Research On Energy Efficiency Evaluation For DC Distribution Network With Hybrid Energy Storage Device Based On Ultracapacitor

Under the driven force from rapid development of social economy, there is a growing demand for power supply in all industries, and the requirements of power quality are becoming more and more strict. Whether the future power grid planning and power supply, or the energy saving and environment protection, power grid corporation is facing a big challenge. To address the challenge, and meet the needs of social development. For grid construction planning, domestic and foreign scholars have proposed smart grid, active distribution network, and DC distribution network, etc. For power generation, compared to traditional thermal power and hydropower, power grid structure incorporates wind power and solar power. For transmission link, in order to reduce power consumption and improve grid energy efficiency, energy-saving projects can be taken.Due to the fluctuation and intermittence of renewable energy, there may exist a great impact on power quality and reliable operation of power grid after its connection to grid, the application of energy storage technology can cope with the above problems. If main power grid is AC, rectifier and inverter and other PCS interface are needed for renewable energy grid-connection, while the number of PCS interface almost reduce by half in DC system. As a result of, the power loss in transmission link is lowered directly, and eventually the system energy efficiency is enhanced.This thesis elaborates the advantages and disadvantages of DC distribution network, the key technical difficulties, development status, current research of energy efficiency evaluation of distribution network. A discussion is made, which is about effect on DC distribution network caused by hybrid energy storage system, a simulation model of hybrid energy storage based on ultracapacitor is established by MATLAB, and the discharge and charge control strategy are presented. Meanwhile, simulation models for PWM rectifier, PWM inverter, bi-direction DC/DC chopper, and PV system, and corresponding control strategies are established. Eventually, a simulation model of400V DC distribution network with voltage droop control strategy is set up. Then, a series of simulation analysis have been done to analyze the effect on voltage quality, power support, and energy efficiency level of DC distribution network caused by hybrid energy storage system.On the basis of simulation data of DC distribution network, combining with mathematical theory deduction, and with the application of AHP and PCA, a set of energy efficiency index for DC distribution network, which includes11input indexes and2output indexes, has been established from the aspect of power saving and energy savings, such as energy storage capacity ratio, DG capacity ratio, bus voltage qualification rate. A set of index reference value for400V DC distribution network has been put forward, index contribution obtained by data calculation is used to correct index weight, and then a new comprehensive evaluation model is constructed by the combination of AHP, GRAP, and DEA. Firstly, raw data should be normalized through GRAP. Secondly, index contribution can be got by simulation data analysis and multi-dimensional function partial derivative method, then the final index weight,which is the weight vector for different DMU under the same baseline, can be work out through AHP. Finally, the comprehensive score of each DMU can be acquired with DEA.