doubly fed induction
generator.
Fig -7: Waveform of input voltage
Fig -8: Stator Current of DFIG

Fig -9: Rotor Current of DFIG
Fig -10: Output Power of DFIG
5. CONCLUSION
Induction machine with stator end windings are analyzed
with twin inverters connected to the machine. The floating
capacitor connected at one end of the device are often used
atone for the voltage drop. The floating dc link voltage value
are kept constant by charging and dischargingofthefloating
bridge capacitor by correct switching combinations. The
space vector modulation will avoid the unwanted voltage
levels and might improve the wave shape quality of the
floating bridge topology.
APPENDIX A: DFIG PARAMETERS
Rated voltage = 400 V
Rated power = 4 KW
Rated speed = 1800 rpm
No. of poles = 4
Stator winding resistance, Rs = 1.405 Ω
Rotor resistance, Rr = 1.395 Ω
Stator leakage inductance, Lls = 0.005839 H
Rotor leakage inductance, Llr = 0.005839 H
Mutual Inductance, Lm = 0.1722
Moment of inertia, J = 0.131 Kg m2
REFERENCES
[1] P. Wheeler, L. Xu, L. Meng Yeong, L. Empringham, C.
Klumpner, and J. Clare, “A review of multi-level matrix
converter topologies,” in Proc. 4th IET Conf. Power
Electron., Mach. Drives, 2008, pp. 286–290.
[2] J. Rodriguez, L. Jih-Sheng, and P. Fang Zheng, “Multilevel
inverters: A survey of topologies, controls, and
applications,” IEEE Trans.Ind.Electron.,vol.49,no.4,pp.
724–738, Aug. 2002.
[3] Y. Jiao, S. Lu, and F. C. Lee, “Switching performance
optimization of a high power high frequency three-level
active neutral point clamped phase leg,” IEEE Trans.
Power Electron., vol. 29, no. 7, pp. 3255–3266, Jul.2014.
[4] P. P. Rajeevan, K. Sivakumar, K. Gopakumar,C.Patel,and
H. Abu-Rub, “A nine-level invertertopologyformedium-
voltage induction motor drive with open-end stator
winding,” IEEE Trans. Ind. Electron., vol. 60, no. 9, pp.
3627–3636, Sep. 2013.
[5] V. T. Somasekhar, B. Venugopal Reddy, and K.
Sivakumar, “A four-level inversion scheme for a six-n-
pole open-end winding induction motor drive for an
improved DC-link utilization,”IEEETrans.Ind.Electron.,
vol. 61, no. 9, pp. 4565–4572, Sep. 2014.
[6] S. Kouro, J. Rodriguez, W. Bin, S. Bernet, and M. Perez,
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[7] Dr. P.S. Bimbra, “Power Electronics”, Khanna
publications, Fourth edition 2012
[8] B. A.Welchko, “A double-ended inverter system for the
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IRJET- Simulation of a Doubly Fed Induction Generator based Wind Energy Conversion System using MATLAB

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