I have been researching AC inverters that control 3phase ac motors with a single phase input. My question is how is the third leg made up to drive the 3 phase motor? We also use a 110AC input inverter to run a 3 phase ac motor. I understand the PWM but do not understand how the additional "legs" are produced.

 

The ac is converted to dc, and an oscillator with a microcontroller produces a 3 phase output. this is varied in voltage and frequency by the micro to suit the user settings, like a Vfd.

 

The ac is converted to dc, and an oscillator with a microcontroller produces a 3 phase output. this is varied in voltage and frequency by the micro to suit the user settings, like a Vfd.

Thank you! So the oscillator is what makes the other leg. Is this done through a transformer?

 

No, the oscillator uses 6 mosfets in an H bridge form, two fets for each phase, to produce the sinewave output.

 

No, the oscillator uses 6 mosfets in an H bridge form, two fets for each phase, to produce the sinewave output.

Awesome! So the PWM is done with the DC bridge to change the frequency of the motor speed directed by human or electronic intervention correct?

 

Yes, the pwm is done by a microcontroller, there will be limits for the frequency and voltage outputs.set by the user for the load. Here is an example of how they work

http://www.achrnews.com/articles/89311-variable-frequency-drives-and-ac-motor-speed