The integration of large-scale power electronic devices increases the complexity of the system’s dynamic characteristics

posing challenges to its safe and stable operation. This paper investigates the necessary constraints for constructing a renewable power system from a small-signal system strength perspective

proposing mathematical constraints in three dimensions: voltage magnitude

phase angle

and frequency. First

using a model reduction method based on characteristic subspaces

low-order subsystems are derived to describe the system’s voltage

phase angle

and frequency dynamics

which reflect the key dynamic characteristics of the original system. Next

based on these subsystems

new system strength indicators are proposed

including the generalized short-circuit ratio for voltage

phase angle

and frequency dynamic deviation

with three inequalities defining the necessary strength constraints for system construction. Finally

simulation results validate the effectiveness of the proposed dynamic analysis framework and strength constraints.