Temperature regulation for thermoplastic micro-forming of bulk metallic glass: Robust control design using buck converter

This article presents the design, identification, simulation, and control of a buck converter implemented for bulk metallic glass thermoplastic micro-forming. In manufacturing of multi-faceted bulk metallic glass knife edge, the temperature of the micro-forming sample is critical to the thermoplastic deformation, which determines the quality of the blade edge shape. We propose a nested inner-current outer-temperature control system for high-fidelity temperature regulation. The inner-current control loop is implemented on a modified buck converter, which allows high-power rectified AC input and outputs current that can be regulated with a precision of 2 % over a bandwidth of 5 Hz. We use switch-averaged electrical model together with feedback linearization to address complex nonlinear dynamics that describe a buck converter, and to enable it using linear control design methods. The outer-temperature control design ensures temperature regulation of a heater by prescribing real-time reference power that the current-control loop should provide. The challenge of nonlinear relationship between the required reference power and the regulated current is addressed by exploiting the high-bandwidth of the inner-current loop. The control objectives of regulation performance and robustness to modelling uncertainties are posed and solved in an optimal control (H_∞) framework. Experimental results demonstrate that our control design achieved the required temperature regulation at 673 K within 0.03 K. An improvement of over 5000 % is demonstrated when compared with previously implemented control designs. Moreover, the buck converter-based system enables regulation accuracies that were not possible with other popular existing methods such as TRIAC and traditional relay switches.