flying capacitor multilevel converter voltage regulator

[danilorj]

Hi guys,

do you know someway of regulating the voltages in these three capacitors at the levels shown in the picture?

 

[schmitt trigger]

The voltage across a capacitor is derived from the charge balance equation:

I*Δt = C*Δv

solving for voltage:

Δv = I*Δt/C

So by altering the capacitor's values ratio, the amount of charging current, or the charge time, you can obtain the required voltages

 

[mtwieg]

One way is to use separate isolated DC/DC converters, but this adds cost and complexity. Another way is to control their charge by modifying the switching patterns of FETs to maintain charge balance, but this requires a much more sophisticated control scheme. Look for literature on "virtual vectors" in multilevel converters.

 

[BradtheRad]

Your schematic appears to have a lot in common with the one at this discussion:

https://www.edaboard.com/threads/314185/

Timing waveforms are displayed. You might be able to adapt these to your circuit, to obtain desired performance.

 

[D.A.(Tony)Stewart]

using Logic Level Drive Mosfets, have you considered OptoIso or differential feedback to sense voltage and control gate?

 

[kappa_am]

There are many methods to regulate capacitor voltage in a FCMLI. open-loop methods mainly implemented by PWM methods. but because of non-linearity and unbalancement, it may have malfunction. close-loop methods like predictive control,... however you need voltage feed-back, but they guarantee a good performance. this is just 3 level FCMLI and easy to deal with capacitor voltages.

P.s: Oh, I have not have noticed the voltage ratio. This is a FCMLI with unevenly distributed DC link. I am preparing a paper about this issue. However, Keith Corzine's work can help you; search for Extended operation of FCMLI.

 

[D.A.(Tony)Stewart]

Dr. Corzine and Dr. Venkataramanan each well respected Prof. and well funded on FCMLI research, but I have yet to see any details on gate drive design or commercial viable solutions. It is always left up to your imagination.

 

[kappa_am]

Dear Sunny,
The question is not about driving. what problem may be risen about gate drive?
The main issue is about 1-precharging Capacitors 2 maintaining capacitor charges constant.
and there is some theoretical solutions that can be implemented very easily even with cheap MCUs.
I would be happy if you share your mind with me. because I am interested to this application.

Thank you

 

[D.A.(Tony)Stewart]

The precharge voltage levels may be useful for efficient FCMLI, but the secret to success is how to control the gates best to achieve those with stability, efficiency and EMI control.

The big boys in VFD control, like Mitsubishi have been doing this for a long time. I would look there 1st for the ideas you need, from 10kW to >1GW IGBT controlled VFDs.

There is a huge difference between ideas in Univ. R&D and Commercial state of the art. I know this from being involved at both sides. If Carlos Lucas was still alive, he might agree.

 

[kappa_am]

OK, I name it control section. In my word, Drive section is the section which interface mCU to power switches.
This converter has many redundancy in switching ( not with above shown voltage distribution). suppose it has evenly distributed DC voltages 2VDC and VDC. in constructing VDC we have two possibilities. 10 or 01 ( just one switch gets ON). This possibilities increase rapidly by increasing cell numbers. since these redundancies provide different capacitor charging/discharging states. they can be used for DC voltage regulating purpose.


I would like to talk more about this if you are interested.