Energy and Power E ngineering, 2013, 5, 382-386
doi:10.4236/epe.2013.54B074 Published Online July 2013 (http://www.scirp.o rg/journal/epe)
Copyright © 2013 SciRes. EPE
Grid Interconnection of Wind Energy System at
Distribution Level Using Intelligence Controller
W. Z. Gandhare1, S. C. Hete2
1Principal, Government College of Engineering Amravati, India
2Electri cal Engineer ing Depart ment, Government College of Engineering Amravati, India
Received February, 2013
Wind generation is being increasingly connected at distribution level due to increasing load demand. Permanent magnet
synchronous generator (PM S G) is connected to the wind turbine directly. Through the full power control of AC-DC-AC
converters, the electrical power is then connected to the power grid. The power conversion circuits are made up of ge-
nerator-side three phase diode rectifiers, boost converter and the gri d-side three bridges and four wire inverter s. A boost
converter is controlle d throu gh an inte lligence c ontrolle r to mai ntai ned DC power constant d espite of Variab le o utput of
PMSG, the grid-connected operation is constructed using the hysteresis current control method. The inverter is con-
trolled to perform follo wing function 1) power converter to inject power generated from RES to the grid, and 2) shunt
APF to compensate current unbalance, load current harmonics, load reactive power demand and load neutral current.
The model is implemented in M ATLAB/ Simulink using sim power system.
Keywords: Point of Common Coupling (PCC); Distrib uted Generatio n (D G ); Intelligence Controller
1. Introduction
Electric utilities and end users of electric power are be-
coming increasingly concerned about meeting the grow-
ing energy demand. Seventy five percent of total global
ener gy de mand i s supp lied b y the b urni ng of fossil fuel s.
But increasing air pollution, global warming concerns,
diminishing fossil fuels and their increasing cost have
made it necessary to look towards renewable sources as a
future energy solution. Since the past decade, there has
been an enormous interest in many countries on renewa-
ble energy for power generation. The market liberaliza-
tion a nd gover nment's incentives have further accelerated
the renewable energy sector growth. The wind energy is
the alternative energy sources. Previously, they were
used to supply local loads in remote areas, outside the
national grid. Later, they have become some of main
sourc es. The utility is co ncerne d due to the hi gh penetra-
tion level of i ntermittent W ind energ y system in distrib u-
tion systems as it may pose a threat to network in terms
of stability, voltage regulation and power-quality (PQ)
issues a t PCC [1,2].
Direct-driven permanent magnet synchronous genera-
tor (PMSG) is widely used in wind-power generating
system [7]. The power converter is a key part of the sys-
tem for the electrical energy fed into the power grid.
With the i ncreasing of power capacity and high demand
for power quality, the study of topology of high power
converters based on multi-level converter is attracting
more and more attention.
The non-linear load current harmonics may result in
voltage harmonics and can create a serious PQ problem
in the power system network. Active power filters (APF)
are extensively used to compensate the load current har-
monics and load unbalance at distribution level. This
results in an additional hardware cost. However, in this
paper control method incorporated the features of APF,
conventional inverter interfacing WECS with the grid,
without any additional hardware cost and intelligence
controller for boost converter.
2. System Description
The proposed WECS is composed of a direct-drive 3
PMG that has its output fed into a 3
diode rectifier.
The output of the generator-end rectifier is fed into a
Artificial neural network controlled dcdc converter,
which supplies the hysteresis current controlled 3
grid-side inverter. The grid-side inverter supplies its out-
puts to a 400-V 50-Hz grid through a Transformer.
The voltage source inverter is a key element of a
WECS system as it interfaces the wind energy source to
the grid and delivers the generated power. The variable
speed wind turbines generate power at variable ac vol-
tage. Thus, the power generated from this needs power
conditioning (i.e ., dc/dc or ac/dc) before connecting on
Copyright © 2013 SciRes. EPE
dc-link. Figure 1 shows General Scheme of the wind
ener gy conversi on syste m
Figure 1. General Scheme of the Wind Energy Conversion
3. Intelligence Controller for Boost
The control of a dcdc converter employed in PMG
based WECS can be established to achieve the following
goals [3,4].
1) To maintain a close-to-fixed d c input voltage to the
grid side inverter under wind speed variations as well as
under changes in the output power (P and/or Q) of the
grid-side inverter;
2) To supply energy to the grid-side inverter during
transient changes in the wind speed.
The goals of controlling the dc–dc converter can be
achieved through adjusting its duty cycle by following
formula which regulates the dc output voltage of the ge-
nerator-end rectifier using artificial intelligence network.
Output voltage is step-up and maintained constant using
Vo - Output voltage of boost converter
Vi - Input voltage of boost converter
D – Duty ratio of boost converter
The duty ratio of the bo ost converter is varied to com-
pensate the variations in the input voltage. Therefore
output voltage is kept at a d esired value. Con trol strate gy
for closed loop DC-DC boost converter is shown in Fig-
ure 2. Here output voltage is sensed and is compared
with a set reference voltage. The error is processed
through a intelligence controller whose output is used to
modulate the pulses that drive the IGBT gate. Gate sig-
nals of IGBT are generated by PWM by comparing a
carrier signal with the signal generated by intelligence
controller. We have developed a feed-forward network
which is trained by back propagation algorithm. The
simplest way to generate a PWM signal is the intercep-
tive method, which requires only a saw tooth or a trian-
gular waveform and a comparator.
Figure 2 . Simulink Mo del of Boost C onve r ter.
Figure 3. Programme to develop feed-forward network in
When the value of the reference signal is more than
the mod ulat ion wa vefor m, the PWM signal is i n the hi gh
state, other wise it is in t he lo w state [ 5] . Figure 3. S hows
programmed to develop Feed forward network in
4. Control of Grid Interfacing Inverter
TBFW inverter incorporates the features of APF in the
conventional interfacing inverter. The inverter can per-
form the following functions:
1) Transfer of active power from the generator to the
2) Reactive power demand support
3) Current unbalance, cur rent harmonics compensation
With adequate control of grid-interfacing inverter, all
the objectives can be accomplished either individually or
simultaneously. The Power quality constraints can there-
fore be strictly maintained within the utility standards
Copyright © 2013 SciRes. EPE
without add itional hardware cost.
The DC-link voltage carries the information regarding
the exchange of active power in between PMG and grid.
Thus t he o utp ut o f D C -link volta ge r e gul at or r esul ts i n a n
active current. The multiplication of active current com-
ponent with unity grid voltage vector templates (Ua, Ub
and Uc) generates the reference grid currents (Ia*,Ib*
and Ic*). The grid synchronizing angle obtained from
phase locked loop (PLL) is used to generate unity vector
Ua = Sinθ (1)
Ub = Sin(θ-2π/3) (2)
Uc = Sin(θ+2π/3) (3)
The actual DC-link voltage is sensed and compared
with reference DC-link voltage. The difference of this
DC-link voltage and r efere nce DC -link voltage (Vdc *) is
given to a discrete-PI regulator to maintain a constant
DC-link voltage. The output of the discrete-PI regulator
is Im. The instantaneous values of reference three phase
grid currents are computed as
Ia* = Im • Ua (4)
Ib* = Im • Ub (5)
Ic* = Im • Uc (6)
The reference grid currents (Ia*, Ib* and Ic*) are
compared with actual grid currents (Ia, Ib and Ic) to
compute the current errors which are given to the hyste-
resis current controller. The hysteresis controller then
generates the switching pulses (P1 to P6) for the gate
terminals of grid-interfacing inverter [6].
The switching pattern of each IGBT inside inverter
can be formulated on the basis of error between actual
and reference current of inverter, which can be explained
( )
binvainva hII −≥ then upper switch S1 will be
OFF and lower switch S4 will be ON
in the phase “a” leg of inverter.
( )
binvainva hII −≤ then upper switch S1 will be
ON and lower switch S4 will be OFF
in the phase “a” leg of inverter.
5. Simulation Model of WTG System
Figure 4 shows complete model of WTG system, which
is implemented in the MATLAB/Simulink Sim Power
System library. The Wind Turbine Generation (WTG)
system takes wind speed and angular speed of PMSM as
input. The torque output of the wind turbine is given as
an input mechanical torque for the PMSG. The direction
of torque is positive during motoring mode and made
negative during generating mode of PMSG. Boost con-
verter is controlled through the intelligence controller
and Grid side converter is controlled through hysteresis
current control method. The switching pattern of each
IGBT inside inverter can be formulated on the basis of
error between actual and reference current of inverter.
6. Simulation Result
The simulation of the proposed system is done by using
MATLAB/Si mulink wit h referring to t he control strate g y
shown in Figure 4. The simulation is done for 4.5 KW
system. The output voltage of boost converter is
represent in Figure 5. Which demonstrate that the effec-
tiveness of proposed intelligence controller. The output
voltage of boost converter is perfectly constant Equal to
400 V.
The TBFW inverter connected to a 3 phase network
can be effectively controlled by using hysteresis control-
ler. The TBFW inverter is actively controlled to achieve
sinusoidal grid currents despite highly unbalanced non-
linear load. WPG with variable output is connected on
the dc link of grid interfacing inverter. Simulation is
performed on a three phase balanced non-linear load
which consists of a three phase diode rectifier supplying
DC voltage to an R-L load. Table 1 gives the specifica-
tion of various system parameters.
Figure 4. Model of WECS Connected to Grid in SIMU-
Figure 5 . Boost converter output.
Copyright © 2013 SciRes. EPE
Table 1. Sys te m parameters.
PI Controller
Kp=0, Ki=1, Sample time 100e-6
Three pha se voltage sour ce
Voltage=400 V, Fn=50 Hz
Series RLC lo ad
DC volta ge Vdc= 400 V
Three pha se transformer
P=10MVA,Fn=50Hz ,Rm=200pu,
6.1. When WECS is Not Connecte d to Grid
Initially the grid interfacing inverter is not connected to
the network. The waveforms of grid currents, load cur-
rents a nd i nver ter c urr ents a re sho wn in Figure 6. At this
time the grid current profile is identical to the load cur-
rent profile because the load power demand is supplied
by grid alone.
Figure 6 . WECS Not connecte d to grid.
The waveform of grid c urrent, load c urrent and inverter
current represented by ‘Y-axis’ and by ‘X- axis’ are
sho wn in Figure 6.
6.2. When WECS is Connected to Grid
When inverter is connected to the network it starts in-
jecting the current in such a way that the grid current
profile changes from unbalanced non-linear to balanced
sinusoidal as shown in Figure 7.
Figure 7 sho ws wave fo rm of gri d cur re nt, lo a d current
and inverter current represented by ‘X-axis’ and time on
‘Y-axis’ for when inverter connected to grid.
Figure 7 . WECS connected to grid.
7. Conclusions
The direct drive variable-speed grid-connected PMG based
WECS has been simulated. A simple Artificial intelli-
gence controller for boost converter is designed to main-
tain the constant o utput volta ge of three phase dio de rec-
tifier despite the variable output of PMSG. The intelli-
gence controller is able to change the DC output voltage
of diode rectifier to constant value under changes in the
wind speed and changes in power delivered to the grid.
The grid side inverter is controlled using hysteresis cur-
rent controller which can be utilized to:
1) Inject real power generated fro m WES to grid
2) Operate as shunt active power filter ( APF)
This contro l method eli minates the need for additional
power conditioning equipment to improve the quality of
power at PCC.
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