Tentative Research On Curtailed Energy Utilization Mode For Wind Curtailment

Renewable energy,such as wind power and solar power,is developing rapidly,but still there are problems remain to be solved: One of them is the curtailment,resulted from problems such as the uneven distribution of energy and load center,the limited transmission capacity and the intermittent and fluctuating nature of renewable energy,wastes a lot of resources and also limits the further penetration of renewable energy.On the user side,as Electric Vehicle(EV)is currently dominated by the charging mode,the problem of range anxiety still exists due to the long waiting time for charging.Besides,the current EV did not achieve the goal of emission reduction fundamentally,but only transferred the carbon emissions from the automobiles exhaust in the city to the carbon emissions of the thermal power plants in the suburb.Comprehensively considering the above problems,it is of great significance to explore a new mode for electricity transmission,so as to solve the problems exist in the power generation side and enduser side simultaneously during the process of renewable energy development.The research of this paper is a kind of prospective exploration and attempt,hoping to provide new ideas for the development and utilization of renewable energy in the future.The main work of this paper are as follows:(1)Take wind power as an example,in order to solve the problem of wind curtailment,this paper designs and proposes a Curtailed-Energy Utilization(CEU)mode,where discharged batteries from battery exchange stations in high-load areas are transported to wind farms through low-cost transportation method such as railway and centrally charged using curtailed energy.Meanwhile,the battery can be used to smooth the wind power output.The overall structure and the operation mode of CEU mode is presented.The feasibility of the CEU mode in the future is researched according to five aspects including the commercial operation pattern,battery type selection,design of logistics,economy,and efficiency.The features and advantages of the CEU mode are analyzed and listed.(2)The charging device topology of battery under CEU mode is designed.The simulation model of components comprising wind turbine generation,battery,convertor and of the whole system are established under Matlab/Simulink and PSCAD/EMTDC environment,and the control principles are designed.Besides,as the charging batteries in the wind farm could be of various types in the CEU mode,modified structures and principles are designed and modeled which also avail different charging strategies.Based on the wind speed data of a typical day,a case study is given to analyze the battery charging and power control process in the CEU mode,through which the feasibility of the mode and the effectiveness of the controlling principle is verified on the simulation level.Aiming at the battery standardization in the CEU mode,the concept of battery module charging container is proposed.(3)According to the CEU mode,the necessity and advantages for using Super Capacitors(SC)to assist the batteries to smooth the wind power output are analyzed,and the method for capacity determination of SC is designed.Discrete Fourier Transform is used to conduct spectral analysis for the ideal output power of smoothing part.Based on the results of spectrum analysis,aiming at the minimum Net Present Value(NPV)of the smoothing cost during engineering period,the optimal capacity of SC is determined according to the best crossover frequency between the battery and SC after considering influence factors such as the available range of State of Charge(SOC),charge-discharge efficiency,cycle life and capital discount rate of battery and SC,respectively.The result of case study shows that compared with only using battery to smooth the wind power,this method can reduce the NPV of the smoothing cost by 26.7% via allocating SC with reasonable capacity.Besides,considering the SOC initialvalue constraint according to the optimal SC capacity and the extreme wind conditions,fuzzy control is used to control the SOC of SC,thereby releasing SOC initial-value constraint and preventing SC from being in overcharge or over-discharge state too frequently.The research of CEU mode may fundamentally solve the problem of energy curtailment,greatly improve the penetration rate of renewable energy,and at the same time prominently promote the development of EV battery exchange mode and battery industries.