Heating Element Thyristor Control

Hi all!


Hope everyone is staying safe and healthy.


I am (still) working on a program, involving thyristor control of a heating element. Seems I finally have things working alright.


I do have one question, do you guys have any recommendation for control mode? The ABB DCT880 offers the options in the poll (U*U = U squared, a = alpha), and they seem to recommend full wave fixed/variable cycle. But to me it seems that would be identical to using PWM with a couple of SSR's. What would be the advantage of using the thyristor?


Any recommendations?

Depends on the heating element and system configuration. For example if you are using low voltage to the elements via a transformer in order to get high current, then you can't use the variable cycle method at all, you must use Phase Angle control. No idea however just how that translates to the terms they are using, most of those are not industry standard terminologies that I have ever seen.

Depends on what the element is made from.


If the elements are nichrome you can use on-off (contactor of SSR) or time proportional control with SSR or thyristor.


Silicon carbide elements vary in resistance with both temperature and age and require more care in a control algorithm, typically with thyristor control.


Here's a link to some details on silicon carbide control.
https://www.eurotherm.com/en/glass-manufacturing-applications-en/silicon-carbide-heating-elements/

Thanks.

They are regular steel immersion heater elements. Nothing special about them or the supply.
Power is supplied directly, no trafos. 400 VAC to first and 690 VAC to other. Appropriate sized elements for those voltages.

The names of the control modes are taken directly from the abb manual.

The heating element is enclosed in a steel sheath, probably a stainless steel sheath. Most likely the heating element is nichrome wire.

Nichrome - can handle any control mode.

Which mode works best depends process conditions like where the sensor is and how well it represents the needed temperature and how well the heat is transferred to the medium.

The plastics industry uses lots of plain old time proportional control with SS heater cartridges driven by a plain old SSR (zero cross, not phase angle fired).

I suspect that "full wave, fixed cycle" is the same as time proportional. If ABB has the terms, they also have a description somewhere, probably with a diagram.