Aboelsood Zidan

A Cooperative Multiagent Framework for Self-Healing Mechanisms in Distribution Systems

Because of societys full dependence on electricity and high cost of system outages, one important goal is to increase the reliability of the power system, which means that a salient attractive feature of smart grid is its self-healing ability. Smart grids will develop and enhance the automation of distribution by operating in a distributed manner through new digital technologies such as monitoring, automatic control, two-way communication, and data management. In this work, the smart grid concept and technologies have been applied to construct a self-healing framework for use in smart distribution systems. The proposed multiagent system is designed to locate and isolate faults, then decide and implement the switching operations to restore the out-of-service loads. The proposed control structure has two layers: zone and feeder. The function of zone agents in the first layer is monitoring, making simple calculations, and implementing control actions. Feeder agents in the second layer are assigned to negotiation. The constraints include voltage limits, line current limits, and radial topology. Load variation has been taken into consideration to avoid the need for further reconfigurations during the restoration period. The results of the simulation conducted using the new framework demonstrate the effectiveness of the proposed control structure.

Uncoordinated charging impacts of electric vehicles on electric distribution grids: Normal and fast charging comparison

Plug-in electric vehicles (PEVs) have uncertain penetration in electric grids due to uncertainties in charging and discharging patterns. This uncertainty together with various driving habits makes it difficult to accurately assess the effects on local distribution network. Extra electrical loads due uncoordinated charging of electric vehicles have different impacts on the local distribution grid. This paper proposes a method to evaluate the impacts of uncoordinated PEVs charging on the distribution grid during peak period. Two PEVs charging scenarios are studied, including normal and fast charging. The impact analysis is evaluated in terms of voltage violations, power losses and line loading, which is implemented on a real distribution system in Canada. The results of the analysis indicate that there are significant impacts on distribution networks due to PEVs charging, which limits the accommodation of desired penetration levels of PEVs.

Network reconfiguration in balanced and unbalanced distribution systems with high DG penetration

This paper presents a simple and efficient reconfiguration approach for balanced and unbalanced distribution networks with DG. The proposed approach that is based on load flow, begins with meshed networks by closing all tie switches. Branch currents were used as switching index to determine the open/closed states of the tie and sectionalizing switches with an objective of system losses reduction. The radial configuration was restored by opening the switch with smallest switching index in each loop. The proposed method has been tested on one balanced and two unbalanced systems with and without distributed generation, and compared with those reported in the literature.

Network reconfiguration in balanced and unbalanced distribution systems with variable load demand for loss reduction and service restoration

This paper presents a simple and efficient reconfiguration approach for balanced and unbalanced radial distribution networks with Distributed Generators. The proposed approach starts with meshed networks by closing all tie switches. A switching index is defined for reconfiguration using apparent power flow in lines. The radial configuration was restored by opening one switch in each loop subjected to system operational constraints. The switching index can be used for both loss reduction and service restoration during normal and emergency situations respectively. The time varying nature of loads through using daily load profiles was considered. The results concluded the effectiveness of: (i) fixed configuration compared to hourly reconfiguration in terms of energy losses and number of switching operations during normal operation; and (ii) building restoration plans with the consideration of load variation compared to plans based on pre-fault or peak load values. The proposed method has been tested on one balanced and one unbalanced systems.

Network reconfiguration in balanced distribution systems with variable load demand and variable renewable resources generation

There is increasing interest in renewable energy sources interconnections in distribution systems since they are inexhaustible and nonpolluting. Wind and photovoltaic are among most mature renewable energy sources, and their penetration continues to increase. This paper proposes a method for distribution network reconfiguration to minimize annual energy losses by determining the optimal configuration for each season of the year. Uncertainties including the daily time varying load and stochastic power generation of renewable distributed generators (DGs) are modeled and taken into account. The method is based on generating a probabilistic generation-load model that combines all possible operating conditions of the renewable DGs with their probabilities of occurrence, then accommodating this model in the reconfiguration problem. The reconfiguration problem, based on Genetic Algorithm, aims at achieving minimum annual energy losses. The constraints include the voltage limits, line current limits, radial topology, and feeding of all loads. The proposed method has been tested on two systems. Simulation results show significant reductions in the seasonal and annual energy losses for all the studied cases.

Fault Detection, Isolation, and Service Restoration in Distribution Systems: State-of-the-Art and Future Trends

This paper surveys the conceptual aspects, as well as recent developments in fault detection, isolation, and service restoration (FDIR) following an outage in an electric distribution system. This paper starts with a discussion of the rationale for FDIR, and then investigates different areas of the FDIR problem. Recently reported approaches are compared and related to discussions on current practices. This paper then addresses some of the often-cited associated technical, environmental, and economic challenges of implementing self-healing for the distribution grid. The review concludes by pointing toward the need and directions for future research.

A cooperative agent-based architecture for self-healing distributed power systems

This paper proposes a two-stage distributed method for the restoration problem using multi-agent system. The first stage gets a quick solution and implements it to restore as much loads as possible based on their priorities. The second stage will be applied to faults which expected to take longer time in order to maximize the restored loads (if there are loads still not energized from the first stage), minimize the power losses, and relieve the overloaded lines for more efficient and economical operation. Distribution system is represented as a multi-agent system with hierarchical architecture. Four types of agents are included, which are Bus Agents (BAGs) for monitoring and implementing the switching actions, DG Agents (DGAs) to represent DGs as supporting sources of power, Zone Agents (ZAGs) for negotiation and decision in the first-stage of restoration, and Global Agent (GAG) for decision in the second-stage of restoration. The proposed method is implemented in JADE and simulation results of 16-Bus system are included.

Optimal DG Allocation in Radial Distribution Systems with High Penetration of Non-linear Loads

Abstract This paper addresses the optimal distributed generation sizing and siting for voltage profile improvement, power losses, and total harmonic distortion (THD) reduction in a distribution network with high penetration of non-linear loads. The proposed planning methodology takes into consideration the load profile, the frequency spectrum of non-linear loads, and the technical constraints such as voltage limits at different buses (slack and load buses) of the system, feeder capacity, THD limits, and maximum penetration limit of DG units. The optimization process is based on the Genetic Algorithm (GA) method with three scenarios of objective function: system power losses, THD, and multi-objective function-based power losses and THD. This method is executed on the IEEE 31-bus system under sinusoidal and non-sinusoidal (harmonics) operating conditions including load variations within the 24-hr period. The simulation results using Matlab environment show the robustness of this method in optimal sizing and siting of DG, efficiency for improvement of voltage profile, reduction of power losses, and THD. A comparison with particle swarm optimization (PSO) method shows that the proposed method is better than PSO in reducing the power losses and THD in all suggested scenarios.

Service restoration in balanced and unbalanced distribution systems with high DG penetration

This paper presents a simple yet efficient service restoration algorithm for balanced and unbalanced radial distribution networks including Distributed Generators DG. The proposed algorithm that is based on load flow, begins with identifying the de-energized loads group due to fault isolation. All tie switches connecting this group with the rest of the network are the candidate switches for restoration. Branch currents from meshed network (i.e. closing all tie switches) were used as switching index to determine which one of these candidate tie switches should be closed for restoration. The restoration is carried out with objectives of maximizing the restored loads and minimizing the number of switching operations under line current limits, bus voltage limits and radial topology constraints. Each out-of-service group restored by closing the candidate tie switch with highest switching index. The proposed method has been tested on one balanced and two unbalanced systems with and without distributed generation, and compared with those reported in the literature.

Load model effect on distributed generation allocation and feeders' reconfiguration in unbalanced distribution systems

Limitation of fossil fuels and the environmental constraints established by the Kyoto Protocol and other governmental initiatives caused the allocation of distributed generation (DG) to be a vital pillar in power system planning. Improper selection of the sizing and siting of DG systems can reduce their advantages. Network reconfiguration problem is to find a best configuration of distribution systems that gives minimum energy loss with satisfying the imposed operating constraints. This paper investigates the effect of load model on DG allocation and network reconfiguration problems. The proposed algorithm implemented and tested on the 25-bus unbalanced distribution system and the impact of load models is demonstrated. The constraints involved include voltage limits, line current limits, and radial topology.