Resonant Converter with Third-Order Commutation Network

In this paper, a new converter is derived by adding an inductor in parallel with the resonant capacitor of the con- ventional series resonant converter (SRC), which is called LLC- SRC. It will be shown that the control characteristics of the new converter are much improved in contrast with those of the conventional SRC. Another advantage of the new converter over the conventional SRC is that it has less component stresses. Based on the characteristic curves derived from the analysis, a systematical design procedure for the new converter is derived. Experimental results are also presented. I. INTRODCUTION HE conventional series resonant converter (SRC) T possesses the properties of zero-current-switching, low-order converter voltage gain, and incorporating the leakage inductance of the output transformer in the con- verter design (l), (2). These are desirable features for high-frequency and low-output voltage applications. However, the output voltage regulation of the SRC is very poor because a very wide range of switching frequency is required for both the load and line regulations. To over- come this difficulty, we may use the PWM or phase-shift control scheme and operate the SRC at its resonant fre- quency, but this results in the increase of the circuit com- plexity and the design difficulty (3)-(5).