Active recycling of surplus energy in PV MVDC systems with coordinated fault current limitation

The rapid dissipation of instantaneous surplus energy during AC faults is critical for ensuring fault ride-through (FRT) capability in photovoltaic (PV) medium-voltage direct current (MVDC) systems. This article introduces an integrated scheme that combines active energy recovery with fault current limiting. The proposed approach first ensures fault current limitatio n in the grid-forming converter through power outer-loop blocking and voltage reference adjustment. Following this, the reserve for active energy recovery via the modular multilevel converter (MMC) is evaluated and enhanced through a margin enhancement strategy, thereby demonstrating the feasibility of utilizing the MMC's submodule (SM) capacitor voltage margin. A surplus power recycling control strategy is further proposed to enable efficient recovery of surplus power during grid faults and its smooth release after fault clearance. Finally, the effectiveness of the overall strategy is validated through MATLAB/Simulink simulations under various low-voltage ride-through (LVRT) scenarios induced by AC faults.