The flexible multi-state switch（FMSS） is a new type of feeder interconnection power device

which is composed of the multi-terminal common DC bus converter. When the grid voltage is unbalanced

the fluctuation of DC voltage of the FMSS will seriously affect its normal operation and the service life of the device. After analyzing the principle of DC-side voltage fluctuation

a new dual-loop DC-side voltage control strategy is proposed to solve this problem. The positive-sequence loop uses power feedforward control to stabilize the DC voltage steady-state error

and the negative-sequence loop uses the single sinusoidal signal resonance feedback control to suppress periodic ripple of DC voltage. Finally

a simulation platform is built to simulate the DC-side voltage fluctuation under different conditions. The simulation results verify the effectiveness of the proposed scheme. This strategy can effectively suppress the ripple of the DC side voltage of the flexible multi-state switch under multi-port simultaneous unbalance

the output current has no harmonic current

and the current peak is limited to the rated range.