Development of cost-functions for the remuneration of new ancillary services in distribution networks

INSPEC Accession Number: 21129600The higher penetration of intermittent and volatile Distributed Renewable Energy Sources (DRES) in distribution grids is gradually replacing the bulk synchronous generators (SGs) of the transmission system, resulting in poor reaction after a grid event. Conventionally, in order to ensure the stable and safe operation of the electrical grid, the Transmission System Operators (TSOs) request the participation of SGs in Ancillary Services (AS) markets. On the other side, the DRES are mainly regarded as negative loads complying with certain grid codes requirements and no participation to such markets. However, new control algorithms are emerged, including the DRES operation with P-f droop curves, their reactive power contribution according to voltage variations, ramp-rate limitation and fault-ride-through (FRT) capability. Moreover, other support functions have also been proposed in the literature, e.g. provision of virtual inertia, power smoothing and harmonic mitigation. Such support functions, provided that they are properly quantified, can be traded in the AS markets already existing at transmission system level. This paper develops cost-functions for the procurement of the aforementioned AS in a parametric form after conducting a cost-benefit analysis per AS, considering several factors, such as the location, the size and the capability for providing the AS.Horizonte 2020 76409

Ancillary Services Market Design in Distribution Networks: Review and Identification of Barriers

The high proliferation of converter-dominated Distributed Renewable Energy Sources (DRESs) at the distribution grid level has gradually replaced the conventional synchronous generators (SGs) of the transmission system, resulting in emerging stability and security challenges. The inherent characteristics of the SGs are currently used for providing ancillary services (ASs), following the instructions of the Transmission System Operator, while the DRESs are obliged to o er specific system support functions, without being remunerated for these functions, but only for the energy they inject. This changing environment has prompted the integration of energy storage systems as a solution for transfusing new characteristics and elaborating their business in the electricity markets, while the smart grid infrastructure and the upcoming microgrid architectures contribute to the transformation of the distribution grid. This review investigates the existing ASs in transmission system with the respective markets (emphasizing the DRESs’ participation in these markets) and proposes new ASs at distribution grid level, with emphasis to inertial response, active power ramp rate control, frequency response, voltage regulation, fault contribution and harmonic mitigation. The market tools and mechanisms for the procurement of these ASs are presented evolving the existing role of the Operators. Finally, potential barriers in the technical, regulatory, and financial framework have been identified and analyzed.Unión Europea (Programa Horizonte 2020) 76409

An international inter-laboratory study on Nosema spp. spore detection and quantification through microscopic examination of crushed honey bee abdomens

Nosemosis is a microsporidian disease causing mortality and weakening of honey bee colonies, especially in the event of co-exposure to other sources of stress. As a result, the disease is regulated in some countries. Reliable and harmonised diagnosis is crucial to ensure the quality of surveillance and research results. For this reason, the first European Interlaboratory Comparison (ILC) was organised in 2017 in order to assess both the methods and the results obtained by National Reference Laboratories (NRLs) in counting Nosema spp. spores by microscopy. Implementing their own routine conditions of analysis, the 23 participants were asked to perform an assay on & nbsp;a & nbsp;panel of ten positive and negative samples of crushed honey bee abdomens. They were asked to report results from a qualitative and quantitative standpoint. The assessment covered specificity, sensitivity, trueness and precision. Quantitative results were analysed in compliance with international standards NF ISO 13528 (2015) and NF ISO 5725-2 (1994). Three results showed a lack of precision and five a lack of trueness. However, overall results indicated a global specificity of 98% and a global sensitivity of 100%, thus demonstrating the advanced performance of the microscopic methods applied to Nosema spores by the NRLs. Therefore, the study concluded that using microscopy to detect and quantify spores of Nosema spp. was reliable and valid.panel of ten positive and negative samples of crushed honey bee abdomens. They were asked to report results from a qualitative and quantitative standpoint. The assessment covered specificity, sensitivity, trueness and precision. Quantitative results were analysed in compliance with international standards NF ISO 13528 (2015) and NF ISO 5725-2 (1994). Three results showed a lack of precision and five a lack of trueness. However, overall results indicated a global specificity of 98% and a global sensitivity of 100%, thus demonstrating the advanced performance of the microscopic methods applied to Nosema spores by the NRLs. Therefore, the study conclude

A pan-European epidemiological study reveals honey bee colony survival depends on beekeeper education and disease control

Reports of honey bee population decline has spurred many national efforts to understand the extent of the problem and to identify causative or associated factors. However, our collective understanding of the factors has been hampered by a lack of joined up trans-national effort. Moreover, the impacts of beekeeper knowledge and beekeeping management practices have often been overlooked, despite honey bees being a managed pollinator. Here, we established a standardised active monitoring network for 5 798 apiaries over two consecutive years to quantify honey bee colony mortality across 17 European countries. Our data demonstrate that overwinter losses ranged between 2% and 32%, and that high summer losses were likely to follow high winter losses. Multivariate Poisson regression models revealed that hobbyist beekeepers with small apiaries and little experience in beekeeping had double the winter mortality rate when compared to professional beekeepers. Furthermore, honey bees kept by professional beekeepers never showed signs of disease, unlike apiaries from hobbyist beekeepers that had symptoms of bacterial infection and heavy Varroa infestation. Our data highlight beekeeper background and apicultural practices as major drivers of honey bee colony losses. The benefits of conducting trans-national monitoring schemes and improving beekeeper training are discussed

Ancillary Services Market Design in Distribution Networks: Review and Identification of Barriers

The high proliferation of converter-dominated Distributed Renewable Energy Sources (DRESs) at the distribution grid level has gradually replaced the conventional synchronous generators (SGs) of the transmission system, resulting in emerging stability and security challenges. The inherent characteristics of the SGs are currently used for providing ancillary services (ASs), following the instructions of the Transmission System Operator, while the DRESs are obliged to offer specific system support functions, without being remunerated for these functions, but only for the energy they inject. This changing environment has prompted the integration of energy storage systems as a solution for transfusing new characteristics and elaborating their business in the electricity markets, while the smart grid infrastructure and the upcoming microgrid architectures contribute to the transformation of the distribution grid. This review investigates the existing ASs in transmission system with the respective markets (emphasizing the DRESs’ participation in these markets) and proposes new ASs at distribution grid level, with emphasis to inertial response, active power ramp rate control, frequency response, voltage regulation, fault contribution and harmonic mitigation. The market tools and mechanisms for the procurement of these ASs are presented evolving the existing role of the Operators. Finally, potential barriers in the technical, regulatory, and financial framework have been identified and analyzed

Decentralized control methods of microgrids with RES for the improvement of steady-state and transient operation

The operation of modern distribution grids has changed due to the high integration ofDistributed Energy Sources (DER). For this reason, quantities of DERs, energy storagesystems (ESS) and loads form subsystems, called microgrids. The microgrids can operateboth grid-connected and isolated in island mode. As the majority of DERs are connectedto microgrid through DC/AC or AC/DC/AC converters, the operation of the microgrid canbe controlled by developing the proper control strategies for these converters.The operation of the microgrid can be divided in several control levels. The primarylevel aims mainly in the steady state operation. In order to avoid communicationinterconnections among the DERs or among the DERs and a central controller, the droopcontrol methodology is mainly adopted. According to this method, each DER injects activeand reactive power, forming the frequency and the voltage of each node, with respect topermissible limits. This operation emulates the parallel operation of synchronousgenerators. However, the different R/X ratio of the connection lines affects the reactivepower sharing. For overcoming this problem, the virtual impedance control is added,which decouples the active and the reactive power. This dissertation proposes theadaptation of the virtual impedance, according to the power factor each DER operates.The power factor should be above 0.8. Therefore, the reactive power does not relyanymore on the impedance of the connection line.Furthermore, in order to enhance the reliable islanded operation of the microgrid, theDERs perform ancillary services, such as feeding of non-linear and asymmetrical loads.Therefore, the converters incorporate the active filter operation, in order to reduce theharmonic distortion and asymmetry of the voltage. A new control strategy is proposed,which transforms the harmonic voltage and the current in dq0 rotating frame, byimplementing the Park transformation. The advantage of the proposed control strategylies on using constant values, which are not affected by the normal frequency variations.Another issue is the cooperation of the microgrid with an Energy Storage System (ESS).The ESS is strategically placed at the Point of Common Coupling (PCC) with the main grid,controlling the connection switch and performing the following services: absorption ofany mismatches between the power production and consumption, detection of the maingrid, synchronization process of the microgrid with the main gird and loss reduction ingrid-connected mode. Contrary to the literature, the proposed strategy does not rely onany kind of physical communication, but only on local measurements. In order to performthis task, the converter of ESS adjusts the microgrid frequency and voltage at the PCC andthe synchronization takes place with seamless transient effects. Moreover, when the gridis connected, the ESS measures the reactive power exchange with the grid and injects a7th harmonic zero-sequence voltage. This voltage is identified by each DER, which in turnadjust their reactive power according to a proposed curve. Due to the load reactive powerfulfillment from the DERs, the reactive currents along the distribution lines are reduced,leading to a loss reduction, too. This dissertation deals with the protection issue of a looped islanded converterdominatedmicrogrid, which is protected by conventional overcurrent devices. In case ofa fault within the microgrid, the microgrid impedance is suddenly reduced, causing thefault detection. In order to calculate the microgrid impedance, the control angle is slightlydistorted, causing a respective distortion in the injected current. The feedback of thedistorted current can be identified in the voltage, calculating in this way the microgridimpedance at the output of each DER. Consequently, each DER injects a fault currentproportional to the measured impedance, following a proposed droop curve. The faultclearing is implemented in a selective way, as the DERs closer to the fault inject largercurrents, compared with the other DERs. Therefore, the microgrid can be protected withconventional overcurrent devices, without any further communication.Finally, a control strategy for loss reduction in island operation mode is also developed.This method utilizes the droop control with adaptive droop coefficients, according to themeasured microgrid impedance. The DERs closer to the loads inject larger currents, whilethe far ones smaller currents, leading to line loss reduction. The proposed methodologycan be implemented in every microgrid topology, irrespective of the location of the DERsand loads. Furthermore, a virtual impedance control is not necessary, as the impact of thedifferent line impedances is inherently adopted in the adaptive droop coefficients.Η ραγδαία ενσωμάτωση των Διανεμημένων Πηγών Ενέργειας (ΔΠΕ) έχει οδηγήσει στην αλλαγή της φιλοσοφίας για τη λειτουργία του δικτύου. Για το λόγο αυτό, οντότητες αποτελούμενες από ΔΠΕ, συστήματα αποθήκευσης και φορτία σχηματίζουν επιμέρους υποδίκτυα, τα οποία ονομάζονται μικροδίκτυα. Τα μικροδίκτυα μπορούν να λειτουργήσουν είτε σε συνεργασία με το κυρίως δίκτυο σε διασυνδεμένη κατάσταση λειτουργίας, είτε αυτόνομα σε νησιδοποιημένη κατάσταση. Επειδή οι περισσότερες ΔΠΕ συνδέονται στο μικροδίκτυο μέσω DC/AC ή AC/DC/AC μετατροπέων, ο έλεγχος του μικροδικτύου μπορεί να επιτευχθεί μέσω της ανάπτυξης κατάλληλων στρατηγικών ελέγχου των μετατροπέων τους.Η λειτουργία του μικροδικτύου χωρίζεται σε επιμέρους επίπεδα ελέγχου. Tο πρωτεύον επίπεδο στοχεύει κυρίως στην ορθή λειτουργία του μικροδικτύου σε μόνιμη κατάσταση. Προκειμένου να αποφευχθεί η χρήση συστημάτων επικοινωνίας ανάμεσα στις ΔΠΕ ή ανάμεσα στις ΔΠΕ και κάποιου κεντρικού συστήματος ελέγχου, προτείνεται η μέθοδος των στατικών χαρακτηριστικών. Σύμφωνα με αυτή τη μέθοδο, κάθε μετατροπέας εγχέει ενεργό και άεργο ισχύ προκείμενου η συχνότητα και η τάση του μικροδικτύου να βρίσκεται εντός των προκαθορισμένων ορίων, προσομοιώνοντας τη λειτουργία των παράλληλων σύγχρονων γεννητριών. Ωστόσο, οι γραμμές σύνδεσης των ΔΠΕ ενδέχεται να έχουν διαφορετικό λόγο R/X, επηρεάζοντας σημαντικά την κατανομήτης άεργου ισχύος, με αποτέλεσμα να υπάρχουν κυκλοφορούντα ρεύματα άεργου ισχύος εντός του μικροδικτύου. Για την αντιμετώπιση του προβλήματος, προτείνεται η προσθήκη μιας εικονικής σύνθετης αντίστασης, η οποία θα απομπλέκει την επίδραση των μεταβολών της ενεργού ισχύος στην κατανομή της άεργου ισχύος, με αποτέλεσμα τη μείωση των κυκλοφορούντων ρευμάτων. Στην παρούσα διατριβή, προτείνεται η χρήση επαγωγικής εικονικής σύνθετης αντίστασης με αναπροσαρμοζόμενη τιμή βάσει του συντελεστή ισχύος των μετατροπέων, ο οποίος δε θα πρέπει να είναι μικρότερος από 0.8. Επομένως, όλοι οι μετατροπείς κατανέμουν την άεργο ισχύ ανεξάρτητα από τα ηλεκτρικά χαρακτηριστικά των γραμμών σύνδεσης.Παράλληλα, για την βελτίωση της αξιόπιστης λειτουργίας του μικροδικτύου σε κατάσταση νησιδοποιημένης λειτουργίας, οι ΔΠΕ αναλαμβάνουν επιπρόσθετους βοηθητικούς ρόλους. Οι βοηθητικοί ρόλοι περιλαμβάνουν την τροφοδότηση μη γραμμικών και ασύμμετρων φορτίων. Έτσι, οι μετατροπείς αναλαμβάνουν ρόλο ενεργού φίλτρου, στοχεύοντας στη μείωση της παραμόρφωσης και της ασυμμετρίας της τάσης στα επιτρεπτά επίπεδα. Στην παρούσα διατριβή, ο προτεινόμενος έλεγχος υλοποιείται στο στρεφόμενο dq0 πλαίσιο ελέγχου, εφαρμόζοντας τον μετασχηματισμό Park στην κυματομορφή της τάσης και του ρεύματος εξόδου. Το κυριότερο πλεονέκτημα έγκειται στην απεξάρτηση του ελέγχου από μεταβολές στη συχνότητα λειτουργίας, αφού η γωνία ελέγχου τις συμπεριλαμβάνει με έμμεσο τρόπο. Στη συνέχεια, εξετάστηκε η συνεργατική λειτουργία του μικροδικτύου με ένα σύστημα αποθήκευσης. Το σύστημα αποθήκευσης τοποθετείται στρατηγικά στο σημείο κοινής σύνδεσης (ΣΚΣ) του μικροδικτύου με το κυρίως δίκτυο, ελέγχοντας τον διακόπτη διασύνδεσης, προκειμένου να εκτελεί συγκεκριμένες λειτουργίες: απορρόφηση της αναντιστοιχίας μεταξύ παραγωγής και κατανάλωσης σε νησιδοποιημένη κατάσταση λειτουργίας, εντοπισμός του κυρίως δικτύου, συγχρονισμός του μικροδικτύου με το κυρίως δίκτυο και μείωση των απωλειών σε κατάσταση διασυνδεδεμένης λειτουργίας.Σε αντίθεση με τις μεθόδους που έχουν αναπτυχθεί, για το συγχρονισμό του μικροδικτύου δεν απαιτείται κάποια επικοινωνία. Ο μετατροπέας του συστήματος αποθήκευσης ρυθμίζει τη συχνότητα και την τάση στο ΣΚΣ μέχρι να συμπέσουν με τις αντίστοιχες του δικτύου και επομένως να αποφευχθούν τυχόν μεταβατικά φαινόμενα κατά τη σύνδεση. Επίσης, όταν το δίκτυο έχει συνδεθεί, το σύστημα αποθήκευσης μετράει την ανταλλαγή άεργου ισχύος στο ΣΚΣ και αποστέλλει μία τάση 7ης αρμονικής στο ομοπολικό σύστημα. Η τάση αυτή γίνεται αντιληπτή από όλες τις ΔΠΕ, οι οποίες αναπροσαρμόζουν την εγχεόμενη άεργο ισχύ τους σύμφωνα με μια προτεινόμενη στατική χαρακτηριστική. Άρα, όλη η ζήτηση της άεργου ισχύος των φορτίων ικανοποιείται από τις ΔΠΕ και όχι από το κυρίως δίκτυο, με αποτέλεσμα να μειώνεται το πλάτος των ρευμάτων των γραμμών και επομένως να μειώνονται οι απώλειες στη διασυνδεδεμένη κατάσταση λειτουργίας.Ένα άλλο πρόβλημα που εξετάστηκε είναι η ύπαρξη σφάλματος σε ένα νησιδοποιημένο μικροδίκτυο αποτελούμενο από ΔΠΕ με μετατροπέα, χρησιμοποιώντας αποκλειστικά συμβατικά μέσα προστασίας. Η ύπαρξη του σφάλματος γίνεται αντιληπτή μέσω της απότομης μεταβολής της σύνθετης αντίστασης του μικροδικτύου. Για τον υπολογισμό της σύνθετης αντίστασης του μικροδικτύου, παραμορφώνεται εσκεμμένα η γωνία ελέγχου, με αποτέλεσμα να εισάγεται στο μικροδίκτυο ένα παραμορφωμένο ρεύμα. Η επίδραση του αλλοιωμένου ρεύματος αναγνωρίζεται στην τάση, επομένως υπολογίζεται έμμεσα το μέτρο της σύνθετης αντίστασης του μικροδικτύου στα άκρα του κάθε μετατροπέα. Στη συνέχεια, κάθε μετατροπέας εγχέει ένα ρεύμα σφάλματος αντιστρόφως ανάλογο του μέτρου της μετρούμενης σύνθετης αντίστασης. Η εκκαθάριση του σφάλματος πραγματοποιείται με επιλεκτικό τρόπο, αφού οι πιο κοντινοί στοσφάλμα μετατροπείς εγχέουν μεγαλύτερα ρεύματα σε σχέση με τους πιο απομακρυσμένους. Σε αντίθεση με τις υπόλοιπες μεθοδολογίες που παρουσιάζονται στη βιβλιογραφία, δεν απαιτείται κανένα είδος επιπρόσθετης επικοινωνίας.Τέλος, προτείνεται μία στρατηγική ελέγχου για μείωση των απωλειών σε νησιδοποιημένα μικροδίκτυα. Η μέθοδος προσαρμόζει τις κλίσεις των στατικών χαρακτηριστικών σύμφωνα με τη μετρούμενη σύνθετη αντίσταση του μικροδικτύου. Επομένως, οι πιο απομακρυσμένες ΔΠΕ εγχέουν μικρότερα ρεύματα, συμβάλλοντας στη μείωση των απωλειών. Η προτεινόμενη μέθοδος μπορεί να εφαρμοστεί σε οποιαδήποτε τοπολογία μικροδικτύου, ανεξάρτητα από τη θέση των ΔΠΕ ή των φορτίων και χωρίς τη χρήση επικοινωνίας. Επιπλέον, με την προτεινόμενη μέθοδο ελέγχου, δεν απαιτείται η εισαγωγή της εικονικής αντίδρασης

An enhanced role for an energy storage system in a microgrid with converter-interfaced sources

An enhanced role for the energy storage system (ESS), strategically placed at the point of common coupling (PCC) of the microgrid with the utility grid, is proposed. During island operation, the ESS ensures that the frequency and magnitude of the voltage will remain within the limits specified by the Standard EN 50160. By implementing an adjustable droop control method, the distributed energy resources (DERs) adjust their active and reactive powers in order to fulfil the load demand. When the grid is recovered, the ESS detects its presence and achieves a seamless synchronisation of the microgrid with the main grid, without any kind of communication. In grid-connected mode, the DERs deliver their available active power, whereas their reactive power is determined by a zero-sequence voltage. This voltage is injected by the ESS and aims to the zeroing of the amount of reactive power at the PCC. In this way, a reduction of power losses in the distribution lines of the microgrid is achieved. The effectiveness of the proposed control method in all operation modes, without any physical communication means, is demonstrated through detailed simulation in a representative microgrid with DERs fed by photovoltaics

A Control Method for Balancing the SoC of Distributed Batteries in Islanded Converter-Interfaced Microgrids

In a low-voltage islanded microgrid powered by renewable energy sources, the energy storage systems (ESSs) are considered necessary, in order to maintain the power balance. Since a microgrid can be composed of several distributed ESSs (DESSs), a coordinated control of their state-of-charge (SoC) should be implemented, ensuring the prolonged lifespan. This paper proposes a new decentralized control method for balancing the SoC of DESSs in islanded microgrids, without physical communication. Each DESS injects a current distortion at 175 Hz, when its SoC changes by 10%. This distortion is recognized by every DESS, through a phase-locked loop (PLL). In order to distinguish the origin of the distortion, each DESS injects a distortion of different time duration. This intermediate frequency has been selected in order to avoid the concurrence with the usual harmonics. The DESSs take advantage of this information and inject a current proportional to the SoC. Implementing this strategy, a comparable number of charging/discharging cycles for each DESS are achieved. Furthermore, an active filter operation, implemented in the dq rotating frame for each individual harmonic, is integrated in the control of the distributed generation units, supplying nonlinear loads with high-quality voltage. The effectiveness of this method is verified by detailed simulation results

Congestion management in coupled TSO and DSO networks

This paper proposes a three-stage coordination methodology to optimally manage congestion in day-ahead operation planning for Transmission Systems (TS) and Distribution Systems (DSs). The first stage provides the day-ahead model (DAM) results for the power units in the TS, and Energy Storage Systems (ESSs) and Electric Vehicles (EVs) in the DSs. The second stage applies the DAM results to the modelled TS to reveal any congestion issues. If congestion is depicted the need for congestion management (CM) by the Transmission System Operator (TSO) arises. Thus, the TSO performs an AC Optimal Power Flow (OPF) analysis, under power loss minimization, to provide the redispatch schedule in the TS and quantify the power transactions between TSO and the Distribution System Operators (DSOs). Finally, the DSOs examine if they can deliver these power transactions without congestion in their DSs, by applying AC OPF to minimize power losses. If this is not possible, then a relaxation scheme is applied to these power transactions in order to define the maximum DSO flexibility without congestion in the DS. The proposed methodology is applied to the simulated Greek TS and the results indicate that it can optimally redispatch the available assets with a coordinated interaction between TSO-DSO(s)