Equivalent Impedance Analysis and Compensation of Full-Wave Bridge Rectifier under High-Frequency Operation with Extended Impedance Method

Abstract

Full-wave bridge rectifiers are widely used in power electronics for ac-dc conversion. In most of the conventional rectifier analysis, the diodes were modeled as unidirectional ideal switches with a constant threshold voltage. Prior knowledge was needed for specifying the on/off state of a diode in different phases, as well as whether the circuit works under continuous or discontinuous condition modes (CCM or DCM). However, under high-frequency operation, whose frequency might be up to several MHz, the influence of parasitic components, such as the junction capacitor, is more significant. Such a simple ideal switch model and preliminary on/off assignment are not accurate enough to describe the actual switching dynamics. Given this insufficiency, this paper proposes an equivalent impedance analysis and compensation study of full-wave bridge rectifiers based on the extended impedance method (EIM). EIM provides an efficient frequency-domain numeric solution for nonlinear circuit analysis. The steady-state characteristics of a rectifier circuit can be easily and efficiently simulated with EIM, no matter it operates in CCM or DCM, under low or high frequencies. Taking the bridge rectifier in the secondary side of a 6.78MHz wireless power transfer (WPT) system, for example, we demonstrate that EIM can model its dynamics very well. The efficient numeric method is further utilized to optimize the rectifier circuit through impedance compensation towards zero phase angle (ZPA) operation. Both the commercial simulator PSpice and experiment results validate the feasibility of this EIM based analysis and optimization.