How do I fix my Triac based control circuit used for induction motor speed control?

[Daelin]

Curcuit Diagram

Incorrect Output

Correct Output

Hi guys, so I have designed a speed control circuit for an induction motor. The circuit consists of a zero cross detector circuit whose output pulse is the input to a 555 timer. The 555 timer is used to generate a PWM wave that is then inputted into an optocoupler. The TRIAC control circuit then applies a chopped AC waveform to the induction motor. The 1st picture is the circuit diagram.The 2nd picture is the chopped waveform (incorrect) applied to the motor (used a lamp in multisim as there is no motor), the 3rd picture is how the chopped waveform should look. I am having trouble (with the negative half cycle) with getting the waveform in the 2nd picture to look like the correct waveform in the 3rd picture. I suspect that the problem is the MCT6 optoisolator, but I am unsure about which component to use instead of that. Can you guys please help fix the design?

[benmarforces]

Look at U6 on the negative part of the AC the opto-coupler Collector pin will be negative compared to the Emitter pin. Try an opto-coupler with a diac output instead.

[tipa]

Хай!
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