This article is about the four-phase voltage source converter (FP-VSC) as the key equipment of the low-frequency four-phase independent power system. The paper discusses the average model of the proposed converter topology and FP-VSC grid-forming and grid-following control strategy based on two-phase independent control. The smooth switching method of low-frequency four-phase to three-phase mode under line fault and operation maintenance conditions is analyzed respectively. The effectiveness of the proposed FP-VSC grid-forming and grid-following control strategy is verified by the simulation and experimental results.