Showing papers on "Power factor published in 1991"

Switching Power Supply Design

Abstract: Using this book as a guide, Pressman promises, even a novice can immediately design a complete switching power supply circuit. No other book has such complete instruction in one volume. Using a tutorial, how-to approach, Pressman covers every aspect of this new technology, including circuit and transformer design, using higher switching frequencies, new topologies, and integrated PWM chips. For this latest edition, Pressman has added in-depth discussion of power factor correction, high-frequency ballasts for fluorescent lamps, and low-input voltage power supplies for laptop computers. Table of contents Part I:Fundamental Switching Regulators Buck, Boost, and Investor Topologies.Push-Pull and Forward Converter Topologies.Half- and Full-Bridge Converter Topologies.Flyback Converter Topologies.Current-Mode and Current-Fed Topologies.Miscellaneous Topologies.Part II: Magnetics and Circuits Designs.Transformer and Magnetic Design.Bipolar Power Translator Base Drives.MOSFET Power Transistors and Input Drive Circuits.Magnetic-Amplifier Postregulators.Turnon, Turnoff Switching Losses and Snubbers.Feedback-Loop Stabilization.Resonant Converters.Part III: Typical Switching Power Supply Warehouse.Part IV: Newer Applications for Switching Power Supply Technique.Power Factor, Power Factor Correction.High-Frequency Power Sources for Fluorescent Lamps.Low-Input-Voltage Regulators for Laptop Computers and Portable Electronics.

Variable speed wind turbine with reduced power fluctuation and a static VAR mode of operation

Abstract: A wind turbine power converter is disclosed herein that smooths the output power from a variable speed wind turbine, to reduce or eliminate substantial power fluctuations on the output line. The power converter has an AC-to-DC converter connected to a variable speed generator that converts wind energy to electric energy, a DC-to-AC inverter connected to a utility grid, and DC voltage link connected to an electrical energy storage device such as a battery or a fuel cell, or a photovoltaic or solar cell. Also, an apparatus and method is disclosed herein for controlling the instantaneous current flowing through the active switches at the line side inverter to supply reactive power to the utility grid. The inverter can control reactive power output as a power factor angle, or directly as a number of VARs independent of the real power. Reactive power can be controlled in an operating mode when the wind turbine is generating power, or in a static VAR mode when the wind turbine is not operating to produce real power. To control the reactive power, a voltage waveform is used as a reference to form a current control waveform for each output phase. The current control waveform for each phase is applied to a current regulator which regulates the drive circuit that controls the currents for each phase of the inverter. Means for controlling the charge/discharge ratio and the regulating the voltage on the DC voltage link is also disclosed.

Real-time pricing of reactive power: theory and case study results

Abstract: An analysis is made of real-time pricing policies of reactive power using a modification of the OPF (optimal power flow) model. The theory of real-time pricing of reactive power is presented, followed by a case study illustrating the magnitudes and ranges that real-time prices of reactive power might take on under different circumstances. The efficiency implications of real-time pricing of reactive power are compared with traditional power factor penalties. It is concluded that real-time pricing of reactive power should develop simultaneously with that of active power for maximum economic efficiency and smooth operation of the electricity marketplace. >

A new approach to the definition of power components in three-phase systems under nonsinusoidal conditions

Abstract: A method has been proposed for the definition of active and nonactive power components in three-phase systems under nonsinusoidal conditions. The method is more attractive than others since it is not a mere extension of methods employed in single-phase systems, but comes from the application of a quite powerful and synthetic mathematical tool specifically studied for the representation of three-wire three-phase systems in any possible condition: the Park transformation and the Park vectors. It is proven that the application of this method leads to the definition of two quantities, the real and the imaginary power, that are measurable in a quite simpler way than those proposed by other theories. The two satisfy all properties typical of the electrical power and are directly related, under sinusoidal and balanced conditions, to the active and reactive powers. It is shown how this method fits with other proposed methods that can be regarded in terms of this more general theory. >

A novel active current waveshaping technique for solid-state input power factor conditioners

Abstract: A novel input power factor correction method that uses a closed-loop active current waveshaping technique is presented. The novel feature of the method is that nearly sinusoidal input currents are obtained at constant switching frequencies. Moreover, the method exhibits instantaneous current control, which results in very fast response and increased switch reliability. Selected predicted system performance and design methods were verified experimentally on a 1 kVA laboratory prototype. >

A fast-response high power factor converter with a single power stage

Abstract: An offline switching converter which operates with high input power factor while maintaining fast transient response at its output is described. A single power stage with dual output produces both the desired DC output and a boosting supply in series with the input. The resonant boosting supply at the input is controlled by frequency modulation of the power stage, while the desired DC output is PWM controlled. Since both the input boost supply and the output supply can be controlled independently, a fast transient response can be maintained at both the input (for active current wave-shaping), and at the output (for good output regulation). In addition, even without active control of the boost supply, a reasonably good input current waveshape results due to the natural gain characteristics of the boost resonant circuit. Zero voltage switching is maintained, allowing the circuit to be designed at high frequency to reduce size and cost, and increase performance. >

Tuning of power system stabilizers using an artificial neural network

Abstract: A new approach using an artificial neural network is proposed to adapt power system stabilizer (PSS) parameters in real time. A pair of online measurements i.e., generator real-power output and power factor which are representative of the generator's operating condition, are chosen as the input signals to the neural net. The outputs of the neural net are the desired PSS parameters. The neural net, once trained by a set of input-output patterns in the training set, can yield proper PSS parameters under any generator loading condition. Digital simulations of a synchronous machine subject to a major disturbance of a three-phase fault under different operating conditions are performed to demonstrate the effectiveness of the proposed neural network. >

Integrated motor drive and recharge system

Abstract: A drive and recharge system is disclosed that includes a bidirectional dc power source, two voltage-fed inverters, two induction motors, and a control unit. In the drive mode, power is bidirectionally connected between the dc power source and the motors. In the recharge mode, single-phase power applied to the neutral ports of the two motors is converted with unity power factor to return energy to the dc power source. An alternate scheme is also presented which uses a single motor having two sets of windings.

Battery enhanced power generation for mobile X-ray machine

Abstract: A mobile X-ray machine utilizes batteries to provide electrical power to produce high-voltage necessary to generate X-rays during a X-ray exposure. A battery charger circuit is used to supplement the battery during the X-ray exposure and charges the batteries during non-exposure periods. By using batteries to power the X-ray generating device, the X-ray machine is capable of being operated from 110 volt AC power sources permitting the machine to be mobile due to its ability of being operated from ordinary house current.

Power factor correction control for switch-mode power converters

Abstract: A PFC controller (FIG. 5) provides power factor correction and peak current limiting for a switch-mode power converter of any topology (buck, boost or buck-boost), without having to directly sense inductor current. The PFC control technique involves using a piecewise-polynomial analog computer (AC) to compute power transistor on-times in accordance with separate polynomial transfer functions for power-factor control and peak-current-linking using as inputs current representations of line input voltage (VLN), load output voltage (VLD), and long-term current demand (VCD). A conduction cycle is initiated by sensing when the rate of change in the inductor current reaches zero using an auxiliary winding on the current storage inductor (Wzd), and terminated after the computed on-time to implement either power-factor control or peak-current-limiting.

Class D voltage-switching MOSFET power amplifier

Abstract: An analysis of a class D voltage-switching tuned power amplifier is given, along with experimental results. Analytical equations are derived for performance parameters at any operating frequency normalised with respect to the resonant frequency and at any load resistance normalised with respect to the characteristic impedance of the resonant circuit. The analysis is carried out under the high loaded quality factor assumption, using Fourier series techniques. The behaviour of power MOSFETs in class D circuits for both capacitive and inductive loads is discussed in detail. It is shown that the operation above the resonant frequency (an inductive load) is preferred. The theoretical results were in good agreement with measured circuit performance parameters. The equations provide easy-to-use design tools, which can find a broad application, e.g. in designing DC/DC resonant converters and DC/AC inverters.

Method and system for electricity storage and discharge

Abstract: The present invention features a method and system for storing electrical energy, and then using the stored energy to recharge automobiles. The system of the invention features a number of storage and recharging facilities that are connected to a main power generating station. Power is generally demanded from the power station in the evening or during off-peak power demand periods, in order to obtain lower rates from the power utility. Also, off-peak power loading does not put a strain on the power system. The energy obtained from the power utility company is then stored at each recharging facility in a bank of capacitors. A high voltage transformer and rectifier arranged ahead of the capacitor banks converts the incoming AC high voltage power from the utility to the required DC voltage for capacitor storage. The controller distributes power to a number of charging bays that are connected to the capacitor bank. A vehicle needing charging pulls into an individual bay in the recharging facility, and is connected to a metering device having feedback control. A sensing unit interrogates the power remaining in the batteries of the vehicle, and passes this information onto a controller. In this manner, the exact amount of required energy is transferred to the vehicle.

Frequency doubled solid state laser having programmable pump power modes and method for controllable lasers

Abstract: A laser system using non-linear crystals for second harmonic generation and solid state gain media is operated under data processor control so that a plurality of pump power modes are available. The data processor modulates the pump power in a low power mode, and supplies continuous pump power in combination with Q-switching in a high power mode. Alternatively, modulation may be used in both low power and high power modes, with the parameters of the modulation adjusted under program control. Second harmonic generation without a Q-switch in high power modes can be achieved as well. The data processing control of pump power allows optimization of pump energy consumption and the generation of waste heat so that the laser resonator may be air-cooled in many environments. Also other design objectives can be achieved for specific laser applications using the program controlled data processor to drive the pump power source.

A comparison of load commutated inverter systems for induction heating and melting applications

Abstract: A comparative analysis of a current source inverter and a voltage source inverter suitable for induction heating and melting applications is presented. Both power supplies considered operate on the principle of load commutation. The comparison is based on criteria such as input power factor, component ratings, maximum and minimum operating frequencies, operation under varying load conditions, inverter starting capability, and system and control simplicity. The voltage source series resonant inverter is found to offer the best overall performance with respect to converter utilization. >

Power amplifying apparatus for wireless transmitter

Abstract: A power amplifying apparatus according to the present invention can provide a stable electric power output with wide range by controlling both of the output amplifier for amplifying the electric power and the pre-amplifier disposed at the front of the output amplifier. Furthermore, in order to avoid the disadvantage that a transmission spectrum is expanded because of no supply of a stable voltage to be supplied to the electric power amplifier, thereby producing a cross-talk, a stabilizing power source circuit is provided to stabilize the voltage between the power amplifier and the power source for supplying the voltage.

A high frequency AC/DC converter with unity power factor and minimum harmonic distortion

Abstract: A novel forced commutated AC/DC converter and control strategy is proposed that is able to draw nearly sinusoidal currents at unity power factor from three-phase power lines. The power factor is controlled by adjusting the relative position of the fundamental component of an optimized pulse-width-modulation (PWM) type voltage with respect to the supply voltage. Current harmonic distortion is minimized by the use of optimized firing angles for the converter at a frequency where gate turn-off thyristors (GTOs) can be used. This feature makes this approach attractive at power levels of 100 kW to 600 kW. An 8096 microcontroller is used to minimize the interface hardware requirements. The theoretical analysis of the converter, the control energy, and experimental results for a low-power prototype are presented. >

Improving power factor correction in distributed power supply systems using PWM and ZCS-QR SEPIC topologies

Abstract: The single-ended primary inductance converter (SEPIC) presents several advantages over boost and flyback topologies which make this converter convenient for use as a power factor preregulator (PFP). Due to this fact, both the pulsewidth modulation (PWM) and the zero-current switched quasi-resonant (ZCS-QR) SEPIC used as PFPs are studied. Stress in components and operation in continuous and discontinuous conduction mode are considered in the PWM case, while the use of full-wave and half-wave resonant switches is considered in the ZCS-QR case. The study of the PWM SEPIC used as a PFP reveals that both types of PFP control, multiplier approach and voltage-follower approach, can be used in PWM SEPIC, the first one when it operates in continuous conduction mode and the second one when it operates in discontinuous conduction mode. Regarding the ZCS-QR SEPIC used as PFP, both types of resonant switch (half-wave and full-wave) can be used. >

Harmonics from compact fluorescent lamps

Abstract: The measured performance of compact fluorescent lamps (CFLs) and some rectified incandescent lamps, which can cause considerable harmonic distortion of the input power, is discussed. These include both the electronically and magnetically ballasted CFLs with poor power factors and/or high harmonics. Using the model of a building's electrical load, it is shown that there is little cause for concern for power supply quality problems when the CFLs are less than 25% of the building's total load. Several reasonable low-cost passive circuits that can improve the power factor as well as suppress the harmonic distortion are described. The use of active circuits will be more effective but more costly and are best considered for CFLs above 30 W and for special applications where minimum harmonics are required. >

Characteristics of load resonant converters operated in a high power factor mode

Abstract: The performance of the parallel resonant converter and the combination series/parallel resonant converter (LCC converter) when operated above resonance in a high power factor mode are determined and compared for single-phase applications. When the DC voltage applied to the input of these converters is obtained from a single-phase rectifier with a small DC link capacitor, a relatively high power factor inherently results, even with no active control of the input line current. This behaviour is due to the pulsating nature of the DC link and the inherent capability of the converters to boost voltage during the valleys of the input AC wave. With no active control of the input line current, the power factor depends on the ratio of operating frequency to tank resonant frequency. With active control of the input line current, near unity power factor and low input harmonic currents can be obtained. >

Space vector modulation with unity input power factor for forced commutated cycloconverters

Abstract: A new modulation technique for three phase to three phase (3 Phi -3 Phi ) forced commutated cycloconverters (FCCs) is presented. It is based on the space vector representation of the output voltages and input currents in the complex plane. The resultant output line voltages and input phase currents do not contain low frequency harmonics. The input current displacement factor and the converter voltage gain can be freely varied, regardless of the load power factor; the only restriction being the equality of input and output active powers. The modulation technique holds for any input and output frequencies, so that it can be also applied for 3 Phi AC to DC and DC to 3 Phi AC conversion, thus making FCC a universal power conversion module. >

Scattered and reactive current, voltage, and power in circuits with nonsinusoidal waveforms and their compensation (power systems)

Abstract: Properties of the current and power decomposition into the active, scattered and reactive components are discussed. The relative character of this decomposition is analyzed along with orthogonal decomposition of the load voltage. It is shown that this relative character emphasizes the change of the power flow with the cross section observed. The difference in the efficiency of the source apparent power compensation that can be obtained with a shunt and with a series compensator is emphasized. It is also shown that not only the reactive power Q/sub r/, but also the scattered power D/sub s/ can be wholly compensated by a linear reactive compensator, so that the apparent power S of the load can be minimized to its active power P. >

Performance analysis of a PWM inverter VAr compensator

Abstract: The performance of a three-phase solid-state reactive power compensator with fast dynamic response is analyzed. The compensator consists of a three-phase pulse-width modulated voltage-source inverter connected to a self-controlled DC bus. The principal advantage of this scheme is that it can maintain a near-unity source power factor without sensing and computation of the associated reactive power component. A mathematical model for the compensator connected across a variable power factor load is derived. The frequency response is obtained for open-loop operation. This allows the design of the controller. Predicted results are verified experimentally for both open and closed-loop responses. >

Emergency power supply for small computer systems

Abstract: A small size emergency power supply was investigated. This was realized by adopting a quick detector of momentary power failure and a compact DC-DC converter. The power failure detector has a novel type of T-V (time-voltage) conversion using an SC (switched capacitor) integrator and can detect power failures at its earliest stage. The DC-DC converter was constructed by an SC transformer in which the voltage of each stage increases according to the form of the Fibonacci sequence. The proposed power supply is supplied with power from chargeable batteries for several minutes, while the computer system saves important data to an auxiliary memory such as a disk and can complete its emergency quit operation. The circuit configurations, operations and experimental results are presented. >

Apparatus for controlling the input impedance of a power converter

Abstract: A DC-DC power converter, which can be adapted for use with a single- or multiple-phase AC input, uses energy control because it transcends the modulators and is linear. The use of feed back control is minimized by the use of feed forward control, and in particular the feed forward of the output power to control the input power. The dynamic resistance of the input is controlled, ensuring high power factor in the AC input embodiments of the converter. A multiple-input buck derived converter can have parallel or series inputs, and one or more of the inputs can be lower than the output, even zero or negative. A multiple output boost derived converter can have parallel or series outputs, and one or more of the outputs can be lower than the input, even zero.

Novel full bridge semicontrolled switch mode rectifier

Abstract: A novel semicontrolled switch mode rectifier (SMR) topology is proposed and analysed. Its advantages when compared with other existing SMR topologies are high true power factor at the AC source (almost unity), high displacement power factor at the input of the SMR unit (almost unity), high efficiency, low implementation cost and high power density.

A unity power factor multiple isolated outputs switching mode power supply using a single switch

Abstract: The authors present an offline switching power supply with multiple isolated outputs and unity power factor with the use of only one power processing stage, based on the DC-DC SEPIC (single ended primary inductance converter) modulated by variable hysteresis current control. The principle of operation, the theoretical analysis, the design procedure, an example, and simulation results are presented. A laboratory prototype, rated at 160 W, operating at a maximum switching frequency of 100 kHz, with isolated outputs rated at +5 V/15 A, -5 V/1 A, +12 V/6 A and -12 V/1 A, has been built given an input power factor near unity. >

Circuit for sustaining power supply output following momentary interruption of commercial A.C. power

Abstract: Circuitry for extending the sustain time of a computer power supply in the event of interruption of commercial A.C. power includes a capacitor bank, an associated charge path for controllably charging the capacitor bank during stable operation of the commercial A.C. power source, and discharge and disconnect paths for discharging the energy stored in the capacitor bank to sustain operation of the computer during interruption of the commercial A.C. power source and for disconnecting the capacitor from the computer power supply when the voltage across the capacitor bank has discharged below a threshold level.

Estimation of parameters and performance of rare-earth permanent-magnet motors avoiding measurement of load angle

Abstract: The paper describes a static test which, in conjunction with a no-load test, can be used to determine the parameters needed to apply the two-axis machine analysis to modern rare-earth permanent magnet synchronous motors. An iterative solution of the two-axis theory is presented which, together with the static test, avoids the use of the load angle. The solution includes the effect of core (iron) loss and allows for the estimation of current, power factor and efficiency for a motor running normally from inputs of terminal voltage and torque alone. The parameter values and machine performance predicted by the new methods are confirmed against test data obtained from a samarium-cobalt synchronous motor which has an asymmetrical buried magnet rotor. For this configuration, it is observed that saturation can cause significant variation in the permanent magnet excitation and the direct-axis synchronous reactance as well as the quadratureaxis synchronous reactance. When the variation of each of these parameters is included in the analysis, it is found that the two-axis theory gives a good representation of the motor performance in both the preferred and nonpreferred directions of rotation at a variety of voltages, frequencies and loads.

High power factor, voltage-doubler rectifier

Abstract: A voltage-doubler rectifier includes an ac fullbridge diode rectifier and a dc-to-dc converter having two output boost circuits. One of the output boost circuits is coupled between the rectifier and a dc link, and the other output boost circuit is coupled, with opposite polarity, between the rectifier and the circuit common. Two series-connected filter capacitors are also coupled between the dc link and the circuit common. In a preferred embodiment, the two output boost circuits each comprise either a series, parallel, or combination series/parallel resonant circuit and a rectifier. A switch is coupled between the junction joining one pair of diodes of the rectifier and the junction joining the two filter capacitors. For a relatively high ac line voltage, the switch is open, and the circuit operates in a low boost mode. For a relatively low ac line voltage, the switch is closed, and the circuit operates in a high boost, or voltage-doubling, mode.

A switching power supply of 99% power factor by the dither rectifier

Abstract: The authors present a current waveform improvement method, based on the dither effect normally used in the linearization of nonlinear functions. The proposed circuit utilizes this principle to linearize the dead-zone characteristic which is present in the input of capacitor input rectifiers. The principal characteristics of this method are its simple composition and, more importantly, that it avoids the need for current control. The same switching device realizes the input current waveform improvement and the high frequency inverting output. The experimental circuit achieved over 99% input power factor and current distortion below 9%. >