In 400 Hz inverter, the filter inductance Lf usually varies in a wide range under the overload scenario, which may deteriorate the system stability and harmonics. To enhance the active damping (AD) performance under the variation of the LC resonant frequency fr, an adaptive online adjustment of the AD gain is explored. The damping ratio is maintained to be constant, which leads to the unchanged LC resonance damping performance. As the low-order harmonics are relatively high and approaching fr, the traditional voltage controller fails to effectively suppress the harmonics located outside the control bandwidth. Therefore, the harmonic resonant control with phase compensation, together with its non-minimum-phase design guideline, are proposed to improve the quality of the output voltage. Finally, experimental results under the overload condition validate that the stability and the harmonic suppression are guaranteed simultaneously by the elaborated control strategy.