Evaluation of enhancements to Thevenin equivalent based methods for real-time voltage stability assessment

Abstract

The possibilities offered by the use of Phasor Measurement Units (PMU) in real-time monitoring provide interesting ways to ensure secure operation of power systems. This paper studies the specific case of voltage stability and the possible improvements to the Thevenin equivalent methods, which is applied generally with local measurements. This paper uses the PMU measurements to calculate the grid transformation coefficients to obtain wide-area information. This is achieved by studying the generator's electromotive force estimated using values in the coefficient transformation matrix. The improvements are tested in a small system and a through comparison with traditional Thevenin equivalent methods is carried out.

Improved Thévenin equivalent methods for real-time voltage stability assessment

“…Namely, as soon as a generator field current exceeds the limit, and before it is effectively limited by the OEL, the equations of the limited generator are anticipatively used in the Thévenin equivalent computation; • improved calculation of the generator e.m.f. The latter is used as detailed in [13]. The saturated q-axis e.m.f.…”

“…The first descriptions of TEM used a least-square procedure to determined the parameters from local measurements [19]. The approach followed in this paper is to compute the parameters from wide-area measurements together with the network model [13,14,20].…”

“…Correction of Thévenin equivalent [13,14] Voltage stability assessment [13,14] OEL activation? (anticipation and saturation corrections)…”

“…The value ofĒ g,k when the generator is under voltage control (k ∈ G vc ) is represented as in [13], with a phasor that equals to the one where the voltage is being controlled and Z g,k = 0; it is updated with each new PMU snapshot.…”

“…Some limitations of the TEMs were identified in [11], after which a number of improvements have been explored, dealing with: synchronous generator limits [13], wind-farms limits [14] and HVDC interconnections [15]. A further set of improvements is presented in this paper, inspired of techniques This work has received funding from the Danish Council for Strategic Research as a part of the project Secure Operation of Sustainable Power Systems (SOSPO) 1 www.naspi.org 2 www.sospo.dk proposed in [16] in complement to the sensitivity computation and monitoring.…”