3-Phase AC motor control help required

Thread Starter

abicash

Joined Oct 18, 2007
7
Hello

I have designed a PWM based 3-phase sine generator .
PWM freq = 16KHZ using a Microcontroller and a Look up table for sine

The bridge stage is 3 nos Dual IGBT modules with 10000uf/600v electrolytic capacitor across the input to the bridge and 3 nos 0.22uf/600v capacitors across each module.

I have attached the waveform across R-Y phases and i see a lot of oscillations on the scope.
On looking closely i see this to be the effect of BEMF from the AC motor.

1)The waveform is seen on a CRO since surprisingly the oscillation doesn't show up on a DSO.The frequency which you see is a 30Hz envelope by a 8KHz PWM sine
2)The rating of the motor is 1HP and the leads are quite long (close to 15 meters).

I request someone to comment on this.Maybe pointers or desirably a solution.
Please help
 

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tcmtech

Joined Nov 4, 2013
2,867
What are you intending to use the motor for?

Is this a exercise in learning how to build a 3ph motor driver or something else?

Just curious being that a used but good working 1 HP VFD unit can be bought for around $30 or less.
 
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