Research On Optimal Control Strategy Of Power Quality In New Distribution Network With Participation Of Distributed Generation

In recent years,distributed generation(DG)has been widely integrated into the distribution network.The impact of its access method and operating status on the distribution network has become increasingly prominent,greatly increasing the complexity of voltage control in the distribution network.The nonlinearity of its power electronic devices also introduces additional harmonic pollution,affecting the safe and stable operation of the distribution network.DG has a similar topology to static var generator(SVG),active power filter(APF),and other devices through inverter grid connection.By improving existing control strategies,power quality management can be carried out while grid connection is in progress.This thesis focuses on analyzing and discussing the impact of DG grid connection on the power quality of the distribution network,fast power flow calculation methods,grid connected inverter control strategies,reactive power optimization models,and intelligent optimization algorithms.Based on the above issues,a hierarchical optimization and control strategy for power quality with DG participation is proposed.At the decentralized control layer,the remaining capacity of grid connected inverters is fully explored,and the optimization and governance of harmonic and voltage at the grid connection point are achieved simultaneously,In the global optimization control layer,DG and traditional reactive power compensation devices are unified and optimized for scheduling,and the advantages of DG decentralized compensation are fully utilized to achieve optimal voltage governance of distribution network.At the decentralized control layer,research is conducted on grid connected inverters with active power quality control functions.A mathematical model of LCL type two-level grid connected inverters is established,and reactive power and harmonic currents are detected in real-time based on instantaneous reactive power theory.Compensation coefficients are introduced and fitted into grid connected power generation instructions to achieve power quality control while grid connected.Considering the limited remaining capacity of grid connected inverters,this thesis evaluates the power quality of grid connected points based on the mutation series method,establishes a reactive harmonic optimization compensation model,and obtains the optimal solution set through the particle swarm optimization algorithm with improved constraint conditions.After selecting the compromise solution,the compensation coefficient is obtained,achieving power quality optimization compensation and customized governance.In the global optimization control layer,research is carried out on the reactive power optimization governance strategy of multi-source cooperation,and the distribution network is partitioned by comprehensively considering the interaction between nodes and the regional reactive power regulation capability;A fast power flow calculation method based on cluster partitioning is proposed.A linear voltage power causal equation system is established based on knowledge of voltage sensitivity,and an equivalent distribution network is established to simplify information exchange between partitions.Precision correction is made based on the partitioning results,and a correction model for voltage amplitude and phase angle changing with power is established.When load fluctuations occur,complex iterative processes are not required,and the power flow distribution is quickly calculated through the correction model,Effectively improving the speed of power flow calculation while ensuring accuracy;Then,based on cluster partitioning,a reactive power optimization model for the distribution network containing multiple power quality regulation resources is further established.Feedback regulation is used to cope with load fluctuations,with DG reactive power output and active power cutting as control variables.After optimization,the algorithm obtains the optimal scheduling plan for DG capacity.Based on the DG scheduling plan,power distribution between traditional compensation devices is carried out to obtain the optimal compensation plan for reactive power in the distribution network,Realize unified optimization and scheduling of multiple equipment in the distribution network to improve the voltage level of the distribution network.The thesis has 52 pictures,7 tables and 102 references.