Linear three-phase state estimation for LV grids using pseudo-measurements based on approximate power distributions

Abstract

The large increase of distributed generation (DG) of photovoltaic (PV) systems in low voltage (LV) grids results in increasing voltage magnitudes and line loadings. Due to a lack of network observability in present LV grids, distribution system operators (DSOs) cannot detect and respond to any limit violations. Even with data collected by the expected rollout of smart meters, full network observability will not be achieved. Thus, the network state will not be completely known. LV-State Estimation (SE) in combination with pseudo-value generation can provide a way to determine the required network states with respect to voltage magnitudes and line loadings. This paper presents a linear three-phase LV-SE approach computed in phase sequences. The performance of the presented SE approach was investigated on a realistic grid model for different cases with and without pseudo-values. The performance is promising and the approach can be used to provide DSOs with input data for control actions to avoid limit violations and thus will contribute to the further integration of DG.

Applications of optimization models for electricity distribution networks

“…As the objective of SE is to obtain a picture of the operating conditions of the grid which is as accurate as possible, it is undesirable to introduce errors due to inexact models. However, the complexity of using exact power flow equations, together with the need for fast solutions in real‐time applications, still resulted in research works addressing linear approximations to tackle this problem (Brandalik et al, 2017; Haughton & Heydt, 2013; Waeresch et al, 2015). Brandalik et al (2017) approximate the measurement equations by means of a Taylor expansion, while Waeresch et al (2015) and Haughton and Heydt (2013) rely on the “small angle” approximation.…”

“…Similarly, LP also ensures convergence, and if the network is fully monitored with phasor measurement units, the SE problem becomes linear even in its exact formulation (Carquex et al, 2018). Alternatively, linear approximations have been used, too (Brandalik et al, 2017; Haughton & Heydt, 2013; Waeresch et al, 2015).…”