Speed control of 3phase motor

[Ogu Reginald]

Please I need help on speed control of 3phase motor using thyristor.
Please is there anybody who has done such a project? If yes can you help me with guidelines and if possible if there is a project report help me by uploading it. Thank you.

 

[chuckey]

what you are trying to do is to build a VFD (variable frequency drive). The way to do it is to rectify the incoming mains to give you ~700V, then use three H bridge output amplifiers to handle the PWM for each phase and use a low level PWM generator that has three outputs each with the required sinewave modulation and the required different phase relationship. Changing the modulation frequency will then control the motor speed.
I do not think that thyristors are the correct device to use, as once they are turned on they do not turn off until the incoming voltage goes to zero. i.e. they are incapable of "chopping" an incoming DC supply.
Frank

 

[Ogu Reginald]

Does it mean that thyristors cannot be used for speed control of 3phase motors.
I know of VFD designs but the project assigned to me is specifically on the use of thyristors for motor speed control.

 

[albert22]

Thyristors and triacs have been used for 3 phase motor speed control. The method is different. The AC is not rectified, snubbers and inductances are used to turn off the SCR once it started conduction. You can search for cycloconverter to see how it works.
Some schemes uses GTOs that are basically thyristors that you can turn off using the gate.

 

[schmitt trigger]

As Albert mentions, SCRs can be used......... but turning them off is significantly more challenging than Mosfets or IGBTs.

How large is your motor load?

 

[goldsmith]

Please I need help on speed control of 3phase motor using thyristor.
Please is there anybody who has done such a project? If yes can you help me with guidelines and if possible if there is a project report help me by uploading it. Thank you.

Hi Ogu Reginald
You simply mentioned a three phase speed control but you didn't mention anything ! like nominal power . accuracy . with or without feedback . what kind of three phase motor ? with or without load ?

Mention them and then be hopeful for more helps !
Best Wishes
Goldsmith

 

[Ogu Reginald]

Hi Ogu Reginald
You simply mentioned a three phase speed control but you didn't mention anything ! like nominal power . accuracy . with or without feedback . what kind of three phase motor ? with or without load ?

Mention them and then be hopeful for more helps !
Best Wishes
Goldsmith

The motor is a 3phase induction motor with power of 10kVA and power factor of 0.8, feedback is included.

 

[schmitt trigger]

check this:
**broken link removed**

- - - Updated - - -

check this:
http://www.ece.ualberta.ca/~knight/variable_speed_drives/hp/cyclo.html

 

[goldsmith]

The motor is a 3phase induction motor with power of 10kVA and power factor of 0.8, feedback is included.

Hi Ogu Reginald
Well , a question ( suggestion ) why you are not attempting to use IGBT instead of SCR for this aim ? i say IGBT because you can control it more easier in this case !
For controlling the speed of scu a motor , you have to do some actions in parallel . when you are increase the voltage of the motor , you have to increase it's frequency and vice versa ( when you are increasing the amplitude by 10 percent you have to increase the frequency by 10 percent and when you are decreasing the amplitude by 10 percent then you have to decrease the amplitude by 10 percent . if you want to use SCR , you have to use at least , 12 SCR ( 6 high power SCR and 6 low power SCR ) but i highly recommend you to use IGBT instead . because you'll be able to control it pretty simple and of course with lower price and higher precision .

For feedback you have many ways . e.g encoder or perhaps tacho generator or ....

By the way , is your motor with star arrangement or delta ?
Best Wishes
Goldsmith