Power System Extensional Frequency Response Model And Development Of Comprehensive Program

In recent decades,the events of frequency collapse and the blackouts have occurred through the world frequently due to power system large frequency deviation.With large-scale renewable energy integrated into power grid,the frequency deviation range will be larger with the same disturbance.When frequency deviation is out of the allowed range,the possibility of appearing power system cascading failure will greatly increase.In some severe cases,large frequency deviation will even result in frequency collapse.The relevant researches of frequency are mostly based on calculating frequency response curve.Full time domain simulation model and simplified frequency response model are commonly methods,which are often used to calculate system frequency response.However,some simplified frequency response models cannot consider the influence between frequency and boiler/auxiliary equipments.There are lots of auxiliary equipments in thermal power plants and the output of these equipments is related to frequency dynamic characteristics.Also,the outputs of auxiliary equipment have greatly effect on generator.Therefore,in order to illustrate the system frequency response characteristics when large frequency deviation happens,it is necessary to study the extensional system frequency response model considering boiler and auxiliary equipment.With the continuous expansion of power system,the time-consuming for solving problems of full time domain simulation cannot satisfy the requirement of fast calculation.Therefore,it is necessary to use simplified model to calculate system frequency response curve quickly with acceptable accuracy.Full time domain simulation has been used in commercial power system analysis software extensively,however,the reduced models were coded by researchers repeatedly for specific study,and there is no comprehensive frequency response calculation software package incorporating the main reduced models.Consequently,developing a comprehensive frequency response calculation software package has significant impact on power system frequency security assessment,stability analysis and emergency control.The main contributions are state below:Firstly,according to the characteristics of boiler,turbine-governor,generator rotor equation and thermal power plant auxiliary equipment(e.g.feed water pump)and their dynamic behaviors,the extensional system frequency response model considering boiler/auxiliary equipment is built.The drum pressure and steam pressure control systems of boiler,coordinated control system and the adjusting process of steam flow and feed water flow are considered in this model.By analyzing the actual operation data and data fitting,the corresponding relation and mathematical transformation relation between the main parameters in this model are established.Secondly,the influence of extensional system frequency response model which considers boiler/auxiliary equipment on power system frequency stability(static frequency stability and transient frequency stability)is studied.By using this extensional model,the system frequency stability can be analyzed when consider the thermal power plant auxiliary equipment(feed water pump)dynamic frequency characteristics.The feed water flow is the main control object in this model.Frequency and feed water flow has mathematical relation which determines the fuel input of boiler and then the output power of generator can be controlled indirectly.According to model simulation,power system frequency characteristics can be illustrated when large frequency deviation occurs.Then,for further studying the frequency static characteristics of power system,the extensional system frequency response model is regarded as the research object By applying fixed load disturbance,the power-frequency operation point can be obtained with simulation.Finally,the static power-frequency characteristic curve with large frequency deviation can be obtained by repeating model simulation.According to the static power-frequency curve,the static stable operation area and static stable region boundary are put forward.The static stability and transient stability of frequency are analyzed and the concept of frequency unstable equilibrium point is proposed.Finally,full time domain simulation is extensively used in commercial power system analysis software.The reduced models,however,were coded by researchers repeatedly for specific study,and there is no conprehensive frequency response calculation package incorporating the main reduced models.Developing a comprehensive calculation program incorporating these main reduced models can improve the systemic and flexibility of frequency dynamic analysis.This comprehensive program commonly uses high-level language(such as Python)and compiler.Program structure and each function are modular.Application program interface(API)can realize the characteristic of programmable and openness of the comprehensive program.Not only does API realize the basic function,but also more complex advanced function.The functions of frequency response calculation,under frequency load shedding,frequency security assessment and emergency critical load shedding have been realized.