Hi Sir

[CaseyK]

I think it is a strange project.

I don't see a real world application. Is there one?

But I guess it is better, or at least more challeging, then having the whole class make a one tube GDO.

(Grid Dip Oscillator).

regards.....casey

 

[JesperMP]

Crying Baby.
This is post # 77.
Please state EXACTLY what your project is really about.
Is it about creating a VFD or VFD-like device to control an AC motor ?
Or is it about controlling something physically (by "something" I dont mean the motor it self)?
Or ... ?

 

[crying_baby]

I think your Professor, or you may be confusing PWM with PTO (Pulse Train Output).



PWM signal:

__|-|_|--|_|---|_|----|_|---|_|--|_|-|___

PTO signal:

___|----|____|---|___|--|__|-|_|--|__|---|___|----|____



Do you see the difference? The PWM signal off cycles are all of the same duration. Only the on cycles are of different durations..

By using offset PWM signals your motor will go nowhere, and your array will become shorted out due to overlapping on cycles on any single given phase...

thanks elevmike, i managed to discuss he for me to get some drives to aid me to achieve the outcome.
ok, where to start, do i get a vfd first, or programming. i decided to use a vfd to control the acmotor, 3 phase, the vfd and the ac motor is costly, as the budget control is ridiculous, . hence, i consider only a vfd and acmotor(possibly 2nd handed 1)

please advice,

 

[JesperMP]

Crying Baby,

what is it that the VFD + AC motor is supposed to control ?
Dont go out and buy anything before you have specified what the real application is !

i decided to use a vfd to control the acmotor, 3 phase, the vfd and the ac motor is costly, as the budget control is ridiculous, . hence, i consider only a vfd and acmotor

Do you mean to say that you want to go single-phase and not 3-phase ?

(post # 79 !)

 

[crying_baby]

what is it that the VFD + AC motor is supposed to control ?
Dont go out and buy anything before you have specified what the real application is !

thank you jesper
i want to control motion of ac3phase motor, is it still requires more modules to do it? yes, i want to try achieve the outcome, i aint buying yet, just started searching and keep an eye on those i going to need later

 

[JesperMP]

i want to control motion of ac3phase motor

* sigh * (post # 81)

What is it then that the MOTION of the 3 phase motor is supposed to control ?
Or, is it that you are making some kind of test stand that isnt supposed to control anything, but is rather for experimenting with AC motors ?
If so, then you need to put a load on the AC motor somehow. Making the AC motor run on empty load doesnt really say anything.

 

[crying_baby]

* sigh * (post # 81)

What is it then that the MOTION of the 3 phase motor is supposed to control ?
Or, is it that you are making some kind of test stand that isnt supposed to control anything, but is rather for experimenting with AC motors ?
If so, then you need to put a load on the AC motor somehow. Making the AC motor run on empty load doesnt really say anything.

__________________

it is noload. he professor is interested in only to c the PLC able to control the motion of the ac motor,
the motion r start, stop, forward, reverse, and brake, and possibly crude position control using open loop no feedback

the professor, wants to c that, PLC can actually control the ac3phasemotor, compared to the conventional, connect to supply and turn the switch on that kind of stuff.

to connect it to another load , will be out of the scope of the proposal .

 

[JesperMP]

The diagram that you posted, that you said that your professor dont really know what a PLC is, and that he wants to see a PLC control a 3-phase AC motor, and that he want to see only the control of the motor regardless of any load, and the talk about "PWM" makes me think that he/you are really determined to control the AC motor with the PLC acting VFD somehow.

The PLC cannot be used to mimic the control circuitry in a VFD that fires the 6 transistors in the outlet stage of the VFD.
However, the PLC can easily control a VFD by means of analog or digital signals. On the other hand, this is so trivial that I cannot see how this can be enough to fill a final project.
Alternatively, you could start to consider designing some analog electronic circuitry to control a do-it-yourself VFD (and forget the PLC in the proces). Now THAT would be worthy of a final project.

(end of post # 83).

 

[crying_baby]

The diagram that you posted, that you said that your professor dont really know what a PLC is, and that he wants to see a PLC control a 3-phase AC motor, and that he want to see only the control of the motor regardless of any load, and the talk about "PWM" makes me think that he/you are really determined to control the AC motor with the PLC acting VFD somehow.

The PLC cannot be used to mimic the control circuitry in a VFD that fires the 6 transistors in the outlet stage of the VFD.
However, the PLC can easily control a VFD by means of analog or digital signals. On the other hand, this is so trivial that I cannot see how this can be enough to fill a final project.
Alternatively, you could start to consider designing some analog electronic circuitry to control a do-it-yourself VFD (and forget the PLC in the proces). Now THAT would be worthy of a final project.

could you give me some suggestions. maby can i achieve it using a single phase acmotor? please, i cant capsize everything now...

i talk'd to the professor today, and he allows me to get a vfd, instead of the idea to fire the inverters to drive the ac3phase motor.

please enlighten me

 

[twbtxnca]

What school are you going to? Why does your Professor want to see a plc control a vfd? Sounds strange to me.
Regards,
Tom

 

[crying_baby]

tom, i whispered u plz check ur box

 

[crying_baby]

What school are you going to? Why does your Professor want to see a plc control a vfd? Sounds strange to me.
Regards,
Tom

electrical engineering.

i wish i can work something out .. i dun want to regret taking this proposal.
but.. there isnt any hope so far. . can any1 kind enough to suggest so that it realli a working proposal..

 

[elevmike]

Crying baby,

You need to do a LOT of reading.. Try downloading a manual.
http://web2.automationdirect.com/static/manuals/gs1m/gs1m.html

You can search ebay for "ac drive" to find a used drive.

Also search the form for the threat titled "learning by doing" read the entire thread, and you'll get a better idea of what you need to do to meet your requirements....

 

[crying_baby]

thank you. elevmike.

 

[twbtxnca]

This is the PM he sent me. I think all of jespers many replys have fallen on deaf ears.
In reply YES! a vfd can control a 3 phase motor that is what all of these fine people have been telling you. YES! a vfd does have some control of its on.
Regards,
Tom
jesper I must use one of your statements *sigh*

dear, mr twi,

do you mean that a vfd can control a ac3phase motor? without a pLC itself? is vfd a PLC module?

please, i m getting more desperate. i didnt know this topic spells doom.