How does the Z-source inverter boost voltage in shoot-through mode?

[kiamzattu]

Hello Every1

I'm doing a project on PWM Z-source inverter(Forget about the voltage ratings for now). I have a basic doubt in its operation. As we all Know Z-source inverter can provide both Buck and Boost output. For a boost output (in case of 1phase H-Bridge type) we have to fire both the Thyristors of the same leg simultaneously.This is called the shoot through mode Operation of Z-Source inverters. My question is How is the Voltage boosted in this mode? in the same way for a current source inverter if v apply the shoot through mode(It is allowed in CSI) do we get boosted output? Even if the output is boosted across where do we get it? i mean in the shoot through mode of Z-source inverter the inverter bridge is short circuited just as in the Current source inverter. Even in the schematic diagram of Z-source inverter the Inverter bridge in replaced by a current source. So where do v get the Output and How is it boosted in both Z-source inverters and the CSI?

Regards
Anand

PS-Plz help as i have my project review in a couple of days and still I'm not getting the basics right.

 

[anorlunda]

ping @Tom.G can you help? Spring cleaning.

 

[Tom.G]

Here is a schematic of a Z-Source Inverter.

In place of the cross connected L and C, a conventional Inverter would have either a C between the two DC lines for filtering (yielding a Constant Voltage {CV} source), or an L in series with one of the DC lines (yielding a Constant Current {CC} source) to feed the Inverter output switches.

A normal DC-AC inverter would switch On the upper switch in one output leg and the lower switch in the other output leg. The switching frequency determining the output AC frequency, and the duty cycle determining the output voltage.

With a Constant Voltage source you have a buck converter. A Constant Current source gives you a boost converter.

A Z-Source (Constant Impedance source), as in the schematic, allows both buck and boost operation. Buck is by the usual duty cycle variation.

The magic occurs when you want to boost the output voltage. In what would normally be the dead time, both the upper and lower switches, in one or both, leg are turned on at the same time. This is called Shoot-Thru (ST), and in the usual converters often destroys the device.

With the Z-Source configuration this connects the C in parallel with the L and transfers the energy in Cs into the Ls. Since the L is in series with the incoming power, its energy is added to the input as a voltage for the next output half cycle.

A longer and more detailed explanation can be found at:
https://pdfs.semanticscholar.org/f907/973118b053aa68c273a231890049bb59af72.pdf(note: this article was published six years after the original post here asked the question... and then it took us another five years to answer it. oh well, hope it helps someone!)

For those that wish to dig deeper, the above was found with:
https://www.google.com/search?&q=z+source+inverter+working+principle
Cheers,
Tom

 

[essenmein]

Funny, I've simulated various Z source inverters, on the surface for applications in my field they are very interesting, unfortunately have not been able to convince my company and I guess our customer(s) to try this, too weird looking schematic and they don't believe it can do what the simulations say (keep the thing out of field weakening much longer, way more power etc etc).