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IGBT based static Voltage stabilizer

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calvinwings

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I am using an Isolation transformer to achieve a voltage, like a buck-boost transformer but I am confused with the static voltage transformer how it works in adding the voltage and subtracted can anyone explain to me the idea so I can design the Transformer and the IGBT using DSP.

I have attached a diagram to understand the idea based on the link https://www.irjet.net/archives/V5/i1/IRJET-V5I118.pdf

\\ Capture.PNG
 

Wouldn't it be funny for authors to leave out one or two key points in their description? I suspect that's common.

The article suggests that a supplementary transformer can be switched so it adds to mains AC (boost, or waveforms in phase), or subtracts from mains AC (buck, or waveforms out of phase).

PWM adjusts the amplitude of voltage through the transformer.

The diagrams show an 'IGBT power stage' consisting only of transistor icons. It's not truly a working schematic. I imagine the real-life hardware is a full H-bridge. The job of reversing transformer polarity could be done by a DPDT switch, to select whether it's in phase with mains AC (adding both voltages), or in opposite phase (subtracting its voltage from mains). However today's trend is to prefer solid-state switching.
 

The compensating transformer has to be shorted out by the IGBT's ( or a relay ) in case of a fault too - otherwise it represents a high impedance to the load.

Under normal working conditions the IGBT sine wave PWM inverter has to carry the reflected load current in the compensating transformer - as Brad says, if it is in phase and generating output volts it adds to the mains supply, but of course extra current is drawn overall from the mains supply to achieve this - similarly if the phase is reversed then it will be bucking - reducing net volts applied to the load. These are very common in industry - especially for semiconductor processing factories - from 50kVA to 500kVA ...
 

Hello Team,

Thank you for your reply, I am sure the PWM is used to correct the voltage but I am confused with the transformer working principles since the secondary of the transformer is in series with the mainline and the corrected voltage is induced in the primary of the transformer how does the buck-boost will work how it is getting added or subtracted. for example, PWM is generating 40 V and the mainline is 180 V. Primary of the transformer will get 40V which is getting added up with mainline of 180 V in the secondary (Here I am struck what transformer to be used and how to achieve it)
 

Hi,

Assume you have a 180V sine and a 40V sine of same frequency.
Add both and get a sine of 220V .... but only if they are in phase. If one is shifted by 180° then the resulting voltage will be 140V.

Thus - even if you don't change the amplitudes - you may adjust output voltage from 140V to 220V ... by changing phase of one sine (with respect to the other).

Klaus
 

Here I am struck what transformer to be used and how to achieve it
It's just a general purpose isolation transformer, 1:1 voltage ratio according to the paper. We can however discuss if a transformer with 2:1 or even 4:1 ratio would be more appropriate for a limited voltage variation. With 1:1 transformer, the secondary IGBT bridge has to be rated for the full load current, also the transformer for the full power. So the converter effort isn't far from a transformerless SVS.
 

can anyone please help me design the transformer part, how do I add the voltage I understand the buck-boost transformer but here it is something different and I did not get exactly how to add or subtract the voltage. I also know if it is in phase it gets added up and vice-versa. my question is based on the article it says Primary of the transformer gets the voltage difference which is either added or subtracted with the supply voltage. here is the link for the video https://www.youtube.com/watch?v=avdc3RyxumM .

I am confused if I supply voltage at one end of the transformer it also gets induced in the other end of it but how it gets added up with the mainline, please check the video hope you understand it.
 

just choose a 4:1 transformer with the 40V side able to handle full load current
 

Thank you for your reply, can you please let me know how to set the transformer like the wire diagram, considered I have generated a PWM of 40V sinusoidal and I have a mainline of 180 V (How these two can be added )that will help me understand how this system works. Thank you
 

I just got my TS circuit for boost and buck mode please correct me if I am wrong ..I just need to design a feedback circuit

Boost mode.PNG
 

I thought I'd try to create a semblance of the operating concept. Here's my best effort.

A feedback voltage is produced from a crude sample-and-hold circuit. It goes to one input of the op amp. The other input gets a sawtooth wave (at any convenient carrier frequency). Duty cycle varies depending on where the feedback voltage crosses the carrier waveform.

transformer boosts under-voltage mains AC PWM w op amp feedback.png

Notice that the power supply must provide extra current, through the primary (left half) of the transformer, as well as the secondary (load portion). It's sort of like robbing Peter to pay Paul, nevertheless it seems to work to boost amplitude received at the load.

The pulses need to be filtered (at some position) in order to obtain smooth output.

The screenshot was snapped while the switch is open. The switch is a 'cheat' component which simplifies operation. An op amp opens and closes the switch.
 

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