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Since hybrid power plants (HPPs) play an intensive role in the energy supply balance of future energy systems, there is today increased attention on co-located wind-battery HPPs both in industry and academia. This paper proposes an energy management system (EMS) methodology for wind-battery plants participating in two sequential electricity markets, namely in the spot market (SM) and the balancing market (BM). The proposed and implemented EMS consists of day-ahead (DA) spot market optimization, hour-ahead (HA) balancing market optimization, and intra-hour re-dispatch optimization to allow HPPs to achieve energy arbitrage, to offer regulation power at the HA stage, and to reduce real-time imbalances. The optimization models used in the EMS incorporate an accurate battery degradation model and grid connection constraints. This paper presents a detailed case analysis of the profitability of HPPs in markets towards 2030 based on the proposed EMS. Furthermore, the value of intra-hour re-dispatch optimization in improving the feasibility of generation plans, as well as the impacts of overplanting on wind energy curtailment and battery degradation, is also investigated based on the proposed EMS.

This report constitutes part of the work package deliverable 3.1 of the EUDP IEA Task 41 project, funded by Energy Technology Development and Demonstration Program (EUDP) of the Danish Energy Agency. The report presents a brief snapshot of the current research on wind power plant support from weather dependent active distribution networks, research carried out at DTU Wind and Energy systems department. It draws upon the research work carried out by the PhD student Aeishwarya Baviskar, under the supervision of Anca D. Hansen and Kaushik Das.

Utility-scale and small scale wind and solar power installations along with electric vehicle charging stations, and other active sources of energy are increasing at the medium and lower voltage levels in the distribution grid. This situation required a better understanding of the impact of high penetration of weather-dependent renewable energy sources on the operating conditions of the distribution network at both medium and low voltage levels. Despite the need, a multi-voltage level distribution network model, based on real network data and weather-dependent renewable generation data, has not been presented for distribution grid studies. This paper presents a comprehensive multi-voltage level active distribution network model based on real network data along with load and generation time-series for about a year. The network topology is modelled based on geographical data for various rural, semi-urban, and urban locations. The distribution network is embodied with a large share of renewable generation sources, with generation time-series simulated from meteorological data. The network is also flexible to incorporate other assets such as electric vehicle charging stations, storage, etc. Thus, the presented active distribution network model can be used to study, optimize, and control the effects of weather-dependent generation and other network assets in the distribution grid.

Network operators have been increasingly concerned with procuring reactive power sources as more synchronous generators are planned to be decommissioned and number of distributed generation is on the rise. Reactive power is necessary in the evolving grid with distributed generation to support the additional power flow and avoid expensive grid reinforcements. Converter connected renewable generators can be a solution both to provide the much needed reactive power support in distribution grids and the voltage regulation support to the transmission network via altering the reactive power feed-in. This research explores the reactive power capabilities of a mutlivoltage active distribution network. A semidefinite programming based optimal power flow is implemented to find the maximum reactive power support from converter connected generation having two different objectives, namely loss minimization in the distribution network and following a reactive power reference from the transmission network. Changes in voltage profiles in correlation to altering reactive power flow in the distribution network is also analyzed.

The aim of this paper is to review and compare present European and Indian grid code requirements imposed to hybrid power plants (HPPs) combining wind, solar and storage technologies. Since there are no grid codes specifically for HPPs, the paper will review grid codes for the power plant based on individual renewable technology in the HPP. European grid codes specifies ranges for parameters inside which each national transmission system operators (TSO) has to specify the set of national parameters (Danish specifications in this paper). The comparisons are performed with respect to fault-ride-through capability, frequency and voltage operation ranges, active power control/frequency support as well as reactive power control/voltage support.

Increasing renewable energy sources in power system has brought forth many challenges in terms of power system stability, one of which is voltage stability. Preventive and corrective actions to alleviate voltage instability are mainly developed for traditional power systems without high share of renewables. This article aims to assess the reactive power based voltage support from wind power plants under stressed voltage conditions. Firstly, the performances of the conventional wind power plant control strategies applied during stressed voltage conditions are studied. A novel enhanced wind power plant control strategy is developed, which increases wind power plant reactive power capability through control of wind power plant tap changing transformer. Performance of this novel strategy is compared and evaluated against the conventional wind power plant control strategies applied during the stressed voltage conditions. Results show that the developed control strategy helps in alleviating voltage instability 5% more effectively when compared to the conventional WPP control strategies applied during stressed voltage conditions. The developed control strategy is implemented and simulated in a snapshot of the Hellenic power system to verify the implementation feasibility and effectiveness in a real large power system.

An alternative approach for combined frequency control in multi-area power systems with significant wind power plant integration is described and discussed in detail. Demand response is considered as a decentralized and distributed resource by incorporating innovative frequency-sensitive load controllers into certain thermostatically controlled loads. Wind power plants comprising variable speed wind turbines include an auxiliary frequency control loop contributing to increase total system inertia in a combined manner, which further improves the system frequency performance. Results for interconnected power systems show how the proposed control strategy substantially improves frequency stability and decreases peak frequency excursion (nadir) values. The total need for frequency regulation reserves is reduced as well. Moreover, the requirements to exchange power in multi-area scenarios are significantly decreased. Extensive simulations under power imbalance conditions for interconnected power systems are also presented in the paper.

Presently, there is a large need for a better understanding and extensive quantification of grid stability for different grid conditions and controller settings. This article therefore proposes and develops a novel mathematical model to study and perform sensitivity studies for the capabilities of different technologies to provide Frequency Containment Process (FCP) in different grid conditions. A detailed mathematical analytical approach for designing inertia-dependent droop-based FCP is developed and presented in this article. Impacts of different droop settings for generation technologies operating with different inertia of power system can be analyzed through this mathematical approach resulting in proper design of droop settings. In contrast to the simulation-based model, the proposed novel mathematical model allows mathematical quantification of frequency characteristics such as nadir, settling time, ROCOF, time to reach the nadir with respect to controller parameters such as gain, droop, or system parameters such as inertia, volume, of imbalance. Comparative studies between cases of frequency containment reserves (FCR) provision from conventional generators and wind turbines (WTs) are performed. Observations from these simulations are analyzed and explained with the help of an analytical approach which provides the feasible range of droop settings for different values of system inertia. The proposed mathematical approach is validated on simulated Continental Europe (CE) network. The results show that the proposed methodology can be used to design the droop for different technology providing FCP in a power system operating within a certain range of inertia.

This paper analyses impact of different load types on voltage stability of a power system with wind power. To analyse voltage stability, dynamic as well as static voltage stability assessment are performed. Dynamic model of wind turbine based on Type 4A IEC 61400-27-1 is used to develop an aggregated wind power plant model including the wind power collection system. Polynomial load model is used to represent different load types, namely, constant impedance, constant current and constant power loads. With respect to voltage stability assessment to determine stability of a particular operating point. Voltage collapse proximity indicator is used as dynamic voltage stability assessment tool to analyse the proximity of an operating point from voltage collapse. Impact of load type on voltage stability is discussed. Impact of reactive power support from wind power plant for the different load types is analysed and discussed. From the case studies performed, it is observed that effect of reactive power support from WPP varies depending on the load type. Results show that distance to instability for the same reactive power support from WPPs can be greater in case of voltage dependent loads than that of constant power loads.

The objective of this paper is to review and elaborate qualitatively and quantitatively the benefits of wind-based hybrid power plant (HPP) as compared to individual wind/PV power plant. A set of analyses are performed to assess annual energy production/capacity factor, power fluctuations and ramp rates of HPP production and to identify different operating conditions to understand the benefit of combining wind with solar and energy storage in an HPP. The analyses are performed based on spatio-temporally correlated wind power and solar power time series as well as on historical market price time series. Correlation of market price with wind-solar combined times series is exploited to assess the flexibility of having storage by moving the power production to hours where market prices are high from the hours when market prices are low.

Increasing large-scale integration of renewables in conventional power system has led to an increase in reserve power requirement owing to the forecasting error. Innovative operating strategies are required for maintaining balance between load and generation in real time, while keeping the reserve power requirement at its minimum. This research work proposes a control strategy for active power balance control without compromising power system security, emphasizing the integration of wind power and flexible load in automatic generation control. Simulations were performed in DIgSILENT for forecasting the modern Danish power system with bulk wind power integration. A high wind day of year 2020 was selected for analysis when wind power plants were contributing 76.7% of the total electricity production. Conventional power plants and power exchange with interconnected power systems utilize an hour-ahead power regulation schedule, while real-time series are used for wind power plants and load demand. Analysis showed that flexible load units along with wind power plants can actively help in reducing real-time power imbalances introduced due to large-scale integration of wind power, thus increasing power system reliability without enhancing the reserve power requirement from conventional power plants.

This article presents the development of a reactive power capability model for a wind power plant (WPP) based on an aggregated wind power collection system. The voltage and active power dependent reactive power capability are thus calculated by using aggregated WPP collection system parameters and considering losses in the WPP collection system. The strength of this proposed reactive power capability model is that it not only requires less parameters and substantially less computational time compared to typical detailed models of WPPs, but it also provides an accurate estimation of the available reactive power. The proposed model is based on a set of analytical equations which represent converter voltage and current limitations. Aggregated impedance and susceptance of the WPP collection system are also included in the analytical equations, thereby incorporating losses in the collection system in the WPP reactive power capability calculation. The proposed WPP reactive power capability model is compared to available methodologies from literature and for different WPP topologies, namely, Horns Rev 2 WPP and Burbo Bank WPP. Performance of the proposed model is assessed and discussed by means of simulations of various case studies demonstrating that the error between the calculated reactive power using the proposed model and the detailed model is below 4% as compared to an 11% error in the available method from literature. The efficacy of the proposed method is further exemplified through an application of the proposed method in power system integration studies. The article provides new insights and better understanding of the WPPs’ limits to deliver reactive power support that can be used for power system stability assessment, particularly long-term voltage stability.

An alternative approach for combined frequency control in multi-area power systems with significant wind power plant integration is described and discussed in detail. Demand response is considered as a decentralized and distributed resource by incorporating innovative frequency-sensitive load controllers into certain thermostatically controlled loads. Wind power plants comprising variable speed wind turbines include an auxiliary frequency control loop contributing to increase total system inertia in a combined manner, which further improves the system frequency performance. Results for interconnected power systems show how the proposed control strategy substantially improves frequency stability and decreases peak frequency excursion (nadir) values. The total need for frequency regulation reserves is reduced as well. Moreover, the requirements to exchange power in multi-area scenarios are significantly decreased. Extensive simulations under power imbalance conditions for interconnected power systems are also presented in the paper.

This paper presents two methods for frequency control of onshore AC grids from offshore wind power plants (OWPPs) connected to a multi-terminal DC (MTDC) grid. The first method is based on communicating the onshore frequency to the OWPP and the other voltage source converters (VSCs) in the MTDC grid. The second method is based on a coordinated strategy between the VSCs in the MTDC grid, where the onshore frequency is replicated at the offshore grid using additional control blocks implemented locally at the VSCs of the MTDC grid. The proposed control methods are first verified through simulations on a test set up with an OWPP connected to a three-terminal DC grid using DIgSILENT PowerFactory and then validated experimentally on a laboratory scaled three-terminal DC grid. The simulation and experimental results prove that, with the proposed control strategies, OWPPs and the VSCs in the MTDC grid can participate in frequency control and support the onshore grid frequency stability.

Emphasis in this article is on the optimization of the short-term overproduction response of variable speed wind turbines for synthetic inertia provision or fast frequency control. The short-term overproduction response of wind turbines plays a crucial role in the enhancement of the resilience of future power systems with low inertia especially during large frequency disturbances. Novel optimization approaches employing the genetic algorithm are proposed to maximize the released energy from the wind turbine during its overproduction period considering the electrical and mechanical constraints. Based on the optimization results, the article identifies and analyses a set of relevant aspects to be taken into account by power system operators and wind turbine developers in the process of designing the synthetic inertia provision or the fast frequency control. Additionally, the impact of the short-term over production response on the wind turbine structural loading is analyzed through a set of aeroelastic simulations to further investigate aerodynamic limitations.

This article concentrates on designing of frequency control and protection strategies for wind turbines during overfrequency emergencies. Critical overfrequency event on North-Eastern part of the UCTE network on 4th November 2006 is considered as a base case for investigation. A single bus power system model is developed to analyse the protection settings for this case and then to propose and discuss the design and recommendations for overfrequency control settings for wind turbines. The results of the investigation show that modification of the protection settings alone may not be sufficient to prevent frequency instability especially when wind power penetration is high and system inertia is low. Robust overfrequency emergency control strategies from wind turbines can therefore be required. The article provides the design for control parameter settings for different degrees of wind power penetration. The performance of the proposed frequency control with the developed settings is validated by means of simulations with the large scale pan-European model.

In this paper the emphasis is on the optimization of synthetic inertial response of wind power plants (WPPs) for power systems with high wind power penetration levels, considering different wind speed operating conditions. The synthetic inertial response of wind power plants can play an important role in the resilience of future power systems with low inertia during large frequency disturbances. In order to investigate this role, a generic optimization methodology employing the genetic algorithm is proposed, taking into consideration the frequency nadir, second frequency dip, and time to reach the quasi-steady-state frequency. This optimization methodology comprehends the inertial response capability of WPPs and the frequency control dynamics of the power system. Accordingly, offline parameter tuning of synthetic inertial response is performed at the power system level with the proposed methodology. Based on the optimization results, the relevant aspects to be considered by transmission system operators and wind power plant developers in the process of designing and planning synthetic inertia are identified and analyzed. Additionally, sensitivity analyses are carried out to assess the impact of synthetic inertial response parameters on power system frequency control performance under different contingencies and wind power penetration levels.

Most European countries have concerns about the integration of large amounts of renewable energy sources (RES) into electric power systems, and this is currently a topic of growing interest. In January 2008, the European Commission published the 2020 package, which proposes committing the European Union to a 20% reduction in greenhouse gas emissions, to achieve a target of deriving 20% of the European Union's final energy consumption from renewable sources, and to achieve 20% improvement in energy efficiency both by the year 2020 [1]. Member states have different individual goals to meet these overall objectives, and they each need to provide a detailed roadmap describing how they will meet these legally binding targets [2]. At this time, RES are an indispensable part of the global energy mix, which has been partially motivated by the continuous increases in hydropower as well as the rapid expansion of wind and solar photovoltaic (PV). The International Energy Agency's 2012 edition of the World Energy Outlook stated that the rapid increases in RES integration are underpinned by falling technology costs as well as rising fossilfuel prices and carbon pricing, but RES integration is also encouraged by continued subsidies: from $88 billion globally in 2011 (compared to $523 billion in fossil-fuel subsidies in 2012 [3], with a share of $131 billion for electricity generation) to an estimated $240 billion in 2035 [4]. According to [3], in 2015 RES accounted for 22% of electricity generation, which was approximately the same level as gas and about one-half the level of coal.

We examine how corporate governance changes over the industrial life cycle when places commit firms to certain governance structures. Focus is on industries where a significant part of the economic value is created by technological knowledge changing the conditions for corporate financing. The article extends this view to include knowledge needed to accumulate governance capabilities. The board is a crucial governance institution emphasized in the study. We find that changes in this institution depend on shareholders’ concern regarding innovation management. We also find that boards are changed over time to improve the conversational exchange, which is attained by extending the boards with directors holding degrees in engineering. The main finding is that the most successful firms recruit board members from the geographic setting in which they were founded at all stages of the industrial life cycle. The Danish wind turbine industry serves as empirical evidence.

Increading levels of penetration of renewables may pose challenges to power system security. When security is compromised due to some disturbances, defence plans have been developed without considering large penetration of renewable generations. Therefore, opportunities and threats of renewable generations towards defence plans need to be studied in order to properly revise the defence plans for future. This paper discusses the traditional defence plans with some exemplary case studies. The aim of this paper is to show how renewable generations like wind power can be relevant to the power system defence plans. Recommendation for protection and control strategies as well design for power systems with high penetration of renewable generations are discussed in this paper.

With increasing penetrations of wind generation, based on power-electronic converters, power systems are transitioning away from well-understood synchronous generator-based systems, with growing implications for their stability. Issues of concern will vary with system size, wind penetration level, geographical distribution and turbine type, network topology, electricity market structure, unit commitment procedures, and other factors. However, variable-speed wind turbines, both onshore and connected offshore through DC grids, offer many control opportunities to either replace or enhance existing capabilities. Achieving a complete understanding of future stability issues, and ensuring the effectiveness of new measures and policies, is an iterative procedure involving portfolio development and flexibility assessment, generation cost simulations, load flow, and security analysis, in addition to the stability analysis itself, while being supported by field demonstrations and real-world model validation.

High penetration of renewable energy sources poses numerous challenges on stability and security of power systems. Wind power plants (WPPs) of considerable size when connected to a weak grid by long transmission line results in low short circuit ratio at the point of connection. This may result in both transient voltage fluctuations and poor steady-state voltage profile at the point of connection. In this paper, transient and steady-state voltage support from WPPs are investigated. Low voltage ride through capability of WPP is studied for two different control modes namely, V control and Q control, during transient voltage dips. Steady-state analysis is performed for stressed system conditions. Results are validated through simulation in a detailed power system model.

This paper addresses the challenges associated with the operation of a distribution system with high penetration of wind power. The paper presents some preliminary investigations of an ongoing Danish research work, which has as main objective to reduce the network losses by optimizing the reactive power flow in 60kV distribution networks through controlling the ability of wind power plants (WPPs) to generate or absorb reactive power. This paper aims to understand the characteristics of a distribution network with high penetration of distributed generation. A detailed analysis of the active and reactive power flows in a real distribution network under different wind and load conditions based on actual measurements is performed in order to understand the correlation between the consumption, wind power production, and the network losses. Conclusive remarks are presented, briefly expressing the track for the future work.

In this article, a new methodology is developed to assess the adequacy of frequency reserves to handle power imbalances caused by wind power forecast errors. The goal of this methodology is to estimate the adequate volume and speed of activation of frequency reserves required to handle power imbalances caused due to high penetration of wind power. An algorithm is proposed and developed to estimate the power imbalances due to wind power forecast error following activation of different operating reserves. Frequency containment reserve requirements for mitigating these power imbalances are developed through this methodology. Furthermore, the probability of reducing this frequency containment reserve requirement is investigated through this methodology with activation of different volumes and speed of frequency restoration reserve. Wind power generation for 2020 and 2030 scenarios for Continental Europe network are investigated based on which recommendations are made for requirements of frequency reserves in these scenarios. It has been observed through simulations that frequency containment reserve requirements reduce exponentially with increase in volume of frequency restoration reserve and remains almost unaffected by increase activation speed of frequency restoration reserve.

Highly wind power integrated power system requires continuous active power regulation to tackle the power imbalances resulting from the wind power forecast errors. The active power balance is maintained in real-time with the automatic generation control and also from the control room, where regulating power bids are activated manually. In this article, an algorithm is developed to simulate the activation of regulating power bids, as performed in the control room, during power imbalance between generation and load demand. In addition, the active power balance is also controlled through automatic generation control, where coordinated control strategy between combined heat and power plants and wind power plant enhances the secure power system operation. The developed algorithm emulating the control room response, to deal with real-time power imbalance, is applied and investigated on the future Danish power system model. The power system model takes the hour-ahead regulating power plan from power balancing model and the generation and power exchange capacities for the year 2020 into account. The real-time impact of power balancing in a highly wind power integrated power system is assessed and discussed by means of simulations for different possible scenarios.

With high penetration of distributed generation (DG), the conventional under-frequency load shedding (UFLS) face many challenges and may not perform as expected. This article proposes new UFLS schemes, which are designed to overcome the shortcomings of traditional load shedding scheme. These schemes utilize directional relays, power flow through feeders, wind and PV measurements to optimally select the feeders to be disconnected during load shedding such that DG disconnection is minimized while disconnecting required amount of consumption. These different UFLS schemes are compared in terms of frequency response, amount of consumption and DG disconnected during load shedding.