Sharif Digital Repository

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 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... 

DC microgrids (DC-MGs) are becoming popular as an effective means to integrate various renewable energy resources. Conventionally, the droop control is adopted as a decentralized control strategy for proper power sharing without using any communication link. However, the conventional droop control often deteriorates due to the effects of unequal line resistances. In this paper, a control strategy is proposed for a DC-MG to achieve perfect power sharing considering the effects of line resistances. The DC-MG under study consists of a photovoltaic system, two energy storage systems, a grid-connected converter system, and dc loads. The control strategy of the converters is addressed under... 

This paper presents an effective control strategy for autonomous operation of a multi-bus medium voltage (MV) microgrid (MG) consisting of several dispatchable distributed generation (DG) units. Each electronically-coupled DG unit supplies the loads which can be unbalanced due to the inclusion of single-phase loads. The proportional resonance (PR) and droop controllers are, respectively, used to regulate the load voltage and share the average powers among the DG units. The virtual negative-sequence impedance controller (VNSIC) is proposed to effectively compensate the negative-sequence currents of the unbalanced loads. Moreover, the VNSIC minimizes the negative-sequence currents in the MV... 

DC microgrids (MGs) are becoming popular as effective means to integrate different energy resources. Conventionally, the droop control is adopted as a decentralized control method for power sharing in DC MGs. However, current sharing accuracy or voltage regulation deteriorates due to the effects of line impedances. In this paper, a new adaptive control strategy is proposed for DC MGs. In low load conditions, the output currents of the DGs are far from their maximum acceptable limits. Therefore, current sharing accuracy is not important. As load increases, the output currents of the DGs approach their maximum acceptable limits. Therefore, at high load conditions, accurate current sharing is... 

This paper describes how Enexis, one of the largest distribution network operators in the Netherlands, has adapted its load forecasting method for HV/MVtransformers to incorporate the influence of distributed generation. This new method involves the making of separate forecasts for demand and generation and determining the resulting transformer loading, based on the known correlation between demand and generation  

Islanding detection is a great challenge in connecting distributed generation (DG) in electrical power systems. Islanding detection methods are categorized into three groups, i.e., communication based methods, active, and passive methods. Communication based methods are established upon communication between utilities and DGs and have the inconvenience of being expensive and are limited in use. Active methods perturb the system with a disturbance and the system response to the disturbance is analyzed. Although, these methods have small Non Detection Zone, (NDZ) they degrade the power quality. Passive methods monitor one of the grid variables. Their implementation is easy but their NDZ is... 

This paper presents a stochastic framework for short-term operation of a distribution company (disco). The proposed framework optimizes disco's operational decisions in two hierarchical stages. The first stage, called day-ahead operation stage (DAOS), deals with the operational decisions on purchases from the day-ahead market and commitment of distributed generation (DG) units. The objective of this stage is to minimize the expected operating cost while the financial risk exposed by uncertain real-time prices and loads is restricted to a given level. The model associated with this stage is based on the mixed-integer programming (MIP) format. The second stage, named real-time operation stage... 

This paper presents a control strategy for an islanded medium voltage microgrid to coordinate hybrid power source (HPS) units and to control interfaced multilevel inverters under unbalanced and nonlinear load conditions. The proposed HPS systems are connected to the loads through a cascaded H-bridge (CHB) multilevel inverter. The CHB multilevel inverters increase the output voltage level and enhance power quality. The HPS employs fuel cell (FC) and photovoltaic sources as the main and supercapacitors as the complementary power sources. Fast transient response, high performance, high power density, and low FC fuel consumption are the main advantages of the proposed HPS system. The proposed... 

This paper proposes a frequency control strategy for an islanded inverter-based microgrid which based on the priority of supply, has got two distinct types of loads, namely sensitive and deferrable. The proposed strategy consists of primary and secondary levels of generation control supported by a loadshedding scheme. The primary control regulates the output power of the distributed generator (DG) units to be proportional to their ratings while secondary control has got the duty of frequency restoration after each load change. Functionality of these two levels is demonstrated to be independent of each other. Both controls are in distributed forms which have no need of communication... 

This paper presents an effective voltage control strategy for the autonomous operation of a medium voltage (MV) microgrid under nonlinear and unbalanced load conditions. The main objectives of this strategy are to effectively compensate the harmonic and negative-sequence currents of nonlinear and unbalanced loads using distributed generation (DG) units. The proposed control strategy consists of a multi-proportional resonant controller (MPRC) whose parameters are assigned with particle swarm optimization (PSO) algorithm. The optimization function is defined to minimize the tracking error at the specific harmonics considering the stability limitations. In this paper the performance of the... 

This paper presents the application of information gap decision theory (IGDT) to help the distribution network operators (DNOs) in choosing the supplying resources for meeting the demand of their customers. The three main energy resources are pool market, distributed generations (DGs), and the bilateral contracts. In deregulated environment, the DNO is faced with many uncertainties associated to the mentioned resources which may not have enough information about their nature and behaviors. In such cases, the classical methods like probabilistic methods or fuzzy methods are not applicable for uncertainty modeling because they need some information about the uncertainty behaviors like... 

Microbial fuel cells (MFCs) represent a new method for simultaneous wastewater treatment and biological electricity generation. In this study, petrochemical wastewater with 8000 mg/l of chemical oxygen demand was examined in a membrane-less single chamber MFC. Effects of wastewater concentration as substrate for microbial oxidation, and anode material (stainless steel or carbon brush) were investigated as designing parameters  

The introduction of demand response concept, in addition to increment of penetration of distributed generation (DG) based on renewable energies, make opportunities for the novel control schemes to be integrated in power system on a smart grid framework. Voltage control methods in power systems needs proper coordination among reactive power resources and conventional volt/var control equipments. In this work, potential reactive power resources are investigated and then, reactive power output of renewable DG units and controllable loads along with operation of conventional voltage controllers are optimized using a centralized control scheme. Considering the variability of demand and... 

Pre-compensators are used in multivariable control systems to reduce (or eliminate) open loop system interactions. Classical methods for the design of pre-compensator are traditionally based on static designs. Static pre-compensators are preferred for their simplicity, but are highly unsystematic in the amounts of achievable diagonal dominance. In many applications, only the more powerful dynamic pre-compensators are able to deliver the desired amounts of decoupling. This paper proposes a new method for the design of dynamic pre-compensators which is based on a Quadratic Programming (QP) optimization. Using the proposed approach the total pre-compensator is found through several smaller... 

The islanding of a distributed generation (DG)-fed distribution system generally results in frequency drop, which means less power is generated than it is needed. The only way of dealing with this problem is shedding loads as the system cannot generate any more electricity. Load shedding is intended to restore balance between generated and consumed power. This paper proposes a new method for load shedding based on the rate of change of frequency (RoCoF) at the first step and on voltage drop at subsequent steps. For this purpose, three lookup tables were created in order to prioritize loads to be shed according to the willingness of subscribers to pay and the RoCoF. The strength of the... 

This paper presents a stochastic framework for day-ahead scheduling of microgrid energy storage systems (ESSs) in the context of multi-objective (MO) optimization. Operation cost of microgrid in normal conditions and load curtailment index in case of unscheduled islanding events (initiated by disturbances in the main grid) are chosen as main criteria of the proposed scheme. In practice, duration of disconnection from the upstream network is unknown in unscheduled islanding incidents and cannot be predicted with certainty. To properly handle the uncertainties associated with time and duration of such events as well as microgrid load and renewable power generation, stochastic models are... 

Proliferation of distributed generations (DGs) and power-electronics-based loads is bringing about more harmonic-polluted power signals. While some failures may occur as a consequence of nonsinusoidal current or voltage waveforms, existing reliability models of protection relays have not taken the harmonic-related failures into consideration. This paper develops a comprehensive Markov reliability model to categorize the possible functional states of a component, say a transmission line, protected by a relay, operating in a harmonic-polluted environment. In order to make the proposed model practically tractable, it is further simplified in two ways, through merging the states of the same...