Heat Transport Modelling and Adaptive Model Predictive Temperature Control of the Direct Current Plasma Nitriding Process

This paper focuses on exact modelling and model-based predictive temperature control of the direct current plasma nitriding (DCPN) system. The DCPN process is a well-known type of industrial technology. However, the mathematical modelling of this process from a control point of view is not developed. Thus, the aim of this paper is to develop a systematic modelling procedure for heat transport and pressure dynamics. Heat transport modelling was performed taldng into account the heat transported by the gas flow, the conducted heat, and the radiated heat. The emissivity of the treated part was estimated and the temperature dependence of the emissivity modelled. Finally, the pressure dynamics was modelled and validated. The model obtained for temperature dynamics is highly nonlinear, mainly due to heat-radiation, and the model contains variable paratheters such as the mass of the treated parts. An adaptive model predictive controller (A-MPC) is therefore proposed for accurate temperature control. The performance of the A-MPC is compared with the classical PM controller, proving the benefits of the adaptive model-based control versus the classical model-based control.