Abstract: In order to meet the power quality requirements of large-scale PV connected to weak power grid system, a power quality control scheme with smooth switching, low consumption and resistance fundamental frequency is introduced to be suitable for the special application scenario. Through a specific project as an example, the high-frequency harmonic pollution and sufficient reactive power characteristics of photovoltaic power generation connected to the weak grid are explained. In order to meet the power quality requirements of photovoltaic grid-connected in this scenario, a special high-pass filter topology with fundamental resonance and smooth switching is designed. By deducing the frequency-resistance characteristic and resonance phenomenon of the high-pass filter, the superior suppression performance of the high-pass filter to high-order harmonics and the principle of not changing the reactive power flow distribution are revealed. At the same time, the smooth switching control and parameter setting method are given for the safe and stable operation of the equipment. Finally, the simulation model built in ETAP and the one-week grid-connected power quality test of the PV all prove the rationality and effectiveness of the proposed method.