The concept of constant voltage operation is proposed in this paper and it is demonstrated that the ultimate goal of power grid development is constant voltage operation. The topic is expanded into three aspects: the benefits of constant voltage operation

the technology and equipment to realize constant voltage operation

and the reactive power compensation capacity needed for constant voltage operation. The benefits of constant voltage operation have four aspects: 1) Constant voltage operation is the ultimate presentation of the strong smart grid; 2) Constant voltage operation can resist grid disturbances in the most powerful manner and greatly improve the power system stability; 3) Constant voltage operation can effectively eliminate the voltage fluctuation problem involved with the integration of large scale renewable energy; 4) Constant voltage operation can minimize the grid power loss. The means to realize constant voltage operation is primarily the modular multilevel converter based STATCOM (MMC-STATCOM)

which has encountered great acceptance during recent years. Simulation verifications are run in a modified IEEE 300-bus system and the Pearl River Delta grid in PSS/E. The results indicate that constant voltage operation can greatly improve the stability of power systems and the capacity of installed MMC-STATCOMs is within an acceptable range.