Modelling, Impedance Design, and Efficiency Analysis of Battery Assists PV Tied Quasi-Z Source Inverter

International Journal of Power Electronics and Drive System (IJPEDS)
Vol. 7, No. 3, September 2016, pp. 812~821
ISSN: 2088-8694, DOI: 10.11591/ijpeds.v7i3.10502  812
Journal homepage: http://iaesjournal.com/online/index.php/IJPEDS
Modelling, Impedance Design, and Efficiency Analysis of
Battery Assists PV Tied Quasi-Z Source Inverter
T.K.S Sathayanarayanan1
, M. Ramasamy2
, C. Bharatiraja 3
, 4
, J.L. Munda4
1
Research Scholar Anna University, Chennai, India
2
Department of Electrical and Electronics Engineering, KSR College of Technology, India
3
Department of Electrical and Electronics Engineering, SRM University, Chennai, India
4
Centre for Energy and Electric Power, Department of Electrical Engineering Tshwane University of Technology, South
Africa
Article Info ABSTRACT
Article history:
Received Nov 12, 2015
Revised Mar 24, 2016
Accepted Apr 25, 2016
The photovoltaic (PV) power cohort becoming more and more attractive in
modern power systems era to meet out the power demand in the globe.
Consequently, the extraction of maximum power and reduced power
electronics stuff for PV based power generation system research studies are
growing continuously to meet out the large power-scale/high-voltage grid-tie
demands. In this junction, to improve the efficiency of the existing PV tied
Quasi-Z source inverter (QZSI), in this paper the new attempt has proposed
here by connecting two batteries across to the QZ capacitors. When a battery
connected across each capacitor, this system can deliver power to the load
power when the PV panel outputs a variable power with fluctuations. The
battery can be charged or discharged without any extra circuit, because of the
unique impedance network of QZSI. New PWM techniques and principles
are proposed to control the new energy stored QZSI when applied to the PV
power system. They can control the inverter output power and manage the
battery power simultaneously. The operating principle and power flow of this
system are analysed. The Simulated and experimental results through using
the planned 0.2-kW prototype validate the proposed analytic model and the
design method. In addition, this paper analyzes all of the functioning states
for a QZSI and calculates the power loss.
Keyword:
Energy stored QZSI
Impedance network
Photovoltaic (PV)
Quasi-Z source inverter (QZSI)
Copyright © 2016 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
T.K.S Sathayanarayanan
Research Scholar Anna University, Chennai, India
Email: tkssujaakil@gmail.com
1. INTRODUCTION
The Z-source inverter employs a unique impedance network to couple the inverter main circuit to
the power source, which provides a novel power conversion concept [1-7]. By controlling the shoot-through
(ST) duty ratio and modulation index, the Z-source inverter can step up and down the input voltage using
passive components with improved reliability and reduced cost, thus providing unique features, such as ride-
through capability during voltage sags, reduced line harmonics, improved power factor and reliability, and
Extended output voltage rang e [2]–[5]. In a basic quasi z source inverter (QZSI), circuit the total output of a
PV system depends upon the light intensity, radiation. The output is provided not on the basis of load demand
in a conventional QZSI. Due to disadvantages in the conventional QZSI and to meet the load demand, two
batteries are connected across both the capacitors in boosting circuit. This provides the additional power
required during low intensity period and charges itself during high intensity period. QZSIs have some new
attractive advantages more suitable for application in PV systems [7]. QZSIs, as an improved ZSI, has some
new advantages well suitable for application in PV systems [14]–[20], as it draws a constant current from the
PV panel, there is no need for extra filtering capacitors and reduces switching ripples seen by the PV panels.

IJPEDS ISSN: 2088-8694 
Modelling, Impedance Design, and Efficiency Analysis of Battery Assists PV … (T.K.S Sathayanarayanan)
813
This will make the PV system simpler and will lower cost, because of two reason. One is QZSI
draws a constant current from the PV panel and thus, there is no need for extra filtering capacitors. Another
is basically ZSI features a lower component (capacitor) rating and the QZSI reduces switching ripples seen
by the PV panels. For the battery charging current control of the QZSI, there are several challenges for the
controller design as follows: (1) Both output voltage and the battery charging current of the QZSI system
with battery have to be controlled by the shoot-through state, which makes the design of a steady and fast
regulator more difficult [18, 21]. (2) Similar to the boost converter, the QZSI operating in the continuous-
condition mode, which limits the bandwidth of the controller and makes the dynamic reply of the system
sluggish, and (3).Numerous control methods to achieve fast response and small overshoot have been
proposed for the nonlinear system control [20]. Among them, nonlinear-carrier control and one-cycle control
have been found practical in some applications. However, either method has some limitations. Given battery
current control methods was seldom investigated in the literature [ ], however the inverter performance is still
suffering due to the single capacitors stability. Hence, in this paper is trying to cover the research gap by
using two capacitor batteries and New PWM techniques and principles are proposed to control the new
energy stored QZSI when applied to the PV power system. They can control the inverter output power and
manage the battery power simultaneously. The operating principle and power flow of this system are
analyzed. The Simulated and experimental results through using the planned 0.2-kW prototype validate the
proposed analytic model and the design method. In addition, this paper analyzes all of the functioning states
for a QZSI and calculates the power loss.
2. QUASI-Z SOURCE INVERTER
Both the voltage and current fed QZSIs can be controlled using methods used to control the
traditional ZSIs. Regardless of the control strategy used, for the voltage fed ZSI and QZSIs, the operation can
be listed into three modes; active, ST, and non-ST mode. In Active mode, one and only one device in each
phase leg conducts. During the active mode, the inverter is controlled in the same manner as a standard VSI.
The ST mode occurs when both switches in at least one phase conduct. The voltage across the inverter during
this mode is zero. The discontinuous modes can occur when the inductors, L1 and L2, have a small value
relative to other system parameters. In general, the discontinuous modes occurs when the inverter is gated as
if in the active mode, but one phase current is greater than or equal to the sum of the inductor currents. In this
situation, no current flows through the diode, D1. For the current fed ZSI and QZSIs, the operation can be
divided into modes in a similar manner. In the active mode one and only one upper device, and one and only
one lower device conduct. During the active mode, the inverter is controlled in the same manner as a standard
CSI. During the ST mode, the entire upper and/or all of the lower switches are gated off. During the
discontinuous mode, the switches are gated as if in an active state, but one line-to-line voltage is greater than
or equal to the sum of the capacitor voltages. When this occurs, the diode, D1, conducts and the inverter
behaves as if it is an open circuit. In the active state the current flows through the voltage source to the first
inductor then the second inductor and finally to the source via the load. The diode is forward biased and
allows the current flow.
In ST mode the both the inductors are already charged, the current flows from capacitor C1 through
the inductor L1 and from capacitor C2 through the inductor L2. For these reasons QZSI is used instead of
other ZVSIs. In addition, the intermittent and unscheduled characteristics of solar power limit the
applicability of PV systems. Therefore, addition of an energy storage system (ESS) to PV power generation
to make its output power continuous, stable, and smooth Without requirements of any additional dc/dc
converters or components, the QZSI with energy storage was first proposed for PV system in [1], [2]. By
connecting the battery in parallel with capacitor C2 [2] of the QZSI, this system is able to do the following
simultaneously.
a. Produce the desired output ac voltage to the grid/load [20]
b. Regulate the battery state of charge (SOC) and
c. Control the PV panel output power (or voltage) to maximize energy production.
But it has a big discharging power limitation due to the existence of the DCM. This limits the
inverter output power. As a counterpart, we connect the battery in parallel to the capacitor C1, leading to a
new topology.
They have common points
d. There are three power sources, PV panels, batteries, and the grid/load
e. As long as controlling two power flows, the third one automatically matches the power difference,
according to the power equation
(1)

 ISSN: 2088-8694
IJPEDS Vol. 7, No. 3, September 2016 : 812 – 821
814
The output is provided not on the basis of load demand in a conventional quasi z source inverter for the PV
system.To meet the load demand, a battery is connected across one of the capacitors in boosting circuit.
This provides the additional power required during low intensity period and charges itself during high
intensity period.
The demerits of the existing system are
– (2)
f. Based on the above equation, the Voltage stress on the capacitor which is connected across battery
increases.
g. To overcome this new circuit is proposed. In which two batteries are connected across both the
capacitors in the boosting circuit.
h. This will lessen the Voltage stress on the each capacitor.
Figure 1. Conventional QZSI Figure 2. QZSI with battery
connected across C2
Figure 3. QZSI with battery
connected across C1
3. PROPOSED TWO BATTERY CONNECTED QZSI
In The three topologies which we are going to use, for the reduction of leakage currents and the
filter used for the inverter to grid connection is presented here
In the new system the two batteries are used each across individual capacitors in the boosting circuit. This
prevents the voltage stress on individual capacitor.
Based on the power equation
(3)
We have 3 modes of operation
a.
b.
c.
Here, when both the batteries contributes towards the equation and hence the output resulting in low voltage
stress on individual battery. This will in a way make the output smooth and constant as desired with no wear
on the capacitors or the circuit.
The following table shows the status of battery and inductor current during various modes
Table 1. Mode of operation for 2 battery connected QZSI
Input and output
power
PB1 PB2 Inductor currents

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Figure 4. Proposed QZSI with B1, B2 Figure 5. Non Shoot through mode Figure 6. Shoot through mode
This circuit have two modes of operation as a normal quasi z source inverter has
a. Shoot through mode
b. Non shoot through mode
3.1. Shoot Through Mode
In mode raises when two Thrusters of same leg or any pair of the two Thyristor legs or all the
Thyristors are switched ON. Here a point arises that when an inverter is shorted there is no way of passing
infinite current to the load, but this is not happening because of existing unique impedance network between
source and inverter. During this stage the output voltage remains zero and the pre-charged inductor
discharges by decreasing its current by raising the potentials of capacitors. Here inductor L1 charges C2 and
L2 charges C1. During which the potentials across the diode gets reversed and hence it is reverse biased in
shoot through mode. The net voltage stored in both the capacitors is applied across inverter arms. The
amount of shoot through time period is 0.25T. Where T is the total time period. T0 is the shoot through time
period.
3.2. Non Shoot Through Mode
This mode is applied to operate the inverter in normal operating state, during which output voltage
appears across the inverter. The voltage across both the capacitors gets added and hence boosted voltage is
applied to the inverter circuit. This occurs for 0.75T. T1 is denoted as active mode time period or non-shoot
through time period. In this mode the capacitor delivers voltage along with inductor and both the inductors
gets pre-charged for next stage of shoot through period.
Loop equations in shoot through mode
(4)
(5)
(6)
(7)
Loop equations in non-shoot through mode
– (8)
(9)
– (10)
– (11)

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From above equations we can derive that voltage across capacitor C1 and C2 is
Difference in the capacitor voltages
Power equation of circuit is
(12)
Table 1. Comparison of Merits of Different Proposed QZSI
B1 across C1 B2 across C2 B2 Across C2 and B1 Across C1
1. Output power continuous, stable, and
smooth in spite fluctuating input by
PV panel
2. Produce the desired output ac voltage
to the grid/load
3. Regulate the battery state of charge
(SOC)
smooth in spite of fluctuating input by
PV panel
2. Produce the desired output ac voltage
to the grid/load
(SOC)
4. The discharging battery is limited to
ensure that the system
5. Operates in the CCM always operates
in the CCM during battery charging
6. A wider battery discharging power
range
7. Can be used to high voltage
smooth in spite of fluctuating input by
PV panel
2. Produce the desired output ac voltage to
the grid/load
(SOC)
4. The discharging battery is limited to
ensure that the system
5. Operates in the CCM always operates
in the CCM during battery charging
6. A wider battery discharging power
range
7. Can be used to high voltage
8. Reduces the stress on one battery
9. Better THD performance
Matrix form of the equations is after solving the transfer function of proposed two battery connected QZSI
Let[ ] .[ ] (13)
[ ] [ ] [
( ) ( )
( ) ( ) ( )] (14)
4. SIMULATION STUDY
The aforesaid energy stored QZSI and its control scheme are performed in MATLAB / SIMULINK.
The main simulation parameters are: the quasi-Z-source capacitor is C1 =C2 = 400micro F; inductor is L1 =
L2 = 50mH; the grid line voltage is 208 V, and the grid frequency is 50 Hz; the command peak dc-link
voltage, Vac is fixed as 400 V. The Simulation test is carried out in three cases, where battery connected in C1
alone, C2 alone and battery connected for both C1 and C2. For the input voltage source for the proposed QZSI
uses the P&O- MMPT based PV based 1kW structure. The simulation initially carried out with 800W PV
output with 400 V DC-link. The test is carried out for the variation of the power and voltage of the PV
output. The variation has been achieved through variation of the irradiation. All the simulation is carried out
for the same variation to test the predominance of the inverter. The figure 7 displays the Mat lab/SIMULINK
simulation Diagram for QZSI with B1 connected across C1 and B2 connected across C2. In figure 8, shows the
PWM control scheme for proposed inverter.

817
Figure 7. Simulation Diagram for QZSI with B1 connected across C1 and B2 connected across C2
Figure 8. SVPWM generated for the proposed two battery connected QZSI
The Figure 11 shows the capacitor voltage response (VC1 and VC2), when battery connected only
cross C1 and Figure 12, shows the capacitor voltage response, when battery connected only cross C2. Based
on the results, it could understand that, through the inverter stability is increased. The capacitors’ not
balanced due to the influence of the battery voltages on C1 and C2. Here, Capacitor charging and discharging
gives the boosted voltage at the inverting legs. When a battery is connected across one of the capacitor then
the voltage that appears across that capacitor is large when compared with the other capacitor. This shows
that the capacitor holds large voltage and stress on it increases. The harmonic distortion of the output at the
inverter circuit is measured and is found very high. Hence the distortion of wave is high when compared with
fundamental frequency which is shown in Figure 9 and 10.
Figure 9. QZSI VC1 and VC2 performance with B Figure 10. QZSI VC1 and VC2 performance, with
affect irradiation

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Figure 11. VC1 and VC2 performance with B across C2 Figure 12. VC1and VC2 performance with B across C1
Figure 13. VTHD spectra, when QZSI B across C2 Figure 14. VTHD spectra, when QZSI B across C1
Figure 15. Proposed two battery QZSI VC1 and VC2
Performance
Figure 16. Proposed two battery QZSI VC1 and VC2
performance with change in solar irradiation at 0,78sec
Figure 17. Line Voltage for proposed two battery
QZSI
Figure 18. VTHD spectra, Proposed two battery QZSI

819
The Figure 15 and 16 illustrations the inverter capacitors balancing for both irritation effect and
constant solar power. The live voltage profile for proposed proposed two battery QZSI and its
harmonicspectra. Due to the capacitor balancing the help of B1 and B2 for the proposed inverter is much
better then, one can compare with battery connected only in C1 and C2. The proposed QZSI performance and
capacitor voltage regulation, when two batteries are operating across the capacitors. In the proposed circuit,
the batteries are connected across both the capacitors in which the power that is deficient at the load is
supplied from the batteries. Batteries deliver power to the circuit by discharging current into the inductors
further which is dissipated to the capacitor. Here the voltage across both the capacitors is almost decreased
from the previous comparison. Hence the stress on the capacitors is decreased. In this circuit, THD value has
been decreased 7.8%, which is a large value when compared with the other two topologies. Hence the output
wave form is with less distortion, continuous. The voltage across the inverter is with less distortion. The
distortion in this wave is due to the high frequency carrier wave interference. The table shown the
comparison of qZSI, when operating single battery connected and proposed two battery connected qZSI.
Based the table data, the proposed inverter is proving the advantages all way comparing with other battery
connected topology (note, these values are measured for the maximum modulation depth of the inverter.
Table 3. Comparison of QZSI, when Operating Single Battery Connected and Proposed Two Battery -QZSI
PROPERTY QUASI B1 across C1 B2 across C2 Both B1&B2 at C1&C2
Vin 388V 394V 395V 400V
In 16.7A 18A 12A 13A
VDC 475V 471 514 490
VC1 357 370 350 390
VC2 3669 350 376 3870
Vinv 500 484 515 501
I out 16.9 17.3 15 12.36
THD % 85.72 86.28 85.63 39.88
5. EXPERIMENTAL STUDY
In the experiments, the Solar powered to the two battery connected qZSI is verified with a
laboratory prototype of 200W with constant lamp load as shown in Figure 19. Here, the DC-link voltage is
set as 80V to 45V from fixed solar plant. The soalr plant is used here as single string type with TI-C2000
microcontroller MMPT. Here the MMPT is giving the boosted function to the inverter ST. According to the
miniature level circuit the hardware parameters are calculated and used: the quasi-Z-source capacitor is C1
=C2 = 400moicoF; inductor is L1 = L2 = 2.8mH. The input voltage can be changed from range between 0 to
80 V by adjusting the solar irradiation irration through (test bench lamp arrrangement), which provides a
general bench to achieve various experiments. The two 30-V Niche-Metal battery is connected across to C1
and C2 of qZSI network. Here the PWM generation PIC MC is used for the PWM generation to control the
proposed inverter.
Figure 19. Experimental setup for qZSI
The R-load is connected to qZSI output terminals through an LC-filter. The switching frequency of
the inverter is 3 kHz. Due to the batteries (B1 and B2) are connected across both the capacitors in which the
power that is deficient at the load is supplied from the batteries. Batteries deliver power to the circuit by
discharging current into the inductors further which is dissipated to the capacitor. The batteries (B1 and B2)
ensure the reliability of the inverter, whenever the voltage tip in the solar plant. Hence the stress on the

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capacitors is decreased.The Figure 14 shows the qZSI line voltage profile. Here, the measured harmonics
spectra (THD=9.5%) for the 3kHz switching frequency. These values are measured, when the irradiation
came 30% tip from the maximum values of the solar plant. The inverter perform uninterruptedly for the
different case of solar variation. Hence the stress on the capacitors is decreased.
Figure 20. Experimental setup for qZSI Figure 21. Experimental setup for qZSI
6. CONCLUSION
The PV power generation system based on the QZSI with two battery connected topology is
proposed, and its principle and operating states are analyzed. The battery can be charged and discharged
through the QZS-network. The MPPT can be implemented through adjusting shoot-through duty ratio to
change the PV panel’s voltage. The modulation signal is controlled to ensure a constant output voltage. The
battery will balance the difference between the input power and output power. The simulated and
experimental results verified the proposed PV power generation system. A novel topology for an energy-
stored QZSI has been proposed to overcome the shortcoming of the existing solutions in PV power system.
The effectiveness of the proposed controllers were verified by both the simulation and experimental results.
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