Research On Reactive Power And Voltage Optimization Strategy Of Large Grid-Connected Photovoltaic Power Stations

As an inexhaustible source of renewable green energy,solar energy plays an important role in the field of new energy power generation.In China,centralized large-scale grid-connected photovoltaic power stations facilitate the centralized development of solar energy resources,and are included in the national power grid management,making a significant contribution to energy conservation and carbon reduction.With the rapid expansion of the scale of photovoltaic power stations,their participation in reactive power regulation of the power system is becoming increasingly frequent,and the issue of static voltage stability is increasingly prominent.Ensuring that photovoltaic power stations transmit as much power as possible under the premise of stable operation of the power grid is of great significance to the power dispatching department.However,most of the current literature does not consider both the voltage stability at the junction point and the voltage stability within the station,which is not very reasonable in terms of reactive power coordination and allocation,and the solution speed of the optimization strategy is relatively slow.Therefore,this paper conducts research on the shortcomings of reactive power and voltage optimization in current large-scale grid connected photovoltaic power stations,and the work done is as follows:Firstly,a steady-state mathematical model of large-scale grid-connected photovoltaic power stations is constructed.Derive static voltage stability criteria for grid-connected nodes,analyze the mechanism of high voltage exceeding the limit,low voltage exceeding the limit,and voltage cascading disconnection within the station.Build a model and complete the simulation using the power system power flow calculation and optimization program MATPOWER 7.0 based on MATLAB.Secondly,the local voltage stability L index is selected to analyze the static voltage stability of large grid connected photovoltaic power stations.Change the operating parameters such as transmission line impedance,collector line impedance,number of photovoltaic power generation units,illumination intensity,and reactive power compensation capacity to obtain a series of local voltage stability L index values,and then study the change rule of static voltage stability of photovoltaic power stations.Subsequently,the full differential equation of the local voltage stability L index was introduced to obtain the sensitivity formula of the local voltage stability L index.It was found that the power flow results based on sensitivity calculation were basically consistent with the power flow results based on the Niula method,but the former calculation efficiency was higher,providing a theoretical basis for formulating optimization strategies aimed at improving the static voltage stability of large-scale grid connected photovoltaic power stations.Then,a "layered and phased" reactive power and voltage optimization control strategy is proposed.Establish an objective function that minimizes the node voltage deviation within the station and minimizes the grid connection margin of the system.In the first level optimization control model,simulate the photovoltaic output in units of 1 hour.Complete the "coarse adjustment" of hourly reactive power optimization by adjusting the voltage regulating gear of the main transformer’s on-load switch and putting the power capacitor bank into operation.In the second level optimization control model,considering the impact of light intensity fluctuations,the output of the photovoltaic power station is simulated in units of 15 minutes.Under the linear power flow constraints based on the L-Q sensitivity method,the reactive power of the photovoltaic power generation unit is calculated using the node voltage amplitude and phase angle in the first level optimization results as initial values,and then an instruction is issued to complete the minute level reactive power optimization "fine tuning" to achieve flexible adjustment of reactive power in the station.Finally,a meta heuristic algorithm(MA)is used to solve the optimal control strategy.Select six MA class algorithms to compare the performance of various algorithms by taking the fitness value of the standard test function,and select the traditional Particle Swarm Optimization(PSO)algorithm with the strongest fitness.In addition,considering the characteristic that PSO algorithms may fall into local optimal solutions,Grey Wolf Optimization(GWO),which ranks second in fitness value,is used as a solution control group to display optimization results such as node voltage deviation and static voltage stability margin(SVS)for grid connection in the station.The simulation results show that under the two algorithms,the "layered and phased" reactive power optimization control strategy established in this paper fully utilizes the autonomous regulation ability of reactive power and voltage of large-scale grid-connected photovoltaic power stations,effectively improves the static voltage stability of the stations,saves solving time of reactive power optimization strategy,and provides ideas for solving the reactive power and voltage problems caused by "centralized grid connection and remote absorption".