Current-Summing Multilevel LCC Inverter for Radiated EMI Harmonic Reduction in Wireless Power Transfer

This article proposes a parallel current-summing LCC multilevel inverter (MLI) to suppress harmonic distortion of radiated EMI for wireless power transfer. Traditionally, ZVS has been an issue for staircase voltage output multilevel inverters because a shared current output became faster than some of the voltage transitions in staircase voltage output. The other common problem was capacitor voltage imbalance and resultant output voltage distortion if a sophisticated voltage balancing function is not used. The proposed LCC MLI ensures ZVS by separating each voltage transition into multiple bridge legs. Each bridge leg outputs different phases of currents for each voltage transition. The individual output currents are summed at the matching network of wireless power transfer, generating a near-sinusoid output current to suppress harmonic distortions. In this way, each leg achieves ZVS even though the summed output current at the LCC network is faster than some of the voltage transitions. To avoid the capacitor voltage imbalance issue, the proposed MLI eliminated the flying capacitor. Instead, the four parallel legs are supplied by a shared DC input link. Therefore, the four legs can output identical voltages without using a typical DC flying capacitor. The necessity of multiple input voltage sources is, therefore, also eliminated. Measurement demonstrates that the proposed method effectively reduces radiated harmonic EMI by up to 14 dB.