Research On DC-ice-melting Device Based On Hybrid Modular Multilevel Converter

With the increasing demand for electric power resources in modern society,the power system is increasingly large and complex,and ice-laying of transmission lines is one of the major safety threats to power systems.Although the deicing technology of power grids has been developed for decades,it is limited the cost,functionality,operability,and abrupt climate change of ice-melting devices have caused power system failures due to ice on transmission lines.In this paper,a new DC ice-melting scheme based on hybrid modular multilevel converter(MMC)is proposed considering the problems of existing DC ice-melting device,such as high harmonic content,complicated mode switching operation,large size and so on.In the scheme,a novel structure of MMC is composed of the upper bridge arm all using full bridge sub-module(FBSM)and the lower bridge arm all using half bridge sub-module(HBSM).In normal operation,the device implement reactive power compensation as static synchronous compensation(STATCOM),and under the condition of grid icing,the device can output continuous controllable DC voltage and current ranging from 0 to the set value for grid ice-melting.In this way,the economic benefits can be improved effectively.Firstly,the outstanding advantages of the device based on MMC are described,and analysis of mathematical model and power to the structure is presented in this paper.The working principle of the two sub-modules of the hybrid MMC half-bridge sub-module and the full-bridge sub-module is analyzed in detail.At the same time,the design process of the parameters of the hybrid MMC main device is given.Secondly,according to the mathematical analysis of the hybrid MMC structure and the power analysis results,the corresponding current inner loop control strategy and voltage outer loop control strategy are proposed.The current inner loop has two control methods and the voltage outer loop is a three-layer hierarchical control strategy..Then the PSIM simulation software was used to verify the control strategy of the current inner loop and voltage outer loop,and the selection of current inner loop control mode was determined.Furthermore,a more complex hybrid MMC simulation circuit was built in the PSCAD/EMTDC simulation software,and DC ice melting,reactive power compensation and their simultaneous working conditions were designed.The feasibility and effectiveness of the scheme and control strategy are verified by simulation in PSCAD/EMTDC.The concept and advantage of the hardware-in-the-loop simulation system are introduced.Then the hybrid MMC circuit is transformed into a hardware-in-the-loop simulation circuit based on the design method of the hardware-in-the-loop simulation system.The hardware circuit of the hardware-in-the-loop simulation MMC circuit is composed.Hardware-in-the-loop simulation experiment platform,and hardware experiments on the hardware-in-the-loop simulation experiment platform.