Comprehensive power MOSFET model for LLC resonant converter in renewable energy applications

LLC resonant converters are widely used in distribution systems for energy conversion. Having a detailed simulation model of the power MOSFETs in an LLC resonant converter can significantly improve the dead time calculation and subsequently improve the DC-DC converter's efficiency. In this paper, a new model for power MOSFET employed in an LLC resonant converter will be presented to predict the transient time for the MOSFET drain-to-source voltage. This non-ideal model of power MOSFETs in an LLC converter can be very useful for applications requiring fast and efficient energy transfer such as charging batteries from PV cells or wind farms. Renewable sources of energy have variable input depending on natural conditions and variable output to a battery, and a model is required to provide adaptive dead time. The aim of developing this model is to provide the ability to better approximate dead time to maximize efficiency at different operating points. The simulation model includes the MOSFET on-state resistance, the variable output capacitance, and the diode forward voltage. The approach used in this paper is to model the variable output capacitance and to simulate the effects of this parasitic element on the behavior of the drain-to-source voltage during the transient. A new set of equations will be proposed for the output capacitance based on the data sheet of a power MOSFET. The experimental results obtained from a 1.2 kW LLC resonant converter at different operating points, prove the accuracy of this simulation model.