The power supply radius in areas with weak grids is limited

accompanied with severe issues such as three-phase imbalance at the end of weak grids and within isolated microgrids. To address these challenges

a chain-type interconnection device suitable for strip-shaped power supply areas and an improved network control strategy are proposed. The device comprises a grid-side converter and a converter on the source and load side

with their DC sides cascaded. Firstly

the control principle of a virtual synchronous generator (VSG) is briefly introduced

and the mechanism behind three-phase voltage unbalance is analyzed. Subsequently

two improved VSG control strategies are proposed. For the grid-side converter

a DC voltage droop control loop is integrated into the VSG active power loop to regulate DC voltage. Additionally

dual second-order generalized integrator (DSOGI) is employed for phase-locking and positive-sequence grid voltage extraction. Positive-sequence grid voltage feedforward control is introduced to achieve balanced grid-side current under unbalanced grid voltage conditions. For the converter on the source and load side

a quasi-proportional resonant control loop is cascaded with the VSG power loop to suppress negative-sequence and zero-sequence voltage components

ensuring three-phase voltage balance-particularly under unbalanced DGs and loads. Finally

the effectiveness and correctness of the proposed control strategies are verified by simulation and experimental results.