I'm working on a project "single phase ac induction motor speed controller". The spec of the motor that im going to use is

230v,1/8hp ,8000rpm@no load

I want to know whether it is possible to control the motor for speed upto 5000 and in steps of 100 from 0 without having the problem of overshoot and delay to achieve max speed

my control options are only phase angle control using triac or slip control using IGBT.

which is the best suitable option out of this ?

Any help would be appreciated

Thanks in advance

  • \$\begingroup\$ Generally speaking, speed control of single phase induction motors is a bad idea; by the time you go to the trouble of building a frequency drive, you might as well add a 5th and 6th FET to use a 3-phase motor and avoid all of the single phase starting issues, even if the input power to your rectifiers is single phase. In fact, many 3 phase VFDs have explicit derating for single-phase input supply. \$\endgroup\$ Commented Oct 8, 2017 at 19:53
  • \$\begingroup\$ 8000RPM is not a standard speed for a mains frequency induction motor. It's likely a universal motor. \$\endgroup\$ Commented Sep 14, 2018 at 7:58

1 Answer 1


If it's an induction motor and the speed controller supplies the AC at the frequency required for a given speed there won't be overshoot. Obviously slip will need to be corrected for but that can be detected and corrected for but it can be a little tricky.

Without more details on your controller i.e. whether it can produce variable frequency drive power I can't really say any more. It does sound like the type of circuit you mentioned may not be suitable for variable speed control.

  • \$\begingroup\$ is it not possible to control speed by applying PW modulated AC voltage across motor @ a constant frequency ? I would like to use a mid range pic mcu to produce pwm and a high frequency IGBT to drive ac motor \$\endgroup\$
    – raforanz
    Commented Mar 20, 2013 at 12:19
  • \$\begingroup\$ @raforanz the speed of an induction motor is directly related to the frequency of the AC and there is a load dependent factor that produces slip causing it not to run exactly at synchronous AC speed. What you are suggesting controls the amplitude of the AC signal such as in a light-dimming circuit - it doesn't control frequency. Look up variable speed inductor motor drives in google. They convert AC to DC via a bridge rectifier then they regenerate an AC output by PWM on three outputs each at 120º apart thus you get a variable speed drive for 3-phase induction motors. \$\endgroup\$
    – Andy aka
    Commented Mar 20, 2013 at 12:44
  • \$\begingroup\$ when i searched in google i see that there are methods like voltz/hertz control .so it is not possible to control speed by varying rms voltage @ a constant frequency?. and i read that slip control technique is controlling the speed by varying voltage only. \$\endgroup\$
    – raforanz
    Commented Mar 20, 2013 at 13:14
  • \$\begingroup\$ @raforanz volts-hertz control is to do with low speed running - the RMS voltage must be reduced when the frequency is lower or the motor overloads - it's basically an inductor and with low frequency, potentially the currents are much higher. So varying the rms voltage at a given frequency is not a solution you ought to consider. \$\endgroup\$
    – Andy aka
    Commented Mar 20, 2013 at 13:37

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