Proc. of Int. Conf. on Control, Communication and Power Engineering 2010
A New Inverter Topology for Adjustable Speed
Drive Systems
Amitava Das1, Debasish Lahiri1, and Arup Kumar Goswami2
1
Electrical Engineering Department, TI, Kolkata, India
Email: amitavadas@ieee.org, dlsir.ti@gmail.com
2
Electrical Engineering Department, NIT - Silchar, India
Email: gosarup@gmail.com
inverters (qZSI) [4, 5]. The main advantages of qZSI
circuits are improved input profiles and a common DC
rail between the Z-source and inverter, unlike the
traditional ZSI circuits. Another approach to ZSI concept
with use of transmission line model can be found in [7]
and [8]. Present research indicates another possibility:
that is, to incorporate different passive networks at the
input to the inverters, a technique that differs from the
symmetrical LC lattice network [1, 2, 3] which is
typically used in ZSI. These alternative passive networks
have been known from many years from circuit theory.
Utilization of there will open new possibilities for onestep, energy processing Buck-Boost voltage converters.
This paper outlines the most significant alternative
passive networks (Fig. 1) and their selected applications
in inverters. Simulation results are shown for this
approach. The method involves the use of the T-source
inverter (TSI). The goal of this paper is to present a
topology similar to that of the ZSI with use of impulse
transformer with small inductive leakage. The indirect
goal is to demonstrate, with the help of above mentioned
transformer, that in the topology presented here it is
possible to increase the output voltage.
Abstract— This paper presents a new topologies of voltage
source inverters with alternative input LC networks for
adjustable speed drive system. The basic topology is known
in the literature as a Z-source inverter (ZSI). Alternative
passive networks were named as T-sources inverter (TSI).
T-source inverter has fewer reactive components in
comparison to conventional Z-source inverter. The most
significant advantage of the T-source inverter (TSI) is its use
of a common voltage source of the passive arrangement.
Simulation results for the TSI are in agreement with
theoretical prediction. PSIM software is used for simulation
studies.
Index Terms— LC network, ZSI, T-source inverter, motor
drive, quasi Z –source inverter, PWM.
I. INTRODUCTION
Fossil fuel reserve availability and environmental
concerns are now the driving forces behind the use of
new clean and renewable energy sources, such as
photovoltaic (PV) energy, wind energy, and fuel cell,
which are the input sources of alternative generation
system [1]. Moreover, the inverter plays an important role
in alternative generation system. Inverters with variable
voltage which have an input from a low voltage DC
source (eg., a PV cell) are mostly realized in the
following three basic topologies: (a) PWM VSI+DC/DC
boost converter without transformer (b) PWM VSI +
DC/DC boost converter with transformer (c) PWM CSI.
None of these solutions is fully satisfactory. Therefore
there is a continuous effort to find newer and better
solutions. A more interesting solution utilizes the Z –
source inverter. The distinguishing feature of this inverter
is its input symmetrical LC lattice network which has
four impedances. In this design, ZSI provides the single
stage voltage Buck-Boost operation, which results in
lower costs and decreased losses. The ZSI can be made
bidirectional by replacing the input diode with a
bidirectional conducting, unidirectional blocking switch
[3, 4]. There is also interesting research into NPC
(Neutral Point Clamped) ZSI circuits which has been
presented in detail in the following papers [5, 6, 7, 8,
9].These findings do not differ from those that result
when using basic symmetrical LC lattice network [1, 2,
3]. Rather, they focus on changing the topology
arrangement of the connections and don’t focus on either
changing the basic structure or improving the ZSI. To
eliminate the inconvenience of the typically Z-source
inverter, there were modifications of its basic structure
that consisted mainly in the change of primary source
position. These modifications led to quasi-Z-source
Fig 1:Passive networks alternative to basic LC lattice network
II. T – SOURCE INVERTER
The LC lattice applied in the ZSI successfully replaces
the DC-DC input stage in boost-type voltage source
inverters. To minimize the Z-source size, the couple
inductors are designed, and the two inductors are built
together on one core. To show the possibility of
extending the operation range of the ZSI, the use of a low
leakage inductance transformer and one capacitor instead
of the LC-lattice is proposed here. A high frequency
transformer based T-source inverter (TSI) is developed in
this section. The topologies of TSI using modifications
from Fig. 1(e) and Fig.1 (f) are shown in the Fig.2 (a) and
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Proc. of Int. Conf. on Control, Communication and Power Engineering 2010
In practice, the influence of leakage on inductance of
the transformer is very important. The lower the
inductance, the closer it is to theoretical dependences.
The performance of TSI depends on the precision of the
transformer design.
Fig.2 (b), while Fig.3 shows the joint equivalent circuit of
the both TSI topologies in two operational modes for
transformer ratio n: 1.
IV. MINIMIZING THE IMPACT OF LEAKAGE INDUCTANCE
If the transformer which is used to build the TSI has
excessive leakage inductance, the efficiency of the Tinverter worsens. An increase of leakage inductance
causes lower amplitude of output voltage, worse DC
voltage VDC and increase in voltage stress on the
transistors.
Regardless of the leakage inductance value the high
performance of the T-inverter can be also achieved using
additional snubber circuit shown in Fig.4. In order to
reduce the overshoot of the devices caused by large
leakage inductance an active snubber circuit as shown in
Fig.4 (a) is applied in proposed system. The use of an
active snubber ensures effective use of energy which
might otherwise be lost due to voltage spikes. Moreover
the active circuit can be used to control the charging
cycle if additional energy storage is connected to the
main capacitor of the TSI. The reduction of voltage stress
can be accomplished also by using a simple snubber with
a passive clamped circuit shown in Fig. 4(b). This circuit
is similar to clamped circuits used in bidirectional ZSI.
Two capacitors CS1, CS2 and one diode DS1 connected in
series are connected right across dc rails of the inverter
bridge. The capacitor CS2 is non inductive. The clamped
circuit is connected with the middle point of the T-source.
Due to the discharge of the capacitors, the passive
clamped circuit will reduce voltage spikes. As the voltage
vDC is lowered due to large inductive leakage, selecting a
transformer ratio larger than 1 can compensate the effect.
Fig 2:Low leakage induction transformer based T – Source inverter
topology (a) shoot-through mode (b) non shoot-through mode
The TSI topology requires a very low leakage
inductance transformer which should be made with high
precision. In such a way, the number of passive elements
is reduced because only the transformer and the capacitor
are needed. It should be noted that the function of the
input diode can be served by other power electronics
systems as well, including a diode rectifier similar to Zsource inverter.
Fig 3: Operation modes of TSI in switching time period T=T0 + TI
III. PRINCIPLES OF OPERATION
As with a conventional ZSI, the TSI can handle shoot
through states when both switches in the same phase leg
are turned on. The T-network is used instead of the LCnetwork for boosting the output voltage by inserting
shoot through states in the PWM. The TSI governing
equations can be developed for the Fig.3 using
Kirchhoff’s laws and voltage averaging [12]. The average
voltage through the transformer inductances should be
equal to zero for the switching time period T.
VL = vL = [T0 .VC + T1.(VIN − VC ) / n] / T = 0
(1)
Both capacitor voltage VC and output voltage VOUT are
functions of the shoot-through coefficient D = T0 / T.
VC
(1 − D)
T1
=
=
VIN T1 − n.T0 [1 − ( n + 1).D ]
Fig 4: (a) Active snubber (b) Passive clamped circuit
(2)
V. SIMULATIONS RESULTS
Simulations and experimental investigations of the TSI
inverter with proposed alternative passive network from
Fig.5 were performed using PSIM simulation software.
Where D satisfies a condition D<1/(n+1). Hence the
maximum value of D for TSI n>1 is smaller than for the
conventional Z-source. This is the advantage of the TSI
with n>1 in comparison with ZSI because the same
output voltage can be obtained with smaller time period
of short-circuits transistor current.
Using (2) the amplitude VDC of voltage vDC in nonshoot through states can obtain from:
VDC = VC + (VC − VIN ) / n = VIN / [1 − (n + 1).D] (3)
Fig 5: Simulation circuit setup
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© 2009 ACEEE
Proc. of Int. Conf. on Control, Communication and Power Engineering 2010
CONCLUSIONS
Simulations results confirm the reliability of the new
TSI operation. The new topology uses a transformer with
very low leakage inductance. For larger inductances, an
active snubber and a passive clamped circuit are
proposed. The input arrangement of the passive TSI
consists of three impedances, two coupled inductors, and
one capacitor. In comparison to the passive ZSI, these are
less reactive components. The most significant advantage
of the TSI is the extended possibility of manipulation of
inverter output voltage and shoot-through coefficient
using transformer turns ratio different than 1. The
presented results encourage to continue research on TSI
with different turns ratios and also demonstrate the other
unconventional ZSI topologies using transformers. The
best advantage of the TSI is the use of a common voltage
source for the passive arrangement and the converter.
This provides grounding of the configuration and solves
many problems involving electromagnetic compatibility
which are present in the ZSI.
Fig 6: DC voltage vDC on the T-source output
Fig 7: Input diode voltage vD
REFERENCES
[1] F.Z. Peng: Z-Source Inverter, Proc. of the 37th IAS Annual
Meeting, 2002, pp.775-781.
[2] F.Z Peng: Z-Source Inverter, IEEE Trans. on Industry
Applications, No.2, Vol.39, 2003, pp.504-510.
[3] Xu Haiping, F.Z. Peng, Chen Lihua, Wen Xuhui: Analysis
and design of Bi-directional Z-source inverter for
electrical vehicles, Proc. of 23rd Annual IEEE APEC’08,
2008, pp. 1252-1257.
[4] J. Anderson, F.Z. Peng: Four Quasi-Z-Source Inverters,
Proc. of IEEE PESC 2008, 15-19 June 2008, pp . 2743 –
2749.
[5] J. Anderson, F. Z.Peng,: A Class of Quasi-Z-Source
Inverters, in Proc of 43rd IAS Annual Meeting, 2008, pp.
1-7.
[6] R. Strzelecki, M. Adamowicz, D. Wojciechowski: BuckBoost Inverters with Symmetrical Passive Four-terminal
Networks. Proc. of 5th Int. Conference-Workshop CPE’07,
Gdansk, Poland, 2007, pp. 1-9.
[7] R. Strzelecki, D. Wojciechowski, M. Adamowicz, A. Wilk,
I. Mosoń: Three-phase NPC Z-source inverter,
Electrotechnical Review, No. 10, 2006, pp. 54-60.
[8] F. Z. Peng: Z-Source Networks for Power Conversion,
Proc. of 23rd Annual IEEE APEC’08, 2008, pp. 1258-1265.
[9] A.Das, S.Chowdhury, S.P.Chowdhury, A.Domijan:
“Performance analysis of Z –source inverter based ASD
system with reduced Harmonics” Proc. of IEEE Power and
Energy Society General Meeting PESGM08, USA, 2008.
pp. 1 – 7.
[10] M. Fusachika: Synthesis of a One-Port Utilizing a Lattice
Construction, IEEE Tran. on Circuit Theory, June 1963,
pp.227-234
Fig 8: T – inverter capacitor voltage
Fig 9: Output current
Fig 10: Output line to line voltage
Maximum Constant Boost Control (MCBC) strategy
using modulation reference with 3rd harmonics addition
was applied in simulations set up. The results of
simulations are shown in Fig.6 to Fig.10
Fig.6 shows the output TSI voltage vDC. The input
diode voltage vD is shown in Fig.7 and capacitor voltage
VC in Fig.8 The output currents shown in Fig.9 is
sinusoidal and proper operation of induction motor is
achieved [10].
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