Standalone Microgrid Research Articles

Optimized droop controller based energy management for stand-alone micro-grid using hybrid monarch butterfly and sine-cosine algorithm

Microgrids with hybrid renewable energy systems are an advance and useful technology for the development of environment-friendly sustainability. A microgrid mainly consists of small units like PV, wind, diesel generator and battery storage and an energy management system. The main objective of this research is to enhance the performance of energy management system by archiving economical optimal scheduling of the generation units and battery storage and maintain the stability of the microgrid. Thus, it is very much important for the energy management system to make sure that the power is shared among various sources to meet the required load demand and at the same time the operational cost of the microgrid is kept as small as possible. This problem can be developed by using an optimization algorithm. Therefore, to resolve the problem an optimization algorithm named as sine–cosine based monarch butterfly optimization (SCMBO) is proposed in this work to obtain the optimal energy management solutions for day-ahead scheduling in a stand-alone DC microgrid. The proposed algorithm efficacy is validated by comparing its results with other conventional optimization algorithms like MBO and PSO. Further, a control mechanism known as coordinated droop control is proposed for the DC microgrid.

Robust frequency control in a standalone microgrid: An adaptive fuzzy based fractional order cascade PD‐PI approach

AbstractIn addition to low system inertia and stochastic nature of the load, the intermittent nature of renewable output power causes hefty frequency deviations in a standalone microgrid (SMG) that lead to weakening and blackout of SMG. Hence in the SMG, the frequency control issue is always a challenging issue for the operators. To enhance the frequency stability of MG, the control action needs to be more efficient and robust. To answer the above challenge, in this article, a novel adaptive fuzzy based fractional order cascade PD‐PI controller is proposed for frequency control of SMG. The proposed controller inherits the merits of both fuzzy and fractional order cascade PD‐PI controllers by ignoring the individual limitations. The parameters of the proposed controller are tuned using a recently developed future search algorithm. The proposed controller is tested against various load and renewable disturbances on a real‐time MG test system. The simulation outcomes reveal that the proposed controller and algorithm enhance the dynamic response of SMG significantly compared to various powerful controllers in the literature. Moreover, the proposed controller performance is more robust to the uncertainties in the MG and energy storage system as compared to the various robust controllers in the literature.

An Optimal Non-Integer Model Predictive Virtual Inertia Control in Inverter-Based Modern AC Power Grids-Based V2G Technology

In this study, virtual inertia control-based vehicle-to-grid (V2G) concept for the secondary load frequency control of AC islanded microgrids (MGs) is presented. Since autonomous modern power grids typically have much smaller inertia in comparison to conventional grids, a very fast and high-performance control plant is necessitated for controlling reserved power plants (e.g., batteries) to overcome any voltage and frequency instability. This issue can be solved by the short-term battery energy storage system, inverter, and proper inertia control technique. Because of the high cost of the battery energy storage system, utilization of controllable loads like electric vehicle (EV) to low-inertia modern power grids is presented for the decreasing of the needed capacity of the energy storage system. Hence, an optimal non-integer model predictive control is applied for the secondary frequency regulation in low-inertia stand-alone MGs with the V2G technology. Since the performance and accuracy of the applied non-integer controller are depended on its parameters’ value, a modified heuristic optimization algorithm is proposed for tuning the controller's parameters. In the end, the validity and feasibility of the proposed method are investigated by the model-in-the-loop experimental results.

Intelligent Control Strategy to Enhance Power Smoothing of Renewable based Microgrid with Hybrid Energy Storage

A stand-alone renewable based microgrid (MG) performance with a hybrid energy storage system has been examined in this work. Stand-alone MG system mainly consists of a solar photovoltaic (PV) and permanent magnet synchronous generator (PMSG) based wind system. The hybrid energy storage system is based on Ni-Metal- Hydride (NiMH) battery and a supercapacitor (SC). The paper's primary goal is to propose an artificial neural network (ANN) based control strategy for charging/discharging control of Ni-Metal- Hydride battery & supercapacitor. The proposed maximum power tracking techniques (MPPT) include perturb and observe (P& O) algorithm for solar PV system while optimum torque (OT) MPPT for PMSG based wind turbine. The ANN-based control mechanism can maintain the DC bus voltage constant and trigger the supercapacitor to limit the battery current when the battery charging/ discharging current reached its threshold value. The proposed model responds quickly to intermittent nature PV-wind power generation or load power variation.

Distributed Energy-Resource Design Method to Improve Energy Security in Critical Facilities

This paper presents a user-friendly design method for accurately sizing the distributed energy resources of a stand-alone microgrid to meet the critical load demands of a military, commercial, industrial, or residential facility when utility power is not available. The microgrid combines renewable resources such as photovoltaics (PV) with an energy-storage system to increase energy security for facilities with critical loads. The design method’s novelty complies with IEEE Standards 1562 and 1013, and addresses resilience, which is not taken into account in existing design methods. Several case studies simulated with a physics-based model validate the proposed design method and demonstrate how resilience can be included in the design process. Additionally, the design and the simulations were validated by 24 h laboratory experiments conducted on a microgrid assembled using commercial off-the-shelf components.

A Quantitative Risk-Averse Model for Optimal Management of Multi-Source Standalone Microgrid with Demand Response and Pumped Hydro Storage

High renewable energy integrated standalone microgrid requires greater ramping capabilities from other dispatchable resources to compensate for effects of the intermittent and variability of the renewable energy available in the system. To address this, a wind-solar-thermal-hydro-coupled multi-source standalone microgrid (WSTHcMSSM) considering demand response and pumped hydro storage is proposed to maximize the operating profit and get the optimal solution of the multi-source generation system by taking advantage of multi-resource complementarity. In WSTHcMSSM, we present a conditional value-at-credibility (CVaC)-based quantitative risk-averse model for uncertain wind and solar power by thoroughly examining the randomness and fuzziness characteristics. Additionally, the most severe issues caused by wind and solar power fluctuation happen during the peak load, and this paper proposes a load partitioning method to get the time-of-use (TOU) in demand response for peak load shaving. A case study is conducted for the validation of the proposed method. It is found from the study case that the CVaC can well evaluate the uncertainty in WSTHcMSSM with wind and solar integration. Additionally, the WSTHcMSSM can efficiently explore the potential flexibility in multi-source complementarity for promoting the penetration of renewable energy.

Optimal Operation of a Hybrid Power System as an Island Microgrid in South-Korea

The microgrid is a power distribution system that supplies power from distributed generation to end-users. Demonstration projects and R&D regarding microgrids are currently in development in several advanced countries. In South Korea, renewable energy-based microgrid demonstration projects are carried out mainly as island or university campus grids. These R&D efforts aim to popularize microgrid systems in South Korea while considering the limited land availability, which impedes the widespread distribution of photovoltaic systems and the microgrid market’s growth. This study presents a floating photovoltaic system configured as an island microgrid combined with a hybrid power system. The floating photovoltaic system is configured on an idle water body integrated with an existing pumped hydroelectric system. The integration of a current pumped hydroelectric system minimizes a battery energy storage requirement, which compensates for the renewable energy sources’ intermittent power output. We evaluate the optimal power flow of the setup using a reliability index to ensure a stable power supply within the standalone microgrid and maximize the supply power range according to the demand response.

A Three-Level Planning Model for Optimal Sizing of Networked Microgrids Considering a Trade-Off Between Resilience and Cost

Extreme events can cause severe power system damage. Resilience-driven operation of networked microgrids (MGs) has been heavily studied in literature. There is, though, little research considering the influence of resilience on decision making for planning. In this paper, a three-level model is suggested to solve the optimal sizing problem of networked MGs considering both resilience and cost. In the first level, a meta-heuristic technique based on an adaptive genetic algorithm (AGA) is utilized to tackle the normal sizing problem, while a time-coupled AC OPF is utilized to capture stability properties for accurate decision-making. The second and third levels are combined as a defender-attacker-defender model. In the former, the suggested AGA is utilized to generate attacking plans capturing load profile uncertainty and contingencies for load shedding maximization, while a multi-objective optimization problem is suggested for the latter to obtain a trade-off between cost and resilience. Simulations considering meshed networks and load distinction into critical and non-critical are developed to demonstrate algorithm effectiveness on capturing resilience at the planning stage and optimally sizing multiple parameters. The results indicate that higher resilience levels lead to higher investment cost, while sizing networked MGs leads to decreased investment in comparison with standalone MGs sizing.

Agent-Based Coordinated Control of Power Electronic Converters in a Microgrid

This paper presents the implementation of an agent-based architecture suitable for the coordination of power electronic converters in stand-alone microgrids. To this end, a publish-subscribe agent architecture was utilized as a distributed microgrid control platform. Over a distributed hash table (DHT) searching overlay, the publish-subscribe architecture was identified based on a numerical analysis as a scalable agent-based technology for the distributed real-time coordination of power converters in microgrids. The developed framework was set up to deploy power-sharing distributed optimization algorithms while keeping a deterministic time period of a few tens of milliseconds for a system with tens of converters and when multiple events might happen concurrently. Several agents participate in supervisory control to regulate optimum power-sharing for the converters. To test the design, a notional shipboard system, including several converters, was used as a case study. Results of implementing the agent-based publish-subscribe control system using the Java Agent Development Framework (JADE) are presented.

Optimization of Two-Stage IPD-(1+I) Controllers for Frequency Regulation of Sustainable Energy Based Hybrid Microgrid Network

Sustainable energy based hybrid microgrids are advantageous in meeting constantly increasing energy demands. Conversely, the intermittent nature of renewable sources represents the main challenge to achieving a reliable supply. Hence, load frequency regulation by adjusting the amount of power shared between subsystems is considered as a promising research field. Therefore, this paper presents a new stratagem for frequency regulation by developing a novel two stage integral-proportional-derivative with one plus integral (IPD-(1+I)) controller for multi sources islanded microgrid system (MS-IμGS). The proposed stratagem has been tested in an MS-IμGS comprising of a wind turbine, parabolic trough, biodiesel generators, solid-oxide fuel cell, and electric water heater. The proposed model under different scenarios is simulated in MATLAB environment considering the real-time recorded wind data. A recently developed sine-cosine algorithmic technique (SCA) has been leveraged for optimal regulation of frequency in the considered microgrid. To identify the supremacy of the proposed technique, comparative studies with other classical controllers with different optimization techniques have been performed. From the comparison, it is clearly evident that, SCA-(IPD-(1+I)) controller gives better performance over other considered stratagems in terms of various time domain specific parameters, such as peak deviations (overshoot, undershoot) and settling time. Finally, the robustness of the proposed stratagem is evaluated by conducting sensitivity analysis under ±30% parametric variations and +30% load demand. The lab tests results validate the operation of the proposed system and show that it can be used to regulate the frequency in stand-alone microgrids with a high penetration of renewable energy.

Sliding Mode Control of Hybrid Renewable Energy System

This paperpresents an ANFIS based adaptive sliding mode control (ASMC) of a standalone single phase microgrid system. The proposed microgrid system integrates a micro-hydro turbine driven single-phase two winding self-excited induction generator (SEIG) with a wind driven permanent magnet brushless DC (PMBLDC) generator, solar photo-voltaic (PV) array and a battery energy storage system (BESS). These renewable energy sources are integrated using a single-phase voltage source converter (VSC). The ASMC based control algorithm is used to estimate the reference source current which controls the single-phase VSC and regulates the voltage and frequency of the microgrid in addition to harmonics current mitigation. The adaptive sliding mode control with ANFIS is used to maintain the energy balance among wind, micro-hydro, solar PV power and BESS, which controls the frequency of standalone microgrid. Simulation results from MATLAB/SIMULINK of the proposed microgrid shows that the grid voltage and frequency are maintained constant while the system is following various changes in dynamic state such as sudden change in wind speed, changes in solar insolation level and changes in loads.

A Study on the Economic Feasibility of Stand-Alone Microgrid for Carbon-Free Island in Korea

The power industry is rapidly changing as demand for eco-friendly and stable power supply increases along with global greenhouse gas emission regulations. Small-capacity renewable power sources represented by photovoltaics and wind are continuously increasing as a form of microgrid to supply electric power to a community or island. As a result, microgrids based on renewable resources have come into wide usage around small areas or islands in Korea. In particular, the microgrid development policy of Korea is focused on electric power quality, as well as expansion in renewable energy supply for reducing greenhouse gas emissions. From 2009, the government began to develop independent carbon-free microgrids with photovoltaic and wind powers instead of traditional power diesel generators for small islands. The goal of this paper is to investigate a feasible economic microgrid topology for implementing the carbon-free island (CFI) under an acceptable level of reliability. First, we derive three scenarios of power systems including photovoltaics, wind, battery, and fuel cells. Next, we assess economic feasibility on top of the power supply reliability of the scenarios. Then, we perform a sensitivity test to suggest economic conditions for achieving the CFI goals. Finally, we present carbon-free-based microgrid models considering the CFI policy of Korea.

Modified V-I droop based adaptive vector control scheme for demand side management in a stand-alone microgrid

The concept of conservative voltage reduction (CVR) is widely adopted in the distribution sector to curtail the load demand with the regulation of bus voltage to the lower value. The reduction of the peak demand and energy saving are the two key attributes furnished by implementing the CVR strategy. The voltage source inverter (VSI) based AC microgrid enables the integration of renewable energy sources (RES) to the AC network. Apart from facilitating the process of power generation, the VSI enabled renewable energy sources conducts the ancillary service such as demand side management (DSM) with the enforcement of CVR. The CVR’s applicability for demand side management considered to be prospective research for stand-alone microgrid. However, least exploration is being conducted in this direction for autonomous microgrid and hence, the paper is intended to investigate CVR’s performance on VSI enabled stand-alone microgrid. A 2-degree of freedom enabled adaptive vector control is being utilized to synchronize the frequency parameter of the microgrid network which utilizes the set parameter of static and transient droop gain function. A new approach is devised to compute the droop parameter for V-I droop which performs CVR action to realize demand side management. The proposed strategy utilizes the voltage reduction mechanism to establish voltage at the load side with the coordination of high and low bandwidth controller. The verification of the proposed work is established with 5 bus microgrid test system and further, three phases to ground fault condition is being put on the controller to test its adequacy. The simulation results are furnished through MATLAB/Simulink software.

Real-Time Implementation of the Predictive-Based Control with Bacterial Foraging Optimization Technique for Power Management in Standalone Microgrid Application

In this paper, the predictive-based control with bacterial foraging optimization technique for power management in a standalone microgrid is studied and implemented. The heuristic optimization method based on the social foraging behavior of Escherichia coli bacteria is employed to determine the power references from the non-renewable energy sources and loads of the proposed configuration, which consists of a fixed speed diesel generator and battery storage system (BES). The two-stage configuration is controlled to maintain the DC-link voltage constant, regulate the AC voltage and frequency, and improve the power quality, simultaneously. For these tasks, on the AC side, the obtained power references are used as input signals to the predictive-based control. With the help of the system parameters, the predictive-based control computes all possible states of the system on the next sampling time and compares them with the estimated power references obtained using the bacterial foraging optimization (BFO) technique to get the inverter current reference. For the DC side, the same concept based on the predictive approach is employed to control the DC-DC buck-boost converter by regulating the DC-link voltage using the forward Euler method to generate the discrete-time model to predict in real-time the BES current. The proposed control strategies are evaluated using simulation results obtained with Matlab/Simulink in presence of different types of loads, as well as experimental results obtained with a small-scale microgrid.

Implementation and comparison of droop control, virtual synchronous machine, and virtual oscillator control for parallel inverters in standalone microgrid

In recent times, renewable energy sources (RESs) have been potential alternatives over the conventional generation systems connected to the grid. The power electronic inverters are the principal media of interface for connecting the RESs to the utility grid system. This work is primarily focused on the comparative analysis of Droop, virtual synchronous machine (VSM), and virtual oscillator control (VOC) techniques for the parallel operated inverters in a standalone Microgrid (MG). Droop control emulates only the droop characteristics of synchronous machines such that the transient response of this controller is not significant. VSM imitates not only the droop characteristics of synchronous machines but also the swing equation. Therefore, VSM has a remarkable difference in the dynamic performance of the system. In droop and VSM, the feedback signals such as voltage and current are measured to calculate the averaged real and reactive powers. However, the VOC works on instantaneous feedback signals such that it achieves much faster synchronization and good power-sharing. The philosophy of the proposed VOC is to control an inverter such that it emulates the behavior of a nonlinear dead-zone oscillator. The performance analysis of the system with the aforementioned controllers has been studied based on MATLAB/Simulink and Opal-RT digital simulation. From the comparative analysis, it is observed that the VOC gives a better performance compared to droop and VSM control. The experimental results show the efficacy of the proposed VOC control method.

Techno-economic analysis with energy flow modeling for investigating the investment risks related to consumption changes within a standalone microgrid in Sweden

A techno-economic energy flow model for a standalone microgrid was developed to investigate the investment risks related to consumption changes and compare the results to a conventional grid-connection in Sweden. Two different design strategies for a standalone microgrid was used, one with the objective to minimize the life-cycle cost and the other to provide a lower investment risk. It was shown that the largest investment risk for both design strategies was a potential increase in annual energy consumption within the standalone microgrid. The design strategy with the objective to reduce the investment risk eliminated the influence on the life-cycle cost from an increase in peak consumption and reduced the overall investment risk in comparison to the design strategy with the objective to minimize the life-cycle cost. However, a larger life-cycle cost was the drawback of that design strategy. It was concluded that locations with larger annual mean capacity factors reduced the investment risk for standalone microgrids due to lower diesel fuel dependence. It was also concluded that a conventional grid-connection had a lower investment risk than a standalone microgrid, since adverse changes in consumption always increased the life-cycle cost less for a conventional grid-connection than for a standalone microgrid.

The Use of Power Line Communication in Standalone Microgrids

Standalone microgrids are used in various industrial operations to supply critical loads. The authors have proposed a stable and robust decentralized ac microgrid architecture that provides an automatic and equitable load sharing between distributed generators, without the use of droop control. To deal with faults or real-time changes in the distributed generation levels, a flexible reconfiguration of the microgrid can be advantageous. To achieve that, this article proposes the use of power line communication (PLC). Two PLC strategies are explored in this article: the first is based on using a single and constant PLC frequency, and the second is based on using a variable PLC frequency within a given range. This article details PLC injection, detection, and suppression methods, as well as the overall communication logic. It demonstrates the ability of the microgrid to adapt to changes while minimizing the amount of battery support. Findings of this article are supported by simulations and validated by experiments.

Hybridizing Lead–Acid Batteries with Supercapacitors: A Methodology

Hybridizing a lead–acid battery energy storage system (ESS) with supercapacitors is a promising solution to cope with the increased battery degradation in standalone microgrids that suffer from irregular electricity profiles. There are many studies in the literature on such hybrid energy storage systems (HESS), usually examining the various hybridization aspects separately. This paper provides a holistic look at the design of an HESS. A new control scheme is proposed that applies power filtering to smooth out the battery profile, while strictly adhering to the supercapacitors’ voltage limits. A new lead–acid battery model is introduced, which accounts for the combined effects of a microcycle’s depth of discharge (DoD) and battery temperature, usually considered separately in the literature. Furthermore, a sensitivity analysis on the thermal parameters and an economic analysis were performed using a 90-day electricity profile from an actual DC microgrid in India to infer the hybridization benefit. The results show that the hybridization is beneficial mainly at poor thermal conditions and highlight the need for a battery degradation model that considers both the DoD effect with microcycle resolution and temperate impact to accurately assess the gain from such a hybridization.

Design Framework of a Stand-Alone Microgrid Considering Power System Performance and Economic Efficiency

Stand-alone microgrids integrating renewable energy sources have emerged as an efficient energy solution for electrifying isolated sites, such as islands and remote areas. The design of a microgrid involves various influential factors, including technological development, economic feasibility, and environmental impacts, based on the conditions and regulations of a particular site. This paper proposes a comprehensive microgrid design framework based on power system analysis and techno-economic analysis. The obtained optimal microgrid configuration satisfies both the design objective and power system performance regulations. The proposed design approach focuses on using practical data and can adapt to any microgrid design problems based on the local characteristics of a specific site. The practicality and effectiveness of the design framework are validated by applying it to the design of a stand-alone microgrid for Deokjeok Island in South Korea. The case study results justify the importance of considering site-specific characteristics and the impacts of power system conditions on the optimal microgrid design.

Improving the Transient Response of Hybrid Energy Storage System for Voltage Stability in DC Microgrids Using an Autonomous Control Strategy

In renewable microgrid systems, energy storage system (ESS) plays an important role, as an energy buffer, to stabilize the system by compensating the demand-generation mismatch. Battery energy storage system serves as a decisive and critical component. However, due to low power density and consequently slow dynamic response the lifetime of BESS is observably reduced due to high current stress, specifically experienced during abrupt/transient power variations. Hence, hybridization with supercapacitor storage system is conferred. Additionally, the controllers designed for energy storage systems should substantially respond for compensating the transient requirement of the system. In this article, we propose a decoupled control strategy for batteries and supercapacitors based on k - Type compensators and a nonlinear PI controller (NPIC) respectively. The formulated control design is tested for voltage regulation in a standalone microgrid. Furthermore, a comparative analysis is presented with benchmark low-pass-filter (LPF) based controller. The results obtained shows the proposed control technique possess a faster response with improved voltage regulation capabilities. For the test system regulated at 48 V for various abrupt load-generation various case studies presented, the proposed methodology maintains a significantly reduced voltage deviation between 47 V - 51 V in contrast to 45 V - 56 V observed in the LPF methodology. Furthermore, the complexity is simpler in comparison to LPF based control strategy and a comparative obviation of additional sensing devices is achieved, that inherently reduces the detrimental effect on ESS response during transient condition.