# Speed control of 3 phase induction motor using thyristor

I am working on project of controlling speed of 3 phase induction motor. To control the speed of motor I am using thyristor TYN16-600CT. As I am searching for different research papers and study material on speed control of 3 phase induction motor I found this MATLAB simulation...

In this simulation, I found that there is individual pulse required for each thyristor. This firing pusle is generated using this equation,

t = alpha/omega= alpha/2*pi*f

For, simplicity if alpha = 30 degree then t= 30/50*360

My question is, Is it possible to operate all thyristor by applying same pulse??

Can I use below schematic to control speed of motor??

But as I said I have to use thyristor and in this schematic there is use of triac.

So if this schematic can work fine, what changes I have to do to replace triac with thyristor??

• You should use additional support tyristor which short capacitor to close them. Commented Sep 30, 2019 at 13:18
• Connect the inputs of optocouplers in series Commented Apr 29, 2023 at 19:05

Is it possible to operate all thyristor by applying same pulse?

No. For induction motor voltage control, the pulses need to be timed for each phase to occur at a point delayed from the zero crossing point the same number of degrees for each phase. The same portion of each cycle is passed. Stopping or passing selected numbers of cycles is too crude for motor control.

In addition, controlling the speed of an induction motor by controlling the voltage is very limited in its application. With three-phase motors, a high-slip design is required. The only suitable loads for this approach are fans and centrifugal pumps.

Look at:

Calculating the value of the resistance for controlling the speed of AC fan