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This paper summarizes the findings of Danish project - NSON-DK regarding the balancing requirements for future power system of North Sea countries with focus on the Danish power system and its regions DK1 and DK2. The study covers all the steps of the operation from the Day Ahead Market to the Real Time balancing of generation and demand. For that reason, DTU Balancing Tool Chain is used. The paper analyses a) the value of offshore grid on balancing of forecast errors, b) the impact of forecast errors on manual and automatic reserves and c) the quality of electrical frequency in the near future considering high VRE penetration d) value of including wake in the balancing studies with high share of renewables. Recommendations are provided in terms of balancing requirements for future power systems. [ABSTRACT FROM AUTHOR]

The impedance-based stability criterion has been widely accepted as an effective method to study power system with a high penetration level of Voltage Sourced Converters (VSCs). In this paper, a power circuit using the current perturbation method is established in the Flex Power Grid Lab (FPGL) in Arnhem, the Netherlands. The power circuit is used to measure the input-impedance of a physical 1 MW type-4 Wind Turbine Generator (WTG) power converter. The results confirms that the current perturbation method is feasible and can be applied to verify the harmonic impedance model and meet the growing demand of offshore wind power with an increasing wind turbine size. Furthermore, the paper provides benchmarking results between the PHIL (i.e. power circuit) and CHIL (i.e. controller replica) setup paving the way for the harmonic model validation and measurement methodology standardization broadly. [ABSTRACT FROM AUTHOR]

This paper proposes the analysis of the frequency support from a Type-IV wind turbine interfaced to the grid via a grid-forming converter. The frequency support including the inertial response and the fast primary frequency support is implemented by integrating a grid-forming control to the control a back-to-back converter. Knowing that the inertial response from a grid-forming converter can be tuned by varying the inertia constant of a grid-forming control, it is possible to extract different amounts of kinetic energy from the rotating masses of a wind turbine and positively impact the grid frequency dynamics during a grid frequency event. However, the increased inertial response may lead to an increased loading imposed on the mechanical components of a wind turbine. To elaborate and verify these statements, the analysis is aimed at two objectives. Firstly, it is estimated through time domain simulations whether the inertial response from a grid-forming control-based wind turbine has a significant active power contribution or can be neglected compared to the share of the primary frequency support. Secondly, based on the analyzed impact of the inertial response on the grid frequency and the mechanical loading, a value of the inertia required from a wind turbine with a grid-forming converter is recommended. [ABSTRACT FROM AUTHOR]

An economic evaluation tool for solar power self-consumption system with battery storage was implemented. This tool calculates output power of solar system and battery storage system to evaluate reduced purchased electric power by installing self-consumption system. System control methods can also be evaluated with this tool to confirm the value it claims. As a result, indexes like Return of Investment and self-consumption rate can be calculated according to system conditions and system control candidates. It is expected that a balanced system design can be obtained, in the phase of system planning, by using this tool to address concerns of equipment investor and solution provider. In this paper, several evaluation results were presented as use cases of this tool, where a self-consumption system with system control methods was tested for a system of 250 kW load consumption. [ABSTRACT FROM AUTHOR]

An economic evaluation tool for solar power selfconsumption system with battery storage was implemented. This tool calculates output power of solar system and battery storage system to evaluate reduced purchased electric power by installing self-consumption system. System control methods can also be evaluated with this tool to confirm the value it claims. As a result, indexes like Return of Investment and self-consumption rate can be calculated according to system conditions and system control candidates. It is expected that a balanced system design can be obtained, in the phase of system planning, by using this tool to address concerns of equipment investor and solution provider. In this paper, several evaluation results were presented as use cases of this tool, where a self-consumption system with system control methods was tested for a system of 250 kW load consumption. [ABSTRACT FROM AUTHOR]

With the increase in renewable generation in the power system, system planners have to account for the uncertainty introduced by these sources. However, in the time frame of a traditional transient stability simulation, the uncertainty can be assumed to be negligible. The importance of the uncertainty subsequently arises in the time period between two consecutive dispatch intervals. Further, with large number of uncertain sources, an enormous number of simulations are required to cover the entire search space. In this paper, the feasibility of longer time transient simulations with uncertainty is explored and the impacts of this uncertainty on the response of the system is observed. Further, the application of an analytical method of obtaining the statistical characteristics of the required output parameters is explored resulting in a computationally efficient analysis. [ABSTRACT FROM AUTHOR]

With the establishment of the Paris Climate Treaty in 2015, South Korea has set its ambitious goal of 'Reduce emissions by 37% compared to 2030 Greenhouse Gas Emissions Outlook (BAU)' as of June 2015. As a measure to reduce carbon, countries are increasing the ratio of renewable energy sources in each country. South Korea also aims to increase the proportion of renewable energy sources to 53GW by 2030. In this paper, we will study the methodology for the power system development plan of the future power system which consists of various scenarios such as the amount of renewable energy and the installation of new transmission line. First, we describe the construction process of database w.r.t the ratio of renewable energy and load level. In order to increase the stability of future power system in South Korea, we have come up with various scenarios for a combination of transmission line, VSC-HVDC and FACTS. Then, the comprehensive tests based on static and dynamic analysis are processed using the proposed simulator based on PSS/E Python. Through the above process, the optimum future system reinforcement plan is calculated. The automatic simulator with various function of DB creation, simulation and decision based on PSS/E Python have been developed to validate the proposed methodology and tested using the large-scale future power system. [ABSTRACT FROM AUTHOR]

This paper introduces a virtual synchronous machine (VSM) control scheme which is based on a minimized emulation of the model of a synchronous generator (SG) for a grid-forming wind turbine (WT) inverter. Based on this VSM control scheme, state-space representation and block diagram of the small-signal model for the VSM-controlled grid-forming inverter connected to an infinite bus are derived, which are used for small-signal stability analysis of the power angle in the VSM control scheme. This power angle small-signal stability (PAS) analysis is proposed as a simpler way for analyzing the influence on the rotor angle stability of power system from large share of VSM-controlled grid-forming inverters. Influence of parameters in the power loop of the control scheme on the PAS is investigated by analyzing the eigenvalue trajectories of the state matrix. [ABSTRACT FROM AUTHOR]

A power grid with a high penetration of renewable power generation faces new issues that have not been there before. The frequency in the power system is highly related to the mass and the rotational speed of the operational synchronous machines. With more and more power electronic converters as energy generation units, the mechanical rotating mass is decreasing, which causes more and higher frequency disturbances. Several controls for short term frequency controls in the power electronic based generation units have been proposed, but their impact on the frequency reliability is only a minor researched topic. This paper will analyze different basic control strategies in power electronic converters to enhance operational reliability of the power system regarding the short term frequency reliability. [ABSTRACT FROM AUTHOR]

Near-to-shore wind power plants, such as the UK's Round 1, connect their generation to shore at 33kV. This is also currently the standard distribution voltage (or collection voltage) for inter-array networks. Larger, further-from-shore wind power plants typically use offshore substations to step the operating voltage up to transmission level voltages, e.g.132kV/220kV for export to shore. Recent research shows that a subsea cable appropriate for use with 66kV collector networks, i.e. a "wet-type" cable, could be type-tested and made available. The Carbon Trust is currently progressing work to type-test this cable, which presents opportunities for offshore wind collection voltages to increase from 33kV to 66kV. This paper presents the benefits of utilising 66kV for nearshore and medium distance offshore wind power plants, for UK demonstration wind farm projects. The benefits include the potential to reduce the amount of subsea cabling required, reduced losses in the connection at 66kV versus 33kV, and the potential to reduce the number of offshore substations in some cases. The costs and benefits have been quantitatively and qualitatively assessed and detail is provided for 33kV/66kV equipment cost comparisons (including switchgear, cable and transformers), cost reduction/benefit impacts of substation and cabling rationalisation, and full-life difference in losses and hence revenue from generation. The paper specifically addresses the feasibility of developing 66kV wind turbine connection systems at the Blyth Offshore Demonstration (BOD) site and the Hunterston Offshore Wind Turbine Test facility. Also presented are potential enablers and barriers to 66kV market uptake such as supply chain readiness, the feasibility of demonstrating the proposed 66kV technology at dedicated sites in the UK and outline design and feasibility considerations for certification at 66kV with an emphasis on Low Voltage Ride-Through (LVRT) certification. It is concluded that moving to 66kV could lead to capital cost and full-life benefits compared with the present standard voltage of 33kV for many near and medium distance-to-shore wind power plants. However, steps to accelerate market uptake should also be considered by exploring enablers (testing, demonstration, certification) and solutions to overcome the associated barriers. [ABSTRACT FROM AUTHOR]

Paralleled inverters with asynchronous carriers are increasingly emerging into renewable power plants and other power-electronic-based power systems. The sideband harmonics resulting from the pulse width modulation tend to be different from one inverter to another, which may trigger sideband harmonic resonances among the paralleled inverters. To address the sideband harmonic instability, the nonlinearity of the digital pulse width modulator is analyzed first in this paper based on the harmonic balance principle. It is revealed that the dynamic sideband components corresponding to a given small-signal perturbation can be far below the Nyquist frequency, and they may not be effectively attenuated by anti-aliasing filters. A multi-frequency impedance model is then developed for the inverter, which characterizes the dynamic coupling between the perturbed frequency component and the sideband frequency component. The impact of asynchronous carriers on the sideband harmonic instability of paralleled inverters can thus be analyzed, and the frequency and phase sequence of the resulting oscillation components are predicted. Experimental results of two paralleled inverters confirm the effectiveness of the developed model and the stability analysis. [ABSTRACT FROM AUTHOR]

This paper presents a method to design and tune the main controller of a Wind Power Plant (WPP), with focus on the active power and frequency control. The controller requirements are based on the Danish grid codes. The controller functionality is successfully verified using the model and the layout of an actual WPP rated at 160 MW, that consists of 80 wind turbines. Two reference dispatch strategies are investigated, equal and proportional. The proportional dispatch is preferred due to better tracking accuracy and robustness. The work described in this article is meant to help WPP developers and researchers to design the main controller of a WPP using the well-known single input-single output (SISO) tools. [ABSTRACT FROM AUTHOR]

The operation of a system with 100% converterinterfaced generation poses several questions and challenges regarding various aspects of the dynamic characteristics of the system. The effects related to the power-frequency control are among the most relevant issues which need to be investigated. The paper takes into examination the case of an existing isolated power network of a geographical island assuming a completely converter-interfaced generation. The factors playing a fundamental role in the assessment of which sources should be designated to be grid-forming are identified with a smallsignal model formulation of a generic multiple oscillators system. Simulations and analysis performed on the case study of the island’s power network performed with the software NEPLAN are used to show the impact of different aspects which can play a role in the design and the operation of the system: these aspects are the operating mode of power converters control, location and distribution of the generation sources with grid-forming capabilities, as well as number and ratings of these sources. The impact of relevant control parameters such as virtual inertia constant and virtual impedance is also investigated. [ABSTRACT FROM AUTHOR]

Purpose: This paper presents the development and implementation process of a service-oriented, economically viable business model that deals with the use of electricity from photovoltaic systems that are no longer state-subsidized. The research is funded within the context of the innovative research project “Citizen Energy Transition”, subsidized by the Ministry of Science, Research and the Arts Baden-Württemberg (funding code Kap. 1403 Titelgruppe75) Design/Methodology/Approach: First the catalyst for the innovative business model is investigated. Then the development and implementation process for the business model is explained and the business model itself. Findings: The end of the guaranteed feed-in tariff for the first photovoltaic systems leads to the necessity for new business models in the energy sector. Originality/Value: In design thinking workshops and ongoing feedback loops all stakeholders were involved in the development process. After refining and iteratively adapting the business model, it can be adjusted for further requirements due to regulative influences, customer needs, and ecological possibilities. [ABSTRACT FROM AUTHOR]

Off-grid and decentralized Hybrid Renewable Electricity Systems (OHRES) offer a promising solution for addressing global energy poverty as they provide sustainable and reliable energy, and are adaptable to many geographical contexts. Building scalable solutions to alleviate global energy poverty requires a deeper understanding of OHRES and the factors for their success. This study focuses on the development and optimization of the Hybrid Off-grid and decentralized systems Techno-Economic Model (HOTEM), used to understand the technical and economic factors affecting the feasibility, sustainability, and reliability of OHRES. This model development is part of a comprehensive study methodology that aims to increase the level of understanding, acceptance, and deployment of such systems on a global level. The paper also covers the OHRES technical layout including an integrated 48V DC Hybrid lead-acid & lithium ion Battery Storage System (HBSS). HOTEM is an OHRES sizing and technoeconomic assessment tool. The model can perform feasibility analysis for electrical energy production, in order to obtain the best configuration and sizing of the hybrid system at the off-grid or decentralized location. The development of HOTEM is based on the on-ground experience gained from the deployment of two OHRES in highly contrasting case studies in Uganda and Canada, which allows HOTEM to be a practical tool, reflecting the practical market needs. The presented model includes optimized technical and economical sub-models, covering the technical modeling of Solar PV, Wind, Genset, battery storage, and load profiling. Besides, the calculation of the dynamic economic indicator, using detailed economical modeling through the newly integrated Weighted Average Cost of Capital (WACC) model. HOTEM performance is analyzed using the OHRES case study in Canada and benchmarked against an existing commercial software, showing that HOTEM can be successfully used in the planning and optimization of off-grid hybrid systems. [ABSTRACT FROM AUTHOR]

Off-grid and decentralized Hybrid Renewable Electricity Systems (OHRES) offer a promising solution for addressing global energy poverty as they provide sustainable and reliable energy, and are adaptable to many geographical contexts. Building scalable solutions to alleviate global energy poverty requires a deeper understanding of OHRES and the factors for their success. This study focuses on the development and optimization of the Hybrid Off-grid and decentralized systems Techno-Economic Model (HOTEM), used to understand the technical and economic factors affecting the feasibility, sustainability, and reliability of OHRES. This model development is part of a comprehensive study methodology that aims to increase the level of understanding, acceptance, and deployment of such systems on a global level. The paper also covers the OHRES technical layout including an integrated 48V DC Hybrid lead-acid & lithium ion Battery Storage System (HBSS). HOTEM is an OHRES sizing and technoeconomic assessment tool. The model can perform feasibility analysis for electrical energy production, in order to obtain the best configuration and sizing of the hybrid system at the off-grid or decentralized location. The development of HOTEM is based on the on-ground experience gained from the deployment of two OHRES in highly contrasting case studies in Uganda and Canada, which allows HOTEM to be a practical tool, reflecting the practical market needs. The presented model includes optimized technical and economical sub-models, covering the technical modeling of Solar PV, Wind, Genset, battery storage, and load profiling. Besides, the calculation of the dynamic economic indicator, using detailed economical modeling through the newly integrated Weighted Average Cost of Capital (WACC) model. HOTEM performance is analyzed using the OHRES case study in Canada and benchmarked against an existing commercial software, showing that HOTEM can be successfully used in the planning and optimization of off-grid hybrid systems. [ABSTRACT FROM AUTHOR]

This paper presents the overview, current status and outline of the new CIGRE working group C4.49 entitled "Multi-frequency stability of converter-based modern power systems". It provides concise definitions, a literature review covering state-of-the-art contributions, and aspects of modelling and analysis methods are discussed and aided by examples based on a proposed benchmark system. The working group's objective is to describe the phenomena, harmonize definitions and explain available methods for analyses with their advantages and disadvantages as well as providing a common understanding on modelling, analysis, evaluation and mitigation techniques. Furthermore, guidelines on the general approach to such studies and the availability as well as choice of tools will be provided by the working group. [ABSTRACT FROM AUTHOR]

The energy setor is changing rapidly. The traditional power system, mainly based on centralized production, is transformed to a power system with a large number of small PV-systems and an increasing load due to an increasing number of heat pumps and electric vehicles. This will especially increase the burden on the distribution grid and in these grids more bottlenecks are expected in near future. Solving these bottlenecks with traditinal grid reinforcements leads to massive investments therefore energy flexibility in both supply and demand is needed. In this paper the Universal Smart Energy Framework (USEF) is used to optimally use the available capacity in the Low Voltage (LV) grid. This framework is applied in a pilot project of an all electric neighborhood in the Netherlands. A detailed description of USEF is given as well as a description of the sources which provided the flexibility. Some preliminary results of the pilot project are shown to discuss the idea and the potential of USEF in unleashing flexibility in LV-grids. [ABSTRACT FROM AUTHOR]

The ongoing energy system transition, empowered by technology developments, fueled by shifting investments, and motivated by decarbonization, is one of the 21st century's most urgent tasks. However, our current suite of modelling tools has failed to adapt to emerging trends and deliver the holistic perspective required by decision-makers to navigate complex policy choices. Instead, energy system analyses are plagued by rigid model platforms and discretized researchers who focus on specific sectors (buildings, transport, power), spatial-temporal scales (municipal, provincial, federal), or energy vectors (electricity, fuels, thermal). /In this paper, we introduce a novel formulation to integrate distinct models that span spatial-temporal scales - from individual buildings to system operation, system planning, and integrated assessment modelling - as well as infrastructure systems - the water, power, transport, and fuel distribution systems. [ABSTRACT FROM AUTHOR]

The electrical power system is facing several challenges as the penetration of converter based renewable power increases, including a reduction of the synchronous based inertia, loss of converter synchronism and weakened grids. Grid forming converter controllers, especially the socalled Virtual Synchronous Machines (VSMs), are seen as a potential solution for some of these issues. VSM controllers mimic the behaviour of a synchronous machine to different degrees of detail. Of these implementations, those that do not use Phase Locked Loops (PLLs) or current loops have been shown to be advantageous. This paper presents several proposals for a Fault Ride Through controller for a VSM controlled converter without a PLL or vector current control loop, which are imposing limitations on the stability of the inverter in low Short Circuit Ratio grids. Also, a method to limit the power and voltage/reactive power references, considering the converter maximum current, is presented. This paper validates and shows the advantages and limitations for the proposed control structures through extensive simulations using MATLAB Simulink for different grid conditions applied to a wind turbine. [ABSTRACT FROM AUTHOR]

There has been considerable interest in convertor solutions which to a greater or lesser extent mimic the behaviour of synchronous machines, thus overcoming many of the disadvantages of the existing technology which are potentially destabilizing at high penetration. These solutions are frequently referred to as Grid Forming Convertors (GFC). For offshore installations, where some equipment is on shore, locating equipment offshore is more expensive and carries greater commercial risks, requiring extensive testing and confidence building prior to deployment in real applications. This is time consuming and particularly significant for GB and where there are significant quantities of offshore generation. Onshore solutions to stability are therefore desirable for Off-Shore Transmission Owners (OFTOs) and might also be applied by retrofitting to existing conventional converter plant. This paper presents and discusses findings of the second stage of the research focusing on the enhanced control algorithm for Hybrid Grid Forming Convertors for Offshore Wind Applications and its performance, while the previous paper [3] presents the initial findings comparing various hybrid solutions for offshore networks where the STATCOM onshore is replaced by synchronous compensator and GFC or Virtual Synchronous Machines (VSM) converter of similar rating with the aim to achieve levels of Grid-Forming capability. [ABSTRACT FROM AUTHOR]

We are in the middle of an important transition of electrical power systems. Conventional power plants are being replaced by renewable energy sources, which are mainly connected to the grid via power electronic converters. Whenever a conventional, synchronous generator (SG) based, power plant is decommissioned some inertia, frequency and voltage control mechanism are lost. Conventional plant is being replaced by converter-based generation, creating critical challenges in power systems. A main interest is how these systems will operate with the known level of effectiveness and reliability. Nowadays, the converter-based generation that is connected to the grid is grid-feeding. They can operate sufficiently under the presumption that they are connected to a strong AC network. New control techniques for converters, for example grid-forming strategies, are being developed to address these challenges and to offer ancillary services that until now have been provided by SGs. In this paper, a gridforming system and control strategy is explained and developed. Its impact on the wider electrical power system will be discussed and a grid forming grid forming control strategy will be presented. The grid forming system is tested on a IEEE sample 9 bus network that is 80% and 100% converter based. The system behavior will be presented subject to load increase/decrease and post fault behavior. [ABSTRACT FROM AUTHOR]

This paper analyzes the impact of Wind Turbine (WT) Voltage Source Converters on harmonic emissions levels and harmonic stability by performing two case studies for several Offshore Wind Power Plants (OWPPs) in the North- Sea. Firstly, it was investigated to what extent the expected harmonic emission levels at the Point of Connection (POC) are affected when the WT converters are modelled as active elements instead of constant current sources in PowerFactory. The impact of connecting an increasing amount of OWPPs to the same POC on the harmonic emission levels was studied as well. Secondly, the harmonic stability of the offshore network was assessed by utilizing both an impedance-based analytical model and a full model in PSCAD/EMTDC. The effect of connecting more OWPPs, and thus WT converters, on the harmonic stability was analyzed. The results of the harmonic stability assessment were verified with time-domain simulations in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

An increase in percentage of inverter-based generation in large power systems causes a reduction in the available fault current, resulting in a reduction of traditional system strength. A tool developed by EPRI called the Grid Strength Assessment Tool (GSAT) calculates various system strength metrics from a steady state analysis of the network model. This paper will outline the challenges associated with low system strength in inverter-based systems, the difficulty determining potential instabilities, details of the GSAT tool and the metrics available including an advanced Short Circuit Strenght (SCS) metric. [ABSTRACT FROM AUTHOR]

The operational strategy of an African transmission system operator was evaluated for a future wind power penetration of 16%. We performed the analysis with the help of an economic dispatch simulation program (PLEXOS) and with help of a model to simulate the real time power balancing (KERMIT). The merits of our approach are the use of well-developed in-house tools (such as wind power forecasts based on the experiences of DNV GL), innovative procedures (dynamic spinning reserve) as well an appropriate interaction of those tools (real-time balancing and economic dispatch). This paper gives an overview of our approach and results for a case study. [ABSTRACT FROM AUTHOR]

In South Africa wind power plants grid integration capabilities have to be tested on site and accompanied by the grid operator ESKOM to achieve the compliance certificate. The tests are carried out according to a grid code testing procedure. The certificate allows the wind power plant to be connected to the south african grid operated by ESKOM. Nordex wind power plants have achieved compliance certficates successfully. The scope of testing, field test results and challenges are presented in this paper. [ABSTRACT FROM AUTHOR]

Due to the penetration of renewable energy sources such as wind turbines and photovoltaics, it becomes more complex issue to assess transient stability. In particular, there is a possibility that the transient stability decreases because inertia constant can be reduced if conventional generators are replaced with renewable energy sources. In order to overcome this difficulties, the contribution of renewable energy sources to the stabilizing control is effective. For example, wind power plants can behave as synchronous generators with inertial response by using the kinetic energy control of the rotator. On the other hand, in Japanese western 60Hz power system, weakly-damped low-frequency oscillation is caused by a fault and it is required that system operation is determined in order that this oscillation can be stabilized with the N-1 criterion. To this end, the stabilization by using inertia control of wind turbines should be one of the important countermeasures. However, the controllability of the inertia might be limited in the case of wind turbines because the rotational speed must be also controlled within a proper range. Hence, in this paper, the relationship between the controllability of inertia control and its effectiveness was analyzed based on the IEEJ Japanese standard 60Hz power system model. [ABSTRACT FROM AUTHOR]

This paper proposes a simulation tool to investigate the effects of integrating EcoGrid into the Danish regulating power market. The EU project EcoGrid demonstrates a realtime market designed to incorporate flexible demand into the existing power system markets. The hour-ahead regulating power market is adjusted such that some balancing is left for the EcoGrid real-time market. The proposed tool builds on SimBa, which simulates the regulating power market. Results indicate that the effect of the demand side response in the regulating power market much depends on the elasticity of the demand. Generally, the activation of conventional regulating power is reduced. [ABSTRACT FROM AUTHOR]

with increase of non-synchronous generation resource in ERCOT generation mix, the system's synchronous inertia is decreasing. Through a series of dynamic studies it was determined that current frequency control practices are insufficient for reliable operation below inertia level of 100 GW⋅s. It is there for important to forecast future inertia going forward. In this paper historic analysis of low inertia conditions in ERCOT is presented and several methods for future inertia forecasting are tested. [ABSTRACT FROM AUTHOR]

In this paper, impact of current priority dispatch rule on the demand and supply operation, the unlimited and uncompensated curtailment and the wholesale power market trading were analyzed. As a matter of the current priority dispatch rule, first is that the Japan's priority dispatch rule focus to maintain supply and demand mainly within the region. Second, Japan's electricity system can't afford to connect large amount of variable renewable energy because it focuses on individual supply-demand balance in each area and gives high priority of long-term fixed power sources. Furthermore, it is expected that the economic rational cross-regional operation will be expanded through wholesale electricity market, but curtailment of variable renewable energy starts at zero yen. On the other hand, It is possible for long-term fixed power sources to supply electricity at a constant output without negative price risk. Furthermore, evaluation of curtailment prospects in FY2017 turned out that there is possibility that future restart of nuclear power plant is trigger of start of curtailment of variable renewable energy during low demand period in Kyushu area. There is possibility that current priority dispatch rule gives a disincentive to transit more flexible system in the market. It is necessary to discuss for improvement that enables economic curtailment through cross-regional real-time market, negative price etc. [ABSTRACT FROM AUTHOR]

Current practice of wind turbines' start-up relies on the electricity available at the network that they are connected. Hence, in case of a long duration of electricity shortage, external auxiliary power supplies are needed for starting and running the wind turbines or at least for powering their internal auxiliary loads. The state of the art wind turbines with power electronics based converters can be equipped with functions such that they can start and run without the need for external auxiliary power supplies; and furthermore wind power plants composed of the state of the art wind turbines can form grid voltage and operate as a stiff voltage source, as long as wind blows. This can help fast and environmental friendly black start solutions by wind turbines for power system restoration and also use of cost effective offshore HVDC converters (e.g. diode rectifier) as well. Additionally, this would help to avoid today's necessity of auxiliary diesel generators for offshore wind power plants, which in turn would increase reliability and decrease cost. In this paper the background and existing solutions for wind turbine and wind power plant (self) start-up and island operation are presented, while the challenges are identified as future focus areas. [ABSTRACT FROM AUTHOR]

HVDC- transmission is the medium of choice to connect offshore wind power plants to the onshore grid when longer distances have to be overcome. To generate cost savings and hence to push further extension of offshore wind power plants uncontrolled diode rectifier HVDC-systems, instead of VSC-HVDC converters, may be used in the future. Besides the need for a grid forming capability of the wind turbine converters, also the unidirectional power flow of uncontrolled diode rectifiers evokes a challenge during calm wind situations. Hence, solutions for supplying auxiliary power to the offshore wind farm during a lack of wind have to be found. This paper presents one possible option of the auxiliary power supply where a sample offshore wind power plant is connected to the onshore grid via additional umbilical AC cable. Investigations, carried out by simulation using PSCAD™/EMTDC™, show how the wind power plants either can be operated with a fixed reference frame (FixReF) control in the normal case or with conventional PLL based control during calm wind situations. During the transition between both cases, synchronization processes have to be done when connecting and disconnecting the umbilical AC cable. [ABSTRACT FROM AUTHOR]

This paper presents and assesses the outcomes of inertial response tests performed on a transmission systemconnected wind power plant in the Canadian province of Quebec. Frequency signals representing a response to a typical loss of generation event were injected into the wind turbines' control systems to artificially trigger an active power increase. The measurement campaign aimed to fulfill two main objectives. First, to validate the performance of a wind turbine control algorithm designed to optimize the active power behavior after inertial response activation. Second, to study the correlation between individual wind turbine and wind power plant behaviors during, and immediately after, an inertial response event. This publication offers an update on capabilities and limitations of type 4 wind turbines for providing inertial response functionalities. Furthermore, it underlines the importance of understanding the various parameters that have an impact on the aggregate inertial response of a wind power plant in reality as well as in dynamic simulations. Final results suggest that current approaches for integrating and evaluating inertial response from wind power plants in system planning studies should be revisited. [ABSTRACT FROM AUTHOR]

with an increasing share of power converter-based renewables (e.g. wind power or photovoltaics) the impact to its connected electrical power system needs to be thoroughly assessed to fulfil grid code requirements imposed by system operators. One of the most important topics of the grid compliance assessment is harmonic emissions as widely used power converters actively contribute harmonics. However harmonic requirements and assessment processes are not reached consensus among grid codes. This adds a challenge for Wind turbine (WT) manufactures and Wind Power Plant (WPP) developers to design generic WTs and WPPs for multiple markets. Another challenge is that, prior to the construction and connection of WPPs, WPP developers often need to perform assessment studies in order to verify the impact of wind power plants (WPPs) on harmonic emission levels at the point of common coupling (PCC) based on the harmonic measurement of single WT. Results of the studies serves to make a decision on whether there is a need to install additional harmonic filters at the plant level to comply with harmonic limits of the grid code. Such filters have a long lead time and largely contribute to the overall grid connection costs. In offshore WPPs there is often not enough space for additional installation of filters due to compact offshore platform design. Hence it is crucial that an accurate method of harmonics assessment is used for WPPs harmonic study. The paper compares and summarizes harmonic requirements of relevant standards and typical country grid codes like in Germany and UK. Both, common ground and difference from those grid codes are discussed. Furthermore, two main methods, grid compliance assessment based on measurement data and simulation model respectively, are compared against for an example of WPP. Differences of results are presented and practical engineering suggestions will be provided. [ABSTRACT FROM AUTHOR]

In power systems with high penetration rates of inverter-based generation, the system inertia decreases. This causes an increased rate of change of frequency (ROCOF) for active power imbalances. Power electronic converters (esp. in wind turbines) can provide synthetic inertia. This paper focuses on the system split scenario, i.e. where a grid area is suddenly isolated from the bulk power system. For this case, load response and load shedding significantly influence the overall system behavior. The effectiveness of a df/dt-based inertia control scheme is evaluated for different shares of three load types: resistive loads, asynchronous motors (AM) and converter-interfaced loads with constant input power. The converter load represents a pump drive. An additional load control for the pump drive is investigated regarding its contribution to frequency stability in conjunction with the df/dt control. Potential violations of frequency and voltage limits are identified for each scenario, and the robustness is compared among the load configurations. [ABSTRACT FROM AUTHOR]

with increase of non-synchronous generation resource in ERCOT generation mix, the system's synchronous inertia is decreasing. Through a series of dynamic studies it was determined that current frequency control practices are insufficient for reliable operation below inertia level of 100 GW·s. It is there for important to forecast future inertia going forward. In this paper historic analysis of low inertia conditions in ERCOT is presented and several methods for future inertia forecasting are tested. [ABSTRACT FROM AUTHOR]

HVDC- transmission is the medium of choice to connect offshore wind power plants to the onshore grid when longer distances have to be overcome. To generate cost savings and hence to push further extension of offshore wind power plants uncontrolled diode rectifier HVDC-systems, instead of VSC-HVDC converters, may be used in the future. Besides the need for a grid forming capability of the wind turbine converters, also the unidirectional power flow of uncontrolled diode rectifiers evokes a challenge during calm wind situations. Hence, solutions for supplying auxiliary power to the offshore wind farm during a lack of wind have to be found. This paper presents one possible option of the auxiliary power supply where a sample offshore wind power plant is connected to the onshore grid via additional umbilical AC cable. Investigations, carried out by simulation using PSCAD?/EMTDC?, show how the wind power plants either can be operated with a fixed reference frame (FixReF) control in the normal case or with conventional PLL based control during calm wind situations. During the transition between both cases, synchronization processes have to be done when connecting and disconnecting the umbilical AC cable. [ABSTRACT FROM AUTHOR]

Mainly new requirements of VDE-AR-N 4120 [1] have led to versioning of the three FGW guidelines which cover power quality topics and certification for grid connection of renewable power generating units (PGU's) and systems (PGS') (TR 3 [2], TR 4 [3] and TR 8 [4]). This paper will present the three guidelines, discuss major changes in the new revision and give an outlook on the upcoming work, for example regarding the just published European grid code NC RfG as well as the upcoming VDEAR-N 4110 medium voltage (MV). [ABSTRACT FROM AUTHOR]

Congestion management methods are useful regulatory mechanisms to prevent transmission capacity problems. This paper intends to assess whether congestion management can be cost-efficiently used to postpone or even avoid network capacity reinforcements while increasing the hosting capacity of wind power on the island of Gotland in Sweden. Two methods, re-dispatch and market splitting, are studied in detail and applied to the Gotland case. A simplified electricity market model using historical data from Gotland was designed to perform the simulations. These methods pass on the cost of lack of transmission capacity to different actors in the electricity market (mainly grid owner for re-dispatch and consumers and producers for market splitting). Simulations indicate however that both methods could be employed to raise the installed production capacity of wind power on Gotland by at least 26 MW above the stated limit of 195 MW without negatively impacting the income of any actor. Moreover, market splitting efficiently reflects the transmission problems on the energy price of Gotland, thus giving economic incentive for flexible power consumption to alleviate the problems. [ABSTRACT FROM AUTHOR]

The paper presents issues concerning power system modelling and model validation, with particular emphasis on renewable energy sources and their integration in large electrical networks. These issues were raised at a workshop organized by UVIG and IREQ held earlier this year. From the presentations and discussions, we synthesize a general framework to summarize the model validation process. Presented in the form of tables, this framework can serve as a checklist of considerations to help model designers validate their models. [ABSTRACT FROM AUTHOR]

Renewable generation is mainly connected through converters. It can provide more and more services to the grid such as voltage support or frequency control. However, these services may not be sufficient for extremely high penetrations. As the share of such generating units is growing rapidly, some synchronous areas could in the future occasionally be operated without synchronous machines. In such conditions, system stability will have to be ensured with the same level of reliability as today. Presently, operation of power systems is based on the presence of synchronous machines. Frequency is linked to the balance between load and generation via the rotating masses equation. This will not be inherently valid for grids without synchronous machines. The matter of operating a network with 100 % power electronics is quite well resolved for small isolated systems. The same doesn't apply for large transmission systems where grid topology and power injections are highly variable and are not known at every moment by all system components or even by a centralized entity. This paper describes the research that needs to be achieved to remove barriers for high penetrations of converters. [ABSTRACT FROM AUTHOR]

Large-scale integration of Inverter-based Resources (IBRs) such as wind parks brings new challenges in modelling, analysis and simulation of power systems for protection engineers and system operators. IBRs have complex controller and electronic circuit structures but the use of faster solvers in protection studies will save valuable engineering time and alleviate transfer of black box models between different parties including Original Equipment Manufacturers (OEMs) and system operators. This paper aims to evaluate solver relaxation in an objective manner for the first time in the analysis of impact of IBRs on power swing protections. The foundation of this work is a detailed Electromagnetic Transients-type (EMT-type) model of a wind park built in PowerFactory® software. Then, an equivalent of this model compatible with RMS solvers is developed in the same software by mapping circuit and controller components to ensure objective comparisons. The two models are equivalent in terms of power, short circuit ratings and fault behavior within the typical range of simulation resolution of RMS solvers. By using these two equivalent models, the impact of wind generation on power swing protection elements based on a conventional approach are studied in EMT and RMS solvers. The results suggest consistency in the response of the two solvers for the PSRC WG-D6 test case under investigation. [ABSTRACT FROM AUTHOR]

In this paper, a fault detection algorithm for photovoltaic systems based on artificial neural networks (ANN) is proposed. Numerous literatures can be found on the topic of PV fault detection through the implementation of artificial intelligence. The novel part of this research is the successful development, deployment and validation of a fault detection PV system using radial basis function (RBF), requiring only two parameters as the input to the ANN (solar irradiance and output power). The results obtained through the testing of the developed ANN on a PV installation of 2.2 kW capacity, provided an accuracy of 97.9%. [ABSTRACT FROM AUTHOR]

Recently proposed ambitious targets for Ireland and Northern Ireland will require that the power system of Ireland and Northern Ireland is capable of operating with significantly high levels of non-synchronous variable renewable generation. Ensuring such high levels of RES-E on the Ireland and Northern Ireland power system will require operation of the system with instantaneous penetration of non-synchronous renewables in excess of 90%. Such high levels of non-synchronous generation in an island system are unprecedented and pose considerable technical challenges. Transitioning from a level of instantaneous non-synchronous penetration of renewables of 75% to more than 90% will exacerbate existing technical challenges and may reveal new, as of yet, unaccounted-for-scarcities. The focus of this paper is on a sample of the detailed analysis for the Ireland and Northern Ireland power system from Work Package 2 of the Horizon 2020 funded EU-SysFlex project. [ABSTRACT FROM AUTHOR]

The "Load Flow" project is aimed at creating a system that can model a stable predictive power flow of the electrical networks (EN). Whereas stability is achieved through bottleneck analysis module and contingency analysis (n-1 criteria). The model contains a flexible system, that can be adjusted to different electrical networks types. Currently, the program uses the CGMES data format that is used as a data exchange standard between the transmission system operators (TSOs) and the distribution system operators (DSOs). The model is based on a modified Newton-Raphson method, that is well-known and widely used in power flow studies. The ultimate goal of EU electricity market is a liberalization of the electricity sector and creation of a truly internal electricity market. However, the TSOs have not previously designed their networks and interconnections between them with the primary objective of facilitating internal power trade. Consequently, the integration of the national electricity markets is impeded by the limited amount of cross border transmission capacity. Bottleneck analysis: The key feature of the "Load Flow" project is the possibility to forecast the bottlenecks in the EN, what is achieved through the deep integration with other emsys products. Based on predicted energy production and loads the system can perform predictive power flow simulation and point the critical elements of EN. Contingency analysis: Another important feature of the project is a resilience check of the EN (n-1 criteria checking). The idea is to recognize and prevent appearances of dangerous regimes of the EN. The program changes topology of the considered network for each EN element. After each topology modification, a full load flow calculation takes place in order to monitor load flows of the elements. If the system finds an overload on some monitored elements, this is to be recorded. After a completed calculation, a load flow module report is created. Based on the results of the n-1 criteria-test, a grid operator may perform actions to increase stability under critical circumstances and a fault tolerance of the system. Based on the data and models generated in the "Load flow" project a grid operator can perform different redispatch measures to achieve a stability of an EN. The awareness of the network bottlenecks may help grid operators to restructure its own transmission network to minimize the electricity redispatch and therefore achieve better utilization of the generated energy. [ABSTRACT FROM AUTHOR]

Deployment of a vast amount of wind power can be induce large fluctuations of system frequency. In smaller balancing areas, the fluctuation of wind power generation more easily comes up to the surface. Balancing areas in Japan can provide characteristic cases of fluctuations of renewable energies, because each balancing area is small and has interconnections with small capacity. One way to deal the fluctuation is mitigation control. However, there is a trade-off between the effects of the control on mitigation of the fluctuation and the amount of energy loss. We focus on mitigation control of the short-term fluctuation which can be a major factor in fluctuation of system frequency when the share of wind power is accelerated. We use high-resolution data of wind power generation in a balancing area and simulate numerically the mitigation control. [ABSTRACT FROM AUTHOR]

Balancing control in power systems with renewable energy integration is an important issue to realize stable power supply. It is expected that not only renewable energy sources but also electric vehicles (EV) will be exceedingly introduced in the near future and they can contribute to frequency control. Therefore, in this study, a coordinated frequency control strategy based on inertial response control of wind power and charging and discharging control of EVs is proposed. In particular, EVs are classified into three groups according to SOC and different control methods are given to those groups. The effectiveness of the proposed control strategy was tested based on the IEEJ Automatic Generation Control (AGC30) Model. [ABSTRACT FROM AUTHOR]

e-Highway2050 EU-funded project has predicted how an integrated transmission grid in Europe could evolve by 2050, supporting greater use of green power and a secure, reliable electricity supply. The simulations performed confirmed that Europe's electricity transmission network would need to be expanded by 2050 to distribute all the energy that renewables would generate. A basic set of new transmission infrastructure was identified across all five scenarios studied. [ABSTRACT FROM AUTHOR]

In order to evaluate the impact of photovoltaic (PV) yield forecasting on future power system operations in Japan, we adapted the day ahead Unit Commitment (UC) model which can consider the PV yield forecasting and the forecast errors as confidence intervals and real time Economic Dispatch Control model using actual PV yield. Our results demonstrated the Japanese power system operation in 2030 when high PV penetration was expected. In the daytime, PV yield was abundant and stored by pumping operation of pumped storage generators. Pumping and generation of pumped storage generators coexisted in the daytime to satisfy the secondary reserve requirement. We also verified that to consider the CI in the day ahead UC is useful to decrease the amount of unserved energy in real time economic dispatch control. As the CI widens, reliability of power systems operation increase. However, there was the power shortage still occurred even in the widest CI case. The minimum cost was occurred when the day ahead UC was used with 90% CI and the fuel cost of peak load plants to compensate the unserved energy was average residential electricity price in Japan. However, the total cost was sensitive to the cost of the peak load plant. [ABSTRACT FROM AUTHOR]