queries regarding ALTIVAR 58

Hello, Our chemical plant is having a crane (40/5 Te) with MH, CT, LT motion and was operated by slip ring motor (for two speeds 100% & 10%) with
rotor resistance control (may be and mechanical gear boxes) by our electrical and mechanical operators etc, i am an electronic engineer and been called to take the job 'now', as the installation is changed to an induction motor with ALTIVAR 58 drive (flux vector control sensorless)for MH and ALTIVAR 28 drive for CT, LT.
The queries are as following regarding this 1) the literature says that the 58 drive is a sensorless flux vector control but has an encoder card option for speed control? also it says that there is a series called ALTIVAR 58F which is flux vector control with or without sensor and is recomendaded for material handling operations, vertical and horizontal where high dynamics and precision etc is required, i have learnt while searching the postings that, for crane applications it is good to have a FVC drive in close loop etc, so now i dont understand that after puting the encoder card to altivar 58, will it become a close loop FVC? ALso the term "sensor" in the literature i guess, does not refer to the speed sensor, is it so ?(the 58F drive which is titled as flux vector control with sensor is also having an option card for speed feedback), so what is this sensor and how the drive can function with or without this sensor?
2)i am also not sure which type of control this drive uses in its algorithms, how can i understand is it indirect or direct torque control?
3)also the literature of ALTIVAR 58F suggests that DC injection braking is not compatible with FVC close loop and sugests dynamic braking, since we have ALTIVAR58 and there is no such incompatibility shown for DC injection braking i have a doubt regarding this as follows: for crane application which is good combination "DC injection braking, dynamic braking resistor and openloop FVC drive (our installation)" OR "FVC close loop drive (like altivar 58f) AND no DC injection braking (dynamic resistor braking in its place)" considering the safety? also why is it incompatible, please explain?
D'jay 16 mar 2005
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How about the guy that sold it to ya, then a 1800 number for senior tech support.
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D'jay, it sounds like you need to do some reading up on the operation of variable speed drives - and there is plenty of info available on the Web - but to get you going:
For your Hoist control, you should fit an encoder card wired to a suitable rotary encoder (possibly the 'sensor' you speak of) on the shaft of the hoist motor. This will allow the drive to ensure you don't get 'slip' or 'drop' when the hoist stops with a load on board.
For both the Hoist and Travel drives you will need to fit braking resistors (Dynamic Braking) to enable the drives to properly stop the crane. When the crane is decelerating (stopping) there is a large amount of energy that needs to be dissipated and if you use DC Injection the drive will likely fail and your crane will crash.
Have fun, Cameron:-)
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dhananjay wrote:

The sensor referred to is a (quadrature) encoder for measuring shaft speed.
To be honest, google the damned thing.
An altivar 58F is an IP55 Altivar 58.
I cant be bothered researching the Altivar 58 sensorless algorithm, but invariably sensorless operation is not as good as that obtained with a speed sensor. Sensorless Flux Vector Control (SFVC) algorithms have some method of estimating rotor speed. A common technique is to estimate flux by integrating the output voltage (less the IR drop). SFVC algorithms invariably have problems at very low speed, as the output voltage is is no longer large compared with the voltage drop across the IGBTs, so obtaining an accurate measure (often its an estimate) becomes tricky. Accurate values of stator resistance are required, and this can be quite a challenge, especially since its all over the show with temperature.
Not to mention the fact that an integrator becomes a right PITA at very low speeds (slow response, runs away with small errors, stuff like that). Ultimately if you need really good dynamic performance, a speed sensor is required.
A sensorless FOC set to zero speed (ie hold shaft still) will be a lot "softer" than one with a sensor - IOW if you do this, then load the shaft with a torque (eg a 1m lever with 3 fat people standing on it) the shaft will turn far more without the sensor. some sensorless drives I have played with are so bad (using little 1kW setups) that you can spin the shaft by hand (albeit with some effort). OTOH with a sensor the shaft wont budge at all.
Its not that surprising really - if you dont look at the shaft, it is rather hard to tell if it *really* moves. Whereas if you do look, its rather trivial. Problem is, encoders are expensive and fragile, and if not correctly aligned they will flog themselves to bits.
As to how the controller can use (or not use) the speed sensor, its easy. If the speed sensor input is not doing anything, the SFVCA just uses its estimated speed. OTOH if it can see the speed sensor is doing something (or perhaps you tell it the sensor is connected) then it uses that for an actual shaft speed measurement.

there isnt really any such thing as "indirect torque control"
DTC is an algorithm that runs at the IGBT switching frequency, and uses measured voltages and currents to estimate torque error, then chooses the most appropriate set of switch states to force the torque error to zero. In theory its really good, in practice very few companies use it (ABB does, and they sank many tens of millions of dollars into making it work right)
Direct and Indirect refer to the type of Field-Oriented Control implemented.
Direct FOC either measures or estimates (from I,V) flux and torque, and controls them (usually with synchonous PI controllers)
Indirect FOC regulates torque by controlling Iq and slip speed, and regulates machine flux by controlling Id (note there are 2 definitions of Id and Iq, which are exactly opposite, just for fun)
IMO stator flux oriented DFOC is far better than IFOC, because there are a hell of a lot less parameters involved - meaning fewer calculations (ie higher torque bandwidth for a given processor speed) and greatly reduced sensitivity (if it doesnt use, say, rotor resistance at all in the algorithm, then who gives a shit how bad the estimate is)

you *can* do DC injection braking with FOC, providing the software supports it. But DC injection braking, by definition, dumps all of the braking energy into the stator of the machine. If you dont have much energy to throw away, DC injection braking is nice and cheap. If you have a lot of energy to throw away it gets expensive, as the machine will cook and need replacing. A big machine has a very low surface-area-to-volume ratio, so is terrible at getting rid of heat. This thermal time constraint further hampers the dynamic response available from DCIB. DB resistors are designed to have massive SA/V ratios, and get really, really hot - many hundreds of degrees C. On a cold day, standing next to a 400kW DB running full tit is nice.
In the case of a crane, when you are lowering a load then you must dump the change in gravitational potential energy of the load, i.e. m*g*(start_height - finish_height). This is usually a LOT. If you try to use DC injection braking you will likely cook the machine and drop the load, quite possibly killing people. This is bad.

Cheers Terry
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hi, thanks for your elaborated responce regarding my queries,

.................
here i guessed that initially,but OP query originated from a product literature where the sensor(ed) FVC drive ALtivar58F (as titled), also has an option card for speed encoder, just like the ALtivar 58 which has title (as) Sensorless FVC (but it too have an option card for speed encoder),
so my conclusion was, the sensor these guys are refering to, may not be a speed sensor, as speed sensor is optional to both, (sensorless and (with) sensor FVC).
Also regarding the indirect FVC, since that estimates the controlled variables (torq, speed) indirectly, using I,V etc (position etc), it may be a sensorless FVC (as it runs on estimation) and one you said as direct FVC must be the FVC with close loop control (and may be the altivar 58F with speed encoder option card installed)
since ours is a constant torq application (as said in application guide of schneider), the controlled loop is of torq and speed variations may be tolerated and may be thats why the speed sensor is an optional entity to these FVC drives and not an integral part.
i guess that the speed encoder will be a must accessory and not an optional card when the drive will be used to synchronise with other motor speeds or used in constant speed applications.
regarding the holding a load standstill, as per company's catalogs, a FVC close loop drive (it doesnt mean a speed sensor on a sensorless FVC(altivar 58), again, the altivar 58F too have an optional speed encoder card) will be the best. Since mine is having a Altivar 58 (sensorless) and there is no speed encoder either, so i guess it is an open loop FVC and may not be used to hold the load standstill on its own.
I think thats why our original mechanical brake assembly is still used in this new installation as that is default lock (energised to open) for fail safe condition.
The FVC closeloop too may be useless if there is a power drop/cut to drive etc in such cases, mechanical brake will be useful in crane type applications, may be the FVC close loop, without mechanical brakes, is for the uninterrupted type powered plants.
thank you for arranging my thoughts in this case so fast.
i enjoyed this D'jay 18 mar 2005
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dhananjay wrote:

of course they dont supply the sensor, just a place to connect it :)
and there are probably a wide variety of add-ons - analogue I/O that sort of thing.

ultimately its a matter of semantics. A suitable field-orientation decouples the amchine into orthogonal torque- and flux-producing currents, which are then controlled independently (a-la seperately excited DC machine)
just to add to the confusion, some (not Schneider) manufacturers are pretty casual with the term "Vector Control" and often use it where its not deserved (eg if they have a V/Hz controller that uses space-vector modulation to generate the PWM)

it all depends on the dynamic response you require - if its wicked good (eg hold full load at zero speed with imperceptible shaft rotation) you will need an encoder, if its not so tricky you wont.

Yes. it will comprise 2 parts:
1) the *interface* to which the encoder attaches. This may or may not be an option (it probably is)
2) the encoder itself (and mounting hardware, interconnect cable, 6'5" electrician to wire it up, crate of beer to drink afterwards), which *you* have to obtain and connect (but is probably available as an option too, perhaps sans beer)

"closed-" and "open-loop" refer only to the presence or absence of an encoder. The drive itself will work either way. This is particularly handy when a fitted encoder breaks - the drive can figure this out, transition to open-loop control and the plant keeps on running. yay for software

only a mad bastard implements a crane without a mechanical brake. Or one who relishes losing lawsuits.

bingo.
You're welcome, I seldom get to think about drives nowadays.
Cheers Terry
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