Precise Modeling of Nonlinear Rectifier Loads in Wireless Power Transfer Systems

The load of the receiver coil in a wireless power transfer (WPT) system can be considered as a subcircuit, typically comprising a diode rectifier, a filter capacitor, and an equivalent resistor R-L. Such subcircuit is nonlinear but is usually represented as an equivalent linear resistor model 8R(L)/pi(2) based on the fundamental approximation of Fourier analysis. Such simplified approach is inaccurate particularly when the receiver current is distorted. This article presents two novel models for the nonlinear rectifier load with full consideration of harmonics and parasitic components of the rectifier. One intermediate model is applicable for systems with continuous rectifier currents, while an advanced model is valid for systems with both continuous and discontinuous rectifier currents. The advanced model is proven to be accurate for any load conditions, including extreme-light load conditions with highly distorted receiver currents. It can be reduced to the intermediate model if the rectifier currents are continuous. The intermediate model can in turn be simplified to the classic linear model if harmonics are ignored. Both simulation and experimental results have verified the accuracies of the proposed models over the conventional linear resistor model for a wider range of load conditions.