Research On Harmonic Level Of Photovoltaic Power Generation And Electric Vehicle Connected To Distribution Network

With the increasing global resource shortage and environmental pollution,the development of new energy and electric energy substitution will become the consistent sexual selection of all countries in the world.The high penetration integration of photovoltaic power generation and electric vehicles will become an important feature of China’s future power grid.The integration of a large number of photovoltaic grids connected inverters and electric vehicle chargers has led to increasingly prominent harmonic problems introduced in their transmission and distribution systems.More accurate harmonic source modeling of photovoltaic grid connected inverters and electric vehicle chargers,and analysis of the impact of harmonic injection of photovoltaic power generation and electric vehicles on the distribution network,can help to more accurately understand the source and impact of harmonics,and develop corresponding control strategies to reduce harmonic levels and ensure the stability and reliability of the power grid.Firstly,establish a harmonic source model for photovoltaic grid connected inverters and electric vehicle chargers.This article injects the harmonic voltage generated by the modulation process and dead time effect of the inverter as the disturbance voltage of the inverter grid connection point,and uses a multi harmonic linearization method to establish a three-phase LCL photovoltaic grid connected inverter output impedance model considering frequency coupling effect,thereby obtaining the harmonic current output of the photovoltaic grid connected inverter.Consider the impact of constant current and voltage charging process on the harmonic output of electric vehicle chargers,and analyze the harmonic output of three types of electric vehicle chargers based on this.Then,conduct a harmonic injection analysis of high proportion photovoltaic power generation considering transmission line resonance.By combining the harmonic source model of photovoltaic grid connected inverters and considering the impact of weather changes on the harmonic output of inverters and the amplification effect of transmission line resonance characteristics on harmonics,the variation of harmonic distortion rate of distribution network in several typical weather days of the year under different photovoltaic penetration rates was analyzed through simulation.The simulation results show that as the permeability increases,the harmonic injection of distributed power sources such as photovoltaic power generation generally exhibits characteristics of high peak value,large peak valley difference,and short peak time.Finally,conduct a harmonic injection analysis of photovoltaic power generation and electric vehicles considering the impact of time series.Firstly,by combining the mathematical models of charging start time,remaining State of Charge of electric vehicles,and charging duration,the Monte Carlo simulation charging probability prediction method is used to obtain the distribution of electric vehicle charging probability in the distribution network.Then,through simulation analysis,the changes in harmonic distortion rate at each time of the day in the distribution network under different photovoltaic power generation and electric vehicle permeability are given.The simulation results indicate that as the penetration rate increases,the harmonic injection of distributed power sources such as photovoltaic power generation and new power electronic loads such as electric vehicles may cause multiple peaks in the harmonic level of the distribution network,and keep the harmonic level of the distribution network at a high level for a long time.The use of charging functions with smaller harmonic output effectively alleviates this phenomenon.