Has anyone here ever worked with "active front end" VFDs? Line reactors' per unit impedance for an Active Front Drive is a function of full load current which means the impedance can be designed lower for larger drives. But does that mean larger drives cannot be run at lower current? I am confused.
Active Front End Drives
- Thread starter LMAO
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I don't see a problem with it.
We've built a few - they tend to be relatively expensive and relatively complex as you can see from the pic below of a 315kW unit.
I don't have the test data to hand but it was tested on probably a 30kW motor running uncoupled. There were no problems in doing that.
I don't see a problem with it.
We've built a few - they tend to be relatively expensive and relatively complex as you can see from the pic below of a 315kW unit.
I don't have the test data to hand but it was tested on probably a 30kW motor running uncoupled. There were no problems in doing that.
Correct me if I am wrong. Incoming power comes in right side into your fused contactor. Are the modules on the right side rectifiers and the four smaller ones on the left inverters?
Where are your line reactors? I can't see them. Don't see any RC filter either.
My understanding is that PWM filter for an active front end drive should look like this:
iceworm
Curmudgeon still using printed IEEE Color Books
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LM -
Give us some context. I don't expect to help, VSD system design is not even close to any of my areas of expertise. I'm hoping to learn something.
I am associated with active front end, 8000hp drives. There is testing ongoing that has installed temporary, small, series line reactors, and has changed the front-end capacitance. The drives had to be retuned for the change in front-end reactances. Other than that the drives seemed to run fine.
So, I'm thinking you may have an area of study or references that will be of interest. I'm interested in having a better understanding of the design/physics issues.
ice
Give us some context. I don't expect to help, VSD system design is not even close to any of my areas of expertise. I'm hoping to learn something.
I am associated with active front end, 8000hp drives. There is testing ongoing that has installed temporary, small, series line reactors, and has changed the front-end capacitance. The drives had to be retuned for the change in front-end reactances. Other than that the drives seemed to run fine.
So, I'm thinking you may have an area of study or references that will be of interest. I'm interested in having a better understanding of the design/physics issues.
ice
iceworm
Curmudgeon still using printed IEEE Color Books
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- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
The ones I work with do not have a series resistance in the capacitor connection, and do not have the second reactor between the capacitors and the front-end.
ice
I am not really an expert. My understanding is that AFE drives are used to mitigate harmonics and transfer regenerative power back into grid. To accomplish this, the rectifier (aka front) becomes "ACTIVE", meaning its diodes are replaced by IGBTs. This way the DC voltage can be controlled. How it is controlled is very complicated...
Anyways, again, my understanding is that you need a set of reactors, capacitors and resistors upstream to "Front". So if you look at the schematic I drew, left reactor should be about 5% impedance and the right one about 14%. Also you need some R/C in the middle that are chosen independent of load size and total time constant should be 150us.
The part confuses me is underlined; reactor impedance is given in per unit so it is a function of full load current. Then what if you run the drive at lower current? now you have lower impedance incapable of blocking harmonics?
The incoming supply in the RHS is via a fused switch (not a contactor) dollowed by a contactor - the sort of cream coloured device below the fused switch. The two tall items, also in the RHS, are LCL filters.
The LHS has four modules, all IGBT bridges. The active front end has essentially the same IGBT circuit as the output inverter so they all look the same.
I don't know if that helps but I hope it does.
Oh, OK. Any idea how LCL filters were designed? Seem to be pre-packaged; I guess VFD manufacturer supplied the LCL. LCL design is the part that confuses me.
It is. Much of what we do is system integration. We take responsibility for the system design as a whole and we will buy in components to make that system. We can, and and do, design from component level when no standard products are available. Including input filters and harmonic filters.
The LCL filter has much the same job to do as a harmonic filter.
The input IGBT active rectifier operates at a few kHz as a rule. That has to be decoupled from the supply. Maybe 6kHz modulated current being drawn from the supply could upset a few other things on that supply or customers using it.
The capacitor allows the high frequency component to flow locally and the L part stops it being taken from the supply.
We could build you one.
What size did you have in mind?
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