Modeling and Design of a Frequency-Regulated Series Resonant Inverter With a Linear Variable Capacitor

Resonant power inverters are among the most efficient power conversion topologies. However, their widespread adoption is hindered by inefficient operation and control limitations under light-load conditions. This research focuses on facilitating the operation of a series resonant inverter (SRI) by utilizing the recently introduced passive linear variable capacitor (LVC) structure. LVC utilizes the nonlinear parasitic capacitance of two back-to-back reverse-biased diodes to establish a voltage- or current-dependent linear capacitor. This research analyzes combining LVC and constant linear capacitors to dynamically change SRI’s resonant frequency for varying load and, that way, reduce the frequency regulation band of the SRI. This article presents a complete analytical framework and describes a design procedure for an SRI with integrated LVC. The proposed framework is verified through simulations and experimentation. A control frequency band reduction of 39% and 37% is experimentally demonstrated for the two studied SRI designs. In addition, the effects of temperature variation and device heterogeneity on LVC characteristics are analyzed, along with their impact on SRI performance.