Abstract
An online estimation method for the power system inertia constant under normal operating conditions is proposed. First of all, a dynamic model relating the active power to the bus frequency at the generation node is identified in the frequency domain using ambient data measured with the phasor measurement units (PMUs). Then, the inertia constant at the generation node is extracted from the unit step response of the identified model in the time domain using the swing equation. Finally, with the sliding window method and the exponential smoothing method, the estimated inertia constant is updated in real-time. Compared to the conventional methods using large disturbance data or field test data, the proposed method can estimate the inertia constant under normal operating conditions, and therefore, can provide the tracking trajectory of the power system inertia constant in real-time. The effectiveness of the proposed method is validated in the IEEE 39-bus system. The results show that the relative error of the identified inertia constant is below 5% and the identified inertia constant can be updated within 1s.
Highlights
INTRODUCTIONIn the point view of physics, the inertia of a power system is its capability to resist energy fluctuations caused by external disturbances, which, in conventional power systems, are supplied mainly by the kinetic energy stored in the rotating mass of the synchronous generators and quantified by the inertia constant [1]
In the point view of physics, the inertia of a power system is its capability to resist energy fluctuations caused by external disturbances, which, in conventional power systems, are supplied mainly by the kinetic energy stored in the rotating mass of the synchronous generators and quantified by the inertia constant [1].With the increasing share of the power electronic inverter interfaced renewable energy sources (RESs), some changes have taken place in power system inertia
The proposed method was tested in the IEEE 39-bus system, which is a simplified model of high voltage transmission system in the northeast of the USA (New England area)
Summary
In the point view of physics, the inertia of a power system is its capability to resist energy fluctuations caused by external disturbances, which, in conventional power systems, are supplied mainly by the kinetic energy stored in the rotating mass of the synchronous generators and quantified by the inertia constant [1]. For most of the estimation methods based on disturbance measurements, the inertia (constant) is estimated using the swing equation, utilizing post-event data that record the transient active power and frequency characteristics of the generators [10]–[21]. Based on the transient and steady state characteristics of the frequency response after a disturbance, a method to estimate the equivalent inertia and damping constant simultaneously was proposed in [18]. VOLUME 8, 2020 based on transient test, probing and etc., the proposed method can achieve a precise inertia constant estimation without any disturbance event and probing injection, and can provide the tracking trajectory of the inertia constant in real-time. When estimating the equivalent inertia constant of the converter-interfaced RESs, it is reasonable to regard them as the equivalent synchronous generators and the proposed estimation method can be employed. Where Hsys is the equivalent inertia constant of the system, Ssys is the rated capacity of the system and N is the number of generators
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