Study On Power System Reliability With Wind-Storage System Integration

With the continuous exploitation of traditional fossil energy,the environmental pollution and energy crisis are becoming increasingly prominent.Wind energy as a green and clean renewable energy source,has gradually attracted people's attention.However,wind energy has the characteristics of randomness and intermittentness,which makes the output of wind turbines have greater volatility.When wind power is connected to the grid on a large scale,it will adversely affect the safety and reliable operation of the power system.Therefore,detailed reliability analysis and estimation of wind power system impact are critical to the increasing popularity of wind power generation.The energy storage system can dynamically absorb and release electric energy,which can effectively smooth the output of the wind turbine and reduce the randomness and intermittent impact of wind power on the grid,it has been widely used in wind farms.This paper mainly studies the reliability of the wind-storage system grid connection.The specific work is as follows:(1)The wind speed probability distribution model is improved,and a wind speed prediction model based on semi-invariant method is established.The model considers the time series characteristics of wind speed change,and retains the annual and daily variation characteristics of wind speed,taking the uncertainty into account.The validity of the wind speed prediction model is verified by a simulation,which is suitable for the reliability simulation experiment of wind power system.In addition,according to the relationship between the fan output and the wind speed,the wind power characteristic curve is obtained.Besides,the time series load model is established.(2)The basic theory of Monte Carlo simulation,reliability evaluation index,power flow calculation method and optimal load shedding model have been introduced,the reliability evaluation system of wind power system has been established.Then,based on the annual and daily variation characteristics of wind turbine output and load,the Spearman correlation coefficient is used to quantitatively describe the annual correlation and the daily correlation between them.The annual correlation and daily correlation between different output sequences and loads are analyzed by numerical examples.The annual correlation and daily correlation of wind turbine output and load are also studied to research the reliability of wind power system reliability.(3)The two modes and basic operating parameters of the energy storage system connected to the wind farm are introduced.Then,two charging and discharging strategies of the energy storage system are established:tracking load charging and discharging strategy,tracking fuzzy reference output charging and discharging strategy.Based on the improved IEEE-RTS79 system,the Monte Carlo evaluation method was used to evaluate the reliability of the wind energy system after energy storage.The effects of energy storage on system reliability and the correlation between wind-storage output and load under the two charging and discharging strategies are compared and analyzed.The fluctuation of real-time wind-storage output is further compared.(4)The energy storage state regulation strategy is proposed,the adjustment coefficient to adjust the charge and discharge power of the energy storage system is introduced,solve the overcharge and over-discharge problem of the energy storage system,which can be used to improve the state of charge distribution of energy storage,and improve its service life.Then,the adjustment strategy is verified by an example.Based on the state of charge and the probability distribution of the energy storage system,the state of charge of the energy storage system is close to the ideal range after the state of charge regulation is added.Besides,it can effectively improve the problem of overcharge and over-discharge of the energy storage system.Compared the reliability indexes of the system before and after the state of charge regulation,which are added under different energy storage capacity levels,the system reliability after adjustment has been improved.