A low-order system frequency response model

Abstract

This tutorial paper presents the derivation of a simple, low order System Frequency Response (SFR) model that can be used for estimating the frequency behavior of a large power system, o r islanded portion thereof, t o sudden load disturbances. The SFR model is a simplification of other models used for this purpose, but it is believed to include the essential system dynamics. The SFR model is based on neglecting nonlinearities and all but the largest time constants in the equations of the generating units of the power system, with the added assumption that the generation is dominated by reheat steam turbine generators. This means that the generating unit inertia and reheat time constants predominate the system average frequency response. Moreover, since only two time constants predominate, the resulting system response can be computed in closed form, thereby providing a simple, but fairly accurate, method of estimating the essential characteristics of the system frequency response.

A Low-Order System Frequency Response Model for DFIG Distributed Wind Power Generation Systems Based on Small Signal Analysis

“…Compared with the results from the traditional SFR model [19], it can be found that both the IROCOF and QSFD increase 1/(1 − L p ) times after L p percent of the stream turbine capacity replaced by the DFIG with equal installed capacity. Thus, under the low wind condition, the frequency response ability of the power system would be weakened greatly.…”

“…In order to present the core content clearly, it is necessary to make two reasonable assumptions: (I) the traditional power system shown in Figure 1 is dominated by a reheat-stream turbine [19]; and (II) the wind speed during the whole process of frequency response with a time scale of a minute is assumed constant. According to small-signal eigenvalue analysis results of the detailed DFIG model in [22], it discovered that only the modal related to rotor speed ω r plays a dominant role in system dynamic behaviors.…”

“…It can be shown very easy from Equation (3) that the extra active power ∆P e_low is zero just because the rotor speed is completely decoupled from the power system frequency ω s . Thus, when L p percent of the reheat stream turbine unit capacity is replaced by DFIGs, the traditional SFR model [19] should be amended as the novel model shown in Figure 2. The only thing that needs to change is the active load disturbance (the original "∆P L " has been changed to…”

Impact of Demand Side Response on a Commercial Retail Refrigeration System

“…For small groups of domestic refrigerators, computationally demanding stochastic decentralized control has been proposed to ameliorate the effects of these power oscillations [20][21][22]. Initial studies suggested that networks of refrigerators can trigger sequential under-frequency events particularly after switching off and return to operation [23]. Moreover, stability can be further degraded by post recovery inrush currents and this has yet to be investigated and reported.…”

Sequential Outage Checkers for Analyzing Cascading Outages and Preventing Large Blackouts

“…In the frequency outage checker, the system frequency response (SFR) model [19] is used as a frequency change model. The idea of uniform or average frequency is the basic concept in the SFR model, where synchronizing oscillations between generators are filtered out, but the average frequency behavior is retained.…”