Model-Assisted Dual-Adaptive SMC for Electric Furnace Temperature Control

Sliding mode control (SMC) is widely recognized for its robustness against modeling uncertainties and external disturbances. However, asymmetric actuator dynamics, excessive switching activity, and the absence of active cooling challenge its application to electric heating systems. This paper proposes a Model-Assisted Dual-Adaptive Parameter Adjustment Sliding-Mode Controller (DAPA-SMC) for PWM-based temperature control of an electric furnace. The proposed controller combines a nominal model-based heating component with an adaptive sliding-mode correction and simultaneously adjusts the switching gain and boundary-layer width using a unified adaptation indicator derived from the sliding variable. Hysteresis-based operating-mode logic, together with an adaptive cooling attenuation mechanism, explicitly addresses the asymmetric heating and passive-cooling characteristics of thermal processes. The controller output is directly interpreted as a PWM duty cycle, enabling straightforward implementation in industrial programmable logic controllers (PLCs). The proposed approach is evaluated through both simulation and experimental validation on a laboratory bell-type electric furnace and compared with a conventional clipped SMC and a model-assisted fixed-parameter SMC. Simulation results demonstrate improved transient performance and substantially reduced duty-cycle variation. Experimental results confirm comparable temperature regulation performance, while the control total variation is reduced to 7.61, compared with 57.72 for the conventional SMC and 66.57 for the MA-SMC, corresponding to reductions of 86.8% and 88.6%, respectively. This smoother commanded duty cycle is accompanied by 587 recorded binary PWM transitions, compared with 365 and 345 for the two reference controllers. Furthermore, reducing the cooling attenuation parameter from μ=0.06 to μ=0.02 decreases the experimental cooling undershoot from 29.33 °C to 21.22 °C for the 500→400 °C transition and from 22.64 °C to 14.09 °C for the 400→300 °C transition, corresponding to reductions of 27.7% and 37.8%, respectively, without materially changing the overall tracking performance. The proposed DAPA-SMC provides a computationally simple control architecture that can be implemented directly on an industrial PLC and offers a practical approach to PWM-based temperature control of thermal processes with asymmetric heating and passive-cooling dynamics.