| With the reverse distribution of energy and load in China,and the continuous connection of a large number of new energy and electronic devices to the grid,the AC/HVDC hybrid transmission can not only ensure the stability of power transmission,but also improve efficiency,which make it become an important way of regional transfer.At the same time,the state of the system has changed,leading to new stability problems.In the current AC/HVDC system,the proportion of thermal power units is still relatively high,and they undertake important tasks such as frequency regulation and voltage regulation.The improvement of their performance is great significance to ensuring the stability of the system.In this thesis,aiming at the AC/HVDC transmission system with different power sources,it studies the effect of the Asynchronous Turbogenerator（ASTG）connection on the other components and the improvement of the overall system stability.Firstly,the working principle of ASTG is analyzed.Based on the mathematical model of generator and excitation system,its static and transient operation characteristics are studied.Then the ASTG model was built in the electromagnetic simulation software,and the time-domain simulation was carried out in the singlemachine infinite system and the 4-machine 11-node system to verify the correctness of the model and its applicability in the multi-machine system,which laid a foundation for the subsequent stability analysis.Secondly,based on Extended Equal Area Criterion（EEAC）,the stability of AC/HVDC transmission system is studied.The influence of ASTG access on system stability under different fault types was analyzed in the AC/HVDC system powered by thermal power and wind-fire bundling power respectively.It is pointed out that the access of ASTG can improve the operation characteristics of dc system and wind turbine,and make the power characteristic curve of the system shift equivalent,so as to effectively improve the transient stability of the system.The simulation shows that with the increase of the proportion of wind turbines,the operation state of the system changes,and the access of ASTG is more conducive to the operation of the system under the condition of high wind power permeability.Finally,the influence of regional incoherence on the stability of the system when the short-circuit fault occurs in the power supply area of the system is analyzed.In view of the mutual coupling of power angles of equivalent units in the system motion equation,the variation relationship of regional potential is fully considered to determine the state of the system.Through simulation,the influence of ASTG access to different areas on system operation is discussed,and it is clear that the system stability changes with the tightness of electrical connection under the same access mode. |
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