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In contactless power transfer (CPT) system, voltage-source inverters are widely used with a resonant tank. However, because of the influence of the working environment, aging, and other factors, the resonant frequency of the primary varies. Moreover, the reflected equivalent impedance of the secondary coil may affect the design of a resonant tank with a constant switching frequency. In this brief, a multilevel inverter (MLI) without the resonant circuit tuning is proposed for the CPT system. The proposed inverter can produce a high-frequency ac voltage with an approximated sinusoidal envelope for the primary coil. According to the equation developed for the inverter, low-order harmonics can be eliminated by selecting an appropriate input voltage ratio and switching angles for the switches. Furthermore, the cancelation of multiple harmonics can be achieved by designing multilevel circuits. The advantages of the proposed MLI include the reduction in low-order harmonics, low voltage stress, and high reliability. Hardware experimental results were obtained for a CPT system prototype to verify the performance of the proposed MLI.
Lee et al. (2020) studied this question.