Standalone Microgrid Research Articles

Design of tariff schemes as demand response mechanisms for stand-alone microgrids planning

Stand Alone Microgrids provide electric energy to isolated communities when the grid’s extension is not feasible. However, Stand Alone Microgrids face technical, financial, and regulatory challenges before reaching most rural populations. This paper explores how energy tariffs and public subsidies for rural electrification are related to the optimal operation and design of Stand Alone Microgrids. It aims to propose a holistic methodology to determine the optimal sizing, optimal energy management, optimal tariffs, and public subsidies for Stand Alone Microgrids using Disciplined Convex Programming. The study guarantees the convexity of the proposed formulation and the uniqueness of the optimal solution by following the rules of Disciplined Convex Programming. A case study shows a non-negligible impact of time-varying tariffs over the sizing, energy management, and fuel consumption. Compared with flat tariffs, using a variable tariff reduces costumers’ payments up to 21% and diesel consumption of 11%. However, investor profits can be reduced by up to 18%. In this regard, the study reveals and propose a solution to the challenge that governments and policymakers face trying to define tariffs to attract private investors interest in funding rural electrification projects on one side, and create fair tariffs for the customers on the other side.

Economic emission dispatch on unit commitment-based microgrid system considering wind and load uncertainty using hybrid MGWOSCACSA

Economic emission dispatch (EED) of a three-unit stand-alone microgrid system supported by a wind farm is percolated in this paper. The adverse effects of stochastic and uncertainty nature of wind energy in raising the generation cost of the microgrid system are studied in this article. Unit commitment (UC) of the generating units is taken into account which helps in reducing the generation cost and provides relaxation time to the generation units. Three cases are contemplated for the study. For the first two cases, the generation cost of the test system was minimized without and with the involvement of wind power, respectively. The third case considered the involvement of wind power along with the UC of the conventional generation units. A novel hybrid of recently developed superior optimization algorithms, viz. grey wolf optimizer (GWO), sine–cosine algorithm (SCA) and crow search algorithm (CSA), is implemented to perform EED, and the results are compared with basic GWO and other hybrid algorithms. Results are then analysed to compare and contrast among these cases and justify the reliable and profitable one. Statistical analysis claims the superiority of the proposed hybrid MGWOSCACSA over other hybrids and GWO.

Robust MMSOGI‐FLL control algorithm for power quality improvement of solar PV‐SyRG pico hydro‐BES based islanded microgrid with dynamic load

The islanded microgrids are vulnerable to stability problems during high penetration of dynamic loads like induction motors (IMs), which results in continuous oscillations in voltage and frequency, resulting in disturbances in the islanded microgrid. In this work, a modified multi-second-order generalised frequency locked loop (MMSOGI-FLL) control algorithm is implemented. This control provides a fast response of the power converter; thereby the microgrid voltage/frequency are stabilised rapidly. Besides, the control also provides the dynamic reactive power for the sudden start of an IM load and regulates the common coupling point voltage in the islanded system. The MMSOGI-FLL control also provides harmonics elimination, fast convergence, DC offset removal and reactive power compensation in the islanded system. The implemented islanded system is a combination of a pico-hydro-based synchronous reluctance generator (SyRG), solar photovoltaic (PV) array and a battery energy storage (BES). The BES is connected at DC link to maintain the power equilibrium under a change in the load and power generation. Moreover, the system used in this work is proficient in feeding the non-linear load and dynamic load of an IM. The performance of this standalone microgrid is validated with extensive tests on the developed prototype, which meets the power quality requirement of the 1547.4 standards.

Modeling of Interconnected Voltage and Current Controlled Converters With Coupled LC–LCL Filters

Nowadays, more and more converters under voltage control mode with LC filter and current control mode with L / LCL filter are interconnected, forming a more complicated impedance network and resulting in coupled control behaviors. This type of interconnected converter system can be commonly seen in a stand-alone microgrid and some advanced testing benches for power electronics converters. In this article, a system consisting of a voltage-controlled converter with LC filter and a current-controlled converter with LCL filter have been studied. A detailed mathematical model is proposed to describe the stability and coupling characteristics of such system. It is found that the stability problem in this type of configuration may arise in an uncommon way, which is different from the typical resonance in a grid-connected converter system and can be triggered in higher frequency band. Meanwhile, the voltage and current behaviors of interconnected converters are strongly coupled through the complicated filter impedances and control loops in low-frequency band and mid-frequency band.

Decentralized Cooperative Optimal Power Flow of Multiple Interconnected Microgrids via Negotiation

The microgrid is widely recognized as a promising concept for integrating distributed energy resources (DERs). Considering the enormous number of DERs, the future smart grid will likely be a grid containing a number of interconnected microgrids. Thus, the optimal power flow (OPF) problem should be studied by properly taking account of the coupling between the microgrids. In this paper, the models of standalone microgrid and coupled microgrids are formulated first. Then, a decentralized approach is shown in detail to cooperatively solve the coupled OPF problem. Specifically, each microgrid solves the local OPF problem, leading to the optimal solution of the coupled OPF problem via negotiation between microgrids. The privacy of each microgrid is also preserved since no sensitive information is shared between microgrids. Finally, simulation results show that the optimality gaps between the proposed approach and an existing solver are small for both the AC OPF and the DC OPF. Furthermore, the total cost of the microgrids is reduced by the cooperative OPF.

A Novel Hybrid Fuzzy PD-TID Controller for Load Frequency Control of a Standalone Microgrid

Uncertainties related to the power output from the renewable energy sources and low inertia of a standalone microgrid (SMG) demand a robust control strategy for continuous frequency control of the SMG. Consequently, this paper proposes a novel hybrid fuzzy proportional derivative–tilt integral derivative (FPD-TID) controller for the load frequency control (LFC) analysis of a SMG. Inspiration for the proposed controller comes from combining the advantages of both the FPD and the TID controllers. Gains of the proposed controller are optimized using a robust chaotic crow search algorithm (CCSA). In order to validate the proposed control scheme, comparative frequency deviation responses of the SMG are presented considering multiple disturbances. Also, the proposed controller is put to test for its sensitivity and robustness subject to a ± 30% variation in the SMG parameters and disconnection of various SMG subsystems, respectively. Since operational stability of the SMG is highly desirable under such circumstances, the proposed control scheme aims to achieve a trade-off between its performance and the operational stability of the SMG. The operational stability of the SMG is established through eigenvalue and root locus analysis.

A Robust Cascade Controller for Load Frequency Control of a Standalone Microgrid Incorporating Electric Vehicles

Intermittency in the output power of renewable and green energy sources (RGES) and low inertia of a standalone microgrid (SMG) result in large frequency deviations. Use of energy storage systems (ESSs) alleviate the SMG frequency deviations in an adorable manner but their high cost and low power density calls for alternative sources to balance the mismatch between power supply and demand. In recent years, utilization of the battery of an electric vehicle (EV) to minimize the frequency deviations has gained a lot of attention. Consequently, this paper proposes a robust and newly developed bio-inspired Salp Swarm Optimization (SSO) algorithm based PI-PD cascade controller for load frequency control (LFC) of the SMG integrated with the EVs. To demonstrate the efficacy of the proposed controller, its performance has been compared with other well-known controllers and algorithms considering diverse SMG operating scenarios. Simulation results distinctly prove the superiority of the proposed controller over the other controllers. Also, robustness of the proposed controller has been tested subject to ±50% variation in certain SMG parameters. Results clearly justify the robustness of the proposed controller. Additionally, operational stability of the SMG has been appraised through Eigenvalue and Bode diagram analysis for all the scenarios.

Energy demand and quality management of standalone diesel/ PV /battery microgrid using reconfiguration

Power quality has become one of the most vital challenges in the planning of smart distribution grids due to popularity and myriad applications of power electronic devices. This paper introduces a new method based on network reconfiguration to efficiently deliver the energy demand of standalone Diesel/PV/Battery microgrids with improved power quality. The feeder reconfiguration is performed to decrease power loss, decrease the total harmonic distortion (THD), and improve voltage sag indices. Mathematical models of Diesel/PV/Battery standalone system are integrated with harmonic power flow algorithms to implement the concept. Reconfiguration algebraic equations along with nonlinearities introduced by Diesel/PV/Battery standalone system are solved by means of Non-Dominated Sorting Differential Evolution Algorithm (NDSDEA). The proposed methodology is carried out on a 33-bus standalone microgrid. The results have shown that reconfiguration not only improves the overall performance of the standalone energy system but also is effective to improve the quality of power delivered to the significant consumers. The method has both economic and technical benefits for such islanded networks.

Multi-objective operation of smart stand-alone microgrid with the optimal performance of customers to improve economic and technical indices

Abstract he operation problem of the Smart Stand-Alone Microgrids (SSAMGs) considering the economic and the technical indices is investigated in many studies. The aim of the most studies is to meet the demand of the system with the minimum cost and high reliability considering the technical constraints of the system. In this paper, maximizing the RES penetration and improving the voltage profile of the system are modeled besides the minimization of the operation cost through a multi-objective optimization model. Moreover, the demand side management (DSM) strategies consisting of the demand shifting (DS) and the demand curtailing (DC) are employed in the decision-making problem of the SSAMGs to improve its economic and technical indices. To analysis the performance of the system, the battery bank (BB) lifetime and the peak-to-average ratio (PAR) indices are used. The resulted model is solved by the augmented epsilon-constraint approach in General Algebraic Modeling System (GAMS) optimization software environment. The best solution is selected using the fuzzy and the weight sum approaches. To investigate the effectiveness of the model and its solution methodology, it is applied on the IEEE 33-bus through defining four case studies. The results show the better performance of the objective functions in the presence of DSM strategies. Moreover, the PAR and the BB lifetime indices are improved when the DSM strategies are used in the SSAMGs to meet the demand.

Techno-Economic Investigation Using Several Metaheuristic Algorithms for Optimal Sizing of Stand-Alone Microgrid Incorporating Hybrid Renewable Energy Sources and Hybrid Energy Storage System

Increasing energy demand worldwide has resulted in more penetration of renewable sources for developing non-polluted electric energy despite their prices are not economically competitive to traditional generation systems due to intermittent nature of renewable resources. Energy storage systems are used to counteract the intermittent nature of renewable sources. Therefore, the optimal sizing and design of stand-alone renewable generating systems is a significant concern to get a more cost-effective system. This paper focuses on achieving the optimum design and size of a microgrid to meet the load requirements and reducing the total cost including capital, investment, operational and maintenance costs. For this aim, the sizing problem is formulated to be solved using three well-known metaheuristic algorithms, namely, Particle Swarm Optimization (PSO), Grey Wolf Optimization (GWO) and Cuckoo Search Optimization (CSO). The employed microgrid comprises hybrid renewable energy sources of PV/Wind systems integrated with a hybrid energy storage system of Battery and FC/Electrolyzer set for supplying AC loads located in Zafarana, Egypt. On the basis of real meteorological data of the studied location, the produced energies from the renewable sources are estimated using MATLAB developed algorithms. The simulation results showed that the optimized design using CSO can robustly and efficiently yield the optimal design of a microgrid.

Load Frequency Control of a Two-Area Power System With a Stand-Alone Microgrid Based on Adaptive Model Predictive Control

This article proposes an adaptive model predictive control (AMPC) technique for load frequency control of a two-area interconnected power system with a stand-alone microgrid. A generalized state-space model of a typical stand-alone microgrid having controllable and uncontrollable generating power sources is derived to predict the future output and control inputs for the microgrid frequency control. The main aim is to solve the problems of frequency deviation against variations in system parameters and load disturbance. The effect of system parameters variation on the control performance for frequency control in a stand-alone microgrid is also investigated. The closed-loop response obtained by the proposed AMPC has proven to be faster and adaptable for different cases considered. Moreover, the robustness of AMPC against the variation of the system parameters is studied. In addition, impacts of certain physical constraints affecting the dynamic performance of the power system, such as reheat turbine (RT), the time delay (TD), the generation rate constraint (GRC), and the dead band (DB) for steam turbine were investigated. The simulation results of the proposed model demonstrated good dynamic response, robustness, optimum performance, and superiority of the proposed AMPC technique to the MPC control technique.

Two‐parameter Kautz network‐based LTV‐MPC for non‐linear standalone micro‐grid control

This study proposes a novel linear time-variant model predictive controller (LTV-MPC) for the centralised control of non-linear standalone micro-grids. At each sample, within the prediction horizon, LTV-MPC linearises the non-linear micro-grid model around the state and input reference trajectories resulting in a linear time-variant (LTV) model. The LTV model is used for predicting the forced response of the micro-grid. The natural response is predicted by solving the non-linear model along the state and input reference trajectories. An optimal control problem for the LTV-MPC is formulated using the complete predicted response, which is a quadratic programming problem instead of a non-convex non-linear programming problem. The quadratic programming problem is solved online at each sample to generate the optimal control trajectories within the control horizon. The study recommends the use of two-parameter orthonormal Kautz networks in the LTV-MPC design for the control trajectories approximation. The approximation drastically reduces the number of optimising variables in the optimal control problem without compromising LTV-MPC performance. A standalone eight bus micro-grid with one synchronous distributed generator (DG) and one photovoltaic-DG is considered for the analysis. The LTV-MPC performance is assessed for the different load disturbance and source intermittency scenarios. The results are compared with the existing MPC designs.

Small signal stability analysis of stand-alone microgrid with composite load

Microgrid concept provides suitable context for installing distributed generation resources and providing reliability and power quality for loads. During grid connected mode of microgrid, all stability issues are getting handled by main grid due to its sufficient inertia. But when islanding occurs, microgrid faces stability-related problems. This paper presents the state space model of isolated microgrid along with load dynamics. This paper investigates the effect of static load, induction motor type of dynamic load and composite load on the stability of the island microgrid. The paper also studies the effect of damping and inertia on the stability of the microgrid. The performance of the test system is evaluated using MATLAB simulation software. The present studies show that during the planning of the microgrid, effect of types of loads and load changes should be considered for stable operation of the system.

Cascaded controller for a standalone microgrid‐connected inverter based on triple‐action controller and particle swarm optimisation

In this study, power quality (PQ) improvement has been addressed, in the form of total harmonic distortion (THD) minimisation, as well as, voltage regulation using two cascaded schemes. The first scheme is the optimised triple action controller (TAC)-based pulse width modulated voltage source inverter. TAC consists of a proportional resonant controller, selective harmonic compensator, and a new added current-assisted feed forward controller. The second scheme is the optimised cascaded dual-level control of a standalone microgrid. Cascaded level control consists of droop, secondary, and synchronisation control loops. The two approaches have been optimised for best parameter selection out of the possible solution space using a particle swarm optimisation algorithm to satisfy the study objectives. The optimisation objectives/constraints were to minimise THD and minimise overshoot/undershoot, rise time, and steady-state error for voltage compensation under two disturbance scenarios, sudden load change, and voltage flicker injection as a power frequency disturbance. These research results have been compared to other existing simulation and experimental work. The results proved to be better in output voltage, frequency, response time, and THD. Furthermore, the proposed schemes ensure power factor improvement, high efficiency, overall system PQ, and reliability at various load conditions.

Parametric studies on a stand-alone polygeneration microgrid with battery storage

Polygeneration Microgrids (PMG) can be configured to deliver multiple outputs such as, electricity, heat, cold, fuel (hydrogen) and clean water. In an earlier paper the authors presented an analysis of a PMG consisting of solar photovoltaic field, fuel cell, solid state hydrogen storage and electrolyzer using commercial software HOMER. Keeping in mind the fact that battery storage is preferred for stand-alone microgrids, in this paper, the influence of battery storage on the performance of a PMG is presented. An added advantage of solid state hydrogen storage – fuel cell system is the availability heat released during adsorption of metal hydride in addition to that rejected by the fuel cell. A comparison of battery alone versus battery + fuel cell is made.

Power management of hybrid energy storage system in a standalone DC microgrid

Abstract Standalone microgrids with renewable energy sources (like solar photovoltaic and wind systems) utilize energy storage devices (ESDs) to supply uninterrupted power to their system loads. To utilize the characteristic advantages of different ESDs, they are combined to form a hybrid energy storage system (HESS). Efficient control algorithms are necessary for power sharing among the multiple ESDs in a HESS to ensure maximum utilization of all the storage devices in the microgrid. Conventional fuzzy logic controllers (FLCs) are used to decide the power output of an ESD considering state of charge (SoC) of the fuzzy controlled ESD and the overall power demand (or availability) in the microgrid. However in a standalone DC microgrid with multiple ESDs, such conventional FLC algorithms cause over or under utilization of the ESDs since the instantaneous SoC status of other ESDs are not considered in its control logic. Thus a novel adaptive FLC (AFLC) algorithm is proposed in this paper to dynamically change the controlling rules of the AFLC as per the average SoC of other ESDs of the microgrid. The performance of the proposed AFLC algorithm is compared with the conventional FLC algorithm on the basis of duration of discharge, average power delivered and utilization factor of the ESDs in a DC microgrid using real time simulation study in OPAL RT 4510 simulator. The merits of using the AFLC for power sharing among multiple ESDs are further validated through experimental study performed on a microgrid hardware setup at Indian Institute of Technology Kharagpur, India.

Voltage unbalance compensation using new structure of decouple double synchronous reference frame in stand‐alone microgrids

In distribution networks, the voltage unbalance occurrence is inevitable. The voltage unbalance can have negative impacts on the customer equipment and the network performance if it exceeds the permissible limit. This study proposes a novel control strategy to compensate for the voltage unbalance in stand-alone microgrids. The proposed control method applies to the inverter-interfaced distributed generation units. The suggested control strategy is based on the decouple double synchronous reference frame (DDSRF) that is modified to improve its effectiveness. The modified DDSRF can effectively decouple the positive and negative sequence components. The simulation results depict that the proposed control strategy provides faster dynamic response and more effective voltage unbalance compensation comparing to the DSRF-based control method.

Integrated approach for optimal techno-economic planning for high renewable energy-based isolated microgrid considering cost of energy storage and demand response strategies

To realize an efficient energy supply system for an isolated microgrid, a joint design framework that considered the capacity sizing alongside operational planning is essential. In this work, an integrated planning model was developed to investigate the techno-economic performances of a high renewable energy-based standalone microgrid. The approach combines capacity sizing and operation scheduling, considering demand-side management strategies for different system design scenarios. The evaluated scenarios involved the combination of wind turbine, photovoltaic system, diesel generator, with either battery energy storage or pumped thermal energy storage. A demand response program based on instantaneous renewable energy availability is proposed with dynamic pricing economic model for improving the overall system flexibility. Mixed-integer linear programming algorithm on MATLAB® is deployed as the optimization solver. The minimization of the sum of system costs which includes equivalent annual costs of the investments, running costs and costs based on demand-side management strategies is the objective function. The combination of photovoltaic, wind turbine and pumped thermal energy storage is found to be the most techno-economically efficient system configuration for the considered microgrid. More so, the proposed demand response strategy minimizes the mismatch between the generation and the load demand profile effectively, thereby increasing the system flexibility.

Integrated Modelling and Enhanced Utilization of Power-to-Ammonia for High Renewable Penetrated Multi-Energy Systems

This paper proposes an integrated model of power-to-ammonia (P2A) to exploit the inherent operational dispatchability of nitrogen-ammonia (N2-NH3) cycles for high-renewable multi-energy systems. In this model, the steady-state electrolytic processis mathematically formulated into a thermodynamic system based on thermo-electrochemical effects, and the long-term degradation process of P2A is transformed as the short-term degradation cost to characterize its cost-efficiency. Furthermore, the enhanced utilization of P2A is explored to form a renewable energy hubfor coupled multi-energy supplies, and a coupling matrix is formulated for the optimal synergies of electrical, ammonia and thermal energy carriers. An iterative solution approach is furtherdeveloped to schedule the hub-internal multi-energy conversion and storage devices for high-efficiency utilization of available hybrid solar-wind renewables. Numerical studies on a stand-alone microgrid over a 24-hour scheduling periods are presented to confirm the effectiveness and superiority of the proposed methodology over regularbattery and power-to-gas (P2G) storages on system operational economy and renewable energy accommodation.

Optimal Design of a Stand-Alone Residential Hybrid Microgrid System for Enhancing Renewable Energy Deployment in Japan

This paper aims at the optimal designing of a stand-alone microgrid (PV/wind/battery/diesel) system, which can be utilized to meet the demand load requirements of a small residential area in Kasuga City, Fukuoka. The simulation part is developed to estimate the electrical power generated by each component, taking into account the variation of the weather parameters, such as wind, solar irradiation, and ambient temperature. The optimal system design is then based on the Particle Swarm Optimization (PSO) method to find the optimal configuration of the proposed system, using the least-cost perspective approach.