Accurate load modeling is essential for power system stability analysis and control. This topic has regained interest, due to the high penetration of new types of loads and the increased availability of measurements in extended power grids. In this paper, an aggregated load model based on measurement data is formulated for dynamic simulations of large power systems. The proposed model employs variable-order transfer functions, enabling the accurate simulation of complex load dynamics. A complete methodology for the automatic derivation of the minimum-required model order is proposed with the model parameters calculated via a robust multi-signal identification procedure. For this purpose, the Vector Fitting method is introduced as a technique for measurement-based load modeling. Several simulations are performed using the NEPLAN software to investigate the accuracy and the generalization capabilities of the proposed model. The model performance is thoroughly compared with other conventional load models, using also measurements recorded on a laboratory-scale microgrid.

Narrowband power-line communication (PLC) over distribution networks is gaining the attention of researchers, as a communication medium in future power grids. This paper investigates the application of narrowband PLC in smart distribution grids, starting from a historical overview on the accomplished technological progress and continuing with a comparison of the advantages and drawbacks of PLC technology to other smart-grid communication solutions. The analysis shows that narrowband PLC applications are best suitable for medium-voltage (MV) networks, due to the vast and complex geographical extent. The channel and topological characteristics of MV distribution networks are examined for different operational states and configurations, since they are important for the optimal design and implementation of the PLC infrastructure. The analysis is also extended to an existing overhead MV distribution network with distributed-generation units. The obtained results and the proposed methodology are useful and comprehensive tools for the efficient implementation of PLC technology in future smart grids.

In this letter, a new methodology is proposed to extend the applicability of conventional power flow methods to islanded microgrids (MGs), operating with the droop control method. A slack bus is considered to be connected at a random MG node. The operational conditions of this slack bus as well as of the rest MG nodes are determined through an iterative procedure. The objective of this procedure is to force the active and reactive power flowing through the slack bus to zero, representing the islanded MG operation. The proposed approach has a similar accuracy with time-domain simulations, while it reduces significantly the required computational burden.

In this paper, a centralized control strategy for low-voltage networks is proposed, aiming to coordinate the droop characteristics of the distributed renewable energy sources. The main objectives are the overvoltage mitigation and the optimal network operation in terms of maximum power injection and uniform power curtailment. The distinct features of the proposed method are the incorporation of droop-based control techniques into the conventional optimal power flow formulation and the use of the sensitivity theory as a means to significantly decrease the computational burden. The validity of the developed method is justified using a genetic algorithm, while extensive comparisons with conventional centralized and decentralized control strategies indicate its superior performance in the operation of low-voltage networks.

The increased penetration of renewable distributed energy sources increases the challenges for distribution systems operators to keep the voltage variations within the prescribed limits. One of the voltage problems is caused by single-phase systems leading to voltage unbalance. Another problem is overvoltages caused by local injection of distributed energy sources. An effective solution for this problem is by active power curtailment. In this paper, a control strategy is proposed that mitigates voltage unbalance by using active power and it is equipped with a linear active power curtailment solution. The effect of the proposed control strategy and three state-of-the-art control strategies on the voltage profile and the curtailed power are studied. It can be concluded that the proposed control strategy has a beneficial effect on the voltage profile along a feeder and leads to less power curtailment compared to the state-of-the-art solutions. The proposed control strategy thus allows an increased penetration of distributed energy sources in the low-voltage grid.

The accurate estimation of the influence of the imperfect earth on the propagation characteristics of conductors is a crucial issue in electromagnetic (EM) transient analysis. In this aspect, the frequency-dependence of the soil electrical properties should be also considered. The effects of the dispersion of soil electrical properties on EM propagation have been investigated mostly for overhead transmission lines. This article presents a detailed EM transient analysis of underground cable systems taking into consideration the frequency-dependent (FD) soil properties. A generalized earth formulation of cable earth return impedance and shunt admittance is adopted. Propagation characteristics and transient responses are calculated by using both FD soil models and constant soil properties, as well as approximate earth formulations, neglecting the influence of the imperfect earth on shunt admittances; significant differences are observed. Guidelines for the accurate evaluation of earth conduction effects on the transient performance of underground cable systems are also introduced.