Showing papers by "Pierluigi Mancarella published in 2019"

Flexibility in Multi-Energy Communities With Electrical and Thermal Storage: A Stochastic, Robust Approach for Multi-Service Demand Response

Abstract: There is increasing interest in multi-energy communities, which could become important sources of demand response flexibility, especially when equipped with storage. Their location on distribution networks mean their exploitation to solve local capacity congestions may be particularly valuable, whilst their ability to partake in energy/reserve markets can improve their business cases. However, maximizing this flexibility potential by providing multiple services that are subject to uncertain calls is a challenging modeling task. To address this, we present a stochastic energy/reserve mixed integer linear program for a community energy system with consideration of local network constraints. By covering all the relevant energy vectors, the multi-energy formulation allows comprehensive modeling of different flexibility options, namely, multi-energy storage, energy vector substitution, end-service curtailment, and power factor manipulation. A key feature of the approach is its robustness against any reserve call, ensuring that occupant thermal comfort cannot be degraded beyond agreed limits in the event of a call. The approach is demonstrated through a case study that illustrates how the different flexibility options can be used to integrate more electric heat pumps into a capacity constrained smart district that is managed as a community energy system, while maximizing its revenues from multiple markets/services.

Energy Systems Integration in Smart Districts: Robust Optimisation of Multi-Energy Flows in Integrated Electricity, Heat and Gas Networks

Abstract: Smart districts can provide flexibility from emerging distributed multi-energy technologies, thus bringing benefits to the district and the wider energy system. However, due to nonlinearity and modeling complexity, constraints associated with the internal energy network (e.g., electricity, heat, and gas) and operational uncertainties (for example, in energy demand) are often overlooked. For this purpose, a robust operational optimization framework for smart districts with multi-energy devices and integrated energy networks is proposed. The framework is based on two-stage iterative modeling that involves mixed integer linear programming (MILP) and linear approximations of the nonlinear network equations. In the MILP optimization stage, the time-ahead set points of all controllable devices (e.g., electrical and thermal storage) are optimized considering uncertainty and a linear approximation of the integrated electricity, heat, and gas networks. The accuracy of the linear model is then improved at a second stage by using a detailed nonlinear integrated network model, and through iterations between the models in the two stages. To efficiently model uncertainty and improve computational efficiency, multi-dimensional linked lists are also used. The proposed approach is illustrated with a real U.K. district; the results demonstrate the model’s ability to capture network limits and uncertainty, which is critical to assess flexibility under stressed conditions.

A Graph-Based Loss Allocation Framework for Transactive Energy Markets in Unbalanced Radial Distribution Networks

Abstract: Future distributed transactive energy markets are envisioned to integrate multiple entities located mainly at the distribution level of the grid, so that consumers and prosumers can trade power either directly with the upstream wholesale energy market or through local pricing mechanisms (e.g., through “ peer-to-peer ” contracts or by forming “ energy communities ”). In such market environments, a transparent loss allocation framework is required to guarantee economic efficiency and fairness. Nevertheless, the unbalanced power flow nature associated with the distribution networks should be fundamentally integrated in the loss allocation process. To this end, this paper presents a graph-based loss allocation framework that harmonizes the physical attributes of the distribution grid with the underlying financial transactions in distributed market settings. The latter is achieved via representing distribution networks as multilayered radial graphs. The proposed loss allocation framework is tested on an actual LV feeder that is experiencing rapid growth in DG applications.

On Feasibility and Flexibility Operating Regions of Virtual Power Plants and TSO/DSO Interfaces

Abstract: Distributed energy resources are an ideal candidate for the provision of additional flexibility required by the power system to support the increasing penetration of renewable energy sources. The integrating large number of resources in the existing market structure, particularly in the light of providing flexibility services, is envisioned through the concept of virtual power plant (VPP). To this end, it is crucial to establish a clear methodology for VPP flexibility modelling. In this context, this paper first puts forward the need to clarify the difference between feasibility and flexibility potential of a VPP, and then propose a methodology for the evaluation of relevant operating regions. Similar concepts can also be used to modelling TSO/DSO interface operation. Several case studies are designed to reflect the distinct information conveyed by feasibility and flexibility operating regions in the presence of “slow” and “fast” responding resources for a VPP partaking in the provision of energy and grid support services. The results also highlight the impact of flexible load and importantly network topology on the VPP feasibility (FOR) and flexibility (FXOR) operating regions.

Spatial Risk Analysis of Power Systems Resilience During Extreme Events

Abstract: The increased frequency of extreme events in recent years highlights the emerging need for the development of methods that could contribute to the mitigation of the impact of such events on critical infrastructures, as well as boost their resilience against them. This article proposes an online spatial risk analysis capable of providing an indication of the evolving risk of power systems regions subject to extreme events. A Severity Risk Index (SRI) with the support of real-time monitoring assesses the impact of the extreme events on the power system resilience, with application to the effect of windstorms on transmission networks. The index considers the spatial and temporal evolution of the extreme event, system operating conditions, and the degraded system performance during the event. SRI is based on probabilistic risk by condensing the probability and impact of possible failure scenarios while the event is spatially moving across a power system. Due to the large number of possible failures during an extreme event, a scenario generation and reduction algorithm is applied in order to reduce the computation time. SRI provides the operator with a probabilistic assessment that could lead to effective resilience-based decisions for risk mitigation. The IEEE 24-bus Reliability Test System has been used to demonstrate the effectiveness of the proposed online risk analysis, which was embedded in a sequential Monte Carlo simulation for capturing the spatiotemporal effects of extreme events and evaluating the effectiveness of the proposed method.

Effect of inertia heterogeneity on frequency dynamics of low-inertia power systems

Abstract: Based on fundamental dynamic simulation principles and illustrative case studies, this study aims to identify key changes in the dynamic behaviour of the system due to the high penetration of renewable energy sources (RES) affecting frequency dynamics and provide guidelines for performing frequency stability analysis in low-inertia power systems with a large penetration of RES. First, a critical comparison of the frequency responses obtained using a system equivalent model and a detailed dynamic model following an active power disturbance are presented. It is then demonstrated, using detailed dynamic models of two multi-area systems, such that when the proportion of RES prevails over the share of synchronous generator (SG), the dynamic coupling among areas (even separated by short-medium length lines) reduces and the inertia of the system should be considered as heterogeneous instead of a global parameter. Following this, the study discusses how frequency dynamics may be strongly and complexly affected by the physical characteristics of converter-connected generation leading to increased frequency and voltage interactions when the proportion of converter connected RES becomes greater than SG. The resulting changes in the system's dynamic behaviour due to frequency and voltage interactions can increase the actual active power imbalance size following a credible contingency so that careful considerations to protect the system against an excessively high rate of change of frequency should be made. In order to evaluate the extent of this change in system dynamic behaviour, an appropriate dynamic model of the network should be used with adequate multi-area representation of RES and loads.

Data-Driven Dynamic Probabilistic Reserve Sizing Based on Dynamic Bayesian Belief Networks

Abstract: Due to the variability and partial unpredictability of renewable energy sources (RES), generation reserve sizing is key for managing operational risks and enhancing grid reliability. Most existing approaches for reserve sizing estimate the forecasting error for RES using either simple point forecasts, or probabilistic forecasts that assume a predefined parametric model of the underlying distribution, such as a Gaussian distribution. However, these approaches are unable to accurately model the probability of critical events that occur in the tails of the distributions, which is vital for operational risk management. Further, they do not account for multiple dynamic factors that may impact operational risk. In this paper, we introduce a data-driven dynamic probabilistic reserve sizing method based on the artificial intelligence technique of dynamic Bayesian belief networks. The method considers the actual underlying distribution of forecasting errors from the availability of conventional generators (forecasting errors of their available generation capacity), demand, RES, and prevailing conditions such as weather and market prices. In addition, we introduce a new dynamic metric for calculating the reliability level of the power grid in order to provide a real-time stochastic decision support tool for power system operators. The proposed method is demonstrated using seven years of real historical data with a granularity of 30 min from the power system in Australia, and has been implemented and is currently used by the Australian system operator.

Application of Utility-Connected Battery Energy Storage System for Integrated Dynamic Services

Abstract: The rapid uptake of renewable energy sources (RES) and displacement of synchronous generators is introducing a number of security challenges, particularly in terms of frequency and voltage stability, whose interactions in RES-dominated systems are to be fully understood yet. This paper models and discusses the application of utility-connected battery energy storage system (BESS) for provision of integrated dynamic services, i.e., simultaneous provision of primary frequency/active power and voltage/reactive power control. To investigate how BESS should respond to system contingencies, a detailed BESS dynamic model is presented along with comprehensive discussions on interaction of frequency and voltage responses and proposing suitable control signal generation algorithms. Simulation results illustrate the BESS capability to provide integrated dynamic services as proposed, highlighting the significance of response prioritization.

On Feasibility and Flexibility Operating Regions of Virtual Power Plants and TSO/DSO interfaces

Abstract: Distributed energy resources are an ideal candidate for the provision of additional flexibility required by power system to support the increasing penetration of renewable energy sources. The integrating large number of resources in the existing market structure, particularly in the light of providing flexibility services, is envisioned through the concept of virtual power plant (VPP). To this end, it is crucial to establish a clear methodology for VPP flexibility modelling. In this context, this paper first puts forward the need to clarify the difference between feasibility and flexibility potential of a VPP, and then propose a methodology for the evaluation of relevant operating regions. Similar concepts can also be used to modelling TSO/DSO interface operation. Several case studies are designed to reflect the distinct information conveyed by feasibility and flexibility operating regions in the presence of "slow" and "fast" responding resources for a VPP partaking in provision of energy and grid support services. The results also highlight the impact of flexible load and importantly network topology on the VPP feasibility (FOR) and flexibility (FXOR) operating regions.

Frequency Response Capabilities of Utility-scale Battery Energy Storage Systems, with Application to the August 2018 Separation Event in Australia

Abstract: This paper is aimed to investigate the capabilities of utility-scale energy storage system (BESS) in provision of both contingency and regulation frequency control ancillary services (FCAS). In particular, the fast mode-change capability of battery and its corresponding impacts on its frequency support ability is investigated through dynamic modelling of the 100 MW Hornsdale battery during the August 2018 separation events in Australia. In this regard, a converter-based battery dynamic model is presented which includes current- bidirectional DC-DC converter, thereby being able to observe its fast mode change as a response to severe frequency excursions. Also, an active power-frequency characteristic is proposed which considers the impact of battery pre-contingency operating point on its available headroom for primary frequency response provision. Moreover, an active power reference generation strategy is suggested which takes into account regulation FCAS provision through automatic generation control (AGC) as well as contingency FCAS provision through droop controller. Finally, it will be shown how BESS installed in Victoria might have potentially prevented the severity of the August 2018 event by prevention of both under-frequency load shedding (UFLS) and secondary photovoltaic (PV) trip.

Frequency Stability Provision From Battery Energy Storage System Considering Cascading Failure s with Applications to Separation Events in Australia

Abstract: The increasing penetration of non-synchronous generators, accompanied by retiring/displacement of synchronous generators has created a number of new operational issues in the Australian National Electricity Market (NEM) network, such as low-inertia conditions. Low-inertia power systems are likely to experience relatively large frequency variations following a generation/load mismatch. This is evidenced by a recently occurred event in the Australian National Electricity Market (NEM) grid, which led to cascading failures and electrical separation of the two states of Queensland and South Australia from the rest of the NEM. This paper first provides an extensive description of the event occurred on 25th August 2018, whose high-level dynamic behaviour was simulated in a NEM reduced test system. Secondly, the use of grid-scale battery energy storage system (BESS) in providing primary frequency response (PFR) is investigated as a potential countermeasure to cascading failures. Simulation results show BESS could have potentially avoided under-frequency load shedding (UFLS).

Flexibility in Sustainable Electricity Systems: Multivector and Multisector Nexus Perspectives

Abstract: As environmental concerns increase, researchers, policy makers, and the public in general are becoming more interested in options to make energy more sustainable while at the same time ensuring that energy systems are affordable, reliable, and resilient. This dynamic is bringing about challenges across the world, as established energy systems (such as those in cities) must be enhanced to integrate large volumes of renewable energy sources (RES), while new or evolving systems (for instance, in developing economies) must be planned to manage the increasingly extreme conditions associated with climate change. In these contexts, the flexibility to intelligently use and invest in resources that go beyond the power system (e.g., other energy vectors such as heat, gas, or water dams) can be extremely valuable from the perspective of sustainable development.

A Modelling Framework for a Virtual Power Plant with Multiple Energy Vectors Providing Multiple Services

Abstract: The deep penetration of distributed energy resources (DER) and renewables into electrical networks is increasing generation variability and uncertainty. One way of addressing this issue is Virtual Power Plants (VPPs), which aggregate a diverse set of DER to act in various electricity markets as a single entity. This work introduces a modelling framework which allows a VPP to operate in multiple markets, considers multiple energy vectors, and dispatches devices at 5-minute intervals, while operating within local network constraints. To ensure framework tractability, it is divided into a three-stage optimization: the high-level scheduling the devices; the mid-level dispatching them with 30-minute timesteps over a 24-hour horizon; the low-level performing the 5-minute dispatch. A real case study with electricity and hydrogen in South Australia is conducted. Results show the VPP coordinating renewable generation, dispatchable load, hydrogen storage and thermal generation to maximize earnings over multiple markets whilst adhering to local network constraints.

Possible Negative Interactions between Fast Frequency Response from Utility-scale Battery Storage and Interconnector Protection Schemes

Abstract: Grid integration of renewables and replacement of conventional synchronous power plants may significantly decrease system inertia, which can potentially lead to frequency stability issues. Among alternative solutions to support system frequency in low-inertia conditions, and thanks to their unique technology features and highly controllable power electronic converters, utility-scale battery energy storage system (BESS) can be deployed to provide fast frequency response (FFR). However, possible undesired knock-on effects from such FFR operation, e.g., its negative interaction with equipment protection relays, and particularly for interconnectors, have not been adequately investigated. In this context, this paper first demonstrates with an illustrative analytical example how BESS FFR could potentially induce undesired trip in out-of-step interconnector protection schemes. Then, a case study example based on an Australian test system is presented to discuss how FFR from the 100 MW Hornsdale BESS located in South Australia might have contributed to the trip of the Heywood interconnector with Victoria during the August 2018 separation event. Finally, it is shown how FFR from BESS in Victoria could have enhanced frequency control and even prevent system separation, hence highlighting the importance of FFR location.

Demand Response from an Integrated Electricity-Hydrogen Virtual Power Plant

Abstract: The rapid growth of large-scale renewables and Distributed Energy Resources (DER) leads to increased uncertainty and reduced controllability of energy generation. Thus, control of demand is becoming more necessary to maintain network energy balancing. Individually these devices are often too small to operate in the electrical markets and operated individually can have negative impact on the local network. One method to address this is by the use of Virtual Power Plants (VPPs), which aggregate a diverse set of DR devices with a similar network location to act as a single entity. Integrating different energy vectors into the VPP can both provide additional storage and flexibility to the VPP, but also provide additional revenues. Hydrogen storage is a promising technology that will be considered in this paper for integration with DR. This paper will present the applications of a framework for modelling an electricity-hydrogen VPP that can schedule and dispatch devices providing DR; compete in multiple wholesale markets; and provide local network support. This VPP operates with a 24-hour planning horizon, and a 5minute dispatch. A case study has been conducted on a VPP that contains renewable generation, thermal generation, curtailable load and hydrogen-based devices with hydrogen storage. The results show that the VPP can effectively control the devices providing DR and utilize the hydrogen storage and maximize VPP earnings while providing local network support whilst effectively adapting to price changes.

Integrated Energy-Water Model for Interdependent Storage, Run-of-River and Pump Hydropower

Abstract: The dispatch of different types of hydropower plants such as storage, Run of River (RoR) and pumped affects downstream water flows and power generation. These short-term operational impacts (e.g., hourly water release) must be properly modelled and quantified to capture the flexibility of interdependent hydropower plants to provide system support (e.g., reduce energy costs). This paper presents a Linear Programming (LP) model to simulate the operation of interdependent hydropower plants where dedicated hydrologic routing constraints are used to track the flow of water, and quantify relevant impacts on generation. The contribution of this work is the explicit quantification in cost and energy terms of the value of capturing short–term interdependencies between hydropower plants associated with the use and release of water by upstream plants. The results demonstrate that, by explicitly considering interdependencies, it is possible to better coordinate their operation and optimize hydropower generation.

Capacity Credit Evaluation Framework of Wind, Solar and Pumped Hydro Storage Considering Generation Adequacy and Flexibility

Abstract: Conventional capacity credit evaluation only focuses on generation adequacy. It is assumed that as long as there is sufficient capacity in the system to cover demand, there will be enough facilities to keep real time balancing of system load and generation, namely system flexibility. However, recent studies have demonstrated that system may suffer from lack of flexibility at operational stage in the process of increasing penetration level of wind or solar. Thus, consideration of flexibility is necessary in capacity credit evaluation in high wind and solar penetrated system. In this work, the concept of capacity credit is extended with consideration of both generation adequacy and flexibility. Then, a framework to evaluate the capacity credit with the extended definition is proposed. The proposed framework is applied to evaluate the capacity credit of wind, solar and pumped hydro storage in the renewable energy zones proposed in AEMO’s Integrated System Plan. It is demonstrated that allowing wind and solar curtailment at operational stage can improve capacity credit to some extent. Also, coordination of wind, solar and pumped hydro storage can increase their capacity credits significantly.

Adequacy Assessment of Renewables-Dominated Power Systems with Large-Scale Energy Storage

Abstract: Most research relevant to power system adequacy with large-scale penetration of variable renewable energy sources (RES), including assessment of RES capacity credit, has focused on relatively small penetration levels, up to some 30%. However, RES contribution to supply peak demand with much higher shares of renewable energy, and even close to 100%, has been less studied, and the actual feasibility of such a RES-dominated system in terms of preserving a certain level of system reliability is as yet unclear. In this work, a Monte Carlo simulation model is adopted to quantify the system adequacy level. The availability curves of conventional generation units are simulated based on the state-duration sampling method combined with a three-state transition model of generation units. Parametric studies are conducted to explore the characteristics of system adequacy levels under different RES penetration levels as well as different wind and solar installed capacity mixes. At the same time, the benefits of coordinating large-scale energy storage, modelled as pumped-hydro storage plant, with RES are assessed and demonstrated. The results from several case studies on a reduced test version of the Australian eastern interconnected power system highlight how the proposed characterization method can inform strategic, reliability-aware planning of future RES-dominated power systems.

Increased Frequency and Voltage Interactions Affecting Frequency and Transient Stability in Networks with Large Penetration of Renewable Generation

Abstract: The paper investigates the frequency and voltage dynamics and stability in power systems with increased penetration of inverter-based renewable energy sources (RES). The case studies presented within the paper show that the frequency dynamics (frequency nadir and rate of change of frequency) is not only affected by the decrease in system inertia but also by increasing frequency/voltage interactions when the proportion of RES exceeds that of synchronous generation. Furthermore, the critical fault clearing Time (CCT) analysis for transient stability indicates that RES fault ride through (FRT) and their settings can have a significant impact on the nearby generators. The studies also demonstrate that voltage and frequency interactions can be reduced and transient stability of synchronous generators improved by applying dynamic voltage support in weak areas of the system.