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A Novel Strategy for DC Distribution Start-up Based on MMC

In the DC power distribution system which needs to supply power for the passive network, because of the modular multilevel converter (MMC) connected to the passive network has no power supply, the MMC control mode can't directly be set to the constant voltage when to start MMC. Accordingly, the particular start-up control strategy must be adopted. This paper presents a novel start-up approach to the DC distribution network. Firstly, the process of the start-up is divided into an uncontrolled charging stage and a controllable charging stage. By placing a current limiting resistor in MMC AC-side, designing the AC-side and DC-side circuit breaker closing sequence of the converter station, and setting the reference voltage by the slope, the start-up of the DC distribution network can be achieved no large impact current. Secondly, by setting one end of the converter station as the master station and designing the control mode of connecting the passive network converter station, the local and the remote MMC sub-module capacitors can be charged at the same time, the start-up of the DC distribution network can be completed without the help of another auxiliary power supply or equipment. Finally, the mathematical model is established by Matlab/Simulink to verify the effectiveness of the proposed method. The studies we have performed showed that the designed start-up strategy is simple, easy to implement, reliable and economical.