2. OUTLINE
Introduction
Objective
Steady state operation of ZSC
Dynamic modeling of ZSC
Simulation parameter
Step response of the system
Comparison
Result
Conclusion
Future works
References
3. INTRODUCTION
The Z-source converter (ZSC) is an alternative power
conversion topology that can both buck and boost the input
voltage using passive components. It uses a unique LC
impedance network for coupling the converter main circuit to
the power source, which provides a way of boosting the input
voltage, a condition that cannot be obtained in the traditional
inverters. It also allows the use of the shoot-through switching
state, which eliminates the need for dead-times that are used in
the traditional inverters to avoid the risk of damaging the
inverter circuit.
4. OBJECTIVE
Most of the papers are on Z-source inverter but some recent
paper discussed about Z-source DC-DC converter. The
limitations of traditional power converter and Z-source
converter so far discussed are mentioned below.
Buck and Boost converter provides output voltage always in
same polarity with input.
Buck-boost and cuk converter always provide voltage polarity
reversal.
5. Contd..
The single switch ZSC model can only boost the output voltage
with same polarity within duty cycle 0 to 0.5 and cannot be
used for buck operation. As the output voltage reversal is not
possible it is not suitable for 4-quadrant operation. For duty
cycle greater than 0.5 it gives the absurd result because during
shoot-through state both switch and diode remains on
simultaneously. Figure 1 shows the single switch ZSC model.
6. Contd..
To overcome the above mentioned problem my proposed
model is given in Figure 2 which is ZSC model with two
switches. This proposed model is capable for both buck and
boost operation. For duty cycle 0 -0.5 it provides the voltage
with same polarity and above 0.5 voltage reversal is possible
which makes the converter to be used in four-quadrant
operation.
9. Steady state operation of ZSC
Operation of ZSC in continuous conduction mode (CCM)
based on two state
1.Shoot-through state (S2 is on & S1 is off)
2.Active state (S1 is on & S2 is off)
11. Contd..
For Z-source network to be symmetrical
Let the converter is in the shoot-through state for an
interval of T0 during a switching cycle T , from the
equivalent circuit in Figure we have,
13. Contd..
Similarly, if the converter is in the active state for an interval of
T1 , during the switching cycle T , from the equivalent circuit in
Figure we have,
Voltage across an inductor in steady state
28. Conclusions
Systems involving power converters are becoming more
common in applications like alternative energy sources and
hybrid electric vehicles (HEV). Efficiency, low cost and
reliability are major objectives for power electronics designers.
Classical power converter topologies still give satisfactory
results and their performances are being improved by advanced
control techniques. New topologies in power conversion are
also being introduced and give better results in some
applications. The Z-source converter (ZSC) is a new power
conversion topology that is very promising in power
conditioning of alternative energy sources and applications like
HEVs and utility interfacing. Unique buck and boost capability
of the ZSC allows a wider input voltage range and eliminates
the usage of DC/DC boost stage which improves overall
efficiency. Also, the shoot-through state is allowed and the
system reliability is improved.
29. Future works
The small signal model of ZSC derived in this research is used
for current programmed mode (CPM) and voltage mode (VM)
of ZSC. By the help of transfer function controllers are
designed for both VM and CPM control.
In this research the experimental verifications are carried out
using the simplified ZSC. The Z-source inverter (ZSI) can be
implemented by replacing the parallel switch with an inverter
bridge.
The small signal model used in this research assumed ideal
components. A new model including the non-idealities can be
derived for more accurate transfer functions.
30. References
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Gokhan Sen and Malik Elbuluk,” Voltage and Current Programmed Modes in Control of the Z-
source converter”IEEE Transaction 2008
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31. References
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