Validation of a Discrete-Time-Domain Model of a High-Power Medium-Voltage Resonant Converter*

Abstract

The widespread deployment of LLC resonant converters in DC technologies has attached a profound significance to the modeling and controlling of such power converters. Compared to the conventional DC-DC converters that could be modeled through small-signal analysis, the Modeling of the LLC resonant converters is complicated. This complexity comes from the way that the electrical energy in a resonant tank is processed, which leads to high non-linearity. Therefore, small-signal analysis is traditionally performed via empirical approaches or iterative simulation methods at around the resonant frequency. But, the weak spot associated with these methods is that they provide superficial and limited insight into the system's dynamic. Moreover, the accuracy of the model is adversely affected as far as the switching frequency deviates from the resonant frequency. This inaccuracy issue becomes serious when the converter operates in sub-resonant mode as this mode is preferred for medium voltage applications. This article, therefore, presents a discrete-time domain approach through which the model of a medium-voltage LLC resonant is derived. Then, the dynamic and static behaviors of the plant are briefly investigated. Finally, a meaningful comparison between the simulation and experimental results obtained from a scaled prototype is provided to validate the modeling approach.