DSP-based control for a series resonant heating generator

A digital control for a series resonant induction heating generator has been developed and tested. The paper describes the migration from analogue to digital control with some detail. Analogue regulation of the generator is achieved by controlling three different loops. Only one of them is active depending on the application. In addition to this control loop, a certain number of limitation loops were available to avoid illegal or dangerous operations. In the digital domain, the control loops are 4th order IIR structures realized as a cascade of two second-order blocks. A dominant pole is placed at very low frequency to assure stability under unexpected conditions. Given time constraints and in order to reduce risks, the prototype board maintained most of the well-established blocks of the previous analogue versions and substituted processing and measurement blocks. A modular solution based on the TMS320C31 as the processing unit was selected as the first solution. A final robust and cost-effective mezzanine board was developed based on the TMS320F241. The prototype has been working in real conditions on a 50 kW, 20 kHz switching frequency series generator.