Frequency Control Ancillary Services Research Articles

Integrated techno-economic assessment of Liquid Air Energy Storage (LAES) under off-design conditions: Links between provision of market services and thermodynamic performance

This paper deals with Liquid Air Energy Storage (LAES) – one of the most promising thermo-mechanical technologies with the potential to provide bulk energy storage functionalities. More specifically, an integrated technical and economic assessment of the performance of LAES when providing multiple energy and frequency control ancillary services is carried out. To this end, an off-design thermodynamic model of LAES was developed and validated against experimental data from the literature to allow understanding the links between the specific requirements of the market services to provide and the performance of each component of the LAES plant, and from here the performance of whole LAES process. The model was then applied to assess how a stand-alone LAES plant performs when providing three specific assets in the UK electricity market: arbitrage, short term operating reserve (STOR), and fast reserve (FR). The results obtained clearly demonstrate that (a) a strong link between type of service and LAES off-design conditions exists and cannot be neglected; (b) roundtrip efficiency and liquid air consumption can vary by up to 30% during off-design operation, causing some 10 k£/MW of missed revenue; (c) the effect of off-design conditions is unevenly distributed across LAES components, with low-pressure turbines affected the most; (d) a suitable regulation strategy can alleviate but not prevent off-design performance variations, improving roundtrip efficiency by up to 4 percentage points. The modelling developed is thus essential for a realistic assessment of the value and constraints for LAES to participate in electricity markets and support low-carbon power system operation and development.

Integrated techno-economic modeling, flexibility analysis, and business case assessment of an urban virtual power plant with multi-market co-optimization

The concept of Virtual Power Plant (VPP) is recognized as an effective option to aggregate and operate Distributed Energy Resources (DER) to participate in wholesale energy markets and provide flexibility and associated grid services that are needed in a renewable-rich energy system. Also, as most of the DER are available in urban areas, there are increasing interests in assessing the potential to develop urban VPP, for example in university campuses. However, exploiting the flexibility of VPP and developing robust business cases require advanced considerations on their technical and commercial constraints and trade-offs in deploying the VPP’s flexibility when simultaneously participating in multiple markets. In this context, this paper presents a comprehensive, integrated techno-economic modeling approach that assesses the technical and commercial flexibility opportunities and develops a relevant business case framework based on co-optimized participation in multiple markets for an urban VPP. A real-world case study based on the University of Melbourne’s new campus under development is used to demonstrate the proposed approach, including the VPP’s participation in the energy, frequency control ancillary services, demand response, and hedging contract markets. The technical analysis shows that diversity of DER portfolio results in improved participation of VPP in various markets. From an economic perspective, a multi-market co-optimization model such as the one proposed here, fully exploiting the DER’s aggregated flexibility, results in attractive business cases for operating DER in urban areas as a VPP. The proposed approach and examples provided may be seen as a blueprint for more VPP applications and unlocking the great flexibility available in urban areas.

Contribution of frequency linked pricing control on ALFC and AVR power system integrated with DFIG based wind farms

This research article presents the participation of frequency linked pricing control (FPC) scheme for frequency and voltage control ancillary services in multi-area power system having automatic load frequency control (ALFC) loop and automatic voltage regulator (AVR) loop and integrated with doubly fed induction generator (DFIG) based wind farms. Mutual coupling effects are shown between the two loops by extending linearised ALFC system to include excitation model using AVR loop. FPC based on availability based tariff (ABT) mechanism is used under small load perturbations in power system to provide secondary control to reset frequency and voltage to their nominal values. Dynamic participation of DFIG based wind farms is shown by using modified inertial control scheme to inject active power quickly into the power system, thereby arresting deviations in frequency and voltage during transient conditions. Results reveal that coordinated action of DFIG based wind farms under FPC environment provides better dynamic frequency and voltage responses by reducing their deviations from nominal values.

Evaluation of a Li-Titanate battery module in primary frequency control ancillary service conditions

• A lithium-Titanate battery module was tested for 250 days under frequency control endurance test profile. • No variation in both the discharged capacity and in discharged energy was found. • The Li-Titanate battery module is good for primary frequency control dynamics. • The module energy content is not sufficient for one-day continuous operation in primary frequency control conditions. • The tool developed suggests to oversize the energy content up to 1.5C/Cn - 2C/Cn for continuous service availability. Power networks are deeply changing in recent years due to the rapid deployment of renewable energies and a growing worldwide energy demand. Energy storage systems are promising technologies to provide electric networks with ancillary services. Currently, only few data referred to batteries operation in power network ancillary services utilization are available. This could limit the evaluation of battery technologies in relation to those applications. Li-Titanate technology is characterized by a high specific power, long lifetime, and it guarantees high safety in stressful conditions. In this framework, the performance of a Li-Titanate battery module, subjected to a Primary Frequency Control (PFC) cycle, was studied. This paper reports the results coming from the testing campaign, where Li-Titanate battery demonstrated no degradation after 250 test days. Due to the module low energy content with respect the PFC profile, the battery resulted discharged two times per day. Therefore, a numerical tool was developed in order to obtain a valid instrument for optimal design in relation to PFC application and for simulating Li-Titanate battery module behavior.

Frequency Support by BESS – Review and Analysis

This work reviews and analyzes the feasibility of frequency support by Battery Energy Storage System (BESS). If power generation and load demand are unbalanced, it would cause serious problems on frequency stability. BESS is an effective method to balance power generation and load demand since it has fast response characteristics. This work analyzes the concept of frequency support by BESS, including the design of BESS and the battery characteristics for frequency support. Various battery energy storage technologies for frequency support are compared and analyzed. In addition, the cost analysis using the BESS frequency support service are reviewed, and the international experiences concerning about the BESS participating in UK Firm Frequency Response (FFR) and Australia Frequency Control Ancillary Services (FCAS) markets are introduced, which provides power system operators important references.

Minimum Synchronous Inertia Requirement of Renewable Power Systems

The installed capacity of wind generation and photovoltaics (PV) in many countries is going to dominate generation fleets in a bid to meet growing renewable energy targets. Synchronous inertia has never been problematic as there was more available than needed, but it is being significantly reduced due to the increasing integration of nonsynchronous renewable generation. When the low bidding priced generation of wind and PV becomes considerably large, conventional economic dispatch algorithms can result in less online synchronous inertia and put power system security at risk. However, the compromise of power system security due to synchronous inertia shortage is not well studied in the literature. This paper develops a synchronous inertia constrained economic dispatch algorithm to satisfy the minimum required synchronous inertia of frequency control. Synchronous condensers and wind reserve are economically allocated to alleviate any shortage of synchronous inertia and frequency control ancillary services (FCAS). A Gaussian particle swarm optimization algorithm is introduced to simultaneously co-optimize the dispatch of synchronous generators and their FCAS, wind reserve, and synchronous condensers.

Investigation of Load Frequency Relief From Field Measurements and Its Impact on Contingency Reserve Evaluation

Any mismatch between load and generation (due to a generator or an interconnection trip) is intended to be balanced and stabilized by contingency reserve, which is also known as contingency Frequency Control Ancillary Services (FCAS) requirement. Load Frequency Relief (LFR), which represents the effect of frequency dependent loads on power system frequency excursion, is crucial for correctly evaluating contingency reserve requirement during generation dispatch to ensure an adequate frequency response. Over estimation of LFR can be accountable for less planned reserve during an economic dispatch that may cause undesirable frequency performance. On the other hand, under estimation of LFR can result in an excessive reserve and hence could unnecessarily increase system operational cost. Conventionally, LFR is considered as a fixed quantity during the evaluation of FCAS requirement. However, recent experience in the Australian power grid suggests that such an assumption may lead to an inaccurate outcome. To explore the above issue, this research investigates the LFR using field measurement data, which were captured at different locations of the southern states of Australia (e.g., Tasmania and Victoria). An approach is developed to identify the predominating factors affecting the LFR and subsequently a technique is proposed to appropriately determine contingency FCAS requirement.

Wind power variations during storms and their impact on balancing generators and carbon emissions in the Australian National Electricity Market

This paper examines changes in Frequency Control Ancillary Services (FCAS) generator output due to several large wind farm power variations occurring in the Australian National Electricity Market (NEM) during 2012 and 2013. Using data from actual FCAS generator output fluctuations during selected storm events and reconstructed heat rate curves for each FCAS generator, the authors address the research question of what effect such variations have on net carbon emissions from electricity generation, given balancing fossil-fueled FCAS generators will be pushed back into less efficient operating ranges. The study finds that, for all storm events evaluated, net carbon emissions decreased with each large increase in wind power, even though FCAS generator carbon intensity increased in two of the three events. This finding is consistent with the conclusions of other studies that while FCAS generators do move into less efficient operating ranges, the generation of zero carbon emission wind power displaces other fossil fuel generators and more than compensates for this efficiency reduction, creating an overall positive carbon effect. This is a significant finding as it shows that the inclusion of wind farms in the generation mix serving the Australian NEM can lower carbon emissions in both short and long time frames.

Frequency regulation capabilities in wind power plant

The design of frequency regulation services plays a vital role in automation and eventually reliable operation of power system at a satisfactory and stable level. Frequency response capability offered by wind plant is not same as the primary control capability of conventional plants, hence the integration of wind energy based generation at large scale has widespread impacts on power system stability and reliability. With the changing generation mix, modern electric power systems are facing a critical challenge in the real‐time balancing of demand and supply. This paper comprehensively reviews the various control functionalities available in wind energy systems for supporting frequency regulation at different levels of frequency control services starting from inertial control to the secondary control. An insight to new research challenges for better frequency control ancillary services in wind integrated system is also provided. Though wind-based ancillary services are still in research and development stage in most of the countries, future wind energy system participation is expected to contribute to enhanced market efficiency, improved system reliability and macro economic benefits to all stakeholders.

Frequency Control Ancillary Service Provided by Efficient Power Plants Integrated in Queuing-Controlled Domestic Water Heaters

Frequency is an important parameter of a power system. It is of great significance to maintain its stability, especially in the current development scenario of large-scale interconnected power systems. Thermostatically controlled appliances (TCAs) are good controllable resources for demand response owing to their rapid response capabilities and relatively wide controllable ranges. In this study, domestic water heaters, which have wider deadbands compared with other typical TCAs, such as heat pumps, are used as frequency regulation resources. The main contribution of this paper is that it proposes a queuing-controlled strategy with lock-on and off constraints for controlling an efficient power plant consisting of water heaters (EPP-WH). The queuing-controlled strategy enables TCAs to provide frequency regulation ancillary service for the normal operation of the power system. The thermal dynamic process of the water heater and the formation of the EPP-WH are first discussed. Based on the developed model, a series of strategies are proposed, including load shedding calculation, top layer optimization, and improved temperature priority list (TPL) strategy with lock-on and off constraints. Finally, typical case studies are discussed to illustrate the frequency regulation effects and the effects of two characteristic parameters—users’ willingness and lock time limits. Reasonable targets are generated based on various consideration from top layer optimization module. The results indicate that using the model and proposed strategies, the EPP-WH has good frequency regulation performance.

MGSO optimised TID‐based GCSC damping controller in coordination with AGC for diverse‐GENCOs multi‐DISCOs power system with considering GDB and GRC non‐linearity effects

This study presents automatic generation control (AGC) in the presence of a gate controlled series capacitor (GCSC) to provide an effective frequency control ancillary service for a two-area diverse-GENCOs multi-DISCOs power system. First, the contribution of the GCSC in tie-line power exchange is formulated mathematically and then a tilt-integral-derivative (TID)-based damping controller is proposed. The effectiveness of the proposed TID-based GCSC-AGC coordinated controller is compared with just AGC, proportional-integral-derivative-based GCSC-AGC, thyristor controlled series capacitor-AGC, static synchronous series compensator-AGC, and thyristor controlled phase shifter-AGC. A modified group search optimisation (MGSO) algorithm is employed to adjust the considered controllers. Physical limitations of generation rate constraint (GRC) non-linearity and governor dead-band (GDB) effect are taken into account in the evaluations to obtain realistic results. Bilateral contracts and pool-co transactions are considered concurrently for the realisation of a competitive environment. Simulations reveal that the proposed controller outperforms the other controllers in providing better dynamic responses. Additional evaluations are performed under the un-contracted step, sinusoidal and random load demands seen as contract violations to demonstrate the superiority of the proposed controller over other controllers. Sensitivity analyses are performed for different uncertainty scenarios to show the robustness of the proposed control approach.

Frequency Control Ancillary Service Market Design: Insights from the Australian National Electricity Market

FCAS markets offer three features that may reduce costs and facilitate the integration of larger quantities of variable renewables, such as wind and solar photovoltaics. These have been successfully implemented in the Australian National Electricity Market and may serve as an effective model for other electricity systems.

Smart microgrid hierarchical frequency control ancillary service provision based on virtual inertia concept: An integrated demand response and droop controlled distributed generation framework

Low inertia stack, high penetration levels of renewable energy source and great ratio of power deviations in a small power delivery system put microgrid frequency at risk of instability. On the basis of the close coupling between the microgrid frequency and system security requirements, procurement of adequate ancillary services from cost-effective and environmental friendly resources is a great challenge requests an efficient energy management system. Motivated by this need, this paper presents a novel energy management system that is aimed to coordinately manage the demand response and distributed generation resources. The proposed approach is carried out by constructing a hierarchical frequency control structure in which the frequency dependent control functions of the microgrid components are modeled comprehensively. On the basis of the derived modeling, both the static and dynamic frequency securities of an islanded microgrid are provided in primary and secondary control levels. Besides, to cope with the low inertia stack of islanded microgrids, novel virtual inertia concept is devised based on the precise modeling of droop controlled distributed generation resources. The proposed approach is applied to typical test microgrid. Energy and hierarchical reserve resource are scheduled precisely using a scenario-based stochastic programming methodology. Moreover, analyzing the results verifies the impressiveness of the proposed energy management system in cost-effectively optimizing the microgrid ancillary service procurement.

Designing electricity markets for a high penetration of variable renewables

Renewable technologies are often characterized as being somewhat different to ‘conventional’ generating technologies in three ways, each with different implications for electricity markets. Firstly, some have highly variable and somewhat uncertain availability, meaning that electricity markets must be designed to elicit adequate flexibility. Secondly, many have very low short‐run marginal costs (operating costs), meaning that the mechanisms for managing resource adequacy must be carefully considered. Thirdly, some are nonsynchronous, meaning that grid codes and regulatory requirements must be appropriately designed. Access to flexibility can be enhanced by a range of market design choices, such as short dispatch intervals, short delays from gate closure to dispatch, large balancing areas, high demand side participation, and exposing renewable technologies to market price signals commensurate with other technologies. The design of markets for frequency control ancillary services (FCAS) also provides opportunities to increase access to flexibility, by creating active real‐time markets for a wide range of FCAS, allowing renewable technologies to provide FCAS, and determining FCAS reserve requirements dynamically in real time. Mechanisms for managing resource adequacy are a source of ongoing debate, with many of the key issues having been exacerbated by the entry of renewables. Rapid market change makes investment decisions difficult, regardless of the market model applied. Ultimately, given the existence of arguably successful examples of both energy‐only and capacity market designs, the choice of market model may be less important than the quality of governance with which it is implemented and maintained. WIREs Energy Environ 2015, 4:279–289. doi: 10.1002/wene.137This article is categorized under: Energy Infrastructure > Economics and Policy Energy Infrastructure > Systems and Infrastructure Energy Systems Economics > Economics and Policy Energy Policy and Planning > Economics and Policy

Frequency control ancillary service provided by a wind farm: dual-BESS scheme

Network frequency control function is incorporated into a grid-connected wind farm-dual battery energy storage system (BESS) scheme. The design of the scheme takes advantage of the rapid response characteristics of the BESS and the in-built short-term overloading capability of the associated power conversion devices. A control strategy to regulate the BESS output power is then proposed. It is shown that the frequency control action offered by the BESS complements amicably with that of conventional generators in enhancing the frequency regulation attribute of the grid system.

Market-Based Ancillary Services in the Australian National Electricity Market for Increased Levels of Wind Integration

This paper provides an overview of Australia's National Electricity Market (NEM) with a focus on its design and implementation features that benefit an increasing level of wind generation. The NEM design is discussed both in terms the ability of the system operator to manage threats to the security of the power system that an increasing level of wind integration may pose through the use of market-based frequency control ancillary services (FCAS) as well as the extent to which the commercial decision-making processes are suitable for participation of wind farm operators in the electricity market. In this way, the features of the NEM that facilitate wind integration are identified along with aspects of the market design that could be refined. This allows for comparisons to be made to other electricity market designs in terms of their ability to support an increasing level of wind integration.

A Survey of Frequency and Voltage Control Ancillary Services—Part I: Technical Features

This two-part paper surveys the frequency and voltage control ancillary services in power systems from various parts of the world. In this first part, the nomenclature used to describe active power reserves across 11 systems is first reviewed in order to facilitate the comparison of frequency control ancillary services. The essential technical features of frequency and voltage control ancillary services are then described. Finally, the technical requirements adopted in eight jurisdictions (North America, continental Europe, Germany, France, Spain, the Netherlands, Belgium, and Great Britain) are compared. The companion paper surveys the economic features of these ancillary services

A Survey of Frequency and Voltage Control Ancillary Services—Part II: Economic Features

This two-part paper surveys the frequency and voltage control ancillary services in power systems from various parts of the world. In this second part, essential economic features that must be taken into account when designing markets for ancillary services are first discussed. The methods adopted in eight different systems (Australia, France, Germany, Great Britain, New Zealand, PJM, Spain, and Sweden) for trading frequency and voltage control ancillary services are then compared. Lastly, new indicators for comparing volumes and costs of ancillary services across systems are proposed and calculated for the systems included in this survey. The companion paper surveys the technical features of these ancillary services