Temperature control of diffusion/CVD furnaces using robust multivariable loop-shaping techniques

This paper describes the application of modern tools from robust control theory to the design of high-performance multivariable temperature controllers for diffusion furnaces. The process is modeled from input-output data, collected in a identification experiment at the desired operating conditions. An important component of the identification is the computation of uncertainty bounds describing the confidence limits of the model, in a manner consistent with robust control theory. The identification results are then used to design an H-infinity controller with a cascade, hierarchical structure. The gain-scheduling of several linear controllers is also investigated in an effort to achieve good performance in a wide range of operating conditions. Experimental results demonstrate the success of the approach.