Coordinated VSG Control for Grid-Connected, Islanded, and Grid-Reconnection Operations in Rural Low-Voltage Distribution Networks Considering Feeder Length and Load Disturbances

Long rural low-voltage feeders are prone to end-of-feeder voltage deviations. Maintaining voltage support during transitions between grid-connected and islanded operation adds a further control challenge. This paper proposes a coordinated virtual synchronous generator (VSG) control method for grid-connected operation, islanding, and reconnection. The method links feeder length, impedance, and load power to the end-of-feeder voltage. It uses line-drop compensation (LDC) with a joint capacity/current-margin constraint to balance voltage support against converter limits. A six-state coordinator manages hybrid passive–active islanding detection, control takeover after grid-connection switch (QS) position feedback, islanded voltage support, and phase-locked-loop-free (PLL-free) presynchronization. It also defines enable, interlock, fallback, and smooth-withdrawal conditions for these functions. The method is evaluated in a switching-level model and on a 1.5 kVA three-phase three-level neutral-point-clamped (NPC) prototype. Simulations show voltage regulation across the tested feeder lengths and loads and reveal the support boundary as the capacity margin decreases. On the prototype, LDC reduces the end-of-feeder line-to-line voltage deviation from 2.42% to 0.21%. The load remains continuously supplied during the tested disturbances, presynchronization, and mode transitions. These results demonstrate coordinated voltage support and grid reconnection within the tested operating range.