  Utility-scale renewable power-to-hydrogen (ReP2H) production typically uses
thyristor rectifiers (TRs) to supply power to multiple electrolyzers (ELZs).
They exhibit a nonlinear and non-decouplable relation between active and
reactive power. The on-off scheduling and load allocation of multiple ELZs
simultaneously impact energy conversion efficiency and AC-side active and
reactive power flow. Improper scheduling may result in excessive reactive power
demand, causing voltage violations and increased network losses, compromising
safety and economy. To address these challenges, this paper first explores
trade-offs between the efficiency and the reactive load of the electrolyzers.
Subsequently, we propose a coordinated approach for scheduling the active and
reactive power in the ReP2H system. A mixed-integer second-order cone
programming (MISOCP) is established to jointly optimize active and reactive
power by coordinating the ELZs, renewable energy sources, energy storage (ES),
and var compensations. Case studies demonstrate that the proposed method
reduces losses by 3.06% in an off-grid ReP2H system while increasing hydrogen
production by 5.27% in average.
