Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

ac motor speed control

Status
Not open for further replies.

garg29

New Member
hi friends,
me want to design a three phase ac motor speed controller.........the motor ratings are: three phase, ac, 220v,50hz,960rpm,2hp ,induction motor.
please help me out guys ...how to proceed from scrap....should i use traic or igbt'sor what else. :?:
 

Styx

Active Member
you are going to have to use an IGBT 3ph H-bridge brick

It is not easy to just drop in a cct.

Basically teh speed of an AC machine (Syncrous or Induction) is related to the frequency of the 3ph power going to it

A Syncronous machine ONLY developes torque at Syncrous speed
An Induction machine DOES NOT develope torque at sycrnous speed


You will need to generate a sinewave somewhere with variable frequency (the frequency of which will relate to the speed you want)

This sine wave will then need to be phase shifted by 120deg and 240 deg to give you your 3 reference sine wave. By comparing these 3 with the voltage reference from the 3 machine terminals you can generate the PWM needed to fire the IGBT brick with the right pulse width to synthisis a SINEWAVE at the terminals. High enough switching freqency and it will be very good

You said speed controoler. Thus you wll need some form of speed-feedback. IF the rotor goes out of sync with the stator on a Syncrous machine you will loose sync - a problem with no-feedback cheep syncrous drives.

An induction machine however will just slip BUT you will NOT have speed control, the rotor angular velocity will just slip for that given torque.

For true speed control you need speed-feedback to adjust the frequency of the generated sinewave


just for a start


Synthasis of the sinewaves easisest done with an FPGA (or a PIC) with a lookup table with 120deg, 240deg offset ripple counter through the addresses at the speed related to the frequency of the motor terminal voltage frequency
 

panic mode

Well-Known Member
it's correct but i would have to say it's not worth the effort.
VFDs are so cheap nowdays...
 

Styx

Active Member
but he hasn't said what it is for and how accurate he needs to control the speed.

If it is a cheap crude approach then a V/F inverter is ideal, otherwise whole-hog

INFOMATION
 

phalanx

Member
You should have a look at Microchip's application notes. They have several motor control notes that you can use free of charge so long as you use a PIC microcontroller. I threw in some DC motor appnotes for reference because similar principals govern AC and DC motors and it is worth reading about both.

AN887 - AC Induction Motor Fundamentals:
**broken link removed**

AN900 - Controlling 3-Phase AC Induction Motors Using the PIC18F4431:
**broken link removed**

AN843 - Speed Control of 3-Phase Induction Motor Using PIC18 Microcontrollers:
**broken link removed**

AN855 - Brushless DC (BLDC) Motor Fundamentals:
**broken link removed**

AN899 - Brushless DC Motor Control Using PIC18FXX31 MCUs:
**broken link removed**
 
Status
Not open for further replies.
Top