Global Journal of Advanced Engineering Technologies-Vol1-Issue1-2012
ISSN: 2277-6370
Z- Source Inverter
Simulation and Harmonic Study
Atul Kushwaha(1),
Mohd. Arif Khan(2) ,
Atif Iqbal(3) Senior Member, IEEE, and Zakir Husain(4)
Abstract - The Z-source inverter is an alternative power
conversion topology that can both buck and boost the input
voltage using passive components. With its unique structure, Zsource inverter can utilize the shoot through states to boost the
output voltage, which improves the inverter reliability greatly,
and provides an attractive single stage dc to ac conversion that is
able to buck and boost the voltage. The shoot-through duty cycle
is used for controlling the dc link voltage boost and hence the
output voltage boost of the inverter. This paper focuses on step
by step development of MATLAB/SIMULINK model of Z-source
inverter followed by their harmonics study as compared to
traditional inverters i.e. voltage and current source inverter.
Analysis and simulation results will be presented to demonstrate
that it reduces harmonics, electromagnetic interference noise and
it has low common made noise.
Index Terms - Shoot-through states, simulation, duty cycle and
Z-source inverter.
I. INTRODUCTION
T
HERE exist mainly two types of traditional inverters:
•
Voltage source (fed) inverters
•
Current source (fed) inverters
Fig.1 shows the topology of the voltage source inverter. The
input to the inverter is a dc voltage source usually with a
capacitor in parallel to absorb the high frequency ripple. The
inverter bridge consists of six switches with a freewheeling
diode in parallel with each of them.
The voltage source inverter has several limitations as listed
below:
The output voltage range is limited; the inverter cannot output
a higher voltage than the dc bus voltage. For many
applications, when the input dc voltage is not always constant,
like a fuel cell, photovoltaic array, and during voltage sag etc,
a dc/dc boost converter is often needed to boost the dc voltage
to meet the required output voltage. This increases the system
complexity and the cost and reduces the system reliability.
The two switches on the same phase leg cannot be gated on
the same time, otherwise a short-circuit will occur and destroy
the inverter. The mistrigger caused by electromagnetic
interference (EMI) is a major killer of the inverter.
For safety reasons, there is always a dead time to make sure
that the two switches will not be turned on simultaneously.
However, the dead time can cause output voltage distortion
and harmonic problems. The harmonic problem can be solved
www.gjaet.com
by implementing a current/voltage feedback control; however,
this increases the system complexity.
Fig.:1 Voltage source inverter
The current source inverter is shown in Fig. 2. A dc current
source feeds the main converter circuit, a three-phase bridge.
The dc current source can be a relatively large dc inductor fed
by a voltage source such as a battery, fuel-cell stack, diode
rectifier. The inverter bridge consists of six switches with a
reverse blocking diode in series or switches with reverse
blocking capability. Three capacitors are connected at the ac
side of the inverter to provide a leading power factor load.
The current source inverter has several limitations as listed
below:
Current source inverter is basically a boost converter. For
applications where a wide voltage range is required, extra
circuitry has to be used to obtain the required voltage.
However, this increases the circuit complexity and reduces the
efficiency as well as the reliability.
At least one switch in the upper three devices and one in the
lower three devices has to be turned on at the same time, or an
open circuit will occur and destroy the inverter.Mistrigger
caused by the EMI noise could significantly reduces the
system reliability.
To make sure that there will be no open circuit, overlap time is
often needed, which will cause output waveform distortion
and low frequency harmonic problem.
The switches of the current source converter have to block
reverse voltage that requires a series diode to be used in
combination with high-speed and high-performance transistors
such as insulated gate bipolar transistors (IGBTs).
Page 5
Global Journal of Advanced Engineering Technologies-Vol1-Issue1-2012
ISSN: 2277-6370
Fig. 4 Z-source inverter
Fig. 2. Current source inverter
Fig. 5 shows the equivalent circuit of the Z-source inverter
shown in Fig. 4 when viewed from the dc link.
II. Z SOURCE INVERTER – AN INTRODUCTION
To overcome the problems associated with the traditional
voltage source and current source inverters, this paper presents
an impedance-source inverter (abbreviated as Z-source
inverter) and its control method for implementing dc-to-ac, acto-dc, ac-to-ac, and dc-to-dc power conversion. Fig. 3 shows
the general structure of Z-source inverter.
Fig. 5 Equivalent circuit of the Z-source inverter viewed from the dc link
The inverter bridge is equivalent to a short circuit when the
inverter bridge is in the shoot-through zero state, as shown in
Fig. 6, whereas the inverter bridge becomes an equivalent
current source as shown in Fig. 7 when in one of the six active
states.
Fig. 3 General structure of the Z-source converter
The traditional voltage and current source inverter has six
active vectors (or switching states), when the dc voltage is
impressed across the load, and two zero vectors when the load
terminals are shorted through either the lower or upper three
devices. Theses total eight switching states and their
combinations have spawn many pwm control schemes.
The Z-source inverter has an additional zero vector, the shootthrough switching state, which is forbidden in the traditional
voltage and current source inverters. How to insert this shoot
through state becomes the key point of the control methods. It
is obvious that during the shoot through state, the output
terminals of the inverter are shorted and the output voltage to
the load is zero. The output voltage of the shoot-through state
is zero, which is the same as the traditional zero states,
therefore the duty ratio of the active states has to be
maintained to output a sinusoidal voltage, which means shoot
through only replaces some or all of the traditional zero states.
To describe the operating principle and control of the Z-source
inverter consider the Z-source inverter structure shown in Fig.
4.
Fig.6. Equivalent circuit of the Z-source inverter viewed from the dc link
when the inverter bridge is in the shoot-through zero state
Fig. 7 Equivalent circuit of the Z-source inverter viewed from the dc link
when the inverter bridge is in one of the eight non- shoot-through switching
states
www.gjaet.com
Page 6
Global Journal of Advanced Engineering Technologies-Vol1-Issue1-2012
As described in [1], the voltage gain of the Z-source inverter
can be expressed as,
Vac = M.B.
(1)
Where Vac is the output peak phase voltage, V0 is the input dc
voltage, M is the modulation index, and B is the boost factor,
which is determined by,
ISSN: 2277-6370
B=
/
(2)
Where T0 is the shoot-through time interval over a switching
cycle T, or (T0/T) = D0 is the shoot-through duty ratio.
The switching states sequence is shown in Fig. 8 and can be
generated through carrier-based implementation.
Fig. 8 Continuous modulation of three-phase-leg Z-source inverter
Table I shows all the fifteen switching states of a three-phaseleg Z-source inverter.
Fig. 11(a) input voltage to z source inverter
III.
SIMULINK MODEL AND RESULTS
The Matlab/Simulink software has used for the simulation of
Z source inverter. The Simulink model has shown in Fig. 9
&10. The simulation results have shown in Fig. 11 & 12.
Fig. 11(b) Filtered output voltage to z source inverter
www.gjaet.com
Page 7
Global Journal of Advanced Engineering Technologies-Vol1-Issue1-2012
ISSN: 2277-6370
Double click here to
Set the value of Vdc ,freq
modulation index (0<mi <1) & CarrierFreq (Fc)
inside this box
IL1
+ i
-
Conn2
Conn1
Conn2
Conn3
Conn3
Conn4
Conn4
Conn5
Conn6
Conn1
Current Measurement
Diode
VARIABLE LOAD
Conn5
Subsystem
Subsystem1
Vc1
+v
-
Double click here to plot
the FFT of Voltage
Voltage Measurement
Isolated Load
Continuous
powergui
Scope 2
Fig. 9 Simulink model for the Z Sourc3e inverter
g
g
G5
From 4
D
Mosfet 4
D
G3
From 2
D
G1
From
g
1
Conn 1
Mosfet 1
S
S
S
Mosfet 2
G1
G4
Conn 2
2
Conn 3
Z SOURCE INVERTER
SWITCHING SIGNAL
GENERATION CONTROL
3
+v
-
G3
G6
G5
4
Scope 6
G2
g
S
Mosfet 3
S
S
Mosfet 5
Mosfet
D
D
g
Conn 5
From 3
D
G2
From 5
G6
G4
From 1
5
g
Conn 4
Fig. 10 Simulink model for the switching selection
IV.
PERFORMANCE ANALYSIS OF Z-SOURCE
INVERTER
The method of comparing the effectiveness of modulation is
by comparing the unwanted components i.e. the distortion in
the output voltage or current waveform, relative to that of an
ideal sine wave, it can be assumed that by proper control, the
positive and negative portions of the output are symmetrical
(no DC or even harmonics). The total harmonics distortion
factor reduces to,
 vn

n =3, 5, 7..  v1
∞
THD =
∑



2
(3)
Normalizing this expression with respect to the quantity (V1)
i.e. fundamental, the weighted total harmonic distortion
(WTHD) becomes defined as
∞
WTHD =
 Vn 
 
∑
n = 3, 5, 7..  n 
V1
www.gjaet.com
Taking the advantage of MATLAB, Z source inverter control
system is built up, and the output line voltages are obtained by
simulation.
Then the total harmonics distortion (THD) rate of those
schemes is obtained by FFT method. In simulation the
switching period is taken as 0.2ms, and the inverter output
frequency is designed as 50Hz. The results of the simulation
are shown in figure 12.
Fig. 12 shows the harmonic spectrum for the filtered output
voltage for phase ‘a’. The spectrum shows that there is a
fundamental component of the output voltage obtained at 50
Hz frequency and the magnitude is 114.427 r.m.s. (161.8242
peak) voltage. The THD is 0.02% of the fundamental and the
WTHD is 0.02% of the fundamental. It shows that the quality
of the output voltage is pure sinusoidal.
2
(4)
Page 8
Global Journal of Advanced Engineering Technologies-Vol1-Issue1-2012
Fig. 12 harmonic spectrum for the phase ‘a’ filtered output voltage
V.
CONCLUSION
In this paper Z source inverter has studied and simulated
and harmonic analysis has studied. Then with the help of
Matlab/Simulink the scheme is simulated and their simulation
results are obtained. The simulation results show that the
output contains fundamental component at the 50 Hz
frequency. The output voltage spectrum shows that the output
contains single component at 50 Hz frequency. The
performance of the scheme has evaluated on the basis of
THD & WTHD and found that the output voltage quality is
good and pure sinusoidal.
VI.
REFERENCES
[1] G.K.Singh; Multi-phase induction machine drive research – a survey,
Electric Power System Research, vol. 61, 2002, pp. 139-147.
[2] G.D.Holmes, T.A.Lipo, “Pulse Width Modulation for Power Converters Principles and Practice,” IEEE Press Series on Power Engineering, John
Wiley and Sons, Piscataway, NJ, USA, 2003.
[3] M.P. Kazmierkowski, R. Krishnan and F. Blaabjerg, “Control in power
electronics- selected problems”, Academic Press, California, USA, 2002.
[4] Zhou K and Wang D, “Relationship between Space vector modulation
and Three-phase carrier based PWM – A comprehensive analysis”, IEEE
Trans. Ind. Electron., 2002,49,(1),pp 186-196.
[5] Wang FEE,” Sine-triangle versus space vector modul;ation for three-level
PWM voltage source inverters”, Proc. IEEE-IAS Annual Meeting ,
Rome,2000,pp. 2482-24888.
[6] Iqbal A , Levi, E., Jones, M. and Vukosavic, S.N., (2006), “Generalised
Sinusoidal PWM with harmonic injection for multi-phase VSIs”, IEEE
37th Power Electronics Specialist conf. (PESC) Jeju, Korea, 18-22 June
2006, CD_ROM paper No. ThB2-3, pp. 2871-2877.
[7] A.Iqbal, E.Levi, “Space vector PWM techniques for sinusoidal output
voltage generation with a five-phase voltage source inverter,” Electric
Power Components and Systems, 2006, vol. 34 no.
[8] H.A.Toliyat, M.M.Rahmian and T.A.Lipo, “Analysis and modelling of
five-phase converters for adjustable speed drive applications”, Proc. 5th
European Conference on Power Electronics and Applications EPE,
Brighton, UK, IEE Conf. Pub. No. 377, 1993, pp. 194-199.
[9] R.Shi, H.A.Toliyat, “Vector control of five-phase synchronous reluctance
motor with space vector pulse width modulation (SVPWM) for minimum
switching losses,” Proc. IEEE Applied Power Elec. Conf. APEC, Dallas,
Texas, 2002, pp. 57-63.
www.gjaet.com
ISSN: 2277-6370
[10] H.A.Toliyat, R.Shi, H.Xu, “DSP-based vector control of five-phase
synchronous reluctance motor,” IEEE Industry Applications Society
Annual Meeting IAS, Rome, Italy, 2000, CD-ROM paper no. 40_05.
[11] P.S.N.deSilva, J.E.Fletcher, B.W.Williams, “Development of space
vector modulation strategies for five-phase voltage source inverters”,
Proc. IEE Power Electronics, Machines and Drives Conf. PEMD,
Edinburgh, UK, 2004, pp. 650-655.
[12] H. W. vander Broek, H. C. Skudelny, and G. V. Stanke, “Analysis and
realization of PWM based on voltage space vectors”, IEEE Trans. Ind.
Applicat., vol. 24, no. 1, pp. 142–150, 1988.
[13] D. Grahame Holmes and Thomas A. Lipo , “ Pulse Width Modulation
For Power Converters – Principles and Practices”, IEE Press, Wiley
Publications2000.
[14] V. Blasko, “A hybrid PWM strategy combining modified space vector
and triangle comparison methods”, in IEEE PESC Conf. Rec., 1996,
pp.1872–1878.
[15] H. S. Patel and R. G. Hoft, “Generalized techniques of harmonic
elimination and voltage control in thyristor inverters: Part I—Harmonic
elimination,” IEEE Trans. Ind. Applicat., vol. 9, pp. 310–317, May/June
1973.
[16] J.O.P. Pinto, B.K. Bose, L.E. Borges da Silva and M.P. Kazmierkowski,
“A Neural Network based space vector pwm controller for voltage fed
inverter induction motor drive”, IEEE Trans, Ind. Appl. Vol. 36, No.6,
pp.1628-1636 November/December 2000.
[17] R. J. Kerkman, B. J. Seibel, D. M. Brod, T. M. Rowan, and D. Leggate,
“A simplified inverter model for on-line control and simulation”, IEEE
Trans. Ind. Applicat., vol. 27, no. 3, pp. 567–573, 1991.
[18] Simon Haykin, “Neural Networks”, ND prentice Hall, 2004.
[19] Muthuramalingam and S.Himavathi.” Performance Evaluation of a
Neural Network based General Purpose Space Vector Modulator”,
IJECSE Vol.1, No.1, pp.19-26,April 2007.
[20] K. Zhou and D. Wang, “Relationship between space vector modulation
and three phase carrier base PWM – A comprehensive analysis”, IEEE
Trans, Ind. Electr, Vol 49, No.1,pp 186-196, Feb. 2002.
[21] Bakhshai, J. Espinoza, G. Joos, and H. Jin, “A combined artificial neural
network and DSP approach to the implementation of space vector
modulation techniques, “In Conf, Rec. IEEE-IAS Annu, Meeting,. 1996
pp.934-940.
[22] H.W. Van Der Brock, H.C. Skundelny and G.V. Stanke, “Analysis and
realization of a pulsewidth modulator based on voltage space vectors’,
IEEE Trans Ind. Appl., 24. pp. 140-150, Jan/Feb 1998.
[23] O.Ogasawara, H. Akagi, and Nabel, “ A novel PWM scheme of voltage
source inverters based on space vector theory,” in proc. EPE European
conf. Power Electronics and Applications pp. 1197-1202, 1989.
[24] S.R. Bowes and Y.S. Lai, “The relationship between space vector
modulation and regular-sampled PWM, “IEE Trans. Power Electron,
Vol. 14, pp. 670-679, Sept. 1997.
ABOUT AUTHORS
(1) Atul Kushwaha, is a M. Tech. student in Deptt. of Electrical &
Electronics Engg., Krishna Institute of Engg. & Technology, Ghaziabad
INDIA, (E-mail: atulkushwaha1980@gmail.com).
(2) Mohd Arif Khan, is with Deptt. of Electrical & Electronics Engg.,
Krishna Institute of Engg. & Technology, Ghaziabad INDIA, (E-mail:
mdarif27@rediffmail.com).
(3) Atif Iqbal ,is with Deptt. of Electrical Engg., Qatar University, Doha,
QATAR. (E-mail: atif2004@gmail.com).
(4) Zakir Husain, is with Department of Electrical and Electronics
Engineering, NIT Hamirpur, INDIA. (Email: zahusain2@gmail.com)
Page 9