Integration Of Microgrids Research Articles

TSFLC based DC link voltage regulation of grid connected DC micro grid

Integration of micro grid with utility power network has major concerns such as active power control and maintaining desired power quality (PQ) standards. Among several power quality issues, voltage dip and harmonics are critical concerns impacting the overall performance and stability of system. In this paper, a grid connected DC micro grid (DCMG) is designed and controlled to ensure requisite power allocation between the micro-grid and utility grid system vis-a-vis DC link voltage regulation, load balancing and harmonic elimination. The utility grid and DCMG system are interfaced via voltage source converter (VSC). The DC link voltage of VSC is regulated using Takagi-Sugeno fuzzy logic controller (TSFLC) based synchronous reference frame technique to compensate for the reactive power demanded by the load. In the proposed architecture, DCMG consists of 8 kW photovoltaic (PV) energy system with maximum power point tracking (MPPT), 6 kW wind energy generation system with MPPT, 3 kW fuel cell (FC) energy systems and a VSC interfaced to three phase utility grid. Further, the TSFLC is compared with conventional PI controller under different operating conditions. It has advantages over classical controller such as better performance under dynamics and can be expressed in the form of the exact linear function. The effectiveness of proposed control method is validated under MALAB/SIMULINK software under different loading conditions.

A Comprehensive Model of Data Center: From CPU to Cooling Tower

Aiming at addressing environmental challenges, large data centers, such as Facebook, Google, and Yahoo, are increasing share of green power in their daily energy consumption. Such trends drive research into new directions, e.g., sustainable data centers. The research often relies on expressive models that provide sufficient details, however, practical to re-use and expand. There is a lack of available data center models that capture internal operating states of the facility from the CPU to the cooling tower. It is a challenge to develop a model that allows to describe complete data center of any scale including its connection to the grid. This paper proposes such a model building on the existing work. The challenge was to put the pieces of data center together and model behavior of each element so that interdependencies between components and parameters and operating states are captured correctly and in sufficient details. The proposed model was used in the project “Data center microgrid integration” and proven to be adequate and important to support such study.

Hybrid Energy Storage System Microgrids Integration for Power Quality Improvement Using Four-Leg Three-Level NPC Inverter and Second-Order Sliding Mode Control

Rising demand for distributed generation based on renewable energy sources (RES) has led to several issues in the operation of utility grids. The microgrid is a promising solution to solve these problems. A dedicated energy storage system could contribute to a better integration of RES into the microgrid by smoothing the renewable resource's intermittency, improving the quality of the injected power and enabling additional services like voltage and frequency regulation. However, due to energy/power technological limitations, it is often necessary to use hybrid energy storage systems (HESS). In this paper, a second-order sliding mode controller is proposed for the power flow control of a HESS, using a four-leg three-level neutral-point-clamped (4-Leg 3L-NPC) inverter as the only interface between the RES/HESS and the microgrid. A 3-D space vector modulation and a sequence-decomposition-based ac-side control allow the inverter to work in unbalanced load conditions while maintaining a balanced ac voltage at the point of common coupling. DC current harmonics caused by unbalanced load and the NPC floating middle point voltage, together with the power division limits, are carefully addressed in this paper. The effectiveness of the proposed technique for the HESS power flow control is compared to a classical PI control scheme and is proven through simulations and experimentally using a 4-Leg 3L-NPC prototype on a test bench.

Optimal Control of Active Power of Two Micro-grids Interconnected with Two AC Tie-Lines

Active power balance and frequency control are important tasks in the daily management of a power system. With the integration of several microgrids in the modern power system, the balancing of sources of energy has become a major concern for electrical power engineers and researchers worldwide. New power systems require more flexibility in optimization and control design to ensure their ability to maintain the balance between generation and load of the system. The present paper discusses an optimal control design for minimization of the power flow in tie-lines and frequency deviations in the microgrid, which will lead to power balance between the generation and load demand of the system. The system being studied consists of two microgrids, each made up of a wind farm, conventional power system (large hydro or thermal plant), photovoltaic system, battery energy storage system and the system load. Optimal control theory is applied to control the power flow between two microgrids. The Matlab environment is used for simulations.

Economic and emission-saving benefits of utilizing demand response and distributed renewables in microgrids

The authors present several scenarios of demand response actions based on adjustments to a building’s temperature management system in combination with renewable DER integration in microgrids. Economic benefits from $9,000 to $167,000 appear possible when implementing demand response in a microgrid of 30 to 50 additional buildings. The scenarios also demonstrate the potential emission-saving effects of demand response at the grid level.

Optimal voltage regulation for distribution networks with multi-microgrids

With the increasing penetration of renewables, microgrid integration has been considered as one of the most promising approaches to enhance the utilizations of various types of energy resources in smart distribution systems. In the near future, with the higher levels of intermittent renewables are envisaged, the distribution network operators will face significant challenges to the control and operation of distribution networks dispersedly. Consequently, the development of effective and motivating ancillary service schemes in a decentralized way for executing real-time control and reducing calculation and communication burden is still in its infancy and needs to be researched. To address this issue, this paper explores an optimal voltage regulation method with the participants of multi-microgrids based on multiple agent systems. Without an arbitration agent, peer agents in the multiple agent system calculate voltage sensitivities by local and neighbourhood measurements only. In this paper, a bi-level game model is proposed for voltage control process. In the upper-level, the distribution network operator searches the reasonable incentive mechanism based on the Stackelberg game. In the lower-level, microgrids make voltage control strategies autonomously based on a static game among microgrids. In the proposed method, microgrids participate in voltage control in distribution networks as ancillary service providers while maximizing their own profits. Meanwhile, the distribution network operator reduces the infrastructure reinforcement and avoids unnecessary renewable energy curtailment. Finally, the feasibility and effectiveness of the proposed method has been demonstrated on a modified IEEE 33-bus system.

Integration of DC Microgrids as Virtual Synchronous Machines Into the AC Grid

A smart and autonomous integration concept for dc microgrids into the legacy ac grid is proposed based on the virtual synchronous machine (VSM) concept. It utilizes a dc–ac converter as a universal VSM-based interface (VSMBI) between the ac grid and various distributed energy resources (DER) connected on the dc side. The control strategy of it includes: 1) a frequency regulation improved from previous VSM works, which is suitable for the microgrid integration; 2) an improved dual droop control between the ac frequency and the dc side energy storages; 3) a power system stabilizer to enhance the system stability. Under this concept, the VSMBI integrates the DERs, loads and energy storages in the dc microgrid into a VSM. The VSMBI and the dc microgrid together will respond to short-term and long-term requirements of the grid frequency regulation, and achieve autonomous power management for the ac grid and the dc microgrid. It is therefore an important step forward in supporting high DER penetration. The concept, its design and small-signal analysis are presented in this paper. Its effectiveness and functions are verified by simulation and experimental results.

Genetic Algorithm-based Modeling of PEM Fuel Cells Suitable for Integration in DC Microgrids

Operating conditions such as temperature and pressure affect the fuel cell performance. Proton Exchange Membrane (PEM) fuel cells work at its maximum efficiency when it is operated within temperature limits. To improve the heat transfer properties of PEM fuel cells, nano coolants are added. Identification of a suitable combination of thermal conductivity, relative humidity, and parametric coefficients for performance assessment of PEM fuel cells in real time is mandatory. Conventional methods follow complex computations and trial and error procedure to model fuel cell without thermal management parameters. Hence, in this paper, the objective of parameter set identification is framed as an optimization problem and solved using Genetic Algorithm method. The performance of the proposed approach is evaluated for different test conditions and validated through simulation findings.

A Micro grid design for a kind of household energy efficiency management system based on high permeability

After the access of household distributed photovoltaic, conditions of high permeability generally occur, which cut off the connection between distributed power supply and major network rapidly and use energy storage device to realize electrical energy storage. The above operations cannot be adequate for the power grid health after distributed power supply access any more from the perspective of economy and rationality. This paper uses the integration between device and device, integration between device and system and integration between system and system of household microgrid and household energy efficiency management, to design household microgrid building program and operation strategy containing household energy efficiency management, to achieve efficient integration of household energy efficiency management and household microgrid, to effectively solve problems of high permeability of household distributed power supply and so on.

A Game-Theoretic Framework for Resilient and Distributed Generation Control of Renewable Energies in Microgrids

The integration of microgrids that depend on the renewable distributed energy resources with the current power systems is a critical issue in the smart grid. In this paper, we propose a non-cooperative game-theoretic framework to study the strategic behavior of distributed microgrids that generate renewable energies and characterize the power generation solutions by using the Nash equilibrium concept. Our framework not only incorporates economic factors but also takes into account the stability and efficiency of the microgrids, including the power flow constraints and voltage angle regulations. We develop two decentralized update schemes for microgrids and show their convergence to a unique Nash equilibrium. Also, we propose a novel fully distributed PMU-enabled algorithm which only needs the information of voltage angle at the bus. To show the resiliency of the distributed algorithm, we introduce two failure models of the smart grid. Case studies based on the IEEE 14-bus system are used to corroborate the effectiveness and resiliency of the proposed algorithms.

Using microgrids to enhance energy security and resilience

Although microgrids are now widely studied, challenges still exist. A reliable control architecture needs to be developed to coordinate different devices. Advanced forecasting and demand response management approaches should be implemented to cope with the intermittence of renewable generation. Moreover, interconnection issues should be further studied to eliminate the influence of microgrid integration and achieve coordinated operation throughout the system.

Integration of SOFC/GT hybrid systems in Micro-Grids

SOFC/GT hybrid systems (HS) thanks to their high performance, in term of efficiency, emissions and fuel flexibility can represent a remarkable solution for Micro-Grids power range.In particular, due to the synergistic effect of using a high temperature fuel cell such as Solid Oxide Fuel Cell (SOFC) and a recuperative gas turbine (GT), the integrated system efficiency and flexibility can be significantly increased during load following operation.Specifically, the goal of this paper is to demonstrate the enhanced flexibility of the hybrid plant obtained through the development of a suitable main control strategy to regulate both GT and SOFC, following a daily load demand typical of a Micro-Grid. In particular, in the model, thanks to the implemented thermal SOFC management, also SOFC takes part to the partialization process.In this way, the developed model permits to guarantee high HS efficiency performance (54.5% mean efficiency on daily basis), short time response and a wide part-load degree (up to 42.8% of nominal HS power), proving the feasibility of SOFC/GT hybrid system integration in Micro-Grids.

A dynamic model for generation expansion planning based on Conditional Value-at-Risk theory under Low-Carbon Economy

Realizing low-carbon development of power system is one of the most urgent issues among power industry, especially under the era of Low-Carbon Economy. Generation expansion planning (GEP) plays a key role in reducing carbon emission. In this paper, after revealing the impact of uncertainties on GEP, simulating the uncertainties of fuel price, carbon dioxide (CO2) emission reduction technology and carbon price, considering high grid integration of micro-grids, a dynamic model for GEP based on Conditional Value-at-Risk theory is proposed. On the basis of traditional GEP, the model analyzes the investment decisions which are made by generation company in different risk scenarios and considers the constraint of the risk of uncertainties. An actual case is studied based on a provincial grid in China by applying the proposed model, and the results prove it to be more adaptable and effective for the sustainable development of future power system.

Integration of Plug-in Electric Vehicles Into Microgrids as Energy and Reactive Power Providers in Market Environment

The concept of electricity markets in the deregulated environment generally refers to energy market and reactive power market is not paid attention as much as it deserves to. However, reactive power plays an important role in distribution networks to improve network conditions such as voltage profile improvement and loss reduction. Plug-in electric vehicles (PEVs) are mobile sources of active and reactive power, capable of being participated in energy market, and also in reactive power market without battery degradation. Active and reactive powers are coupled through the ac power flow equations and branch loading limits, as well as PEVs and synchronous generators capability curves. This paper presents a coupled energy and reactive power market in the presence of PEVs. The objective function is threefold, namely offers cost (for energy market), total payment function (for reactive power market), and lost opportunity cost, all to be minimized. The effectiveness of the proposed coupled energy and reactive power market is studied based on a 134-node microgrid with and without PEV participation.

A Hierarchical Electricity Market Structure for the Smart Grid Paradigm

This paper proposed a hierarchical structure for the electricity market to facilitate the coordination of energy markets in distribution and transmission networks. The proposed market structure enables the integration of microgrids, which provide energy and ancillary services in distribution networks. In the proposed hierarchical structure, microgrids participate in the energy market at the distribution networks settled by the distribution network operator (DNO), and load aggregators (LAs) interact with microgrids and generation companies (GENCOs) to import/export energy to/from the distribution network electricity markets from/to the wholesale electricity market. The proposed approach addressed the synergy of energy markets by introducing dynamic game with complete information for GENCOs, microgrids, and LAs. The proposed hierarchical competition is composed of bi-level optimization problems in which the respective upper-level problems maximize the individual market participants’ payoff, and the lower-level problems represent the market settlement accomplished by the DNO or the independent system operator. The bi-level problems are solved by developing sensitivity functions for market participants’ payoff with respect to their bidding strategies. A case study is employed to illustrate the effectiveness of the proposed approach.

Sizing and control of a Solid Oxide Fuel Cell/Gas microTurbine hybrid power system using a unique inverter for rural microgrid integration

MicroGrids (MGs) are one of the most useful and efficient ways to integrate renewable energy technologies in rural areas. In these areas, the biogas produced by transformation of organic waste can be electrically valorized in a MG using a Hybrid Power System (HPS) based on a Solid Oxide Fuel Cell (SOFC) and a Gas microTurbine (GT), in order to obtain a high electrical efficiency. In this study, in order to keep the best efficiency while ensuring a safe operation, the HPS is controlled using a single Three-Level Neutral Point Clamped (3LNPC) inverter. After sizing the hybrid system, digital robust R-S-T type controllers are designed to regulate the SOFC power in the DC side of the inverter and the voltage and frequency in the AC side, in an islanded MG. Then, the feasibility and the performance of the 3LNPC inverter together with the associated controllers are evaluated in simulation and experimentally using a SOFC/GT emulator.

The Stochastic Bidding Strategy of Micro grid for Participation in Energy and Ancillary Services

Typically, micro-grid is considered as an effective way to integration of distributed generations. However, in the deregulated environment integration of micro-grid in power system should be further considered. In this paper, a stochastic bidding strategy of joint market for the energy and spinning reserve services markets, with taking into account of the uncertainties of renewable distributed generation output power, load and electricity market prices to maximize the profits of micro-grid, is recommended. The bidding strategy is modeled as an optimization problem and is divided into two stages. First the predictions for uncertainties was carried out by using Adaptive Neural Fuzzy Inference System(ANFIS) and according to the forecast errors and Latin Hyperbolic Sampling (LHS) method, scenarios for micro-grid produced and these scenarios is reduced by using backward scenario reducing. In the second stage, according to the generated scenarios in the previous stage, the profit of micro-grid bidding including the revenue of micro-grid bidding, operation and imbalance costs is optimized by genetic algorithm. In the end, micro-grid bids is sent to market. The effectiveness of the proposed method is discussed on a sample micro-grid and results show the effectiveness of the proposed method.

A control plan for the stable operation of microgrids during grid-connected and islanded modes

This paper presents a control technique that enhances microgrids stability during the grid-connected and islanded modes. The proposed technique is compared with several existing control strategies in the context of microgrids integration into smart grids. The Lyapunov control theory is utilized in this paper to investigate the operation stability of DG units operating along with the utility grid. As the main contribution, the proposed technique compensates for the instantaneous variations of the reference current components of DG units in the ac-side of the converters. The presented method also considers and properly addresses the dc-voltage variations in the dc-side of the interfacing system. Under the proposed control strategy, DG units are able to deliver active and reactive power to the local loads and/or the main grid in fundamental and harmonic frequencies, with a fast dynamic response and without any interruption. Several simulation scenarios are carried out to demonstrate effectiveness of the proposed control strategy in microgrids during the transient and steady-state operation.

그린에너지 자립섬을 위한 계통 독립형 마이크로그리드 모니터링 시스템 설계 및 구현

국내 섬지역의 전력 수급은 계통 연계가 어려워 일반적으로 디젤 발전기에 의존하고 있어 관리 비용이 매우 높다. 이러한 문제를 해결하기 위해 최근 계통 독립형 마이크로그리드 기술에 대한 연구 및 실증이 활발히 진행 중이다. 본 논문은 에너지 자립섬을 위한 계통 독립형 마이크로그리드 통합 모니터링 시스템을 제안한다. 먼저 태양광, 풍력, 디젤 발전설비, 송 배전망의 상태 및 부하, 그리고 에너지 저장 시스템의 모니터링을 위한 소프트웨어 시스템 아키텍처를 설계한 후 관리자가 쉽게 파악할 수 있는 모니터링 소프트웨어를 구현한다. 구현된 모니터링 소프트웨어는 발전설비의 상태 및 오류를 실시간으로 시각화함으로써 관리자의 신속한 의사 결정이 가능하다. In domestic island regions, the power supply generally depends on diesel generators due to difficulties of grid connection. To solve this issue, recently, the study on the stand-alone microgrid technology and its test are being actively conducted. In this paper, we propose the stand-alone microgrid integration monitoring system for energy independence island. First, we design the software architecture for monitoring of solar, wind, diesel power generation facilities, transmission and distribution of grid network, and energy storage system. Then, we implement the monitoring software that allows administrators to identify and run the monitoring software easily.

Efficient Energy Management in Smart Micro-Grids: ZERO Grid Impact Buildings

In a smart micro-grid (MG) each generator or load has to take part in the network management, joining in reactive power supply/voltage control, active power supply/frequency control, fault ride-through capability, and power quality control. This paper includes a new concept for building integration in MGs with zero grid-impact so improving the MG efficiency. These aims are shown to be achievable with an intelligent system, based on a dc/ac converter connected to the building point of coupling with the main grid. This system can provide active and reactive power services also including a dc link where storage, generation, and loads can be installed. The system employed for validation is a prototype available at ENEA Laboratories (Italian National Agency for New Technologies). A complete and versatile model in MATLAB/SIMULINK is also presented. The simulations results and the experimental test validation are included. The trial confirms the model goodness and the system usefulness in MG applications.