REGENERATIVE ENERGY WHILE BRAKING BY VDF
REGENERATIVE ENERGY WHILE BRAKING BY VDF
(OP)
Dear guys yesterday I have seen an equipment which sends back the regenerrative energy while braking through VFD back into the system, although it is very common in 4th quadrant dc drive application but strangely the same is not very popular in vfd.Can you guys tell me about the pros and cons of using such device especially when the energy price is going higher.
regards
regards





RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
Bill
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"Why not the best?"
Jimmy Carter
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
Keith Cress
kcress - http://www.flaminsystems.com
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
Their are other reasons. Maybe the heat thrown off from your present brake resistor adds heat to your building interior causing additional air conditioning load. Or, maybe there is a hazard associated with the having a red-hot resistor in the area.
It seems to me that the easiest way to estimate the value of the recovered energy is to put a voltage-time recorder on the existing brake resistor. Volts squared divided by the resistor ohms is watts. Divide by 1000 to get kw and multiple by the total time the brake is energized (in hours) to kwhr. That, times your cost of electric energy is the value of the braking energy.
Prepare to be disappointed on the savings! Unless your energy is very expensive, my experience is that a crane travel brake does not produce enough energy to make it pay.
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
regards
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
The cheaper way to do it is to just have a basic 6 step inverter connected to and triggered by the DC bus. When the DC bus voltage level goes higher than its design threshold, it begins firing into the line at a frequency fixed to match with (and synchronized to ) the line. This is essentially the same way your DB resistor system is working now, so the only difference is what is done with the excess energy. In the DB resistor system, it is burned off as waste heat, in the Regen system it is dumped back into the source. By the way, no need to go to China to get a cheap knock-off version with no history of usage, there is a company called Bonitron here in the US who has been making them for retrofit to existing VFDs for years. http://www.bonitron.com/o-r-m3345.html
The more robust version is a lot more sophisticated. The difference is that instead of just a simplistic 6 step inverter with an output frequency fixed at the line frequency, it has another full blown PWM inverter on the front end. The advantage is, it can not only move excess power into the source, but can also detect and correct harmonics as well so that the VFD ends up cleaning up after itself (layman's version, it's a lot more complicated than it sounds). It also has the advantage of being able to accomplish regen at virtually any level of excess energy, not just when the DC bus voltage climbs, so it can affect braking even at low loads.
So the more robust versions are essentially two back-to-back complete VFDs; all they share is the DC bus section, and the commensurate cost is reflective of that. A fully regenerative AC VFD of this type is typically twice the price of one without it. But these are not typically a retrofit device; they are an option on some high-end VFDs that are built this way from the ground-up. ABB has been doing this for a long time very successfully, along with Siemens and a number of other major manufacturers. But if you already have a VFD, then this option would require replacing it and may be a cost burden.
A third method is what is called a "common DC bus" package where you have multiple AC motors, some of which will be regenerating while others are motoring. In this scheme, nothing goes back to the line, but is used by other connected loads and thus less energy is pulled fro the line, which also saves energy. but that doesn't apply to a single motor system such as yours.
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RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
regards
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
The input bridge has an IGBT across each diode. This bridge is controlled so that the pair of diodes which are conducting at any one time have their complementary IGBT switched on. This means that if the DC bus goes "outside" of the mains, the power flow is back to the supply. No overvoltage trips, no expensive PWM control of the input bridge. The DC bus has a reduced capacitance (a few uF), so electrolytics don't dry out either. These drives are more expensive than conventional units, but the difference will certainly be much less than a "Full" AFE.
Cheers,
Mort.
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
There are Siemens products which use this technology. The PM250 power modules from the Sinamics G120 range are the standard drive version, there are distributed versions for conveyors (G120D) and also inverters and motor starters for the ET200 range.
/end sales mode/
Cheers,
Mort
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
Thanks.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
Cheers,
Mort
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: REGENERATIVE ENERGY WHILE BRAKING BY VDF
The lack of DC link capacitors creates a resonance level with high impedance supplies.
Apart from this, it is a good technology. Simple and relatively low cost compared to active front ends.