Comparison of Overload Protection Methods for LLC Resonant Converters in MVDC Applications

This paper compares four different overload protection methods for LLC resonant converters that are designed to provide only voltage adaptation functionality in the MVDC grids. Thus, they do not have line regulation capability and hence do not need any sophisticated closed-loop control. The four different protection methods includes; reducing the duty cycle, increasing the switching frequency, the clamping of resonant capacitor voltage using diodes and the damping of resonant tank using a resistor. The comparisons between these methods were made based on their ability to sustain output voltage under overload condition, the time they can give to the grid protection devices to clear the fault and their maximum overload handling capability. It was found that the clamping and the damping methods offer a good compromise between the chosen performance criteria.