Low voltage distribution grids (LVDGs) are evolving from their traditional passive behavior into highly active systems. Their secure and reliable operation will require effective control schemes which in return require reliable and accurate monitoring systems. Most of the related existing works rely on the threephase Weighted Least Squares (WLS) state estimation method which is used mainly on Medium Voltage Distribution Grids (MVDGs). However due to different characteristics between MVDGs and LVDGs this method may not be suitable for monitoring LVDGs. This paper investigates the performance of the WLS state estimator on a radial low voltage test feeder and due to the random nature of the measurement errors, the analysis is conducted in a Monte Carlo fashion. The investigation indicates that a significant error is imposed in the monitoring of the LVDG which is related to the loading conditions and the asymmetric operation of the distribution grid.

Distribution system state estimation (DSSE) has been enabled by the deployment of smart meters and is currently the subject of active research, focused mainly in medium voltage distribution grids (MVDGs). This paper proposes a modified weighted least squares (WLS) DSSE for low voltage distribution grids (LVDGs) where the neutral conductor is grounded only at the MV-LV substation. DSSE methods developed for MVDGs are not applicable in such systems due to the significant voltage drop across the neutral conductor. The proposed DSSE includes the neutral voltage in the state vector and the measurement functions are modified accordingly. To address any convergence issues and to enhance the accuracy of the proposed DSSE, virtual measurements are introduced for the neutral voltage. The effectiveness of the proposed DSSE is illustrated in a real LVDG and in the IEEE European low voltage test feeder under different operating conditions, smart meter classes and system layouts. In addition, a Monte Carlo analysis is performed for highlighting the importance of the proposed modifications to the WLS DSSE. Among others the analysis indicate that the proposed method converged in all trials, despite including the neutral voltage in the state vector.

The forward/backward sweep is the most commonly used power flow method in radial Low Voltage Distribution Grids (LVDGs). In most cases, Kron's reduction is used to merge the neutral conductor with the phase conductors. However, important information can be lost by ignoring the effect of the neutral conductor through the Kron's reduction method, since in LVDGs the majority of loads are single-phase connected and are supplied through a phase conductor and the neutral. In this paper, a modification to the forward/backward sweep method is proposed to account for the neutral voltage as well. Test results indicate the significance of knowing the exact configuration of the neutral conductor in an LVDG before conducting power flow studies as it can affect greatly the accuracy of the results.

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The increasing penetration of distributed energy resources in Low Voltage Distribution Grids (LVDGs) has a severe impact on the grid's voltage profile. In active LVDGs the controllable assets are mainly single-phase inverters which most often they are unevenly distributed amongst the supply phases. The majority of voltage support schemes in the literature assume that the phases are decoupled and utilize the singlephase inverters in per-phase regulation methods. However, the particularities of LVDGs, namely the inductive coupling from the distribution lines and the neutral coupling from the fourth wire, can result to a strong phase coupling. Consequently, conventional voltage support schemes by single-phase inverters in active LVDGs can cause unbalanced power deviations in one phase and due to the phase coupling it can have a significant impact on the voltage of a different phase. In this paper, the phase coupling, its impact on voltage regulation, and the factors that contribute to its intensity are analysed. In addition, it is demonstrated how two traditional voltage regulation schemes become ineffective due to the phase coupling. Finally, a reactive power compensation scheme is presented that exploits the mutual voltage deviations induced by the phase couplings in order to improve the voltage regulation capabilities in LVDGs.