Static synchronous compensator（STATCOM）is commonly composed of the H bridge link with same structure.In this paper

the vector and mathematical model is analyzed in accordance with the topology of star STATCOM

then the selection principle and calculation method of DC capacitance are given from the point view of energy pulsation together with fluctuation coefficient of capacitive voltage.The principle of full voltage and link voltage control is described in detail for the voltage balancing problem of DC capacitor

which is furthermore implemented in the double closed-loop of voltage and current control strategy.Finally

the pre-control value and fine tuning variable of link voltage is obtained

thus achieving voltage balance between links of STATCOM and the active power balance with the gird.It is shown by the simulation analysis and the experimental result of industrial prototype that both transient and dynamic performance of the proposed method is good

which can provide reference for the STATCOM engineering design.