06-03-2013, 11:08 AM
Z-SOURCE INVERTER
Z-SOURCE.ppt (Size: 1.28 MB / Downloads: 209)
INTRODUCTION
There exist two traditional converters: voltage-source
and current-source converters.
The ac output voltage is limited below and cannot exceed. The dc-rail voltage has to be greater than the ac input voltage.
Therefore, the V-source inverter is a buck inverter for dc-to-ac power conversion and the V-source converter is a boost rectifier for ac-to-dc power conversion
An output LC filter is needed for providing a sinusoidal voltage compared with the current-source inverter, which causes additional power loss and control complexity.
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.
To overcome the problems of the traditional V-source and I-source converters, this paper presents an impedance-source power converter and its control method for implementing dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power conversion.
Common problems for both VSI & CSI
They are either a boost or a buck converter and cannot be a buck-boost converter.
The main circuits cannot be interchangeable. In other words, neither the V-source converter main circuit can be used for the I-source converter, nor vise versa.
They are vulnerable to EMI noise in terms of reliability.
Z-SOURCE CONVERTER
It employs a impedence network to couple the converter main circuit to the source
It provides a unique features that cannot be observed in traditional V and I source converters where a capacitor and inductor are used.
A two port network that consists of a split inductor L1 and L2 and capacitors C1 and C2 connected in X-shape is employed to provide an Z-source.
APPLICATION OF Z-SOURCE
A Z-source inverter for dc-ac power conversion needed for fuel-cell application.
Fuel cells usually produce a voltage that changes widely depending on current drawn from the stacks.
Z-source inverter can produce directly an ac voltage greater and less than the fuel-cell voltage.
INDUCTOR AND CAPACITOR REQUIREMENT OF THE Z-SOURCE NETWORK
Z-source network is a combination of two inductors and two capacitors.
It is a energy storage/filtering elements of Z-source inverter.
It provides a second-order filter and is more effective to suppress voltage and current ripples.
Considering additional filtering and energy storage by the capacitors, the Z-source network should require less inductance and smaller size compared with the traditional I-source inverter.
CONCLUSIONS
Z-source overcomes the conceptual and theoretical barriers and limitations of the traditional voltage-source converter and current-source converter.
Z-source inverter can boost–buck voltage, minimize component count, increase efficiency, and reduce cost.
Z-source concept can be easily applied to adjustable-speed drive (ASD) systems.