Low-harmonic-distortion and high-efficiency class E2 DC-DC converter for 6.78 MHz WPT

The Class E2 dc-dc converter, composed by soft-switching based Class E power amplifier (PA) and rectifier, is popular for 6.78 MHz wireless power transfer (WPT) for its high efficiency and simple topology. Here, we take a comprehensive analysis on the harmonic voltages and currents on the transmitting and receiving coils in a Class E2 dc-dc converter. These harmonics can be radiated into the free space through the coils, causing low system efficiency and electromagnetic interference (EMI) issues. And thus, it is expected to eliminate these harmonics. Next, an improved Class E2 dc-dc converter with low harmonic distortion and high efficiency is proposed. The harmonic distortions on both receiving and transmitting coils are greatly reduced by the employment of the full-wave Class E rectifier and Pi impedance transformation network. The total harmonic distortion (THD) of voltages and currents are less than 57.5% of those of the classical system. In addition to the reduction of harmonic distortion, the proposed converter is able to maintain high efficiencies, over 70%, when the coil coupling changes, by carefully designing the Pi network.