Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349-2260, ISSN (Print): 2349-2252
Volume 02 Issue 4 Apr 2015
Asmita M. Gaikwad
1
, Ravi R. Kundankar
2
, Dhiraj D. Shejale
3
123
Department. of Electrical Engineering, RIT, Sakharale, India.
Abstract : A new method of quasi Z- source inverter for PV system which is associated to 1-Φ residential load is preferred in this paper. qZSI is advanced technology obtained from ZSI. qZSI consists of a passive network for associating inverter to PV module and it is a one stage power conversion. As compared to other buck boost converter, quasi has some unique feature such as low component rating and draws constant DC current. In this paper, closed loop control strategy is designed for associated PV system to 1-Φ load. In the control anatomy, by managing modulation index via PIS controller, the maximum p.f and less harmonics current is supplied to load. By simulating different operating mode, the aim of tracking maximum power point is obtained. The simulation and experimental result are provided to signify the virtuosity of the system.
Keywords : PV modeling, qZSI, MPPT, Controlling method.
I.INTRODUCTION
Due to the shortage of fossil fuel and high two or single stage converters. In two stage price of fossil fuel, the entire world is moving conversion, it consists of dc-dc converter and towards effective utilization of renewable dc – ac converter. The switching devices in dc- energy sources as increase in power demand.
Solar energy is abundantly available dc converter will increases the cost and increases complexity in control system. It also renewable energy and it is absorbed easily reduces the efficiency. Therefore single stage with photovoltaic system.The V-I converter is proposed for PV system. The Zcharacteristics of PV system is nonlinear. It source inverter (ZSI) is a single stage inverter varies with irradiation and temperature. The maximum power point technique is used to to achieve the voltage both buck or boost in single stage power conversion. It is used in PV achieve maximum power from PV system.
There are many different types of algorithms system which connected to single phase load
[3]. The impedance network is employed are available for PV system to track maximum between the PV system and inverter. The power. The P&O algorithm [1] and incremental conductance algorithm [2] of proposed qZSI inverter is derived from z source inverter [4]. The block diagram of
MPPT. proposed system is shown in Fig.1. As compared to ZSI, the qZSI have some new
For PV generation, power converter technique advantages and more suitable for PV power are employed and they are characterized by generation. www.jrret.com 163

Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349-2260, ISSN (Print): 2349-2252
Volume 02 Issue 4 Apr 2015
R
PV Module
With MPPT
I
+
I pv I d
D V
Fig 1 proposed method of qZSI
The main advantages of qZSI are i) reduced component rating and less cost. ii) It draws constant current from PV panel. And iii) It reduces switching ripple in PV panel. In three phase standalone PV system, This technology is used [5].
In the following section PV modeling, incremental conductance methods for MPPT, circuit analysis of quasi impedance source inverter discussed and in last section simulation result are given.
II.PV MODELING
Solar energy is non-conventional source of energy. PV system which converts photon from sunlight in to electrical energy. Output of
PV cell is very small therefore no. of cells linked in series and parallel combination to form PV module. In Fig. (2) The equivalent circuit diagram of single PV cell is shown , which converts solar light in to electrical energy. This circuit is also called as single diode model of solar cell [6].
-
Fig 2 equivalent circuit of PV cell
By applying Kirchhoff laws,
(1)
] (2)
( ) and (3)
Where,
Diode current.
I pv
– Light generated current.
R – Series resistance.
K – Boltzmann’s constant. q – Electron charge.
T – PN- junction temperature.
A – Diode ideality factor .
Ns– no. of cell connected in series.
Open circuit voltage is given by,
] (4)
Let, and are current and voltage of pv module www.jrret.com 165

Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349-2260, ISSN (Print): 2349-2252
Volume 02 Issue 4 Apr 2015
(5)
Where, m
– Series resistance of module.
I pvm
– Generation of current across the PV module, I m
– reverse saturation current in PV module.
If there are Ns cells connected in series in the module the, then can be written as,
(6)
If there are Np cells connected in parallel in the module then,
If no. of module connected in series and parallel combination then voltage across the module,
(7)
Fig 3 Basic recommendation of incremental conductance method on a P-V Curve.
Fig.3 Shows that slope of the PV array in which at MPP, power curve is zero, left side of
MPP is +ve and right side of the MPP power curve is -ve, as it is given by basic equation below,
(at point A) (9)
(8)
Here, number of modules connected in series. number of modules connected in parallel.
III.MPPT
As referred before, incremental conductance algorithm used here for MPPT. In incremental conductance mechanism the array terminal voltage is continually managed, depending on the MPP voltage, it is built on the incremental conductance and instantaneous conductance of the PV module [7].
(at point B) (10)
(at point C) (11)
In above equation (8-10), V and I are output voltage and current of PV array respectively.
By comparing the instantaneous conductance to the incremental conductance, the MPP can be tracked as shown in flowchart Fig.4. The solar energy will be operating at the MPP, when the ratio of change in output conductance is directly proportional to the negative output conductance. www.jrret.com 166

Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349-2260, ISSN (Print): 2349-2252
Volume 02 Issue 4 Apr 2015
START dV=v(t)-v(t-1) dI=I(t)-I(t-1)
D L
1
Load
V in
C
1 C
2
No dV=0 Yes
dI/dV = -I/V dI=0
Yes
No change
Yes
Increase Duty
Cycle
No
No dI/dV>-I/V dI>0
No
Decrease Duty
Cycle
No
Decrease Duty
Cycle
No change
Yes
Increase Duty
Cycle
V(t-1)=V(t)
I(t-1)=I(t)
RETURN
Fig 4 Incremental conductance algorithm.
IV.QUASI Z-SOURCE INVERTER
The Fig. (5) and Fig. (6) Shows the Z-source inverter and Quasi Z source inverter. the main difference between the ZSI and qZSI is arrangement of inductors and capacitors in the network. qZSI has more advantages than ZSI. i) The size and rating of capacitor is reduced and ii) it draws constant direct current from
PV array due to inductor (L
1
).
C
1
L
1
D L
2
1¢ load
V in
C
2
L
2
Fig 6 Single phase ZSI.
The PV panel has very large variation in its output voltage due to irradiation level and temperature. The qZSI converts the dc voltage of PV array to boosted ac voltage.
The operation of qZSI and ZSI is same. It has two operating state shoot through state shown in Fig. (7) And non-shoot through state shown in Fig. (8).
V in
V
L1
+
I
L1
-
I in
V
C2
V
C1
-
I
C2
+
V
L2
+
+
I
L2
-
I
C1
+
V pv
I pv
-
Fig 7 qZSI in shoot through state.
In shoot through state, the devices in same leg conduct for short time i.e. in shoot through time. Due to conduction of devices in same leg the supply gets short circuited. Because of this short circuit the energy from the supply is stored in passive component in network.
Fig 5 Single phase qZSI. www.jrret.com 167

Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349-2260, ISSN (Print): 2349-2252
Volume 02 Issue 4 Apr 2015
V
C2
(15)
V in
+
V
L1
I
L1
-
I in
-
V
C1
I
C2
+
+
+
-
I
C1
V
L2
I
L2
-
+
V
0
Peak to peak to peak dc link voltage is,
)
(16)
-
Fig 8 qZSI in non-shoot through state. inverter,
And output amplitude of single phase
(17) In non-shoot through state, this stored energy in passive component in network gives back to the load. Therefore output voltage will be boosted in single stage.
Where, B is boost factor and M is modulation index.
V.CIRCUIT
ANALYSIS
In Fig. (7) and Fig. (8) Voltage polarity and current direction are shown. Let during one switching cycle T the shoot through state T
0 and non shoot through state T
1
is,
(11)
In shoot through mode,
(12)
In non-shoot through mode,
;
At steady state average voltage of inductor over one switching cycle is zero.
(13)
Fig 9 Switching scheme of qZSI.
In qZSI ac voltage can be controlled by using modulation index. Fig. (9) Shows switching scheme of qZSI by controlling shoot through duty cycle output voltage can be controlled.
Usc and –Usc are the short circuit reference and short circuit vector will be produced when carrier signal is higher than Usc and lower than –Usc.
Voltage across capacitor is,
(14)
VI.CONTROLLING METHOD
It contains two loop shown in Fig. (10). i)
Managing the power delivered to the load ii)
Maximum power.
The main purpose of proposed system is transferring the maximum power from PV system to connected load. Two loops are utilized for Qzsi, interior loop and exterior www.jrret.com 168

Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349-2260, ISSN (Print): 2349-2252
Volume 02 Issue 4 Apr 2015 loop. In interior loop inverter output current and power factor is controlled and in exterior loop capacitor voltage and output power is controlled.
A. Capacitor voltage control interior loop
In qZSI passive network, voltage across capacitor (C
1
) drops slowly. Due to this modulation index and output power is decreases as well as harmonics in output current increases. If the capacitor voltage increases switching of inverter and capacitor will be damaged.
Therefore exterior loop is proposed for capacitor voltage regulation. Capacitor voltage is directly proportional to output of PV. PI controller is used for capacitor voltage regulation. In this capacitor voltage is compared with output power and output power is controlled.
Modifying modulation index of inverter output current can be controlled. By utilizing this controller current will be injected with low
THD. The eq.(18) gives for PIS controller.
Where,
VII. SIMULATION
(18)
To demonstrate the proposed system, table I and II shows PV array and qZSI networks parameter respectively.
Fig.11 &Fig.12 shows the output voltage and current of PV array.Fig.13 Represents voltage across the capacitor (C
1
) and Fig.14 output current and voltage of inverter.
Table 1 PV array parameter at solar radiation
60
(1000W/sq.m)
L
C
I pv
V pv
4.85A
52V
P max
253W
Table 2 qZSI network parameter
1mH
1000μF
50
40
Fig 10 Control structure of proposed method
B. Current control interior loop
In this, PIS controller is used for feeding a current with unity power factor to load.
30
20
10
0
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
T i m e (sec)
Fig 11 Output voltage of PV array www.jrret.com 169

Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349-2260, ISSN (Print): 2349-2252
Volume 02 Issue 4 Apr 2015
5
4
3
2
1
0
0 0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
T i m e (Sec)
100
0
0
-10
-20
0
200
20
10
-100
-200
0
Fig 12 Output current of PV array
200
150
100
-50
-100
50
0
-150
0 0.5
1 1.5
2
T i m e (s e c)
2.5
3
Fig 13 Voltage across capacitor C
1
3.5
x 10
4
0.1
0.1
0.2
0.2
I load
0.3
V inverter
0.4
0.5
0.5
0.6
0.6
0.3
Time
0.4
0.7
0.7
Fig 14 Inverter output current and voltage
VIII. CONCLUSION
In this paper, a new method of qZSI for photovoltaic system connected to a single phase residential load was proposed. An appropriate control structure was suggested for application of qZSI in PV connected to single phase load. The control method utilizes two control loops for feeding maximum power with unity power factor, low current THD, and qZSI capacitor voltage regulation. By using shoot through duty cycle PV maximum power point tracking is employed. The proposed system feeds the PV power to the load with single stage, therefore the cost is reduced and efficiency is increased. The proposed qZSI inherits all the advantages of the ZSI and features its unique merits. The qZSI has advantages of continuous input current, reduced source stress, and lower component rating when compared to the traditional ZSI.
REFERENCES
[1] T. Esram, P. L. Chapman, "Comparison of
Photovoltaic Array Maximum Power Point
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Spec. Con/, pp. 1531-1534, 2002.
[3] P. Xu, X. Zhang, C. Zhang, R. X. Cao and
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[5] 1. Anderson, F.l. Peng, "Four Quasi-Z-
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[6] Y. Li, 1. Anderson, F. Z. Peng, D. Liu,
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