I’m trying to control the temperature of the heating surface of an electric cooking pan, filled with water (between room temp and boiling temp).
The heating power (controller output) is made by applying a duty cycle signal to an SSR heating, at 1Hz.
I heated the surface to 60°C and let the temperature stabilize. Then I made a step increase from 0% to 30% on the duty cycle.
I am unable to figure out what is the best plant model to use on my PID control since the step response (see attachment) shows a hybrid between 1) first-order plus dead time (FOPDT) and 2) Integrating plus dead time response. The ripples are caused by the SSR switching ON & OFF (effect of the duty cycle).