A Novel Approach for Improving the LCC Resonant Converter Efficiency Over Wide Load Variation Ranges

LCC resonant converters widely used in battery charging applications, due to its soft switching operation, wide input voltage variation ranges, and so forth. But its low efficiency under the light-load and no-load conditions is one of its main drawbacks and weakness, which is mainly due to its switching frequency far from the resonant frequency under these conditions, that increases the circulation currents and conduction losses. Here, a control approach and design procedure are introduced to overcome this issue and improve its efficiency over wide input voltage and load variation ranges. The control algorithm is based on the frequency variation and variable resonant inductor to design the converter to operate in its voltage step-up operation area. The converter voltage gain strongly depends on both quality factor and switching frequency. Consequently, the converter can operate in its resonant frequency to overcome its circulating currents issue, which provides high efficiency values, by means of variable quality factor of the resonant tank. Based on the given approach and mathematical analyses, a 180-220 V to 48 V LCC resonant converter is designed and controlled to deliver 100-500 W to the load. The simulation results clearly show that efficiency value more than 95% is achieved over this wide operating conditions.