The evolution of power distribution grids from passive to active systems creates reliability and efficiency challenges to the distribution system operators. In this paper, an energy management and control scheme for managing the operation of an active distribution grid with prosumers is proposed. A multi-objective optimization model to minimize (i) the prosumers electricity cost and (ii) the cost of the grid energy losses, while guaranteeing safe and reliable grid operation is formulated. This is done by determining the active and reactive power set-points of the photovoltaic and storage systems integrated in the grid buildings. The resulting optimization model is non-convex, thus a convex second-order cone program is developed by appropriately relaxing the non-convex constraints which yields optimal results in most operating conditions. The convexified model is further utilized to develop an algorithm that yields feasible solutions to the non-convex problem under any operating conditions. Moreover, a second novel algorithm to find the operating point that provides fairness between the prosumers and the grid costs is proposed. Simulation results demonstrate the effectiveness and superiority of the proposed scheme in managing an industrial distribution grid compared to a self-consumption approach.

In this paper, a flexibility adequacy assessment of the South East Europe region countries is being presented. Novel technology integration is being considered in order to provide more flexibility resources to the power system to absorb more renewable energy. A flexibility analysis based on the International Energy Agency methodology provided an overall estimation of the flexibility needs and resources of the Bulgarian and Cypriot power systems. Additionally, several flexibility indices have been calculated providing indications of the potential that both systems have to serve more volatile renewable energy sources without jeopardizing the balancing requirements for frequency regulation and security of supply. A detailed algorithm has been developed, in close cooperation with the national stakeholders in Bulgaria and Cyprus, in order to simulate the variations in demand and generation for the following years and calculate statistical indices for flexibility, such as the Insufficient Ramping Rate expectation and Flexibility Residual, apart from the traditional Loss of Load Expectation used in adequacy studies.

Power electronics converters are utilized for interconnecting distributed energy storage systems into the grid. These converters can support the stability of the power system under abnormal grid conditions. In this article, a new coordinated voltage-frequency support strategy is proposed for energy storage systems considering the reactance-to-resistance ratio of the grid impedance. Unlike conventional support schemes for transmission grids, where voltage and frequency support is decoupled, the proposed strategy considers the coupling between voltage and frequency due to the resistive characteristics of the grid impedance in low-voltage distribution grids. An advanced frequency support scheme is also developed considering both droop-based frequency support and virtual inertia control for improving frequency stability. The proposed strategy ensures a fair compensation between voltage and frequency support by utilizing an adaptive gain that is calculated online according to the short-circuit fault characteristics. Simulations and experimental tests are carried out using a laboratory setup to validate the proposed strategy.

The decision-making process during system planning of power systems is something that requires integrated tools that evaluate technical parameters, environmental impact, and overall costs and benefits with various performance indicators (i.e., key performance indicators KPIs). Several cost–benefit analysis approaches have been presented worldwide, providing analytic procedures to quantify the impact and practical effects of specific electricity projects. The implementation of innovation technology into the electricity networks play a critical role to optimizing overall costs. The targets set by the Clean Energy Package have been the main driver for the disruption occurring in the electricity sector, setting electrification of sectors and digitalization as additional emerging challenges. In the present paper, an evaluation approach for the flexibility benefits of smart grid innovations will be presented, as it has been developed and implemented in the context of the Horizon 2020 Research and Innovation project FLEXITRANSTORE. Flexibility is a prerequisite in an effort to achieve an electrical system of low CO2 emissions. Moreover, flexibility contributes to the increase of renewable energy sources penetration, to the network investments deferral and to the enhancement of the efficiency of the system operation, avoiding generation capacity oversizing. Thus, flexibility has been the scope of many projects lately. FLEXITRANSTORE pilot projects are implemented in various sites across Europe and are briefly presented and the respective technologies are propagated on system level approach, evaluating the respective benefits on a specific use case for the power system of Cyprus, where the one of the pilots is located. The paper tries to show the big picture of the project and presents system study use case to highlight the system impacts of the technologies. To this direction, the installation of a BESS to the Cypriot power system is studied, in an effort to examine its impact to the enhancement of the system’s flexibility, considering IRRE as an indicator.

Designing pricing schemes for the electricity retail market is an emerging area with significant impact on the smart grid. This paper proposes the Intraday Increasing Block Pricing scheme, where charging is based on intraday pricing periods. The electricity consumed in each pricing period is split into consumption-blocks with increasing prices. The goal of consumers is to reduce their consumption within each pricing period by distributing their load throughout the day to avoid higher prices. In addition to explaining the proposed pricing scheme, the paper models the retail market behaviour when considering rational consumers. The resulting model is a convex optimization problem that can be utilized as a tool to evaluate the impact of the proposed pricing scheme on consumers and the power system. Different case studies demonstrate the consumer interaction with the proposed scheme and provide evidence on the improvement of power system efficiency, consumer surplus and social equity promotion.

The vast majority of the proposed Wide Area Control (WAC) methodologies is tested and evaluated under the assumption that the system consists only of constant power loads. However, in practice power systems are dominated by non-linear loads, which can potentially affect the smooth operation of the wide area controller and deteriorate the system's stability. This paper is firstly focused on examining the impact of various and commonly used non-linear load models (static and dynamic), such as the exponential, exponential dynamic, ZIP and ZIP-Induction Motor (ZIP-IM) load models on the WAC performance. Real-time simulations on the IEEE 39-bus dynamic test system indicate that the load recovery dynamics of the exponential dynamic load model have a severe impact on the WAC operation, leading the system to instability. Furthermore, it is illustrated that, loads with constant power/current/impedance characteristics have limited effect on the WAC damping capability, even with dynamics included. To address the impact of the exponential dynamic loads on the WAC performance, a novel wide area controller is proposed for coordinating simultaneously all the synchronous generators and controllable loads of the system. Finally, the effect of the size and flexibility of the controllable demand on the performance of the proposed scheme is also investigated, while the robustness of the proposed scheme is evaluated under measurement errors and erroneous generator parameters.

Peak shaving applications provided by energy storage systems are sustainable solutions for enhancing the existing capacity of distribution feeders and transformers in order to maintain their safe and reliable operation under an increased penetration of renewable energy sources and load demand growth. This work investigates the integration of a flywheel energy storage system installed in a feeder of a distribution network to provide peak shaving services. An empirical model is defined to determine the energy losses of a prototype flywheel system using an experimental setup. Furthermore, a multi-objective optimization scheme is proposed to minimize the flywheel energy losses along with the violated peak power of the feeder. Three different objective functions for applying peak shaving are presented and their efficiency is investigated in the simulation results. Finally, the impact of the flywheel energy losses on the peak shaving application of the distribution feeder is examined using a prototype and a commercial-grade flywheel energy storage system.

European and global electricity sector decarbonisation is driving changes in wholesale electricity markets as market operators, regulators and system operators encourage increased levels of flexibility. Existing wholesale market design characteristics are changing; new, parallel marketplaces are also emerging. This paper analyses the design space for ancillary services and balancing markets, considers settings in Europe using ENTSO-E annual survey data and discusses changes to market settings that promote flexibility. Finally, it proposes some basic changes to the intraday market.

The international research experiences for students (IRES) program addresses multidisciplinary research at the overlap of sustainability, power systems, and signal processing with the aim of improving efficiency in PV power generation. The IRES program engages faculty at the ASU SenSIP Center and at the University of Cyprus’ (UCy) KIOS Center to address fault detection and other research problems in solar energy arrays. IRES participants are tasked with studying algorithms and software to monitor and control solar arrays. Research involves using data from programmable sensors embedded in smart monitoring devices (SMDs) that are attached to solar panels. The SMDs have sensors, actuators and radios that enable researchers to work with a solar array where every panel provides data. IRES participants are trained to use machine learning to assess the solar array condition. The program also trains the students to perform research and present results in international settings. In the first year of the project, four students travelled to the University of Cyprus and worked with UCy faculty on fault detection. The program included weekly research presentations by the students at UCy, presentations at a local workshop and continued engagement after the summer experience at ASU. Two of the students were able to present and publish their work in international conferences.

This paper presents the formulation of Wide Area Control (WAC) signals for either coordinating all the governors of the system or coordinating simultaneously both the governor and the Power System Stabilizer (PSS) of each generator. This is achieved through the development of suitable WAC signals intended for the coordination of their common input signal (rotor speed deviation) having as objective the compensation of all the local and inter-area oscillations. Furthermore, an adaptive tuning method to estimate weights for each inter-generator interaction is also presented. This is required to regulate adaptively the level of the WAC contribution to all the local controllers. The weights are computed according to the electric connectivity between the generators. For the evaluation of the proposed methods, both offline and real-time simulations are performed on the IEEE 39-bus test system. The results indicate the substantial improvement of the system’s stability when the proposed governor/PSS coordination is considered. The performance of the WAC scheme is further increased when the adaptive tuning procedure is applied. Finally, the requirement of having PMUs at each generator bus is relaxed by utilizing the coherency concept.

Increased level of flexibility is essential in power systems with high penetration of renewable energy sources in order to maintain the balance between the demand and generation. Actually, the flexibility provided by energy storage systems and flexible conventional resources (i.e., generating units) can play a vital role in the compensation of the renewable energy sources variability. In this paper, the flexibility of the conventional generating units is quantified and incorporated in a unit commitment model in order to evaluate the impact of different system flexibility levels on the optimal generation dispatch and on the operational cost of the power system. An emerging flexible option such as the battery storage is included in the unit commitment formulation, evaluating the flexibility contribution of the storage and its effect on the system operational cost. In this paper, the flexibility of a real power system is assessed while the unit commitment problem is formulated as a mixed-integer linear program. The results show that the integration of a storage unit in the power generation portfolio provides a significant amount of flexibility and reduces the system operational cost due to the peak shaving and valley filling.

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 article 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 indicates that the proposed method converged in all trials, despite including the neutral voltage in the state vector.

Power system operators are continuously striving to achieve more economical, environmental friendly, and stable operation of the system. The integration of Renewable Energy Sources (RES) can benefit the system in terms of cost and environmental friendliness but at the same time it poses challenges related to system stability. One way for achieving an increased penetration of RES while maintaining the system integrity is the installation of Battery Energy Storage Systems (BESS). In this paper, the effect of a large scale BESS on the power system operating condition is investigated. A MILP-based unit commitment algorithm is used for obtaining the optimal generation scheduling in the system when a BESS is employed and the results are used for evaluating the improvement in several indices such as system operating cost, CO2 emissions, and system flexibility. Through a case study, the positive impact of the deployment of a BESS on a power system is verified, indicating that the aforementioned indices are improved in the presence of a BESS.

The increasing integration of distributed energy resources (DERs) in distribution grids imposes an imperative need for reliable and accurate monitoring of the grids' operating condition. Consequently, electric utilities have recently started considering the deployment of Phasor Measurement Units (PMUs) in Medium Voltage Distribution Grids (MVDGs) in order to enhance and improve the monitoring capabilities of the operator. In this paper, a fast reporting measurement device is considered at a MV-LV transformer substation for enhancing the monitoring of the MVDG. A monitoring scheme is then proposed that utilizes the capabilities of this device not only for enhancing the monitoring of the MVDG, but also to simultaneously improve the monitoring of the Low Voltage Distribution Grid (LVDG). The results of the numerical simulations indicate that the proposed scheme exhibits good performance in all the considered scenarios.

This paper presents a fault-tolerant secondary and adaptive primary microgrid control scheme using a hybrid multi-agent system (MAS), capable of operating either in a semi-centralised or distributed manner. The proposed scheme includes a droop-based primary level that considers the microgrid energy reserves in production and storage. The secondary level is responsible for: a) the microgrid units' coordination, b) voltage and frequency restoration and c) calculation of the droop/ reversed-droop coefficients. The suggested architecture is arranged upon a group of dedicated asset agents that collect local measurements, take decisions independently and, collaborate in order to achieve more complex control objectives. Additionally, a supervising agent is added to fulfill secondary level objectives. The hybrid MAS can operate either with or without the supervising agent operational, manifesting fast redistribution of the supervising agent tasks. The proposed hybrid scheme is tested in simulation upon two separate physical microgrids using three scenarios. Additionally, a comparison with conventional control methodologies is performed in order to illustrate further the operation of a hybrid approach. Overall, results show that the proposed control framework exhibits unique characteristics regarding reconfigurability and fault-tolerance, while power quality and improved load sharing are ensured even in case of critical component failure.

The operation of a typical 4-wire, radial, Low Voltage Distribution Grid (LVDG) in the Cyprus power system, where the neutral conductor is grounded only at the MV/LV transformer, is investigated under different scenarios. These include seasonal loading profiles and different penetration levels of photovoltaics (PVs) and electric vehicles (EVs). The analysis is focused on the impact of PVs and EVs on the voltage profile of the LVDG, the loading conditions of the distribution lines/cables and on the system losses. The results indicate that even with a moderate number of PVs, the admissible voltage limits can be exceeded due to the significant voltage drop across the neutral conductor. Moreover, the distribution lines/cables near the transformer can be overloaded if the charging process of the electric vehicles is not coordinated and is left freely to end users.

An increase in grid-connected photovoltaic arrays creates a need for efficient and reliable fault detection. In this paper, machine learning strategies for fault detection are presented. An Artificial Neural Network was studied with the goal of detecting three photovoltaic module conditions. In addition, an unsupervised approach was successfully implemented using the -means clustering algorithm, successfully detecting arc and ground faults. To distinguish and localize additional faults such as shading and soiling, a supervised approach is adopted using a Radial Basis Function Network. A solar array dataset with voltage, current, temperature, and irradiance was examined. This dataset had labeled data with normal conditions and faults due to soiling and shading. A radial basis network was trained to classify faults, resulting in an error rate below 2% on synthetic data with realistic levels of noise.

Renewable sources are expected to be a key element of future power systems. With many challenges ahead, thinking out of the box is necessary in order to equip the power system with additional advanced functionalities and capabilities to combat the anticipated challenges. The associated equipment of distributed generation can be seen as a grid asset upgrade because of the increased number of elements connected to the grid, such as grid side converters (GSC) of photovoltaics and battery storage systems. It therefore makes sense to think of ways to diversify the role of distributed renewables in a way that benefits the grid, consumers, and prosumers in terms of power quality. The work proposes an advanced, multi-function GSC control technique for improving the distribution grid power quality by enabling the injection of asymmetric, DC and harmonic currents in case it is needed. Injecting for example such currents locally through the GSC of a residential photovoltaic system can compensate undesired characteristics of the prosumer loads in order to allow the flow of symmetric and high quality currents between the prosumer and the distribution grid. Experiments and simulation results are presented to validate the performance of proposed control technique.

This work proposes a sensor-less controller for grid tied photovoltaic (PV) inverters to enable phase balancing functionalities for compensating asymmetric loading conditions imposed by building loads in low voltage distribution grids. For enabling such an advanced functional operation by PV inverter, the first step is to enable the inverter to estimate the equivalent grid impedance. Then, the grid impedance is utilized to approximate the nearby load asymmetries without using any additional current sensors. Finally, advanced control schemes have been developed for PV inverters in order to enable the new phase balancing operation mode, where the inverter can compensate the asymmetric loading conditions of a distribution feeder. The effectiveness of the proposed method has been experimentally validated in a prototype where the grid tied PV inverter is able to compensate nearby load asymmetries and maintain a purely symmetrical interaction with the grid. Further, a simulation-based investigation in a realistic distribution feeder has been performed in order to highlight the benefits of the proposed approach regarding the power quality, the energy losses and the effective utilization of distribution grid capacity.