Harmonic Suppression in Active-Clamped High-Frequency Link Inverters Under Non-Unity Power Factor Loads

High-frequency link inverters (HFLI) inherently suffer from voltage ringing, and the issue becomes more severe under non-unity power factor loads. Although active clamping circuits can effectively suppress the voltage ringing, they cause severe distortion in the output voltage and current waveforms under such loads. To address this problem, this paper proposes an improved modulation strategy with leakage energy feedback for active-clamped high-frequency link inverters (ACHFLI). In the proposed strategy, two secondary-side MOSFETs achieve zero-current switching (ZCS) turn-off, while the other two MOSFETs operate at low frequency throughout the entire line cycle. By feeding the leakage inductance energy back to the primary side, the voltage balance of the clamping capacitor can be better maintained under non-unity power factor loads, thereby mitigating the waveform distortion in the output voltage and current during the intervals when their polarities are opposite. A prototype with 48 V_in input, 110 V_o output, and 300 W rated power was built to verify the proposed strategy. Experimental results show that the modulation strategy alleviates the waveform distortion when the voltage and current have opposite polarities, and the total harmonic distortion (THD) of the output voltage is reduced by a maximum of 2.74%.