from the Automation List department...
Speed control of induction motor using pwm techniques
Application Questions and Problems topic
Posted by nimi s anand on 27 May, 2003 - 4:28 pm
Dear sir,

We are doing a pjt on the speed control of IM using pwm techniques. We have used speed encoder to detect the speed of the IM. the speed encoder we are using is MoC7811. we have searched the net for its details but went in vain. Also we would like to know details of pwm inverter which uses IGBT as its switches. The following is the details of the project.

This project deals with the innovative method of speed control of induction motor using sinusoidal PWM technique using PC. The basic idea behind this project is to compare the speed of the motor with the speed of the reference voltage and if any change, can be corrected by the generation of PWM pulses corresponding to the desired speed. These PWM pulses are then fed to an pulse modulated inverter whose AC output given to the motor controls the speed and runs the motor at the desired speed. The unique feature of this project is the implementation of closed loop system. The advantage of this method is the reduction of harmonics, high starting torque and smooth speed control. Hence this technique can be used for industrial drives and variable speed drives.

Hope u could help us out.

With regards, nimi

Posted by Vikas Meshram on 28 May, 2003 - 11:58 am
Hi nimi

Do you want the data about the MOC7811? But there is other way to test the encoder as given below. Many encoder have wire color code marked on the encoder itself. If VCC and ground is marked on the encoder then you can easily check the other lines. Usually encoder has eight lines two are power lines and other six for A,A*,B,B*,I,I*. I stands for Index pulse you may not need this. A and A* are inverted signal of each other. B and B* are also same. A and B signal are 90 degree phase shifted to each other. You can apply the power and ground and figure out the signal relationships on CRO.

As for as inverter is concerned you can visit for IGBT inverters. You will get lot of information regarging the motor control. IR2110 the high side driver widely used for MOSFET as well as IGBT.

I hope this helps.

If you need information you can contact me on my email.

Vikas Meshram

Posted by yogesh on 28 May, 2003 - 11:17 pm
Dear nimi,

plz visit
The component you are looking for is Motorola make and after accessing this link you need to register for getting price and details.

I will be thankful if you give more details about generating PWM using PC.


Posted by Ganesh on 19 August, 2003 - 9:31 am
Dear Sir,
i am also doing project on speed control of 3-phase IM using Microcontroller 80C552. i am using
tachogenerator for feedback. i have also made pulses using sinusoidal technique.i have used 120 conduction mode.
first i have made 3- phase rectifier and inverter,
between micorocontroller and inverter gate i have used optocoupler(MCT2E) and schimitt- trigger ic 7411.
but, when i had connected inverter to supply voltage, on 28v all mosfet burn out.
what may be the problem ,can u tell me.
waiting for ur reply.....

Posted by Fred Townsend on 20 August, 2003 - 12:08 pm
Sounds like you had a successful smoke test. You haven't given nearly enough information for us to troubleshoot your system but I would raise one question. Given that the speed of induction motors is primarily governed by the power supply frequency and not the voltage or current of the power supply, why do you think pwm techniques are appropriate for such a design? Also have you incorporated over current detection into your design? Without over current detection your FETs become fuses.

Fred Townsend

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