Research On Simulation Of Low Voltage Ride Through Control Of Photovoltaic Power System Based On Average Modeling

With the continuous increase in the scale of photovoltaic power generation,the grid-connected operation of large-capacity photovoltaic power plants with low voltage ride-through poses new challenges to the safe and stable operation of power systems.Therefore,the standards for grid-connected operation at home and abroad provide the requirements that the PV inverter should have low voltage ride through(LVRT)capabilities.At the same time,in order to deal with the problems brought by new energy access and new regulation methods,the modeling and calculation methods for transient simulation should be continuously improved to describe the complex dynamic process of smart grids accurately.In this dissertation,it studies the low voltage ride through simulation for photovoltaic power generation systems through establishing an average model of inverters and distributed power supplies.And in order to evaluate the impact of centralized access of photovoltaic power plants on the power grid,a large-scale photovoltaic power station was established.The main research contents of this dissertation are as follows:The detailed principles of the grid-connected photovoltaic power generation system model and its components are introduced before studying the relationship between photovoltaic cell output power and light intensity(G)and temperature(T).Secondly,the MPPT model of disturbance observation method is established to verify that the algorithm has a good tracking effect.Thirdly,it analyzes the mathematical model of the inverter and introduces the average model of the inverter used in this dissertation.Finally,it achieves the basic method of low voltage ride through from hardware device and control strategy.Based on the descriptions of the research status of PWM converter transient modeling,Furthermore,an improved averaging method for nonlinear dynamic systems is proposed,and an averaged model of the PWM converter is established using this method.It emphatically analyzes the deficiency of the existing average modeling method like the unsuitability for direct algebra solving and difficult parallel simulations.The model has the advantages of high accuracy,wide application,etc.,and can be solved with a larger integration step to improve simulation efficiency.An averaged model of distributed power supply taken low voltage ride through control link into consideration is established based on the averaged model theory.First,judge the situation of voltage drop,take corresponding measures according to different drop situations,and inject the reactive current to support voltage of PCC.An improved low-voltage ride-through control method is proposed.And the active power oscillations can be eliminated by adding the active currents in the proposed low voltage traversal method.At the same time,reactive current can be injected to raise the voltage at the point of rise according to the voltage drop condition.Besides,the simulation results verify the correctness of the proposed average modeling theory through comparing these two kinds of low voltage ride-through methods.A cluster modeling method for photovoltaic power stations with low voltage crossing control is proposed,which including the a photovoltaic power plant grouping model consisting of an inverter clustering model and a low voltage ride through control link model.And simulation results shows that the proposed method can be applied to low-voltage crossing control Clustering modeling of photovoltaic power plants because the changes of the characteristics of photovoltaic power plants under different voltage drops can be tracked through the dynamic characteristics of active and reactive power provided by this clustering method can track.