Microgrid Test Bed Research Articles

A novel SVM based adaptive scheme for accurate fault identification in microgrid

Microgrids, which include distributed energy resources, provide a more reliable power supply. However, despite the fast advancements in microgrid protection, the microgrid’s dynamic behaviour challenges the protection. The large-scale integration of renewable energy sources (RES) and the addition of electric vehicle (EV) charging loads cause additional protection issues on the grid due to its volatile nature. Conventional fault prediction schemes do not provide reliable protection with the dynamic nature of microgrids. This article proposes an adaptive scheme that accurately detects the volatile changes in the microgrid under normal and fault conditions. The novelty of the proposed approach is that the general-purpose adaptive scheme is based on a two-level SVM classifier model to ensure accuracy and speed of operation. The SVM-1 model identifies the mode of operation, the variations in RES generation, the random addition of EV charging load, and the occurrence of a fault in the microgrid. SVM-2 identifies the exact type and location of fault that occurred. The SVM model uses RMS values of three-phase voltage and current measurements as data inputs. The efficacy of the proposed scheme is tested on an IEEE 9-bus microgrid test bed by simulation experiments using MATLAB/SIMULINK. The sensitivity analysis results prove the robustness of the proposed scheme. Moreover, the proposed method is validated using real-time experiments on Hardware-In-Loop (HIL) real-time simulator, OPAL-RT, and Raspberry Pi microcontroller. Accurate online detection of faulted lines and fault types is obtained within a cycle of AC in grid-connected and islanded modes of operation.

Development of an H ∞ controller for a microgrid using LabVIEW

Abstract This paper focuses on designing a simple yet efficient H ∞ controller for regulating the voltage/frequency, output current, and active/reactive power-sharing in a microgrid (MG). The purpose of designing the robust H ∞ controller is to regulate the frequency and voltage in face of the uncertainties in the microgrid and load variation. The studied DC MG test bed includes an SMPS (switching-mode power supply) and DC-DC converter, necessary sensor and data acquisition systems. The proposed control scheme is simulated using MATLAB/Simulink and is then verified in real-time using LabVIEW. The control scheme is developed in the LabVIEW software’s block diagram panel of the virtual instrumentation interface. From both simulation and LabVIEW implementation, load sharing among the DGs, and voltage and frequency regulation at the nominal values are achieved by employing the proposed H ∞ controller. The robustness of the proposed controller is evaluated by comparing it with a robust observer-based controller (Zarei A, Mousavi Y, Mosalanezhad R, Atazadegan MH. Robust voltage control in inverter-interfaced microgrids under plug-and-play functionalities. IEEE Syst J 2020;14:2813–24) under balanced, unbalanced, and non-linear loads. The comparison results envisage that the proposed controller provides improved voltage/frequency regulation and power-sharing during disturbances including the addition of non-linear load to the MG system.

Alternating-Current Microgrid Testbed Built with Low-Cost Modular Hardware

With the growing popularity of microgrids for alternative energy management, there is demand for tools that allow us to study the effect of microgrids in distributed power systems. Popular methods involve software simulation and prototype validation with physical hardware. Simulations often do not capture the complex interactions, and combinations of software simulations with hardware testbeds promise to give a more accurate picture. These testbeds, however, usually aim at the validation of hardware for industrial-scale use, which makes them expensive and not readily accessible. To fill the gap between full-scale hardware and software simulation, we propose a modular lab-scale grid model at a 1:100 power scale over residential single-phase networks with 12 V AC and 60 Hz grid voltage. We present different modules-power sources, inverters, demanders, grid monitors, and grid-to-grid bridges-that can be assembled into distributed grids of almost arbitrary complexity. The model voltage poses no electrical hazards, and microgrids can readily be assembled with an open power line model. Unlike a prior DC-based grid testbed, the proposed AC model allows us to examine additional aspects, such as frequency, phase, active and apparent power, and reactive loads. Grid metrics, including the discretely sampled voltage and current waveforms, can be collected and sent to higher-tier grid management systems. We integrated the modules with Beagle Bone micro-PCs, which in turn connect any such microgrid with an emulation platform built on CORE (Common Open Research Emulator) and the Gridlab-D power simulator, thereby allowing hybrid software/hardware simulations. Our grid modules were shown to fully operate in this environment. Through the CORE system, multitiered control and even remote grid management is possible. However, we also found that the AC waveform poses design challenges that require us to balance accurate emulation (most notably with respect to harmonic distortion) with per-module costs.

A State-Observer-Based Protection Scheme for AC Microgrids with Recurrent Neural Network Assistance

The microgrids operate in tie-up (TU) mode with the main grid normally, and operate in isolation (IN) mode without the main grid during faults. In a dynamic operational regime, protecting the microgrids is highly challenging. This article proposes a new microgrid protection scheme based on a state observer (SO) aided by a recurrent neural network (RNN). Initially, the particle filter (PF) serves as a SO to estimate the measured current/voltage signals from the corresponding bus. Then, a natural log of the difference between the estimated and measured current signal is taken to estimate the per-phase particle filter deviation (PFD). If the PFD of any single phase exceeds the preset threshold limit, the proposed scheme successfully detects and classifies the faults. Finally, the RNN is implemented on the SO-estimated voltage and current signals to retrieve the non-fundamental harmonic features, which are then utilized to compute RNN-based state observation energy (SOE). The directional attributes of the RNN-based SOE are employed for the localization of faults in a microgrid. The scheme is tested using Matlab® Simulink 2022b on an International Electrotechnical Commission (IEC) microgrid test bed. The results indicate the efficacy of the proposed method in the TU and IN operation regimes on radial, loop, and meshed networks. Furthermore, the scheme can detect both high-impedance (HI) and low-impedance (LI) faults with 99.6% of accuracy.

Establishing and Operating Experiential Benchmark Setups of dc Microgrids: A Guideline

Increased attention is given to microgrids for their numerous advantages over conventional power networks. However, there are still a limited number of real microgrid networks that are currently in service, and this raises shortages in expertise on microgrids testing and evaluation before actual deployment. Low-cost, rapid, realistic, and flexible testing are the key challenges that face the microgrids’ validation. This article focuses on the importance of experiential validations to reduce the risks and ensure the desired microgrids performances. It highlights the major challenges for establishing and operating realistic and accurate experimental microgrid testbeds. It also provides guidelines and recommendations for the validation of microgrid studies. An experimental dc microgrid setup showcase is demonstrated, and helpful tips and remarks are suggested. Different case studies on the developed dc microgrid’s setup are presented, and the authors’ experiences and analyses are shared. The experimental results show the accuracy of microgrid testbeds and their expansion capabilities as well as their effectiveness in testing various microgrid conditions.

A Microgrid Testbed With Hybrid Renewables, Energy Storage, and Controllable Loads

A Microgrid Testbed With Hybrid Renewables, Energy Storage, and Controllable Loads

Short-Circuit Analysis of DER-Based Microgrids in Connected and Islanded Modes of Operation

Since microgrids should be able to smoothly operate in two distinct modes—grid-connected and islanded, their fault currents can widely fluctuate depending on the operational mode. When the microgrid is connected to the grid, the highest fault current, by far, is supplied by the utility grid. In this mode, the fault current contribution from distributed energy resources (DERs) is less than 20%. However, when the microgrid switches to the islanded mode, the fault current contribution from the utility grid is lost and DERs are the sole fault current sources. Thus, the overall fault current in the islanded mode is multiple times lower when compared to the grid connected mode. Moreover, most of the DERs are inverter-based, with limited fault currents, which further reduces the overall fault current in the islanded mode. With the rapid rise of the microgrid penetration around the globe, this phenomenon can adversely influence the relay protection, and thus the microgrid fault current needs to be precisely analyzed. Therefore, the main purpose of this paper is to thoroughly analyze the fault current differences in two distinct operation modes of a microgrid, and to consequently derive conclusions regarding the required improvements in fault calculations and relay protection analysis in emerging microgrids. A representative microgrid test bed is developed and modelled using the in-house developed software as well as in a state-of-the-art hardware-in-the-loop environment. Several different short-circuit faults were simulated and analyzed in both grid-connected and islanded modes. The results show that the fault currents significantly differ depending on the operating mode, and thus highly influence the protection system. Moreover, test results show that the fault calculation algorithms aimed at radial distribution grids, mostly used for microgrid fault calculations in the available literature, need to be further improved to provide precise and time-efficient results when the emerging microgrids are considered. These results provide a valuable insight into the current state of the microgrids’ fault calculation and protection and reveal several important directions for future research.

Optimal market-based operation of microgrid with the integration of wind turbines, energy storage system and demand response resources

This paper deals with an optimal operation of a microgrid in the electricity market and presents the communication between the distribution market operator and microgrid operator. The distribution market operator controls and manages the electricity market established in the distribution level, determining the amount of both electricity price and power exchange between market participants. The microgrid operator is able to purchase active and reactive power from the local distribution market. An effective short-term scheduling of the microgrid is implemented to ensure optimal operation. A risk-based stochastic model is used to model the prevailing uncertainties such as loads, wind generation, and main-grid availability in a market-based operation framework. Moreover, in this model, a linearized AC power flow is added to the mathematical formulations to offer a comprehensive solution to the security-constraint operation of the microgrid. The stochastic operation strategy is formulated as a mixed integer linear programming problem. Regarding the uncertainty modeling, the substation equipment failure is modeled with Monte-Carlo algorithm. The effectiveness of the risk-based stochastic method is demonstrated using a microgrid test bed in the presence of demand response resources, dispatchable and wind generation units as well as energy storage system. The results demonstrate demand response program can significantly reduce the operation cost in worst scenarios. Also, it is indicated that the risk-averse decisions reduce the risk of experiencing costly scenario. The proposed framework incorporating the distribution market constraints reduces the uncertainty in real-time operation as it can specified the required energy before running the problem. The deviations from assigned energy to the microgrid are penalized through the distribution market operator.

A Center of Mass Determination for Optimum Placement of Renewable Energy Sources in Microgrids

The objective of this article is to determine the location and size of the renewable energy sources (RESs) to be installed in microgrid networks that have multiple distributed generators. Since RESs have faster dynamics and low inertia, microgrid sources could encounter large disturbances in their power production when RESs are deployed. When the disturbance magnitude exceeds a certain limit, the stable operation of the microgrid can be compromised. In this study, the impact of installing a certain RES capacity on a microgrid is numerically evaluated. A novel methodology is developed to accurately determine the location and size of a newly installed RES in a microgrid. The proposed methodology considers the complete system dynamics in the process of locating and sizing the installed RES. The stability of the microgrid is examined using a modified microgrid load flow model. The proposed method automatically checks for the optimum RES placement to ensure minimal effect on microgrid stability. The effectiveness of the proposed methodology is verified experimentally on a microgrid testbed.

Optimization- and Rule-based Energy Management Systems at the Canadian Renewable Energy Laboratory microgrid facility

This paper presents the development, implementation, and commissioning of two different Energy Management Systems (EMSs) for the Canadian Renewable Energy Laboratory (CANREL), a microgrid testbed located in Guelph, ON, Canada, for the existing hardware, software, and communication infrastructure, which constrained the implementation options. A Rule-based EMS (RBEMS), which is typically found in microgrid controllers nowadays, and an implementation of an Optimization-based EMS (OBEMS), which is not usual in today’s controllers, are proposed, tested, and demonstrated in the microgrid testbed. The RBEMS consists of a state machine that represents the commitment of different genset units in the system and the curtailment of load and renewable generation. The OBEMS is based on a unit commitment model for microgrids that minimizes the generation and curtailment costs, while operating the microgrid equipment according to technical limits. Both EMS systems are integrated into a Python application which integrates various open-source packages and solvers, making it affordable, flexible and easy to replicate and upgrade. The successful implementation and performance of the EMS is discussed, showing that the components of the microgrid follow the dispatch commands, with the OBEMS yielding better overall results than the RBEMS, as expected, using the existing communications links and maintaining the stability of the microgrid.

Proposal of the Communication Layer for a Renewable Energy Microgrid Testbed

Proposal of the Communication Layer for a Renewable Energy Microgrid Testbed

A Nearly Zero-Energy Microgrid Testbed Laboratory: Centralized Control Strategy Based on SCADA System

Currently, despite the use of renewable energy sources (RESs), distribution networks are facing problems, such as complexity and low productivity. Emerging microgrids (MGs) with RESs based on supervisory control and data acquisition (SCADA) are an effective solution to control, manage, and finally deal with these challenges. The development and success of MGs is highly dependent on the use of power electronic interfaces. The use of these interfaces is directly related to the progress of SCADA systems and communication infrastructures. The use of SCADA systems for the control and operation of MGs and active distribution networks promotes productivity and efficiency. This paper presents a real MG case study called the LAMBDA MG testbed laboratory, which has been implemented in the electrical department of the Sapienza University of Rome with a centralized energy management system (CEMS). The real-time results of the SCADA system show that a CEMS can create proper energy balance in a LAMBDA MG testbed and, consequently, minimize the exchange power of the LAMBDA MG and main grid.

Establishment of an auxiliary virtual damping loop for the superior inertial response in the microgrid

Low inertial microgrids in the power network are extremely sensitive toward any uncertainties. Therefore, the practise of complementing inertia virtually in microgrids has earned huge attention in recent time. However, the effect of inertia emulation virtually on the overall damping characteristics of the network has not been explored yet. Concerning to the fact, the study has put an effort to establish a decisive relationship between the inertial and damping powers. Furthermore, a trajectory analysis has been performed to acutely measure the individual effects of the virtual inertia and the virtual damping on the power network. On the basis of the observation from the trajectory analysis, the study has introduced the concept of the dynamic computation of virtual inertial constant by realising the novel self-tuned proportional-integral-based control mechanism. The study further has proposed the superimposed auxiliary dynamic virtual damping loop to suppress the frequency deflection time. To evaluate and justify the improvement of the system performance, the proposed integrated inertia-damping emulation system has been relatively compared with the conventional virtual inertia emulation scheme in a microgrid testbed.

Coordinated Control of PV-Ultracapacitor System for Enhanced Operation Under Variable Solar Irradiance and Short-Term Voltage Dips

Utilization of an ultracapacitor (UC)-based energy storage device can provide one of the most efficient solutions for short-term operational challenges in grid-connected photovoltaic (PV) systems. This paper proposes an algorithm for coordinated control of PV and ultracapacitor-based energy storage system to minimize the effects of sudden changes in solar irradiance and the presence of low voltages at the point of common coupling. In addition, this work proposes an improved multi-mode operational scheme for control of an ultracapacitor-based energy storage system that takes into consideration various associated limits during charging and discharging modes. The effectiveness of the proposed algorithm in mitigating the impacts of low voltages and short term changes in irradiance is demonstrated using simulation analysis carried out on the modified Consortium for Electric Reliability Technology Solutions (CERTS) microgrid testbed.

Impact of Harmonics and Unbalance on the Dynamics of Grid-Forming, Frequency-Droop-Controlled Inverters

Due to its multiple advantages, the grid-forming, droop-controlled (GFDC) inverter is a strong contender for large-scale deployment in the future power systems. However, it is still unclear whether higher harmonics can play an important role in the dynamics of GFDC inverter networks. The major objective of this article is to gain insight into whether certain higher harmonics influence or interact with GFDC inverter network dynamics and to characterize this harmonic interaction. For this purpose, a multiple-harmonic dynamic phasor model (DPM) of a representative GFDC network is derived, which can be conveniently extended to hundreds of DPM equations in order to rigorously investigate the effects of dc offsets and/or second-harmonic content, six-step switching harmonics, and unbalance. For a representative network, the results from eigenvalue migration studies show that GFDC dynamics are not strongly influenced by the presence of six-step switching harmonics nor unbalance. For the first time, it is shown that under conditions of high droop slope and high-bandwidth power filtering, dc offsets and second-harmonic content can excite a resonance within the network and even influence the location of the eigenvalues of the linearized DPM. All DPM results are thoroughly validated using Simulink, and the selected results are validated experimentally using the Wisconsin Energy Institute (WEI) microgrid testbed.

Survivability of Prime-Mover Powered Inverter-Based Distributed Energy Resources During Microgrid Islanding

Inverter-based distributed energy resources (DERs) can supply high-quality ac power in a microgrid due to their fast dynamic response. To achieve high reliability in an islanded microgrid, they are normally operated as voltage-controlled sources. However, the net load supplied by voltage-controlled inverter-based DERs can exceed their rated capacity, particularly during their transition from the grid-connected operation mode. Therefore, a comprehensive analysis of the DER survivability for overload conditions is crucial. Several experimental tests were conducted at the Consortium for Electric Reliability Technology Solutions Microgrid Testbed on the prime-mover powered inverter-based DER for learning about its survivability during overload conditions. In this paper, a thorough investigation of the inverter-based DER's survivability is carried out based on the prime-mover stalling phenomenon. Analytical expressions are derived for key design parameters of load-shedding algorithms, such as time-to-threshold frequency, maximum time delay , and maximum survivability time . The theoretical estimates are validated with the results obtained from the experimental testing. Furthermore, the minimum load-shedding estimate is determined for any prime-mover powered inverter-based DER to survive a transient overload condition.

Islanded Mode Response Verification of AC Microgrid under Symmetrical and Non-symmetrical Short Circuits

The assumptions and parameters required in modeling a microgrid depend on the platform, among other variables. It is therefore pertinent to verify the response of a modeled testbed to establish its validity. This work reports on verification of the response of a wind turbines-based microgrid to symmetrical and non-symmetrical short circuits. The testbed consists of 2 units of 5.5 kW 400 V wind turbines capable of connecting to the utility. Short circuits are introduced at 6.00 second and withdrawn at 8.00 second, measuring the dynamic response of the testbed while the microgrid is in islanded mode alternately under voltage and reactive power control strategies. The response is shown to be consistent, symptomatic of the type of short circuit and therefore suitable for short circuit detection and diagnosis, verifying validity of the microgrid testbed. The testbed can therefore be used for short circuit related studies, design optimization and performance prediction.

Power Converters Based Advanced Experimental Platform for Integrated Study of Power and Controls

With increasing interest in smart grid and renewable energy, significant investments have been allocated to promote related studies. Since there is a wide spectrum of topics to study, it is necessary to have an advanced experimental platform that can accommodate both system- and component-level studies, both hardware and algorithm designs, and both teaching and research. Unfortunately, such experimental platform is not commercially available. In this paper, an advanced power electronics based experimental platform is introduced. The system is consisted of one OPAL-RT real-time simulator, two one-bus microgrid testbeds, and two modular multilevel converters. The subsystems can form a multiple-bus microgrid testbed if connected through emulated power lines. The system can provide real-time simulation, controller hardware-in-the-loop (HIL) simulation, and power HIL simulation for power systems study. Various converter topologies can be configured with the modular converters for power electronics study. Both real-time simulator and DSP control boards can be used to implement advanced control algorithms. The designs and experiences shared in the paper will benefit many researchers that are in need of such system and promote power and energy related studies.

Survivability of Synchronous Generator-Based Distributed Energy Resources for Transient Overload Conditions in a Microgrid

A synchronous generator-based distributed energy resource (DER) is commonly employed in microgrids due to its low cost and simple controls. However, there are many challenges to the DER operation when it is sized for supplying the critical loads alone in a microgrid. In particular, the DER would experience an overload condition during the microgrid transition from grid-connection to islanded operation, when the noncritical loads are also supplied momentarily. Therefore, it is very important to have a clear understanding on the survivability of a synchronous generator-based DER for transient overload conditions. Recently, experimental tests on survivability of the DER were carried out in the Consortium for Electric Reliability Technology Solutions Microgrid Testbed at American Electric Power. In this paper, an in-depth analysis of the synchronous generator-based DER operation during transient overload conditions is presented. The key relationships governing the system dynamic behavior of synchronous generator-based DER are analyzed to design the load shedding scheme for its survivability. Several case studies are illustrated to demonstrate the validity of the proposed load shedding method.

Schedule-Based Operation Method Using Market Data for an Energy Storage System of a Customer in the Ontario Electricity Market

A new operation method for an energy storage system (ESS) was proposed to reduce the electricity charges of a customer paying the wholesale price and participating in the industrial conservation initiative (ICI) in the Ontario electricity market of Canada. Electricity charges were overviewed and classified into four components: fixed cost, electricity usage cost, peak demand cost, and Ontario peak contribution cost (OPCC). Additionally, the online market data provided by the independent electricity system operator (IESO), which operates the Ontario electricity market, were reviewed. From the reviews, it was identified that (1) the portion of the OPCC in the electricity charges increased continuously, and (2) large errors can sometimes exist in the forecasted data given by the IESO. In order to reflect these, a new schedule-based operation method for the ESS was proposed in this paper. In the proposed method, the operation schedule for the ESS is determined by solving an optimization problem to minimize the electricity charges, where the OPCC is considered and the online market data provided by the IESO is used. The active power reference for the ESS is then calculated from the scheduled output for the current time interval. To reflect the most recent market data, the operation schedule and the active power reference for the ESS are iteratively determined for every five minutes. In addition, in order to cope with the prediction errors, methods to correct the forecasted data for the current time interval and secure the energy reserve are presented. The results obtained from the case study and actual operation at the Penetanguishene microgrid test bed in Ontario are presented to validate the proposed method.