Grid-connected Microgrid System Research Articles

Hybrid PV-Wind System With Power Quality Improvement Using PV-DVR

Owing to the rapid growth of Renewable Energy Sources, Microgrid finds greater significance in satisfying consumer need in today’s world. However, the increased number of Distributed Energy Resources might introduce power quality issues in a grid connected microgrid system due to the intermittent nature of such natural resources and power electronic converters associated with their conversion. So as to compensate such power quality issues, this paper proposes a Custom Power Device (CPD) namely Photovoltaic -Dynamic Voltage Restorer (PV-DVR), which uses a PV as a source for the Battery Energy Storage System (BESS). A PMSG driven PV Microgrid system with a MPPT controller for maximum power extraction from PV source and a hysteresis controller for effective grid synchronization and lesser harmonic distortion is taken for analysis. The dynamic performance of the grid connected microgrid system with DVR is analyzed for various loads and different power quality issues like voltage sag/swell, harmonics, interruption etc. Wavelet Transform based switching controller is used to detect the power quality event occurring and operate the PV-DVR accordingly.

Event-triggered model predictive control for grid-connected three-phase inverter

With advantage of dealing with various nonlinear system, model predictive control (MPC) strategy has been applied commonly in power system, however, there is a large computation burden in the traditional MPC strategy. To overcome the shortcoming of MPC, this paper implements event triggered model predictive control (ET-MPC) strategy in grid-connected microgrid system (GMS), which activates MPC once the triggered condition is satisfied; otherwise MPC operation will be stopped. Therefore, it helps to reduce online calculation amount and switching action greatly. To verify the feasibility and superiority of the proposed ET-MPC strategy applied in GMS, the corresponding simulation studies have been conducted in Matlab/Simulink. The various simulation and comparison results, demonstrate the effectiveness of proposed ET-MPC strategy for the GMS.

Techno-Economic Feasibility Analysis of Grid-Connected Microgrid Design by Using a Modified Multi-Strategy Fusion Artificial Bee Colony Algorithm

The present work investigates the techno-economic solution that can address the problem of rural electrification. To maintain a continuous power supply to this village area, a grid-connected microgrid system was designed that consists of solar photovoltaic (SPV) and battery energy storage systems (BESS). The recently introduced multi-strategy fusion artificial bee colony (MFABC) algorithm was hybridized with the simulated annealing approach and is referred to as the MFABC+ algorithm. This was employed to determine the optimal sizing of different components comprising the integrated system as well as to maximize the techno-economic objectives. For validation, the simulation results obtained by the MFABC+ algorithm are compared with the results obtained using HOMER software, the particle swarm optimization algorithms and the original MFABC algorithm. It was revealed that the MFABC+ algorithm has a better convergence rate and the potential ability to provide compromising results in comparison to these existing optimization tools. It was also discovered through the comprehensive evaluation that the proposed system has the potential capability to meet the electricity demand of the village for 24 × 7 at the lowest levelized cost of electricity.

Operational Cost Minimization of Grid Connected Microgrid System Using Fire Fly Technique

Present time, green energy sources interfacing to the utility grid by utilizing microgrid system is very vital to satisfy the ever increasing energy demand. Optimal operation of the microgrid system improved the generation from the distributed renewable energy sources at the lowest operational cost. Large amount of constraints and variables are associated with the microgrid economic operation problem. Thus, this problem is very complex and required efficient technique for handing the problem adequately. Therefore, this research utilized the efficient fire fly optimization technique for solving the formulated microgrid operation control problem. Fire fly algorithm is based on the behavior and nature of the fire flies. A microgrid system modelling which incorporated various distributed energy sources such as solar photo voltaic, wind turbine, micro turbine, fuel cell, diesel generator, electric vehicle technology, battery energy storage system and demands. Energy storage system is utilized in this research for supporting renewable energy sources’ integration in more reliable and qualitative way. Further, the electric vehicle technology i.e. battery electric vehicle, plug-in hybrid electric vehicle and fuel cell electric vehicle are utilized to support the microgrid and utility grid systems with respect to variable demands. Optimal operational cost minimization problem of the developed microgrid system is solved by fire fly algorithm and compared with the grey wolf optimization and particle swarm optimization techniques. By comparative analysis it is clear that the fire fly algorithm provides the minimum operational cost of microgrid system as compared to the GWO and PSO. MATLAB software is utilized to model the microgrid system and implementation of the optimization techniques.

A hybrid RFCRO approach for the energy management of the grid connected microgrid system

A hybrid <scp>RFCRO</scp> approach for the energy management of the grid connected microgrid system

Seamless Transition in Grid-connected Microgrid System using Proportional Resonant Controller

In this paper, the design of an inverter control structure based on the Proportional Resonant (PR) controller is dealt with in detail for attaining smooth transitions between the operating modes of a grid- connected microgrid system. The control strategy applied for the inverter is cascaded three-loop control viz., the grid current, voltage across the load, and the inverter output current loops. The inverter control is mainly focused to retain the voltage magnitude within the prescribed set limits and to have a good quality of the voltage across the load under all the modes of operation. A proportional resonant controller is designed by considering the transients and stability criteria into account under varying modes of operation. The design procedure of the Proportional resonant controller is given in detail. The three-phase grid-connected microgrid system considered under study is simulated in MATLAB/Simulink environment to operate under islanding condition as well as grid-connected condition and also changing modes from islanding to grid connected and vice versa. The simulation results are presented under various modes of operation to validate the controller design for a smooth transition between the modes of operation.

Control strategies for seamless transfer between the grid-connected and islanded modes of a microgrid system

Design of control strategies for Distributed generation systems is very important to achieve smoother transition between the grid connected and islanding modes of operation. The transition between these two modes of operation should be seamless, without any severe transients during the changeover. In this paper, two different control strategies namely inverter output current control and indirect grid current control for the seamless transfer between the modes of operation has been explored for the suitability. The design and analysis of the cascaded control loops based on Proportional Integral (PI) controller has been dealt in detail for both inverter output current control and indirect grid current control strategy. Control parameters are designed using the control system toolbox in MATLAB. A 10kW grid connected microgrid system has been designed and simulated in MATLAB/Simulink and the results are presented under grid connected operation, islanding operation and the transition between the modes considering fault condition in the grid side. The simulation studies are carried out using both the control strategies and the results are presented to validate the design methodology.

A Hierarchical Coordinative Control Strategy for Solid State Transformer Based DC Microgrids

A solid state transformer (SST), as a kind of energy router in the Energy Internet, provides a unified access point for AC or DC distributed power subjects. However, the DC-link capacitors inside the SST will suffer huge voltage fluctuations when the output power of the microgrid changes dramatically. With respect to this problem, caused by the random and intermittent characteristics of distributed generation (DG), a hierarchical coordinative control strategy is proposed. Compared with the common independent control, the proposed method not only makes full use of the regulation capacity of super capacitors, but also enhances the dynamic power tracking speed and reduces the speed difference between different stages of an SST. The dynamic voltage response under the proposed method is analyzed in frequency domain and compared with the independent control. To validate the effectiveness of the coordinative control strategy, a simulation model of an SST-based grid-connected DC microgrid system is established, and the topology of the SST is improved. The voltage stability of the DC bus is compared under different control strategies, and the coordinative control strategy is also verified, effectively under transition conditions.

Management of Voltage Profile and Power Loss Minimization in a Grid-Connected Microgrid System Using Fuzzy-Based STATCOM Controller

The expansion of renewable energy is continuing powerfully. Electrical system ought to transmit power with diminished loss, improved power quality, and reliability while pleasing the need of customer’s load demand. Nevertheless, owing to the exhaustion of fossil fuels and their environmental impact, the availability of quality, stable, and reliable power in developing countries is worrying. Integrating a solar-wind based microgrid to the distribution network is the more feasible and best alternative solution to gratify the customer intensifying power demand while seeing the strict environmental regulations of generating power. However, the microgrid system connected in a distribution network has diverse problems and challenges. The problems comprise the development of voltage sag and swell, voltage unbalance, and power losses because of the intermittent nature of PV and wind resources. The objective of this study is to integrate microgrid system with STATCOM (static synchronous compensator) controller to ensure the higher power flow with enhanced voltage profile and reduced power loss. MATLAB/PSAT is used to model microgrid and STATCOM controller connected to the grid. Proportional integral (PI) and fuzzy logic controllers (FLC) are also applied to control the STATCOM. The effectiveness of STATCOM with microgrid integration is tested by connecting to the main distribution system using standard IEEE 30-bus system. Finally, it was observed that STATCOM raises the capacity of the distribution line and contributes to voltage profile improvements and power loss reduction.

Techno‐economic analysis of photovoltaic‐biomass‐based microgrid system for reliable rural electrification

Burning of crop residues aggravates already existing pollution caused by coal-based thermal power plants in most of the developing countries such as India. Crop residue consists mainly of organic compounds and can be efficiently utilized to produce biogas in a sustainable way through anaerobic digestion. This study proposes a microgrid (MG) system for the effective utilization of available renewable resources and reliable rural electrification. The detailed techno-economic analysis of the design of a solar and biomass-based MG system was performed. Two MG systems, namely, MG-A having photovoltaic (PV), biomass-based generating units, connected to an unreliable grid, and MG-B having PV, biomass, and battery units working in the isolated mode, were designed for reliable rural electrification. Different performance-assessment parameters such as generation responses, component cost, project feasibility, emissions, inflation rate, and fuel prices were taken into account during the investigation. This study concludes that a grid-connected MG system is more capable of providing reliable electricity with reduced energy costs than an islanded MG system. In addition, the proposed MG power system helps to mitigate pollutant emission into the atmosphere by effectively utilizing the abundant biomass resources.

A Hybrid PV-Battery System for ON-Grid and OFF-Grid Applications—Controller-In-Loop Simulation Validation

In remote locations such as villages, islands and hilly areas, there is a possibility of frequent power failures, voltage drops or power fluctuations due to grid-side faults. Grid-connected renewable energy systems or micro-grid systems are preferable for such remote locations to meet the local critical load requirements during grid-side failures. In renewable energy systems, solar photovoltaic (PV) power systems are accessible and hybrid PV-battery systems or energy storage systems (ESS) are more capable of providing uninterruptible power to the local critical loads during grid-side faults. This energy storage system also improves the system dynamics during power fluctuations. In present work, a PV-battery hybrid system with DC-side coupling is considered, and a power balancing control (PBC) is proposed to transfer the power to grid/load and the battery. In this system, a solar power conditioning system (PCS) acts as an interface across PV source, battery and the load/central grid. With the proposed PBC technique, the system can operate in following operational modes: (a) PCS can be able to work in grid-connected mode during regular operation; (b) PCS can be able to charge the batteries and (c) PCS can be able to operate in standalone mode during grid side faults and deliver power to the local loads. The proposed controls are explained, and the system response during transient and steady-state conditions is described. With the help of controller-in-loop simulation results, the proposed power balancing controls are validated, for both off-grid and on-grid conditions.

Multi-objective economic dispatch of a microgrid considering electric vehicle and transferable load

In order to investigate the impact of electric vehicles’ charging-discharging behaviour and demand side response resources on the economic operation of photovoltaic grid-connected microgrid system, a multi-objective model of microgrid economic dispatching with electric vehicles, transferable load and other distributed generations (diesel engines and energy storage unit) is proposed in this paper. The model takes the comprehensive operating cost of microgrid, the utilization rate of photovoltaic energy and the power fluctuation between the microgrid and main grid as objectives. Moreover, four different cases of microgrid economic dispatch considering electric vehicles and transferable load are put forward, which are electric vehicles’ orderly charging and discharging and transferable load participating in demand response in Case 1, electric vehicles’ charging randomly and the transferable load participating in demand response in Case 2, electric vehicles orderly charging and discharging and transferable load not participating in demand response in Case 3, electric vehicles’ charging randomly and the transferable load not participating in the demand response in Case 4. Multi-objective Seeker Optimization Algorithm and the method of fuzzy membership function are applied in this study to obtain the optimal results. The simulation analysis shows that the orderly charging-discharging behaviour of electric vehicles and the participation of transferable load can effectively improve the economic costs, efficiency and security of microgrid economic operation.

Optimal Siting and Sizing of Grid-Connected Microgrid System for an Educational Institution Using HOMER Software

This paper analyses the sizing of PV system installation in a selected location for optimal operation using Hybrid Optimization Model for Electric Renewable, HOMER software. The main objective is to reduce the total net present cost (NPC) and the size of the system. A grid-connected mode of operation is considered in which the main grid is used as a backup power system. The hourly real-time electric load demands, monthly temperature, and solar irradiance data are collected and used as input for the analysis. A centralized and distributed type of load demand is compared and found the optimal solution which gives the optimal size and costs of the system.

A Comprehensive Review of Hybrid Energy Storage Systems: Converter Topologies, Control Strategies and Future Prospects

The ever increasing trend of renewable energy sources (RES) into the power system has increased the uncertainty in the operation and control of power system. The vulnerability of RES towards the unforeseeable variation of meteorological conditions demands additional resources to support. In such instance, energy storage systems (ESS) are inevitable as they are one among the various resources to support RES penetration. However, ESS has limited ability to fulfil all the requirements of a certain application. So, hybridization of multiple ESS to form a composite ESS is a potential solution. While integrating these different ESS, their power sharing control plays a crucial role to exploit the complementary characteristics of each other. Therefore, this article attempts to bring the numerous control strategies proposed in the literature at one place. Various control techniques implemented for HESS are critically reviewed and the notable observations are tabulated for better insights. Furthermore, the control techniques are classified into broad categories and they are briefly discussed with their limitations. From the carried-out analysis, the challenges faced towards the implementation of HESS for standalone and grid connected microgrid systems are presented. Finally, the future directions are laid out for the researchers to carry out the research and implementation of HESS technologies. Overall, this article would serve as a thorough guide on various control techniques implemented for HESS including their features, limitations and real-time applications.

Impact of market prices on energy scheduling of microgrid operating with renewable energy sources and storage

In this paper, mathematical modeling of the grid-connected microgrid system having intermittent renewable energy resources along with the diesel generators operating to fulfill the system dynamic electrical and thermal demand has been presented. The generation intermittency of the solar and wind renewable distributed generators and the dynamic load variations can be taken care of by installing the quick response based optimal sized energy storage system as the main component of the microgrid system. The charging and discharging operations of the battery storage system depend upon the operating constraint and the market prices for the power exchange between the microgrid and the grid. Minimum charging and discharging constraints in the battery-operated microgrid systems increase the life span of the storage system working as an essential part of the system having intermittent resources. The simulation results show the impact of the market prices on the state of charge of the storage system and the optimal operation of a microgrid system operating under various constraints.

MPC-based frequency control strategy with a dynamic energy interaction scheme for the grid-connected microgrid system

In a microgrid system (MGS), effective frequency control strategies are extremely significant for maintaining the system frequency stabilization. Therefore, a model predicted control (MPC) method is presented to regulate the frequency fluctuation of the grid-connected microgrid system (GCMGS). The primary frequency control for the diesel generator (DG) and the secondary frequency control with the (MPC) for the energy storage (ES) are proposed in this paper. Simultaneously, in order to mitigate the power fluctuation caused by the load demand side and the renewable energy sources, a dynamic energy interaction scheme (DEIS) is designed. The power exchange between the MGS and utility grid can be achieved. Due to the randomness of the renewable energy sources, the system frequency is hard to remain stable. Thus, a constant constraint renewable energy sources power output is utilized to reduce the uncertainty of the renewable energy sources. Finally, several comparison experiments have been executed to illustrate the availability of the proposed control strategy.

An Efficient Technique-Based Distributed Energy Management for Hybrid MG System: A Hybrid RFCFA Technique

This paper presents an efficient hybrid approach-based energy management strategy for grid-connected microgrid (MG) system. The proposed hybrid technique is the combination of both random forest (RF) and cuttlefish algorithm (CFA) named as RFCFA. The proposed hybrid technique is utilized to decrease the electricity cost and increase the power flow between the source and load side. The MG system is tracked by the RF technique. The CFA is optimized based on the MG with the predicted load demand. MG employs two energy management strategies to reduce the impact of renewable energy prediction errors. The first strategy seeks at minimizing electricity costs during MG’s operation. And the second strategy is aimed at balancing the power flow and reducing forecast error effects. In the grid-connected MG system, the objective function of the proposed technique is characterized with the inclusion of fuel cost, grid power variation, operation and maintenance cost. Battery energy storage systems (BESSs) can stabilize the output power and allow renewable power system units to operate at stable rate of output power. The proposed hybrid technique is executed in the working platform of MATLAB/Simulink, and the execution is evaluated using existing techniques such as GA, CFA and RBFNBBMO.

Optimal energy management strategy in microgrids with mixed energy resources and energy storage system

The continued growth of distributed generation (DG) in the electrical grid has led to the expansion of microgrids. Microgrids contain distributed power generation units, energy storage devices, and controllable loads with the capability to operate in both grid-connected and island modes. The economic operation of a microgrid is achieved through an energy management system that optimally schedules DGs and storage devices and continuously balances supply and demand. In this study, a formulation of optimal unit commitment (UC) and dispatch scheduling of DGs in a grid-connected microgrid system is presented. Mixed-integer linear programming is used to implement the optimal UC and dispatch scheduling model. The objective is to minimise the overall operating cost of the system by optimally utilising an energy storage device and a combined heat and power (CHP) generation unit using load and renewable energy generation prediction. Operational constraints such as generation limits of DGs, battery charging/discharging limits and state-of-charge limits are to be satisfied during all intervals of operation. Simulation results indicate that the operational cost of the system is significantly reduced through optimal scheduling of an energy storage system and a CHP unit using the proposed strategy.

Techno-economic evaluation of a grid-connected microgrid system

ABSTRACTThe availability of solar resources has led to the utilization of photovoltaic (PV) system for the generation of a clean electricity and reduction of greenhouse gas (GHG) emissions. The techno-economic assessment of a medium scale microgrid system is investigated in this work by utilizing some key performance indicators (KPIs). These KPIs are used as the benchmarks to study the economic impacts of PV in the grid-connected power system for 10 selected locations across the nine provinces of South Africa. The HOMER package is utilized in the study to obtain viable solutions that will mitigate the undesirable technical and economic issues that come up during the grid integration. The research work is carried out by utilizing the surface meteorology and solar energy data provided by the National Aeronautics and Space Administration (NASA) for assessment of the proposed microgrid system. The outcomes of the study show that the annual average daily radiation varies from 4.3 kWh/m2/day in Durban to 5.749617 kWh/m2/day in De Aar. It is deduced from the work that De Aar is the most feasible location among the 10 selected sites for the installation of PV in terms of cost of energy (COE), net present cost (NPC), net energy purchased, energy purchased, energy sold, energy charge, annual utility bill savings and revenue with the following values: 0.181 R/kWh, R 219244.90, 3676 kWh, 32979 kWh, 29303 kWh, R7942.9891, R62473.0109, and R22759.6401. The outcomes of the research work indicate that exploitation of solar resources is an efficient means of accomplishing sustainable energy development.

Optimal Configuration of Island Microgrid Considering Wind/Photovoltaic/Line/Storage and Seawater Desalination Load

Safe and reliable power supply is the basic guarantee for the development and construction of the island. Aimed at the problem of lack of electricity and water on the island, the paper proposes an optimal configuration method of island microgrid considering wind/photovoltaic/line/storage and seawater desalination loads. Firstly, the paper analyzes the load demand and the characteristics of renewable resources on the island, and proposes a grid-connected island microgrid system with multiple energy types and seawater desalination load. On this basis, an optimization model with the minimum annual cost as the objective function is established. The mixed integer linear programming(MILP) algorithm is used to optimize the capacity configuration and operation mode of the island microgrid system simultaneously. Finally, taking an island in the eastern coast of China as an example, the effectiveness of the optimal configuration method is verified through scenario analysis.