International Journal of Engineering Trends and Technology (IJETT) – Volume 12 Number 10 - Jun 2014
Space Vector PWM Implementation for
Z-Source Inverter
K Veera Reddy1 M Vinod2 M Niranjan3 M Durga Raj4 A V Ravi Kanth K5
Dept. of EEE, KLUniversity, Vaddeswaram, Guntur, A.P., India
Abstract: Space Vector Modulation (SVM)
Technique has become the most popular and
important PWM technique for three phase Voltage
Source Inverters. Z-Source Inverters have the
ability to boost the dc link voltage, thus increasing
the output ac voltage beyond the values reached by
conventional inverters. The enhanced ratio from ac
output voltage to dc link voltage is possible due to
an impedance network connected between the dc
power supply and the main converter. This paper
presents implementation of Space Vector
Modulation technique for Two Level Z Source
Inverter using MATLAB.
Keywords: Z source inverter, Space vector PWM,
impedance network, dc bus utilisation.
I.
INTRODUCTION
Space Vector modulation (SVM) technique was
originally developed as a vector approach to pulsewidth
modulation
(PWM)
for
three-phase
inverters[1].It is a more sophisticated technique for
generating sine wave that provides a higher voltage to
the motor with lower total harmonic distortion. It
confines space vectors to be applied according to the
region where the output voltage vector is located. A
different approach to PWM modulation is based on the
space vector representation of voltage in the α-β plane.
The α-β components are found by transformations [2][4]. The determination of switching instant may be
achieved using space vector modulation technique
based on the representation of switching vectors in α-β
plane. The Space vector modulation technique is an
advanced, computation intensive PWM technique and
is possibly the best among all the PWM techniques for
drives applications. Because of its superior
performance characteristics, it is been finding wide
spread application in recent years [5],[6]. The purpose
of this paper is to present the space vector modulation
technique and then to simplify the explanation of how
it can be implemented using software packages.
II.
FEATURES OF SPACE VECTOR PWM
The main aim of any modulation technique is to obtain
variable output having a maximum fundamental
component with minimum harmonics. During the past
years many PWM techniques have been developed for
letting the inverters to posses various desired output
characteristics to achieve the following aim:
ISSN: 2231-5381



wide linear modulation range
Less switching loss.
Lower total harmonic distortion.
The space vector modulation (SVM) technique is more
popular than conventional technique because of the
following excellent features:
o
o
o
o
o
o
o
o
o
It achieves the wide linear modulation range
associated with PWM third-harmonic
injection automatically.
It has lower base band harmonics than regular
PWM or other sine based modulation
methods, or otherwise optimizes harmonics.
15% more output voltage then conventional
modulation, i.e. better DC-link utilization.
More efficient use of DC supply voltage.
SVM increases the output capability of
SPWM without distorting line-line output
voltage waveform.
Advanced and computation intensive PWM
technique.
Higher efficiency.
Prevent un-necessary switching hence less
commutation losses.
A different approach to PWM modulation
base don space vector representation of the
voltages in the α-β plane.
III.
Space Vector concept
The concept of space vector is derived from the
rotating field of AC machine which is used for
modulating the inverter output voltage. In this
modulation technique the three phase quantities can be
transformed to their equivalent 2-phase quantity either
in synchronously rotating frame (or) stationary frame.
From this 2-phase component the reference vector
magnitude can be found and used for modulating the
inverter output. The process of obtaining the rotating
space vector is explained in the following section,
considering the stationary reference frame. Let the
three phase sinusoidal voltage component be,
Va =Vm sin wt
Vb =Vm sin (wt-2π/3)
Vc =Vmsin(wt-4π/3)
When this 3-phase voltage is applied to the AC
machine it produces a rotating flux in the air gap of the
AC machine. This rotating flux component can be
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International Journal of Engineering Trends and Technology (IJETT) – Volume 12 Number 10 - Jun 2014
represented as single rotating voltage vector. The
magnitude and angle of the rotating vector can be
found by mean of Clark’s Transformation as explained
below in the stationary reference frame. The
representation of rotating vector in complex plane is
shown in Figure 1[7]
Solving the above two simultaneous equations, one
gets:
T1 
| v sr | Ts sin(  / 3   )
Vdc sin(  / 3)
T2 
| v sr | Ts sin 
Vdc sin(  / 3)
|Vsr| represents the length of the reference Vector and
 is measured from the start of the vector.
4) Assert the appropriate control signals to affect the
required switching action.
Figure 1.Representation of Rotating Vector in
Complex Plane
A. Realization of Space Vector PWM
1) The sector in which the tip of the reference sector is
situated is to be determined from the instantaneous
phase references Va *, Vb * and Vc*




Va *, Vb *, Vc *
The three pahse voltages are transformed to
two phase using parks transformation.
vα,vβ Θ= tan-1(vβ/vα)
α = Θ- k(600) ; k such that α< 600
Sector number = k + 1
2) Computation of T1 and T2; here lookup tables are
needed to know the values of Sin (600- α) and Sin α
3) Determination of switching vectors.
Using the corresponding sector information the actual
switching time for each inverter leg is generated from
the combination of effective times and zero sequence
time. Equating volt-seconds along the α -axis:
(ІVsrІcosα)* Ts = Vdc *T1 + (Vdccos60 0) *
Ts
Equating volt-seconds along the β -axis:
(ІVsrІsinα) * Ts = (Vdcsin600) *T2
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Fig.2 Switching sequence sector 1[8]
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International Journal of Engineering Trends and Technology (IJETT) – Volume 12 Number 10 - Jun 2014
The sequences varies from one sector to the other
sector
capacitance, the order of the differential equations can
be reduced in two. The state variables of the
intermediate circuit are iz and v z. The inverter is a
two-level VSI formed by six IGBTs. The load is a
three phase RL circuit.
Fig3 Space vector pwm simulation block
IV.
Z SOURCE INVERTER
Voltage Source Inverters (VSI) controlled by Space
Vector Modulators (SVM) produce output voltages
whose fundamental amplitude is given by[9]
Vs = * Vdc
Fig.4 Z source three phase VSI
V.
SIMULATION RESULTS
√
Where M- modulation index
Vdc- DC link voltage
The maximum amplitude is given by
Vs =
√
= 0.57*Vdc when m=1
On the other hand, Z-Source Inverters (ZSI) produce
output voltages that are higher than those obtained by
the Voltage source inverter
Vzs,max > Vs,max
with the same VDc. This is the main advantage of this
configuration.
The intermediate circuit of the ZSI is composed by
two inductors, L z, two capacitors , and a diode D z,
see Fig. 2. Assuming that both inductors have the
same inductance, and both capacitors have the same
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Fig.5 Three phase voltages of Z-Source inverter
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International Journal of Engineering Trends and Technology (IJETT) – Volume 12 Number 10 - Jun 2014
vector pwm is implemented for z source inverter. The
z impedance network when used in gives desired
output voltage and harmonic content is reduced. The
space vector is implemented and corresponding results
low harmonic distortion, more dc bus utilization are
observed.
REFERENCES
Fig.6 THD Analysis of Z-source inverter voltages
CONCLUSION
The DC bus utilisation is increased by space
vector pulse width modulation. In this paper space
ISSN: 2231-5381
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