Showing papers on "Electrical network published in 2010"

Low-Voltage Bipolar-Type DC Microgrid for Super High Quality Distribution

Abstract: Microgrid is one of the new conceptual power systems for smooth installation of many distributed generations (DGs). While most of the microgrids adopt ac distribution as well as conventional power systems, dc microgrids are proposed and researched for the good connection with dc output type sources such as photovoltaic (PV) system, fuel cell, and secondary battery. Moreover, if loads in the system are supplied with dc power, the conversion losses from sources to loads are reduced compared with ac microgrid. As one of the dc microgrids, we propose “low-voltage bipolar-type dc microgrid,” which can supply super high quality power with three-wire dc distribution line. In this paper, one system for a residential complex is presented as an instance of the dc microgrid. In this system, each house has a cogeneration system (CGS) such as gas engine and fuel cell. The output electric power is shared among the houses, and the total power can be controlled by changing the running number of CGSs. Super capacitors are chosen as main energy storage. To confirm the fundamental characteristics and system operations, we experimented with a laboratory scale system. The results showed that the proposed system could supply high-quality power under several conditions.

Resistive Impedance Matching Circuit for Piezoelectric Energy Harvesting

Abstract: A two-stage power conditioning circuit consisting of an AC-DC converter followed by a DC-DC converter is proposed for a vibration-based energy harvesting system. The power conditioning circuit intends to maximize the amount of power extracted from a piezoelectric energy harvester by matching the source impedance with the circuit by adaptively adjusting the duty cycle. An equivalent electrical circuit representation derived from a distributed-parameter piezoelectric energy harvester model is adapted to enable the impedance matching method proposed here. For a given piezoelectric energy harvester, there is a theoretical maximum power output that is determined by the mechanical damping, base acceleration, and the effective mass of the harvester structure under base excitation. Experimental results are given to validate the effectiveness of the proposed resistive impedance matching circuit around the first resonance frequency of a cantilevered piezoelectric energy harvester.

Study of Reconfiguration for the Distribution System With Distributed Generators

Abstract: This paper proposes a reconfiguration methodology based on an Ant Colony Algorithm (ACA) that aims at achieving the minimum power loss and increment load balance factor of radial distribution networks with distributed generators. A 33-bus distribution system and a Tai-Power 11.4-kV distribution system were selected for optimizing the configuration and to demonstrate the effectiveness of the proposed methodology for solving the optimal switching operation of distribution systems. The simulation results have shown that lower system loss and better load balancing will be attained at a distribution system with distributed generation (DG) compared to a system without DG. Furthermore, the simulation results also satisfy and suitability reference merits of the proposal method.

A Generalized Computational Method to Determine Stability of a Multi-inverter Microgrid

Abstract: Microgrid-containing parallel-connected inverters, where each inverter is controlled by decentralized active power/voltage frequency and reactive power/voltage magnitude droop control laws results in flexible and expandable systems. These systems have been known to have stability problems for large values of active power/voltage frequency droop control gain. However, so far the stability analysis of multi-inverter systems has always been performed in a computationally intensive manner by considering the entire microgrid. In a practical microgrid, where the number of inverters may be large or the capacity of the units may differ, it becomes essential to develop a method by which stability can be examined without much computational burden. The system of differential algebraic equations has been simplified using justifiable assumptions to result in a final expression that allows the stability of the microgrid to be examined separately with respect to the droop control laws of each inverter transformed into an equivalent network. Moreover, the procedure allows taking into consideration the R/X ratio of the interconnecting cables. Analysis of final expressions validate the stability results reported in literature. Experimental results on hardware show the stable operation of the microgrid.

An Integrated Four-Port DC/DC Converter for Renewable Energy Applications

Abstract: This paper proposes a novel converter topology that interfaces four power ports: two sources, one bidirectional storage port, and one isolated load port. The proposed four-port dc/dc converter is derived by simply adding two switches and two diodes to the traditional half-bridge topology. Zero-voltage switching is realized for all four main switches. Three of the four ports can be tightly regulated by adjusting their independent duty-cycle values, while the fourth port is left unregulated to maintain the power balance for the system. Circuit analysis and design considerations are presented; the dynamic modeling and close-loop design guidance are given as well. Experimental results verify the proposed topology and confirm its ability to achieve tight independent control over three power-processing paths. This topology promises significant savings in component count and losses for renewable energy power-harvesting systems.

A Control Strategy for a Distributed Power Generation Microgrid Application With Voltage- and Current-Controlled Source Converter

Abstract: This paper presents a pseudodroop control structure integrated within a microgrid system through distributed power generation (DPG) modules capable to function in off-grid islanded, genset-connected, and grid-connected modes of operation. System efficiency has an important role in order to harvest the maximum available renewable energy from dc or ac sources while providing power backup capability. A control strategy is proposed in off-grid islanded mode method based on the microgrid line-frequency control as agent of communication for energy control between the DPG modules. A critical case is where the ac load demand could be lower than the available power from the photovoltaic solar array, where the battery bank can be overcharged with unrecoverable damage consequences. The DPG voltage-forming module controls the battery charge algorithm with a frequency-generator function, and the DPG current source module controls its output current through a frequency-detection function. The physical installation between DPG modules is independent, since no additional communication wiring is needed between power modules, which represent another integration advantage within the microgrid-type application.

Decentralised control of voltage in distribution systems by distributed generators

Abstract: Recently, renewable energy such as wind turbine generators and photovoltaic systems are introduced as distributed generators (DGs). Connection of a large amount of DG causes voltage deviation beyond the statutory range in distribution systems. Reactive power control of inverters interfaced with DGs is one of the solutions against this problem. Additionally, reactive power control has a possibility to contribute to the reduction of distribution loss. In this study, the authors propose a voltage control method in distribution systems by reactive power control of inverters interfaced with DGs. The proposed method has been developed in order to reduce distribution loss and voltage regulation into statutory range without any telecommunication. In the proposed method, each interfaced inverter controls reactive power based on voltage control reference, which is calculated from self-information. The calculation rule of control reference has been developed using optimal data which consist of relations between randomly given inputs and corresponding optimal outputs, which are calculated by an optimisation technique. Simulations are conducted to show the effectiveness of the proposed method.

Methods of Interfacing Rotating Machine Models in Transient Simulation Programs

Abstract: The electromagnetic transient programs (EMTP-like tools) are based on the nodal (or modified nodal) equations that enable an efficient numerical solution and, subsequently, fast time-domain simulations. The state-variable-based simulation programs, such as Simulink, are also used for studying the dynamics of electrical systems. Both the offline and real-time versions of these two types of simulation tools are widely used by the researchers and engineers in industry and academia to study the transient phenomena and dynamics in power systems with rotating electrical machines. This paper provides a summary of the interfacing techniques that are utilized to integrate the general-purpose models of electrical machines with the rest of the power system network for these studies. The interfacing methods are broadly classified as indirect and direct approaches. The paper also describes the numerical properties as well as limitations imposed by the interfacing of the commonly used machine models that should be considered when selecting the simulation parameters and assessing the final results.

Global Voltage Sag Mitigation With FACTS-Based Devices

Abstract: This paper presents an approach to optimally select and allocate flexible ac transmission (FACTS) devices in a distribution network in order to minimize the number of voltage sags at network buses. The method proposed is based on the optimization of a preselected objective function using simple and niching genetic algorithms (GA). The objective of the optimization is to achieve the improvement in overall system sag performance of the network. Using proposed GA-based optimization, the location, the type and the rating of six (in total) FACTS devices are optimized simultaneously. Three types of FACTS devices are implemented in this study, namely, static var compensator, static compensator, and dynamic voltage restorer. The performance of the proposed algorithm is tested and illustrated on 295-bus generic distribution system.

Real-time microgrid power analytics portal for mission critical power systems

Abstract: Systems and method for providing a microgrid power analytics portal for mission critical power systems are provided. The techniques disclosed herein provides for real-time modeling, evaluation, and commodity market pricing and optimization for an electrical network that includes microgrids using data collected from virtually any digital data source. The portal is platform independent and can be configured to collect and aggregate real-time data from sensors interfaced with components of the electrical network regardless of proprietary architectures or vendor-specific limitations imposed by the sensors or data collection software.

The Electrical Double Layer and Its Structure

Abstract: At any electrode immersed in an electrolyte solution, a specific interfacial region is formed This region is called the double layer The electrical properties of such a layer are important, since they significantly affect the electrochemical measurements In an electrical circuit used to measure the current that flows at a particular working electrode, the double layer can be viewed as a capacitor Figure I11 depicts this situation where the electrochemical cell is represented by an electrical circuit and capacitor C d corresponds to the differential capacity of the double layer To obtain a desired potential at the working electrodes, the double-layer capacitor must be first appropriately charged, which means that a capacitive current, not related to the reduction or oxidation of the substrates, flows in the electrical circuit While this capacitive current carries some information concerning the double layer and its structure, and in some cases can be used for analytical purposes, in general, it interferes with electrochemical investigations A variety of methods are used in electrochemistry to depress, isolate, or filter the capacitive current

PABTEC: Passivity-Preserving Balanced Truncation for Electrical Circuits

Abstract: We present a passivity-preserving balanced truncation model reduction method for differential-algebraic equations arising in circuit simulation. This method is based on balancing the solutions of projected Lur'e equations. By making use of the special structure of circuit equations, we can reduce the numerical effort for balanced truncation significantly. It is shown that the property of reciprocity is also preserved in the reduced-order model. Network topological interpretations of certain circuit effects are given. The presented model reduction method is illustrated by numerical examples.

Transformer Core Parameter Identification Using Frequency Response Analysis

Abstract: We present a novel model-based approach for parameter identification of a laminated core, such as magnetic permeability and electrical conductivity, of power transformers on the basis of frequency response analysis (FRA) measurements. The method establishes a transformer core model using the duality principle between magnetic and electrical circuits for parameter identification with genetic algorithms. We use reference input impedance frequency responses, calculated by a well-known lumped parameter model of a three-phase transformer and finite-element computations, to analyze identification accuracy of the method. The results verify the ability of the approach to accurately identify the core lamination parameters with respect to the reference values. The approach can be used for parameter identification of a demagnetized core with known geometrical parameters when the core lamination samples are unavailable for experimental tests. The approach can also be employed for transformer core modeling and FRA result interpretation at low frequencies.

Structural Vibration Reduction by Switch Shunting of Piezoelectric Elements: Modeling and Optimization

Abstract: This work deals with the reduction of structural vibrations by means of synchronized switch damping techniques on piezoelectric elements. Piezoelectric patches are attached to the vibrating structure and connected to an electrical circuit that includes a switch. The latter allows to continuously switch the piezoelectric elements from an open-circuit state to a specific electric impedance, synchronously with the mechanical oscillations. The present study focuses on two goals: (i) the quantification of the added damping, (ii) the optimization of the electric circuit parameters, carried out on a one degree of freedom model. The free and forced responses of one mode of the mechanical structure are studied in detail. The precise time response of the system is obtained with semi-analytical models for the two cases where the electrical impedance is a simple resistance (synchronized switch damping on short circuit) or a resistance in series with an inductance (synchronized switch damping on inductor). The damping...

Method and system for power management

Abstract: A method and a system for power management for a plant electrical network are provided. The power management system over a plant-wide communication network includes both concepts of hierarchical level and distributed level power management using multiple controllers. At least one controller in the power management system is configured for power management in a first local process area within the plant electrical network and is capable to communicate with at least a second controller configured for power management in a second local process area within the plant electrical network over the communication network.

A Clustering-Based Method for Quantifying the Effects of Large On-Grid PV Systems

Abstract: Analyzing the impacts of large on-grid photovoltaic (PV) systems on the performance of the electric network is an essential task prior to the installation of these systems. To quantify these impacts, a method based on chronological simulations can be used. The main advantage of this method is its ability to provide information about the impacts of the fluctuation of the power generated from the PV systems. However, this method requires performing extensive analysis and simulations, making it impractical for utility studies, especially if long historical data with subhourly time resolution is used. In this paper, a new method that utilizes the data efficiently while preserving the temporal information of the generated PV power is proposed. The method takes advantage of the clustering techniques to group together segments of the output PV power having similar features. Hence, a representative segment for each group can be chosen and used in the analysis and simulations. This representative segment can provide information about the expected performance of other segments of the group. The validity and usefulness of the proposed method are demonstrated by identifying the suitable size and site of a large PV system.

Method for operating a wind turbine

Abstract: The invention concerns a method of operating a wind power installation. The wind power installation has a circuit for measuring the frequency prevailing in the electrical supply network connected to a control device for controlling operation of the wind power installation. It is proposed that the power delivered by the generator of the wind power installation to the network is increased quickly and for a short period above the currently prevailing power of the wind power installation if the network frequency of the electrical network is below the desired target frequency of the network by a predetermined frequency value.