IEEE Open Access Journal of Power and Energy - Volume 7

Listed below are the papers that have been published to date in volume 7 of the IEEE Open Access Journal of Power and Energy. Papers will be added to the issue throughout the year as they are accepted and finalized. Click on the titles to access the papers in the PES Resource Center.

• "Inaugural Issue of the IEEE Open Access Journal of Power and Energy: Welcome Note"
  B. Pal

Regular Papers

• "Small-Signal Stability Analysis of the Interactions Between Voltage Source Converters and DC Current Flow Controllers"
  R. Guan, N. Deng, Y. Xue, and X. Zhang
  Abstract

  Small-signal stability analysis of the voltage source converter (VSC) based multi-terminal DC (MTDC) grids has been mainly focused on the dynamics of AC/DC converters while there is a lack of consideration of DC networks with DC power-flow controllers. In this paper, an integrated small-signal model is established to investigate the interactions between VSC and DC current flow controllers (CFC). The impacts of the control system of CFC on small-signal stability of the integrated system and the impacts of the control system of VSC on the DC networks with CFC are discussed via eigenvalue analysis. The above interactions are demonstrated through dynamic simulations against both small and large disturbances using real time digital simulator (RTDS).

• "Accelerated Sparse Matrix-Based Computation of Electromagnetic Transients"
  A. Abusalah, O. Saad, J. Mahseredjian, U. Karaagac, and I. Kocar
  Abstract

  This paper is related to research on parallelization methods for the simulation of electromagnetic transients (EMTs). It presents an automatic parallelization approach based on the solution of sparse matrices resulting from the formulation of network equations. Modified-augmented-nodal analysis is used to formulate network equations. The selected sparse matrix solver is parallelized and adapted to improve performance by pivot validity testing and partial refactorization. Refactorization is needed when dealing with varying topology networks and nonlinear models. The EMT solver employs a fully iterative method for nonlinear functions. Conventional computer CPU-based parallelization is achieved and does not require any user intervention for given arbitrary network topologies. The presented approach is tested on real networks with complex models, including nonlinearities and power-electronics converters for wind generator applications.

• "Aggregation of Residential Water Heaters for Peak Shifting and Frequency Response Services"
  T. Clarke, T. Slay, C. Eustis, and R. B. Bass
  Abstract

  The increased penetration of renewable energy resources poses challenges for grid stability. The stochastic generation of solar and wind power cannot be controlled to follow load. And, the transition away from synchronous generators is reducing the capacity to arrest and recover from frequency disturbances. Smart electric water heaters provide utilities with an appliance that can be remotely controlled and serve as a form of energy storage. They have very fast response times and make up a large amount of residential energy consumption, making them useful for load peak shifting as well as other ancillary grid services. As smart appliances become increasingly widespread, more and more devices can be brought into the utility control network and aggregated into a flexible resource on a multi-megawatt scale. This paper demonstrates the usefulness of aggregated electric water heaters for providing two ancillary services: peak shifting and frequency response. Because a large number of assets are required, emulators are developed based on observations of real devices. Emulated water heaters are then connected to an energy resource aggregator using an internet-of-things network. The aggregator uses these assets to shift consumption away from peak hours and for detecting upward frequency disturbances.

• "Optimal Scheduling of Merchant-Owned Energy Storage Systems With Multiple Ancillary Services"
  C. Opathella, A. Elkasrawy, A. A. Mohamed, and B. Venkatesh
  Abstract

  Electrical energy storage (EES) can improve the flexibility and reliability of electric power systems. At the same time, they can supply different ancillary services. The profit of the energy storage operation can be maximized by deciding the best level of each service. Merchant-owned facilities require a profit-maximizing formulation for grid-connected energy storage systems with multiple ancillary services. This paper proposes a new linear profit-maximizing formulation for grid-connected merchant-owned energy storage systems operating with multiple ancillary services. All technical characteristics of EES have been modelled, including cycle life loss due to fast charge/discharge and low depth of discharge operations. A piece-wise linear model of an EES converter's capability curve has also been included for reactive power modeling. The model was assessed considering a battery EES, a flywheel EES, and a compressed air EES, with the results demonstrating the benefits of the formulation. From case studies, it is clear that the merchant-owned battery EES and the flywheel EES can generate profits, especially from voltage regulation and frequency regulation services. The case studies prove that the proposed model can be used as an optimal planning and operation tool for any type or size of EES.

• "A Benchmark Distribution System for Investigation of Residential Microgrids With Multiple Local Generation and Storage Devices"
  S. A. Raza and J. Jiang
  Abstract

  A benchmark distribution system is developed for investigating control and energy management of distributed generation (DG) at a residential level in the form of three single-phase microgrids. The benchmark is derived from a typical distribution network architecture with common parameters found in North-America systems including wiring specifications, line impedances and connection details for rooftop PV systems. This benchmark system can accommodate microgrids operating in both grid-connected and islanded modes.Within this benchmark, multiple single-phase DG sources located in different phases can be coordinated to form a dynamically balanced three phase system under different load and generation profiles in different phases. The coordination of DG sources in a particular phase is achieved through an intra-phase power management device, while mitigating loads and generation imbalance among all phases are done by an inter-phase power management scheme. It is expected that this benchmark system will facilitate investigation of impacts posed by proliferation of single-phase distributed generation devices and local storage systems in private residences. Three case studies have been carried out to demonstrate the versatility and effectiveness of this benchmark system.

• "A Data-Driven Justification for Dedicated Dynamic Pricing for Residences-Based Plug-in Electric Vehicles in Wind Energy-Rich Electricity Grids"
  F. Eldali and S. Suryanarayanan
  Abstract

  Supply curtailment in wind energy-rich electricity grids occurs when electric energy supply exceeds demand. Grid-level energy storage assets with the potential for storing the excess electric energy generated from wind are yet cost-prohibitive and prone to inefficiencies. An alternative for managing this excess energy is the targeted charging of available plug-in electric vehicles (PEVs). The different power requirements, load duration, and times of usage requires PEVs to be treated differently. Consequently, using a universal pricing mechanism may not lead to the maximum benefit for the utility and the consumers, especially when trying to rely on charging PEVs with wind energy. In this study, we use a data-driven approach to investigate an existing pricing mechanism for a city (Austin, Texas) in a wind energy-rich electricity grid (ERCOT) and with high projections of PEVs. The study provides a general framework for the wind energy-rich utilities to better evaluate their profitability and the benefits of the consumers. In our case study, the results indicate the need for an alternative pricing mechanism (e.g., time-of-use) dedicated to PEVs than the existing choices for maximizing the utility of available energy from wind in the absence of grid-level energy storage.

• "MATLAB-Based Programs for Power System Dynamic Analysis"
  I. Abdulrahman
  Abstract

  This paper presents MATLAB-based programs developed for power system dynamic analysis. The programs can be used for educational purposes and research studies. With the program, time-domain simulation, system linearization, modal analysis, participation factor analysis and visualization, optimal placement of controller, feedback signal selection, frequency response analysis, and control design can be obtained. In addition to solving a power system problem, the package provides a symbolic and vectorized representation of the model in time domain and state space. The package uses the full advantages of MATLAB's powerful solvers for solving non-stiff and stiff problems. Both explicit and implicit techniques are used for solving the differential algebraic equations (DAEs). The synchronous machines are assumed to be equipped with exciter, turbine, and stabilizer. The loads can be modeled as voltage-dependent and independent loads. The test systems used in this paper are the IEEE 9-bus and 68-bus systems, and Texas's 2007-bus synthetic power system. Different types of disturbances are applied to the systems including generator-side and network-side disturbances. The results demonstrate the efficiency and educational values of the package for researchers and students.

• "Wide Area Control of Governors and Power System Stabilizers With an Adaptive Tuning of Coordination Signals"
  L. Zacharia, M. Asprou, and E. Kyriakides
  Abstract

  This paper presents the formulation of Wide Area Control (WAC) signals for either coordinating all the governors of the system or coordinating simultaneously both the governor and the Power System Stabilizer (PSS) of each generator. This is achieved through the development of suitable WAC signals intended for the coordination of their common input signal (rotor speed deviation) having as objective the compensation of all the local and inter-area oscillations. Furthermore, an adaptive tuning method to estimate weights for each inter-generator interaction is also presented. This is required to regulate adaptively the level of the WAC contribution to all the local controllers. The weights are computed according to the electric connectivity between the generators. For the evaluation of the proposed methods, both offline and real-time simulations are performed on the IEEE 39-bus test system. The results indicate the substantial improvement of the system's stability when the proposed governor/PSS coordination is considered. The performance of the WAC scheme is further increased when the adaptive tuning procedure is applied. Finally, the requirement of having PMUs at each generator bus is relaxed by utilizing the coherency concept.

• "Resource Study of Large-Scale Electric Water Heater Aggregation"
  K. Marnell, C. Eustis, and R. B. Bass
  Abstract

  Residential-scale distributed energy assets, like residential electric water heaters, individually present a negligible load to the power grid. When aggregated, however, these assets can impart significant effects within a balancing area; they may be dispatched en masse to provide grid services. An aggregation of water heaters may be controlled to assume generator-like functions with the ability to effectively "decrement power" through dispatch of load. This resource study examines the capabilities of a 10,000 unit water heater aggregation by subjecting the aggregate to dispatch requests of various size and duration, then analyzing how the aggregate responds to and recovers from these requests. Results show that a large-scale aggregation of electric water heaters may effectively decrement power on the scale of megawatts when the dispatch request size and duration are appropriately considered.

• "Visualizing the Impacts of Renewable Energy Growth in the U.S. Midcontinent"
  A. L. Figueroa-Acevedo, C.-H. Tsai, K. Gruchalla, Z. Claes, S. Foley, J. Bakke, J. Okullo, and A. J. Prabhakar
  Abstract

  This paper presents the visualization approach for enhancing analyses of the ongoing Renewable Integration Impact (RIIA) Assessment by the Midcontinent Independent System Operator (MISO), and brings the following contributions. First, this paper details the customization of state-of-the-art, open-source visualization code to complement existing power system visualization tools and data analytic processes used in MISO. Second, this paper describes how MISO integrates this visualization tool within a novel and holistic process for studying renewable integration issues. This visualization tool provides additional insights for RIIA from multiple aspects with fine spatial-temporal granularity, including the comparison of thermal generation performance at different renewable integration scenarios, improved understanding of complex interactions between regions within MISO, the effects of transmission upgrades on curtailment reduction using optimization techniques, and the improved verification of MISO's simulation results. Lastly, we make the updated visualization code package publicly available.

• "Adaptive Droop Control Method for Suppressing Circulating Currents in DC Microgrids"
  N. Ghanbari and S. Bhattacharya
  Abstract

  DC microgrids are introduced to reduce the conversion stages needed for connection of DC sources to the DC loads. They employ the droop control algorithm for managing the power flow from sources to the loads. However, the droop control functionality is affected by circuit parameters, especially line resistances. As a consequence, load sharing as the primary objective of the droop controller lacks accuracy. Parallel-connected converters have mismatched output voltages, resulting in circulating currents. This paper proposes an adaptive droop control algorithm for suppressing circulating currents in a low voltage DC microgrid. Line resistances are estimated through mathematical calculations and droop parameters are adjusted accordingly. Moreover, a distributed secondary controller is proposed to improve the load sharing accuracy and eliminate the effect of line resistances. The secondary controller shifts the droop controller voltage setpoint according to the converter current. Both of the proposed methods result in an accurate load sharing. Each of the participating converters has the rated current and consequently circulating current is suppressed. The effectiveness of the proposed method is verified through simulation and hardware-in-the-loop (HIL) setup.

• "A Low-Loss Thyristor-Based Hybrid Three-Level and Modular Multilevel Converter With DC Fault Blocking Capability for HVDC Transmission"
  L. M. Bieber, L. Wang, and W. Li
  Abstract

  This paper proposes a thyristor-based hybrid three-level converter (TH3LC) equipped with an AC-side full-bridge submodule chain-link (FBCL) for voltage-source converter (VSC) high voltage direct current (HVDC) applications. The TH3LC uses thyristor-based director switches (DSs) to conduct the bulk of transferred power while the AC-FBCL enables a multilevel voltage output. Third-order harmonic voltage injection is used by the AC-FBCL to limit its total blocking voltage to less than or equal to a quarter of the DC-side voltage, reducing the converter footprint, semiconductor count, and losses. The DSs of the TH3LC are force-commutated by an additional neutral-point-connected, low capacitance commutation FBCL (C-FBCL). The C-FBCL enables a stepped-trapezoidal voltage at the output of the three-level converter for straight-forward synchronization with the AC-FBCL and zero-voltage switching for the DSs. Case studies show that the TH3LC provides similar converter efficiency to the half-bridge MMC (HB-MMC) while possessing DC fault blocking capability and a smaller footprint due to a reduced number of submodules.

• "Fault Statistics and Analysis of 220-kV and Above Transmission Lines in a Southern Coastal Provincial Power Grid of China"
  B. Chen
  Abstract

  Because the causes of transmission line faults are not known clearly at present, this paper proposes fault classification for transmission lines, and analyses the characteristics of different faults. Using the transmission line faults data of southern coastal provincial power grid from 2007 to 2018, this paper analyses the influence and distribution of transmission line faults affected by lightning, typhoon, wildfire, foreign object and external damage. These five faults are the main factors affecting the safe and stable operation of transmission lines in this region. According to the different fault classification and statistical rules, the design standards for important transmission lines should be improved. Considering the factors of micro-topography, micro-meteorology and engineering cost, the inspection and maintenance of existing lines should be strengthened. The statistics and analysis will be helpful to the research, development and application of new theories, new technologies and new equipment in disaster prevention and reduction from the aspects of disaster prediction and monitoring.

• "Design Paradigm for Modular Multilevel Converter-Based Generator Rectifier Systems"
  R. Sahu and S. Sudhoff
  Abstract

  Modular Multilevel Converters (MMC) are being widely considered for medium to high voltage DC applications. Designing such converters through multi-objective optimization is of interest because such an approach allows the trade-off between competing objectives (for example mass and loss) to be explicitly and quantitatively identified. In this work, an optimization based design paradigm for MMC based generator rectifier systems is proposed. Such development typically requires detailed component design and simulation models for the electric machine and converter which are computationally expensive. As an alternative, the proposed work utilizes an electric machine metamodel, inductor metamodel, and high-speed steady-state simulation model for the MMC to facilitate multi-objective optimization minimizing system metrics of interest while satisfying system constraints. A case study is undertaken to demonstrate the functionality of the proposed design paradigm.

• "Data-Driven Risk Analysis of Joint Electric Vehicle and Solar Operation in Distribution Networks"
  A. Palomino and M. Parvania
  Abstract

  Increasing electric vehicle (EV) charging demand and residential solar photovoltaic (PV) generation greatly alter traditional distribution system operation and have the potential to overload and otherwise threaten the operating life of legacy infrastructure. The rate and location of adoption of these technologies on residential distribution systems introduce operational uncertainties for which traditional utilities may not be prepared. This paper proposes a user-defined, data-driven risk assessment method to quantify the severity and likelihood of transformer and secondary conductor overload conditions posed by high levels of EV charging demand coupled with rooftop solar PV. The stochasticity inherent in the operation of a distribution secondary system is captured by employing data-driven probability distribution functions for residential loading, EV charging, rooftop solar generation and ambient temperature. Samples then are repeatedly drawn from each function as inputs to a Monte-Carlo, multi-period power flow analysis to calculate secondary line currents, total loading and accelerated transformer aging. The proposed approach is utilized to study transformer and secondary conductor overload risk as well as transformer loss-of-life for multiple EV and PV penetration scenarios using historical EV charging profiles and residential Salt Lake City load profile data for a peak summer load day.

• "Quantifying Performance of Distribution System State Estimators in Supporting Advanced Applications"
  J. Schoene, M. Humayun, B. Russell, G. Sun, J. Bui, A. Salazar, N. Badayos, M. Zhong, M. Lak, and C. R. Clarke
  Abstract

  A common challenge forward-looking utilities are facing when deploying advanced applications that facilitate voltage optimization and service restoration is to provide adequate sensor data for a Distribution System State Estimator (DSSE) so that it provides sufficiently accurate estimates of the system states to enable these applications in an operational environment. We developed a stochastic method that informs telemetry and operational forecasting requirements by quantifying the DSSE performance in supporting advanced applications. The performance metric used is the α risk, which is the likelihood of a DSSE giving a false positive when determining if voltage and loading constraints are met. We applied this method to six real-world industrial/commercial/residential distribution circuits and evaluated α risk improvements provided by circuit-level sensors and operational forecasting. The results show that a combination of sensor deployment schemes was needed to reduce the α risk for undervoltage to effectively zero. Also, sensors deployed at large loads significantly reduce α risks on industrial/commercial circuits while operational forecasting consistently reduces α risks on all circuits. The practical method does not require advanced mathematics and can be readily used by utilities to inform grid modernization investments in sensor technologies so that advanced applications can be executed optimally and violation-free.

• "Thévenin Equivalent Circuits for Modeling Common-Mode Behavior in Power Electronic Systems"
  T. J. Donnelly, S. D. Pekarek, D. R. Fudge, and N. Zarate
  Abstract

  Modeling the common-mode behavior of power electronic systems can be a challenge. This research aims to simplify the process by developing a modeling approach based on Thévenin common-mode equivalent circuits. The Thévenin common-mode equivalent circuits prove to be both straightforward to construct and reliable in predicting worst-case common-mode behavior. In this paper, a theoretical understanding of the Thévenin-based modeling approach is first provided. Subsequently, methods to characterize the Thévenin parameters are established. The modeling approach is then validated experimentally on a dc micro-grid.

• "Software-Defined Microgrid Control: The Genesis of Decoupled Cyber-Physical Microgrids"
  L. Wang, Y. Qin, Z. Tang, and P. Zhang
  Abstract

  Nowadays, microgrid controllers are often embedded in specialized hardware such as PLC and DSP. The hardware-dependency and fit-and-forget design make it difficult and costly for microgrid controllers to evolve and upgrade under frequent changes such as plug-and-play of microgrid components. Furthermore, different distributed energy resources in a microgrid require customized controllers, leading to long development cycles and high operational costs for deploying microgrid services. To tackle the challenges, a software-defined control (SDC) architecture for microgrid is devised, which virtualizes traditionally hardware-dependent microgrid control functions as software services decoupled from the underlying hardware infrastructure, fully resolving hardware dependence issues and enabling unprecedentedly low costs. A generic SDC prototype is designed to generate microgrid controllers autonomously in edge computing facilities such as distributed virtual machines. Extensive experiments verify that SDC outperforms traditional hardware-based microgrid control in that it empowers a decoupled cyber-physical microgrid and thus makes microgrid operations unprecedentedly affordable, autonomic, and secure.

• "Active System Grounding With a Novel Distribution Transformer Design"
  M. D. Everton
  Abstract

  A novel Wye-wye transformer design for active system grounding, is described in this paper. Proposed as a solution to improve the ground fault performance in distribution line networks, the zero-sequence flux developed in the magnetic core of a transformer is on a ground fault harvested by coils wound around three limbs, or extra limb(s) in a Wye-wye transformer. Built with three limbs, and no tertiary winding, the flux developed in the core on a ground fault is forced to return through air, which has a high reluctance, but with four or more limbs, the flux circulates in the transformer magnetic core, which has a low reluctance. Connected to one or more single-phase windings, the transformer neutral current is on a ground fault actively altered by fixed and switched load impedances. In theory, a ground fault arc is with a low current and delay in recovery voltage self-extinguishing, and no interruption in supply is required, but sustained, must be isolated. Proposed in this paper, for an active load switched grounding method, the neutral current on a sustained ground fault is increased to enable plain overcurrent and fuse protection to operate without the need of sensitive directional relay protection.

• "Fast Frequency Support From Wind Turbine Systems by Arresting Frequency Nadir Close to Settling Frequency"
  X. Zhao, Y. Xue, and X.-P. Zhang
  Abstract

  The recent power cut incident in the UK on 9th August 2019 indicated that frequency control to raise frequency nadir and eliminate frequency second dip is highly desirable for power grids with high penetration of wind energy. This paper proposes a fast frequency support scheme for wind turbine systems (WTSs) that can enable frequency nadir to be significantly raised and close to the settling frequency and eliminate frequency second dip. In the proposed frequency support scheme, in order to achieve similar frequency support performance and ensure stability of WTSs under varying wind speeds, different levels of wind power penetration and system conditions, an adaptive gain, which is a function of real-time rotor speed and wind power penetration level, is proposed. In the proposed scheme, rotor speeds of WTSs are proposed not to be recovered to the optimal operating points during the primary frequency control, but recovered during the secondary frequency control. Simulation results on the IEEE two-area power system with a doubly fed induction generator (DFIG)-based wind farm and the IEEE 39-bus power system with permanent magnetic synchronous generator (PMSG)-based wind farms using real-time digital simulator (RTDS) and Dymola are presented to verify the effectiveness of the proposed scheme.

• "Meeting Temporary Facility Energy Demand With Climate-Optimized Off-Grid Energy Systems"
  J. Pearson, T. Wagner, J. Delorit, and S. Schuldt
  Abstract

  Remote and contingency operations, including military and disaster-relief activities, often require the use of temporary facilities powered by inefficient diesel generators that are expensive to operate and maintain. Site planners can reduce operating costs by increasing shelter insulation and augmenting generators with photovoltaic-battery hybrid energy systems, but they must select the optimal design configuration based on the region's climate to meet the power demand at the lowest cost. To assist planners, this paper proposes an innovative, climate-optimized, hybrid energy system selection model capable of selecting the facility insulation type, solar array size, and battery backup system to minimize the annual operating cost. To demonstrate the model's capability in various climates, model performance was evaluated for applications in southwest Asia and the Caribbean. For a facility in Southwest Asia, the model reduced fuel consumption by 93% and saved $271 thousand compared to operating a diesel generator. The simulated facility in the Caribbean resulted in more significant savings, decreasing fuel consumption by 92% and saving $291 thousand. This capability is expected to support planners of remote sites in their ongoing effort to minimize fuel supply requirements and annual operating costs of temporary facilities.

• "Mosaic Packing to Visualize Large-Scale Electric Grid Data"
  A. B. Birchfield and T. J. Overbye
  Abstract

  For large power systems, a continual challenge is to display wide-area data in a way that maximizes human users' situational awareness. This paper describes a new visualization technique that draws a mosaic of colored tiles to represent multiple data fields for electric grid objects, arranged to preserve geographic context. The key problem in creating these diagrams is packing the tiles onto the display space, minimizing the total displacement while forbidding overlaps. This paper formulates that problem and presents a horizontal-packing algorithm which is able to produce a feasible, quality solution at an interactive time scale. Illustrative examples are shown for using mosaics to monitor wide-area generator status and dispatch, bus voltages, and line and transformer limits. Mosaics can be customized in numerous ways to show different aspects of the system state, providing for human users a simultaneous sense of the wide-area summary, regional trends, and prominent outliers.

• "Energy Consumption Model for Indoor Cannabis Cultivation Facility"
  N. Mehboob, H. E. Z. Farag, and A. M. Sawas
  Abstract

  The recent legalization of cannabis is facilitating very rapid growth in the cannabis cultivation industry, with the energy intensive indoor cultivation facilities becoming more prevalent. This presents a challenge to utilities as the high energy demand from this industry can overburden the existing utility infrastructure. Hence, from both planning and operational perspectives, it is crucial to understand the energy consumption of the rapidly growing load. This paper proposes a deterministic energy consumption model for indoor cannabis cultivation operations for the two major loads in these facilities, i.e., lighting and HVAC, over a 24-hour period based on equipment specifications and operational requirements of the facility. This model can further be used to estimate or forecast short-term and long-term energy demands and costs of indoor cannabis operation(s). The proposed model successfully simulated the environmental conditions in a real-world cannabis facility, and the model's energy consumption output is validated using actual measurements taken from this facility as well as model output using GridLab-D.

• "A Hybrid Optimization Method Combining Network Expansion Planning and Switching State Optimization"
  F. Schäfer, A. Scheidler, and M. Braun
  Abstract

  Combining switching state optimization (SSO) and network expansion planning (NEP) in AC systems results in a mixed-integer non-linear optimization problem. Two methodically different solution approaches are mathematical programming and heuristic methods. In this paper, we develop a hybrid optimization method combining both methods to solve the combined optimization of SSO and NEP. The presented hybrid method applies a DC programming model as an initialization strategy to reduce the search space of the heuristic. A greedy heuristic ensures that the obtained solutions are AC feasible. We compare the hybrid method with other heuristic methods and three mathematical programming models on the same set of planning problems. We show optimization results for four realistic sized power system study cases. Evaluation criteria are convergence, solution cost, and run time. Results show that the hybrid method is able to find a higher number of valid AC-solutions in comparisons to the mathematical programming methods. Furthermore, the obtained solutions have lower expansions costs and are obtained in a shorter run-time compared to the remaining methods for the analyzed study cases. As an addition to this paper, the hybrid implementation and the defined benchmark cases are available as open-source software.

• "Impact of Energy Storage on Economic Dispatch of Distribution Systems: A Multi-Parametric Linear Programming Approach and Its Implications"
  W. Wei, D. Wu, Z. Wang, S. Mei, and J. P. S. Catalão
  Abstract

  As a main flexible resource, energy storage helps smooth the volatility of renewable generation and reshape the load profile. This paper aims to characterize the impact of energy storage unit on the economic operation of distribution systems in a geometric manner that is convenient for visualization. Posed as a multi-parametric linear programming problem, the optimal operation cost is explicitly expressed as a convex piecewise linear function in the MW/MWh parameter of the energy storage unit. Based on duality theory, a dual linear programming based algorithm is proposed to calculate an approximate optimal value function (OVF) and critical regions, circumventing the difficulty of degeneracy, a common challenge in the existing multi-parametric linear programming solvers. When the uncertainty of renewable generation is considered, the expected OVF can be readily established based on OVFs in the individual scenarios, which is scalable in the number of scenarios. The OVF delivers abundant sensitivity information that is useful in energy storage sizing. Leveraging the OVFs, a robust stochastic optimization model is proposed to determine the optimal MW-MWh size of the storage unit subject to a given budget, which gives rise to a simple linear program. Case study provides a clear sketch of the outcome of the proposed method, and suggests that the optimal energy-power ratio of an energy storage unit is between 5 and 6 from the economical perspective.

• "Turbine Startup and Shutdown in Wind Farms Featuring Partial Power Processing Converters"
  M. Pape and M. Kazerani
  Abstract

  The wind turbine startup and shutdown procedures for electrical subsystems are straightforward for wind turbines featuring full-scale power electronic converters and have not required significant attentions from the research community. However, for offshore wind farms featuring series-connected dc collection systems and differential power processing capabilities, the controllable wind turbine power converters might not be rated in such a way that a full-scale output power difference can be handled within a series string. As startup and shutdown procedures can require a transition from zero to full power, a more elaborate design is required to ensure that wind turbines can still start and stop reliably under all conditions, without compromising advantages in reduced wind turbine converter ratings with differential power processing capabilities. In this paper, the startup and shutdown procedures for a series-dc wind farm featuring diode-bridge rectifiers and partial power processing converters as wind turbine converters, are investigated and constraints on converter ratings are evaluated.

• "Adaptive Coordination of Damping Controllers for Enhanced Power System Stability"
  H. Silva-Saravia, H. Pulgar-Painemal, D. A. Schoenwald, and W. Ju
  Abstract

  This paper introduces the concept of adaptive coordination of damping controllers for enhancing power system stability. The coordination uses phasor measurement units (PMUs) to adapt to different disturbances by selecting the switching status (on/off) of damping controllers that minimizes an energy-based dynamic performance measure. This dynamic performance measure, referred to as total action (TA), uses a physical interpretation of excited modes rather than fixed targeted modes as in the traditional damping control design. The coordination is formulated as a binary integer programming problem, which is solved by using the total action sensitivity (TAS). The concept of oscillation energy and the implementation of the adaptive coordination scheme is tested in the western North America power system (wNAPS). The results show that the proposed adaptive control scheme can improve oscillation damping for different short-circuit locations even in the presence of large communication delays.

• "FAPI Controller for Frequency Support in Low-Inertia Power Systems"
  E. Rakhshani, A. Perilla, J. L. Rueda Torres, F. M. Gonzalez-Longatt, T. Batista Soeiro, and M. A. M. M. Van Der Meijden
  Abstract

  This paper presents different forms of Fast Active Power Injection (FAPI) control schemes for the analysis and development of different mitigation measures to address the frequency stability problem due to the growth of the penetration level of the Power Electronic Interfaced Generation (PEIG) in sustainable interconnected energy systems. Among the studied FAPI control schemes, two different approaches in the form of a derivative-based control and a virtual synchronous power (VSP) based control for wind turbine applications are also proposed. All schemes are attached to the PEIG represented by a generic model of wind turbines type 4. The derivative-based FAPI control is applied as an extension of the droop based control scheme, which is dependent on the measurement of the network frequency. By contrast, the proposed VSP-based FAPI is fed by the measurement of the active power deviation. Additionally, unlike existing approaches for virtual synchronous machines, which are characterized by high-order transfer functions, the proposed VSP-based FAPI is defined by a second-order transfer function, which can contribute to fast mitigation of the system primary frequency deviations during containment period. The Great Britain (GB) test system, for the Gone-Green planning scenario for the year 2030 (GG2030), is used to evaluate the effects of the proposed FAPI controllers on the dynamics of the system frequency within the frequency containment period. Thanks to proposed FAPI controllers, it is possible to reach up to 70% for the share of wind power generation without violating the threshold limits for frequency stability. For verification purposes, a full-scale wind turbine facilitated with each FAPI controller is tested in EMT real-time simulation environment.

• "Optimal Energy Dispatch of Distributed PVs for the Next Generation of Distribution Management Systems"
  F. Ding, Y. Zhang, J. Simpson, A. Bernstein, and S. Vadari
  Abstract

  Advanced Distribution Management Systems (ADMS) are being widely adopted by electric utilities for managing and optimizing the operations of their distribution systems. Distributed photovoltaic (DPV) systems with smart inverters can be controlled to adjust active power and reactive power outputs, and they are envisioned to become a part of (centrally or distributed) controllable assets managed by the ADMS for optimizing grid operations. This paper proposes an optimal energy dispatch strategy controlling DPV systems for regulating distribution voltages and achieving conservation voltage reduction. A convex optimization model is proposed with the use of linearized power flow, and the gradient projection algorithm is used to solve the optimal active power and reactive power outputs of smart inverters. The proposed optimal energy dispatch is implemented using an open-source ADMS platform, and simulation results have demonstrated the effectiveness of the proposed approach on improving distribution grid operations.

• "Parallel-in-Time Object-Oriented Electromagnetic Transient Simulation of Power Systems"
  T. Cheng, T. Duan, and V. Dinavahi
  Abstract

  Parallel-in-time methods are emerging to accelerate the solution of time-consuming problems in different research fields. However, the complexity of power system component models brings challenges to realize the parallel-in-time power system electromagnetic transient (EMT) simulation, including the traveling wave transmission lines. This paper proposes a system-level parallel-in-time EMT simulation method based on traditional nodal analysis and the Parareal algorithm. A new interpretation scheme is proposed to solve the transmission line convergence problem. To integrate different kinds of traditional EMT models, a component-based EMT system solver architecture is proposed to address the increasing model complexity. An object-oriented C++ implementation is proposed to realize the parallel-in-time Parareal algorithm based on the proposed architecture. The results on the IEEE-118 test system show 2.30x speed-up compared to the sequential algorithm under the same accuracy with 6 CPU threads, and a high parallel efficiency around 40%. The performance comparison of various IEEE test cases shows that the system's time-domain characteristics determine the speed-up of Parareal algorithm, and the delays in transmission lines significantly affect the performance of parallel-in-time power system EMT simulations.

• "Hardware-in-the-Loop Testing of Dynamic Grid Voltages for Static Var Compensator Controllers With Single-Phase Induction Motor Loads"
  B. Poudel, E. Amiri, J. R. Ramamurthy, I. Leevongwat, T. E. Field, R. Rastgoufard, and P. Rastgoufard
  Abstract

  This paper investigates the interaction between two Static var Compensators (SVCs) to verify dynamic grid voltage support is maintained and that the SVC controllers do not negatively interact with each other. For this purpose, the controls of the SVCs with all of the remotely controlled Mechanically-Switched Capacitors (MSCs) have been tested in a closed-loop real-time simulator environment using SVC replicas (physical controllers) of the actual field installations. To accurately capture the power system's response to phenomenon such as potential Fault Induced Delayed Voltage Recovery (FIDVR), the dynamics of the generators and the motor loads are modeled in the simulations. A hybrid model consisting of real and reactive power (P-Q) loads and aggregated motor load of a single-phase induction motor suitable for three-phase time-domain simulation was developed and connected to the power system. The developed aggregate motor load model includes details such as the main winding, auxiliary winding, starting capacitor, motor inertia, and distribution transformers. It is observed that dynamic grid voltage support can be maintained and the SVC controllers do not negatively interact with each other if all the SVC control blocks are enabled and function normally.

• "Reinforcement Learning for Building Energy Optimization Through Controlling of Central HVAC System"
  J. Hao, D. W. Gao, and J. J. Zhang
  Abstract

  This paper presents a novel methodology to control HVAC system and minimize energy cost on the premise of satisfying power system constraints. A multi-agent architecture based on game theory and reinforcement learning is developed so as to reduce the cost and computational complexity of the microgrid. The multi-agent architecture comprising agents, state variables, action variables, reward function and cost game is formulated. The paper fills the gap between multi-agent HVAC systems control and power system optimization and planning. The results and analysis indicate that the proposed algorithm is beneficial to deal with the problem of "curse of dimensionality" for multi-agent microgrid HVAC system control and speed up learning of unknown power system conditions.

Special Section on Emerging Topics in Power and Energy Society

• "Editorial on Special Section: Invited Papers on Emerging Topics in the Power and Energy Society"
  F. Li and J. P. S. Catalão
• "The Evolution of Research in Microgrids Control"
  A. Vasilakis, I. Zafeiratou, D. T. Lagos, and N. D. Hatziargyriou
  Abstract

  Microgrids (MGs), as novel paradigms of active Distribution Networks, have been gaining increasing interest by the research community in the last 20 years. Currently, they are considered as key components in power system decentralization, providing viable solutions for rural electrification, enhancing resilience and supporting local energy communities. Their main characteristic is the coordinated control of the interconnected distributed energy resources (DER), which can be realized by various methods, ranging from decentralized communication-free approaches to centralized ones, where decisions are taken at a central point. This paper provides an overview of this development focusing on the technical control solutions proposed by reseachers for the various levels of MG organization hierarchy. A critical assessment of selected, popular technologies is provided and open research questions regarding the trend to more decentralized power systems are discussed.

• "Complementarity, not Optimization, is the Language of Markets"
  A. J. Conejo and C. Ruiz
  Abstract

  Each market agent (producer or consumer) in a power market pursues its own objective, typically to maximize its own profit. As such, the specific behavior of each agent in the market is conveniently formulated as a bi-level optimization problem whose upper-level problem represents the profit seeking behavior of the agent and whose lower-level problem represents the clearing of the market. The objective function and the constraints of this bi-level problem depend on the agent's own decision variables and on those of other agents as well. Understanding the outcomes of the market requires considering and solving jointly the interrelated bi-level problems of all market agents, which is beyond the purview of optimization. Solving jointly a set of bi-level (or single-level) optimization problems that are interrelated is the purview of complementarity. In this paper and in the context of power markets, we review complementarity using a tutorial approach.

• "Recent Development of Frequency Estimation Methods for Future Smart Grid"
  J. Zhao, L. Zhan, H. Yin, F. Li, W. Yao, and Y. Liu
  Abstract

  The frequency estimated by the Phasor Measurement Unit (PMU) is a critical index of power system status and supports many smart grid applications. The future smart grid features high penetration of renewables and more fast-moving power electronics inverters but raises challenges to the reliable frequency estimation. This article presents three methods to address these challenges. First, an enhanced zero-crossing algorithm was developed to track the fast-changing frequency in system dynamics. Second, we propose a technology that can tolerate the system transient and suppress the outliers. Third, an algorithm was developed to export high time-resolution frequency estimations with minimum computational effort. All of the proposed methods are realized in hardware and compared with classical frequency estimation methods. The testing results indicate that the proposed methods have excellent performance. They can be used in future PMUs and provide reliable and high time resolution data for smart grid applications.

• "Wildfire Risk Mitigation: A Paradigm Shift in Power Systems Planning and Operation"
  J. W. Muhs, M. Parvania, and M. Shahidehpour
  Abstract

  Managing the risk of wildfires has been arguably the biggest recent challenge of electric utilities with infrastructure located in the wildland-urban interface. Utilities are deploying solutions for wildfire risk mitigation, such as public safety power shutoffs, which are counter-intuitive from a reliability-centric operation paradigm. This article presents an overview of the challenges, implications, and potential strategies for wildfire risk mitigation in power systems, and introduces the vision for a wildfire-resilient power system. The wildfire risk management strategies presented in this article range from fault prevention methods such as structural hardening, vegetation management and implementing advanced protection systems, to arc-suppression and ignition prevention methods. This article also identifies relevant research opportunities associated with implementing wildfire mitigation techniques on power systems.

• "Energy Forecasting: A Review and Outlook"
  T. Hong, P. Pinson, Y. Wang, R. Weron, D. Yang, and H. Zareipour
  Abstract

  Forecasting has been an essential part of the power and energy industry. Researchers and practitioners have contributed thousands of papers on forecasting electricity demand and prices, and renewable generation (e.g., wind and solar power). This article offers a brief review of influential energy forecasting papers; summarizes research trends; discusses importance of reproducible research and points out six valuable open data sources; makes recommendations about publishing high-quality research papers; and offers an outlook into the future of energy forecasting.

• "Decentralized Intrusion Prevention (DIP) Against Co-Ordinated Cyberattacks on Distribution Automation Systems"
  J. Appiah-Kubi and C.-C. Liu
  Abstract

  Integration of Information and Communications Technology (ICT) into the distribution system makes today's power grid more remotely monitored and controlled than it has been. The fast increasing connectivity, however, also implies that the distribution grid today, or smart grid, is more vulnerable. Thus, research into intrusion/anomaly detection systems at the distribution level is in critical need. Current research on Intrusion Detection Systems for the power grid has been focused primarily on cyber security at the Supervisory Control And Data Acquisition, and single node levels with little attention on coordinated cyberattacks at multiple nodes. A holistic approach toward system-wide cyber security for distribution systems is yet to be developed. This paper presents a novel approach toward intrusion prevention, using a multi-agent system, at the distribution system level. Simulations of the method have been performed on the IEEE 13-Node Test Feeder, and the results compared to those obtained from existing methods. The results have validated the performance of the proposed method for protection against cyber intrusions at the distribution system level.

• "Composite System Reliability Evaluation With Essential Reliability Services Assessment of Wind Power Integrated Power Systems"
  Y. Wang, V. Vittal, M. Khorsand, and C. Singh
  Abstract

  With the increasing penetration of renewable resources and the retirements of conventional coal-fired generation units, power systems are undergoing significant transformation with the instantaneous renewable generation penetration sometimes approaching over 50 percent of the demand. This transformation makes the need for comprehensive reliability assessment critical to properly account for the composite system adequacy and the sufficiency of essential reliability services (ERSs). This paper introduces a probabilistic approach to evaluate the reliability of wind power integrated power systems considering ERSs including frequency and voltage support, in conjunction with resource adequacy. To consider stochasticity in system operating conditions, the proposed approach utilizes sequential Monte-Carlo Simulation (SMCS) as the probabilistic analysis methodology and formulates probabilistic reliability metrics representing the composite system adequacy and the ERSs. The proposed approach and metrics are demonstrated on a synthetic test system. Simulation results illustrate the efficacy of the proposed approach and its importance in analyzing the impact of increasing wind power penetration as well as wind turbine generators (WTGs) providing ERSs on system reliability.

• "System-Level Design for Reliability and Maintenance Scheduling in Modern Power Electronic-Based Power Systems"
  S. Peyghami, P. Palensky, M. Fotuhi-Firuzabad, and F. Blaabjerg
  Abstract

  Power electronic converters will serve as the fundamental components of modern power systems. However, they may suffer from poorer reliability if not properly designed, consequently affecting the overall performance of power systems. Accordingly, the converter reliability should be taken into account in design and planning of Power Electronic-based Power Systems (PEPSs). Optimal decision-making in planning of PEPSs requires precise reliability modeling in converters from component up to system-level. This paper proposes model-based system-level design and maintenance strategies in PEPSs based on the reliability model of converters. This will yield a reliable and economic planning of PEPSs by proper sizing of converters, cost-effective design of converter components, identifying and strengthening the converter weakest links, as well as optimal maintenance scheduling of converters. Numerical case studies demonstrate the effectiveness of the proposed design and planning strategies for modern power systems.

• "Energy Quality: A Definition"
  X.-P. Zhang and Z. Yan
  Abstract

  In literature, variations and distortions, and interruptions of voltages (or voltage waveforms) and currents (or current waveforms) have been considered in the framework of power quality (or voltage quality). With the massive penetration of renewable energy into power systems, variations including fluctuations and intermittences of output powers of these renewable sources are of great concerns. It is evidenced that with the high penetration of renewable energy, variations of renewable energy have increased the costs of UK's balancing markets by 39% in this spring and summer (NGESO, 2020). Therefore, there are needs to introduce a technical framework, namely, 'energy quality' to (a) define the quality of power waveforms; (b) propose measures/indices to characterize the variations (fluctuations and intermittences) of powers and power flows; (c) present methods to improve energy quality. Finally, research directions of energy quality are highlighted to encourage more R&D as well as international collaborations in terms of standards and grid code developments.

• "Technical and Economic Impact of the Inertia Constraints on Power Plant Unit Commitment"
  C. Mosca, E. Bompard, G. Chicco, B. Aluisio, M. Migliori, C. Vergine, and P. Cuccia
  Abstract

  The whole interconnected European network is involved in the energy transition towards power systems based on renewable power electronics interfaced generation. In this context, the major concerns for both network planning and operation are the inertia reduction and the frequency control due to the progressive decommissioning of thermal power plants with synchronous generators. This paper investigates the impact of different frequency control constraints on the unit commitment of power plants resulting from market simulations. The market outputs are compared in terms of system costs, and of frequency stability performance evaluated on the basis of the rate of change of frequency and the maximum frequency excursion. The best compromise solution is found using a multiple-criteria decision analysis method, depending on the choice of the decision maker's weighting factors. The proposed approach is tested on a real case taken from one of the most relevant future scenarios of the Italian transmission system operator. The results show how the best compromise solution that can be found depends on the decision maker preference towards cost-based or frequency stability-based criteria.

• "A Stochastic Two-Stage Model for the Integrated Scheduling of the Electric and Natural Gas Systems"
  N. G. Kanelakis, P. N. Biskas, D. I. Chatzigiannis, and A. G. Bakirtzis
  Abstract

  The inherent coupling of the electric and natural gas systems due to the operation of gas generating units and power-to-gas facilities, along with the uncertainties faced in both systems due to the variability in electricity and gas demand and the vastly increasing volatile renewable injections, create an imperative need to schedule and operate the two systems in a coordinated manner. In this paper a new model for the fully integrated stochastic day-ahead scheduling of electric and gas systems is presented, coping with the uncertainties of both systems. The stochastic parameters comprise the electricity demand and the renewable injections, which collectively create several net electricity load scenarios, and the gas residential/industrial demand. The integrated scheduling problem concerns a unit commitment for the electricity problem, amended with additional constraints imposed by the underlying natural gas transmission system considering steady-state flow. A two-stage stochastic programming model is devised, having as second stage the possible realizations of net electricity load and gas demand in real-time. The model is tested in medium-size real-world test systems – the Greek electricity and gas systems – deriving useful insights on the advantages of the integrated stochastic scheduling versus the deterministic scheduling of the electricity and gas systems.

• "Asynchronous Economic Dispatch for Combined Heat and Power Systems"
  X. Qin, H. Sun, and Y. Guo
  Abstract

  In the day-ahead economic dispatch of combined heat and power systems, the electric power system is adjusted in minutes because of the short dynamic time and the requirement of real-time power balance, while the heating system is dispatched in hours due to its large inertia and long dynamic process. However, the different dispatch time scales of electricity and heat are ignored by existing synchronous dispatch methods, which limits the improvement of system efficiency. To address this challenge, in this article, the asynchronous dispatch method is proposed and instantiated by two different dispatch models featuring a short electric dispatch time scale and a long heat dispatch time scale. Case studies demonstrate the asynchronous dispatch method can overcome the efficiency and reliability problems caused by the existing synchronous dispatch methods.

• "Building Highly Detailed Synthetic Electric Grid Data Sets for Combined Transmission and Distribution Systems"
  H. Li, J. L. Wert, A. B. Birchfield, T. J. Overbye, T. Gomez San Roman, C. Mateo Domingo, F. E. Postigo Marcos, P. Duenas Martinez, T. Elgindy, and B. Palmintier
  Abstract

  This paper introduces a methodology for building synthetic electric grid data sets that represent fictitious, yet realistic, combined transmission and distribution (T&D) systems. Such data sets have important applications, such as in the study of the wide-area interactions of distributed energy resources, in the validation of advanced control schemes, and in network resilience to severe events. The data sets created here are geographically located on an actual North American footprint, with the end-user load information estimated from land parcel data. The grid created to serve these fictional but realistic loads is built starting with low-voltage and medium-voltage distribution systems in full detail, connected to distribution and transmission substations. Bulk generation is added, and a high-voltage transmission grid is created. This paper explains the overall process and challenges addressed in making the combined case. An example test case, syn-austin-TDgrid-v03, is shown for a 307 236-customer case located in central Texas, with 140 substations, 448 feeders, and electric line data at voltages ranging from 120 V to 230 kV. Such new combined test cases help to promote high quality in the research on large-scale systems, particularly since much actual power system data are subject to data confidentiality. The highly detailed, combined T&D data set can also facilitate the modeling and analysis of coupled infrastructures.

• "Reconfigurable Real-Time Power Grid Emulator for Systems With High Penetration of Renewables"
  L. M. Tolbert, F. Wang, K. Tomsovic, K. Sun, J. Wang, Y. Ma, and Y. Liu
  Abstract

  Novel power system control and new utility devices need to be tested before their actual deployment to the power grid. To assist with such a testing need, real-time digital emulators such as RTDS and Opal-RT can be used to connect to the physical world and form a hardware in the loop (HIL) emulation. However, due to the limitations of today's computational resources, the accuracy and fidelity suffer from different levels of model reductions in purely digital simulations. CURENT has developed a reconfigurable electric grid hardware testbed (HTB) to overcome the limitations of digital emulators. The HTB has been used to develop measurement, control, modeling, and actuation techniques for a national grid with a high penetration of renewables. The power electronic-based system includes emulators for synchronous generators; photovoltaics with grid-interfacing inverter; wind turbines; induction motor loads, ZIP loads, power electronic loads; batteries; ac and dc transmission lines; short circuit faults and grid relay protection; and a multiterminal HVDC overlay including power electronics interfaces. The system contains real elements of power flow, measurement, communication, protection, and control that mimic what would be seen in an actual electric grid. This paper presents an overview of the HTB and several scenarios that have been run to determine control and actions needed for the future power grid.

Regular Papers

• "Root-Mean Square Model of Three-Phase Photovoltaic Inverter for Unbalanced Fault"
  H. Satoh, K. Yamashita, K. Shirasaki, and Y. Kitauchi
  Abstract

  The feed-in tariff, introduced in 2012, led to a significant increase in Photovoltaics (PVs) throughout Japan. About half of PVs are three-phase PVs that are connected to low voltage or medium voltage networks. Central Research Institute of Electric Power Industry (CRIEPI) has developed root-mean square-based time-domain power system analysis tools used by all the Japanese utilities for dynamic studies following balanced and unbalanced faults for over the last thirty years. Two 10 kW three-phase PV inverter were tested in the CRIEPI's test lab reproducing various levels of the voltage dips that come from three-phase balanced and unbalanced faults with various fault duration. The PV model was developed and validated, comparing measured responses obtained in the test lab with simulated responses obtained by the time-domain simulation tool. Sensitivities of identified parameters to the model error are carefully examined, which proves that the same model parameters may be used for balanced and unbalanced faults. Derived model parameters are further verified, comparing the simulated response of the combined two PV outputs with the measured response. The excellent match of those responses demonstrates that individually identified parameters for the two single PV inverters are also adequate for representing the combined PV dynamics.

• "Energy Storage as a Service: Optimal Pricing for Transmission Congestion Relief"
  J. Arteaga, H. Zareipour, and N. Amjady
  Abstract

  This paper focuses on pricing Energy Storage as a Service (ESaaS) for Transmission congestion relief (TCR). We consider a merchant storage facility that competes in an electricity market to trade energy and ancillary services on a day-to-day basis. The facility also has the opportunity to provide a firm TCR service to a regional network operator under a long-term contract. Providing the additional TCR service would impose limitations on the facility's ability to fully harvest daily market trade opportunities. Thus, we model the opportunity costs associated with the TCR service and use it in a hybrid cost-value customized pricing technique to determine the risk-constrained optimal price of ESaaS for TCR. Given the long-term nature of the commitment to provide the TCR service, we use the Conditional Value at Risk (CVaR) metric to mitigate the long-term financial risks faced by the facility. The proposed pricing strategy enables the storage owner to estimate the additional financial gains and the associated risks that would likely result from adding the new service to its operation. Numerical simulations are provided to support the proposed methodology.

• "A Probabilistic Reverse Power Flows Scenario Analysis Framework"
  A. Demazy, T. Alpcan, and I. Mareels
  Abstract

  Distributed Energy Resources (DER), mainly residential solar PV, are embedded deep within the power distribution network and their adoption is fast increasing globally. As more customers participate, these power generation units cause Reverse Power Flow (RPF) at the edge of the grid, directed upstream into the network, thus violating one of the traditional design principles for power networks. The effects of a single residential solar PV system is negligible, but as the adoption by end-consumers increases to high percentages, the aggregated effect is no longer negligible and must be considered in the design and configuration of power networks. This article proposes a framework that helps to predict the RPF intensity probability for any given scenario of DER penetration within the distribution network. The considered scenario parameters are the number and location of each residential DERs, their capacity and the daily net-load profiles. Classical simulation-based approach for this is not scalable as it relies on solving the load-flow equations for each individual scenario. The framework leverages machine learning techniques to make fast and precise RPF prediction within the network for each scenario. The framework enables the Distribution Network Service Providers (DNSPs) to assess DERs penetration scenarios at a granular level, derive and localise the RPF risks and assess the respective impacts on the installed assets for network planning purpose. The framework is illustrated with scenario analysis conducted on an IEEE 123 bus system and OpenDSS and shown that it can lead to multiple orders of magnitude savings in computational time while retaining an accuracy of 94% or above compared to classical brute force simulations.

 
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