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The advent of distributed renewable energy sources (DRESs) has led to the progressive transformation of traditional distribution networks to active components of the power system. This transformation, however, may jeopardize the reliable grid operation due to the advent of new technical problems, such as network overloading, over-/under-voltage events, abnormal frequency deviation and dynamic instability. In this challenging scenery, the installation of a modern measuring infrastructure has created new sources of data and information that facilitate the provision of ancillary services (ASs) via measurement-based analysis. The ACTIVATE (ancillary services in active distribution networks based on monitoring and control techniques) project aims to design innovative AS solutions for power system operators. These solutions aim to tackle the technical issues emerged by the ever-increasing DRES penetration and their volatile nature. In this context, in ACTIVATE, a holistic system is proposed comprising centralized and decentralized control features to enhance the overall network performance. Additionally, a network monitoring system is designed to support a number of online and offline dynamic analysis applications by exploiting measurements obtained at the transmission, primary and secondary distribution network. This paper presents a validation of the overall system, which is performed by using simulation and power-hardware-in-the-loop results in combined transmission and distribution network models. [ABSTRACT FROM AUTHOR]

The increasing penetration of distributed renewable energy sources drastically alters the dynamic characteristics of distribution networks (DNs). Therefore, several equivalent models have been recently proposed, to analyze more accurately the complex behavior of modern DNs. However, relatively simple models are still commonly used in practice for dynamic power system studies. In addition, dynamic equivalent models for DNs are sensitive to different operating conditions and there is lack of systematic understanding of their performance. Scope of this paper is to propose a methodology for identifying the applicability range in terms of accuracy and generalization capability of several conventional and newly developed equivalent models for the dynamic analysis of modern DNs. A set of metrics is used for the modelling accuracy assessment and a sensitivity analysis framework is introduced to fully quantify the generalization capabilities of DN equivalent models. Based on the above, guidelines and recommendations for the development of robust equivalent models for DN analysis are proposed. [ABSTRACT FROM AUTHOR]

This paper introduces a two-step methodology for online identification of the participation of generators in power system oscillatory modes, based on measured responses. The dominant modes in generator measured responses are initially identified using a mode identification technique and then introduced, in the next step, as input into a clustering algorithm. Critical groups of generators that exhibit poorly or negatively damped oscillations are identified, in order to enable corrective control actions and stabilize the system. The uncertainties associated with the operation of modern power systems with renewable energy sources (RESs) are investigated as well as the impact of the dynamic behavior of power electronic interfaced RESs. [ABSTRACT FROM AUTHOR]

To facilitate the coordination between transmission and distribution system operators, accurate equivalent models of power system components are required. Towards this objective, in this paper, a black-box model is proposed for developing steady-state reduced-order equivalents of active distribution networks (ADNs) that host converter-interfaced renewable energy sources (CI-RES) and operate under various voltage control schemes. Droop-based and traditional voltage control schemes, such as on-load tap changer (OLTC) control strategies and the use of shunt capacitors, are considered. The performance of the proposed model is evaluated via simulations considering various load types and CI-RES penetration levels. Comparisons against the conventional polynomial and exponential models are also conducted, demonstrating the superior performance of the proposed black-box model. • Development of aggregated equivalent models for active distribution networks (ADNs). • Steady-state analysis and modelling of ADNs. • Control strategies for voltage regulation of ADNs. • Impact of voltage control on power delivered at the transmission/distribution interface. • Assessment of conventional load models for steady-state analysis of ADNs. [ABSTRACT FROM AUTHOR]

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 increasing penetration of converter-interfaced renewable energy sources in the quest to decarbonize power grids has introduced significant challenges considering the safe and reliable operation of modern power systems. Of critical threat are those posed by the reduced system inertia. As a result of these concerns, system operators must monitor and determine close to real-time their system inertia in order to provide proper preventive remedial actions. This is mostly feasible by using measured signals. In this paper, a new measurement-oriented method, based on the time-domain vector fitting technique, is developed for the estimation of inertia constants of synchronous generation units from normal operating condition data and transient responses. The impact of various parameters on the efficiency of the proposed method is investigated by means of Monte Carlo analysis in a simplified system frequency response model. Simulations, conducted in two benchmark power system models, namely the IEEE 9-Bus and the IEEE 39-Bus Test Systems, are used to evaluate the performance of the proposed method. Comparisons with respect to the widely adopted ARMAX-based method are also performed. The applicability of the proposed method is also demonstrated using laboratory measurements. • Time-domain vector fitting technique is used for the estimation of inertia constants. • The method applies to both normal operating condition data and transient responses. • Gaussian and long tail noise distributions are examined. • Investigations with synthetic signals, simulated responses and measured data. • The impact of various parameters on the efficiency of the method is quantified. [ABSTRACT FROM AUTHOR]

Originally, ancillary services (ASs) were provided by large-scale power plants to ensure the secure and reliable operation of power systems. However, with the advent of renewable energy sources either in large-scale or as smaller distributed generation units, there is a strong need to revisit the structure and aim of traditional ASs and reconsider them under two main concepts; ASs provided to distribution networks (DNs), aiming to solve local issues at the distribution level, and ASs offered to transmission system (TS), targeting to solve issues having a wider impact on the power system. The former can be considered as DN-oriented ASs, while the latter as TS-oriented ASs. In this changing environment, the increasing installation of measuring infrastructure has created new sources of data, providing the opportunity to improve the performance of several ASs by applying measurement-based analysis. This review paper gives an insight into the most important DN- and TS-oriented ASs foreseen to apply in future power systems. Additionally, state-of-the-art on measurement-based analysis techniques that can be used to facilitate the provision of several ASs by providing in real-time critical information regarding system dynamic performance is presented. • Detailed review on future ancillary services (ASs) in transmission systems. • Detailed review on future ASs in distribution systems. • Overview of measurement-based techniques to facilitate the provision of ASs. • Discussion on future research areas regarding ASs provision. [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]