Grigoris Papagiannis

Aristotle University of Thessaloniki | AUTH · School of Electrical and Computer Engineering

The largest parts of energy demand within the residential sector are used for space heating (SH), domestic hot water (DHW) and space cooling (SC). The thermal and electrical needs can be mainly covered by energy systems that consist of Photovoltaics (PVs), solar thermal collectors (STCs), heat pumps (HPs) and flexibility sources, e.g. battery energ...

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...

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...

Few small and medium-sized enterprises (SMEs) have undertaken an energy audit to date and even fewer have taken action to implement energy-saving measures. Lack of time, knowledge, and finance, coupled with the low priority that SMEs give to energy management, are the most commonly cited barriers to effective energy management in SMEs. Four project...

The integration of photovoltaics (PVs) in low-voltage (LV) grids is expected to rise within the following years posing technical challenges to the reliable operation of the electrical system. To tackle these challenges, distributed energy storage systems (ESSs) coupled with PVs at prosumer side arise as a promising solution. Therefore, during the l...

The calculation of the influence of the imperfect earth on overhead conductors is an important issue in power system analysis. Rigorous solutions contain infinite integrals; thus, due to their complex form, di�erent simplified closed-form expressions have been proposed in the literature. This paper presents a detailed analysis of the e�ect of di�er...

Over the last few decades, there is a constantly increasing deployment of solar photovoltaic (PV) systems both at the commercial and residential building sector. However, the steadily growing PV penetration poses several technical problems to electric power systems, mainly related to power quality issues. To this context, the exploitation of energy...

During the last two decades, the use of residential photovoltaic systems (PVs) has been widely promoted by governments through various support mechanisms such as feed-in-tariffs, net-metering, net-billing, etc. These support schemes have developed a secure investment environment, increasing the penetration level of PVs in low-voltage distribution g...

Three load matching indicators (self-consumption rate, self-sufficiency rate, loss of load probability) and the CO 2 emissions were evaluated for 55 Cypriot households with 3 kWp rooftop photovoltaic (PV) generators. The calculations were performed using 30-minute generation and consumption data from a large scale smart meter project in Cyprus. To...

Over the last decades, the growing energy consumption of commercial and residential buildings has considerably increased the energy-related carbon dioxide (CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) emissions. At EU level, the Energy Performance of Buildings Directive (EPBD) has intro...

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 propag...

--- The paper has been published: DOI: 10.1016/j.renene.2020.01.061 --- Over the last few decades, there is a constantly increasing deployment of solar photovoltaic (PV) systems both at the commercial and residential building sector. However, the steadily growing PV penetration poses several technical problems to electric power systems, mainly rel...

In this paper, a coordinated control strategy is proposed to effectively address the voltage regulation issue in active unbalanced low-voltage (LV) distribution networks. The proposed control scheme is based on a two-layer centralized approach, consisting of the local and the overlaying control layers. The former is embedded at the hardware level o...

Scope of this paper is to investigate the effect of different load and distributed generation (photovoltaic systems and wind generators) modelling approaches for the steady-state analysis of distribution networks and the development of ancillary services by system operators. Specifically, five different modelling approaches are considered, based on...

During the last decade the dynamic properties of power systems have been altered drastically, due to the emerge of new non-conventional types of loads as well as to the increasing penetration of distributed generation. To analyze the power system dynamics and develop accurate models, measurement-based techniques are usually employed by academia and...

This paper investigates the impact of harmonics in underground medium-voltage cables to the induced voltages on the cable sheaths of the excited system as well as the corresponding electromagnetic interference (EMI) to nearby coated pipelines. To evaluate systematically the harmonic induced voltages on both cable sheaths and pipelines a benchmarkin...

In electromagnetic transient analysis, a major issue is the influence of the imperfect earth on the propagation characteristics of conductors. Although soil electrical properties present significant frequency-dependent (FD) behavior, in most cases earth is considered with constant properties. In this paper, the impact of the FD soil properties on t...

During the last decades, a significant number of mode identification techniques and dynamic equivalent models have been proposed in the literature to analyze the dynamic properties of transmission grids and active distribution networks (ADNs). The majority of these methods are developed using the measurement-based approach, i.e., by exploiting dyna...

This paper presents a methodology for the steady-state analysis, i.e., power flow analysis, of islanded AC microgrids (MGs), operated under the droop control scheme. In the proposed framework, the power flow is computed using conventional power flow methods. For this purpose, a slack bus is considered to be connected to a random node of the examine...

In order to determine the most suitable storage system for buildings with photovoltaic generators (PVs), a holistic analysis of the energy consumption is often required. In that sense, this paper provides a comparative assessment of thermal and battery storage in the context of nearly zero energy buildings (NZEBs). A NZEB with a PV, heat pump and a...

In this paper, a thorough analysis is performed to evaluate the impact of the battery energy storage systems (BESSs) on the electrical behavior of the prosumers. Its distinct feature is the use of real measurements acquired from three pilot case studies located at the region of Northen Greece. Two types of BESS technologies are examined, namely the...

In this work, a two-stage approach is introduced to efficiently solve the optimal voltage regulation problem in radial medium-voltage (MV) distribution networks. The proposed method uses the available reactive power of distributed generation units and the on-load tap changer (OLTC) of the high-/medium-voltage transformer to regulate network voltage...

The main objective of this paper is the effective voltage regulation in radial medium-voltage (MV) distribution networks with high distributed generation (DG) penetration, ensuring near-minimum active power losses. For this purpose, a new control strategy with low computational complexity is proposed. The method exploits the reactive power capabili...

In this paper, we investigate the application of multi-input multi-output (MIMO) orthogonal frequency-division multiplexing (OFDM) to narrowband powerline communications (NB-PLC) over medium-voltage (MV) underground (UG) networks. We study different MIMO transmission scenarios with different injection configurations utilizing both the cable conduct...

Aggregated equivalent models for the dynamic analysis of active distribution networks (ADNs) can be efficiently developed using dynamic responses recorded through field measurements. However, equivalent model parameters are highly affected from the time-varying composition of power system loads and the stochastic behavior of distributed generators....

In this chapter, data transmission in smart distribution grids (SDGs) is analyzed by means of multiple-input multiple-output (MIMO) narrowband (NB) power-line communication (PLC) systems, by applying orthogonal frequency-division multiplexing (OFDM) encoding. Regarding NB-PLC physical layer (PHY) modeling, multiconductor transmission line (MTL) the...

Increase of photovoltaic (PV) systems penetration in distribution networks is being challenged by technical barriers, especially in low voltage (LV) networks, such as over-voltages caused by reverse power flows and high PV power injection to the grid. Among other solutions for over-voltage mitigation, active power management can be a highly effecti...

The determination of soil parameters is an important topic regarding the safe and efficient design of electrical grounding systems as well as the accurate calculation of the per-unit-length parameters of overhead transmission lines and underground cable systems. Scope of this paper is to investigate the seasonal variation of the two-layer earth str...

Decentralized energy storage systems (ESSs) can provide great advantages to low-voltage (LV) distribution networks, enhancing the further penetration of photovoltaic (PV) systems in existing electrical grids. An ESS can locally absorb the PV produced energy during periods of high solar irradiation, thus alleviating potential overvoltages in distrib...

TThis paper examines voltage quality problems in Low Voltage (LV) Distribution Networks (DNs) due to high Photovoltaic (PV) and Electric Vehicles (EVs) penetration. The proposed methodology considers Battery Energy Storage Systems (BESSs) along with the PV units in order to store the energy surplus that causes overvoltage during the high PV generat...

Scope of this paper is to deliver a complete techno-economic model for the economic assessment of lithium-ion battery energy storage systems in the framework of the nearly zero energy buildings (NZEB). The proposed model simulates the combined operation of photovoltaics, solar thermal generators, heat pump generators, electrical and thermal storage...

In this paper, two discretization techniques are combined to present a coupled electro-thermal model for the transient analysis of gas-insulated transmission lines (GILs). The analysis of the thermal problem is based on the volume-element-method (VEM), representing heat transfer equations on a 2D axisymmetric GIL model and determining temperature d...

Mode identification from post-disturbance "ringdown" responses can provide vital information concerning the dynamic performance and the stability margins of power systems. Therefore, several measurement-based identification techniques have been proposed in the literature to analyze ringdown responses of transmission systems and provide close to rea...

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 iter...

This paper presents a novel EQF level 7 Building Educational Program, implemented under MEnS's Horizon2020 project framework. The program has been organized in different countriesacrossEurope with common structure and learning outcomes. The objective is to upgrade professional skills in NZEB design and construction, thus increasing the experts’ cap...

Electrochemical storage technology and especially battery energy storage (BES) is emerging as one of the fastest growing storage technologies for grid-connected applications. It has an important role to play in the proposed energy transition offering suitable services for domestic and utility scale applications such as the balancing of the intermit...

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...

Photovoltaic (PV) penetration in Low-Voltage (LV) networks is expected to increase in the following years, posing a series of problems in the operation pf low-voltage networks. Among the most important challenges imposed, is the reverse power flow caused by high injected energy from distributed PVs during peak irradiation hours. This is the reason...

This letter delivers a method to extend the use of the exponential recovery model (ERM) for the dynamic simulation of active distribution networks (ADNs). The conventional ERM uses exponential functions to describe the steady-state and transient characteristics of the grid, failing to replicate reverse power flow phenomena which may occur in modern...

In this paper, the propagation characteristics of transmission line configurations located above and below imperfect earth are investigated, by means on generalized and approximate earth formulations. The generalized formulations consider earth conduction effects both on series impedances and shunt admittances of the conductors, contrary to the app...

In this paper, detailed mathematical formulation considering a coupled electro-thermal model for transient studies on transmission systems is presented. Regarding the thermal modeling, volume-element-method (VEM) is used to represent heat transfer equations on a 2D axisymmetric line model to be solved and temperature distribution over space and tim...

Several parts of the Mediterranean basin are experiencing grid parity nowadays, which is a sign that Photovoltaic (PV) technology has become competitive to conventional energy sources and may continue to develop without support. The net-metering policy takes advantage of the grid parity situation and is considered a step away from fading Feed-in Ta...

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 la...

In this paper, a centralized control strategy for lowvoltage 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 o...

Photovoltaic systems are increasingly integrated into the low voltage (LV) distribution grid and are particularly installed on buildings. This trend is expected to continue in the following years as new buildings should be Nearly Zero Energy ones that will necessarily incorporate renewables. This situation has already started to produce significant...

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.

In this paper induced voltages and currents caused by underground cables are calculated in cable sheaths and nearby metallic pipelines. The performance of several simulation methods and models are investigated in steady-state, considering also different implementations in ATP-EMTP, EMTP-RV and PSCAD/EMTDC. The analysis is extended in the simulation...

A novel EQF level 7 educational programs for energy and building professionals is presented in this paper. The program is organized by 10 Universities across 10 E.U. countries, with a common structure and learning outcomes. The main goal is to upgrade professional skills in NZEB design and construction with courses of 10 ECTS, while also enhancing...

In this paper, a nearly decentralized voltage regulation algorithm is proposed that effectively coordinates the operation of distributed generation (DG) units in order to minimize the active power losses and the total reactive power consumption in medium-voltage (MV) networks with radial topology. This control requires minimum communication infrast...

The main objective of this paper is to investigate the maximum penetration level of distributed renewable energy sources (DRESs) in a real radial low-voltage network. For this purpose, the business as usual (BAU) scenario, where no control scheme is applied to the installed DRESs, is compared with two conventional droop control techniques, namely t...