Control of full-bridge modular multilevel converter for dc ice-melting application

Due to the high frequency of the ice disasters, Dc ice-melting device has become common equipment in the easy icing areas. The previous thyristor rectifier based Dc ice-melting device consumed too much reactive power and outputs characteristic harmonics, which further affected the system stability when connected to Ac system. Full-bridge modular multilevel converter (FBMMC) has the ability of outputting bidirectional Dc-link voltages and Dc currents, which can meet the requirements of Dc ice-melting and also overcome the defects of the thyristor based Dc ice-melting devices. This paper focuses on the control and valve based modulation algorithms of FBMMC for Dc ice-melting applications. This paper firstly takes the advantage of the full-bridge sub-module (FBSM) which can output positive, zero and negative capacitor voltages, trying to make FBMMC output widely ranged and continuous-tuning Dc voltages and currents to de-ice the Ac conductors of different varieties and length. At the same time, the Ac-side voltages of FBMMC remain regulated and almost sinusoidal even when the Dc voltage is quite small. Finally an electromagnetic transient model of the FBMMC based Dc ice-melting device is simulated on PSCAD/EMTDC and the results have proved the effectiveness of the proposed control and modelling methods.