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Cascaded multi-level converter based STATCOM (CMC-STATCOM), with a topology of modular-cascaded structure, has a wide prospect of applications in both transmission and distribution system. Under the background of application of STATCOM in high voltage power grid, there are many advantages of CMC-STATCOM compared with other kinds of STATCOM. On the basis of mathematical model of main topology, the states feedback decoupled reactive power control strategy based on the d-q coordinate system is studied in this paper, together with the application principle of carrier phase shift PWM modulation method in CMC. The balance of DC bus voltage is a key factor to the stable operation of devices. In this paper, the hierarchical control method is used to achieve a balance of DC bus voltage, and it involves the DC bus voltage overall control and individual control of each cascade module. At last, the simulation results of 10-kV, 1-MVA CMC-STATCOM verify the correctness and effectiveness of the control strategy and modulation method in this paper using PSCAD/EMTDC.