To achieve the goal of reactive power compensation and capacitor voltage balance of modular multiple-level converters（MMC） used in distribution static synchronous compensator（DSTATCOM） to support ac-bus voltage level

a typical hierarchical control system is used. A hierarchical control architecture based on multiple digital signal processors（DSP） will allocate different control tasks for the upper & lower controller reasonably and make it easier to extend the number of modules of MMC-DSTATCOM for future higher voltage application. The basic principle of hierarchical control system and its hardware & software design for MMC-DSTATCOM are analyzed in detail

while the realization of data communication between the upper & lower controller and the synchronous technique of driving signals for each module are brought forward. After the simulation with MATLAB/SIMULINK

a three-phase twelve-module MMC-DSTATCOM prototype is built. The results show that under both inductive and conductive operation conditions

MMC-DSTATCOM can output the expected current and has a quick response which is less than 0.01 s under abrupt change of reactive current reference. The fluctuation of capacitor voltage is less than 5%

all these results show the correctness and effectiveness of hierarchical control system.