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Experimental investigations on grid integrated wind energy storage system using neuro fuzzy
controller
Krishnan Suresh1, Attuluri R.Vijay Babu2*, Perumal M. Venkatesh3
RC-RES, Department of Electrical and Electronics Engineering, Vignan’s Foundation for Science, Technology & Research,
Guntur 522213, Andhra Pradesh, India
Corresponding Author Email: 202vijay@gmail.com
https://doi.org/10.18280/mmc_a.910304
Received: 28 July 2018
Accepted: 30 September 2018
ABSTRACT
This paper presents harnessing of maximum wind energy from natural resource whenever
it’s available. The power electronic converters role is important In between sources and
load. The load may be linear and non-linear in nature, so converters performance decides
the efficiency of the system. Proper controller can switch the converter in the desired time
and improve the system performance and stability. Many controllers are suggests to
control the converter to get better performance in at output side. The proposed system
also has boost converter, bidirectional DC-DC converter and inverter for grid and wind
energy integration. The boost inverter/buck rectifier in this system is controlled by
ANFIS controller is for better output, boost and bidirectional DC-DC converters are
controlled by PID controller in closed loop. Overall operations are based on modes main
controller speedgoat, which is control the system operation in different modes. Any
variation happening in the input, storage and load parameters speedgoat changing the
mode and operate the system is in effective way. Based on the system conditions
speedgoat generates control signal for the control breakers, these control breakers
changing modes of operation. ANFIS, PID and speedgoat are the three controllers
combined together which harness maximum wind energy and this system is applicable for
both linear and non-linear loads in domestic applications.
Keywords:
speedgoat, bidirectional DC-DC converter,
boost inverter, ANFIS
1. INTRODUCTION
Modern controllers are very helpful for energy conversion
system, now days most of the energy storage systems are
fully depends on intelligent controllers such as digital logic
and fuzzy logic [1-2].
Figure 1. Wind energy conversion system with linear and
non-linear load block diagram
This fuzzy logic behavior is good for tremendous
intelligent control technique when compare to digital logic.
The fuzzy logic consist of fuzzy controller and fuzzy sliding
mode controller, these controller are robust [3-5]. Even
though these are in robust, it has some drawbacks related to
control parameter selection constraints and complex theory.
So, this controller performance is not efficient and effective
in the inverter topology [6-8]. These drawbacks are overcome
by an Adaptive Neuro-Fuzzy Inference System (ANFIS), it
has advantages of fuzzy logic and neural networks which are
fulfill the alteration rule based demand and it can determine
the inference logic rules. ANFIS can control the grid tied
bidirectional converter in three modes such as grid tied boost
inverter mode, grid tied buck rectifier mode and stand-alone
mode in an effective way [9].
In conventional energy storage systems the converters like
uncontrolled AC-DC rectifier, PID controlled boost converter,
PID controlled bidirectional DC-DC converters are also using
for power conversion stages with grid tied inverter [10-12].
These converters are connected between Wind Energy
Conversion System (WECS), Energy Storage Device (ESD)
and load/grid for effective wind energy harnessing; the
converters in all the stages are controlled by separate
controllers [13]. But converters in these systems are
operating in closed loop but the overall system is operated by
open loop configuration. There are some serious dis-
advantages related to this open loop configuration such as
non-reliable, inefficient operation and less utilization of
natural energy [14-15]. To overcome these draw back the
system should be operate in closed loop from some parameter
considerations. This proposed system considers the
parameters such as wind speed (v), state of charge (%) and
Modelling, Measurement and Control A
Vol. 91, No. 3, September, 2018, pp. 123-130
Journal homepage:http://iieta.org/Journals/MMC/MMC_A
123
load position (ON/OFF). Based on these parameters the
speedgoat generates control signal and given to control
breakers which operates the system in different modes for an
effective operation with linear and non-linear load is as
shown in figure 1.
2. FIVE MODES OF OPERATION
2.1 Primary source storage mode
Primary source of the system is wind energy. Based on the
first two parameters consideration the wind speed (v) should
be more than 5 m/s and battery charging level has to be less
than 20%. Then the third parameter load position may be
ON/OFF. The primary source is directly supply to only
battery for the purpose of charging. In this mode load is said
to be ON condition, it gets supply from secondary source
otherwise the grid is isolated from the system. Figure 2
represents primary source storage mode.
Figure 2. Primary source storage mode
2.2 Primary source storage-output mode
In the second mode of operation primary source wind
energy is given to output load/grid and battery for charging.
Under the parameters consideration the wind speed (v)
should be more than 5 m/s and battery charging level has to
be in between (40-80) %. Then the third parameter load
position may be ON/OFF. The primary source is supply to
both battery for the purpose of charging and output. In this
mode load is said to be ON condition, it gets supply from
primary source otherwise the generating power is export to
grid. (Fig 3)
2.3 Primary source output mode
Third mode (fig 4) of operation is primary source output
mode. In this mode primary source wind energy is directly
given to output load/grid. The parameters such as wind speed
(v) should be more than 5 m/s and battery charging level has
to be reaching above 90 %. Then the third parameter load
position may be ON/OFF. The primary source is supply to
only output. In this mode load is said to be ON condition, it
gets supply from primary source otherwise the generating
power is directly export to grid. If the load is in ON condition,
the system acts like stand-alone otherwise operates in in grid
connected inverter mode.
Figure 3. Primary source wind storage-output mode
Figure 4. Primary source output mode
2.4 Battery power output mode
Figure 5. Battery power output mode
Back-up source of the system is battery power. In this
mode primary source wind energy is less than 5 m/s. Due to
124
low wind speed, the power is not sufficient for output and
battery charging level is already in above 90 %. Then the
third parameter load position should be in ON position. The
primary source is not available so battery supplies the power
to load. In this mode load is said to be ON condition, it gets
supply from back-up source otherwise the total system is in
OFF until the wind speed reach above 5 m/s. If the load is in
ON condition, the system acts like stand-alone system. (fig 5).
2.5 Grid power storage-load mode
In the fifth mode of operation secondary source grid power
is given to output load and battery for charging. The
condition for this mode is wind speed (v) should be less than
5 m/s and battery charging level is less than 20 %. Then the
third parameter load position may be either ON/OFF. The
primary source is supply to both battery for the purpose of
charging and load. In this mode load is said to be ON
condition, it gets supply from secondary source otherwise
only charging the battery from grid. This mode will continue
until the wind speed reaches the level of 5 m/s. (fig 6).
All the five modes of operations are clearly explained in
the Table 1. By the modes conditions the converters like
UDC, BDC and inverter are controlled by main controller in
different modes. The load and UDC has two positions ON-1
and OFF-0. BDC also two positions 1-boost and 2-buck. The
inverter has four modes namely 0-OFF, 1-standalone, 3-grid-
inverter and 4-grid-rectifier.
Figure 6. Grid power storage-load mode
Table 1. Modes of operation
Mode
Modes condition
Control
UDC
BDC
Inverter mode
Load
Battery(%)
Wind speed
m/s
1
1
<40
>=5
1,2,5 & 11
1
0
0
0
<40
>=5
1,2 & 5
1
0
0
2
1
>=40
>=5
1,2,5, 6 & 10
1
1
1
0
>=40
>=5
1,2,5,6 & 7, 8, 9
1
1
2
3
1
>=40 &<80
>=5
5,6 & 10
1
1
1
0
>=40 &<80
>=5
5,6,7,8 & 9
1
1
2
4
1
>=40
<5
3,4,6 & 10
0
1
1
5
1
<40
<5
3,4,6,7,8,9,& 11
0
2
3
0
<80
<5
3,4,6,7,8 & 9
0
2
3
3. ANALYSIS OF WIND ENERGY SYSTEM
Each stage of conversion is analysed and composed by
mathematical equations. Every stages of conversion consist
of converters and controllers in closed loop and overall
system is controlled by separate main controller called
speedgoat.
3.1 Wind energy conversion
The design of wind turbine is taken from [1], horizontal
axis wind turbine has to analyse from equations 1, 2 and 3.
Wind passes through in area area (A) and wind speed (v) of a
particular velocity. The power of wind is expressed in
equation 1.
3
***5.0 vAp
=
(1)
Mechanical power is expressed in the following eqn 2.
)(*)(***5.0 2
2
2
121 vvvvApT++=
(2)
The rotor coefficient is expressed by the following eqn. 3
)1(*)1(*5.0
1
2
2
1
2
2
v
v
v
v
P
P
CT
p−−==
(3)
3.2 PMSG
Mathematical modeling of Permanent Magnet
Synchronous
Generator (PMSG) can be written in the following
equations 4 and 5.
d
d
q
d
q
d
d
ad u
L
ip
L
L
i
L
R
dt
di 1
+==
(4)
q
q
m
d
d
q
d
q
q
ad u
L
p
L
ip
L
L
i
L
R
dt
di 11 ++==
(5)
The EMF equation of PMSG is written in equation 6.
wphph KTfE
44.4=
(6)
125
3.3 Rectifier unit
The three phase AC power from permanent magnet
synchronous generator is supply to 3 phase bridge rectifier
for AC-DC conversion.
The phase voltage amplitude Vm and output average
voltage Vo is expressed by the equations 7 & 8.
2
rmsm VV =
(7)
VmVr
=23
(8)
3.4 Uni-directional converter (UDC)
The output of unidirectional boost converter can be
analysed in the input voltage and duty cycle. All stages of
boost mode are controlled by adjusting the duty cycle
automatically with closed loop controller. The output voltage
and duty cycle is expressed by the equations 9 and 10.
)1( D
V
Vr
b−
=
(9)
D
T
T
TT
T
s
on
offon
on ==
+
(10)
3.5 Bidirectional converter (BDC)
The primary switch Q1 is ON position during boost mode
it is expressed in equation 11
=
+=
•
XCV
VBXAX
T
batt
S
1
11
(11)
where, x = state variable vector, IL is inductor current and Vc
is capacitor voltage. It consists of inductor and capacitor to
represents current and voltage .It can be re-written in
equation 12.
=
+
−
−
+
−
=
c
L
cbat t
s
c
L
Lc
c
L
v
i
rV
v
LN
v
i
RCC
LL
rr
dt
dv
dt
di
1
0
2
1
11
1
(12)
The state vector X dot is expressed in state variables such
as A2 and B2. The time interval of the primary switches is ON
are expressed in the equation 13.
=
+=
•
XCV
VBXAX
T
batt
S
2
22
(13)
which are re-written in the equation 14.
s
c
L
Lc
c
L
v
v
i
RCC
LL
rr
dt
dv
dt
di
+
−
−
+
−
=
0
0
11
1
(14)
The small signal analysis of AC perturbation in a DC
operating point, the circuit variables is added to the ac
perturbations is expressed in equation 15.
+=+=+= sssssssss vVvxXxdDd
(15)
AC small signal is denoted by cap symbol. The
perturbation approximation is small so negligible. Steady
state value is expressed in equation 16.
111
s
s
ss
ss
V
v
X
x
D
d
(16)
It provides the final linearized ac small signal model.
( ) ( )
•
−+−++= ssss dVBBXAAVBxAx 2121
(17)
The transfer function of boost converter in the boost mode
operation is expressed in s-domain. Thus the s-domain form
of boost converter is expressed in an equation 18.
The current-programmed state equation (19) is minimized
to a function of X(s) &Vcontrol(s). It allows x(s) to an
expression as in Vcontrol(s) in a matrix multiplication,
)(
0
2
)(
0
2
1
)(
)(
11
1
)(
)( sd
LN
V
sv
LN
sv
si
RCC
LL
rr
svs
sis
ss
s
s
c
L
Lc
c
L
+
+
−
−
+
−
=
(18)
)()( 1
1
1sVCAsIsX control
−
−=
(19)
where, I = identity matrix. The small-signal expression for
output voltage is given by
)()( sxCsvbatt
=
(20)
1
2
1//
1
1
)(
)(
C
s
C
s
s
G
sv
sv
cLL
s
vf
contro l
batt
++
+
=
(21)
1
2
1//
1
1
)(
)(
C
s
C
s
s
A
sv
sv
cLL
s
gvf
s
batt
++
+
=
(22)
where, the corner frequencies are identical to those in the
control-to-output transfer function.
126
3.6 ANFIS
Figure 7. ANFIS Interface
ANFIS controller is connected to boost inverter is as
shown in figure 7. This Set up operation is bidirectional and
operates in three modes such as grid-inverter ANFIS control
mode, grid- uncontrolled rectifier mode and stand alone
ANFIS control mode. During first and third mode the
inverter acts like a boost converter and during second mode it
acts like buck rectifier.
4. SIMULATION AND RESULTS
Output waveforms of the entire mode are as shown in the
figure 8. During the load is in ON (manual) position the
control breakers (U1&U2), U5&U6 are turn ON by speed goat
and wind power is supply to charging the battery and supply
to load or else load is in OFF (manual) the control breakers
(U7 U8 U9) turn ON and supply the wind power to grid and
remaining control breakers remain in OFF condition. The
other two conditions are wind speed (v) is >= 5m/s and state
of charge is in between (40-80) %.
127
Figure 8. Simulation output
In this mode the battery is charging and also used to load,
then this mode is called wind sourced battery-load mode. The
carrier and reference signal is compared and the output signal
of PWM controlled by the converter switches. The carrier
and reference signal are compared, and PWM signal is
generated given to the converter switches. The unidirectional
converter output value is now obtained as 24 V, and the
bidirectional converter operates in boost mode and the
getting input voltage from UDC is step-up to 48 V, and the
current value is 1A. Then the filtered pure DC is given to the
inverter then the inverter converts DC-AC and also step-up to
98V. Finally, the electrical AC output is applied to two types
of loads. ANFIS controller is used to control the inverter
switching and finally LC filter is used to filter the output
signal Final inverter output is given to both linear and non-
linear loads. The Total Harmonics Distortions (THD) of
linear load is 2.57% and THD value of non-linear load is
4.35%.
The input of the wind energy conversion system is 8 m/s.
with this wind speed the output of wind profiles values of
rotor torque is -0.5 N-m and rotor speed is 160 rad/sec. The
output of PMSG is 24V. This 24V AC supply is provided to
converters circuit, and the final 24V DC supply is given to
charge the battery and also load. The input is getting from
PMSG the variable 24V AC supply is initially converted to
DC by three phase uncontrolled bridge rectifier.
The output of bridge rectifier is 20V DC because the
rectifier efficiency is only 81.2%. The variable 20V DC
voltage is converted into fixed 24V DC by using
unidirectional boost converter, and the converter current is
almost 2A. This 24V constant DC is supplied to the battery
for charging and also supply to BDC. The bi-directional
converter operates in boost mode, and the input voltage of
BDC 24V is step-up to 48V. Then the filtered pure DC is
given to the inverter. Finally, the electrical AC output is
applied to Load. In the other side battery also charging from
UDC constant output 24V DC.
128
5. HARDWARE AND RESULTS
Hardware implementation is shown in the figure 9. The
output waveform of modes wind sourced battery-load mode
is as shown in figure 10 the output is taken when the wind
speed is at 5.5m/s. During the load is in ON (manual)
position the control breakers (U1&U2), U5&U6 are turn ON
by speed goat and wind power is supply to charging the
battery and supply to load or else load is in OFF (manual) the
control breakers (U7 U8 U9) turn ON and supply the wind
power to grid and remaining control breakers remain in OFF
condition. The other two conditions are wind speed (v) is >=
5m/s and state of charge is in between (40-80) %.
Figure 9. Hardware Implementation
Figure 10. Hardware output result
The BDC again boost up the input 24V constant DC
voltage into 48V DC voltage, and finally, an inverter
converts 48V DC voltage into 98V AC voltage the value is
nearly doubled and given to load. The source is given to both
battery and load so, this mode of operation is called wind
sourced battery-load mode. Real time output values from
PMSG are 15V AC, its rectified into 11.9V DC and supplied
to the UDC. The UDC maintains constant 24V DC, and again
it supplied to charge the battery and also provided to BDC.
The BDC output 47.6V DC is step-up and converts to AC
using an inverter. The inverter output 93.8V is given to the
load.
The output is taken at when the wind speed is at 7m/s.
When compared to wind speed at 5.5 m/s there are some
parameters changed. The BDC again boost up the input 24V
constant DC into 48V DC, and finally, an inverter converts
48V DC into AC then the value nearly doubled and given to
load. The source is provided to battery and load so, this mode
of operation is called wind sourced battery-load mode. Real
time output values from PMSG are 15V AC, its rectified into
11.9V DC and supplied to the UDC. The UDC maintain
constant 24V DC and is provided to charge the battery and
also supplied to BDC. The BDC output 48 DC is step-up and
converts to AC using an inverter.
The inverter output 98V is as given to the load.The
experimental platform of overall system consists of a boost
converter and bi-directional converter with PMSG. The
performance of the unidirectional boost and bi-directional
converters are controlled by DSPIC30F4011 controller with
PID control structure. Inverter is controlled by ANFIS
controller.
Table 2. Output results
Conversion
stages
Simulation results
Hardware results
Linear
load
Non-
Linear
load
Linear
load
Non-
Linear
load
PMSG Output
22
22
15
16
Rectifier
output
20
20
11.9
12
UDC Output
(V)
24
23.9
23.9
23.8
UDC Output
(I)
4
4
4.2
4.11
Battery Output
(V)
4
4
4.1
4.1
Battery Output
(V)
24
24
23.9
23.6
BDC Output
(V)
48
48
47.3
46.8
BDC Output
(I)
25
2.45
2.3
2.41
Inverter
Output (I)
2
2.1
1.7
1.9
Inverter
Output (V)
98
97.3
93.8
92.7
THD (%)
2.57
4.35
7.65
9.35
The hardware result values verified with simulation results.
Its outputs are almost equal to the simulation result. The
system has a robust performance under all the modes. The
THD values are obtained in simulation is below 5% and
hardware results are below 10%.
6. CONCLUSION
In this paper, bidirectional converter operation plays an
important role for mode changing operation and its five
modes of operation were analysed. Wind energy is the main
input sources from renewable energy, based on this source
level the operations are divided into five modes and also
these modes based on state of charge in battery. The
129
electrical energy conversion system consists of a
unidirectional boost converter and bidirectional converter
operates four modes in boost operation and one mode in a
buck operation. Simulink model of whole system including
unidirectional DC-DC boost converter, bidirectional DC-DC
converters were developed for wind energy electrical system
and simulation results were obtained in
MATLAB/SIMULINK. Real time implementation of whole
system including speedgoat real time target machine,
bidirectional DC-DC converters controlled by
DSPIC30F4011 were developed for wind energy electrical
system and real-time results were obtained. A variety of
operating conditions from different inputs were analysed.
The system has a robust performance under mode changing
while input wind speed changes. The hardware results of the
proposed model were verified with simulation results. The
mode changing operation is effectively done in both
simulation and real-time platforms.
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