International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
Comparison between Different Control Methods for Switched
Inductor Quasi Z-Source Inverter
Gaurav Sharma1, Ankita Kosti2
1
M-Tech Student, S.R.I.T. Jabalpur (M.P), India
Assistant Professor, Dept of Electrical Engineering, S.R.I.T. Jabalpur (M.P), India
2
Abstract— This paper explores Switched Inductor (SL)
Quasi Z-source Inverter which has high boost factor and
performance when compared to other Z-Source inverters
along with three control methods: simple boost, maximum
boost and maximum constant boost. The proposed inverter
improves the input current, reduces the passive count and also
the
reliability.
The
simulations
are
done
in
MATLAB/Simulink environment by using same input voltage
ratio and output load. From different control methods
proposed, maximum constant boost provides the highest boost
factor as well as reduces passive component requirement
along with ripples.
Index terms— Duty Ratio, Inverter, Maximum Constant
Boost, Modulation Index.
I. INTRODUCTION
Fig 1 . Continuous input current q-ZSI
Voltage and current-source inverters [1], [2] are widely
used in industries for various purposes like for ac motor
drives, distributed power systems, uninterruptible power
supplies, hybrid electric vehicles etc. However, these
inverters suffer from some major problems such as a
voltage source inverter cannot have an ac output voltage
higher than dc source voltage . Moreover it can only
provide buck dc-ac power conversion. Similarly, a currentsource inverter cannot have an ac output voltage lower than
dc source voltage and hence can only provide voltage boost
dc-ac power conversion. Apart from the various advantages
reduction in noise , both buck and boost ability it also
suffers from disadvantages like input current is
discontinuous .To overcome the short comings of classical
SI [3] a class of quasi –ZSIs has been proposed [4]-[5] as
shown in fig 1.
It has the advantages such as reduced passive component
ratings and improving the input profiles by providing
continuous current .The q ZSI involves lower voltage stress
on capacitors and boost factor of classical ZSI and q ZSI
can be given the relation:
B=
Where D =
(1)
(To is the interval of shoot through state
during switching period T)
The main emphasis still lies on high efficiency, high
power density and simple structure. The concept of SL –
technique has been integrated which is totally different
from others.
260
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
The technique proposed has advantages like high power
quality, high boost factor and power inversion ability. But
despite the above advantages startup inrush current
problem occurs which causes Z- source inductors and
capacitors to resonate and generate the voltage spikes [6].
Hence here is presented SL-qZSI [7] which improves the
input current, reliability and passive components. Moreover
the shoot through current ,voltage and current stress are
lower in proposed SL-qZSI making it applicable in
different applications. Fig 2. shows the proposed topology:
A. Operating Principle :
The proposed SL-q ZSI has extra shoot through zero
state besides the six traditional active states and two zero
states as in classic ZSI. Thus the operating principle is
same to classical ZSI. For the purpose of analysis the
operating states are classified into shoot -through and nonshoot through states .
1. Nonshoot-Through State : In this state as shown in fig 3
inverter has six active states and two zero states .During
this state Din and D1are on while D2and D3 are off. L2 and
L3 are connected in series .The capacitors C1 and C2 are
charged ,while the inductors L1, L2 and L3 transfer energy
from dc voltage source to the main circuit .In this state
voltages across L2 and L3 are VL2non and VL3non . We obtain
following equations:
VL1 = VC1 - VO
VL2 = VL2_non = VC2-VL3_non
VL3 = VL3non = VC2-VL2non
VPN = VC1 + VC2
(2)
(3)
(4)
(5)
Fig 2. SL-qZSI with continuous input current
Hence from all the proposed inverters SL-q ZSI provides
the high boost factor as compared to simple ZSI .The
maximum constant boost control provides the enhanced
voltage boost and reduces the volume and the cost of the
inverter. So Maximum Constant Boost control of SL-qZSI
inverter has following advantages .
1. Switched inductor and shoot through duty ratio
provides boost factor comparatively higher.
2. Less current ripples .
3. Volume and cost of the inverter is reduced.
Fig 3.Nonshoot-through of SL-qZSI
2. Shoot-Through State: In this state as shown in fig 4. both
the upper and lower switches of the same and phase leg are
short circuit. During this state , diodes Din and D1are off,
while D2and D3 are on .The inductor L2 and L3 are
connected in parallel and store energy along with L1. The
following equations are obtained :
II. TOPOLOGY ANALYSIS
As seen in fig 2 the proposed inverter consists of three
inductors (L1, L2 and L3 ), two capacitors (C1 and C2) and
four diodes (Din,D1,D2and D3).The combination of L2L3-D1-D2-D3 acts as a switched inductor cell. The
proposed topology provides inrush current suppression
,however the inductors and capacitors in proposed inverter
still resonate. Compared with a conventional q-ZSI the
proposed inverter adds only three diodes and one inductor.
261
VL1 = -VC2 –VO
(6)
VL2 = VL3 = -VC1
(7)
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
On the other hand, we should maximize B for any given
modulation index to achieve the maximum voltage gain
[6]. The proposed method is quite similar to the
traditional carrier-based PWM control method.
Compared with the simple control method, the voltage
stress in the proposed control method is much lower,
which means that for given devices, the inverter can
be operated to obtain a higher voltage gain.
C. Maximum Constant Boost Control:
In order to reduce the volume and cost, it is
important always to keep the shoot- through duty ratio
constant. At the same time, a greater voltage boost for
any given modulation index is desired to reduce the
voltage stress across the switches. The maximum constant
boost control method achieves the maximum voltage
gain while always keeping the shoot-through duty ratio
constant. There are five modulation curves in this control
method: three reference signals, Va ,Vb, and Vc, and two
shoot-through envelope signals, Vp and Vn.
To summarize, this control method produces the
maximum constant boost while minimizing the voltage
stress. Table 1 gives the summary of different methods.
Fig 4. Shoot-through of SL-qZSI
III. ANALYSIS OF CONTROL METHODS OF SL QUASI - ZSOURCE INVERTER
A. Simple Boost Control:
This control strategy inserts shoot through in all
the PWM traditional zero states during one switching
period this maintains the six active states unchanged as
in the traditional carrier based PWM [7]. Two straight
lines are employed to realize the shoot through duty
ratio (Do). The first one is equal to the peak value of the
three-phase sinusoidal reference voltages while the other
one is the negative of the first one. Whenever the
triangular carrier signal is higher than the positive
straight line or lower than the negative straight line,
the inverter will operate in shoot-through. Otherwise it
works as a traditional PWM inverter.
Table1:
Summary of different PWM control method expressions.
B. Maximum Boost Control:
Reducing the voltage stress under a desired voltage
gain now becomes important to the control of Z source
inverter. As analyzed above, the voltage gain is defined
as MB, and the voltage stress across the switches is
BV0, therefore, to minimize the voltage stress for any
given voltage gain, we have to minimize B and
maximize M, with the restriction of that their product is
the desired value.
262
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
IV. SIMULATION AND EXPERIMENTAL VERIFICATION
Parameters used for the simulation of SL- q-ZSI are
shown in the Table 2 .
Table.2 .
Simulation Parameters
Input DC voltage
48V
Output Line –Line voltage
100 V
L1=L2=L3=L4
10mH
C1=C2
1000mF
Carrier frequency
10KHz
Fig.6.Input Current in different control methods
Lf
20mH
Cf
30uF
Resistive Load
1000W
For the analysis of performance of the different control
methods on switched inductor z-source inverter, the
comparison of the different control methods are performed
at the fixed value of modulation index 0 .8, input DC
voltage 48 V and output load of 1killowatt. Wave forms
are shown in the Figures.
Fig.7 .Voltage across C1in different methods
Fig.5. Shoot through states in different control methods
Fig.8. Laod current in different control methods
263
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 3, March 2015)
REFERENCES
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Fig 9. Shoot Through current in different methods
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V. CONCLUSION
As we can see from the results obtained that for the
same value of modulation index boost factor and gain of
maximum boost control is high as compare to others but
due to high ripple in shoot-through current and input
current, big size of inductor is required and this
disadvantage makes maximum constant boost control best
method available.
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