Sharif Digital Repository

This paper presents a new method for restoration of distribution networks after a fault occurrence. This problem is solved from the viewpoint of the distribution system operator with the main goal of minimizing the operating cost during the fault clearance period. The effects of distributed generation (DG) units and direct load control (DLC) programs are considered in designing the proposed restoration procedure. Moreover, the uncertainties associated with the predicted loads of different nodes and the availability of DG are modeled here. Robust optimization is used to model the uncertainties of restoration problems and manage their associated risks. Finally, a robust reconfiguration plan is... 

Purpose: The purpose of this paper is to investigate the impacts of electric vehicles' (EVs) charging/discharging decisions in energy resources scheduling problem of active distribution networks. Design/methodology/approach: The problem under study is modelled as a two-stage optimisation problem in which the main requirements of EV owners are introduced as an objective function of the first stage. The total energy costs and the emission factor are considered as the main criteria of the second stage. The output generation schedules of distributed generation (DG) technologies together with the charging/discharging schedule of EVs are proposed as decision variables of the energy scheduling... 

Purpose: The purpose of this paper is to investigate the impacts of electric vehicles' (EVs) charging/discharging decisions in energy resources scheduling problem of active distribution networks. Design/methodology/approach: The problem under study is modelled as a two-stage optimisation problem in which the main requirements of EV owners are introduced as an objective function of the first stage. The total energy costs and the emission factor are considered as the main criteria of the second stage. The output generation schedules of distributed generation (DG) technologies together with the charging/discharging schedule of EVs are proposed as decision variables of the energy scheduling... 

The need for independent power generation has increased in recent years, especially with the growing demand in microgrid systems. In a microgrid with several generations of different types and with all kinds of loads of variable nature, an optimal power balance in the system has to be achieved. This optimal objective, which results in minimal energy losses over a specific period of time, requires an optimal location and sizing of the distributed generations (DGs) in a microgrid. This paper proposes a new optimization method in which both optimal location of the DGs and their generation profile according to the load demand profile as well as the type of DG are determined during the life time... 

An energy management system (EMS) was proposed for a campus microgrid (μG) with the incorporation of renewable energy resources to reduce the operational expenses and costs. Many uncertainties have created problems for microgrids that limit the generation of photovoltaics, causing an upsurge in the energy market prices, where regulating the voltage or frequency is a challenging task among several microgrid systems, and in the present era, it is an extremely important research area. This type of difficulty may be mitigated in the distribution system by utilizing the optimal demand response (DR) planning strategy and a distributed generator (DG). The goal of this article was to present a... 

Current energy systems face multiple problems related to inflation in energy prices, reduction of fossil fuels, and greenhouse gas emissions which are disturbing the comfort zone of energy consumers and the affordability of power for large commercial customers. These kinds of problems can be alleviated with the help of optimal planning of demand response policies and with distributed generators in the distribution system. The objective of this article is to give a strategic proposition of an energy management system for a campus microgrid (µG) to minimize the operating costs and to increase the self-consuming energy of the green distributed generators (DGs). To this end, a real-time based... 

Distributed generation connected with AC, DC, or hybrid loads and energy storage systems is known as a microgrid. Campus microgrids are an important load type. A university campus microgrids, usually, contains distributed generation resources, energy storage, and electric vehicles. The main aim of the microgrid is to provide sustainable, economical energy, and a reliable system. The advanced energy management system (AEMS) provides a smooth energy flow to the microgrid. Over the last few years, many studies were carried out to review various aspects such as energy sustainability, demand response strategies, control systems, energy management systems with different types of optimization... 

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... 

Distributed generation (DG) units are increasingly installed in the power systems. Distribution companies (DisCo) can opt to purchase the electricity from DG in an energy purchase contract to supply the customer demand and reduce energy loss. This paper proposes a framework for optimal contract pricing of independent dispatchable DG units considering competition among them. While DG units tend to increase their profit from the energy purchase contract, DisCo minimizes the demand supply cost. Multi-leader follower game theory concept is used to analyze the situation in which competing DG units offer the energy price to DisCo and DisCo determines the DG generation. A bi-level approach is used... 

This study presents a passive model to detect islanding conditions of synchronous distributed generation resources in a distribution network or a microgrid. The proposed approach uses the classification and regression tree algorithm for distinguishing between islanding and non-islanding situations. It utilises the rate of change of frequency (ROCOF) and harmonic content of the equivalent reactance seen at the location of distributed generation as input features for decision tree construction. Indeed the thresholds of the proposed input features are extracted by the decision tree algorithm. The output if-then rules of the decision tree algorithm are then utilised to make a new relay logic for... 

Distributed Generation (DG) has received increasing attention during the last decade. Advantage and constraints of DG application are well known to both DG owner and electric utility. Various technologies are available for DG units among them gas GenSet is, in particular, more attractive to the investors as the technology provides the control on DG generation. However, there are various financial risks associated with dispatchable DG units that prohibit wide private investment in such technologies. This paper examines the use of financial tools to manage dispatchable DG economic risks. A comprehensive framework has been proposed to consider various economic risks to DG owner. Suitable models... 

With anticipated proliferation of electric vehicles and distributed generations in near future, dynamic thermal rating (DTR) as a tool for unlocking network capacities, is becoming critical for distribution network operators. DTR is gaining a great and still growing focus of attention in today's power industries. However, potential benefits of DTR, although have been envisioned to be significant, have not yet been studied quantitatively. This paper intends to comprehensively assess the potential impacts of DTR on the performance of a realistic Finnish distribution network. For doing so, first a step-by-step procedure is devised. Then, weather data and loading information of circuits in the... 

This paper presents a new framework for planning studies of modern distribution networks. Presence of electric vehicles (EVs) and various technologies of distributed generation (DG) technologies are considered in the studies as two upcoming events of the future systems. In this regard, place and capacity of DG units along with the reinforcement of distribution lines are determined running a multi-objective (MO) optimization algorithm. Total losses of the distribution network along with annualized cost of expansion plans including investment, operation and maintenance costs are introduced as the main criteria which should be optimized in the proposed framework. An effective Posteriori... 

Battery chargers are fundamental components for successful deployment of plug-in hybrid electric vehicles (PHEVs) into future smart grid. Recently, an integrated isolated bidirectional battery charger has been proposed for PHEV applications. The proposed charger eliminates the conventional bulky dc-link capacitor by feeding a dual-bridge resonant tank directly from the three-phase grid. The disadvantages associated with the presented charger are the high number of semiconductor switches which contribute to high cost and switching losses of converter as well as complicated control circuitry. In this paper, the previous structure is modified to address the aforementioned drawbacks and is... 

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... 

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... 

This paper presents a stochastic framework for day-ahead scheduling of microgrid energy storage systems 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 involved in... 

Electric distribution system is one of the most important parts of power systems owing to delivering electricity to consumers. The major amount of losses in a power system is in distribution level. Optimal distributed generation (DG) placement and sizing have a significant effect on power loss reduction in distribution systems. In this paper, a mixed integer conic programming (MICP) approach is presented to solve the problem of DG placement, sizing, and hourly generation with the aim of reducing power loss and costs in radial distribution systems. The costs include both investment and operational costs of DGs. Hourly load variations are considered in the model. To verify the effectiveness of... 

Penetration of distributed generation (DG) in distribution networks is rapidly increasing. DGs' application enhances system's reliability and power quality. However, along their benefits, there are some issues. One of the most important issues of DGs' application is the islanding. This paper presents a novel passive islanding detection scheme for synchronous DG based. In the proposed scheme, rate of change of exciter voltage over rate of change of reactive power at the DG-side (dE/dQDG) is taken into account. In reality, the voltage and reactive power of load depend on the exciter of the synchronous generator. Therefore, due to lack of inertia, response of these parameters to small changes... 

Employing more flexibility in power systems is one of the main challenges brought about by integrating more renewable energy sources in power systems. A promising way to overcome this challenge is to have local sources of flexibility in distribution level. In this respect, a novel approach is introduced in this paper for multi-stage distribution system expansion planning which jointly considers expansion of the network assets as well as flexibility enhancement. To this end, construction and reinforcement of feeders and substations are considered as various alternatives for network expansion. Moreover, installation of conventional dispatchable distributed generation units is selected as the...