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

Operation of class-D type resonant power converters on the utility line with improved characteristics is presented. Two types of resonant converters (LCC-type 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 (>0.95) is obtained from full load to light load. Low total harmonic distortion (THD) (<25% at full load and much lower at reduced loads) of line current is obtained for the LCC-type converter (with a capacitor ratio of 1) for wide load range 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 above resonance mode for the entire line cycle and for a wide load variation.<
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