| The ability to resist the change of frequency is closely related to the level of inertia in power system.The equivalent inertial time constant of power system decreases continuously and the resources for frequency control are lacking with the increasing penetration of renewable energy.Frequency stability of power system has been decreased.At the same time,a large number of HVDC projects have been put into operation in China and the risk of large disturbance has increased in the system.As a result,frequency stability of power system is further decreased because of the unbalanced power with the superposition of DC blocking and the fluctuation of renewable energy.On the other hand,renewable energy generations are not unevenly distributed geographically because of the restriction of primary energy.Inertia of power system is unevenly distributed and the frequency response is spatiotemporal after disturbance.Accurate description of the system inertia is the basis of frequency characteristics analysis and strategy formulation of frequency control.Therefore,it is of great significance to analyze the distribution characteristics of inertia and estimate the level of inertia of power system with high-penetration renewable energy.The calculated node inertia is defined to describe the inertia distribution characteristics of power system with high-penetration renewable energy in this paper.On this basis,a partitioning method is proposed to divide the system into several areas which considers the electrical distance and inertia distribution.Finally,a method to estimate inertia level of each area is discussed according to the partitioning results.The main work is as follows:(1)Considering the frequency distribution of different nodes after disturbance,the calculated node inertia is defined to represent the ability of the node to resist the change of frequency and to quantify the distribution characteristics of inertia in power system with high-penetration renewable energy.Then the expressions of the calculated node inertia of the two-generators system and the multi-generators system are derived respectively which consider the physical structure and parameters of power system.Finally,the corrrectness of the calculated node inertia is verified by the simulation examples.And the simulation results show that the calculated node inertia can accurately describe the distribution characteristics of inertia.(2)The factors affecting the inertia distribution characteristics are analyzed according to the calculated node inertia and sensitivity analysis is used to analysis the impact on the calculated node inertia including the electrical distance and inertia of the synchronous generators in different areas.Then,a partitioning method considering the electrical distance and inertia distribution is proposed to divide power system into several areas which can provide the basis for inertia estimation of each areas,Finally,the correctness of the method is verified with 8-generators and 36 nodes system.(3)The frequency response model of power system is established based on the measurement data,Then,a method to estimate the inertia level of each area is proposed.In this method,the inertia level of each area is obtained through model reduction of the the transfer function of frequency response model,which is identified by the ARM AX parameter identification method.The influence coefficient index is proposed to present the influence of renewable energy generators on the inertia of power system.The proposed method is used to estimate inertia of the 8-generators system and the actual power system in a northwest province under two scenarios of steady frequency fluctuation and large disturbance,respectively.The results show that the proposed method has high accuracy under the condition with high-penetration renewable energy or without renewable energy in power system. |
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