Research On Unit Commitment Optimization Considering Frequency Constraint Under Renewable Energy

With the high penetration of renewable power in the power system,the system power change uncertainty increases.At the same time,the proportion of synchronous generator decreases gradually,and the renewable energy such as wind power do not participate in the system frequency regulation under normal circumstances,the inertia level and frequency regulation capability of the system are reduced,which makes the system frequency security face a major challenge.In order to ensure the stability of the system frequency,the unit commitment need to arrange an appropriate generation plan in advance,but traditional unit commitment only reserves part of active power for frequency regulation to deal with disturbance,which cannot ensure the frequency safety of high proportion renewable power system.Therefore,it is of great significance to optimize the unit commitment model,fully excavate the frequency regulation potential of each synchronous generator,and consider the frequency control method of wind turbine to improve the frequency stability of the system.This paper optimizes the traditional unit commitment model from the two perspectives of synchronous generator and wind turbine.The main work is as follows:(1)The frequency response characteristics of the system are analyzed,based on the ASF model,the expression of the minimum frequency value of the disturbed system is derived,and the frequency safety constraint is constructed.On this basis,the unit commitment model considering frequency constraint is constructed to ensure the generation plan has sufficient frequency regulation capability.The fast non-dominated optimization algorithm NSGA-II is used to solve this model,and a 10-machine 39node system with wind turbine is taken as an example to verify the effectiveness of the improved unit commitment model.(2)On the basis of considering the frequency constraint,further explore the frequency regulation potential of the synchronous generator which undertakes the most frequency regulation task of the system.The effect of adjustment coefficient of different units on the maximum frequency deviation has been analyzed,and the sensitivity of the adjustment coefficient is introduced to characterize.The simulation and calculation are used to analyze the influence of disturbance location and disturbance magnitude on sensitivity sequence of generator adjustment coefficients.Add this sensitivity information into the unit commitment model as the second objective function to form a multi-objective optimization problem,and adjust the startup sequence of the synchronous generators.The simulation results show that the improved unit commitment can further restrain the minimum frequency drop and improve the frequency response of the system.(3)On the basis of considering the frequency constraint,the method of frequency regulation of wind turbine is further studied.Considering the virtual inertia control and virtual drooping control of wind turbines,the method of overspeed load reduction of wind turbines combined with pitch angle control is analyzed,which is suitable for the full wind speed conditions.Considering the selection of different load reduction control methods,the wind speed is partitioned,and the dynamic load reduction rate constraints in each section are derived,and on this basis,the unit commitment model considering the wind turbine frequency regulation is constructed.Finally,a 10machine 39-node system with wind turbine is used for simulation and calculation.The results show that the improved unit commitment scheme can further improve the system frequency response and save the power generation cost.