A novel method to simulate the control-to-output transfer function of resonant converters

Nowadays, resonant converters represent a viable option for highly efficient power conversion. Typically, the control of resonant converters uses frequency variation. However, the determination of an accurate control to output transfer function, needed to improve the dynamic behavior, appears to be a challenging task for most designers. Therefore, this paper describes a fast and yet precise method to obtain the desired transfer function by means of simulation (in an early design phase) or by means of measurements (on existing prototypes). This paper applies the method based on a time-discrete model in case of the well-known resonant LLC-converter. In order to demonstrate on one hand the accuracy of the modeling approach and on the other hand the applicability of the same method during measurement of transfer functions, a hardware version of the converter is built. The practical setup shows that by using digital generated gate signals and a modern oscilloscope engineers can obtain the transfer function at their workbench.