Through the comparative analyses between the reactive voltage control device VQC in substation and the reactive voltage control system AVC of interconnected power grid

some defects and shortages are found out in the basic principle and the function of VQC design.The strategy combined with delaminating subarea control and whole grid control for AVC system is suggested

and the comprehensive optimization target is realized ultimately

that is

the most reasonable capacitor switching

the highest voltage qualification rate and the minimum loss of transmission network.