Research On Direct Power Control Strategy Of MMC-HVDC

Many scientific experts give a high rating to flexible HVDC technology based on the voltage sourceconverter in the field of HVDC, called it is the new representative of the new HVDC technologyunanimously. Modular multi-level converter (MMC) with cascade converter features, can easily achievemulti-module and multi-level design, is the ideal multi-level topology application of the VSC-HVDC, canbe called MMC-HVDC. It has a strong technological advantage in a high voltage level and power level ofthe occasion, having a high homeostasis and the transient performance, environmental protection, smallfootprint, etc. In this thesis, analyzes and studies the direct power control strategy of MMC-HVDC system,the main works are organized as follows:(1) The research background and significance of MMC-HVDC is described.A detailed overview of allkinds of topologies of traditional multi-level inverter. Analysis of the research status of MMC-HVDC athome and abroad, defined the main work.(2) The topology and working principle of MMC and specific operating mode and the correspondingworking state of each sub-module are expounded, operational performance and the correspondingmodulation strategy of MMC-HVDC are analyzed.(3) Traditional control methods of VSC-HVDC are analyzed and learned to the MMC. Establishedmathematical model of MMC in different coordinate systems and study the double-loop control strategy ofMMC.and under capacitor voltage balance control in the system controller design.(4) Based on instantaneous power theory, analyzed the power exchange relationship of MMC-HVDC,researches on direct power control strategy used in the MMC. Reducing the system control parameters,improves the speed of dynamic response.Consider the impact of the strength of the grid on converter stationoperating characteristics, calculated direct power control strategy for AC systems intensity range.(5) Learn from virtual flux calculation of AC motors Virtual flux oriented approach to estimate powerof MMC was used, simplifying the system architecture. The with saturation limit amplitude feedback loopintegrator replacement pure integral term solute the issues of traditional observation method.