ADVANCES
in
NATURAL and APPLIED SCIENCES
Published BY AENSI Publication
http://www.aensiweb.com/ANAS
ISSN: 1995-0772
EISSN: 1998-1090
2016 Special 10(10): pages 44-53
Open Access Journal
Hysteresis Current Controller For Harmonic
Reduction In Grid Connected Solar Pv
System
1M.
1PG
Jebastin and 2Dr.P. Rathika
Scholar, Department of EEE, V V College of Engineering, Tirunelveli, TamilNadu.
and Head, Department of EEE, V V College of Engineering, Tirunelveli, TamilNadu.
2Professor
Received 27 May 2016; Accepted 28 June 2016; Available 12 July 2016
Address For Correspondence:
M. Jebastin, PG Scholar, Department of EEE, V V College of Engineering, Tirunelveli, TamilNadu.
Copyright © 2016 by authors and American-Eurasian Network for Scientific Information (AENSI Publication).
This work is licensed under the Creative Commons Attribution International License (CC BY).
http://creativecommons.org/licenses/by/4.0/
ABSTRACT
With development of new functionalities solar energy based Photovoltaic cells are upcoming energy source with higher efficiency.
Solar energy being naturally available in abundance and non- polluting is one of the most promising sources. When integrating
solar power into the grid, harmonics produced due to the use of power electronics converter. Excessive use of power electronics
devices lead to power quality problems. Effects of poor power quality like sag, swell, harmonics, reactive power generation have
affected both grid as well as utility sectors. Among these harmonics is the major power quality issue. Active power filters are
powerful tool for mitigate the harmonics. Active filter suppress harmonic current and compensate reactive power simultaneously.
This paper presents the performance of Shunt active filter with Voltage Source Inverter topology connected to grid connected PV
system. The instantaneous p-q theory is used for extracting the harmonic current. Also a Hysteresis controller based control
algorithm is developed to control the three phase shunt active power filter to compensate harmonics produced by the nonlinear
load to improve power quality. A PI controller is developed to maintain a constant DC voltage across the Capacitor of DC bus side
of the inverter. The simulation is carried out in MATLAB/SIMULINK. The proposed Shunt active filter can suppress harmonics
generated by the non-linear load and it can maintain the THD value within the standard limit.
KEYWORDS:
Grid, Photovoltaic Cell, Phase locked loop, Shunt Active Filter, Hysteresis Current Control, P-Q Theory.
INTRODUCTION
Demand of renewable energy in India is increasing day by day due to less generation of power than demand
and environmental concerns. Among several renewable sources of energy off-grid and grid connected solar
photovoltaic system technology is highly available resources. It requires less maintenance and is capable of
generating outputs from few microwatts to megawatts. The performance of grid-connected solar photovoltaic
system (SPV) depends on many factor such as local climate, inverter efficiency, overall system losses,
photovoltaic (PV) technology used, environmental parameters such as global irradiance and ambient
temperature [3]. Grid connected photovoltaic power systems are energized by PV panels which are connected to
the utility grid via an inverter can upload the excess energy to the grid. Integrating solar PV effects the
functional operation of the power system network like load/frequency control, load following, unbalancing of
voltage and current levels in the network and power quality issues including voltage disturbance, poor power
factor, reactive power compensation flicker and harmonic distortions [7]. When integrating solar power into the
grid harmonics produced due to use of power electronics converter. The application of power electronics
devices such as arc furnaces, adjustable speed drives, computer power supplies etc. are some typical non-linear
characteristic loads used in most of the industrial applications and are increasing rapidly due to technical
To Cite This Article: M. Jebastin and Dr.P. Rathika., Hysteresis Current Controller For Harmonic Reduction In Grid
Connected Solar Pv System. Advances in Natural and Applied Sciences. 10(10); Pages: 44-53
45
M. Jebastin and.P. Rathika., 2016/ Advances in Natural and Applied Sciences. 10(10) Special 2016, Pages: 44-53
improvements of semiconductor devices, digital controller and flexibility in controlling the power usage. The
use of the above power electronic devices in power distribution system gives rise to harmonics and reactive
power disturbances. The harmonics and reactive power cause a number of undesirable effects like heating,
equipment damage and Electromagnetic Interference effects in the power system.
Harmonic distortion is one of the main power quality disturbances frequently encountered by the utilities.
The harmonic disturbances in the power supply are caused by the non-linear characteristics of the loads. The
harmonic currents flow through the power system impedance, causing voltage distortion. The distorted voltage
waveform causes harmonic current to be drawn by other loads connected at the point of common coupling
(PCC). The presence of harmonics leads to transformer heating, electromagnetic interference and solid state
device malfunction. Hence, it is necessary to reduce the dominant harmonics below 5% as specified in IEEE
519-1992 harmonic standard. Active filter injects harmonic current into the grid connected PV system with the
same amplitude but opposite phase than that of the load. The principal components of the active power filter
are the Voltage Source Inverter (VSI), DC energy storage device, coupling transformer and the associated
control circuits. The performance of an active filter depends mainly on the technique used to compute the
reference current and the control method used to inject the compensation current in to the line [4].
II. Grid Connected Pv System:
A grid-connected photovoltaic system is a power generating solar photovoltaic system that is directly
connected to inverter to grid. A grid-connected photovoltaic system consists of solar panels, inverter, power
conditioning unit and grid connection equipment. In PV panels, solar cells are the basic components and it is
made of silicon. A solar cell is generally a P-N junction which is made of silicon. Photons from the sunlight hit
the solar panel and are absorbed by semiconducting materials, such as silicon. The photons are absorbed by the
semiconductor atoms, freeing electrons from the negative layer. This free electron finds its path through an
external circuit toward the positive layer resulting in an electric current from the positive layer to the negative
one. The PV cell circuit model consists of an current source in parallel with the diode as shown in figure 1. In
this circuit, Iph is the photon generated current and Id is the shunt current through the diode.
Fig. 1: Equivalent circuit of PV cell
The circuit above can be described by the following equations.
The output current (I) is given by
I=I −I
Where
I −Current through PV array
I −Diode current which is proportional to the saturation current
The Diode current Id can be written as
I =I
exp
−1
(1)
(2)
Where
V − Voltage imposed on the diode
I − Reverse saturation current flow through the diode
−Thermal voltage
N −Number of cells connected in series
A − Ideality factor
For grid connected system grid synchronization plays an important role. Phase locked loop (PLL) is used to
synchronise the phase sequence and the frequency of the grid with the inverter. It is used to reduce the error
between the output current and the reference current obtained from the controller. Phase Locked Loop is a
feedback signal which locks the two input signal with same frequency and shifted in a single phase. It is used to
compare two frequencies and results the input frequency is equal to the output frequency. Also it is used to
provide rotational frequency at direct and quadrature components. At the point of common coupling (PCC) the
46
M. Jebastin and.P. Rathika., 2016/ Advances in Natural and Applied Sciences. 10(10) Special 2016, Pages: 44-53
abc components are transform into d q component and then force the q component to zero which is used to
minimize the error.
III. Proposed Shunt Active Filter In Grid Connected Pv System:
The Active Power Filter consists of three principal parts, a three phase voltage source inverter, a DC side
capacitor and the coupling inductance Lf. The capacitor is used to store energy and the inductance is used to
smoothen the ripple present in the harmonics current injected by the active power filter. The schematic
representation of a Shunt Active Filter connected in a three phase system feeding a non-linear load is shown in
Figure 2. A three phase power supply with 415V, 50Hz, which is connected to a full bridge diode rectifier as the
nonlinear load.
Fig. 2: Schematic representation of Active Power Filter with the proposed control technique
Due to the nonlinear characteristics of the diodes, the sinusoidal current waveform for the supply is
distorted. The distorted current is fed into the reference current calculated portion to produce the desired
compensated harmonics current which is the inversed of the original harmonics in the line. The reference current
calculated algorithm is based on the instantaneous active and reactive theorem in time domain.
Voltages Va, Vb, Vc and current Ia, Ib, Ic indicate the phase voltages and currents at the load side respectively.
The active filter is connected in parallel with the load to suppress the harmonics. The shunt active filter
generates the compensating currents Ifa, Ifb, Ifc to compensate the load currents Ifa, Ifb, Ifc so as to make the
current drawn from the source as sinusoidal and balanced. The performance of the active filter mainly depends
on the technique used to compute the reference current and the control strategy followed to inject the desired
compensation current into the line.
a. Harmonics Extraction Technique:
Derivation of compensation current is the important part of active filter control. The time domain methods
are mainly used due to its speed with less calculation compared to the frequency domain methods. Instantaneous
p-q theory, one of the time domain methods is followed in this work. The details of instantaneous p-q theory are
presented here.
The p-q theory is based on α-β the transformation, and is known as the Clarke Transformation. It transforms
the three phase voltage and current into α-β stationary reference frame using the following equations:
Vα
Vβ =
!
Iα
Iβ =
!
1
0
−
√
"
−
√
"
V'
% &V( *
V)
(1)
I'
I( *
%
&
(2)
√
√
0
I)
Since in a balanced three-phase three wire system, neutral current is zero, the zero sequence current does
not exist. The power components p and q are related to the α-β voltages and currents, and can be written as,
1
Vα
p
+q- =
−Vβ
−
"
Vβ Iα
Vα Iβ
−
"
(3)
47
M. Jebastin and.P. Rathika., 2016/ Advances in Natural and Applied Sciences. 10(10) Special 2016, Pages: 44-53
where p is the instantaneous real power and q is the instantaneous imaginary power. The instantaneous real
power includes AC and DC values and can be expressed as follows:
p = p. + p0
(4)
Where12 is the alternating value of the instantaneous real power which is exchanged between the source and
load and1. is the average real power.
The alternating (AC) value of instantaneous real power is calculated back to a-b-c frame which represents
the harmonic distortion, given as reference for the current controller. The mean (DC) value of the instantaneous
real power is usually the only desirable power component. The other quantities have to be compensated using
the shunt active filter. To calculate the reference compensation currents in the α-β coordinates, the expression 3
is inverted as given below,
Vα
i∗)α
=
i∗)β
Vβ
−Vβ p0
Vβ q
(5)
Where 12 is the alternating value of the instantaneous real power which is exchanged between the source
and load and q is the instantaneous imaginary power corresponding to the power that is exchanged between the
phases of the load.
In order to obtain the reference compensation currents in the a-b-c coordinates the inverse of the
transformation is applied to eqn 2 and is given as
1
0
i∗)'
7 "
√ : i∗
)α
!i∗)( % = 6− √ − 9 ∗
(6)
i)β
6
9
∗
"
√
i))
− 8
5−
The eqn 6 gives the reference compensation current to be injected to the system.
b. Hysteresis Current Controller:
Hysteresis current controller derives the switching signals of the inverter power switches in a manner that
reduces the current error. The switches are controlled asynchronously to ramp the current through the inductor
up and down so that it follows the reference. The current ramping up and down between two limits is illustrated
in Figure 3. When the current through the inductor exceeds the upper hysteresis limit a negative voltage is
applied by the inverter to the inductor. This causes the current in the inductor to decrease. Once the current
reaches the lower hysteresis limit a positive voltage is applied by the inverter to the inductor and this causes the
current to increase and the cycle repeats.
Fig. 3: Hysteresis Current Control
The current controllers of the three phases are designed to operate independently. Hysteresis current
controller determines the switching signals to the inverter. The switching logic for phase A is formulated as
below,
If ifa< ( ifa* -HB) upper switch (G1) is OFF and lower switch (G4) is ON
If ifa< ( ifa* +HB) upper switch (G1) is ON and lower switch (G4) is OFF
48
M. Jebastin and.P. Rathika., 2016/ Advances in Natural and Applied Sciences. 10(10) Special 2016, Pages: 44-53
Where, HB is the hysteresis band and G1, G4 is the gate switches illustrated in Figure 3. In the same
fashion, the switching of phase B and C devices are derived. The Hysteresis limits relate directly to an offset
from the reference signal and are referred to as the Lower Hysteresis Limit and the Upper Hysteresis Limit.
The current is forced to stay within these limits even while the reference current is changing. Conventional
hysteresis current control operates by comparing a current error between the reference and the current being
injected by the inverter against fixed hysteresis bands. When the error exceeds the upper hysteresis band, the
inverter output is switched low, and when the error falls below the lower hysteresis band, the inverter output
switches high.
c. Voltage controller for DC voltage maintenance:
Another important task in the development of active filter is the maintenance of constant DC voltage across
the capacitor connected to the inverter. This is necessary because there is energy loss due to conduction and
switching power losses associated with the diodes and IGBTs of the inverter in active power filter, which tend to
reduce the value of voltage across the DC capacitor. Generally, PI controller is used to control the DC bus
voltage. The PI controller based approach requires precise mathematical model which is difficult to obtain.
Also, it fails to perform satisfactorily under parameter variations, non-linearity, and load disturbances.
Fig. 4: Block diagram of the current controller using a PI controller
The controller adjusts the real power (Preg) requirement for voltage regulation to keep the constant voltage
across the capacitor.
IV. Simulation Model:
Discrete,
Ts = 2e-006 s.
Va
pow ergui
Vb
Vc
RMS
Vs
415
Vabc
RMS
A
Ia
Iabc
B
Pg_V
Pg_I
a
A
Ib
b
B
C
Ic
C
c
Linear Load
A
A
B
B
C
C
Vabc
Iabc
N
a
b
c
GRID
A
A a
A
A
B b
B
B
C
C
C c
a
b
C
N1
Vabc
Iabc
B
c
A a
A a
B b
B b
C c
C c
N2
N3
A
Vabc
Iabc
B
C
a
A
b
B
c
C
+
+
i
-
-
Nonlinear Load
RMS1
c
b
PV_V
a
402.6
RMS
A
B
C
A
B
Vabc
PV
C
Breaker
A
A
B
Iabc
B
a
C
A a
B b
b
Shunt Active Filter
C
C c
c
N4
PV_I
Iabc
Fig. 5: Simulation in grid connected PV system
The grid connected PV system simulation diagram is shown in the figure 5. In this simulation the non-linear
load is connected in the grid connected PV system. The non-linear loads generate the harmonic current. By
using of shunt active power filter to reduce the harmonic current. In this shunt active power filter is based on PQ
theory calculations, PI controller, PWM techniques and Inverter circuits.
a. Simulation Result without Shunt Active Filter:
The harmonic current compensation is implemented in a grid connected PV system using a shunt active
power filter. The rms value of grid voltage of the system is set as 415V and a combination of 3-phase universal
bridge rectifier with an RLC load across it constitutes the nonlinear load which introduces the harmonics into
the system.
49
M. Jebastin and.P. Rathika., 2016// Advances in Natural and Applied Sciences. 10(10) Special 2016, Pages: 44-53
Discrete,
Ts = 2e-006 s.
Va
pow ergui
Vb
Vc
RMS
Vs
415
Va bc
RMS
A
Ia
Ia bc
B
Pg_V
Pg_I
a
A
b
B
c
C
C
Ib
Ic
Linear Load
A
A
B
B
C
C
Vabc
Iabc
N
a
b
c
GRID
A a
A
B b
A
B
A
B
C c
C
C
Vabc
Iabc
B
a
b
C
c
N1
A a
A a
B b
B b
C c
C c
N2
N3
A
Vabc
Iabc
B
a
A
b
C
+
B
c
C
+
i
-
-
Nonlinear Load
RMS1
c
b
PV_V
a
402.6
RMS
A
B
C
A
B
C
Breaker
Vabc
PV
A
A
B
I abc
B
a
C
A a
B b
b
C
Shunt Active Filter
C c
c
N4
PV_I
Iabc
Fig. 6: grid connected PV system without Shunt Active Filter
Figures 6 present simulation using Matlab/Simulink for a grid connected PV system without a shunt active
filter. And the Figures 7 present simulation results for a grid connected PV system without a shunt active filter.
In this simulation model the circuit breaker is placed in the shunt active power filter. The circuit breaker is open
condition the load current is without connected the filter current. The harmonics current is present on the load
side.
e. The waveform of harmonics in the load side is shown in the figure.
15
Current(A)
10
5
0
-5
-10
-15
0.1
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
0.16
0.17
0.18
0.19
0.2
Time(sec)
(a) Grid current
15
Current(A)
10
5
0
-5
-10
-15
0.1
0.11
0.12
0.13
0.14
0.15
0.2
Time(sec)
(b) Load current
4
3
Current(A)
2
1
0
-1
-2
-3
-4
0.1
0.11
0.12
0.13
0.14
0.15
Time(sec)
(c) Grid connected PV current
Fig. 7: Simulation results without shunt active filter
(a) Grid current
0.16
0.17
0.18
0.19
0.2
50
M. Jebastin and.P. Rathika., 2016// Advances in Natural and Applied Sciences. 10(10) Special 2016, Pages: 44-53
(b) Load current
(c) PV current
Fig. 8: THD Spectrum Analysis without shunt active filter
The grid connected PV system without shunt active filter are shown in Figures 7. It can be seen that the
harmonic has severely disturbed the grid currents. Figure 8 shows the harmonic spectrum of grid
g current without
shunt active filter. It can be found that the THD of grid current, load current and PV current are 19.58%, 15.79%
and 1.06% respectly.
b. Simulation Results with Shunt Active Filter:
Filter
Discrete,
Ts = 2e-006 s.
Va
pow ergui
Vb
Vc
RMS
415
Vs
Vabc
RMS
A
Ia
Iabc
B
Pg_V
Pg_I
a
Ib
A
B
C
b
C
c
Ic
Linear Load
A
A
B
B
C
C
Vabc
Iabc
N
a
b
c
GRID
A
A a
B b
C c
A
B
A
B
C
C
Vabc
Iabc
B
a
b
C
c
N1
A a
A a
B b
B b
C c
C c
N2
N3
A
Vabc
Iabc
B
C
a
A
b
B
c
C
+
+
i
-
-
Nonlinear Load
RMS1
RMS
c
b
PV_V
a
402.6
A
B
C
A
B
Vabc
PV
C
Breaker
A
A
Iabc
B
B
a
C
A a
B b
b
Shunt Active Filter
C
C c
c
N4
PV_I
Iabc
Fig. 9: Grid connected PV system with Shunt Active Filter
The figure 9 evaluate the Simulation model of grid connected PV system with shunt active filter using
Matlab/Simulink and the Figure 10 presents a simulation results of grid connected PV system with shunt active
filter. While the circuit breaker is closed the shunt active filter connected with circuit in order to reduce the
harmonics in grid current.
20
15
Current(A)
10
5
0
-5
-10
-15
-20
0.1
0.11
0.12
0.13
0.14
0.15
Time(sec)
(a) Grid current
0.16
0.17
0.18
0.19
0.2
51
M. Jebastin and.P. Rathika., 2016/ Advances in Natural and Applied Sciences. 10(10) Special 2016, Pages: 44-53
25
20
Current(A)
15
10
5
0
-5
-10
-15
-20
-25
0.1
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
0.2
Time(sec)
(b) Load current
4
3
Current(A)
2
1
0
-1
-2
-3
-4
0.1
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
0.2
Time(sec)
(c) PV current
Fig. 10: Simulation result with shunt active filter
(a) Grid current
(b) Load current
(c) PV current
Fig. 11: THD Spectrum Analysis with shunt active filter
Figure 11 shows the harmonic spectrum of grid current with shunt active filter. It can be seen that the
harmonic reduced the grid current. It can be found that the THD of grid current, load current and PV current are
3.90%, 3.20% and 1.02% respectly.
The grid connected PV system are assumed to be balanced and sinusoidal. The DC side of the inverter is
connected to a capacitor. The development of active filter is used to maintain constant DC voltage across the
capacitor connected to the inverter. This is necessary because there is energy loss due to conduction and
switching power losses associated with the diodes and IGBTs of the inverter in Active Power Filter, which tends
to reduce the value of voltage across the DC capacitor. Generally, PI controller is used to control the DC bus
voltage which is shown in figure 12.
52
M. Jebastin and.P. Rathika., 2016/ Advances in Natural and Applied Sciences. 10(10) Special 2016, Pages: 44-53
800
700
V o lt a g e ( V )
600
500
400
300
200
100
0
6
6.5
7
7.5
8
8.5
Time(ms)
9
4
x 10
Fig. 12: DC Capacitor voltage
In this work by using shunt active power filter, the output voltage of the inverter is controlled by changing
the switching pulses. This causes a flow of instantaneous power into the inverter which charges/discharges the
inverter DC bus capacitor. Despite the resultant DC bus voltage fluctuations, its average value remains constant
in a loss less active filter. However, the converter losses and Active Power Filter exchange causes the capacitor
voltage to vary. Hence the DC bus capacitor must be designed to achieve two goals, i.e., to comply with the
minimum ripple requirement of the DC bus voltage and to limit the DC bus voltage variation during load
transients. The THD value is the vector sum of all harmonics in the power system. The less value of THD is
most important, it is clear that less harmonics and improve power quality.
Table 1: Performance Analysis
Current(A)
Grid
PV
Load
THD%
Without Filter
19.58%
1.06%
15.79%
With filter
3.90%
1.02%
3.20%
From the results of various simulations and after the comparison of %THD for grid connected PV system
with and without filter is tabulated in Table 1. The THD value is the vector sum of all harmonics in the power
system. The less value of THD is most important, it is clear that less harmonics and improve power quality.
Conclusion:
The performance of the grid connected PV system with shunt active power filter is analyzed using
Hysteresis Current Controller technique for minimizing harmonics, in the grid connected PV system. The p-q
theory is used to generate reference current from the distorted load current, also PI controller is used to maintain
the DC side voltage nearly constant. The performance of the Hysteresis Current Controller in shunt active power
filter are verified with the simulation results. The simulation results show that the proposed technique is
effective in current harmonic filtering. Further the proposed technique has quick response time and it keeps the
good quality of filtering.
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