  Large-scale power-to-hydrogen (P2H) systems formed by multi-stack are
potentially powerful peak-shaving resources of power systems. However, due to
the research gap in connecting the grid-side performance with the inherent
operation control, the continuous operation of P2H loads is limited by the PF
assessment under volatile conditions when integrating into the grid. This paper
first fills the gap in proposing the analytical models of active and reactive
power of P2H loads with a typical power converter interface topology. On this
basis, the all-condition PF characteristics of multi-stack P2H loads are
captured as functions of unified current and temperature control variables.
Then, a PF-constrained multi-timescale control framework is constructed to
evaluate flexibility, PF, production, and security comprehensively. A two-level
nexus, including a model-based hour-ahead robust model predictive controller
and a rule-based real-time increment correction algorithm, is proposed to
guarantee the control accuracy and tractability. Case studies verify an
intrinsic control tradeoff between PF and production, resulting in an
unequal-split allocation strategy compared to the traditional
production-oriented control. The significance of the extended PF and security
dimensions is verified to improve the flexibility. Furthermore, five typical
operating modes respectively corresponding to low, medium, and high load levels
at the cluster level are concluded for industrial application.
