Showing papers on "Power factor published in 2006"

Control of permanent-magnet generators applied to variable-speed wind-energy systems connected to the grid

Abstract: Wind energy is a prominent area of application of variable-speed generators operating on the constant grid frequency. This paper describes the operation and control of one of these variable-speed wind generators: the direct driven permanent magnet synchronous generator (PMSG). This generator is connected to the power network by means of a fully controlled frequency converter, which consists of a pulsewidth-modulation (PWM) rectifier, an intermediate dc circuit, and a PWM inverter. The generator is controlled to obtain maximum power from the incident wind with maximum efficiency under different load conditions. Vector control of the grid-side inverter allows power factor regulation of the windmill. This paper shows the dynamic performance of the complete system. Different experimental tests in a 3-kW prototype have been carried out to verify the benefits of the proposed system.

Multiple harmonics control for three-phase grid converter systems with the use of PI-RES current controller in a rotating frame

Abstract: Voltage source inverters connected to the grid in applications such as active rectifiers, active filters, uninterruptible power supplies, and distributed generation systems need an optimal ac current control. To obtain zero steady-state error at the fundamental frequency (i.e., unity power factor), the use of a standard integrator in a rotating frame is as effective as the use of a resonant controller in a stationary frame. However, the grid voltage harmonics influence the current controller and generate current harmonics unless several integrators in multiple rotating frames or resonant compensators in a stationary frame are adopted. In this letter, a hybrid system consisting of a proportional integral (PI) controller plus a generic hth harmonic resonant controller implemented in a frame rotating at the n th harmonic frequency is discussed in detail. The hth harmonic controller is able to decrease both the (h - n)th and (h + n)th harmonics, while the PI controller is able to decrease other harmonics if the synchronization phase signal adopted for the frame transformation is unfiltered. It is demonstrated that the use of a PI and sixth harmonic resonant compensator is effective for both positive and negative sequence fifth and seventh harmonics; hence, four harmonics are compensated with the proportional integral-resonant (PI-RES) controller implemented in a synchronous frame. Simulation and experimental tests validate the proposed analysis

A 950-MHz rectifier circuit for sensor network tags with 10-m distance

Abstract: This paper presents a 950-MHz wireless power transmission system and a high-sensitivity rectifier circuit for ubiquitous sensor network tags. The wireless power transmission offers a battery-life-free sensor tag by recharging the output power of a base station into a secondary battery implemented with the tag. For realizing the system, a high-sensitivity rectifier with dynamic gate-drain biasing has been developed in a 0.3-/spl mu/m CMOS process. The measurement results show that the proposed rectifier can recharge a 1.2-V secondary battery over -14-dBm input RF power at a power conversion efficiency of 1.2%. In the proposed wireless system, this sensitivity corresponds to 10-m distance communication at 4-W output power from a base station.

Interfacing Renewable Energy Sources to the Utility Grid Using a Three-Level Inverter

Abstract: This paper presents a novel approach for the connection of renewable energy sources to the utility grid. Due to the increasing power capability of the available generation systems, a three-level three-phase neutral-point-clamped voltage-source inverter is selected as the heart of the interfacing system. A multivariable control law is used for the regulator because of the intrinsic multivariable structure of the system. A current source (playing the role of a generic renewable energy source) is connected to the grid using a three-level inverter in order to verify the good performance of the proposed approach. Large- and small-signal d-q state-space averaged models of the system are obtained and used to calculate the multivariable controller based on the linear quadratic regulator technique. This controller simultaneously regulates the dc-link voltage (to operate at the maximum power point of the renewable energy source), the mains power factor (the power is delivered to the grid at unity power factor), and the dc-link neutral-point voltage balance. With the model and regulator presented, a specific switching strategy to control the dc-link neutral-point voltage is not required. The proposed controller can be used for any application, since its nature makes possible the control of any system variable. The good performance of the presented interfacing solution in both steady-state and transient operation is verified through simulation and experimentation using a 1-kW neutral-point-clamped voltage-source-inverter prototype, where a PC-embedded digital signal processor board is used for the controller implementation

Electric power systems : a conceptual introduction

Abstract: Preface. 1. The Physics of Electricity. 1.1 Basic Quantities. 1.1.1 Introduction. 1.1.2 Charge. 1.1.3 Potential or Voltage. 1.1.4 Ground. 1.1.5 Conductivity. 1.1.6 Current. 1.2 Ohm's law. 1.2.1 Resistance. 1.2.2 Conductance. 1.2.3 Insulation. 1.3 Circuit Fundamentals. 1.3.1 Static Charge. 1.3.2 Electric Circuits. 1.3.3 Voltage Drop. 1.3.4 Electric Shock. 1.4 Resistive Heating. 1.4.1 Calculating Resistive Heating. 1.4.2 Transmission Voltage and Resistive Losses. 1.5 Electric and Magnetic Fields. 1.5.1 The Field as a Concept. 1.5.2 Electric Fields. 1.5.3 Magnetic Fields. 1.5.4 Electromagnetic Induction. 1.5.5 Electromagnetic Fields and Health Effects. 1.5.6 Electromagnetic Radiation. 2. Basic Circuit Analysis. 2.1 Modeling Circuits. 2.2 Series and Parallel Circuits. 2.2.1 Resistance in Series. 2.2.2 Resistance in Parallel. 2.2.3 Network Reduction. 2.2.4 Practical Aspects. 2.3 Kirchhoff's Laws. 2.3.1 Kirchhoff's Voltage Law. 2.3.2 Kirchhoff's Current Law. 2.3.3 Application to Simple Circuits. 2.3.4 The Superposition Principle. 2.4 Magnetic Circuits. 3. AC Power. 3.1 Alternating Current and Voltage. 3.1.1 Historical Notes. 3.1.2 Mathematical Description. 3.1.3 The rms Value. 3.2 Reactance. 3.2.1 Inductance. 3.2.2 Capacitance. 3.2.3 Impedance. 3.2.4 Admittance. 3.3 Power. 3.3.1 Definition of Electric Power. 3.3.2 Complex Power. 3.3.3 The Significance of Reactive Power. 3.4 Phasor Notation. 3.4.1 Phasors as Graphics. 3.4.2 Phasors as Exponentials. 3.4.3 Operations with Phasors. 4. Generators. 4.1 The Simple Generator. 4.2 The Synchronous Generator. 4.2.1 Basic Components and Functioning. 4.2.2 Other Design Aspects. 4.3 Operational Control of Synchronous Generators. 4.3.1 Single Generator: Real Power. 4.3.2 Single Generator: Reactive Power. 4.3.3 Multiple Generators: Real Power. 4.3.4 Multiple Generators: Reactive Power. 4.4 Operating Limits. 4.5 The Induction Generator. 4.5.1 General Characteristics. 4.5.2 Electromagnetic Characteristics. 4.6 Inverters. 5. Loads. 5.1 Resistive Loads. 5.2 Motors. 5.3 Electronic Devices. 5.4 Load from the System Perspective. 5.4.1 Coincident and Noncoincident Demand. 5.4.2 Load Profiles and Load Duration Curve. 5.5 Single- and Multiphase Connections. 6. Transmission and Distribution. 6.1 System Structure. 6.1.1 Historical Notes. 6.1.2 Structural Features. 6.1.3 Sample Diagram. 6.1.4 Topology. 6.1.5 Loop Flow. 6.1.6 Stations and Substations. 6.1.7 Reconfiguring the System. 6.2 Three-Phase Transmission. 6.2.1 Rationale for Three Phases. 6.2.2 Balancing Loads. 6.2.3 Delta and Wye Connections. 6.2.4 Per-Phase Analysis. 6.2.5 Three-Phase Power. 6.2.6 D.C. Transmission. 6.3 Transformers. 6.3.1 General Properties. 6.3.2 Transformer Heating. 6.3.3 Delta and Wye Transformers. 6.4 Characteristics of Power Lines. 6.4.1 Conductors. 6.4.2 Towers, Insulators, and Other Components. 6.5 Loading. 6.5.1 Thermal Limits. 6.5.2 Stability Limit. 6.6 Voltage Control. 6.7 Protection. 6.7.1 Basics of Protection and Protective Devices. 6.7.2 Protection Coordination. 7. Power Flow Analysis. 7.1 Introduction. 7.2 The Power Flow Problem. 7.2.1 Network Representation. 7.2.2 Choice of Variables. 7.2.3 Types of Buses. 7.2.4 Variables for Balancing Real Power. 7.2.5 Variables for Balancing Reactive Power. 7.2.6 The Slack Bus. 7.2.7 Summary of Variables. 7.3 Example with Interpretation of Results. 7.3.1 Six-Bus Example. 7.3.2 Tweaking the Case. 7.3.3 Conceptualizing Power Flow. 7.4 Power Flow Equations and Solution Methods. 7.4.1 Derivation of Power Flow Equations. 7.4.2 Solution Methods. 7.4.3 Decoupled Power Flow. 7.5 Applications and Optimal Power Flow. 8. System Performance. 8.1 Reliability. 8.1.1 Measures of Reliability. 8.1.2 Valuation of Reliability. 8.2 Security. 8.3 Stability. 8.3.1 The Concept of Stability. 8.3.2 Steady-State Stability. 8.3.3 Dynamic Stability. 8.3.4 Voltage Stability. 8.4 Power Quality. 8.4.1 Voltage. 8.4.2 Frequency. 8.4.3 Waveform. 9. System Operation, Management, and New Technology. 9.1 Operation and Control on Different Time Scales. 9.1.1 The Scale of a Cycle. 9.1.2 The Scale of Real-Time Operation. 9.1.3 The Scale of Scheduling. 9.1.4 The Planning Scale. 9.2 New Technology. 9.2.1 Storage. 9.2.2 Distributed Generation. 9.2.3 Automation. 9.2.4 FACTS. 9.3 Human Factors. 9.3.1 Operators and Engineers. 9.3.2 Cognitive Representations of Power Systems. 9.3.3 Operational Criteria. 9.3.4 Implications for Technological Innovation. 9.4 Implications for Restructuring. Appendix: Symbols, Units, Abbreviations, and Acronyms. Index.

Photovoltaic Power Conditioning System With Line Connection

Abstract: A photovoltaic (PV) power conditioning system (PCS) with line connection is proposed. Using the power slope versus voltage of the PV array, the maximum power point tracking (MPPT) controller that produces a smooth transition to the maximum power point is proposed. The dc current of the PV array is estimated without using a dc current sensor. A current controller is suggested to provide power to the line with an almost-unity power factor that is derived using the feedback linearization concept. The disturbance of the line voltage is detected using a fast sensing technique. All control functions are implemented in software with a single-chip microcontroller. Experimental results obtained on a 2-kW prototype show high performance such as an almost-unity power factor, a power efficiency of 94%, and a total harmonic distortion (THD) of 3.6%

Harmonics and Power Systems

Abstract: FUNDAMENTALS OF HARMONIC DISTORTION AND POWER QUALITY INDICES IN ELECTRIC POWER SYSTEMS Introduction Basics of Harmonic Theory Linear and Nonlinear Loads Fourier Series Power Quality Indices under Harmonic Distortion Power Quantities under Nonsinusoidal Situations References HARMONIC SOURCES Introduction The Signature of Harmonic Distortion Traditional Harmonic Sources Future Sources of Harmonics References STANDARDIZATION OF HARMONIC LEVELS Introduction Harmonic Distortion Limits References EFFECTS OF HARMONICS ON DISTRIBUTION SYSTEMS Introduction Thermal Effects on Transformers Miscellaneous Effects on Capacitor Banks Abnormal Operation of Electronic Relays Lighting Devices Telephone Interference Thermal Effects on Rotating Machines Pulsating Torques in Rotating Machines Abnormal Operation of Solid-State Devices Considerations for Cables and Equipment Operating in Harmonic Environments References HARMONICS MEASUREMENTS Introduction Relevant Harmonic Measurement Questions Measurement Procedure Relevant Aspects References HARMONIC FILTERING TECHNIQUES Introduction General Aspects in the Design of Passive Harmonic Filters Single-Tuned Filters Band-Pass Filters Relevant Aspects to Consider in the Design of Passive Filters Methodology for Design of Tuned Harmonic Filters Example 1: Adaptation of a Power Factor Capacitor Bank into a Fifth Harmonic Filter Example 2: Digital Simulation of Single-Tuned Harmonic Filters Example 3: High-Pass Filter at Generator Terminals Used to Control a Resonant Condition Example 4: Comparison between Several Harmonic Mitigating Schemes Using University of Texas at Austin HASIP Program References OTHER METHODS TO DECREASE HARMONIC DISTORTION LIMITS Introduction Network Topology Reconfiguration Increase of Supply Mode Stiffness Harmonic Cancellation through Use of Multipulse Converters Series Reactors as Harmonic Attenuator Elements Phase Balancing Reference HARMONIC ANALYSES Introduction Power Frequency vs. Harmonic Current Propagation Harmonic Source Representation Harmonic Propagation Facts Flux of Harmonic Currents Interrelation between AC System and Load Parameters Analysis Methods Examples of Harmonic Analysis References FUNDAMENTALS OF POWER LOSSES IN HARMONIC ENVIRONMENTS Introduction Meaning of Harmonic-Related Losses Relevant Aspects of Losses in Power Apparatus and Distribution Systems Harmonic Losses in Equipment Example of Determination of K Factor Rotating Machines References INDEX

Methods and apparatus for high power factor controlled power delivery using a single switching stage per load

Abstract: Methods and apparatus for high power factor power transfer to a load using a single switching stage. In exemplary implementations, a controllable variable power may be delivered to a load using a single switching stage while maintaining high power factor, in some cases without requiring any feedback information relating to the load conditions (i.e., without monitoring load voltage and/or current) to control normal switching operations in the single switching stage, and without requiring regulation of load voltage and/or load current. In one example, a single stage high power factor driver is used to control power delivery to an LED-based light source.

Single-phase single-stage photovoltaic generation system based on a ripple correlation control maximum power point tracking

Abstract: A maximum power point tracking algorithm for single-stage converters connecting photovoltaic (PV) panels to a single-phase grid is presented in this paper. The algorithm is based on the application of the "ripple correlation control" using as perturbation signals the current and voltage low-frequency oscillations introduced in the PV panels by the single-phase utility grid. The proposed control technique allows the generation of sinusoidal grid currents with unity power factor. The algorithm has been developed to allow an array of PV modules to be connected to the grid by using a single-stage converter. This simple structure yields higher efficiency and reliability when compared with standard solutions based on double-stage converter configurations. The proposed maximum power point tracking algorithm has been numerically simulated and experimentally verified by means of a converter prototype connected to a single-phase grid. The results are presented in the paper, showing the effectiveness of the proposed system.

Instantaneous reactive power p-q theory and power properties of three-phase systems

Abstract: This paper investigates how power phenomena and properties of three-phase systems are described and interpreted by the Instantaneous Reactive Power (IRP) p-q Theory. This paper demonstrates that this theory misinterprets power properties of electrical systems or provides some results that at least defy a common sense or meaning of some notions in electrical engineering. For example, it suggests the presence of an instantaneous reactive current in supply lines of purely resistive loads and the presence of an instantaneous active current in supply lines of purely reactive loads. Moreover, it suggests that line currents of linear loads with sinusoidal supply voltage contain a nonsinusoidal component. This paper shows, moreover, that the IRP p-q Theory is not capable to identify power properties of three-phase loads instantaneously. A pair of instantaneous values of p and q powers does not allow us to conclude whether the load is resistive, reactive, balanced, or unbalanced. It is known that a load imbalance reduces power factor. However, the IRP p-q Theory does not identify the load imbalance as the cause of power factor degradation.

Analysis and design of a low-stress buck-boost converter in universal-input PFC applications

Abstract: In converters for power-factor-correction (PFC), the universal-input capability, i.e., the ability to operate from any ac line voltage world-wide, comes with a heavy penalty in terms of component stresses and losses, and with restrictions on the dc output voltage. In this paper, we propose a new two-switch topology, boost-interleaved buck-boost (BoIBB) converter, which can offer significant performance improvements over single-switch buck-boost converters (including flyback, SEPIC, or Cuk topologies) or other two-switch buck-boost converters in universal-input PFC applications. The paper presents an analysis of the converter operation and component stresses, as well as design guidelines. High efficiency (over 93%) throughout the universal-input ac line voltage range is demonstrated on an experimental 100-W, 200-V dc output, universal-input BOIBB PFC rectifier.

Design of charge pump circuit with consideration of gate-oxide reliability in low-voltage CMOS processes

Abstract: A new charge pump circuit with consideration of gate-oxide reliability is designed with two pumping branches in this paper. The charge transfer switches in the new proposed circuit can be completely turned on and turned off, so its pumping efficiency is higher than that of the traditional designs. Moreover, the maximum gate-source and gate-drain voltages of all devices in the proposed charge pump circuit do not exceed the normal operating power supply voltage (VDD). Two test chips have been implemented in a 0.35-/spl mu/m 3.3-V CMOS process to verify the new proposed charge pump circuit. The measured output voltage of the new proposed four-stage charge pump circuit with each pumping capacitor of 2 pF to drive the capacitive output load is around 8.8 V under 3.3-V power supply (VDD = 3.3 V), which is limited by the junction breakdown voltage of the parasitic pn-junction in the given process. The new proposed circuit is suitable for applications in low-voltage CMOS processes because of its high pumping efficiency and no overstress across the gate oxide of devices.

Impact of DG interface control on islanding detection and nondetection zones

Abstract: Islanding detection of Distributed Generation (DG) is considered as one of the most important aspects when interconnecting DGs to the distribution system. With the increasing penetration and reliance of the distribution systems on DGs, new interface control strategies are being proposed. Aside from its main task of supplying active power, the DG could provide voltage support, improve the power factor, or mitigate other power quality problems. This paper examines the impact of the interface control strategy of inverter based DGs on islanding detection. The Nondetective Zone (NDZ) for over/under voltage and over/under frequency is derived analytically for each interface control and validated by simulation.

Carrier-Based Modulation Technique for Matrix Converter

Abstract: This paper presents a carrier-based modulation method for a matrix converter. By using the offset voltage and changing the slope of carrier, it is possible to synthesize the sinusoidal input currents with the unity power factor and desired output voltages. The proposed method is equivalent to the so called space vector pulsewidth modulation method. The proposed method uses a new point of view to understand the matrix converter modulation method such as the voltage source inverter (VSI) modulation method. Using the proposed method, this paper presents the two-phase/three-phase modulation method and dynamic/steady-state overmodulation method for the matrix converter. These methods are well developed in the study of a VSI. By the proposed steady-state overmodulation method, it is possible to synthesize the fundamental component of output voltage to be equal to that of input voltage at the cost of some distortion of input current. The feasibility of the proposed modulation method has been verified by a computer simulation and experimental results. These results show that the proposed carrier-based modulation method can be implemented easily without any tables. It can be used for the application where a higher voltage transfer ratio is essential

Novel Solar-Cell Power Supply System Using a Multiple-Input DC–DC Converter

Abstract: Recently, the clean electric power generation systems have attracted a great deal of social attention to exploit the clean-energy resources such as solar arrays, wind generators, fuel cells, and so forth. In this case, a multiple-input dc–dc converter is useful to combine the several input power sources and to supply the regulated output voltage for the load from the power sources. The novel solar-cell power supply system using the buck–boost-type two-input dc–dc converter is proposed, in which a solar array and a commercial ac line are employed as power sources and are combined by two input windings of the energy-storage reactor. Also, its operation principle and performance characteristics are discussed. Furthermore, the solar-cell optimum-operating-point tracker is proposed and examined. It is confirmed by the experiment that the proposed solar-cell power supply system has excellent performance characteristics.

A neutral-point clamped converter system for direct-drive variable-speed wind power unit

Abstract: Recent and ongoing developments in wind turbine technology indicate a trend towards utilization of high capacity (e.g., up to 5 MW) wind power units in large wind farms. Higher capacity of the wind turbine necessitates operation of the corresponding electric machine and the static converter system at higher voltages. This paper presents a neutral point diode clamped (NPC) converter system that inherently accommodates higher voltage and power ratings of a high capacity wind power unit. The overall control strategy of an NPC-based wind power unit and the details of the ac side and the dc side controls of the NPC converter system are also described. The generator-side NPC converter provides torque-speed control of the turbine-generator unit. The network-side NPC converter controls real and reactive power flow to the network and thus regulates the dc bus voltage and the ac side power-factor (or voltage) respectively. The paper also presents a new control approach to balance the dc capacitor voltages. The NPC converter system is augmented with a dc chopper that controls the synchronous generator field current. The NPC-based converter system is used to interface a 3 MW, direct-drive (gearless), synchronous machine based wind power unit to the utility grid. Performance of the overall NPC-based wind power unit, under the proposed controls, is evaluated based on time domain simulations in the power systems computer aided design (PSCAD) electromagnetic transient for DC (EMTDC) environment.

Sensing current flowing through a power line

Abstract: There is provided a method for measuring a parameter of a power frequency current being carried by a power line. The method that includes (a) transducing a power frequency current flowing through a power line, into a power frequency voltage, via an inductive coupler that couples a communications signal from the power line, (b) separating the power frequency voltage from the communications signal, and (c) determining a value of a parameter of the power frequency current from the power frequency voltage. There is also provided a system and an apparatus for measuring the parameter.

A Compact Digitally Controlled Fuel Cell/Battery Hybrid Power Source

Abstract: A compact digitally controlled fuel cell/battery hybrid power source is presented in this paper. The hybrid power source composed of fuel cells and batteries provides a much higher peak power than each component alone while preserving high energy density, which is important and desirable for many modern electronic devices, through an appropriately controlled dc/dc power converter that handles the power flow shared by the fuel cell and the battery. Rather than being controlled to serve only as a voltage or current regulator, the power converter is regulated to balance the power flow to satisfy the load requirements while ensuring the various limitations of electrochemical components such as battery overcharge, fuel cell current limit (FCCL), etc. Digital technology is applied in the control of power electronics due to many advantages over analog technology such as programmability, less susceptibility to environmental variations, and low parts count. The user can set the FCCL, battery current limit, and battery voltage limit in the digital controller. A control algorithm that is suitable for regulating the multiple variables in the hybrid system is described by using a state-machine-based model; the issues about embedded control implementation are addressed; and the large-signal behavior of the hybrid system is analyzed on a voltage-current plane. The hybrid power source is then tested through simulation and validated on real hardware. This paper also discusses some important issues of the hybrid power source, such as operation under complex load profiles, power enhancement, and optimization of the hybrid system. The design presented here can not only be scaled to larger or smaller power capacities for a variety of applications but also be used for many other hybrid power sources

Single crystals and nonlinear process for outstanding vibration-powered electrical generators

Abstract: This paper compares the performances of vibration-powered electrical generators using a piezoelectric ceramic and a piezoelectric single crystal associated to several power conditioning circuits. A new approach of the piezoelectric power conversion based on a nonlinear voltage processing is presented, leading to three novel high performance power conditioning interfaces. Theoretical predictions and experimental results show that the nonlinear processing technique may increase the power harvested by a factor of 8 compared to standard techniques. Moreover, it is shown that, for a given energy harvesting technique, generators using single crystals deliver 20 times more power than generators using piezoelectric ceramics.

Transformer tank vibration modeling as a method of detecting winding deformations-part II: experimental verification

Abstract: In Part I of the paper, a tank vibration model was proposed as a method to detect the winding deformations in power transformers. This model is incorporated in a model-based monitoring system for power transformers. In this paper, the experimental verification of the proposed model that calculates vibration on the transformer tank is reported. The model was validated in a 1500-kVA experimental transformer constructed as a reduced scale model of a 60-MVA 220-kV unit. In order to load the test transformer, the opposition method described in IEC 60076-2 Standard was used allowing to vary the load and power factor over a wide range. Sensors to measure vibrations and temperature were installed in the test transformer. The model was validated under different test transformer operating conditions. In order to verify the model's ability to detect failures, a deformation was provoked in the test transformer winding. Model predictions were compared with the measured vibration in that situation. The model has also been applied to four (30-40 MVA) grid transformers. Some results of this field validation are presented in this paper.

Boost current multilevel inverter and its application on single-phase grid-connected photovoltaic systems

Abstract: This work presents a novel current multilevel (CML) inverter topology, named boost CML inverter, and its application on energy processing of single-phase grid-connected photovoltaic (PV) systems. The structure allows a high power factor operation of a PV system, injecting a quasi-sinusoidal current into the grid, with virtually no displacement in relation to the line voltage at the point of common coupling among the PV system and the loads. The major appeals of using the CML technique are the balanced current sharing among semiconductor switches and the decrease of the current slope in the circuit devices, with a consequent reduction of conducted and radiated electromagnetic interference (EMI). The CML technique also allows adapting or minimizing current waveforms harmonic content. System description, mathematical approach, and design guidelines are presented, providing an overview of the new topology. In order to validate the proposed concepts, experimental measurements, made in a small-scale laboratory prototype, are also presented. The obtained results evidence the feasibility of the application of this new topology on singlephase grid-connected PV systems.

A comparison of voltage stability indices

Abstract: Voltage stability has become a very important issue of power systems analysis. This paper discusses some important aspects related to voltage stability indices in electric power systems. Some techniques previously studied in the literature are analyzed and a comparison of the performance of several indices is presented. The effectiveness of the analyzed methods are demonstrated through numerical studies in IEEE 14 busbar test system, using several different scenarios of load increase.

Optimized one-cycle control in photovoltaic grid connected applications

Abstract: The use of one-cycle control (OCC) for maximum power point tracking (MPPT) and power factor correction (PFC) in grid connected photovoltaic (PV) applications is discussed. Circuit and operating parameters of the one cycle-based controller of a cost-effective single-stage inverter are optimized in order to obtain the best performances of the system under different irradiance levels. Firstly, design constraints are formulated which allow to get a very efficient OCC operation in terms of power extracted from the PV array, stability, and PFC. Afterwards, such constraints are used to perform the parametric optimization of the one cycle controller by means of suitable heuristic approaches. Various selection criteria of the best parameters set under different conditions are discussed and applied. Finally, a customized perturb and observe (P&O) control is applied to the optimized one cycle controlled single-stage inverter in order to perform a real MPPT in presence of varying irradiance conditions. Subjects described here are covered by the Italian Patent Application SA2005A000014-13.07.2005 and PCT Application PCT/IT2005/000747-20.12.2005

A New Duty Cycle Control Strategy for Power Factor Correction and FPGA Implementation

Abstract: The bottleneck of digital control for power factor correction (PFC) implementations is mainly due to three aspects: high calculation requirements, high cost, and limited switching frequency compared with analog implementations. A new duty cycle control strategy for boost PFC implementations is proposed in this paper. The duty cycle is determined based on the input voltage, reference output voltage, inductor current, and reference current. The duty cycle determination algorithm includes two terms, the current term and the voltage term, which can be calculated in parallel and requires only one multiplication and three additions (subtractions) operations in digital implementation. A 400-kHz switching frequency boost PFC based on field programmable gate array implementation and its test results show that the proposed new duty cycle control strategy has great potential in the next generation of high switching frequency PFC implementations, due to its lower calculation requirement, lower cost, and better performance than the conventional PFC control methods

High-performance solar photovoltaic ( PV) energy conversion system

Abstract: The present invention focuses on the development of a high-performance solar photovoltaic (PV) energy conversion system. The power circuit of the invention is made of a two-stage circuit, connecting a step-up DC-DC converter and a full-bridge inverter in serial. The present invention uses an adaptive perturbation and observation method to increase tracking speed of maximum power position and at the same time reduces energy loss. In addition, the full-bridge inverter's output has to have the same phase with the utility power in order to achieve unit power factor and increase the system efficiency. The present invention uses voltage type current control full-bridge inverter to achieve the goal of merging into utility grid. The present invention provides an active Sun tracking system, by utilizing the character of changing in open circuit output voltage with Sun radiation strength to follow the Sun, and decreases the system cost and increases system effectiveness.

Method and apparatus for controlling power drawn from an energy converter

Abstract: Methods, apparatus, media and signals for controlling power drawn from an energy converter to supply a load, where the energy converter is operable to convert energy from a physical source into electrical energy. Power drawn from the energy converter is changed when a supply voltage of the energy converter meets a criterion. The criterion and the change in the amount of power drawn from the energy converter are dependent upon a present amount of power supplied to the load. The methods, apparatus, media and signals described herein may provide improvements to DC to AC maximum power point tracking in an energy conversion system such as a photovoltaic power generation system.

Fault-Tolerant Operating Strategies Applied to Three-Phase Induction-Motor Drives

Abstract: This paper presents a comparative analysis involving several fault-tolerant operating strategies, applied to three-phase induction-motor drives, that intend to compensate for inverter faults. The results presented show the advantages and the inconveniences of several fault-tolerant drive structures, under different control techniques, such as the field-oriented control and the direct torque control. Experimental results concerning the performance of the three-phase induction motor, based on the analysis of some key parameters, like induction-motor efficiency, motor power factor, and harmonic distortion of both motor line currents and phase voltages, will be presented

Feedforward current control of boost single-phase PFC converters

Abstract: This paper presents the theory and application of feedforward current control for boost single-phase ac-dc converters with power factor correction. The proposed feedforward signal involves the instantaneous line voltage and the derivative of the reference current. The new control method is compared to existing feedback and feedforward control methods and is shown to significantly reduce input current harmonic distortion, particularly for applications where the current loop crossover frequency is relatively low compared to the line frequency. Implementation of the proposed control using analog devices and the associated issues, such as performance sensitivity to parameter variation and uncertainties, are presented. Analysis results are complemented by numerical simulation and experimental results from a prototype converter. Targeted applications of the proposed method are airborne systems where the line frequency is high, as well as low-cost digital control for terrestrial 50-60-Hz systems where the current loop crossover frequency is limited by the speed of the digital controller.

Voltage divider and its application in the two-stage power architecture

Abstract: An ultra-high power density DC/DC converter with fixed conversion ratio is proposed for the two-stage power architecture in the area of power management for the processor based power systems, including server, desktop, laptop, and other battery powered portable applications. Without the magnetic component inside, its power density has been scaled up by an order over the conventional approach. In addition, it also features the capability of holding ultra-high efficiency within whole load range, which is promising to the battery life extension in the laptop, 1 kw/inch/sup 3/ power density and 98% efficiency have been demonstrated in 120W and 60W DC/DC prototypes designed for two-stage VRs.

The Feasibility of Small-Scale Residential DC Distribution Systems

Abstract: The application of DC distribution of electrical power has been suggested as an efficient method of power delivery This concept is inspired by the absence of reactive power, the possibility of efficient integration of small distributed generation units and the fact that, internally, many appliances operate using a DC voltage A suitable choice of rectifier facilitates the improvement of the power quality as well as the power factor at the utility grid interface Stand-by losses can be largely reduced However, because of the inherent danger associated with DC voltages and currents, it is imperative that a considerable amount of design effort is allocated for risk analysis and the conception of protective devices and schemes, in order to guarantee personal and material (especially fire) safety This paper consists of the following topics: topological design, buffering of the DC bus, interfacing distributed generators, efficiency analysis and safety measures The conclusion of this work is that (at the moment) it is generally not efficient to implement a DC distribution system exclusively at the level of the end-user Rather, further research should focus on the extension of DC power delivery to higher levels of the electricity grid