3 Phase Angle Control

[dukea84]

Hi! I have a question for the same problem..
I'm using 3 zero crossing detector with 3 optoisolators..
The problem is that the load of the motor is an inductive type and the triac stops at the zero current...that is not the zero voltage.
I think that the solution could be starting the firing angle at the shift current phase..

Any suggest?
Thanks.

[mark_s]

Hi! I have a question for the same problem..
I'm using 3 zero crossing detector with 3 optoisolators..
The problem is that the load of the motor is an inductive type and the triac stops at the zero current...that is not the zero voltage.
I think that the solution could be starting the firing angle at the shift current phase..

Any suggest?
Thanks.

Take a look at the data sheet for the PIC18F2331, specifically "motion feedback module". It has three capture inputs and the chip also has power control PWM outputs. The Microchip site as many motor control app notes. Keep us posted on your results

Mark

[sougata]

Hi,

You can use two reverse connected SCRs with two gate drivers (common feed) for switching inductive loads.

[dukea84]

Thanks for yours answers..but I am confused anyway..

@sougata: do u think that use 2 scr and not 1 triac for any phase improve the load controller? why? In that way I need 6 pwm output (instead of only 3).

@mark_s: I'm reading "motion feedback module" section and it's really interesting. The problem is that my pic input are three zero crossing phase and I would like control inductive load (like motors) with different phase displacement.

[sougata]

Hi,

Triacs commute at the zero cross. However due to current lag the voltage zero cross and the current zero cross do not coincide. So the other half part of the triac can come into conduction thus phase angle control is not achieved. If you use a 1:1:1 pulse transformer then the firing signal is fed to the pulse transformer. You can AND a logic drive with a 10 KHz PWM of 10%-25% duty to derive the final driving signal for the PulseTr. The two isolated windings then serve the purpose of firing to Anti-Parallel connected SCRs. So you need 3 drive signals only and not six.