Small-signal model of dual half-bridge series resonant inverter sharing resonant capacitor for domestic induction heating

The state-of-the-art of induction heating technology requires more and more multivariable control systems able to provide a suitable response for a wide set of vessels to be heated. The goal of this paper is to propose a small signal model of a multivariable system, a dual half-bridge series resonant inverter sharing a common resonant capacitor. A Phase Shift Square Wave Modulation (PSSWM) is considered to control the output power of two induction heating loads where the switching frequency and the phase shift are the control inputs. Thus, the topology to be controlled is a Two-Input-Two-Output (TITO) system that presents significant interactions between the inputs and the outputs. A transfer function matrix based on the harmonic balance approach is proposed and validated in simulation. Moreover, stability, output controllability and performance limitations are analyzed highlighting the control problems that arise in this particular application.