Heat transport modelling and adaptive model predictive temperature control of the direct current plasma nitriding process performed in a linear non-isotherm plasma reactor

Abstract

The paper focuses on the exact modelling and the model-based predictive temperature control of the direct current plasma nitriding (DCPN) system. The DCPN process is a well-known industrial technology, however the mathematical modelling of the process from the control point of view is not developed, thus the aim of the paper is to develop a systematic modelling procedure for the heat transport and pressure dynamics. The heat transport modelling was performed taking 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 was modelled. The pressure dynamics was modelled and validated. The obtained model for the temperature dynamics is highly nonlinear, mainly due to the heat-radiation, and the model contains variable parameters like the mass of the treated parts, thus an adaptive model predictive controller (A-MPC) is proposed for an accurate temperature control. The performance of the A-MPC is compared with the classical PID controller, proving the benefits of the model-based control.