It is getting more common every day to install inverters that offer several grid support services in parallel. As these services are provided, a simultaneous need arises to know the combined limit of the inverter for those services. In the present paper, operational limits are addressed based on a utility scale for a real inverter scenario with an energy storage system (ESS) (1.5 MW). The paper begins by explaining how active and reactive power limits are calculated, illustrating the PQ maps depending on the converter rated current and voltage. Then, the effect of the negative sequence injection, the phase shift of compensated harmonics and the transformer de-rating are introduced step-by-step. Finally, inverter limits for active filter applications are summarized, to finally estimate active and reactive power limits along with the harmonic current injection for some example cases. The results show that while the phase shift of the injected negative sequence has a significant effect in... [more]

Virtual synchronous generator (VSG) control lacks voltage inertia and powerful decoupling capabilities. The voltage of the distributed generator (DG) unit controlled by the VSG will be easily affected by power fluctuations and high-frequency noise, and the DG coupling usually makes the VSG control effect unsatisfactory. In order to effectively reduce power fluctuations, the influence of high-frequency noise on voltage, the influence of coupling on the power regulation, and effectively improve the economy of the economic system, the improved VSG control that combines voltage inertia and virtual impedance is proposed in this paper. The second-order inertia in the proposed VSG control strategy can minimize the voltage change rate and filter high-frequency noise from the excitation and virtual impedance. The virtual impedance in the proposed VSG control strategy can simulate the actual impedance to change the line characteristics, so the coupling of the DG unit can be reduced. Experimental... [more]

Faults in electrical networks are among the key factors and sources of network disturbances. Control and automation strategies are among the key fault clearing techniques responsible for the safe operation of the system. Several researchers have revealed various constraints of control and automation strategies such as a slow dynamic response, the inability to switch the network on and off remotely, a high fault clearing time and loss minimization. For a system with wind energy technologies, if the power flow of a wind turbine is perturbed by a fault, the intermediate circuit voltage between the machine side converter and line side converter will rise to unacceptably high values due to the accumulation of energy in the DC link capacitor. To overcome the aforementioned issues, this paper used MATLAB simulations and experiments to analyze and validate the results. The results revealed that fault ride through capability with Supervisory Control and Data Acquisition (SCADA) viewer software,... [more]

Aggregated Norton’s equivalent models, with parallel impedance and current injection at different harmonic frequencies are used to model the distribution grid in harmonic studies. These models are derived based on measurements and/or prior knowledge about the grid. The measurement-based distribution (sub-)grid impedance estimation method uses harmonic phasors of 3-phase current and voltage measurements to capture the response of the distribution (sub-)grid before and after an event in the utility side of the grid. However, due to increasing non-linear components in the grid, knowledge about uncertainty in parameters of such equivalent models which intrinsically describe a linear grid becomes important. The aim of this paper is to present two novel methods to calculate the uncertainty of the measurement-based Norton’s equivalent harmonic model of the distribution (sub-)grids as seen from the utility side at the Point of Common Coupling (PCC). The impedance and the uncertainty calculatio... [more]

Recently, the awareness of the severe consequences of greenhouse gases on the environment has escalated. This has encouraged the world to reduce the usage of fossil fuels for power generation and increase the use of cleaner sources, such as solar energy and wind energy. However, the conventional power system itself was designed as a passive power system, in which power generation is centralised, and power flows from substations towards the loads. Decentralised renewable energy sources, also called distributed generators, were introduced to create an active power system in which power generation can occur anywhere in the power system. Decentralised power generation creates challenges for the conventional power system, such as voltage fluctuations, high voltage magnitudes, reverse power flow, and low power factor. In this paper, an adaptive control system that coordinates different distributed generators for voltage regulation and power factor correction is introduced and designed. The c... [more]

The global proliferation of plug-in electric vehicles (PEVs) poses a major challenge for current and future distribution systems. If uncoordinated, their charging process may cause congestion on both network transformers and feeders, resulting in overheating, deterioration, protection triggering and eventual risk of failure, seriously compromising the stability and reliability of the grid. To mitigate such impacts and increase their hosting capacity in radial distribution systems, the present study compares the levels of effectiveness and performances of three alternative centralized thermal management formulations for a real-time agent-based charge control algorithm that aims to minimize the total impact upon car owners. A linear formulation and a convex formulation of the optimization problem are presented and solved respectively by means of integer linear programming and a genetic algorithm. The obtained results are then compared, in terms of their total impact on the end-users and... [more]

The operation of microgrids is a complex task because it involves several stakeholders and controlling a large number of different active and intelligent resources or devices. Management functions, such as frequency control or islanding, are defined in the microgrid concept, but depending on the application, some functions may not be needed. In order to analyze the required functions for network operation and visualize the interactions between the actors operating a particular microgrid, a comprehensive use case analysis is needed. This paper presents the use case modelling method applied for microgrid management from an abstract or concept level to a more practical level. By utilizing case studies, the potential entities can be detected where the development or improvement of practical solutions is necessary. The use case analysis has been conducted from top-down until test use cases by real-time simulation models. Test use cases are applied to a real distribution network model, Sundo... [more]

Along with economic development and development of power systems, new, more effective models of the energy market are sought. Traditional zonal models used on the electricity market have proved to be poorly adapted to new circumstances and phenomena occurring in the macroeconomic environment. The main aim of the research was to show the direction (including the nodal model and prosumer behavior) in which the energy market should develop in order to meet the state-of-the-art technical, ecological and social challenges. Therefore, with the new challenges, a new chapter has opened up on very interesting research for the electrical industry. There are new solutions for the development and modernization of models from the point of view of management and econometrics of the energy market, adapted to new challenges related to ecology, technology, and competition. This article presents the zone model with its imperfections and suggestions for its improvement and proposes a nodal model that may... [more]

With increasing renewable penetration and projected increase in natural disasters, the reliability and resiliency of a power system become crucial issues. As network inertia drops with increasing penetration of renewables, operators search for flexible resources that can help cope with a disruptive event or manage renewable intermittency. Energy storage is a solution, but the type of storage solution needs to be profitable to exist in the current and upcoming power markets. Advanced pumped-storage hydropower (PSH) is one solution that can help cope with such requirements, which will in turn help to increase the renewable penetration in the system. This paper qualitatively compares the revenue earning potential of PSH configurations, including, adjustable-speed PSH (AS-PSH) and ternary PSH (T-PSH) in comparison to conventional PSH (C-PSH) from the arbitrage and regulation markets, with and without the presence of wind penetration. In addition, a framework for quantitative analysis of an... [more]

The objective of this paper is to present a power conversion system, based on a bidirectional DC/DC converter, along with a supercapacitor bank, that mitigates the voltage transients that occur on the DC distribution network of More/All Electric Aircrafts. These transients, such as voltage sags and swells appear on the DC buses of on-board microgrids, mainly due to load variations and are classified according to the aircrafts electric power system standards. First, we shortly describe an aircraft distribution network, that is applicable to the most common actual aircraft architectures, then we present the proposed system, along with the bidirectional DC/DC converter design, the control technique and the supercapacitor bank sizing. Finally, we present simulation and experimental results that support the effectiveness of the proposed system to effectively compensate voltage transients, supporting the DC buses in dynamic conditions. Concluding, the proposed system provides high power qual... [more]

In recent years, rapid advancements have developed in multifunctional and wearable electronics, which call for more lightweight, flexible energy sources. However, traditional disposable batteries and rechargeable batteries are not very suitable because of their bulky appearance, limited capacity, low flexibility, and environmental pollution problem. Here, by applying a mature manufacturing technology that has existed in the textile field for a long time, a woven fabric triboelectric nanogenerator (WF-TENG) with a thinner structure that can be mass-fabricated with low cost, perfect stability, and high flexibility is designed and reported. Due to the good intrinsic quality of TENGs, the maximum voltage of this WF-TENG can easily reach 250 V under a pressure of 3.5 kPa and a tapping frequency of 0.33 Hz. Because of the stable plain-woven structure, the output voltage can remain relatively stable even after the WF-TENG has been working for about 5 h continuously, clearly demonstrating its... [more]

The penetration of distributed generators (DGs) in the existing power system has brought some real challenges regarding the power quality and dynamic response of the power systems. To overcome the above-mentioned issues, the researchers around the world have tried and tested different control methods among which the computational intelligence (CI) based methods have been found as most effective in mitigating the power quality and transient response problems intuitively. The significance of the mentioned optimization approaches in contemporary ac Microgrid (MG) controls can be observed from the increasing number of published articles and book chapters in the recent past. However, literature related to this important subject is scattered with no comprehensive review that provides detailed insight information on this substantial development. As such, this research work provides a detailed overview of four of the most extensively used CI-based optimization techniques, namely, artificial ne... [more]

This paper introduces a modular testbed to simulate AC/DC microgrids. The testbed is implemented in Matlab Simulink and is based on the energetic macroscopic representation (EMR) formalism. It is designed to be a tool to evaluate energy management strategies in AC/DC microgrids. The microgrid simulation model includes a photovoltaic generator, a fuel cell system, ultracapacitors, and batteries on the DC side. It includes voltage source converters (VSC) to couple the DC side with the AC side of the microgrid, which includes a variable AC load and a synchronous generator. Two case studies illustrate the use of the testbed. The model is implemented in Matlab Simulink and made openly available for the scientific community. Using this model, researchers can develop and evaluate energy management strategies in AC/DC microgrids.

This review paper provides a critical interpretation and analysis of almost 150 dedicated optimization research papers in the field of droop-controlled islanded microgrids. The significance of optimal microgrid allocation and operation studies comes from their importance for further deployment of renewable energy, reliable and stable autonomous operation on a larger scale, and the electrification of rural and isolated communities. Additionally, a comprehensive overview of islanded microgrids in terms of structure, type, and hierarchical control strategy was presented. Furthermore, a larger emphasis was given to the main optimization problems faced by droop-controlled islanded microgrids such as allocation, scheduling and dispatch, reconfiguration, control, and energy management systems. The main outcome of this review in relation to optimization problem components is the classification of objective functions, constraints, and decision variables into 10, 9 and 6 distinctive categories,... [more]

The need for accurate measurements and for estimating the uncertainties associated with measures are two pillars for researchers and metrologists. This is particularly true in distribution networks due to a mass deployment of new intelligent electronic devices. Among such devices, phasor measurement units are key enablers for obtaining the full observability of the grid. The phasor measurement unit performance is mostly evaluated by means of the total vector error, which combines the error on amplitude, phase, and time. However, the total vector error is typically provided merely as a number, that could vary within an unknown interval. This may result into the phasor measurement unit incompliance with the final user expectancies. To this purpose, and with the aim of answering practical needs from the industrial world, this paper presents a closed-form expression that allows us to quantify, in a simple way, the confidence interval associated with the total vector error. The input requir... [more]

In the field of microgrids (MGs), steady-state power imbalances and frequency/voltage fluctuations in the transient state have been gaining prominence owing to the advancing distributed energy resources (DERs) connected to MGs via grid-connected inverters. Because a stable, safe power supply and demand must be maintained, accurate analyses of power system dynamics are crucial. However, the natural frequency components present in the dynamics make analyses complex. The nonlinearity and confidentiality of grid-connected inverters also hinder controllability. The MG considered in this study consisted of a synchronous generator (the main power source) and multiple grid-connected inverters with storage batteries and virtual synchronous generator (VSG) control. Although smart inverter controls such as VSG contribute to system stabilization, they induce system nonlinearity. Therefore, Koopman mode decomposition (KMD) was utilized in this study for consideration as a future method of data-driv... [more]

The problem of optimal phase-balancing in three-phase asymmetric distribution networks is addressed in this research from the point of view of combinatorial optimization using a master−slave optimization approach. The master stage employs an improved sine cosine algorithm (ISCA), which is entrusted with determining the load reconfiguration at each node. The slave stage evaluates the energy losses for each set of load connections provided by the master stage by implementing the triangular-based power flow method. The mathematical model that was solved using the ISCA is designed to minimize the annual operating costs of the three-phase network. These costs include the annual costs of the energy losses, considering daily active and reactive power curves, as well as the costs of the working groups tasked with the implementation of the phase-balancing plan at each node. The peak load scenario was evaluated for a 15-bus test system to demonstrate the effectiveness of the proposed ISCA in red... [more]

There is much research about the determinants of investments, but there is a shortage of similar studies for Poland. Therefore, the overall goal of the paper is to analyze the determinants of investments made by enterprises from the energy sector as well as their delays in Poland in the years 2000−2019. In this period, a strong growth of investments in energy was observed in the country. In connection to this, the authors set four hypotheses and verified them with the following statistical methods: canonical analysis, linear and causality correlation, autocorrelation and cointegration tests. The paper found that there is a relationship between public consumption and investment spending of small enterprises in Poland. That means that only some macroeconomic parameters are connected with investments. Moreover, the changes in the value of past investments has a negative influence in current investments.

The improved features of AC/DC converters, the need to enhance cross-country interconnections, the will to make massive remote renewable energy sources available, and the fear of populations about overhead lines have fostered HVDC cable transmission all over the world, leading in the last two decades to an exponential increase of commissioned HVDC cable projects, particularly of the extruded insulation type. Comprehensive surveys of the issues to be faced by HVDC extruded cable systems appeared in the literature some years ago, but they are not so up-to-date, as HVDC extruded cable technology is developing fast. Therefore, the contribution this paper aims at giving is a systematic, comprehensive and updated summary of the main present and future issues and challenges that HVDC cable systems have to face to further improve their performance and competitiveness, so as to meet the growing quest for clean and available energy worldwide. The topics covered in this review−treated in alphabet... [more]

Microgrids operating on renewable energy resources have potential for powering rural areas located far from existing grid infrastructures. These small power systems typically host a hybrid energy system of diverse architecture and size. An effective integration of renewable energies resources requires careful design. Sizing methodologies often lack the consideration for reliability and this aspect is limited to power adequacy. There exists an inherent trade-off between renewable integration, cost, and reliability. To bridge this gap, a sizing methodology has been developed to perform multi-objective optimization, considering the three design objectives mentioned above. This method is based on the non-dominated sorting genetic algorithm (NSGA-II) that returns the set of optimal solutions under all objectives. This method aims to identify the trade-offs between renewable integration, reliability, and cost allowing to choose the adequate architecture and sizing accordingly. As a case stud... [more]

This paper introduces the concept, theory of operation and applications of soft open points for direct current networks (DCSOPs). The DCSOP is based on a bidirectional DC−DC converter actively controlled to behave like a normal conductor. Unlike the normal conductor, the DCSOP can transfer the electric power between nodes at different voltage levels. With this advantage, the DCSOP can effectively control the power flow direction. Thus, DCSOPs can play a vital role in the reconfiguration of DC distribution networks. The operation and control of the DCSOP device was investigated, both in transient and steady-state conditions. Then, a DCSOP was integrated into a DC microgrid model to validate its ability to change the power flow through the modelled feeders. In addition, a set of reliability indicators was calculated for the DC microgrid under different reconfiguration scenarios. It was shown that reliability is improved when the DCSOP device implements network reconfiguration. Finally, a... [more]

This research paper aims to evaluate the effect of social networks on the green innovation of energy sector firms working around the globe. The study also evaluated green dynamic capabilities’ mediating, and green organizational culture’s moderating role in the association of the social networks and green innovation. The study will help electricity production and distribution firms to become more environmentally proactive and achieve green innovation. For this research, study data were collected from employees working in the energy sector firms of Pakistan. Standardized scales were adapted from previous studies and a questionnaire was developed using ‘Google Docs’ and distributed using Facebook. From different energy sectors of Pakistan,476 respondents filled the questionnaires. To examine the research hypotheses, we chose energy firms that act as small and medium enterprises and face problems in the achievement of green innovation. For testing the proposed relationships, descriptive s... [more]

In low voltage (LV) distribution systems, the problem of overvoltage is common during the lower load intervals. This problem arises because of the high value of R/X ration of these systems. Many techniques are available in literature to cope up with this problem at the converter level; mostly these methods control the reactive or active power of the photovoltaic (PV) systems. However, there are certain restrictions and complications with the reactive power control of PV systems. Most of the active power control methods have been implemented at the inverter stage of the PV system, resulting in implementation complexities and excessive oversizing of the converter. Therefore, in this paper, a simple, de-rating based voltage control algorithm is proposed to overcome the problem of overvoltage. So far de-rating technique has been used to enable frequency support functions in PVs; in a first of its kind, de-rating technique is used here to control the voltages in PV rich LV distribution syst... [more]

To improve the prediction accuracy of short-term load series, this paper proposes a hybrid model based on a multi-trait-driven methodology and secondary decomposition. In detail, four steps were performed sequentially, i.e., data decomposition, secondary decomposition, individual prediction, and ensemble output, all of which were designed based on a multi-trait-driven methodology. In particular, the multi-period identification method and the judgment basis of secondary decomposition were designed to assist the construction of the hybrid model. In the numerical experiment, the short-term load data with 15 min intervals was collected as the research object. By analyzing the results of multi-step-ahead forecasting and the Diebold−Mariano (DM) test, the proposed hybrid model was proven to outperform all benchmark models, which can be regarded as an effective solution for short-term load forecasting.

With conventional droop control, the droop relationship between the voltage and reactive power is not purely linear because of the filter reactance. This paper focuses on the theoretical analysis to account for this characteristic and presents a precise power flow method for conventional droop control. The proposed method is universal, which can handle not only conventional droop control, but also other control strategies, such as robust droop control, constant power control, and constant voltage−frequency control. It can also handle frequency-dependent active and reactive power loads and is adapted for islanded and grid-connected systems. The proposed method extends the applicability of conventional power flow methods to microgrids so that the framework of the method is generic; any conventional power flow algorithm can be adapted to this framework. Compared with the time-domain simulation method, the proposed method is accurate, simple, and easy to implement for industrial applicatio... [more]