Operation of high-frequency resonant converters on the utility line with improved characteristics

Operation and characteristics of Class-D-type resonant converters on the utility line are presented. Two types of resonant converters (LCC- and LCL-type) operating with variable frequency control as well as variable pulse width (fixed frequency) are considered. Analysis and simple design procedures (with design examples) are given. SPICE simulation and experimental results obtained for the designed converters (rated at 250 W) are presented to verify the theory. It is shown that high-line power factor (PF) (>0.95) and line-current total harmonic distortion (THD) of <25% are obtained for the LCC-type converter (with a capacitor ratio of one) for a wide-load range (from full load to 10% rated load) without any active control, and the switch-peak current decreases with the load current. Although the LCL-type converter gives about 20% THD at full load, it increases to about 29% at lighter loads. However, the LCL-type resonant converter can operate in lagging PF mode for the entire line cycle and for a wide-load variation.