| The large-scale development of electric vehicle(EV)is an inevitable choice to accelerate the transformation of China’s automobile industry and achieve the goal of "double carbon",so the power quality problems caused by the large number of electric vehicles connected to the power grid are increasingly important to the industry.As the charging load continues to increase,the original tidal distribution in the power network will change slightly,leading to power quality problems such as three-phase unbalance and voltage deviation.In addition,electric vehicles can also be used as energy storage devices,using Vehicle to Grid(V2G)technology to achieve a good interaction of energy and information between the vehicle and the network,so that the "disorderly" charging to "orderly" charging change,as It can reduce the impact of EVs on the power quality of distribution network by discharging during the peak period and charging during the low period to balance the load curve.In this thesis,we will investigate the evaluation method of the voltage quality of the distribution network by the participation of electric vehicles in V2 G.EV load modeling is a prerequisite for studies on orderly vehicle-grid interaction,analysis of the impact of EV access on the distribution network,and siting and capacity determination of charging facilities.An important measure to mitigate the voltage quality problems brought by large-scale EV access to the distribution network is V2 G technology.For the uncertainty of EV charging and travel,etc.,this thesis establishes the charging and discharging characteristics model of EVs in low-voltage residential areas as well as low-voltage industrial and commercial areas based on the charge state of EVs,ambient temperature and other factors,and with reference to the current EV travel data in China.Based on the charging and discharging characteristics model,a new idea of voltage quality assessment of distribution network based on V2 G technology is given from the main impact indicators of V2 G technology on the voltage quality of power system,based on the probabilistic trend calculation of Latin hypercube sampling,the probability distribution of voltage magnitude of charging and discharging load access to distribution network is obtained,and finally the evaluation index is established to quantify the voltage quality of distribution network counting the participation of electric vehicles in V2 G process,and the effectiveness of the proposed method is verified in IEEE 33 node system simulation.Based on the Latin hypercube sampling,the semi-invariant probability tide calculation method with Cornish-Fisher(CF)level expansion is used to obtain the voltage overrun probability distribution of the system and each node,based on which,using the utility function,a voltage overrun severity model is constructed and the risk index of voltage overrun is given.Finally,through the simulation of the IEEE 33-node system,the risk of distribution network operation overrun under different scenarios is analyzed,and the evaluation method ignore this type of error to provide a basis for the safe operation of the distribution network.The simulation results show that proper charging and discharging can effectively mitigate the impact on the voltage quality of the distribution network in the case of large-scale electric vehicles connected to the grid. |
