Efficiency Improvement of a Class E² Converter for Low Power Inductive Links

This work presents a model of a Class E ² converter for wireless medium power transfer applications. The converter operates at frequency of 200 kHz and consists of an inductive link with its primary coil driven by a class E inverter and the secondary coil with voltage driven class E synchronous rectifier. A 7th order linear time invariant LTI state-space model is used to obtain the eigenvalues of the system for the four modes caused by the operation of the converter switches. A participation factor for the four modes is used to find the actual operating point dominant poles for system response. A dynamic analysis is carried out to investigate the effect of changing separation distance between the two coils based on converter performance and the changes required of some circuit parameters to achieve optimum efficiency and stability. The results show an excellent achievement in terms of efficiency (90-98%) and maintaining constant output voltage by the use of a PI controller with dynamical change of capacitors in the inverter.