Showing papers presented at "Clemson University Power Systems Conference in 2015"

The effect of the volt/var control of photovoltaic systems on the time-series steady-state analysis of a distribution network

Abstract: Grid-connected photovoltaic (PV) systems with relatively high capacity effectively reduce peak load, but because of their reverse power flow, they can cause overvoltage along a feeder that can exceed five percent of the rated voltage Modern PV systems with the capability of Volt/Var control can mitigate overvoltage by either injecting or absorbing reactive power Thus, the objectives of this study are to (1) model a distribution network (feeder J1 located in the northeastern United States and enhanced by thirteen PV systems) using OpenDSS; (2) use actual collected load profile data as input data to the simulation model and PV generation output data at 15-minute intervals; and (3) calculate the time-series steady-state power flow of the distribution network when PV systems generate or absorb reactive power Finally, it addresses overvoltage resulting from the deployment of high-capacity grid-connected renewable PV systems and mitigation techniques for such overvoltage issues, particularly Volt/Var management and control

Steady state voltage stability enhancement using shunt and series FACTS devices

Abstract: Power systems consist of generation, transmission, and distribution of power to customers. To meet the ever increasing population demand, the power industry has also grown by increasing the number of devices and incorporating highly complex as well as expensive components into the power system. It becomes specifically important to focus on voltage stability analysis of the power system to avoid worst-case scenarios, such as voltage collapse, which may result in huge losses. One of the main causes of voltage collapse is the insufficient availability of reactive power in the system. This can be overcome by adding reactive power sources such as FACTS devices into it. An attempt on enhancing the steady-state voltage stability using FACTS devices has been made in this work. An IEEE 39-bus test system is built using MATLAB and PSAT. FACTS devices such as Static VAR Compensator (SVC), Static Synchronous Compensator (STATCOM), and Thyristor Controlled Series Capacitor (TCSC), are included into the test system as three separate test cases. Continuation power flow analysis is performed on the system with no FACTS included in it and on the three test cases with different FACTS included in it. The output is displayed in the form of P-V curves, loading margin curves, and active and reactive power losses curves. The results obtained are all compared with each other to draw conclusions on the effectiveness of the each of the FACTS devices in improving the static voltage stability of the power system.

Bidirectional floating interleaved buck-boost DC-DC converter applied to residential PV power systems

Abstract: The main goal of this paper is to design and analyze a bidirectional floating interleaved DC-DC buck-boost converter applied to a residential photovoltaic (PV) power system with energy storage. The floating interleaved bidirectional converter produces a higher DC voltage gain compared to conventional converters, reducing the required number of series connections for the PV and battery modules. This paper provides a smallsignal model of this bidirectional DC-DC converter, and describes control strategies for the DC-DC and DC-AC converters applied in a typical residential PV power system. The papers shows a transitional control strategy from gridconnected to islanded operating modes, as well as the back connection with the boost/buck operating modes for the bidirectional DC-DC converter. The paper describes the DC link management and voltage control where the regulation techniques are demonstrated by analysis and simulation results showing a complete system operation. Experimental results validate the proposed inverter control scheme.

Side channel analysis of multiple PMU data in electric power systems

Abstract: The deployment of Phasor Measurement Units (PMUs) in an electric power grid will enhance real-time monitoring and analysis of grid operations. The PMU collects bus voltage phasors, branch current phasors, and bus frequency measurements and uses a communication network to transmit the measurements to the respective substation(s)/control center(s). PMU information is sensitive, since missing or incorrect PMU data could lead to grid failure and/or damage. It is important to use encrypted communicate channels to avoid cyber attacks. In this study, a side-channel attack using inter-packet delays to isolate the stream of packets of one PMU from an encrypted tunnel is shown. Also, encryption in power system VPNs and vulnerabilities due to side channel analysis is discussed.

A signal acquisition system for non-intrusive load monitoring of residential electrical loads based on switching transient voltages

Abstract: One of the approaches proposed for Non-Intrusive Load Monitoring (NILM) of residential appliances is based on the analysis of switching transient voltages. The transients induced when and appliance is operated can be learned or classified and thus it can be determined when appliances are turned on and off via analysis of the transients. Acquisition of the transient requires two steps: first, the detection of a transient in the ongoing power line signal, and second, the filtering of the electric power signal itself (e.g., in the US, the 60 Hz signal and its harmonics) to provide a clean transient signal to analyze. Here, a detection method using a masked (envelope trigger) oscilloscopetype instrument is adopted. That allows no computation to take place until a transient is actually detected, thus saving greatly on computational requirements. Then, the filtering is performed mathematically. A novel recursive filtering algorithm is presented here, allowing removal of the natural response of the mathematical filter. By using the methods presented in this article, very clean transient signals from household appliances, with full removal of the power signal and its harmonics, can be obtained, thus greatly facilitating the posterior analysis and classification of these transients.

A modular multilevel converter based battery-ultracapacitor hybrid energy storage system for photovoltaic applications

Abstract: To smooth the output power of a Photovoltaic (PV) system, the integration of the Hybrid Energy Storage System (HESS) has been considered as an effective solution. In this paper, a Modular Multilevel Converter (MMC) is proposed for the HESS that combines battery and UltraCapacitor (UC), and a two-layer framework is proposed to control the proposed HESS system. Compared to traditional HESSs and other MMCs for HESS applications, the proposed MMC based HESS increases the overall system efficiency, reduces the cost of dc side passive components, and is favorable for grid energy storage systems. Simulation results are provided to verify the theoretical analysis.

Operational flexibility enhancement in power systems with high penetration of wind power using compressed air energy storage

Abstract: Unquestionably, renewable energy sources (RES) are an indispensable part of the future power systems, so-called smart grids. Since these sources are of variable and uncertain power output, power system operators would come across many challenges in operating future electric power systems. Increasing penetration of variable RES specifically wind power generation could lead to an increased need in operational flexibility within power systems, so that a more flexible power system could accommodate a larger amount of variable RES and effectively deal with increased variability and uncertainty of the system net load that results from the inherent intermittency of RES. Among options available, energy storage systems (ESS) could be considered to address this issue. In this paper, compressed air energy storage (CAES) is introduced and investigated for this purpose. A stochastic programming market-clearing model is presented to examine CAES capability for enhancing operational flexibility in power systems with high penetration of wind power. In order to demonstrate the efficacy of CAES, some case studies are carried out in a three-bus test system. The satisfactory results verify CAES ability at enhancing power system operational flexibility in terms of reduction in wind power curtailment and system operation cost.

Resource scheduling in residential microgrids considering energy selling to external players

Abstract: The operation of distribution networks has been facing changes with the implementation of smart grids and microgrids, and the increasing use of distributed generation. The specific case of distribution networks that accommodate residential buildings, small commerce, and distributed generation as the case of storage and PV generation lead to the concept of microgrids, in the cases that the network is able to operate in islanding mode. The microgrid operator in this context is able to manage the consumption and generation resources, also including demand response programs, obtaining profits from selling electricity to the main network. The present paper proposes a methodology for the energy resource scheduling considering power flow issues and the energy buying and selling from/to the main network in each bus of the microgrid. The case study uses a real distribution network with 25 bus, residential and commercial consumers, PV generation, and storage.

Combined emission and economic dispatch incorporating demand side resources

Abstract: In this paper, a unique formulation for combined emission and economic dispatch (CEED) incorporating demand side resources (CEED-DSRs) is presented. Herein, the target of a generation company is minimizing total cost including power generation cost, penalty cost due to carbon emissions, and cost of demand response program (DRP) implementation. In solving the CEED-DSRs problem, one of the voluntary and incentive-based programs of DRPs, that is, emergency demand response program (EDRP) is chosen, and then different strategies are defined for implementing EDRP. The strategies are prioritized based on minimum cost of the CEED-DSRs problem. Potential benefits of the proposed CEED-DSRs include reduced total cost of problem, diminished carbon emission level of thermal power plants, and improved system load factor.

Electricity theft detection techniques for metered power consumer in GUVNL, GUJARAT, INDIA

Abstract: India faces endemic electrical energy and peaking shortages. These shortages have had a very detrimental effect on the overall economic growth of the country. As total Power losses equals transmission power losses plus distribution power losses. The reasons cited for such high losses are; lack of adequate T & D capacity, too many transformation stages, improper load distribution and extensive rural electrification etc. The sources of transmission power losses may be directly driven by network investment or by network operation. Distribution power losses arise from several areas including theft, un-billed accounts, and estimated customer accounts, errors due to the approximation of consumption by un-metered supplies and metering errors Electricity theft can be in the form of fraud (meter tampering), stealing (illegal connections), billing irregularities, and unpaid bills. Estimates of the extent of electricity theft in a sample of 102 countries are undertaken. The evidence shows that theft is increasing in most regions of the world. Electricity consumer dishonesty is a problem faced by all power utilities. Finding efficient measurements for detecting fraudulent electricity consumption has been an active research area in recent years. Data mining has become increasingly common in both the public and private sectors. This paper presents a new approach towards Distribution Power Loss analysis for electric utilities using a novel intelligence-based technique like Extreme Learning Machine (ELM), an online sequential learning algorithm for single hidden layer feed forward networks (SLFNs) with additive or radial basis function (RBF) hidden nodes in a unified framework. OS-ELM & Support Vector Machine (SVM). The main motivation of this study is to assist Gujarat Urja Vikas Nigam LTD (GUVNL), GUJARAT, INDIA to reduce its Distribution Power Loss due to electricity theft. This approach provides a method of data mining and involves feature extraction from historical customer consumption data. This model preselects suspected customers to be inspected onsite for fraud based on abnormal consumption behavior. The proposed approach uses customer load profile information to expose abnormal behavior that is known to be highly correlated with Distribution Power Loss activities. The approach uses customer load profile information to expose abnormal behavior that is known to be highly correlated with Power Loss activities. Simulation results prove the proposed method is more effective compared to the current actions taken by GUVNL in order to reduce Power Loss activities.

Comparative study of bat & flower pollination optimization algorithms in highly stressed large power system

Abstract: Optimal power flow is an important non-linear optimization task in power systems. In this process, the total power demand is distributed amongst the generating units such that each unit satisfies its generation limit constraints and the cost of power production is minimized. This paper presents a comparative study of new meta-heuristic optimization techniques namely bat and flower pollination algorithm for the optimal solution of optimal power flow problem such as minimizing the fuel cost of a thermal power plant. In this paper PSO is also taken just as a reference for measure the performance of the above two techniques. The numerical results clearly show that the bat algorithm gives better results than flower pollination algorithm in terms of fuel cost value and time required to reach global best solution. In order to illustrate the effectiveness of the proposed algorithm, it has been tested on highly stressed modified IEEE 300-bus test system.

Hybrid controller for transient stability in wind generators

Abstract: In wind power plants typically squirrel-cage induction generators (SCIG) tend to drain large amount of reactive power from the grid, potentially causing a drop voltage. To improve SCIG’s power quality and transient stability, this paper investigates a new pitch angle control strategy, including normal scheme and Fault-Ride-Through (FRT) scheme, based on hybrid of PI and Fuzzy logic technique. In particular, an analytic model for transient stability is implemented using the equivalent circuit of the SCIG and on the concepts of stable and unstable electrical-mechanical equilibrium. This method has been evaluated by comparing the results with the dynamic simulation. The dynamic simulation results show that the proposed hybrid controller can be effective in enhancing output power smoothness and FRT requirements for SCIG in wind power system.

Contextual and environmental awareness laboratory for energy consumption management

Abstract: The recent changes on power systems paradigm requires the active participation of small and medium players in energy management. With an electricity price fluctuation these players must manage the consumption. Lowering costs and ensuring adequate user comfort levels. Demand response can improve the power system management and bring benefits for the small and medium players. The work presented in this paper, which is developed aiming the smart grid context, can also be used in the current power system paradigm. The proposed system is the combination of several fields of research, namely multi-agent systems and artificial neural networks. This system is physically implemented in our laboratories and it is used daily by researchers. The physical implementation gives the system an improvement in the proof of concept, distancing itself from the conventional systems. This paper presents a case study illustrating the simulation of real-time pricing in a laboratory.

Enhancing SCIG-based wind turbine generator performance through reactive power control

Abstract: Increase in the market share of wind energy in total electricity generation and its impact to power grid has imposed new challenges to the stability of each wind turbine generator (WTG) unit. In the case of power undersupply, the problem on voltage stability and voltage collapse will eventually occur. In this paper, the impact of reactive power control in improving the performance of squirrel cage induction generator-based (SCIG-based) WTGs is presented. In the asynchronous operation of induction machine, the increment of wind power generation is feasible by absorption of more reactive power. Increasing the reactive power consumption of induction generator results in reduction of voltage in the bus connected to the wind farm from the grid. In this scenario, inadequate reactive power control can lead to instability in the power network. The studies conducted in this paper are based on the quasi-static time-domain simulations (QSTDS) and continuation power flow (CPF) algorithm framework. The results obtained indicate that with increment of wind power penetration in a power system, adequate reactive power support is required to maintain stability, else the stable performance of the wind farm will be threatened and will lead to over-speeding of SCIGs. The use of SVC and STATCOM as a practical solution in improvement of wind farms-based power system stability is investigated and presented.

Modeling and simulation of a grid-integrated photovoltaic system using a real-time digital simulator

Abstract: This paper discusses the modeling and simulation of a grid-integrated photovoltaic system using a real time digital simulator. The mathematical modeling and derivation of the parameters of the PV array using an analytical and iterative procedure is discussed. The PV array is interfaced to a three-phase grid using a sinusoidal pulse width modulated voltage source converter with maximum power point tracking. A decoupled dq current control strategy is used to control the real and reactive power exchanged between the PV system and the grid. An analysis of the real-time operation of the photovoltaic system is presented.

Decentralized demand side management and control of PEVs connected to a smart grid

Abstract: The recent push for electrified vehicles, including both plug-in hybrid vehicles and pure electric vehicle may further increase peak electrical load if left unmitigated, resulting in more demand for generation and transmission capacities Fortunately, PEVs can be treated as controllable loads or even power sources under extraneous situations for demand side management (DSM) Although centralized approach certainly performs an effective demand side management, an important concept regarding the privacy of the information access is not already considered The objective function for this multi objective problem of demand side power management and decentralized control is the total electricity generation cost and cost associated with implementing the demand side management programs Thus saving a unit of electricity because of implementing demand side management can be treated like producing a unit of electricity by a power plant The main constraint related to DSM is that the maximum expected saving that could be achieved by implementing DSM is capped to a realistic maximum limit The framework is flexible and could incorporate any meta-heuristic for multi-objective optimization This multi objective approach is applied on a test system comprising of 2516 domestic consumers, 296 small consumption firms, 150 medium consumption firms and 4 large consumption firms It is observed that PEVs could utilize information transfer with the grid to shape the effect exhibited on the overall load Also the obtained numerical results show that this approach will improve PEV market penetration, especially relative to centralized strategies that could deter consumers who wish to independently determine their charging strategy

A new electrical method on airflow fault detection of air handling unit (AHU)

Abstract: Air handler unit (AHU) is considered as the main part of the HVAC system consuming nearly half of the total energy. Airflow blockage and leakage has become a significant problem in AHU recently. This paper describes an electrical measurement based study and mainly focuses on the airflow blockage fault detection and the estimation of insufficient airflow. It proposes a relatively simple airflow fault-detection method based on the induction machine diagnostic work. The fan torque and speed are estimated in order to get the relationship between the airflow variation and the stator current of the induction motor. A real AHU system is built to detect the airflow variance and the electrical quantities such as stator current and voltage. The obtained results show correct detection of airflow fault in AHU.

The analysis of voltage increase phenomena in a distribution network with high penetration of distributed generation

Abstract: Various distributed generation (DG) systems with capacities in the range of several kilowatts to tens of megawatts can increase voltage along a feeder when they are injecting power into distribution systems. Thus, the main objective of this study is to analyze the transient behavior of such a distribution system integrated by DG systems. This study (1) models the IEEE 37-bus test feeder as a distribution network enhanced by DG systems in Simulink of MATLAB; (2) proposes case studies of DG systems with their total capacity of 10 and 38 percent of the feeder rating; and then (3) simulates the transient behavior of the test feeder when DG systems inject active power at the unity power factor during a few cycles of 60 Hz. Finally, it addresses the issues of an increase in voltage resulting from the installation of DG systems in a transient state.

Hydro-based, renewable hybrid energy sytem for rural/remote electrification in Nigeria

Abstract: Today, there is a tendency to forget that there are still many locations in the world which do not have an electrical connection to a central utility network. Furthermore, in many places due to remoteness and cost, it is unlikely that a main grid connection will ever be established. However the need for power still exists. Nigeria is abundantly blessed with all major sources of energy; solar power, wind, geothermal and bio-energy. But my country lacks the expertise to control and utilize these sources of power. Many remote areas of developing countries like Nigeria lacked supply of conventional energy sources (oil, grid extension) due to cost and poor infrastructure. However, many of them are also fortunate enough to live in the proximity to potential indigenous renewable energy sources such as hydro, solar, and wind. This paper presents the concept of using more than one renewable energy sources/technologies in solving the energy problem of rural or remote centers, especially in a region with renewable energy potential.

Optimal allocation of power routers in a STATCOM-installed electric grid with high penetration of wind energy

Abstract: Wind generation continues to increase as a source of renewable energy. However, adding intermittent renewable energy may lead to overloaded lines as well as low voltage buses. Static synchronous compensators (STATCOMs) can provide significant reactive power to ensure the voltage stability, but overloaded lines may still exist. Therefore, power routers, which route power away from overloaded lines to underutilized lines, are required. In order to provide the best power-flow control with the lowest cost, the power routers should be optimally designed, for both their ratings and locations. The coordination between the power routers and the STATCOMs should also be taken into consideration. This paper introduces a general approach to determine the optimal location and sizing of the power routers for a power system with overloaded lines, based on a particle swarm optimization (PSO) algorithm. Simulation studies on a 12-bus test system verify the proposed method.

Automated demand response of thermal load with a photovoltaic source for military microgrids

Abstract: Energy consumption by deployed United States Army troops has become an important issue. There is significant fiscal cost and risk of providing diesel fuel for generators due to precautions needed to defend fuel convoys. Photovoltaics can effectively reduce fuel requirements, but without battery storage introduce additional variability in demand due to their intermittent nature. A structurally insulated panel (SIP) housing prototype, or SIP-Hut, has been developed with the potential to greatly reduce thermal load compared to existing structures. This work investigates automated demand response of the SIPHut Environmental Control Unit (ECU), which leverages the increased elasticity of the SIP-Hut thermal demand, with a photovoltaic source. The objectives are to minimize the frequency of generator operation and mitigate variability of the intermittent PV source to reduce diesel fuel consumption. A detailed thermal model of the SIP-Hut is presented and validated, and simulation results of an ECU demand response controller are presented.

Smart grid and WAMS in Indian context – a review

Abstract: The Indian electricity sector faces many problems in trying to reduce the ever increasing demand-supply gap. Energy losses in India’s transmission and distribution sector exceed 30%, which is one of the highest in the world. Upgrading outdated transmission and distribution systems coupled with the need to reduce electricity losses and theft is driving the deployment of Smart Grid technologies in India. The real challenge in the power sector in India lies in managing the upgrading of the transmission, distribution and metering sector efficiently. From last two decades a new technology Wide area Monitoring systems (WAMS) for monitoring and synchronization of wide area networks have come to the fore as a means to address not only reliability concerns but also operational issues such as enhancing transfer capability in real time, advanced automatic corrective actions like adaptive islanding, blocking/DE blocking of distance relay zones under power swings, better visualization through state measurements, decision support tools etc. The present technological advancements have moved WAMS application into the area of smart grid. Several states in India have already implemented WAMS for fast, reliable and synchronous measurement and real time monitoring of system state of geographically spread power network. This paper discusses various technical issues related to smart grid initiatives and implications in context of WAMS technology in Indian power systems.

Scalable cellular computational network based WLS state estimator for power systems

Abstract: Modern interconnected electric power systems are made up of a large number of buses to meet the demand of electricity across large geographical distances. The large number of buses and interconnections across multiple areas result in a complex network and cause an increase in computational requirements on the processor. In order to meet the requirements of this increased complexity for state estimation, distributed estimation is getting attention nowadays. A new approach based on Cellular Computational Network (CCN) for static state estimation is proposed to overcome the computational demand of large power networks in general. The CCN architecture requires a cell at every bus where the states need to be estimated. A cell uses locally available information to estimate voltage magnitude and angle of its bus. The cells exploit output information of other cells in some electrical proximity prior to computing the outputs for next time step. Beside the promise of scalability of the CCN architecture, a fully observable system for state estimation and other applications can be realized. As the traditional estimators take all the measurements at a time and executes the estimation, missing some of the measurements may cause it to loose observability. In this paper, CCN based architecture is implemented with the popular Weighted Least Square (WLS) estimator on nonlinear power flow equations to estimate off-line data. Through simulation, the scalability and observability of the CCN based framework is investigated.

An LMI-SSI model based PSS design approach for a multi-machine power system

Abstract: In recent days, as power systems are operated close to the stability margin, oscillation caused by lack of damping torque is frequently observed. Power System Stabilizer (PSS) enhances generator stability by providing a supplementary signal to the automatic voltage regulator which enhances the damping torque. Stochastic Subspace Identification (SSI) algorithm is applied to obtain a linearized single-input-multiple-output model of a power system and the Linear Matrix Inequality (LMI) approach is then used to design several PSSs. Typical results are presented for the LMI-SSI model based PSS design on the IEEE 68 16- machine power system.

Optimal PMU placement for power system restoration

Abstract: PMU placement is important to achieve full system observability. Traditional PMU placement algorithms only work for systems in normal condition. During power system restoration, system topology and condition change in each step. Synchrophsors can help to improve the reliability and efficiency of restoration strategy. However, the original PMU placement cannot guarantee system observability in each restoration step. In this paper, a new optimal PMU placement is formulated for single and multiple islands restoration. With the aid of PMU, system operator can obtain real-time measurements of voltage (magnitude and angle) and frequency from different islands and perform the parallel restoration precisely. The proposed algorithm is tested in modified IEEE 14-bus system. Simulation results demonstrate the effectiveness of proposed model and the advantage of PMU-aided parallel restoration.

Selective harmonic elimination for extended cascaded multicell multilevel power converters

Abstract: This paper provides general solutions for nonlinear transcendental equations to determine the feasible switching angles for a fundamental frequency-switching-scheme modulated cascaded multicell multilevel power converter with a higher number of modules (H-bridges) and output voltage levels in order to eliminate the dominant low-order line-to-line voltage harmonics. Afterwards, for each cascaded multilevel converter, a feasible range of modulation index that culminates in a viable switching angles for a low switching-frequency selective harmonic elimination strategy is derived. The provided solutions as well as results expedite the burdensome and arduous computations required in solving the transcendental equations of selective harmonic elimination scheme for cascaded multicell converters with higher number of modules. The transcendental equations are solved by Newton iterative method and the solutions are provided for 11-level to 23-level cascaded multicell converters.

Active voltage balancing of five-level H-bridge flying capacitor multicell converter controlled with level-shifted-carrier PWM

Abstract: Flying capacitor multicell (FCM) converter is one of the well-known breeds of multilevel converters. There are several configurations of flying-capacitor-based converters presented and reviewed in the literature. One of the promising topologies of the FCM converter suitable for single/threephase applications requiring isolated converters is H-Bridge (Full-Bridge) FCM converter wherein two FCM converters are connected back-to-back encircling one dc voltage source. Due to a superior line-to-line harmonic performance of the level-shifted-carrier pulse-width-modulation (LSC-PWM), this paper proposes an active voltage control of five-level H-bridge FCM converter operated under LSC-PWMs. The general scheme of the proposed active voltage balancing is implemented by utilization of logic-gates without requiring any lookup table. The five-level H-bridge FCM is simulated in PSCAD and the simulation results are provided. Moreover, the performance of the proposed active voltage balancing is investigated under different LSC-PWM strategies to show which one results in a better harmonic performance and which one results in less voltage ripple across the flying capacitors.

Optimal operation and control for an electrical micro-grid

Abstract: This paper presents an optimization and control scheme for power converters in a micro-grid, which is composed of a wind energy system, an energy storage element (supercapacitor), a load and the interconnection to the utility grid. Based on the results of a dynamic optimization model, which establish the energy flow in the micro-grid, an optimal control scheme uses these results of electrical power values as set-points to efficiently integrate renewable energy to/from the utility grid through the optimal control of power converters. A case study micro-grid is used to integrate the energy from renewable resources, with the facility to storage energy, to provide of energy to loads and to provide/consume energy to/from the utility grid. Simulation results are presented to assess the performance of the proposed controller for the case study micro-grid.

Automatic generation of one-line schematic diagrams of distribution networks

Abstract: The objective of this paper is to present a two-step method for automatic generation of operation screens of distribution systems. The first step consists of reduction of the graph representing the network, based on filtering criteria that determine which elements should and which should not be preserved in the diagrams, as well as which parts of the network should be simplified and represented by equivalent elements. The second part is the automatic layout of the reduced graph according to general aesthetic criteria commonly found in the available literature and specific criteria adopted for this work by the team of operators of an actual network in an electric utility in Brazil, chosen as pilot project on which the results of the method will be presented.

A sensorless flux oriented control scheme for a DFIG connected to a DC link

Abstract: In this paper, a novel sensorless flux-oriented control scheme is presented to connect a DFIG to a dc link with arbitrary stator frequency. The rotor side of the DFIG is connected to the dc link through a converter while the stator is connecting to a three phase diode bridge with the dc side connected to a dc link. The control method used in this paper is regulating the stator frequency and the d-q axis voltage of the diode bridge to operate the DFIG at a desired stator frequency and generate the required power. The low-order harmonics in the stator current of DFIG are detected and regulated through control of the rotor currents based on multiple reference frame theory. Matlab/Simulink is employed to investigate the performance of proposed methods.