| DC transmission technology is already playing an important role incross-regional, long-distance and large-scale power transmission in china. However,in China, the grid’s complexity is rarely seen in other countries of the world.Especially, the ends of DC transmission are centrally located in China’s central andeastern regions, which bring about such a serious problems that our DC transmissioncannot send out and not fall down. The interactions of AC/DC with multiple DC havebeen brought great challenges to power system planning and operation. Based on theabove issues, it’s very necessary to in depth understand the characteristics ofmulti-infeed DC system and put forward the evaluation method of AC and DC powergrid by taking into account the multiple DC system’s interaction. Therefore, in thispaper, in view of the above mentioned problems being faced by multi-indeed DCsystem, several typical problems on power system planning and operation arecorrespondingly investigated. The main and innovatory results are as follow:It first derived the analysis of the relationship between P(V) and Q(V) externalcharacteristics corresponding to DC system’s multiple control modes. Then the DCsystem’s external characteristics of each control mode and change tendency with thesystem voltage fluctuation were analyzed in detail. Finally, an external characteristicsmodel of full voltage process was established. The model’s physical process is clearand easy to use.Based on the P(V) and Q(V) external characteristics model on DC system, theanalytical expression of AC and DC system power flow Jacobin matrix of thecorresponding element was derived. And the research flow of static voltage stabilityof AC/DC system combined with the characteristics of DC system model and thetraditional modal analysis method was also put forward. Furthermore, for themulti-infeed DC system, both the method for calculating the interaction effectbetween the DC systems and the evaluation index of AC/DC Interaction wereproposed. In order to further illustrate the results, an application example was alsogiven.For the DC system commutation process, the factors ignored by conventionalmethods were demonstrated, and the DC commutation process by consideration of the DC converter’s AC filter and capacitor was discussed in detail. Furthermore, In viewof the grid’s multi-infeed DC planning in China, the fault boundary resulting in DCcommutation failures was studied.The influence of the CIGRE DC multi-infeed short circuit ratio (MISCR) indexwas analyzed, the result of which was applied to the actual multi-infeed DC powergrid planning. And for the problem of location selection in the actual DC power gridplanning, it was proposed a selection method of multi-infeed DC system based onMISCR. This method can provide the basis of selection for actual power grid ofarbitrary location schemes. On this basis, considering the factors of power systemshort-circuit current level and the influence of AC grid structure on the system supportability, a receiving-end grid DC power scale calculation method suitable for the actualgrid was put forward. According to the result, the multi-infeed DC power system wasanalyzed in this paper. |
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