Flexibility Evaluation Of Generation System Considering Wind Speeds Correlation And Its Application In Optimal Selection Of Generating Units

Under the energy shortage and environmental protection requirements,more and more clean energy such as wind power is connected to the power system,and the proportion of its installed capacity has increased year by year.However,due to the uncertainty and randomness of wind power,it brings many challenges to power system planning and operation,such as the lack of system flexibility and other issues.At the same time,with the large-scale wind power integration,more and more wind farms are located in geographically similar areas,and their wind speed sequences have certain autocorrelation and cross-correlation.Therefore,these characteristics needs to be taken into account when evaluating the power system flexibility.This paper discusses and studies the flexibility of the generation system that takes into account wind speed correlation of wind farms.The main research contents are as follows:A model for evaluating the flexibility of the generation system,which takes into account the random faults of the generating units and the wind speed prediction error,has been established.Based on the optimal economic dispatch linearization model of wind generation system,this model considers the influence of random faults and the rescheduling process after faults on the system flexibility,and modifies flexibility parameters such as flexibility requirements and resources,solve the generation system flexibility index,and analyze the impact of various factors on the flexibility of the generation system.The example analysis results show that the random faults of the conventional units have a bad influence on the system flexibility,and the system flexibility level decreases with the increase of the failure rate;various factors such as wind speed prediction error,wind power installed capacity,ramping rate,and reserve capacity all have influence on the flexibility of generation system.The current research on flexibility evaluation does not consider the correlation of wind speeds.This paper proposes a model for evaluating the flexibility of generation systems that takes into account wind speeds correlation.The traditional ARMA model cannot take into account the correlation between wind speeds of wind farms.Therefore,in this paper,the wind speed time-shifting method is used to generate simulated wind speed series that meet the correlation requirements;based on the previous research,the generation method of wind speeds considering correlation is embedded into the flexibility evaluation model of the generation system,and establish a model for assessing the flexibility of the generation system taking into account wind speeds correlation,and consider the impact of wind farm capacity configuration on the results of the flexibility assessment.The example analysis results show that taking into account the correlation between wind speeds will lead to a lower level of flexibility of the generation system;when the wind farms integrating the generation system at the same time,rational arrangement of the capacity configuration of the wind farms will increase the flexibility level of the generation system.The optimization model of the unit selection which takes into account the wind speeds correlation and the flexibility of the generation system is established.The method of solving the conventional unit selection scheme based on the improved enumeration method is proposed.This model takes the minimum total cost of the generation system as the objective function,and takes the number of units of each model as the decision variable,taking into account the load shedding penalty and wind curtailment penalty resulting from insufficient flexibility.In order to solve the unit selection scheme,we first establish a preliminary plan for unit selection that meets the minimum requirements for system operation.On this basis,we will increase the candidate units to obtain all the unit selection schemes,and use the optimal economic dispatch model to obtain the costs of the generation system during the planning cycle,and the results of each plan were compared.The analysis of the example shows that the system cost and total cost are relatively high under high wind speed correlation.Taking into account the wind speeds correlation and flexibility loss will affect the optimal unit selection results.