The purpose of this thesis is to provide a method for increasing the resiliency of islanded microgrid using survivability. The survivability is meaning to minimize the load shed of islanded microgrid affected by an event. Microgrid loads are classified in to three categories of critical, non-critical and adjustable loads. Microgrid including consist of a wind farm, a solar farm and a diesel generator (DG) unit. The DG unit consists of 5 diesel generators. Both farms are connected to the battery energy storage system (BESS). Demand response is accomplished through adjustable loads and a fleet of PHEVs. Three scenarios are modeled in this paper.
To simulate the microgrid, the modified CIGRE system has been used.
Three scenarios are modeled in this thesis, in which the impact of BESSs and PHEVs in microgrid is investigated. In the first scenario, BESSs and PHEVs are not present; in the second scenario, BESSs are added to the microgrid, and in the third scenario, the effects of BESSs and PHEVs are examined.
 

 Combining both AC and DC systems, hybrid microgrid, has been proposed by many researchers. The presence of AC and DC sources, requires detail investigation of the control aspects in such systems. The key issues identified by many authors are Power sharing in hybrid structure, AC and DC bus voltage stability, Power exchange between the AC and DC bus, Power quality and system reliability in a hybrid structure. The authors, have identified that the main challenge in such microgrid structure is to manage power flows among all sources distributed in the AC and the DC grids and Suitable control schemes are proposed for such system. The power management system plays a crucial role in any microgrid and can ensure improved steady state performance. In this thesis, a hybrid microgrid structure for a grid connected microgrid with DC connection at back to back (B2B) converters is proposed. While a B2B connection between two AC systems could bestow a reliable, isolated and efficient coupling, an extra DC bus connection can facilitate use of the DC micro sources. The DC bus can supply the local DC loads and can also trade part of the power with the AC grids. The main contribution of this thesis, lies in enabling this new hybrid structure for grid connected microgrid through B2B converters. The controlled power flows between the microgrids and utility provide a new system model (and business) for hybrid microgrid. Different control modes and power flow strategies are developed to demonstrate the efficacy of the proposed microgrid structure and associated controls. In order to implement this thesis, a combined grid including the main grid, loads, microsources in DC microgrid, as well as AC microgrid, is modeled and validated by simulation in MATLAB software and simulation results will be analyzed

 In this thesis, practical methods to limit fault current in single phase to ground fault in a typical substation were studied. In advance, real network information Ahwaz Vahdat substation were gathered, then this network was implemented by system analysis softwer, DIgSILNT to perform simulations. Afterwords, some situations including using NGR, change in type of power transformer connections and using GT and also different methods for parallel operation of power transformers in different conditions were simulated. Considering available information from distribution network, output of simulations illustrate that using NGR in existing transformers to limit fault current technically possible. Moreover, it is possible to change transformators connection and using YNd transformers together with grounding transformer (with resistance to limit fault current) so that all transformers have YNd connection. According to simulation, parallel operation of transformers is appropriate if YNd transformers with GT is paralleld to Dyn transformer that earthed by NGR. In other parallel operation, single phase to ground fault current and neutral current of transformer raises (in comparison with normal condition), therefore parallel operation is not situable in other situations. Studying overvoltages during ground fault in simulated states and studying network equipment illustrates that this overvoltages are tolerable for installed equipment.

In this research work transient response of Coupling Capacitor Voltage (CCVT) and its effects on performance of distance relays are investigated. A detailed core model of the instrument transformers is presented to investigate their transient responses accurately. The adopted magnetic core models represent hysteresis symmetric and asymmetric minor loops, remnant flux, and the eddy current effects. The developed distance relay and instrument transformer models are implemented in the PSCAD/EMTDC software envirement
The impact of Passive and Active Ferroresonance Suppression Circuits (PFSC and AFSC) and Overvoltage Protection Devices (OPDs) for fast suppression of the ferroresonance phenomenon are studied. In addition, a generalized methodology to deduce the AFSC parameters is presented. The study result indicate that the designed AFSC has a better performance in suppression of ferroresonance oscillations. Furthermore, the simulation results indicate that the hysteresis and eddy current effects of the step-down transformer core significantly the CCVT ferroresonance behavior
An improved phasor estimation technique based on least squares method is proposed for estimation of voltage in distance relays. The method minimizes the impact of transient oscillations of the CCVT output voltage on operation of distance relay during faults. The algorithm performance is evaluated during various fault conditions. The proposed method provides higher tripping speed for close-in faults in addition to solving the overreaching problem for systems with high source to line impedance ratio

The expansion of power transmission systems is an important part of the expansion of power systems that require enormous costs for investment. Since the construction of new transmission lines is very expensive, it is necessary to choose the most efficient expansion planning that ensures the system security with minimal new lines to be established. In this thesis, the role of FACTS devices in the effective operation of the power systems and subsequently delays in the expansion of the transmission systems is examined. Effort taken in this thesis is to implement a method based on sensitivity analysis to select the optimal number and location of FACTS devices, lines and other elements of the transmission system. Using this method the transmission expansion planning for both 9 and 39 bus power systems once in lack of FACTS and again in the presence of FACTS series and parallel equipment, using simulation and scripting DPL environment in Digsilent software 15.1 is done. According to the results of the simulations, considering of these devices reduces the need for tens of kilometers of new transmission lines and minimize the costs of investment in this sector. This event proves the high impact of FACTS devices in optimal transmission expansion planning.

 Smart grids with distributed genarations has made a huge change in power systems and energy transmission.These networks, unavoidably are always in danger of faults made by harsh environment or human, so there should be an effective protection system which detects and locates faults as short as possible. The correct performance of this protection system prevents faults to spread and damage power system and lead to blackout. Also, wide area monitoring will be provided using sensors like PMU and FDR which can gather signals from network. in this thesis, a data driven approach for fault detection, identification and location is proposed. This method extracts features from frequency signals using matching pursuit decomposition with gaussian dictionary and then uses the extracted features as data set to learn gaussian mixture model for different condition of network. Using these models, faults will be detected and identified. To locate faults, wavelet coeffitient of voltage signals are extracted by wavelet transform and in compare to other buses, the faulted bus will be located. The performance of this approach has been tested through IEEE New England 39 bus system for four type of faults: transmission line outage, load loss, generator outage and generator ground fault. the results shows better performance of this approach.

Energy management of the Combined Heat and Power (CHP) – based microgrids is more complicated than those with no CHP scheme due to tight dependency upon thermal energy and electricity. In this work, an energy management system is adopted to minimize two economic and environmental objective functions for a sample microgrid in 24 hours. Multi-objective particle swarm optimization technique is employed to minimize both environmental and economic objective functions. In order to improve the static modeling of the CHP units, the operation constraints of the prohibited operating zones and ramp rate limit are considered. Energy storage systems are also employed for optimal performance of the energy management system. Then, a comprehensive model is employed for the energy storages considering their dissipations. A smart strategy, for the thermal storages, is also adopted in dealing with the CHP units such that the thermal loads could be supplied. The proposed energy management system is implemented on a microgrid which consists of the wind and solar Distributed Energy Resources (DER), simultaneous energy resources of electricity, fuel cell and microturbine heat, and energy storages with thermal and electrical loads. Three scenarios based on the various strategies for the CHP units are considered. Then, the results for the optimal power allocation using single and separate environmental and economic objective functions are reported. Lastly, the multi-optimization technique is employed to simultaneously allocate the optimal power to the microgrid and reduce the operation costs and the amount of air pollutants

 Abstract: Photovoltaic systems are a member of solar energy conversion systems that has got particular position in distribution electrical energy systems, in recent years. Because of very variant solar inputs, these systems require controls algorithms to work in the most efficient operating point, called MPPT. In the present work, after studying all of the technologies correspond the solar systems, two of PV cells, analytical model and one diode model are simulated and the results are discussed. Then two photovoltaic systems connected to Micro grid, with battery backup are simulated and the performance of the IncCond MPPT method to track maximum power point is investigated through very variant inputs. Afterward, the IncCond, P&O, and Look-up Table MPPT methods are compared in tracking maximum power point through variable solar irradiance and PV solar cell surface temperature and we see that in the IncCond and Look-up Table MPPT methods, the gains of PI controllers are set deterministically and thus in the case of variant inputs, the deviation from the nominal power is very tremendous. P&O method has a constant steady state error and requires an optimized design. At last we suggest a MPPT method and we see that this method has a very high response in addition to its capability of tracking maximum power point through a very variant PV array inputs with a very great accuracy.

In this study optimal energy management of a microgrid including renewable sources and storage devices, in both deterministic terms and probabilistic and for two different scenarios have been studied. Random variables associated with the uncertainty are: the load demand forecasting error, grid bid changes and WT and PV output power variations. In order to model the uncertainty of these variables, point estimate methoode is used wich use statistical moments for replacing each uncertain point with two deterministic points. Because the investigating in a 24-hour interval for all units is done at the same time, requires a powerful optimization tool so Particle Swarm Optimization algorithm is used. But what distinguishes this study compared to previous ones is that here is closer to the actual operating conditions. The numerical results show that with considering the uncertainty, the operation of various units changed while the final cost really does not change. In terms of the actual operating conditions (losses, modify bids and the second scenario modeling batteries), although the final cost increases, but this increase in cost is real

This thesis proposes an approach of control of Photovoltaic System (PV) with the Maximum Power Point Tracking (MPPT) and Battery Energy Storage System (BESS). The main goal is to provide Voltage & Frequency (v-f) support in islanding mode and Active-Reactive Power (P-Q) Control to meet local or critical load demands like industries and hospitals in grid-connected low voltage microgrid. A new MPPT Algorithm as well as indirectly inverter DC side voltage stability through power balance at various conversion stages is presented and investigated. The control methods are developed by using Proportional-Integral (PI) Controllers. Evaluation and validation of control algorithms in several senarios show effective coordination between v-f (P-Q) control, MPPT Control and Battery Control considering State of Charge (SOC) Constraint. The simulation studies are carried out with the IEEE 13- bus distribution feeder test system acting as a microgrid, in MATLAB and SimpowerSystem Software. The obtained simulation results clearly verify the effectiveness of the mentioned control methods.

 : The Increasing useof nonlinear and unbalanced loads generates harmonics and reduces power qualityin distribution networks. Harmonics generation causes excessive losses and low power factor in distribution systems. Passive filters are usually utilized to reduce current harmonics. Recent development of power electronic devices causesthe increasing utilization of custom power devices. These devicesare widely used to remove current and voltage harmonicsusing reactive power compensation. In this thesis a distribution static compensator (DSTATCOM) with three leg topology is used in a three-phase three-wire distribution system. DSTATCOM is designed for reactive power compensation, load current harmonic compensation, power factor correction and load balancing of unbalanced load currents.
The proposed methods have been tested by sets of simulations. It is found that the performance of DSTATCOM control system to achieve the aforementioned goals for improving the power quality is satis factory.
MATLAB2010 simulation software used for this thesis.

The load of distribution networks includes several components such as residential, industrial, commercial, agricultural and public loads. Some significant factors in load modeling are related to consumer type, time and weather conditions. Most of utilities around the world perform their planning and operational activities using load information which are directly been resulted from load research. Load research includes series of activities consists of measuring and analyzing electrical load characteristics in order to provide perfect and therefore useful knowledge from load profiles and behaviors. Most recently used and known approaches that take into account for load data analyzing are Data Mining (statistics) and Intelligent approaches. Data mining which often is called as data or knowledge discovery is almost new sciences for extracting useful know ledges from a large set of data. This technique is able to analyze that large data set and to introduce acquired results in form of summarized information to use in different applications.
In this study, a principal component analysis (PCA) based method is introduced for identification of load components of distribution networks. PCA is recognized as a useful data mining tool for extracting and exploring interrelations between large set of variables. In this study, with a part of historical data and by use of PCA method, we can extract some useful features and achieve to a model. With this model we can identify the system and then by existing substation load, we will be able to disaggregate the load components.
 

Conventional industrial microgrids (IMGs) consist of factories with distributed energy resources (DERs) and electric loads that rely on combined heat and power (CHP) systems. However, the developing IMGs are expected to include renewable DERs and plug-in electric vehicles (PEVs). This study presents a heat and power generation scheduling method coordinated with PEV charging in an IMG, considering photovoltaic (PV) generation systems coupled with PV storages. The proposed method is based on optimal power flow (OPF) over a 24-hour period and includes security-constrained optimal power flow (SCOPF), IMG’s factories constraints, heat generation constraint, PV storage constraints, and PEVs charging constraints. To demonstrate the efficiency of the proposed method, the simulation results are presented and analyzed for an 18-bus IMG consisting of 12 factories, PV generation systems coupled with storages and 6 types of PEVs, in 12 different modes. The system is divided into grid-connected and stand-alone mode. In this thesis, to solve the optimization problem the DE-PSO algorithm in MATLAB software is used. The results show that using the heat production power by the combined heat and power can reduce the cost of heat generation by the boilers, which can subsequently reduce the overall system costs. Another part of the thesis studies the power transmission to the upstream networks. The transmission of power enables the microgrid to buy electricity when the price of electricity is low, and sell electricity in peak times to increase revenue. The results show that using storages has a positive effect on scheduling heat and power generation. That is, they save power when the price of electricity is low or when there is little load in the microgrid, and inject the saved power to the microgrid in peak times. The time for optimal production of photo-voltaic is during the day and the peak time of IMGs is the same time too. Therefore, the photo-voltaic production systems coupled with the storages reduces the costs of the microgrids to a great extent. PEVs increase the load and cost of the system, and may not be able to produce the needed power for the microgrids in some hours of the day. In conclusion, the results show that electricity transmission with upstream networks, storages, and photo-voltaic generation systems coupled with storages, or a combination of all, greatly decreases the costs.

 Environmental protection issues, economic factors, energy storage resources and rapid increase of the load demand leads to the emersion of the microgrid as a power generation network. The control of the microgrid is the most important challenge in its operation. DG units interface with the utility using power electronic devices such as Voltage Sourced Inverter (VSI) For more reliable operation and better control of the microgrid. So the control of inverters is the main aim. The microgrid can operate in two modes: grid-connected and islanding. Control of the active and reactive power flow between the load and the utility and optimal power sharing among DG units are the main performance parameters during the load change condition. In order to follow the load demand with the specified voltage and frequency, the control of inverter is required in addition to the power control in an autonomous microgrid mode. The aim of this work is to improve the quality of power supply and optimal power sharing (in both grid-connected mode and islanding mode) and to regulate voltage and frequency (in islanding mode). The controller is composed of an inner current control loop and an outer power control loop based on a synchronous reference frame and the conventional PI regulators. The power control loop is designed for two typical control strategies: voltage–frequency (Vf) mode and active–reactive power (PQ) mode. Particle Swarm Optimization (PSO) which is an intelligent searching algorithm, is applied for power control parameters. The results show the satisfied voltage and frequency regulation, high dynamic response and optimal power sharing among the DG unit and the utility proportional to the load change. The results prove that the system is stable for the given operating point and under the proposed power controller and reveals that the microgrid can successfully operate as a controllable power generation unit to support the utility, so as to decrease the dependency on the power system and increase the market penetration of the micro-sources.

Microgrids are known as clusters of distributed energy resources serving a
group of distributed loads in grid-connected and isolated grid modes. Nowadays, the concept
of microgrids has become a key subject in the smart grid area, demanding a systematic
procedure for their optimal construction. According to the IEEE Std 1547.4, large distribution
systems can be clustered into a number of microgrids. in recent approach,there are limited
studies which considered effects of clustering large systems into a set of microgrids with high
reliability is not reported. To fill-out this gap, this thesis presents a systematic and optimized
approach for designing microgrids with high reliability. This optimum design considers
sustained and temporary faults. Reliability of distribution systems has always been an
important objective for the design and operation of power systems. Usually, utilities use
standard indices to evaluate distribution system reliability. These indices include SAIFI,
SAIDI, MAIFI and EENS which are system average interruption frequency, system average
interruption duration, momentary average interruption frequency index and expected energy
not suplied, respectively. The loads are assumed to be variable and different distributed
generation (DG) technologies are considered. optimizatin problem is solved by genetic
algorithm in Matlab software. PG&E69-bus distribution system is selected as the test system.
Several sensivity studies are conducted on the modified PG&E 69-bus distribution system to
evaluate the effects of weighting coefficients on the final constructed microgrids. The sensivity
studies studies show that the optimally designed microgrids depend on the weighting
coefficients. The robustness of the design to the variation of loads and DG penetration levels
and adding new DGs to the system is also investigated. The results show that the final design is
not very sensitive to the DG and and load level as well as adding new DGs to the system. The
proposed strategy for designing reliable microgrids in a distribution system is a step towards
having a more reliable and cost efficient smart distribution network.

In this M.Sc thesis, transient states due to resonance and ferroresonance of earthing transformer in medium voltage network have been studied. First of all, data of a real network belonging to Khuzestan Steel Company have been collected. Then, many simulations have been done by transient states analysis software, PSCAD/EMTDC. These simulations have been executed to analyze the transient states including overvoltages and overcurrents in medium voltage network. Afterwards network’s configurations that are suspectible to resonance and ferroresonance have been recognized. The results of simulations show that neutral current of earthing transformer can be used as a sign of earthing transformer resonance.
Therefore, use of resistor in neutral of earthing transformer has been suggested to damp the resonance oscillations. Also to creat losses in network for damping off the distortions of voltage waveform, it has been suggested to putt a small load permanently in service. Results show that changing the equivalent impedance of network by using compensating capacitor bank and changing protection and control logic of substation are the solutions for prevention and limitation of oscillations due to resonance and ferroresonance. In addition to this, simulations show that 5th harmonic can be used as a sign of resonance in this medium voltage network. Then, it has been suggested to use for detection of resonance phenomena. Moreover, results show that protection and control logics of substation should be changed to prevent earthing transformer’s resonance in network because of existing earthing transformer in circuit after deenergization of main busbar. The results show that distortions of these transient states have same effects on upstream network, but have no effect on downstream network. Simulations show that magnitude of voltage waveform just before switching time has an important role in distortions magnitude. Also results show that distortions magnitude will be amplifying with increasing magnitude of voltage. Furthermore simulations show that equipments with delta or nongrounded star connection have no effect on resonance distortions damping. Besides results show that fault resistance has suitable effect on resonance distortions like neutral grounding resistor.
 

In this thesis, the effect of harmonic on the smart distribution system with a standard 30 buses is studied. At first, power flow analysis has been performed by means of newton-raphson method and considering distorted substation voltage. Afterward, proper size of capacitor has been selected by cuckoo optimization algorithm to reduce the power losses and cost by considering acceptable limit for total harmonic distortion and rms voltages. In the next part, the effect of electric vehicle battery chargers has been investigated on the system as a current harmonic sources nonlinear load. This study has been generalized to the different hours of a day by using daily load curve, and then, optimum time for charging of EVs batteries in the specified buses has been determined by cuckoo optimization algorithm to reduce the costs. Due to the lack of access to communication information, determination of the best time for charging the vehicles battery has been considered in this thesis as an interpretation of being smart grid. The results of this study show that the presence of voltage harmonics increase power losses. Also, the results indicate that further restriction on the maximum of total harmonic distortion, increase the losses of system and decrease the total capacity of the installed capacitors. The results show that the presence effect of the capacitors indicates that the capacitor reduces the power loss at time of peak load; however, influence of the capacitors on the voltage profile is more evident in the time of off peak. Capacitor placing has a major impact on reducing harmonics pressure on system instruments, improving the voltage profile and reduction of losses. In another part of this thesis, the effect of the electric vehicle is studied. By connecting vehicles to determined buses and injecting harmonic currents caused by charging vehicles, drop in the voltage profile is observed and Power losses increases, the increase in peak load hours is significant. As well as vehicle is connected to the system, increase of the total harmonic distortion is relatively large. Moreover, charging the vehicle batteries has more impact on increasing the power losses rather than the harmonic currents effect. Also, current harmonics has a great influence on increasing of THD. Finally, optimum working times of all parking lots was obtained for the utilization cost reduction.

Concern about environmental pollution than power plants and Fluctuations in energy prices have caused emergence of smaller generating systems, including microturbines, photovoltaics, and fuel cells. Nowadays, decrease in distributed generation investment cost is caused to increase penetration of distributed generations in power systems.
Presence of multiple DG units in power system has brought about the concept of microgrid. A microgrid can operate in the grid-connected mode or islanded mode.
Control, protection, operational issues, and energy management strategies of microgrid are significantly, and in some cases conceptually, different than those of convetional inter-connected grids. In this thesis control systems of each source is provided separately and then a control strategy and generation management of whole microgrid system is developed to gain correct operation in both grid-connected and islanding mode. The distributed energy resources of microgrid are microturbine,diesel engine, fuel cell, photovoltaic and battery energy storage system (BESS). To investigate the microgrid operational scenarios and testing control system the benchmark system is used in this thesis.
In this thesis, the BESS handles the frequency and the voltage as a primary control. And then, the power output of the BESS brought back to zero as soon as possible by the secondary control in order to secure the maximum spinning reserve.The study systems designed and the corresponding digital computer simulation model is developed using PSCAD/EMTDC software package. The test results show that the proposed control strategy can regulate the frequency and the voltage.
 

The main object in this thesis is dynamic behavior studies and analysis of DFIG wind turbine during transient state because of voltage sag in network grid .
Then we found solution for implement transient behavior of induction generator with wounded rotor and with three phases bridge converters that linked together with DC line contain capacitor and have installed between rotor and grid.
In other hand we discussed about methods that has controlled DFIG used in variable wind turbine then presented all the equations that are required .
At least we suggested a novel method in order to individual control of active and reactive power in DFIG. then simulated transient state with matlab-software and analyze results.
This scheme controlling use of complete method stator rotational flux for grid converter and series converter compensator .However we compared the results obtain from conventional method and new scheme. This is an aim for us to focus on reactive power in type unit power producer.