Minimizing total harmonic distortion in a multi-level based WPT system

Wireless power transfer (WPT) systems are controlled using phase-shift modulation to reduce switching losses that incur due to high frequency operation. In high power WPT systems, multi-level converters are employed to further reduce switching and conduction losses as well as device ratings, caused by harmonics. However, the level of harmonic distortion of such systems will depend largely on the depth of phase modulation of each level, and the optimum depth of each phase-shift at which the harmonic distortion becomes minimum for a given amount of power is yet to be found. This paper therefore proposes a methodology to obtain an explicit analytical expression for total harmonic distortion in multi-level WPT systems in terms of phase-shifts. Using the proposed methodology, harmonic distortion of a bi-directional hybrid multi-level WPT system is analysed, and results are presented, bench marking against conventional techniques, to demonstrate how the harmonic distortion can be minimized through appropriate selection of phase-shifts.