Inertia Online Estimation And Early Warning Of Renewable Energy Generation Dominated Power System

Frequency is an important indicator for measuring the safe and stable operation of power systems,and frequency stability has always been a concern.In the process of frequency changes after disturbances in the power system,inertia provides the fastest and most direct response,so maintaining sufficient inertia is of great significance for frequency stability.With the proposal of China’s "dual carbon" goal,the proportion of new energy installed in the power grid continues to increase.New energy is connected to the grid through power electronic devices,and cannot actively provide inertia support to the grid when disturbances occur in conventional control mode.In dynamic events,it exhibits negative external characteristics of no inertia or weak inertia.At the same time,due to the operation of the ultra-high voltage AC/DC transmission project,the distribution of inertia at both ends of the transmission and reception is uneven,resulting in a clear spatiotemporal distribution feature of the grid frequency after disturbance.In this scenario,evaluating the inertia level of the new energy grid with a high proportion and timely warning in case of inertia shortage is of great significance for ensuring safe and stable frequency operation.In this dissertation,the minimum safety inertia of high-proportion new energy power grid was calculated,and the actual inertia level of the system was evaluated online.On the basis of the two,the system inertia warning index was obtained through comprehensive comparison,and real-time warning was conducted when the system inertia was insufficient.The main work of this paper is as follows:(1)In order to accurately calculate the minimum safety inertia of renewable energy generation dominated power system,a calculation method of minimum safety inertia of power system was proposed,which considered the constraint of frequency change rate and frequency lowest point.In the aspect of frequency change rate constraint,the load voltage characteristic is introduced into the calculation model,and the frequency spatial distribution characteristic is taken into account,and the frequency change rate near the disturbance point is obtained.In terms of the lowest frequency constraint,the frequency time domain expression is obtained according to the dynamic response model of the system frequency,and the minimum safety inertia is obtained by increasing the constraint solution.Then the minimum safety inertia of the system is obtained by comprehensive comparison of the minimum safety inertia obtained by solving the two constraints.Finally,a simulation example is given to verify the accuracy of the proposed method.(2)To achieve continuous online evaluation of the inertia of the new energy high proportion power grid system,a dynamic equivalent model of power grid frequency based on frequency steady-state fluctuation data was constructed by analyzing the mechanism of power system frequency response;Based on the theory of system identification,an online evaluation method of inertia parameters of power grid frequency dynamic equivalent model based on controlled autoregressive moving average is proposed,and the inertia response link is obtained after its order reduction to obtain the overall inertia time constant of the system.At the same time,the inertia level of the partition is evaluated according to the corresponding partition method.Finally,the accuracy of the proposed inertia evaluation method was demonstrated in a 10 machine 39 node system and an actual power grid.(3)According to the calculation results of minimum inertia and the online evaluation results of inertia of the whole renewable energy generation dominated power system,the comparison between the minimum inertia demand of the system and the actual inertia is proposed,and the early warning index of the whole system inertia is proposed.At the same time,according to the situation that the system’s overall/regional inertia may be insufficient after the change of the operating state of the power grid with low inertia level,the corresponding warning indicators are proposed.Finally,the effectiveness and feasibility of these indicators are verified by simulation.