INVESTIGATION ON LLC RESONANT CONVERTER TRANSIENT HANDLING

Abstract

In this thesis we introduce novel dual input common tank step-down high-power LLC resonant converter topology as well as standard LLC topology for DC distribution with on load start and dynamic load control features intact. Although, the proposed topology used in these converters can be used in range of applications, the operating voltage and power level used in this thesis is in according to off-grid DC energy solutions. The nominal 380V bus voltage is step down to 96V utilizing LLC resonant converter operating at 150kHz switching frequency and 3.3KW power level. The first architecture is the conventional LLC topology. Using Variable frequency control, the tank impedance is controlled as per different load condition. The Proposed Converter discusses the control algorithm to suppress the inrush starting current of the resonant converter with fast dynamics. The Proposed converter is able to handle the inrush current by switching the converter at the start with twice the resonant frequency and reducing the switching frequency to near resonant frequency while at the steady state condition the variable switching frequency control is achieved using look up table method. The second architecture introduces changes in the conventional LLC topology to source power from two Photovoltaic sources operating at differential mode for achieving even faster charging with dynamic control. Both proposed architectures are suitable to handle starting transient current and load perturbations with fast dynamics.