Abstract
The voltage stability is an essential security concern when a system is operating in peak load hours or subjected to an N-1 contingency. Among various voltage stability indices, Local Thevenin Index (LTI) has been a popular one, but mostly applied to the measurement-based framework. The reason is that it requires significant computing effort if applied to model-based approach, even though the model-based LTI calculation can provide more accurate results. In this paper, a new model-based LTI calculation is proposed using graph-computing-based power flow calculation, which is fast enough to fully utilize the advantage of model-based LTI. Then, when the voltage stability index of one or multiple buses exceeds the security limit, a demand response scheme is activated to increase the voltage security margin at the lowest cost. The simulation study of a thousand-level-bus system verifies the computation accuracy and efficiency of the proposed model-based LTI. It also demonstrates that the demand response action can enhance the system security effectively. Thus, the proposed work has advantages if applied to a large-scale Energy Management System (EMS).
Highlights
The modern power system is developing into an increasingly complex and heavy-loaded system, with the integration of a significant amount of renewable energy sources [1]
Continuous power flow (CPF) is successful in power system planning, but is time-consuming for power flow calculations and not always a good choice for online voltage stability monitoring (VSM) of a large-scale system [6]
The Local Thevenin Index (LTI), which is defined as the ratio between |Zth| and |ZL |, measures the voltage stability margin [8]
Summary
The modern power system is developing into an increasingly complex and heavy-loaded system, with the integration of a significant amount of renewable energy sources [1]. Continuous power flow (CPF) is a common model-based algorithm to estimate the steady-state voltage stability margin [5]. The system Thevenin equivalent (Zth) and load impedance (ZL ) are determined by the voltage and current phasors of two distinct snapshots, which are obtained by PMUs. The Local Thevenin Index (LTI), which is defined as the ratio between |Zth| and |ZL |, measures the voltage stability margin [8]. The control strategy was comprehensive but did not show an online computation method of the voltage stability index (VSI) Based on these motivations, a DR scheme is proposed for enhancing the system security with the consideration of voltage stability margin and transmission line capacity.
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