The Research of Power Quality Prediction and Evaluation Method for the Large-scale Charging Load

Combined with the project of the development guidelines for charging infrastructure of the electric car (2015-2016) and the plan of Distribution network’s construction and renovation action (2015-2020), this article is predicted and evaluated to power quality of the large-scale electric vehicle total charging load with the energy gravity method and classification disturbance method. The results of prediction and evaluation has the good reference value to research and plan the charging load accessing and related measures of the large-scale electric vehicle. Introduction Increasing development of electric vehicle can accelerate alternative fuel, reduce emissions from cars, and have important meaning to ensure the energy safety, prevent and control atmospheric pollution, and promote energy saving and emission reduction and our country from a big country to a powerful country in automobile industry. According to the plan of The Development Guidelines for Charging Infrastructure of The Electric Car(2015-2016)and the requirement of The Plan of Distribution Network’s Construction and Renovation Action(2015-2020), the power department should achieve the connection between the distribution network planning and charging electric facility planning, strengthen the construction and reform of the charging electric facilities that matched with power network, and guarantee the barrier-free access of charging electric facilities. They also should accelerate build the intelligent service network for electric vehicle charging, promote the operation technology of the electric vehicle charging orderly, V2G,as well as charging storage integration, and achieve the interconnectivity of charging facilities between cities and inter-cities. By 2020, 12 thousand charging electric station will have been satisfied , and 4.8 millions charging piles will have been connected , which provides charging electric service for 5 millions electric vehicles. Because most of the charging infrastructure consist of power electronic components ,or it will cause some interferences ,and the large-scale planning as well as rapid development of charging electric facilities accessing will affect the power quality of distribution network. Therefore carrying out the detection and evaluation to large-scale charging load power quality not only has important meaning to ensure the power network safe, reliable and highly efficient operation, also promote the . A Review of Domestic and Foreign Research Started relatively late compared with the developed countries, electric cars in China has fast development. To meet the needs of the electric car development of infrastructure, the provinces and energy companies are promoting the building of charging infrastructure. In April 2010, issuing four national standards, namely The Experiment Method to The Light Hybrid Electric Vehicle Energy Consumption Amount, The General Requirements for Electric Vehicle Charging Station, The Communication Protocol between The Management System of The electric Vehicle Battery and Off-board Charger, and The Charging Interface of Electric Cars Conduction Type, the nation will implement the subsidy and supporting policies to new energy vehicles, such as the electric cars. At 6th International Conference on Management, Education, Information and Control (MEICI 2016) © 2016. The authors – Published by Atlantis Press 0507 present, the electric vehicle charging infrastructure has entered a rapid large-scale implementation stage, and some running charging infrastructure has been affecting continuously to the power grid voltage, unbalance, loss, sag, voltage flicker and harmonic, and so on. The power quality influence of power system by large-scale charging stations mainly reflects in harmonic, inter-harmonic and sag to increase power energy disturbance, etc. Therefore, many domestic researchers research the problem of harmonic pollution to power grid through modeling and simulation , and compare a common analysis method by setting up the simulation model on the stage of Matlab Simulink, and research the factors of affecting the size of charging infrastructure harmonic though measurement and proof validation. Or we can use collected data from commercial electric car charger to calculate the harmonic current, set up harmonic analysis mathematical model with multiple harmonic sources by using probability and statistics law of large Numbers and central limit theorem, and then research the harmonic current and probability characteristic with multiple electric car chargers causing. Some scholars propose the method of predicting the total harmonic current which produced by a set of electric vehicle charging machine. This method considers randomness that single charger starts charging time and battery’s remaining power, and use random theory to model. Used the model , the total harmonic currents of a group of chargers producing not only can be simulated and analyzed ,but also the influence that chargers affect transformers and the supply network voltage harmonic. Other scholars study that single-phase charging machine has an effect the supply network total current harmonic distortion rate, total voltage harmonic distortion rate, as well as transformer performance. They also recommend that charger is charged during slack time at night to reduce the impact on the supply network and low the investment of power system. In addition, the power pollution problem of the distribution network rarely is researched deeply to the large-scale electric vehicles charging load assess in domestic. And the present studies are limited to the influence that integral harmonics to the power grid .And there are few researches and analysis to flicker and inter-harmonics. So there exists a problem that researching contents are incomplete and the optimization strategies are not enough deep. The Prediction and Evaluation to the Scale Charging Load Power Quality On the analysis of simulation, fully considering the diversity of power system, the author widely simulates a variety of connection mode to the power grid. When the charging load is modeled , it should be considered that the various types of charging infrastructure((now there are mainly three phase bridge rectifier charger, 12 pulse rectifier charger, APF compensation rectifier charger, PWM rectifier charger),and all kinds of charging ways(mainly slow filling, quick charge, super capacitor charging, etc ). It should be through a comprehensive simulation obtained that the specific characteristics and size of electric energy disturbance such as harmonics, transient voltage drop, flicker, etc by the various the electric car charging infrastructure producing. On this basis, the relevant properties of many charging facilities are simulated and analyzed in different access time, and different the electric car initial capacity, etc. In the analysis and calculation, the multiple frequency electric power harmonic signal is set, which can be expressed as follows: