Study On Reactive Power Optimization Control Technology For New Energy Clusters Connected To VSC-HVDC

Owing to the characteristics of intermittent and fluctuating of new energy power generation,the integration of large-scale new energy clusters brings difficulties for reactive power balance and voltage adjustment.Compared with the AC transmission technology or current source converter based high voltage direct current(LCC-HVDC),voltage source converter based high voltage direct current(VSC-HVDC)has obvious technical advantages in the field of new energy power generation grid-connection and its application prospect is very broad.Therefore,it is of great significance to study on reactive power optimization control technology for new energy clusters connected to VSC-HVDC.First of all,this paper studies the steady-state operation characteristics of the new energy clusters connected to VSC-HVDC.Based on the single-ended modular multilevel converter(MMC)-HVDC model,the method of calculating the steady-state operating range of the converter station is studied.Based on this,the influence rule and influence mechanism of AC voltage reference value provided by VSC-HVDC and connected transformer tap position on the steady-state operating range of the converter station is obtained.In addition,the static voltage stability of the model is studied by using the method of PV curve analysis.By analyzing the static voltage stability limit of the system at the outlet of the equivalent new energy cluster under different operating conditions,the influence of the control capacity constraint of converter station on the PV curve is illustrated and the method to increase the feasible PV operating range of the system is obtained.Secondly,this paper studies the active and reactive power transient regulation characteristics of the new energy clusters connected to VSC-HVDC.In DIgSILENT,the simulation model of the isolated grid of new energy clusters connected to VSC-HVDC is established according to a certain topology,in which the new energy stations are radially assembled to some collection stations and then centralized access to the converter station.The active and reactive power transient regulation characteristics,such as the AC voltage control capability of the sending end converter station,DC voltage control capability of the receiving end converter station and the regulation capacity of the sending end converter station,are respectively studied through setting the corresponding transient simulation.Finally,based on the analysis of the above characteristics,the multi-objective reactive power optimisation approach for the isolated grid of new energy clusters connected to VSC-HVDC is investigated.The multi-objective reactive power optimization model is established,in which the network loss and the reactive power margin of new energy clusters are chosen as the optimization indexes,while the AC system constraints and VSC-HVDC system constraints under normal conditions are taken as constraint conditions.Then,due to the determination of the weight coefficients for the optimization indexes by applying the weighted method,the multi-objective optimization model is transformed into single-objective optimization model.Aiming at a specific example,the optimal solution for the reactive power optimization problem is obtained by means of particle swarm optimization algorithm.