Showing papers on "Power factor published in 2001"

Microprocessor for controlling the speed and frequency of a motor shaft in a power tool

Abstract: A control system for driving a power tool is provided comprising a power source, a motor adapted to drive a shaft, a power switching unit interconnecting the power source and the motor, and a controller The power switching unit applying a pulse width modulated (PWM) drive signal from the power source to the motor The controller monitoring at least one electrical characteristic of at least one of the power source, motor and power switching unit and adjusting the operating duty cycle of the PWM drive signal based on the electrical characteristics

A topology survey of single-stage power factor corrector with a boost type input-current-shaper

Abstract: A topological review of the single stage power factor corrected (PFC) rectifiers is presented in this paper. Most reported single-stage PFC rectifiers cascade a boost-type converter with a forward or a flyback DC-DC converter so that input current shaping, isolation, and fast output voltage regulation are performed in one single stage. The cost and performance of single-stage PFC converters depend greatly on how its input current shaper (ICS) and the DC-DC converter are integrated together. For the cascade connected single-stage PFC rectifiers, the energy storage capacitor is found in either series or parallel path of energy flow. The second group appears to represent the main stream. Therefore, the focus of this paper is on the second group. It is found that many of these topologies can be implemented by combining a two-terminal or three-terminal boost ICS cell with DC-DC converter along with an energy storage capacitor in between. A general rule is observed that translates a three-terminal ICS cell to a two-terminal ICS cell using an additional winding from the transformer and vice verse. According to the translation rule, many of the reported single-stage PFC topologies can be viewed as electrically equivalent to one another. Several new PFC converters were derived from some existing topologies using the translation rule.

A novel matrix converter topology with simple commutation

Abstract: The matrix converter is very simple in structure and has powerful controllability However, the commutation problem and complicated PWM method keep it from being utilized in industry This paper discloses a novel matrix topology with advantages over the usual matrix converter topology Firstly, it has the same performance as a conventional matrix converter in terms of voltage transfer ratio capacity, four quadrant operation, unity input power factor, no DC capacitor and pure sine waveforms with only high order harmonics in both line and load side Secondly, the PWM method utilized for the conventional inverter can be used, which can largely simplify its control complexity Thirdly, all the switches at the line side turn on and turn off at zero current; the converter does not have any commutation problems as required by the conventional matrix converter Theoretical analyses and simulation results are provided to verify its feasibility

Understanding Power System Hannonics

Abstract: Harmonics – Past to Present Power systems are designed to operate at frequencies of 50 or 60Hz. However, certain types of loads produce currents and voltages with frequencies that are integer multiples of the 50 or 60 Hz fundamental frequency. These higher frequencies are a form of electrical pollution known as power system harmonics. Power system harmonics are not a new phenomenon. Concern over harmonic distortion has ebbed and flowed during the history of electric power systems. Steinmetz published a book in 1916 that devoted considerable attention to the study of harmonics in three-phase power systems. His main concern was third harmonic currents caused by saturated iron in transformers and machines, and he was the first to propose delta connections for blocking third harmonic currents. Later, with the advent of rural electrification and telephone service, power and telephone circuits were often placed on common rights-of-way. Harmonic currents produced by transformer magnetizing currents caused inductive interference with open-wire telephone systems. The interference was so severe at times that voice communication was impossible. This problem was studied and alleviated by filtering and by placing design limits on transformer magnetizing currents. Today, the most common sources of harmonics are power electronic loads such as adjustable-speed drives (ASDs) and switch-mode power supplies. These loads use diodes, silicon-controlled rectifiers (SCRs), power transistors, and other electronic switches to chop waveforms to control power or to convert 50/60Hz AC to DC. In the case of ASDs, the DC is then converted to variable-frequency AC to control motor speed. Example uses of ASDs include chillers and pumps. Due to tremendous advantages in efficiency and controllability, power electronic loads are proliferating and can be found at all power levels – from low voltage appliances to high voltage converters. Hence, power systems harmonics are once again an important problem.

Dc to dc converter and power management system

Abstract: A DC to DC Converter includes an electrical circuit that allows batteries and other electrical energy storage devices to be charged from or to discharge to a variable voltage DC bus. This electrical circuit also enables seamless integration with other energy storage devices and/or DC power sources, such as fuel cells, to provide DC power for a Power Management System. A Power Management System preferably provides both full power source management and power conditioning. The Power Management System is able to manage power flow to and from multiple, isolated power sources and energy storage devices to deliver high quality alternating current (“AC”) power to a load.

Maximum efficiency and output of class-F power amplifiers

Abstract: A class-F power amplifier (PA) improves efficiency and power-output capability (over that of class A) by using selected harmonics to shape its drain-voltage and drain-current waveforms. Typically, one waveform (e.g., voltage) approximates a square wave, while the other (e.g., current) approximates a half sine wave. The output power and efficiency of an ideal class-F PA can be related to the Fourier coefficients of the waveforms, and Fourier coefficients for maximally flat waveforms have been determined. This paper extends that theory by determining the coefficients for the maximum power and efficiency possible in a class-F PA with a given set of controlled harmonics.

Buck-boost PWM converters having two independently controlled switches

Abstract: Single-switch step-up/step-down converters, such as the buck-boost, SEPIC and Cuk, have relatively high voltage and current stresses on components compared to the buck or the boost converter. A buck-boost converter with two independently controlled switches can work as a boost or as a buck converter depending on input-output conditions, and thus achieves lower stresses on components. Using the converter synthesis method from D. Zhou (1995), families of two-switch buck-boost converters are generated, including several new converter topologies. The two-switch buck-boost converters are evaluated and compared in terms of component stresses in universal-input power-factor-corrector applications. Among them, one new two-switch converter is identified that has low inductor conduction losses (50% of the boost converter), low inductor volt-seconds (72% of the boost converter), and about the same switch conduction losses and voltage stresses as the boost converter.

The Power Electronics Handbook

Abstract: POWER ELECTRONIC DEVICES Overview Diodes Schottky Diodes Thryistors Bipolar Junction Transistors MOSFETs Gate Turn-Off Thyristors IGBTs IGCTs Comparison Testing of Switches POWER ELECTRONIC CIRCUITS AND CONTROLS DC-CD Converters Choppers Buck Converters Boost Converters Cuk Converters Buck-Boost Converters AC-AC Conversion Cycloconverters Matrix Converters Rectifiers Uncontrolled Single-Phase Uncontrolled and Controlled Rectifiers Three-Phase Pulse-Width-Modulated Boost-Type Rectifiers Inverters DC-AC Conversion Resonant Converters Series-Resonant Inverters Resonant DC-Link Inverters Auxiliary Resonant Commutated Pole Inverters Multilevel Converters Multilevel Voltage Source Modulation Fundamental Multilevel Converter Topologies Cascaded Multilevel Converter Topologies Multilevel Converter Laboratory Examples Modulation Strategies Six Step Modulation Pulse Widrth Modulation Third Harmonic Injection for Voltage Boost of SPWM Signals Generation of PWM Signals Using Microcontrollers and DSPs Voltage-Source-Based Current Regulation Hysteresis Feedback Control Sliding Mode Control of Switched Mode Power Supplies Introduction to Sliding-Mode Control Basics of Sliding-Mode Theory Application of Sliding-Mode Control to DC-DC Converters-Basic Principle Sliding=Mode Control of Buck DC-DC Coverters Extension to Boost and Buck-Boost DC-DC Converters Extension to Cuk and SEPIC DC-DC Converters General-Purpose Sliding-Mode Control Implementation APPLICATIONS AND SYSTEM CONSIDERATIONS DC Motor Drives DC Motor Basics DC Speed Control DC Derive Basics Transistor PWM DC Drives SCR DC Drives AC Machines Controlled as DC Machines Moachine Construction Motor Characteristics Power Electronic Converter Position Sension Pulsating Torque Components Torque-Speed Characteristics Applications Control of Induction Machine Drives Scalar Induction Machine Control Vector Control of Induction Machines Permanent-Magnet Synchronous Motor Drives Construction pf PMSM Drive Systems Simulation and Model Controlling the PMSM Advanced Topics in PMSM Drives Switched Reluctance Machines SRM Configuration Basic Principle of Operation Design Converter Topologies Control Strategies Sensorless Control Applications Step Motor Drives Types and Operation of Step Motorsw Step Motor Models Control of Step Motors Servo Drives DC Drives Induction Motor Drives Uninterruptible Power Supplies UPS Functions Static UPS Topologies Rotary UPSs Alternate AC and DC Sources Power Quality and Utility Interface Issues Power Quality Considerations Passive Harmonic Filters Active Filters for Power Conditioning Unity Power Factor Rectification Photovoltaic Cells and Systems Solar Cell Fundamentals Utility Interactive PV Applications Stand-Alone PV Systems Flexible, Reliable, Intelligent Electric Energy Delivery Systems The Concept of FRIENDS Development of FRIENDS The Advanced Power Electronic Technologies with QCCs Significance of FRIENDS Realization of FRIENDS Unified Power Flow Controller Power Flow on a Transmission Line UPFC Description and Operation UPFC Modeling Control Design Case Study More-Electric Vehicles Aircraft Terrestrial Vehicles Principles of Magnetics Nature of a Magnetic Field Electromagetism Magnetic Flux Density Magnetic Circuits Magnetic Field Intensity Maxwell's Equations Inductance Practical Considerations Computer Simulation of Power Electronics Code Qualification and Model Validation Basic Concepts-Simulation of a Buck Converter Advanced Techniques-Simulation of a Full-Bridge Converter

Methods and apparatus for controlling electric appliances during reduced power conditions

Abstract: An electric power monitoring system includes a source monitor for measuring momentary power output of an electric source supplying electric power to a power distribution system having at least one electric load. The momentary power output is compared with a reference load capability for the electric source to determine the ability of the electric source to support additional load, and load capability data is transmitted based on the load capability. At least one load control receives the transmitted load capability data and controls the supply of power to the at least one corresponding electric load based on the load capability data.

Electrical motor power management system

Abstract: A power control system for an electric traction motor in a vehicle comprising at least one inverter for providing conditioned electrical power to the electric traction motor, a plurality of power stages for providing DC power to the at least one inverter, each stage including a battery and boost/buck DC-DC converter, the power stages wired in parallel, and where the power stages are controlled to maintain an output voltage to the at least one inverter.

Integrated control system and method for controlling mode, synchronization, power factor, and utility outage ride-through for micropower generation systems

Abstract: An integrated system for comprehensive control of an electric power generation system utilizes state machine control having particularly defined control states and permitted control state transitions. In this way, accurate, dependable and safe control of the electric power generation system is provided. Several of these control states may be utilized in conjunction with a utility outage ride-through technique that compensates for a utility outage by predictably controlling the system to bring the system off-line and to bring the system back on-line when the utility returns. Furthermore, a line synchronization technique synchronizes the generated power with the power on the grid when coming back on-line. The line synchronization technique limits the rate of synchronization to permit undesired transient voltages. The line synchronization technique operates in either a stand-alone mode wherein the line frequency is synthesized or in a connected mode which sensed the grid frequency and synchronizes the generated power to this senses grid frequency. The system also includes power factor control via the line synchronization technique or via an alternative power factor control technique. The result is an integrated system providing a high degree of control for an electric power generation system.

A novel neutral point potential stabilization technique using the information of output current polarities and voltage vector

Abstract: This paper proposes a new neutral point potential control technique for the three-level neutral-point-clamped PWM inverter Utilizing the phase current polarity information, this technique distributes the redundant voltage vectors in a manner to obtain stable neutral point voltage under all operating conditions including the zero power factor condition Detailed analysis and computer simulations show the superiority of the proposed method The feasibility of the proposed method has been proven via laboratory experiments

A fast dynamic DC-link power-balancing scheme for a PWM converter-inverter system

Abstract: The authors propose a new power converter control scheme for a converter-inverter system. The strategy is to fully utilize the inverter dynamics in controlling the converter dynamics. The authors obtain the power dynamics for both converter and inverter systems, and control the converter power so that it matches the required inverter power exactly. Then, in the ideal case, no power flows through the DC-link capacitors and, thus, the DC-link voltage does not fluctuate even though a very small amount of the DC-link capacitance is used. In forcing the converter power to match the inverter power, the authors utilize the master-slave control concept. They control the DC-link voltage level indirectly through the stored capacitor energy in order to exploit the advantage of the linear dynamic behavior of the capacitor energy. This helps them to circumvent a complex control method in regulating the DC-link voltage. Through simulation and experimental results, the superiority of the proposed converter control scheme is demonstrated.

Maximum power tracking solar power system

Abstract: A maximum power tracker maximizes the power deliverable from a power source, such as a solar array using increasing, decreasing and maintaining states controlled by a set point signal modulated by a dither signal for stabilized regular power tracking during under demand conditions and maximum power tracking during periods with over demand conditions of a load. Multiple converters and respectively maximum power trackers can be coupled in parallel using shared bus control signal for fault tolerant equalized power conversion through the converters.

Considerations of a shunt active filter based on voltage detection for installation on a long distribution feeder

Abstract: This paper deals with a curious phenomenon referred to as the "whack-a-mole" that may occur in a long-distance distribution feeder having many capacitors for power-factor correction. The idea of whack-a-mole is that installation of an active or passive filter on the feeder makes voltage harmonics increase on some buses, whereas it makes voltage harmonics decrease on other buses, especially at the point of installation. The distributed-parameter representation is applied to a simplified feeder, thus making it possible to perform analysis of the whack-a-mole. As a result, this analysis yields such a basic way as to avoid the whack-a-mole. Moreover, both theory and experiment clarify that installation of the active filter acting as a harmonic terminator on the end bus of the feeder can damp out harmonic propagation throughout the feeder without causing any whack-a-mole.

A family of PFC voltage regulator configurations with reduced redundant power processing

Abstract: This paper discusses a systematic method for deriving basic converter configurations that achieve power factor correction (PFC) and voltage regulation. The discussion begins with a general three-port representation of power supplies that provide PFC and voltage regulation. Based on this representation and a power flow consideration, a systematic procedure is derived to generate all possible minimal configurations. Among these configurations, only a few have been known previously and used in practice. It is found that the efficiency of PFC voltage regulators can be improved by reducing the amount of redundant power to be processed by the constituent converters. A systematic circuit synthesis procedure is proposed for creating PFC voltage regulators with reduced redundant power processing. Experimental measurements verify the improved efficiency.

A three-phase line-interactive UPS system implementation with series-parallel active power-line conditioning capabilities

Abstract: This paper presents a three-phase line-interactive uninterruptible power supply (UPS) system with series-parallel active power-line conditioning capabilities, using a synchronous reference frame (SRF) based controller, which allows an effective power factor correction, load harmonic current suppression and output voltage regulation. The three-phase UPS system is composed of two active power filter topologies. The first one is a series active power filter, which works as a sinusoidal current source in phase with the input voltage. The other is a parallel active power filter, which works as a sinusoidal voltage source in phase with the input voltage, providing to the load a regulated and sinusoidal voltage with low total harmonic distortion (THD). Operation of a three-phase phase-locked loop (PLL) structure, used in the proposed line-interactive UPS implementation, is presented and experimentally verified under distorted utility conditions. The control algorithm using SRF method and the active power flow through the UPS system are described and analytically studied. Design procedures, digital simulations and experimental results for a prototype are presented to verify the good performance of the proposed three-phase line-interactive UPS system.

A multimodule parallelable series-connected PWM voltage regulator

Abstract: This paper presents the analysis and design of a single-phase voltage regulator (VR) and its multinodule parallel control. The VR employs the pulsewidth modulation three-arm rectifier-inverter topology. The inverter side adjusts the load voltage with the series regulating structure aiming to minimize converter capacity and attain higher efficiency. The rectifier side regenerates the load power and executes the active power filter function to achieve unity power factor. Based on such high-performance VR, a resistive droop method combined with the P-V droop and Q-/spl delta/ shift scheme is then proposed to control the current sharing such that multiple VRs can be paralleled directly without any control interconnection. The proposed parallel control technique possesses the features of fast response, precise voltage regulation, equal fundamental and harmonic current sharing, tolerance for parameter mismatch, and so on. Two prototype 1 KVA VRs are implemented, and the effectiveness is demonstrated by some simulation and experimental results.

Six self-lift DC-DC converters, voltage lift technique

Abstract: The voltage lift technique is a popular method widely applied in electronic circuit design. Applying it has created six new DC-DC step-up power converters, namely, self-lift DC-DC power converters, which possess high output voltage with smooth ripple. Therefore, these converters can be used in computer peripheral equipment and industrial applications.

An adaptive passivity-based controller for a unity power factor rectifier

Abstract: We develop a passivity-based control scheme for the feedback regulation of a class of switched power converters commonly addressed as power factor pre-compensators. In such applications, aside from load voltage regulation to a prespecified constant level, a vital additional control objective consists of keeping the input power factor close to unity. By forcing the converter input current to follow a sinusoidal reference signal which is in phase with the supplied voltage, one may approximately satisfy both control objectives within a single power stage. A further complication in our design is to consider the output load, usually modeled by a resistance as an unknown. Experimental results are furnished for assessing the performance of the proposed feedback control law.

Turbogenerator power control system

Abstract: A power control system for a turbogenerator which provides electrical power to one or more pump-jack oil wells. When the induction motor of a pump-jack oil well is powered by three-phase utility power, the speed of the pump-jack shaft varies only slightly over the pumping cycle but the utility power requirements can vary by four times the average pumping power. This power variation makes it impractical to power a pump-jack oil well with a stand-alone turbogenerator controlled by a conventional power control system. This power control system comprises a turbogenerator inverter, a load inverter, and a central processing unit which controls the frequency and voltage/current of each inverter. Throughout the oil well's pumping cycle, the central processing unit increases or decreases the frequency of the load inverter in order to axially accelerate and decelerate the masses of the down hole steel pump rods and oil, and to rotationally accelerate and decelerate the masses of the motor rotors and counter balance weights. This allows kinetic energy to be alternately stored in and extracted from the moving masses of the oil well and allows the oil pumping power to be precisely controlled. Historical data on the load inverter's frequency versus time profile throughout previous pumping cycles, which resulted in nearly constant turbogenerator power requirements, is utilized to further reduce variations in power.

Modeling and simulation of a distribution STATCOM using Simulink's Power System Blockset

Abstract: This paper presents a study on the modeling of a STATCOM (Static Synchronous Compensator) used for reactive power compensation on a distribution network. The power circuits of the D-STATCOM and the distribution network are modeled by specific blocks from the Power System Blockset while the control system is modeled by Simulink blocks. Static and dynamic performance of a /spl plusmn/3 MVar D-STATCOM on a 25-kV network is evaluated. An "average modeling" approach is proposed to simplify the PWM inverter operation and to accelerate the simulation for control parameters adjusting purpose. Simulation performance obtained with both modeling approaches are presented and compared.

Mobile power generation system

Abstract: A power generation system is described for supplying electrical power to a load (128) from at least one of a generator (108) and a battery (110). The power generation system includes a power bus (116) coupled to the generator and a bidirectional conversion unit (106) coupled between the power bus and the battery. The bidirectional conversion unit is capable of transitioning between a first direction wherein electrical power flows from the power bus to the battery and a second direction wherein electrical power flows from the battery to the power bus.

A new hybrid filter to dampen resonances and compensate harmonic currents in industrial power systems with power factor correction equipment

Abstract: A new hybrid power filter is presented for three phase industrial power systems which include passive power factor correction equipment (PFC). The hybrid filter damps resonances occurring between line impedances and the PFC. In addition, the hybrid filter topology can be used to compensate harmonic currents. The capacitors of the PFC, which generally cause resonant problems in harmonic distorted networks, can be used for passive filtering by connecting a transformer with a low magnetizing inductance in series hence creating a single harmonic trap. The primary side of the transformer is connected to a low VA-rated three-phase current controlled inverter which builds the active part of the hybrid topology. Simulation results and experimental results are presented verifying the damping and harmonic compensation performance of the proposed topology.

A high-efficiency driver circuit for capacitive loads

Abstract: The invention relates to a high-efficiency driver circuit for capacitive loads, which circuit comprises a drive portion (12) connected to at least one end (X) of a capacitive electric load (11) being applied a voltage waveform. Advantageously, this circuit further comprises a switching circuit portion (13) having its output connected to the above one end (X) of the capacitive load (11) in order to supply a fraction of the overall current demanded by the load (11). Briefly, the invention is a circuit arrangement aimed at providing a highly efficient drive for the capacitive load, using a combined linear/switching setup and without debasing the quality of the waveform generated across the capacitive load.

Low power mode and feedback arrangement for a switching power converter

Abstract: A low power mode and feedback arrangement for a switching power converter. Two or more main power switches (M1, M2), such as transistors, transfer energy from a supply to load (104) by their opening and closing. When the load (104) requires a relatively low power level, this condition is detected. In response, one or more of the transistor switches (M1, M2) is disabled from switching and the reduced power requirements of the load (104) are handled by the remaining one or more transistor switches (M1, M2). As a result, switching losses are reduced. This is because parasitic gate capacitance and on-resistance associated with the disabled switches no longer consume power from the power source. When additional power is required, one or more previously disabled switches (M1, M2) may be brought back into play to ensure that the power requirements of the load (104) are met.

Fault tolerant maximum power tracking solar power system

Abstract: A maximum power tracker maximizes the power deliverable from a power source, such as a solar array using increasing, decreasing and maintaining states controlled by a set point signal modulated by a dither signal for stabilized regular power tracking during under demand conditions and maximum power tracking during periods with over demand conditions of a load. For multiple power sources, respective multiple sets of parallel-connected converters and respectively maximum power trackers can be coupled in parallel using shared bus and control signals for fault tolerant equalized power conversion among the parallel-connected converters. Among multiple solar array sources that can have quite different characteristics, some maximum power trackers may actively regulate maximum power flows from respective array sources that have deficient power while the remaining maximum power trackers are inactive because respective remaining solar array sources provide sufficient power to allow respective DC-DC converters to regulate the load voltage to a regulated level.

Power convertor with low loss switching

Abstract: A welding power supply includes an input rectifier that receives sinusoidal or alternating line voltage and provides a rectified voltage. A pre-regulator provides a dc bus and a convertor, such as a boost convertor, provides a welding output. The pre-regulator is an SVT (slow voltage transition) and an SCT (slow current transition) switched convertor. It may include a snubber circuit having a diode that is SVT switched. Also, the boost convertor may be SVT and SCT switched. The pre-regulator preferably includes a power factor correction circuit. The power source includes, in one embodiment, an inverter having a snubber circuit having a first switch in anti-parallel with a first diode, and a second switch in anti-parallel with a second diode. The first switch and first diode are connected in series with the second switch and the second diode, and the first and second switches are connected in opposing directions, to form a switched snubber.

Power factor correction: a survey

Abstract: New recommendations and future standards have increased the interest in power factor correction circuits. There are multiple solutions to this problem to obtain sinusoidal line current and in addition, a great number of circuits have been proposed with nonsinusoidal line current. In this paper, a review of the most interesting solutions for single phase applications is carried out. They are classified attending to the line current waveform, energy processing, number of switches, control loops, etc. The major advantages and disadvantages are highlighted and the field of application is found.

Hybrid power sources for pulsed current applications

Abstract: A battery-capacitor hybrid power source was discharged under pulsed current conditions and various ambient temperatures. Significant improvements in voltage drop and run time were obtained with the hybrid device over the battery alone. An equivalent circuit was established to evaluate the voltage behavior of the hybrid device. It was found that at the peak discharge current, as much as 50% of the total energy supplied was provided by a capacitor with only about one-third of the battery's volume.