Research On Adaptability Of Load Model For Electromagnetic Transient Simulation Of Large-Scale Power Grid

With the massive access of HVDC transmission system,power system is gradually realizing nationwide interconnection and AC/DC interconnection.However,the massive access of HVDC systems will have increasingly obvious displacement effect on conventional power supply,which will weaken the support capacity of the receiving end AC system and lead to the increasingly prominent stability problem of AC/DC interconnected system.At the same time,the rapid increase of grid size and the complexity of power system components have brought a series of challenges to large-scale electromagnetic transient simulation.In order to reduce the electromagnetic transient simulation computation,the load model is often simplified.Whether the simplified load model is applicable is debatable,which brings some limitations to electromagnetic transient simulation.Therefore,this paper studies the applicability of load model in electromagnetic simulation of AC/DC interconnected system.The concrete contents of this paper are as follows:(1)Based on the detailed electromagnetic transient simulation models of the DC and AC sides of large-scale AC/DC interconnected system,the impact of DC access on the receiving end system is analyzed in depth;Further,the impact of load model changes on the operation capacity of AC/DC transmission system is evaluated by using short circuit ratio and commutation failure immunity index.Thus,a method for calculating commutation failure immunity factor based on Hooke-Jeeves optimization algorithm considering load characteristics is proposed.The simulation results verify the effectiveness of the proposed method.(2)Aiming at the unique commutation failure problem in AC/DC interconnected system,the influence mechanism of the load model on the commutation problem is deeply analyzed from the impedance characteristics,power characteristics and parameter variation characteristics of load model.The single-feed DC system based on two-zone four-machine system and the doubly-feed DC system based on New England 39-node are used to simulate and verify the common load models of State Grid.The adaptability of the load model in the commutation problem are analyzed and the principle of load model structure and parameter selection in the actual simulation is proposed.(3)On the premise of considering the load characteristics,the measures to improve the stability of AC/DC interconnected system for the purpose of suppressing simultaneous commutation failure are studied.The calculation method of voltage interaction factor considering load characteristics is proposed to determine the reactive power compensation installation boundary for each DC system.On the basis of calculating the voltage stability factor of load model,the sensitivity factor of commutation failure is introduced.Then sort the bus bars in the region based on the sensitivity factor of commutation failure,and determine the optimal location of reactive power compensation device.The simulation verifies the influence of different load models on the distribution point of the reactive power compensation device.In summary,this paper conducts theoretical and technical research on the applicability of the load model.The influence mechanism of the load model on the commutation problem and the applicability of load model is deeply analyzed from the impedance characteristics,power characteristics and parameter variation characteristics of load model.Furthermore,the measure to improve the stability of AC/DC interconnected system is proposed.The simulation results show that the load model plays an important role in the analysis of the operating characteristics of AC/DC interconnected systems.Choosing the appropriate load model and considering the impact of load characteristics in the dynamic simulation analysis will effectively prevent large blackouts and ensure high-quality and reliable power supply for economic construction.So the subject has certain theoretical value.