Microgrid Power System Research Articles

Optimal economic and environment operation of micro-grid power systems

In this paper, an advanced real-time energy management system is proposed in order to optimize micro-grid performance in a real-time operation. The proposed strategy of the management system capitalizes on the power of binary particle swarm optimization algorithm to minimize the energy cost and carbon dioxide and pollutant emissions while maximizing the power of the available renewable energy resources. Advanced real-time interface libraries are used to run the optimization code. The simulation results are considered for three different scenarios considering the complexity of the proposed problem. The proposed management system along with its control system is experimentally tested to validate the simulation results obtained from the optimization algorithm. The experimental results highlight the effectiveness of the proposed management system for micro-grids operation.

독립형 마이크로그리드 내 분산전원별 최적용량 결정 방법

In recent years, the power demand has been increasing steadily and the occurrence of maximum power demand has been moving from the summer season to the winter season in Korea. And since the control of electric power supply and demand is more important under those situations, a micro-grid system began to emerge as a keyword for the sTable operation of electric power system. A micro-gird power system is composed of various kinds of distributed generators(DG) such as small diesel generator, wind turbine, photo-voltaic generator and energy storage system(ESS). This paper introduces a method to determine the optimal capacities of the distributed generators which are installed in a stand-alone type of microgrid power system based on the fundamental proportion of diesel generator. At first, the fundamental proportion of diesel generator will be determined by changing from 0 to 50 percent. And then we will optimize the capacities of renewable energy resources and ESS according to load patterns. Lastly, after recalculating the capacity of ESS with consideration for SOC constraints, the optimal capacities of distributed generators will be decided.

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.

Power Quality Analysis in Microgrid: An Experimental Approach

Microgrid (MG) integrated with Distributed Generation (DG) provides several benefits like reliable, secure, and high efficient of energy supply, while minimizing power loss, deferring expansion of power distribution infrastructures, and reduced carbon emission of energy supply etc. to the communities. Despite of the several benefits, there are several challenges existing due to the integration of different characteristics and technology of DG sources in MG network. Power Quality (PQ) issue is one of the main technical challenges in MG power system. In order to provide improved PQ of energy supply, it is necessary to analyse and quantify the PQ level in MG network. This paper investigates the detail of PQ impacts in a real MG network carried out through an experimental analysis. Voltage and frequency variations/deviations are analysed in both on-grid and off-grid mode of MG operation at varying generation and varying load conditions. Similarly unbalance voltage and current level in neutral are estimated at unbalanced PV generation and uneven load distribution in MG network. Also current and voltage THD are estimated at different PV power level. Finally the results obtained from the analysis are compared to that of Australian network standard level.

An Integrated Security-Constrained Model-Based Dynamic Power Management Approach for Isolated Microgrids in All-Electric Ships

Isolated microgrid power systems are prone to large frequency and voltage deviations, since they have limited generation and finite inertia and may include pulse power loads and large proportion of dynamic loads. Thus, they require effective power management methods to operate optimally, while satisfying operating and security constraints. In this paper, a novel integrated security-constrained model-based power management approach is proposed for isolated microgrids in all-electric ships during the normal/alert operating state. The new power management method was formulated as a multi-objective optimal control problem. A method based on the Nondominated Sorting Genetic Algorithm II was developed to solve the problem. The developed integrated security-constrained power management approach was applied to a notional all-electric ship computer model. The simulation results, conducted in PSCAD, showed the effectiveness of the new power management method.

Thermal management and performance evaluation of a dual bi-directional, soft-switched IGBT-based inverter for the 1st autonomous microgrid power system in Taiwan under various operating conditions

The thermal management of the inverter system is of great importance since very high voltage/current will be switched intermittently and/or continuously and high temperature is excruciably detrimental to the service life of electronics, especially for the switching devices such as insulated gate bipolar transistor (IGBT). In this study, a newly developed dual bi-directional IGBT-based inverter in conjunction with autonomous microgrid system is investigated with particular focus on the thermal management and performance evaluation under various operation conditions. Locally enhanced heat transfer approach such as oblique orientation and heat dissipating materials are experimentally investigated. The studied inverter system is initially packaged by a galvanized steel plate (size 62 × 48 × 18 cm) and the switching power is set in the range of 0.5–3 kW. The module is operated at the switching and pulse frequencies of 60 Hz and 20 kHz, respectively. The adoption of heat dissipating material in either paste or film form had experimentally shown to possess the flexibility tailoring heat transfer performance locally. Experimental studies of heat dissipating film with various hotspot scenarios showed that the temperature difference can be appreciably reduced as much as 13.1 and 15.4 °C, respectively with facilitation of one- and two-layers of heat dissipating film. From the measurement results, the measured peak temperature is highly dominated by the thickness of heat dissipating film, showing the dominance of thickness-dependent thermal resistance and resultant heat accumulation phenomena.

Power Quality Analysis for PV Grid Connected System Using PSCAD/EMTDC

Power quality is the main concern in power distribution systems. Poor power quality could cause disturbance and financial losses to consumers. It may also cause electrical appliances to overheat, damage and operate in undesired regions. Other than that, power distribution components such as transformers could also experience core saturation and overheating to the winding. This paper investigates potential power quality issues in a photovoltaic-grid connected power system. A real-life power distribution system is first modelled in PSCAD and it is then integrated with a photovoltaic system to form a micro-grid power system. Several case studies are conducted to identify any potential power quality issues with the micro-grid power system. The simulation results shows that the micro-grid power system experiences various power quality issues, such as inrush current, power fluctuation, frequency fluctuation, harmonic distortion and low power factor.

Synchronization of Hybrid Microgrids with Communication Latency

A distributed cooperative control scheme is proposed in order to implement a distributed secondary control for hybrid lossy microgrids. The designed distributed control is able to synchronize the frequency of inverse-based distributed generators (DGs) and minisynchronous generators (MSGs/SGs) to the desired state with a virtual leader DG/SG (reference value) in a distribution switching network under the existence of time-varying communication delays. The secondary control stage selects suitable frequencies of each DG/SG such that they can be synchronized at the desired set point. Using the proposed algorithm, each DG/SG only needs to communicate with its neighboring DGs/SGs intermittently even if the communication networks are local, the topology is time-varying, and the communication delays may exist. Therefore, the failure of a single DG/SG will not produce the failing down of the whole system. Sufficient conditions on the requirements for the network connectivity and the delays boundedness which guarantees the stability and synchronization of the controlled hybrid lossy microgrid power systems are presented. The feasibility of the proposed control methodology is verified by the simulation of a given lossy microgrid test system.

Numerical inverse definite minimum time overcurrent relay for microgrid power system protection

Access of distributed generation gets complicated at the distribution level, and hence managing these systems effectively becomes highly challenging. Microgrids have been proposed as a way of integrating a large number of distributed renewable energy sources with a distribution system. They are low to medium voltage networks of small load clusters with distributed generation sources and storages. Microgrids can be operated in the islanded mode or the grid‐connected mode. If a microgrid is connected to the system, it is seen as a single aggregate load. One of the potential advantages of a microgrid is that it could provide more reliable supply to customers by islanding itself from the system in the event of a major disturbance. However, a major problem with microgrid implementation in islanded operation is designing a proper protection scheme. The fault currents for grid‐connected and islanded microgrids are significantly different. Additionally, high penetration of inverter‐connected distributed generation sources leads to conditions where no standard overcurrent protection method will work. Overcurrent protection is considered as the backbone of any protection strategy, especially in distribution systems. Distribution systems constitute the largest portion of the power system network, and therefore the diagnosis of faults in this system is a challenging task. Faults occurring in distribution systems will affect the reliability, security, and quality of a power system. Field‐processable gate array (FPGA) Xilinx Zynq‐based numerical overcurrent relay protection is provided to the microgrid that is operated in islanded mode. This results in faster discrimination and quicker isolation of the faulty section from the microgrid. This improves the reliability of the microgrid because the fault is rapidly diagnosed and isolated from the healthy part, thanks to the high‐speed operation of the 800‐MHz FPGA Xilinx Zynq‐based numerical overcurrent relay. This system is simulated using MATLAB Simulink SimPower system tool box and LabView software. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

CHP Microgrid Optimized Operation Based on Bacterial Foraging Optimization Algorithm

CHP system with Energy saving, environmental protection, economic and other characteristics,have good prospects for the development and application value.This paper directe a micro grid system consisted by photovoltaic cells, wind turbines, fuel cells, microturbines, auxiliary boilers, thermal energy storage systems and batteries and heat load and electrical load.Considering various distributed power generation costs, environmental costs and micro-grid equipment maintenance costs,To meet the constraints of micro-grid operation, optimization of the different micro-grid distributed power and energy storage system power output, make the system's total operating costs are minimized.This paper analyzes the economic and environmental of micro-grid optimal operation characteristics, given a model of CHP micro-grid.For the cost of power generation and emissions of different weights, using bacterial foraging optimization(BFO) algorithm,through a numerical example verified the Correctness and effectiveness of mathematical model and optimization algorithm .

An underfrequency load shedding scheme for islanded microgrids

The underfrequency load shedding scheme is an important protective schemes, responsible for maintaining frequency of power systems within permissible limits in case of severe power deficits and as such, its proper performance is of great interest. In microgirds, disconnecting/connecting power generation sources and loads result in variations in the system parameters. Moreover, the output power of some distributed energy resources such as photovoltaic/wind turbine generators, might change during load shedding process and consequently affect the performance. Hence, an underfrequency load shedding scheme is proposed here which is not only independent of the microgrid parameters, but also considers power generation variations during the process. A microgrid power system with several distributed energy resources is adopted to demonstrate the effectiveness of the proposed method.

Bidding strategy of microgrid with consideration of uncertainty for participating in power market

Microgrid is commonly regarded as an efficient way for integration of distributed generation (DG) in low voltage network. However, the integration method of microgrid in power system for maximum benefit needs to be further promoted. In this paper, a stochastic bidding strategy of microgrid in a joint day-ahead market of energy and spinning reserve service is proposed taking into account of uncertainty of renewable DG units’ output power and load. The stochastic bidding strategy is modeled as bi-level optimization problem and can be divided into two steps. First, Latin Hypercube Sampling (LHS) is utilized for generating microgrid uncertain net power scenarios according to day-ahead uncertain power scenario models, and then reduced by backward scenario reduction technique for less computation. Second, the upper level total bidding profit including bidding revenue, expected imbalance and operation cost is optimized by interior point algorithm in MATLAB for making optimal bids. The expected imbalance and operation cost is calculated by iteratively invoking lower level deterministic unit commitment under each microgrid uncertain net power scenario. The lower level deterministic unit commitment is coded and solved by mixed integer nonlinear programming (MINLP) solver DICOPT in GAMS. Finally, the optimal energy and spinning reserve bids are given by solving the bi-level bidding model. The model is applied to a modified typical low-voltage microgrid and the effectiveness and excellence of proposed strategy is proven by comparing simulation results with traditional deterministic bidding strategy.

A novel modification approach based on MTLBO algorithm for optimal management of renewable micro-grids in power systems

A novel modification approach based on MTLBO algorithm for optimal management of renewable micro-grids in power systems

A Verification of High-efficiency DC Micro-grid Power Systems with High-performance Power Converters and Energy Management Strategy

Abstract The DC-microgrid power system in the Nushima Island consists of highly efficient power converters with a high performance power controller and energy management scheme for regulating power flows. In this paper, the power converter architecture of the newly-developed DC micro grid system is described with the relevant control scheme, and its practical effectiveness is discussed from the aspect of renewable and sustainable energy utilization.

Power Planning Model of Microgrid Based on Minimizing the LCC Cost

The development of micro-grid technology provides power system a variety of forms, flexible ways of power supply schemes, but a lot of basic micro-grid operational problems are different from the traditional large power grids, which need to be studied specifically. This paper studies the power planning problem of micro-grid, namely to meets the system operational constraints, study how to optimize the micro-power configuration of micro-grid, so that the whole micro-grid life cycle cost is the smallest.

Design and Implementation of Microgrid SCADA Platform

Microgrid and traditional power system are different in terms of operation and control. SCADA reliability directly affects the operational control capacity of the microgrid. Based on the actual needs of the microgrid operation control and energy management, the author designed microgrid SCADA platform, including architecture, information exchange mechanism and data services, and then developed actual microgrid SCADA test platform. Through long-time test, the SCADA platform could achieve reliable microgrid operation and management.

A two-stage optimal planning and design method for combined cooling, heat and power microgrid system

In this paper, a two-stage optimal planning and design method for combined cooling, heat and power (CCHP) microgrid system was presented. The optimal objective was to simultaneously minimize the total net present cost and carbon dioxide emission in life circle. On the first stage, multi-objective genetic algorithm based on non-dominated sorting genetic algorithm-II (NSGA-II) was applied to solve the optimal design problem including the optimization of equipment type and capacity. On the second stage, mixed-integer linear programming (MILP) algorithm was used to solve the optimal dispatch problem. The approach was applied to a typical CCHP microgrid system in a hospital as a case study, and the effectiveness of the proposed method was verified.

Research of Micro-Grid Power System Grounding and RCD for Energy Saving

After a large number of micro-grid power has been accessed to energy saving, the system would bring new challenges to the power distribution network in planning, design and construction. RCD directly related to the safety of persons and equipment. This article describes the commonly type of grounding protection, and analyze their respective advantages and disadvantages of the structure and characteristics of the micro-grid power supply system, the structure and characteristics of the ground type in the micro-grid power supply system were studied, the choice of RCD were focused on.

Transient Power Flow in Micro grids with Signal Stability Energy

In micro grids the power management is obtained by energy storage. These changes are being driven from both the demand side where. higher energy availability and efficiency are desired, and from the supply side where the integration of distributed generation and peak-shaving technologies must be accommodated. Distribution systems possessing distributed generation and controllable loads with the ability to operate in both grid-connected and standalone modes are an important class of the so-called Microgrid power system. In this propose work the energy storage capacity varies and raised between the voltage limits, current limits and stability across the power limits. Keywords: Distributed Generator(DG), transient power flow (TPG), smart grid.

Robust PI control of smart controllable load for frequency stabilization of microgrid power system

The intermittent wind power in a stand-alone microgrid power system may cause a serious problem of frequency fluctuation. Energy storage (ES) such as a battery, super capacitor, superconducting magnetic energy storage (SMES) etc., can be used to reduce the frequency fluctuation. However, ES is extremely expensive especially for developing countries. They still prefer to minimize the use of battery or apply cheaper technology to suppress the frequency oscillation such as controllable load. This paper proposes the design of robust PI controllable load to stabilize frequency fluctuation in a remote microgrid power system. The proposed controller is a conventional first-order PI controller. To guarantee the robustness of the proposed PI controller, an inverse additive perturbation is formulated as an optimization problem and a genetic algorithm (GA) is employed to tune and optimize the proposed PI control parameters. Simulation studies have been done to verify the performance and robustness of the proposed robust PI controllable load on remote hybrid wind-diesel power system against various disturbances and system uncertainties.