In order to solve the problem of power quality deterioration at the other port caused by soft normally open point (SNOP) when dealing with three-phase unbalance, this paper first analyzes the causes of the third harmonic and negative sequence components of the normal side current, then proposes a method to suppress the capacitor voltage fluctuation at the DC side by using energy storage, and designs the corresponding control strategy. Finally, the SNOP model with energy storage on the DC side is built and the simulation of unbalance management is carried out, which verifies the good effect of the control strategy proposed in this paper.