Risk Assessment Of Power System With Wind Farms Considering Wind Speed Correlations And Energy Storage

As large-scale wind power penetrate,especially multiple strong correlative wind farms' access will bring great risk to power system,it is necessary to quantitatively analyze the output characteristics of wind power from correlative wind farms in theory and its influence on power system.Installation of the battery energy storage device in a wind farm can reduce the risk to a certain extent,but how to maximize the role of energy storage.Quantitative analysis of the output characteristics of the energy storage and its impact on the power system risk is very significant.The correlation between wind speed in wind farms and the impact of the correlation on power system risk have been discussed.In view of the direct linear transformation method may change the original wind speed probability distribution of wind speed and cause conversion accuracy unstable.This dissertation proposed a indirect linear transformation method based on Gram-Schmidt orthogonalization and Cholesky decomposition.A decentralized conversion technology was proposed considering for the drawback of non-positive definite of correlation coefficient matrix for Cholesky decomposition problem.On this basis,an improved indirect linear transformation method was given to solve the problem of conversion accuracy.For the operating characteristics of wind turbine,the failure rate model established considering for the influence of grid voltage,system frequency and wind speed;Considering for run,outage and derating state of wind turbine,the three-state fault model was built;Considering for the randomness and correlation of the wind speed,wake effects of wind farms,step-up transformer and high-voltage transmission line failure rate and other factors,the reliability model of the wind farm was established.Based on this model,the assessment methods and processes were given and the Monte Carlo method was applied to evaluate the probability characteristics of the active output of wind farms.The reliability of power system is often evaluated based on Monte-Carlo simulation normally with random sampling,namely,MC_RS,but it is not suitable for the power system containing wind power,especially when the wind farms are composed of a plurality of wind turbines,because it needs a large capacity of sample size and have low efficiency.This dissertation will show you an improved assessment method by MC_LHS which is based on the combination of traditional MC(Monte Carlo)method and LHS(Latin Hypercube Sampling)method which both can raise the efficiency of sampling.By this proposed method,the Monte Carlo method was emploied to assess the risk of power system with multiple correlation wind farms,and then provide specific assessment methods and processes.In light of the characteristics of sequential Monte Carlo Simulation,This dissertation proposed a wind turbine multiple reliability model by using the analytical method based on markov chain.And based on the sequential Monte Carlo simulation,the double sampling method was proposed,i.e.,each sample needs two random numbers,one is used to determine the output state or the state of operation,the other one can be used to determine the duration of this state.The two sampling techniques could avoid the shortage of the general sampling method.The duration of the wind turbine's status is independent of the sampling period,and theoretically the wind turbine's status can be extracted at any duration.As for as the battery energy storage system used in wind farm,taking in consideration the charging and discharging constraints,capacity constraints and forced outage rate of the battery energy storage,the output model of battery energy storage system is proposed.And then combining the output models,the integrated model of wind farm can be born based on different scheduling strategies of wind farms.For this integrated model of wind farm,the sequential Monte Carlo method was emploied to assess the risk of power system with wind farms containing battery energy storage system,and then provide specific assessment methods and processes.The related assessment procedures were established in Matlab,and examples of typical wind farms,improved IEEE-RTS79 systems which contain five correlation wind farms and improved IEEE-RTS79 systems whose wind farm containing one battery energy storage system were simulated.The calculation and simulation results validate the proposed model and the proposed method effectiveness.On this basis,analyze the impacts of wind power and battery energy storage on power system risk.