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Power-line communication (PLC) is gaining a renewed interest, due to the smart grid (SG) emerging communication requirements. Among other communication technologies, PLC is a very efficient and feasible solution, especially for the extended SG distribution networks. However, it is very challenging to consider both the medium- and low-voltage parts of the distribution network as a whole communication medium, due to the attenuating effects of distribution transformers, limiting PLC applicability. In this paper, data transmission through distribution transformers is investigated by means of multiple-input multiple-output (MIMO) narrowband power-line communication (NB-PLC) system, utilizing orthogonal frequency-division multiplexing (OFDM) technology. Multi-conductor distribution line and measurement-based transformer models are developed to characterize the MV–LV PLC channel. In addition, OFDM signal processing techniques are applied to enhance the achievable data rates. The transmit power budget and bit allocation across the OFDM sub-channels of the spatial beams are optimized to maximize the data rate through the distribution transformer. The achievable data rates are calculated and systematically analysed for different scenarios to investigate the effects of the distribution lines, connected loads, noise models, etc. Results reveal the superiority of the proposed MIMO design against the traditional SISO systems. In addition, the possibility for an extensive and reliable application of MV–LV PLC communications through distribution transformers is shown. [ABSTRACT FROM AUTHOR]

This short communication introduces vector fitting for mode estimation from ringdown responses of power systems. The performance of the method is evaluated for different power system models and is found to be very accurate. [ABSTRACT FROM AUTHOR]

Online recorded responses can be used for aggregate dynamic load modelling, taking advantage of the advent of smart grids and the growing installation of phasor measurement units. Although several measurement-based dynamic load models have been proposed in the literature, still most network utilities and system operators take advantage of well-known formulations such as the polynomial and the exponential recovery models. However, these types of load models are only valid for a specific range of operating conditions, thus minimizing their applicability and efficiency. This is mainly due to the fact that the model parameter estimation procedure relies on iterative processes. To this extent, the specific scope of this paper is to present a comprehensive identification procedure for evaluating load models under different loading conditions and further to propose two generic modelling approaches that can be used to derive robust load models that are suitable for dynamic simulations over a wide range. Towards achieving the scope of this paper, Monte Carlo simulations are used to train and validate the data of the loading conditions. Finally, several simulations are performed within the DIgSILENT PowerFactory software to assess the accuracy of the proposed models. [ABSTRACT FROM AUTHOR]

In this paper, a multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system is proposed for narrowband power-line communication (NB-PLC) applications in medium-voltage (MV) networks. Multi-conductor transmission line theory is used for accurate MV NB-PLC channel characterization and evaluation of the spatial correlation between the phase conductors. By optimizing the indices of the active OFDM sub-channels, the bit allocation across them, and the transmit power allocation across the spatial beams, the proposed MIMO-OFDM design can achieve significant data rate gains over single-input single-output OFDM transmission. The achievable MIMO-OFDM data rates are evaluated for an MV overhead network with different lengths, coupler impedances and branches, showing that the proposed MIMO-OFDM design is an efficient implementation of NB-PLC technology in MV smart distribution grids. [ABSTRACT FROM AUTHOR]

In this paper, a multi-signal identification technique is developed to estimate oscillatory modes contained in power system responses. The proposed technique utilizes least-squares optimization to analyze simultaneously several system measurements and determine close-to-real-time the modal parameters of the examined power system. The Monte Carlo method is applied to synthetic signals to thoroughly quantify the impact of several parameters on the accuracy of the proposed technique and comparisons with conventional identification techniques are performed. The accuracy of the proposed method is also validated using simulated responses obtained from a combined transmission–distribution network. Finally, the scalability of the proposed technique is demonstrated using power hardware-in-the-loop experiments. • A mode identification multi-signal least-squares-based technique is proposed. • It is evaluated by using synthetic signals, simulations and data from PHIL tests. • The proposed technique is suitable for close to real-time applications. • It can efficiently analyze responses at different sampling rates. • It applies in cases of temporary communication failures and corrupted data streams. [ABSTRACT FROM AUTHOR]

In this paper numerical improvements are proposed to enhance the accuracy and efficiency of frequency-domain transient transmission line modeling. The adopted procedure is based on a robust eigenvector tracking algorithm and an accurate shape-preserving interpolation routine, formulating the highly resonant nodal admittance matrix from a minimal number of frequency data. The proposed method is integrated with the numerical Laplace transform and its performance is demonstrated in a configuration, consisting of an underground cable and an overhead line. Results are validated with the corresponding obtained from a frequency-domain model with regular sampling, revealing the high accuracy of the proposed formulation. The computational efficiency of the proposed numerical improvements is highlighted by comparisons of the execution times in cases of high sampling rates. [ABSTRACT FROM AUTHOR]

Modeling of power distribution transformers in the high-frequency range is of crucial importance in cases such as using power-line communication technology or investigating transient overvoltages at the transformer low-voltage side. This paper presents a simple black-box modeling methodology for distribution transformers using transfer functions defined by the recorded voltage ratios at the transformer terminals. The model parameters are estimated using an optimization method that minimizes the error between the measured and the calculated data. A significant advantage of the proposed methodology is the use of conventional instruments in conducting the measurements rather than high-precision and expensive equipment. The accuracy of the developed model is verified by its implementation in both frequency- and time-domain simulations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Introduction of a model simulating a PLC channel in the narrowband frequency range. [•] Model validation using test measurements by a medium voltage single-core cable. [•] The common and differential modes of propagation are examined. [•] Experimental and simulation results in very good agreement validating the model. [•] Investigation of the influence of different parameters on the transmitted signal. [ABSTRACT FROM AUTHOR]

Abstract: A general formulation for the determination of the influence of imperfect earth on overhead transmission line impedances and admittances is presented in this paper. The resulting model can be used in the simulation of electromagnetic transients in cases of two-layer earth over a wide frequency range, covering most fast transient phenomena of power engineering interest. The propagation characteristics of an overhead transmission line over homogeneous and two-layer earth are investigated using the proposed model. A systematic comparison of the proposed model with other approaches is also presented and the differences due to earth stratification are reported. Finally, the transmission line parameters calculated by the proposed formulation are used in the simulation of fast transient surges in a transmission line excited by double exponential sources. [Copyright &y& Elsevier]

The replacement of conventional synchronous generators with converter-interfaced renewable energy sources (RESs) reduces the overall inertia levels of modern power systems, leading to frequency stability issues. Moreover, the intermittent nature of RESs constitutes system inertia variable during the day, further complicating the frequency control procedure. Therefore, power system operators shall estimate close to real-time the overall inertia levels of their grids in order to ensure their secure and reliable operation. In this context, in this paper, a new methodology for the inertia estimation of multi-area power systems is formulated. The proposed method uses the modal sensitivity matrix to obtain a linear approximation of the relation between modal parameters and inertia constants. During the real-time operation, modal parameters are identified via system responses using the Matrix Pencil method. The identified modes and the derived sensitivity matrix are used to estimate the overall inertia of the examined power system. The effectiveness of the proposed method is validated by means of simulations performed in one-area, two-area, and three-area power system models. • A new methodology for inertia estimation of multi-area power systems is formulated. • A linear approximation between inertia constants and modal parameters is derived. • Modal parameters are identified by applying system identification techniques. [ABSTRACT FROM AUTHOR]

The development of accurate equivalent models of distribution networks (DNs) is one of the most important aspects for power system dynamic analysis. Consequently, during the last decades, several equivalent models have been proposed to analyse the dynamic behaviour of DNs. However, the performance of existing models is sensitive to several factors such as the pre-disturbance operating conditions and the penetration level of distributed generators. Scope of this paper is to evaluate the applicability range of conventional equivalent models for the dynamic analysis of modern DNs by using a recently proposed performance assessment method. Towards this objective, the performance, in terms of accuracy and generalization capability, of 22 conventional equivalent models is assessed. Finally, the most critical parameters of all examined equivalents are identified by applying a variance-based sensitivity analysis. • Methodology to assess the applicability range of equivalent models. • Evaluation both in terms of accuracy and generalization capability. • 22 conventional equivalent models are assessed. • The methodology facilitates dynamic equivalencing and analysis of modern networks. [ABSTRACT FROM AUTHOR]

• The performance of three multi-channel mode estimation methods is evaluated. • A comparative analysis between single- and multi-channel approaches is performed. • Prony, matrix pencil and vector fitting mode identification methods are considered. • Modes from both the transmission and active distribution networks are obtained. • The impact of different parameters on the identification procedure is examined. Mode identification from post-disturbance ringdown responses is a valuable tool for the analysis of the dynamic performance and the stability margins of power systems. In this aspect, several techniques have been proposed, focusing mainly to single-signal analysis. However, considering large-scale power systems and especially future scenarios with high penetration of distributed energy resources, detailed network analysis at all voltage levels is required. As a result of these concerns, multi-channel mode identification algorithms have been developed. Scope of this paper is to evaluate the applicability and the performance of the most known multi-channel measurement-based identification approaches for the modal analysis of modern power systems incorporating active distribution networks. The algorithmic details and distinct characteristics of each method are briefly discussed. The examined methods are used to identify the dominant inter-area modes contained in ringdown responses at different levels of a combined transmission-distribution network. [ABSTRACT FROM AUTHOR]

The advent of renewable energy sources (RESs) has posed several technical challenges related to the operation of modern power systems. These can be classified into two main categories: (a) problems at the power system level, and (b) local problems at the distribution network (DN). To solve these issues, there is a strong need for the development of innovative control schemes that can be employed by converter-based network assets, e.g., battery energy storage (BES) systems and distributed RES. In this context, a unified control system (UCS) for the provision of ancillary services (ASs) by distributed RES-BES systems within a multi-services perspective is introduced in this paper. The proposed UCS comprises different algorithms to provide ASs related to voltage regulation, voltage unbalance mitigation and frequency support. The UCS is implemented in 3-phase, 4-leg converters (3Ph4LCs) to ensure the provision of ASs in unbalanced DNs. In addition, at the dc side of the 3Ph4LC a series dc–dc converter for BES support allows the implementation of the proposed UCS in weak DNs. The transient operational performance of the proposed UCS is evaluated by conducting time-domain simulations. • A unified control system for the provision of ancillary services is introduced. • It employs voltage regulation, voltage unbalance mitigation and frequency support. • The proposed algorithms are integrated into a 3-phase, 4-leg converter. • A power oscillation damping technique is introduced to improve PLL performance. • Time-domain simulation results verify the performance of the proposed control system. [ABSTRACT FROM AUTHOR]

The advent of distributed renewable energy sources (DRESs) has led to a series of technical issues affecting the secure and reliable operation of active distribution networks. Among them, under-/overvoltages, current overload, and voltage unbalance can be considered as the most important problems limiting the increase of DRES penetration. In this paper, a new control architecture is proposed to overcome these issues using the reactive power of DRESs and the active/reactive power of distributed battery energy storage systems (DBESSs). Its distinct feature is the implementation in the symmetrical components domain, allowing the efficient decoupling between under-/overvoltage and voltage unbalance mitigation techniques. Furthermore, a central controller is introduced to improve the system performance in terms of reduced network losses and effective DBESS utilization by coordinating the response of DRESs and DBESSs. The validity of the proposed control strategy is evaluated by performing time-domain and time-series simulations on the IEEE European LV test feeder. • Unified control strategy for unbalanced low voltage distribution grids. • Voltage regulation, voltage unbalance mitigation and congestion management control. • Distributed generation and energy storage are used as the main control units. • Implementation of the control schemes in the symmetrical components domain. • Performance evaluation by conducting time-domain and quasi-static simulations. [ABSTRACT FROM AUTHOR]

• The performance of measurement-based inertia estimation methods is evaluated. • The sliding window method and the ARMAX modeling approach are considered. • Algorithmic details and distinct characteristics of each method are presented. • The impact of different parameters on the inertia estimation is examined. • Methods applicability is demonstrated via experimental results. The increasing penetration of converter-interfaced renewable energy sources (RESs) is expected to reduce the overall system inertia. Additionally, due to the intermittent nature of RESs, the overall inertia of modern power systems will vary significantly during the day, resulting in frequency stability issues. In this uncertain environment, it is important for power system operators to monitor in real-time the overall system inertia. Scope of this paper is to systematically evaluate the performance of the most known measurement-based inertia estimation techniques. These include ARMAX-based methods and methods based on the sliding window concept. Algorithmic details and distinct characteristics of each method are presented and discussed. The effect of several parameters on the accuracy of the examined methods is investigated by means of Monte Carlo simulations. For the analysis both ringdown and ambient data are considered. The performance of the examined methods is evaluated under different network conditions and configurations, using simulation results obtained from a system frequency response model and the IEEE 9-Bus system. The applicability of both approaches is also assessed using laboratory measurements. [ABSTRACT FROM AUTHOR]