 Open Access
 Total Downloads : 186
 Authors : Neenu. V, Binu .K. Baby
 Paper ID : IJERTV6IS040690
 Volume & Issue : Volume 06, Issue 04 (April 2017)
 DOI : http://dx.doi.org/10.17577/IJERTV6IS040690
 Published (First Online): 27042017
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Adaptive Modified Hysteresis Current Controlled Grid Connected Photovoltaic Inverter
Neenu.V 1 and Binu .K.Baby 2
P.G. Scholar1, Assistant Professor2 Department of Electrical & Electronics Engineering
Thejus Engineering College, Thrissur, Kerala
Abstract Harmonics are the major power quality issues produced by the nonlinear loads. The harmonics injection will lead to generation of non sinusoidal grid current. This article intends to optimize Total Harmonic Distortion (THD) of the source current through adaptive controlled modified hysteresis current controller .which also acts as a shunt active filter (SAF). The proposed control scheme uses a combination of I cos theory, which computes the reference compensation currents to be injected by SAF and Adaptive Hysteresis Band Current Controller (AHBC) determines the switching signals of the SAF. Use of Adaptive Hysteresis Band Current Controller instantaneous switching frequency is reduced,optimized and maintained nearly constant and THD is brought to the limits specified by the standards. Effectiveness of The proposed control strategy is analyzed .and checked for various source and load conditions with MATLAB/SIMULINK.
Keywords Adaptivecontrol, Modified Hysteresis Current controller, Total Harmonic Distortion, Switching losses, Switching frequency.
frequency at any instant of time [5]. This will reduces the switching losses to one third of that of conventional hysteresis controller. Even though using the modified hysteresis controller it is insufficient to maintain current THD within the specified limits. To overcome this drawback, pulses are modified with adaptive control mechanism . Main advantage of the adaptive control is sought out Problem of variable switching frequency. The total harmonic distortion (THD) of the grid current is limited to 5%, as recommended in the IEEE 1547 standards [2].

SYSTEM CONFIGURATION AND ANALYSIS
The configuration of a PV fed adaptive hysteresis current controlled grid connected inverter is shown in Fig.

It mainly includes a pv array as a dc power source,DC DC converter including MPPT algorithms, a voltage source inverter (VSI), an output RL filter, local loads, and the utility grid.

INTRODUCTION
Sun is the major source of energy to the entire universe. The recent fall in the cost of solar photovoltaic (SPV) energy, and ever increasing prices of fossil fuels, has moved the worlds attention towards SPV energy systems. Conventionally twostage grid interfaced SPV energy systems are used, in which the first stage performs MPPT (maximum power point tracking) and the second stage is used to feed extracted energy into the grid. These two stage systems suffer from drawback of two power converters of full rating. Several configurations of grid interfaced PV farms are proposed in [1]. In gridconnected photovoltaic systems, threephase current controlled voltagesource inverters (VSIs) are often employed for power conversion, grid synchronization and control optimization [3], [4]. In addition, synchronization to grid by Phase Locked Loop (PLL). Phase Locked Loop (PLL) will tracks the measured phase voltages Ua, Ub and Uc. under balanced and unbalanced voltage conditions Proper operation is ensured by PLL. fluctuation at the dcbus capacitor Voltage was used to calculate extra power loss in inverter .using a ProportionalIntegral differential(PID)controller Corresponding phase current amplitude calculated and it was multiplied with PLL output
.This output current was added to reference compensation current in each phase. The loss in shunt active power filter is thus taken care of by three phase source and dc bus capacitor voltage becomes a self supporting one. In modified hysteresis controller only 2 switches are controlled at high
Fig. 1. Configuration of Shunt Active Power Filter
In this paper current controlled Voltage source inverter based three phase grid connected inverter with control circuit is discussed . It also acts as a shunt active power filter(SAP) and is connected in parallel with the harmonic producing loads at the Point Of Common Coupling (PCC).Shunt active power filter will generates a current which is equal and opposite to that of harmonic current drawn by the load and injects it at the point of common coupling and making the source current purely sinusoidal. the characteristics of harmonic compensation decides Filtering algorithms used for the calculation of load current harmonics. Voltage Source Inverter (VSI) and interfacing inductor together producing the Current waveform for cancelling harmonics. smoothing and isolation of high frequency componentsis achieved by the use of a inductor. Desired current waveform of the source is obtained by controlling the switches of the inverter .

Shunt Active Filter Using I Cos Algorithm
The control strategy employed for Reference current generation is I Cos algorithm. Which computes the reference compensation currents to be injected by the active filter (AF). the accuracy and response time of the filter depends on the The choice of the control algorithm . The calculation steps should be minimal to make the control circuit compact. The SAF is expected to provide compensation for the harmonic and unbalanced source load conditions. This will ensures that a balanced current will be drawn from the three phase source which will be purely sinusoidal and in phase with the three phase voltage source. So the three phase mains is required to supply only the active portion of the load current (i.e, I cos , where I is the amplitude of the fundamental load current and cos is the displacement power factor of the load). So the proposed algorithm is named as Icos algorithm. It is capable of providing 1) harmonic 2) unbalance source load compensation in conjunction with achieving unity power factor at the source side.
Fig. 2. Realization of I Cos algorithm
In Icos algorithm, only the real part of the fundamental component of the load current has to be supply by the source. Remaining parts of load current such as reactive and harmonics parts are to be supplied by the active filter. In a balanced source load condition ,the instantaneous source voltages can be represented by:
Va Vm sin(t)…………..(1)
iLa I La,h sin(ht ha )…………….(4) p
iLb I Lb,h sin(ht 120 hb )………(5) p
iLc I Lc,h sin(ht 120 hc )………..(6) p
where,
a, b, c = phases a, b, c, respectively
iL = instantaneous load current in phases a, b,c
IL, h = peak value of hth harmonic component of load current
h = phase angle of the hth harmonic component with respect to voltage
while passing through a biquad low pass filter the fundamental component of the load current get separated pass filter. During the filtering operation output of fundamental component is delayed by 90
iLfa ILa,1 sin(t 1a 90)…………(7)
iLfb ILb,1 sin(t 1b 120 90)….(8)
iLfc ILc,1 sin(t 1c 120 90)…..(9)
The real part of the fundamental component of load current is estimated as follows:
At the time of negative zero crossing of the input voltage of any one phase, say a phase , instantaneous value of fundamental component of load current is the peak value of real component of the fundamental load current. Similarly, instantaneous values of fundamental components of phase b and c [5] motor drive. At every cycle the real part of fundamental component of load current is updated .The magitude of the desired source current Is(ref ) is equal to the magnitude of real part of the fundamental component of load current .i.e., for phase a it can be Re (ILa) . The magnitude of the desired source current can be expressed as the average of the real components of the fundamental load currents in the three phases.
i.e,
Vb Vm sin(t 120)……(2)
Vc Vm sin(t 120)…….(3)
Is(ref )
Re (ILa
) Re (ILb
3
) Re (ILc )
Where ,
a, b, c = phases a, b, c, respectively
V = peak value of the instantaneous voltage
ILa cosa ILb cosb ILc cosc
3
…….(10)
m
The load current contains fundamental and harmonic components When balanced three phase supply feeds a non linear reactive load.
The DC bus voltage fluctuations are sensed and given to a PID controller .The out put of PID controller is the current which has to meet the power loss in the inverter as well as the coupling inductor. The resultant current is added to the average value of I s (ref ) in equation (4.9) above. For generating unit amplitude sine waves(in phase with source voltages) The three phase source voltages are used as templates .
they are expressed as,
i.e,
Ua 1sin t……………(11)
Ub 1sin(t 120)…..(12)
UC 1sin(t 120)…..(13)
The reference source currents multiplied with the unit amplitude templates of the phase to ground source voltages in the three phases there by getting the desired (reference) source currents in the three phases .
isa(ref ) IS (ref ) *Ua IS (ref ) sint…………..(14)
isb(ref ) IS (ref ) *Ub IS (ref ) sin(t 120)….(15)
isc(ref ) IS (ref ) *Uc IS (ref ) sin(t 120)…..(16)
The difference between the actual load currents and the desired source currents is the compensation currents .which is to be to be injected by the shunt active filter are given below
:
Fig.4.Concept of adaptive control
Figure. 4. shows the pulse width modulated current waves for phase c. When the source current icc cross the lower hysteresis band at point 1, the switch of leg c is on.similarly in the case of lower switch When the source
ia(comp)
iLa

iSa(ref )
……..(17)
current icc+ cross the lower hysteresis band at point 2, the switch of leg c is on. During the switching intervals t1 and
t2 The following equations can be written from the figure4.
ib(comp)
iLb
iSb(ref ) ……..(18)
cc
cc
di
1 (U
U )…..(20)
ic(comp)
iLc

iSc(ref )
………(19)
dt L dc S


Modified hysteresis controller with adaptive band
The main drawbacks of fixed hysteresis band method are variable switching frequency, harmonic content around the
di
cc
cc
dt
1 (U
L dc
US
……(21)
switching side band, irregularity of the modulation pulse position and heavy interference. These drawbacks will cause a high current ripples and acoustic noise. To overcome these
Consider the geometry of Figure. 4. equation can be can be written as,
undesirable effects, this work presents an adaptive modified hysteresis band control. This controller will adjusts the
di
cc t

di
ref
c t
2HB……..(22)
hysteresis bandwidth according to the reference compensator current variation, the switching frequency and THD of supply current.
dt 1
di
dt 1
diref c
cc t2
dt
dt t2 2HB…….(23)
t1 t2 tc
1 ………………..(24)
fc
Adding Equation (24) and Equation (25) and substituting Equation (26) it can be written
di
di
1 diref c
t1 cc t2 cc
0……..(25)
dt dt fc dt
Subtracting Equation (25) from Equation (24), we get


SIMULATION RESULTS


The Simulation was carried out to demonstrate the
di di
4HB t1 cc t2 cc (t1 t2 )
diref c
………(26)
effectiveness of proposed Adaptive modified hysteresis current controlled grid connected photovoltaic inverter to
dt dt dt
Substituting Equation (23) in Equation (28) gives
mitigate harmonics. The analysis mainly consists of a three phase voltage source and a three phase diode bridge rectifier with RL load. The shunt active power filter is connected to
di
4HB (t1 t2 ) cc (t1t2 )
dt
diref c
……….(27)
dt
the system through an interfacing inductor L. The values of the circuit elements used in the simulation are given in Table
Substituting Equation (22) and Equation (23) in Equation
(27) and getting equation (30)
1 U
I. The test work was simulated using MATLAB SIMULINK.
consider the three cases :
s
s
t1 t2 m……….(28)
Udc fc L
Substituting Equation (22), Equation (23) and Equation
(30) in Equation (28) gives equation (31)
1) Case I: Sinusoidal grid voltage and nonlinear local load. 2)Case II: unbalanced grid voltage and nonlinear local
load.
3) Case III: Sinusoidal grid voltage and unbalanced nonlinear local load.
2
2
0.25U L2 U
2
In Cases I ,II and III, the grid voltage is assumed to be a
HB DC 1
s m …….(29)
Where
fc L
U DC L
pure sinusoid. In three Cases, the distorted grid current is supplied with the 5th harmonic and 7th harmonic components.
fc = modulation frequency
m=dIrefc/dt is the slope of reference current wave. UDC=capacitor voltage of voltage source inverter L= Interface inductance
Us = voltage of respective phase.
In the proposed method the Hysteresis band is modulated at different points of fundamental frequency cycle and by the switching pattern of inverter is controlled. From Equation (11)it is clear that the hysteresis band is mainly depends on the system parameters. While substituting the switching frequency and there by getting the hysteresis band value. There by getting a nearly constant frequency.The main function of a Adaptive hysteresis band current controller changes the hysteresis band width according to reference current to optimize switching frequency of inverter and THD of supply current [1517].
TABLE I SYSTEM PARAMETERS
PARAMETERS Values
Source voltage 415 V(LL)
Dc Link Voltage 680V
Bridge Rectifier Three phase diode rectifier
Load 1KW, 600VAR
Interfacing Inductance 1.5mH
AcSide Resistance 1 ohm
Fig.5.load current, filter current, reference current &Compensated source current
In Figure.5.Load current, reference current and filter current , compensated source current are shown .In Figure. 6shows the
System Frequency
50HZ
response of a shunt active power filter under unbalanced
DcBus Capacitance 8000microfarad
source voltage conditions. The unbalanced source voltage conditions is obtained by giving phases Voltages of 230 Volts, 300Volts, 160 volts for phases a, b and c respectively. From the graph the shunt active power filter works well under the unbalanced source voltage condition and also getting a
purely sinusoidal source current. In Figure.7shows the response of a shunt active power filter under unbalance in load currents conditions. The unbalance in load currents is obtained by connecting a single phase diode rectifier feeding a RL load between phases a and c. From the graph the shunt active power filter works well under the unbalance in load currents and also getting a purely sinusoidal source current. In Figure.8.Load current, reference current and filter current , compensated source current for a three phase system are shown . From figure 9 GoodDC bus voltage stabilization was achieved and the voltage is maintained at 680 volts.
Fig.6.The effectiveness of the proposed shunt active power filter under unbalanced source voltage conditions (voltage imbalance in phases b and c).
(b)
Fig.7.The effectiveness of the proposed shunt active power filter under unbalanced load conditions (current imbalance in phases a
Fig.8.load current, filter current, reference current &Compensated source current for a three phase system
Figure. 9. DC bus Capacitor Voltage
III CONCLUSION
This paper proposes an Adaptive modified hysteresis current controlled grid connected photovoltaic inverter for eliminate the effects of nonlinear local loads. which uses an Adaptive modified hysteresis current controller combined with the use of I cos theory for computes the reference compensation currents to be injected by SAF . In which the switching losses are reduced to one third and also making a constant switching frequency . thereby overcoming the disadvantage of conventional and modified hysteresis controller ( variable switching frequency).By employing the Adaptive modified hysteresis current controlled grid connected photovoltaic inverter supply current THD is brought within the 5% limits as specified by the power quality standards .Here in the proposed system THD is reduced to 3.03%. Good DC bus voltage stabilization was achieved and the voltage is maintained at 680 volts. Adaptive modified hysteresis current controlled grid connected photovoltaic inverter works well under unbalanced source and load conditions also.
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