Research On The Mid-long Term Dynamic Simulation Of Power System

The dynamic simulation of the mid-long term process is an organic unity of the electro-mechanical transient simulation and the mid-long term simulation.It is an important calculation mean for researching the cascading faults,the voltage and the frequency of the power system.The integral method for the mid-long term dynamic simulation and the frequency characteristic of the power system are researched in the thesis.The mid-long term process of power system has the characteristics of nonlinear and strong stiff,and its simulation time span is long.Therefore,compared with the numerical integral methods for electro-mechanical transient process,the methods for mid-long term process of power system propose high demand of the methods' numerical stability,convergence and computational efficiency.Based on the analysis of the characteristics of nonlinear stiff system and the existing problems in the numerical integral methods for the mid-long term process of the power system,a new combination integral method is proposed.The implicit trapezoidal integral method is used in the simulation of the electro-mechanical transient process,and the three-step four-derivative implicit Taylor series method is used in the simulation of the mid-long term process.In this thesis,the method for calculating the constant coefficient of the integral formula of Taylor series method is improved,and the stability of the Taylor series method is analyzed.The constructed three-step four-derivative implicit Taylor series method is A-stable and infinite stable,and the order of its accuracy is six.Therefore,the three-step four-derivative implicit Taylor series method is suitable for using large-step in the dynamic simulation of the mid-long term process.In addition,the Newton method is used to solve the differential algebraic equations and a simplified method for forming the constant Jacobi matrix is introduced.The results from simulation cases show that the new combination integral method is effective and feasible.And the new method provides a new thought for the research on the dynamic simulation methods for the mid-long term process of power system.The frequency of power system is an important index to measure the power quality.When the system is disturbed,it is important to keep the balance between active power output and active loads of the system to ensure the stability of the frequency.Based on the mid-long term dynamic simulation of the power system,the effects of the unit power regulation and the governor dead-band on the frequency characteristics are studied.After studying the model of the automatic generation control system,the frequency modulation way which coordinates primary frequency modulation with secondary frequency modulation is adopted in the thesis.Simulations are done,which test and verify the adopted AGC model and frequency modulation way.The simulation results show that the appropriate model parameters and the proper frequency modulation way can make the frequency of the disturbed system return to normal limits quickly and smoothly.