Load Priority Research Articles

Two-Stage Load Shedding for Secondary Control in Hierarchical Operation of Islanded Microgrids

A two-stage load shedding scheme is presented to cope with potential power deficits caused by microgrid islanding. Coordinated with the fast response of inverter-based grid-forming distributed energy resources, the proposed approach estimates the load shedding at each stage and the resulting power flow redistribution. The first stage of load shedding will cease any rapid frequency decline in which the locally measured frequency deviation is employed to guide the load shedding level and process. Once a new steady state is reached at the end of first stage, the second stage is activated, which performs load shedding according to load priorities. The effectiveness of the proposed scheme is verified through time-domain simulations in PSCAD/EMTDC based on a scaled-down microgrid system.

Adaptive Weight-Based Self Reconfiguration of Smart Distribution Network With Intelligent Agents

This work proposes an improved restorative algorithm for distribution systems with load priority consideration. The proposed algorithm takes into consideration about the optimization of the network while continuous monitoring for changes in system load conditions with a prevention mechanism for network reconguration with respect to small load changes. A simple adaptive, weight-based self reconfiguration algorithm is proposed with distributed generators for load sharing and reducing congestion in the lines. Individual node load priority is proposed at the time of restoration rather than taking priority of node to be restored. The proposed method is based on distributed computing with multiagent systems, implementation, and validation in laboratory scale distribution network in real time with low cost hardware. Results are also validated with the IEEE-33 bus distribution system.

Unified Algorithm for Demand-Side Appliance Commitment

Recent energy efficiency and conservation programs have created an unprecedented demand for home energy management systems (HEMS) in the residential sector aimed at reducing electricity consumption and saving on electricity bills. This paper gives a brief review of the basic algorithms found in the literature for HEMS that target optimum scheduling for home appliances participating in demand response (DR) programs. The working principles, as well as the pros and the cons, of these algorithms are explained and analyzed. Then, a unified algorithm to manage the hourly power consumption of home appliances on a daily basis is suggested using two scenarios. The first scenario aims to simultaneously achieve dual utility/customer benefits while avoiding the individual drawbacks of each presented algorithm. The second scenario aims to actively involve DR customers in making the optimum decision regarding their appliances in the face of their dynamic desires. The proposed algorithm is generic in the sense that it has the ability to achieve three different objectives for dual utility/customer benefits. Moreover, the paper takes into consideration a range of constraints, such as load priority, customer preferences, utility request, and electricity dynamic pricing scheme. The essential goal of this algorithm is not only to curtail or control the power consumption of appliances but to also shift it to a better price period based on different tariff rates. The results reflect the effectiveness of the proposed algorithm, which extends the previous findings in the literature by considering a wider range of limitations applied on HEMS.

Modern network reconfiguration techniques for service restoration in distribution systems: A step to a smarter grid

This paper presents state of the art reconfiguration techniques used for service restoration in distribution systems under different practical considerations. The different formulations of the problem together with the different solution methods are presented to show the advantages and disadvantages of each formulation and each solution. Other aspects that enhance the solution practicability such as load variations, load priority, cold load pickup, network connectivity representation, and existence of distributed generation are considered with directions for future research to convert current distribution system into an automatic self-healing system, which is the main pillar of the smart grid. The control method and the communication techniques used in the execution of the reconfiguration problem solution are highlighted and the new research directions in each issue are emphasized. The conclusion about the reconfiguration problem the formulation, the solution method, and the guidelines about unexplored research areas in this topic are presented at the end of the paper.

Experimental 1kW DC Micro-Grid based on PV Systems: Strategy Based on NI LabVIEW Platform

A improved design of a 1 kW and 190 Vbus DC micro-Grid (DC-μG) experimental prototype is presented in this paper. The DC-μG includes two simulators of photovoltaic arrays with 500 W power programed each, a boost power convert for each simulator, a super-capacitors bank of 0.230 F, a battery bank and a full bridge inverter for interconnection with the Main Grid (MG); the loads used for experimental tests of this DC-μG were resistive type and nonlinear loads like LED luminaires, fluorescent luminaires and a computer. Management System and Control (MSC) of DC-μG has been developed using National Instruments Company technology, generating MSC embedded into two NI myRIO-1900 hardware and using LabVIEW as programming language software. The MSC objective is keep the DC-μG voltage bus inside of ±5 % nominal Vbus (190 V) in spite of any connection/disconnection of loads in DC-μG. In addition to take advantage of max power of photovoltaic systems, supplying necessary energy to priority loads and the remaining energy inject to MG. The experimental results obtained show a good dynamic response of DC-μG with shorts setting times and small overshoots in the bus voltage.

Study of Harmonic Pollution Caused by Compact Fluorescent Lamps in Synchronous Generators used in Emergency Generation

This paper presents a study of the effects (thermal and dielectric) of the harmonic pollution caused by compact lamps on synchronous generators that supply the emergency generation system. In small and large establishments, the diesel generator set is triggered in the absence of local power, serving as priority loads and often the generator is limited to the lighting system.

Control and energy management of grid-connected pv system with battery-supercapacitor hybrid energy storage

An optimized energy management technique to reduce the cost and increase the effectiveness of a photovoltaic (PV) system is proposed in this paper. It is based on the optimum sizing of the energy storage system, to meet the needs of the system in normal conditions, while in the critical cases, the AC residential load will be supplied by the grid itself. In addition, the surplus of the PV power will be injected to the grid. However, to extend the battery life and reduce its size, a supercapacitor has been combined with the batteries, to quickly respond to the short-time peak current demand, while the battery will deliver a smooth current. Furthermore, the proposed algorithm will supervise the battery state of charge (SOC) and satisfy the highest priority load demand under different situation. A simulation work is carried out to evaluate the control of the whole PV system and determine the performance of proposed algorithm. Finally, the obtained results show the effectiveness of the proposed management algorithm, including the control techniques of different components of the whole system.

Energy management and performance evaluation of grid connected PV-battery hybrid system with inherent control scheme

To decrease the payback time of the photovoltaic (PV) system and make it financially attractive, we propose a Photovoltaic Customer Grid Supply System (PCGSS) with bi-directional power flow, so the surplus energy fully or partially is delivered of the grid, following its needs, while, for critical operating conditions, the grid supplies the loads directly. For this purpose, a new management algorithm is proposed to optimize the generated power and allows the system to act as a distributed source inside the utility grid. Two scenarios are considered; in the first, the grid absorbs all the power delivered by the distributed system, while in the second, the power is injected to the grid based on the its requirements. Furthermore, to meet the proposed objectives, the PV system is strictly sized to supply only the high priority loads, in addition, the system has to work at the Maximum Power Point (MPP) or at the Limited Power Point (LPP) modes to meet the management algorithm requests. To reach the LPP, a modified Perturbation and Observation (P&O) algorithm is used. Meanwhile, to sustain the functionality of the system and to assure the continues supply of energy, a battery system has been integrated with the PV system.

A New Under-Frequency Load Shedding Scheme Based on Adaptive Neuro-Fuzzy Inference System and Evolutionary Programming Shedding Priority

Frequency stability of islanded distribution system is a topic of interest, due to the significant penetration of distributed generation (DG). This paper proposes a new under frequency load shedding technique, which address the over-shedding issue caused by fixed priority. The proposed scheme consists of two units; first, the power imbalance estimation unit (PIEU), which use adaptive neuro-fuzzy inference system (ANFIS) to estimates the power imbalance. Second, the load shed unit (LSU), which is based on binary evolutionary programming (BEP) technique to shed the optimal loads. To validate the performance of the proposed UFLS scheme, different simulation studies have been conducted using PSCAD software. Moreover, the response of the proposed scheme is compared with another UFLS scheme having fixed priority loads. From the simulation results, the proposed scheme can shed the optimal loads, which is not achieved in the existing load shedding schemes.

Energy Management Strategy for Rural Communities’ DC Micro Grid Power System Structure with Maximum Penetration of Renewable Energy Sources

The AC and DC power system structures need to be modernized to meet consumer demands. DC microgrids are suitably admired due to their high efficiency, consistency, reliability, and load sharing performance, when interconnected to DC renewable and storage sources. The main control objective for any DC microgrid is providing proper load–power balancing based on the Distributed Generator (DG) sources. Due to the intermittent nature of renewable energy sources, batteries play an important role in load–power balancing in a DC microgrid. The existing energy management strategy may be able to meet the load demand. However, that technique is not suitable forrural communities’ power system structure. This research offers an energy management strategy (EMS) for a DC microgrid to supply power to rural communities with solar, wind, fuel cell, and batteries as input sources. The proposed EMS performs the load–power balancing between each source (renewable and storage) in a DC microgrid for dynamic load variation. Here, the EMS handles two battery sources (one is used to deliver power to the priority load, and the other is utilized in the common DC bus) to meet the required demand. The proposed EMS is capable of handling load–power balancing using renewable energy sources with less consumption of non- conventional energy sources (such as a diesel generator). The performance of the system is analyzed based on different operating conditions of the input sources. The MATLAB/Simulink simulation model for the proposed DC microgrid with their EMS control system is developed and investigated, and their results are tabulated under different input and load conditions. The proposed EMS is verified through a laboratory real-time DC microgrid experimental setup, and the results are discussed.

Decentralized three-phase distribution system static state estimation based on phasor measurement units

This paper presents a novel approach for static state estimation in electrical distribution systems, in which the state variables to be estimated are branch currents in rectangular coordinates. Branch current and voltage phasors are measured from a reduced number of PMUs located along a non fully observable electrical distribution system with radial topology. For the non-monitored buses, load pseudo-measurements are considered as a set of inequality constraints varying between upper and lower limits, which are adjusted during the safety barrier interior point optimization solution process (SBIPM). In order to track daily load variations, the initial load limits for the next time interval are obtained from the actual estimated loads at the non-monitored buses, considering the percentage of power variation at the exit of each lateral feeder. At each iteration of the SBIPM solution process, if any load is set to its corresponding limit, then a new limit margin is set accordingly, meaning that at the end of the solution process all the non-monitored loads are within specified bounds. The distribution network is also subdivided into subsystems considering a PMU allocation procedure in which each lateral feeder is estimated individually, yielding a naturally decentralized state estimator. In this decentralization context, priority loads, such as hospitals, police stations, telecom centers and places with high load density concentration can be considered as monitored subareas, exploring the radial topology of the distribution system. Tests are conducted on IEEE 33 bus test feeder and compared with an existing method in the literature to show the effectiveness of the proposed algorithm. Another simulation was conducted on a long lateral feeder of 57 bus in order to show the possibility of using the proposed technique for large scale distribution systems.

Distributed load shedding for microgrid with compensation support via wireless network

Due to the limited generation and finite inertia, microgrid suffers from the large frequency and voltage deviation which can lead to system collapse. Thus, reliable load shedding to keep frequency stable is required. Wireless network, benefiting from the high flexibility and low deployment cost, is considered as a promising technology for fine-grained management. In this paper, for balancing the supply-demand and reducing the load-shedding amount, a distributed load shedding solution via wireless network is proposed. Firstly, active power coordination of different priority loads is formulated as an optimisation problem. To solve it, a distributed load shedding algorithm based on subgradient method (DLSS) is developed for gradually shedding loads. Using this method, power compensation can be utilised and has more time to lower the power deficit so as to reduce the load-shedding amount. Secondly, to increase the response rate and enhance the reliability of our method, a multicast metropolis schedule based on TDMA (MMST) is developed. In this protocol, time slots are dedicatedly allocated and a checking and retransmission mechanism is utilised. Finally, the proposed solution is evaluated by NS3-Matlab co-simulator. The numerical results demonstrate the feasibility and effectiveness of our solution.

Resilience Enhancement Strategy for Distribution Systems Under Extreme Weather Events

This paper proposes an optimal hardening strategy to enhance the resilience of power distribution networks to protect against extreme weather events. Different grid hardening techniques are considered, such as upgrading poles and vegetation management. The problem is formulated as a tri-level optimization problem to minimize grid hardening investment and load shedding in extreme weather events. The first level is to identify vulnerable distribution lines and select hardening strategies, the second level is to determine the set of out-of-service distribution lines so that the damage caused by extreme weather events is maximized, and the third level is to minimize load shedding costs according to load priorities and the set of damaged lines. Since the selection of hardening strategies is coupled with the uncertainty set of out-of-service lines, the original tri-level model is transformed to be an equivalent bi-level problem, which is subsequently solved by a greedy searching algorithm. Case studies demonstrate the effectiveness of the proposed method under multiple severe weather events and different simulation settings.

ENERGY MANAGEMENT SYSTEMS FOR ELECTRIC VEHICLES AND MICROGRIDS

The purpose of study Smart Grid is the evolutions of our electric grid.Our electric components are developing day by day. The purpose of research on Microgrid systems are the integration of renewable energy sources (RES),Enhanced reliability, Reduce peak demand, Smarter consumers, Lower total energy consumption, which outlines power systems interconnection differentVitalityera components (supplyside)with vitality utilization components (request side) and capacity gadgets problem. The integration of RESs and ESSs in a microgrid is studied and analyzed by several authors for different purposes.Create and apply regular cost and advantages technique over all Smart Grid field ventures.
 The method employs including underlying algorithms and assumptions.Ensure that this methodology can easily accommodate algorithms and assumptions .Develop business case for investors, regulators and customers.
 This project has some limitations like it takes more time to configure all over the worlds, so expensive for the consumers. The objective is to keep end-user with more reliable and increased power availability and hence keeping higher priority load connected.
 This study never been done before. This study also was provided current information about smart grid and electric vehicles.

A comprehensive framework for optimal day-ahead operational planning of self-healing smart distribution systems

Providing a cost-efficient and sustainable energy is one of the critical features in modern societies. In response to this demand, this paper proposes a comprehensive framework for optimal day-ahead operational planning of smart distribution systems considering both normal and emergency conditions. The proposed procedure for normal mode minimizes the operation costs and provides sustainability using the seamlessness index. By adjusting this index, the system can be adapted to achieve the desired self-sufficiency level along a specified planning horizon thanks to exploiting the sufficient local generations. The operational planning of emergency mode is integrated into the proposed framework to provide the optimal schemes which can handle the possible abnormal conditions using the available local generations and guarantee the desired resiliency level. In emergency mode, the proposed self-healing strategy will sectionalize the isolated area of the distribution system into island partitions to provide reliable power supply to the critical loads continuously. A set of key operational metrics including power loss, load priority, and system-related constraints are integrated into the proposed island partitioning procedure which promotes the functionality of the method. The proposed framework is implemented on a modified PG&E 69-bus distribution system and is investigated through different case studies. The results of case studies demonstrate significant improvements and benefits which are obtained by applying the proposed framework.

A Smart Under-Frequency Load Shedding Scheme based on Takagi-Sugeno Fuzzy Inference System and Flexible Load Priority

This paper proposes a new smart under frequency load shedding (UFLS) scheme, based on Takagi-Sugeno (TS) fuzzy inference system and flexible load priority. The proposed scheme consists of two parts. First part consists of fuzzy load shed amount estimation module (FLSAEM) which uses TS-fuzzy to estimate the amount of load shed and sends its value to accurate load shedding module (ALSM) to perform accurate load shedding using flexible load priority. The performance of the proposed scheme is tested for intentional islanding case and increment of sudden load in the system. Moreover, the response of the proposed scheme is compared with adaptive UFLS scheme to highlight its advantages. The simulation results show that the proposed UFLS scheme provides the accurate load shedding due to advantage of flexible priority whereas adaptive UFLS scheme due to fixed load priority does not succeed to achieve accurate load shedding.

The Power Usage Allocating System to Optimize Based on the Priority Load

Monitoring energy consumption in a household is an essential thing for optimization of electrical power usage. Unnecessary or excessive power usage can lead to power outages and damage the electronic devices, so the end-user needs a control device to overcome it. In this paper, we propose an easy-access device that can provide real-time information about energy consumption and optimization of power consumption. The method for current measuring is used ZMCT103c whose works on some transformer and for voltage measuring is used ZMPT101b whose works on step down transformer. This system is focused on loads management priority in study case boarding house with total active power 900 watts which are created to scaled loads allocation based on electronic devices susceptible to damage that caused by power outages with assumption 2 (two) rooms and 3 (three) loads each room. The system has priority mechanism for load usage that could not be shut down such as PC (personal computer) and refrigerator. The device works by distributing maximum 55% of active power from excess power room to needed power room so that can avoid power outages and increase the efficiency of power usage.

Framework of intentional islanding operation of active distribution network based on self‐healing perspective

Intentional islanding operation (IIO) is a feasible solution to improve the reliability of active distribution network (ADN) by supplying critical loads through the local DG when a fault occurs. Aiming at this goal, a new two-stage methodology is proposed to supply critical loads based on cost-effective improvement. In the first stage, the interruption cost is proposed as the load priority and the ON/OFF status of switches are considered as the binary decision variables. Therefore, IIO is considered as a mixed integer linear programming (MILP) problem to minimise the interruption cost. At the second stage, the power flow calculation is performed on the initial islands for the real-time operation. The proposed method can be utilised for both long- and short-term studies. In the long-term study, the inherent uncertainty of ADN is considered in MILP by using a Monte-Carlo simulation. This concept is used for clustering ADN into self-sufficient microgrids. Moreover, by taking a snapshot of the ADN status and performing operational feasibility, the proposed method can be considered as a real-time power regulation method. The proposed methodology is implemented on the IEEE 33-bus distribution network, and the results are discussed in detail.

Optimal island partitioning of smart distribution systems to improve system restoration under emergency conditions

In the case of emergency operation, intentional islanding of distributed generations is an interesting solution to maintain the reliable power supply in the smart distribution grid. This paper deals with an optimal systematic strategy to restore the post-contingency distribution grid after the occurrence of severe disturbances causing an outage. Hence, a two-stage solution procedure is developed in this paper. In the first step, the optimal partitioning scheme is addressed through a number of graph-theory related algorithms. By applying these algorithms, the loads are optimally assigned to the distributed generations and optimal load shedding programs are determined and performed if there is a shortage of generation. The second step deals with the adjustments issues. In fact, the preliminarily partitions achieved from the first stage should be checked for feasibility. Also, these partitions should be adjusted if it is necessary in order to satisfy the system related constraints. To this purpose OPF calculation is incorporated and optimal load management measures are taken to mitigate violations considering the voltage constraints, line capacities and controllable loads. Since the proposed method considers the key factors of load priorities, load controllability, power balance, voltage and line capacity constraints, it covers the requirements of practical applications. Numerical results from the PG&E-69 test system are used to verify the effectiveness of the proposed method. The comparison with previous methods demonstrates that the proposed method outperforms other techniques.

Fuzzy logic energy management for a photovoltaic solar home

This paper presents a new energy management strategy for supplying a home with a grid-connected photovoltaic system with a backup. The proposed energy management algorithm is based on a fuzzy logic technique. A strategy has been elaborated in order to manage the home energy demand depending mainly on the energy available from the PV system and according to an established load priority, which is adjusted to satisfy the user’s energy needs and comfort. The case studied concerns a home installed in a coastal region of Bou-Ismaïl (Algeria). The efficiency level of the PV system has been shown through a favourable week in summer (August 2016) and an unfavourable week in winter (January 2016) using the real weather conditions of the site.The developed Fuzzy Home Energy Management has permitted to save 26.49% and 25.54% of energy respectively in winter and summer when compared to the consumption of the same home in the same conditions but without any energy management and or just using a basic load priority.