Three multi-balancing machine load flow models for planning the operation mode of the large-scale power system are presented. The mismatch power of the entire system is apportioned by several slack nodes to improve the convergence region. Differ from conventional load flow model

by replacing the power balancing equations of the balancing machines

we can derive the properly constrained multi-balancing machines load flow equations. The proposed models can not only enlarge the convergence domain of load flow

but also satisfy special requirements of the operation mode such as maintain the central bus voltage as the designated value

flexibly distribute the power of balancing machines and control the cross section power of the interconnected system. Since the order of the load flow equations of the proposed models is the same as that of the conventional model

the calculation difficulty of the proposed models remains unchanged. Simulation results of an IEEE 162-bus system

the Shaanxi-Gansu 1 265-node interconnected system and the actual large-scale 21 479-node interconnected system show the correctness and effectiveness of the proposed models.