AFE/ISU In Drives - Regenerative Breaking.

Thans a lot Mr. JRaef.

In My case we are using ABB ISU for common DC Bus supply for all Inverters.

In each ISU - 1 Filter unit and 2 Converter Modules are installed. (510KVA*2).

1) We have more than 20 On/Off operations of 200T Main Hoist ( 510KVA) and 40T Auxiliary Hoist (250KVA) in One Hour. ISU Remains 'ON' continue.

In that case what will be energy savings ? we forget about monetary savings. but i want to know that how much energy is pumped back into the source. and one more thing that, on what calculation base, ISU capacity is designed ?

Energy SAVINGS = Zero in my opinion, because no energy is really being wasted here, so you don't have an opportunity to eliminate waste.

Energy RECOVERY = variable but only when lowering a load. Energy recovery while lowering is slightly less power than the energy consumed in lifting, likely around 90%, because now you have switching losses on both ends of the drive, not just the back end, plus the losses in the extra filtering necessary. But remember, POWER is not ENERGY, energy is power x time. So when lowering a load on a hoist, you are not going to be regenerating for the entire lowering operation time AND the power you can recover has everything to do with the potential kinetic energy of the load.

For example first lets look at a hypothetical "Sisyphean" situation situation where you lift a load, then lower the exact same load (for some unknown reason). When lifting, if it takes 400kW for 1 minute, that is 6.67kWH. When lowering, most of the time it is going to to coast, but when you want to STOP it at the desired level, it might brake for 5 seconds at the end of travel. Therefore when lowering, it regenerates 380kW for 5 seconds (.00028Hr), so the recovered energy is 1.05 kWH. The percentage of energy you have RECOVERED then is then 1.05/6.67 = 15.8% of that operation. But I doubt that is what will really take place. If you are for example lifting containers onto a ship, you recover almost NOTHING, because you have EXPENDED the energy to lift it, then the ship sails away with it and the potential energy represented by the weight of the container contents. You therefore DO NOT get the benefit of recovering even that small amount of energy. All you are going to be doing is lowering the CRANE ITSELF again, and MAYBE an empty container. So you might recover 90% of whatever potential kinetic energy exists in an empty container (the weight of the crane itself is constant either way). So if it took only 100kW to lift an EMPTY container, you can recover 90% of that for the braking time, .00028Hr x 90kW = 0.25kW, which is .3% energy recovery.

Do you see what I am getting at here? There is no simplistic way to quantify the energy recovery potential, far too many variables. But in my opinion, it's not the REASON you should use AFE drives. The reason is that regen braking is best for highly repetitive operations because it puts less strain on components of the system, which increases reliability.

Capacity is whatever the mfr states it is. If it is a 400kW drive, it can move 400kW in either direction safely.

The heat dissipated by dynamic braking resistors is your energy not recovered. The sizing programs for dynamic braking resistors could help you estimate the recovery rate of your power converter, giving you inputs for time & load, duty cycle.

For a detailed look, see this. On-line calculators are simplified, but might meet your needs for accuracy.

http://literature.rockwellautomation.com/idc/groups/literature/documents/at/pflex-at001_-en-p.pdf

You can estimate the savings of an active front end (converter) using the efficiency ratings of the equipment, which the manufacturer should be able to give you quite accurately. You can consider the published heat gain of the converter equipment as offsetting some of the heat savings when compared with resistors.

Bonus points for me, that's likely the first time in over 40 years I have had the chance to use the word "sisyphean" in a sentence!

A driven DC motor is called a generator. Are you sure the actual power at the wheels is not DC? If it is AC, then I suppose the motors may also be alternators when driven (don't ask me how). The inverters would have to have some sort of back-feed accepting network to rectify the resulting excess AC power present at the output leads of the inverter back to DC for "storage". Doesn't there have to be a phase sensing component to gate this power back to diodes?

(1) how is breaking regenerative? Seems irreversible and destructive to me. Did you mean braking?

(2) to calculate the magnitude of regenerative energy one has to have all the physics present, including mass, velocity, frictional losses, electrical inefficiency of pushing electrons back to the source, etc.

(3) the crane mass rating does not necessarily reveal the physics of the unit in motion.

Question 1) 3 phase SCR Power Converter, a set of thyristors 6 pulse (Fwd & Rev) set up for regeneration as well as motoring (a repurposed DC Drive, in essence) can charge & discharge the dc bus used for the inverters.