Steady-state and dynamic analysis of high-order resonant converters for high-frequency applications

Abstract

Practical steady-state and dynamic design and analysis for high-order dc/dc resonant converters is presented. The analysis is mainly based on two types of the resonant converters, parallel-type and Class-D (a series-type), which are suitable for high-frequency applications. In the analysis of parallel resonant converters, the key step in the derivation of steady-state analytic equations for LLC-type parallel (LLC-PRC) and LLCC-type series-parallel resonant converter (LLCC-SPRC) is to reduce the order of their state-space models. In particular, the analytic equations for LLCC-SPRC can also be used to design and analyze the LC-PRC, LLC-PRC, and LCC-type series-parallel resonant converters. A simple design procedure along with design examples is given based on the derived analytic equations. Experimental LLC-PRC and LLCC-SPRC are implemented to verify the design results. In the analysis of the zero-voltage switch (ZVS) Class-D converter, both steady-state and dynamic analysis methods are presented. The analysis is based on the Class-D converter with a variable capacitance switch (VCS) for voltage regulation at constant frequency. A generalized DC model for steady-state and dynamic analysis of the converter is given. A simplified small-signal model is found from perturbing the DC model and can be used to predict the low-frequency dynamic control- and line-to-output transfer functions. To predict the high-frequency dynamics, two models are derived based on the amplitude and phase modulations from communication theory. Besides the steady-state and small-signal modeling, a strategy to achieve a stable loop gain for closed-loop operation is addressed. A compensation controller for closed-loop operation of the VCS is developed. All the calculated and design results of the dynamic responses are verified based on the experimental measurements from the prototype converter.