Penetration Of Distributed Energy Resources Research Articles

Improving the Power System Dynamic Response Through a Combined Voltage-Frequency Control of Distributed Energy Resources

The paper proposes a control scheme to improve the dynamic response of power systems through the automatic regulators of converter-based Distributed Energy Resources (DERs). In this scheme, both active and reactive power control of DERs are varied to regulate both frequency and voltage, as opposed to current practice where frequency and voltage controllers are decoupled. To assess the proposed control against the current state-of-art, the paper also defines a metric that captures the combined effect of frequency/voltage response at any given bus of the network. Results indicate that the proposed control strategy leads to a significant improvement in the stability and performance of the overall power system. These results are based on a comprehensive case study carried out by employing a modified version of the IEEE 39-bus benchmark system, where a portion of the synchronous machines is substituted by converter-interfaced DERs. The impact on the proposed control of load models, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R/X$</tex-math></inline-formula> ratio of network lines, as well as the level of DER penetration to the grid, are properly evaluated and conclusions are duly drawn.

Tri-Sectional Approximation of the Shortest Path to Long-Term Voltage Stability Boundary With Distributed Energy Resources

Ensuring long-term voltage stability is critical for reliable operations of power grids. High share of distributed energy resources (DERs) can create complicated system operation modes that may invalidate the traditional long-term voltage stability analysis based on typical operation modes. To address this challenge, this paper investigates how to compute the shortest path to the voltage stability boundary in the DER aggregated load space with large dispersion. Instead of working in the Euclidean space, we establish the analysis and computations on the algebraic power flow manifold to better capture the curvature change of the shortest path along the direction of losing stability. A modified optimal control framework is presented for obtaining the ground-truth of the smooth shortest path on the manifold. To efficiently and accurately solve for the shortest path, we further leverage the geometric features of the power flow manifold and propose a tri-sectional approximation model that is scalable for large-scale systems. Several numerical examples, up to the 1354-bus system, with different DER penetration levels and high dimensional renewable power injection variations are evaluated. The simulation results demonstrate that the tri-sectional approximation achieves high accuracy and efficiency to approximate the shortest path to the voltage stability boundary.

Non-Linear Clustering of Distribution Feeders

Distribution network planners are facing a strong shift in the way they plan and analyze the network. With their intermittent nature, the introduction of distributed energy resources (DER) calls for yearly or at least seasonal analysis, which is in contrast to the current practice of analyzing only the highest demand point of the year. It requires not only a large number of simulations but long-term simulations as well. These simulations require significant computational and human resources that not all utilities have available. This article proposes a nonlinear clustering methodology to find a handful of representative medium voltage (MV) distribution feeders for DER penetration studies. It is shown that the proposed methodology is capable of uncovering nonlinear relations between features, resulting in more consistent clusters. Obtained results are compared to the most common linear clustering algorithms.

Enhancing the unbalanced distribution network’s hosting capacity for DERs via optimal load re-phasing

Maximizing the distribution systems’ hosting capacity (HC) for distributed energy resources (DERs) is an integral part of the efforts to increase the share of renewable energy sources (RES) in electricity grids. Hence, a novel strategy is proposed in this paper to enhance the network’s HC for DERs, which considers the technical issues such as voltage unbalance caused by the high share of DERs. Through a novel three-stage optimization model, this paper shows that the HC for DERs such as solar photo-voltaics (PV), residential and public electric vehicle chargers (EVCs), and heat pumps (HPs) can be increased. The proposed approach uses a novel re-phasing strategy to determine the optimal network configuration, which can decrease the voltage unbalance, and hence the available network capacity can accommodate more DERs. In the first stage, the network’s HC for DERs is maximized without any further structural modifications on the existing network. In the second stage, the best configuration of the system is obtained to mitigate the voltage unbalance caused by the DER penetration. Finally, at the third stage and based on the obtained optimal configuration of the network, the HC of the modified system is maximized by adding more DER capacity. The results show that using the proposed re-phasing technique can improve the network’s HC for DERs, without any need to reinforce the existing network.

Double-Loop Control Strategy With Cascaded Model Predictive Control to Improve Frequency Regulation for Islanded Microgrids

The microgrid (MG) which effectively utilizes distributed energy resources (DERs) is crucial to the modern power system. However, since the islanded MG with high penetration of DERs inherently lacks sufficient inertial support, the frequency regulation is challenging for the voltage source converter (VSC)-based MG. This paper presents a cascaded model predictive control (MPC) scheme for both the outer and inner loops of primary control, which improves frequency regulation capability with the advantage of satisfactory dynamic response and high tracking accuracy. In the outer loop, to enhance dynamic frequency characteristics, the MPC-based virtual synchronous generator (VSG) method with two control objectives is proposed. According to the movement direction of frequency under different load switching cases, the corresponding frequency response process speeded up or slowed down properly. In the inner loop, an improved finite-set double vector MPC (DV-MPV) is proposed to follow the output reference from the outer loop, which contributes to accurate frequency control by reducing tracking error, and faster dynamic response as well. The simulation and experimental results further demonstrated the effectiveness of the proposed method.

Distributed energy resource interconnection: An overview of challenges and opportunities in the United States

Decarbonizing the energy sector and electrifying buildings and transportation requires the rapid and cost-efficient build-out of solar, energy storage, demand management, and other distributed energy resources (DERs). Many jurisdictions have recognized the critical importance of DERs to the clean energy transition and are developing solutions to enable the more rapid and cost-efficient integration of DERs onto the electric grid. At the same time, as the scale and speed of DER deployment grows, more challenges are emerging, including lengthy interconnection timelines, costly grid upgrades, and regulatory and technical barriers to enabling the variety of benefits DERs can provide to the grid. Interconnection, in particular, can pose a significant challenge to growing DER penetration. Interconnection rules and regulations spell out the procedural and technical requirements for connecting DERs to the grid. When these rules are well-designed, they can support faster and more cost-effective DER integration, but when they are outdated or poorly designed, they can slow or even halt DER growth. This article describes some of the key challenges that U.S. states are facing with DER interconnection to the distribution system, and highlights leading solutions to address those challenges. While the article focuses on DER interconnection rules and regulations in the United States, many of the lessons learned and solutions are likely applicable to other jurisdictions that are experiencing rapid DER market growth.

Transactive energy revolution: Innovative leverage for reliable operation of modern energy networks—A critical review

The electric industry is developing towards a more efficient, reliable, and resilient electric power network. In this way, utilizing distributed energy resources (DERs), especially renewable DERs (RDERs) are a paradigm change. DERs offer many advantages in power systems, including transmission loss reduction, environmental benefits of RDERs, and enhancement of security, reliability, and resiliency of the network. However, high penetration of DERs increases uncertainty and challenges the efficient and reliable operation of the power system. This paper provides a thorough review of the transactive distribution platform which is essential to address the aforementioned challenges. This distribution platform includes a transactive distribution system operator providing a seamless and coordinated control to dynamically balance supply and demand and follow uncertain generations of RDERs. Indeed, this review paper highlights the capability of transactive energy (TE) by considering its key aspect in providing energy sharing opportunities for the integration of DERs into smart grids (SGs). TE is acombination of economic and control methods that enable optimum, reliable, sustainable, and efficient operation of SGs. Furthermore, a fully transactive framework offers more choices for DERs to control and manage the energy transactions in the retail market, as well as improves the inter operability among various market players.

Non-Bias Allocation of Export Capacity for Distribution Network Planning With High Distributed Energy Resource Integration

A novel distributed energy resources (DER) allocation method focused on grid constraints that avoids topological bias is proposed for distribution networks. A technology-agnostic approach is used, where a non-bias allocation of export capacity (NAEC) not specific to generation type is calculated. Moreover, the proposed NAEC is extended from an export capacity into a hosting capacity (HC) using a statistical approach. The methods are tested using the IEEE 33-bus distribution system, and two typical Irish distribution feeders -one urban, one rural- as case studies. Using a high-resolution year-long quasi-static time series simulation (QSTS) and three different generation profiles, the proposed NAEC method is validated against current practices and state of the art allocation methods in terms of active balancing, security of supply, interactions between users, operational concerns, and fairness. Results show that an equivalent or higher level of DER penetration is achieved using the proposed methodology. There are no additional constraint violations using the NAEC methodology, moreover, time slots with violations are reduced, improving security of supply. Furthermore, results suggest that avoiding topological bias makes the network accessible for more users, and prioritises self-consumption.

A uber‐airbnb mixture flexibility peer‐to‐peer market in integrated TSO‐DSO architecture

With the launch of global decarbonisation, the infiltration of low-carbon distributed energy resources (DERs) is increasing. The future transaction platforms for those flexibilities are considered to be peer-to-peer (P2P) ones conforming to resources' characteristics of small-scale and independence. This research reviews current flexibility-related topics and proposes one P2P flexibility market filling in the gaps. The contribution of this research includes: (1) it constructs a flexibility market combining pricing strategy and matching strategy of the mature and successful real-world P2P business models, accommodating the penetration of DERs. The proposed automatic trading market could mobilise the enthusiasm of market participants and satisfy individuals' needs for a convenient market. (2) it proposes a dynamic pricing strategy where prices fluctuate with the features and portfolios of market participants. More adequate market signals are provided with the promotion of market equity. (3) it discusses the segmentation tendency of the flexibility market when considering energy products as pure commodities following the disintegration from the transmission system operator to the distribution system operator. The feasibility of the proposed market under future energy scenarios is thus explored.

A review of decentralized and distributed control approaches for islanded microgrids: Novel designs, current trends, and emerging challenges

Distributed energy resources (DER) on the demand side have been fast growing, which could boost energy resilience by uninterruptedly supplying the commercial and residential sectors in the form of islanded microgrids when the utility electricity grid is out of service. Nevertheless, simply applying the centralized hierarchical control strategies, traditionally used for utility electricity grids, onto the islanded microgrids would encounter several critical issues. For instance, the control goals in secondary and tertiary control could be activated tardily, the single-point fault could cause critical system failure, and the properties of dynamic plug and play would be hard to achieve. To this end, decentralized and distributed control approaches have been explored to cope with the issues. Specifically, compared to the centralized hierarchical control, decentralized and distributed control strategies can (i) respond to disturbances more promptly, enhancing the performance of islanded microgrids with limited resources; (ii) guarantee system stability especially when a fault occurs and certain DERs are disconnected from the network; and (iii) facilitate deeper penetration of DERs in the microgrid, owning to the low computational complexity and sparse communication network. In this article, the common approaches for decentralized and distributed control are reviewed, and the current design trends and critical technical challenges are discussed to offer a comprehensive understanding of decentralized and distributed controlled microgrids.

Design and Experimentation Guidelines for DER’s Emulation Testbed

Due to the increasing integration of distributed energy resources (DERs) into the national grid, research is needed to understand high DER penetration in relation to grid reliability and stability. Emulation-based research is a viable option to consider hardware intensive investigations. Indeed, DER emulation-based research has advantages over DER software-based simulation and real DER implementation research. Some of these advantages are more realistic performance and boundaries and considerably less expense, higher safety, and modularity. While the downside of DER emulation-based research is the complexity of modeling large scale grid systems. This paper provides a rationalization for the selection of an emulation-based DER laboratory and description of the DER laboratory's capabilities. Additionally, guidelines for running experiments are discussed and two approaches, power scaling using rescaling coefficients and system sizing using Multi-Port Thevenin Equivalence (MPTE), are proposed to emulate realistic complex interconnected DER grid connected systems.

A new approach to retrofit plans for distributed energy resources to mitigate adverse impacts on bulk power systems stability

This work presents a new methodology to assess the need of a retrofit plan to readjust anti-islanding protection of distributed energy resources (DERs) with focus on bulk power systems stability. The proposed approach aims to reduce DERs cascade disconnection during major disturbances in transmission networks, a phenomenon that can amplify or result in major blackouts in power systems with high or moderate DERs penetration. The proposed methodology is based on the assessment of Dynamic Security Regions with the incorporation of a simplified modeling to represent DERs cascade disconnection. As a result, recommendations for executing a retrofit plan with a low cost, preserving an adequate level of security, are provided. Initially, the impact of DERs disconnection on the Brazilian Interconnected Power Systems (BIPS) is demonstrated, highlighting the importance of modeling such effect in stability studies. Then, the proposed methodology is applied to the BIPS, evidencing its benefits by specifying the minimum amount of DERs that needs to be submitted to a retrofit plan to guarantee an adequate level of security.

A hybrid architecture for volt-var control in active distribution grids

Modern active distribution grids are characterized by the increasing penetration of distributed energy resources (DERs). The proper coordination and scheduling of a large numbers of these small-scale and spatially distributed DERs is necessary, and warrants the use of novel distributed approaches. In this paper, we propose a hybrid volt-var control architecture for the distribution grid, which leverages existing centralized and local approaches to planning, decision making, and control, and augments it with distributed optimization and distributed control for DER management. First, we propose a convex model to describe the power physics of distribution grids of meshed topology and unbalanced structure, based on current injection and McCormick Envelopes. Second, we employ the distributed proximal atomic coordination (PAC) algorithm to coordinate DERs to provide voltage support. We implement volt-var optimization by optimally coordinating DERs including PV smart inverters and demand response. We present results using the IEEE-34 bus network, using real data from a distribution feeder in Hawaii, to model load and PV generation. Different levels of DER penetration and objective functions are simulated. Our results show the need for the coordination of DERs to improve voltage profiles, even in networks with existing voltage control devices. Further, we show the need for flexible reactive power capabilities to achieve desired grid performance.

Secured energy ecosystems under Distributed Energy Resources penetration

Renewable energy systems have mushroomed in the form of microgrids and Virtual Power Plants (VPP). In Australia itself, there are over three million Distributed Energy Resources (DERs). Integrating these new energy ecosystems into current systems is becoming a horrendous task as multi-dimensional energy flows and new energy business models are evolving. The stakeholders in the energy sector are focused on reducing costs prematurely while integration standards are still evolving, and interoperability of Internet of things (IoT) with legacy systems has outstanding security concerns. In this paper, the changing energy landscape is examined, and cybersecurity issues associated with the operation of VPPs and renewable energy-based microgrids are highlighted. The security and operational scenarios of new ecosystems are outlined, with an emphasis on DER interoperability, security, and integration. The design and development of these evolving standards into these new energy ecosystems is detailed based on observations from experiments on real-world DER installations. This paper is an extension of work originally reported in proceedings of the 31st Australasian Universities Power Engineering Conference [1].

Transmission-and-Distribution Dynamic Co-Simulation Framework for Distributed Energy Resource Frequency Response

The rapid deployment of distributed energy resources (DERs) in distribution networks has made it challenging to balance the transmission system and stabilize frequency. DERs have the ability to provide frequency regulation services; however, existing frequency dynamic simulation tools—which were developed mainly for the transmission system—lack the capability to simulate distribution network dynamics with high penetrations of DERs. Although electromagnetic transient simulation tools can simulate distribution network dynamics, the computation efficiency limits their use for large-scale transmission-and-distribution (T&D) co-simulation. This paper presents an efficient open-source T&D dynamic co-simulation framework for DER frequency response based on the HELICS platform and off-the-shelf T&D simulators. The challenge of synchronizing the simulation between the transmission network and the DERs in the distribution network is solved through the detailed modeling of DERs in frequency dynamic models while DER power flow models are also preserved in the distribution networks, thereby respecting local voltage constraints when dispatching DER power for frequency response. DER frequency response (primary and secondary) is simulated in case studies to validate the proposed framework. Last, the accuracy of the proposed co-simulation model is benchmarked, and a large T&D system simulation (2k transmission and 1M distribution nodes) is presented to demonstrate the efficiency and effectiveness of the overall framework.

Detailed Primary and Secondary Distribution System Model Enhancement Using AMI Data

Reliable and accurate distribution system modeling, including the secondary network, is essential in examining distribution system performance with high penetration of distributed energy resources (DERs). This paper presents a highly automated, novel method to enhance the accuracy of utility distribution feeder models to capture their performance by matching simulation results with corresponding field measurements. The method is demonstrated using an actual feeder from an electrical utility with high penetration of DERs. The method proposed uses advanced metering infrastructure (AMI) voltage and derived active power measurements at the customer level, and data acquisition systems (DAS) measurements at the feeder-head, in conjunction with an AC optimal power flow (ACOPF) to estimate customer active and reactive power consumption over a time horizon, while accounting for unmetered loads. The ACOPF uses the measured voltage magnitudes, derived active power measurements, and the feeder head measurements to obtain a complete active power and reactive power capture of the feeder loads. Additionally, the method proposed estimates both voltage magnitude and angle for each phase at the unbalanced distribution substation. The accuracy of the method developed is verified in two stages: by comparing the time-series power flow results obtained from the enhancement algorithm with OpenDSS results and with the field measurements available. The proposed approach seamlessly manages the data available from the optimization procedure through the final model verification automatically.

Integration of Utility Distributed Energy Resource Management System and Aggregators for Evolving Distribution System Operators

With the rapid integration of distributed energy resources (DERs), distribution utilities are faced with new and unprecedented issues. New challenges introduced by high penetration of DERs range from poor observability to overload and reverse power flow problems, under-over-voltages, maloperation of legacy protection systems, and requirements for new planning procedures. Distribution utility personnel are not adequately trained, and legacy control centers are not properly equipped to cope with these issues. Fortunately, distribution energy resource management systems (DERMSs) are emerging software technologies aimed to provide distribution system operators (DSOs) with a specialized set of tools to enable them to over-come the issues caused by DERs and to maximize the benefits of the presence of high penetration of these novel resources. However, as DERMS technology is still emerging, its definition is vague and can refer to very different levels of software hierarchies, spanning from decentralized virtual power plants to DER aggregators and fully centralized enterprise systems (called utility DERMS). Although they are all frequently simply called DERMS, these software technologies have different sets of tools and aim to provide different services to different stake-holders. This paper explores how these different software technologies can complement each other, and how they can provide significant benefits to DSOs in enabling them to successfully manage evolving distribution networks with high penetration of DERs when they are integrated together into the control cen-ters of distribution utilities.

Architecture, Control, and Implementation of Networked Microgrids for Future Distribution Systems

Microgrid (MG) is a small-scale, self-sufficient power system that accommodates various distributed energy resources (DERs), controllable loads, and future distribution systems. Networked microgrids (NMGs) are clusters of MGs, which are physically interconnected and functionally coordinated to enhance distribution systems in terms of economics, resilience, and reliability. This paper introduces the architecture and control of NMGs including nanogrid (NG) and MG. To accommodate variable DERs in NMGs, master and distributed control strategies are adopted to manage the high penetration of DERs, where master control focuses on economic operation, while distributed control focuses on reliability and resilience through active power sharing and voltage and frequency regulation. The initial practices of NG, MG, and NMG in the networked Illinois Institute of Technology (IIT) campus microgrid (ICM) and Bronzeville community microgrid (BCM) in the U.S. are presented. The applications of the master and distributed control strategies are illustrated for the networked ICM-BCM to show their benefits to economics, resilience, and reliability.

DESIGNING A 5G BASED SMART DISTRIBUTION GRID PROTECTION SYSTEM

Distribution grid protection, control, and monitoring systems target high levels of safety and reliability and address the need for better state estimation, protection and control schemes. These systems also need to take into account the increase of Distributed Energy Resources (DERs) penetration into the power distribution grids. Moreover, the bulk penetration of DERs on distribution grid will have a considerable impact on the global power system stability. Challenges also arise to re-energize customers faster and more efficiently than today. Fault Detection, Isolation, and Service Restoration (FDIR) systems, which utilize real-time data exchange from various Intelligent Electronic Devices (IEDs), would require better communication technologies to this purpose. To mitigate these risks and provide new functionalities, a new paradigm could be considered for the design and operation of power distribution grids if all the devices could be interconnected through secure, reliable, and low latency communication infrastructure. Wired communication technology services fit the FDIR communication requirements but can be expensive and difficult to deploy over the whole area covered by electric networks already in place. Hence, Smart Grids (SGs) can leverage the use of emerging information and communication technologies (ICTs) such as 5G, to become more cost effective. The conducted work proposes a flexible communication architecture based on 5G, providing highly customized communication services according to diverse performance requirements demanded by the future FDIR schemes. It involves the implementation of new protection functions in order to complete the existing monitoring and automation features of the electric system.

Microgrid modeling for contribution to the frequency control of power system

Recently, Distributed Energy Resources (DERs) are becoming more attractive to supply local loads under the concept of microgrids. These new parts of the power system have basically different dynamics compared with conventional power plants. Most of them are connected to the grid by power electronic interfaces, and their dynamic is determined by their controller. In this paper, the effect of the increased penetration of DERs on the load frequency problem of power systems is studied. The DERs of microgrids in each area are controlled to change their active power at Point of Common Coupling (PCC) after a disturbance in the power system. It is shown that with appropriate control of DERs in microgrids, the frequency deviation of the power system will decrease and the stability margin can be increased.