Research On Mid And Long-term Frequency And Voltage Dynamic Control Of Power System Based On Polynomial Approximation

In modern power systems,the addition of various protection and control equipment makes the system behavior more complex.The uncoordinated actions of different equipment may not only trigger transient stability problems,but also mid and long-term stability problems under stable transient conditions.Compared with transient stability studies,mid and long-term stability problems involves more kinds of equipment,higher degree of non-linearity,and the interleaving of frequency and voltage stability issues is more obvious.In recent years,its impact on the stable operation of power systems has become more significant.Therefore,the establishment of a complete system model for the stability of mid and long-term processes in power systems and the accurate prediction of system state changes are important sources of decision-making for frequency and voltage control of mid and long-term processes in power systems.This contributes to the stability and continuity of modern power systems,state transition capability and controlling the impact range of fault.In view of the above background,the following researches are carried out in this paper:(1)Aiming at the problem of mid and long-term frequency and voltage stability of power systems,a quasi-steady-state model for mid and long-term processes of power systems coupled with frequency and voltage influencing factors is established,and a mid and long-term power systems stimulation method based on power flow calculation is proposed.In order to improve the simulation efficiency,the simulation variable step size strategy and initial value prediction strategy are further proposed and discussed.This paper uses BPA power flow calculation program and MASTES power system analysis toolkit to realize the simulation method.(2)Aiming at the relationship between mid and long-term trajectories of power systems and system parameters,a mid and long-term trajectory polynomial approximation method based on collocation method and simulation was proposed,which realized the algebraic representation of changes in system trajectories within a variable parameter range.And this method adapts to a large calculation scale because of its non-invasive characteristics.(3)The traditional model of model predictive control in power systems is optimized by using the results of mid and long-term trajectory prediction of the power system,and the original constraints with differential equations are transformed into the constraints of pure algebraic equations,which solves the complex constraints of traditional models and reduces calculation difficulty.Based on the MASTES toolkit,this paper implements a mid and long-term model predictive control method for power systems,which can meet the requirements of "effective control,advance control,and avoid unnecessary control".