Design, Optimization, and Control of an Isolated Single-Stage Fixed-Frequency Resonant DC/AC Converter

This article proposes a single-stage isolated dc/ac series resonant converter, a promising technology with advantages, such as reduced part count and enhanced efficiency. These features make it suitable for various applications, including onboard chargers and grid-connected systems. A dual-loop phase-duty control approach is proposed to drive the resonant converter. This control approach employs a fixed-frequency scheme offering benefits over variable frequency modulation techniques such as simplifying the design, analysis, and implementation of the control system, as well as design of magnetic elements. Unlike conventional phase shift controllers, this approach does not require the converter to operate far from its resonant frequency. This article addresses the modeling of beat frequency dynamics and proposes a control design solution to address this issue. A step-by-step controller design with comprehensive analysis of the transient response and robustness of the closed-loop system under system parameter variations is introduced, utilizing a novel small-signal model. The detailed analysis of the operation modes, modulation strategy, and zero-voltage switching (ZVS) regions are addressed. Design guidelines for the components and devices of the proposed converter are presented. Finally, a hardware prototype is designed and constructed to validate the theoretical analysis and assess the feasibility of the proposed resonant converter with the control method.