Research On Minimum Inertia Requirements Assessment Of Converter Dominated Power Systems:Models And Methods

As an increasingly significant means of renewable energy consumption and cross-regional power transmission,power electronic converters are beneficial to the development of clean energy and low-carbon transition of power systems.However,the access of massive converters under conventional control techniques will lead to a substantial decrease in inertia level and be weakening the frequency disturbance rejection ability of the power system.Focused on the converter-dominated power systems,in which the ambiguous inertia floor will restrict the carrying capacity and frequency stability,hence the minimum inertia requirements(MIR)assessment is urgently carried out.In the dissertation,the analysis of the critical inertia and related influence factors is conducted first,the minimum inertia requirements assessment model is established second,thus the inertia security region evaluation method is proposed,and finally,a corresponding hierarchic early warning strategy is completed.The main contributions are described as follows:(1)Given the critical inertia level and correspondingly unclear controlled mechanism,the minimum inertia requirement is specifically defined for the power grids with high converter penetration,and the evaluation of it is suggested to refer to the secondary standard in the code on security and stability for power systems.The definition could provide references for formulating related regulations on the inertia requirements.By analyzing the key influence factors on the safety inertia threshold considering the frequency stability,the inertia requirements are restricted by multiple conditions such as the fault severity,thresholds of critical frequency indices,and frequency regulation strategy.The results from the time-domain simulation demonstrate the correctness of the analysis,and the analysis could provide the theoretical basis and modeling method for the inertia requirements assessment.(2)Aiming at the lack of fine models in inertia threshold assessment,a minimum inertia requirements assessment method is proposed for the converter-dominated power systems,which comprehensively considers the dual-frequency stability constraints and the coordination of primary frequency regulation with security and stability control.The inertia threshold analysis is matched with the secondary standard in the code on security and stability for power systems.And then,based on the multi-machine system frequency response model,the rate of change of frequency(Ro Co F)and the frequency nadir/vertex could be achieved under the collaborative control between the first defense line and the second defense line for system frequency security and stability,which could evaluate the minimum inertia requirement with the largest credible contingency event.The simulation results verify the high accuracy in the calculation of minimum inertia requirement,which could guarantee the system frequency and its rate of change within the allowable range to the security and stability of converter-dominated power systems.(3)To solve the problem that the inertia upward adjustment margin couldn’t be achieved with the inertia requirements,the concept definition and the assessment method are proposed for the inertia security region(ISR)of converter-dominated power systems.Taking the dispatchable inertia as the upper boundary and the minimum inertia requirements as the lower boundary for the inertia security region correspondingly,all the inertia elements in ISR could satisfy the requirements of the secure operation and dispatch.The proposed inertia security region is with low dimension,data discretization,and temporal fluctuation.With the inertia security region,the identification of the current system condition and the situation awareness of the future dispatchable inertia level could be obtained.A framework for inertia evaluation consists of several metrics is also established,such as the inertia security margin(ISM)and inertia reserve coefficient(IRC).A hierarchic early warning strategy is derived based on these proposed indices,and the system inertia can be graded accordingly,which could be applied to help the operators to determine the warning region of the system inertia and enhance the power system monitoring and frequency stability risk analysis.