Sharif Digital Repository

Microgrid (MG) protection is one of the main challenges in proliferation of microgrids. Due to limited fault current feeding of inverter-based distributed generations (DGs), in islanded operation of MG, protection problems become more complicated; and, therefore, conventional protection strategies cannot be applied. Hence, new protection methods that are applicable in islanded and grid-connected modes of operation are necessary. In this paper, a comprehensive digital-relay based protection is introduced for the protection of MGs. The proposed method includes protection of lines, distributed generations, and the point of common coupling. The structure and graphical schematic of the proposed... 

Distribution systems management is becoming an increasingly complicated issue due to the introduction of new technologies, new energy trading strategies and new deregulated environment. In the new deregulated energy market and considering the incentives coming from the technical and economical fields, it is reasonable to consider distributed generation (DG) as a viable option to solve the lacking electric power supply problem. This paper presents a mathematical distribution system planning model considering three planning options to system expansion and to meet the load growth requirements with a reasonable price as well as the system power quality problems. DG is introduced as an attractive... 

Due to the liberalization of the electricity market and the introduction of distributed generation (DG), the importance of distribution loss allocation (LA) has increased. This paper presents a new method for distribution power LA in radial systems. The proposed method, which is based on the results of power flow and considers active and reactive power flows of lines for LA, is composed of three steps. In the first step, starting from the source nodes (i.e., the nodes whose generation is more than their load), the power loss allocated to all nodes is calculated and then the power loss allocated to the loads connected to each node is obtained. In the next step, the total power loss is... 

This study proposes an imperialist competition algorithm (ICA) to maximise the benefits of distribution network operators (DNOs) because of the existence of distributed generation (DG) units. The sum of active loss reduction and network investment deferral incentives has been considered as the objective function to be maximised in this study. The optimal location and size of DG units in the network are found considering various techno-economical issues. The application of the proposed methodology in the UK under current Ofgem financial incentives for DNOs is investigated. The ability of the proposed approach in finding the optimal solution is validated by comparing the obtained results with... 

This paper presents stability analysis of a distributed generation (DG) controller (1), in an islanded mode, based on the Mapping Theorem and the Zero Exclusion Condition, and validates the results based on a laboratory scale experimental setup. The DG unit is interfaced to the host system through a voltage-sourced converter (VSC). The control strategy regulates the load voltage at the desired value in the islanded mode, despite uncertainties in the load parameters. The frequency of the island is controlled in an open loop manner by an internal oscillator. The experimental results show that the controller provides robust voltage control for a wide range of load parameters, and even maintains... 

This paper presents a control scheme for microgrids with passive loads. The existing control techniques for distributed generation systems are designed to operate either in the grid-connected or in the islanded mode. In the grid-connected mode of operation, a currentcontrolled scheme based on d-q variables is used for the regulation of real and reactive powers of the converter. In the islanded mode of operation, the converter is controlled in the voltage-controlled mode. This paper deals with the modeling of both control schemes. Furthermore, reconnection from the islanded mode to the grid-connected mode based on the use of adequate Phase-Locked Loops (PLLs) has been demonstrated  

This paper presents stability analysis of a distributed generation (DG) controller [1], in an islanded mode, based on the Mapping Theorem and the Zero Exclusion Condition, and validates the results based on a laboratory scale experimental setup. The DG unit is interfaced to the host system through a voltage-sourced converter (VSC). The control strategy regulates the load voltage at the desired value in the islanded mode, despite uncertainties in the load parameters. The frequency of the island is controlled in an open loop manner by an internal oscillator. The experimental results show that the controller provides robust voltage control for a wide range of load parameters, and even maintains... 

A method for the reduction of interactions in linear time invariant (LTI) multivariable uncertain systems is proposed. An H∞-norm metric is proposed for the assessment of interactions in interval uncertain multiple-input multiple-output (MIMO) plants. Based on this, a procedure for the design of fixed-order dynamic decoupling precompensators for MIMO plants with interval uncertainty is outlined which can be solved using efficient solvers such as CVX. The proposed methodology is used to develop a low-order robust multivariable controller for voltage and frequency control of an islanded distributed generation (DG) unit. Copyright © 2017 by ASME  

Optimal placement of switches can play a key role in providing resilience to power distribution systems against major faults caused by natural disasters. This study presents a resilience-based framework for optimal switch placement in distribution systems being consistent with the expansion plans of distributed generation units. At first, the impact of hurricanes on distribution system components is modelled using the geographic information system of distribution grid and the strength of components against extreme weather-related events. Then, a new resiliency index is proposed to assess the resilience of distribution grids. This index is involved in a mathematical model of the switch... 

This paper presents a power flow controller for a matrix converter as the power electronic interface between a high-speed micro-turbine generator and a utility distribution system. The matrix converter converts the high-frequency of a micro-turbine generator to a conventional frequency of the utility system, based on a novel switching strategy. The controller regulates magnitude and phase-angle of the converter output voltage to accommodate real and reactive power flow requirements of the utility system. Performance of the matrix converter based microturbine generation system including the power flow controller is evaluated based on digital time-domain simulation studies in the PSCAD/EMTDC... 

This paper presents a new approach for optimal operation of distribution networks with regard to Distributed Generators (DGs). The objective function in this problem includes cost of active and reactive electrical energy generated by DGs, electrical energy markets and capacitors. Also, this paper presents both application and comparison of the metaheuristic techniques such as the Genetic Algorithm (GA), differential evolution, Ant Colony Optimization (ACO), Particle Swarm Optimization (PSO), tabu search, to optimal operation of distribution networks. These methods are tested on two examples distribution network containing an IEEE 34 distribution test feeders and a practical distribution...