Showing papers on "Power factor published in 1981"

Solid-state power conversion: A Fourier analysis approach to generalized transformer synthesis

Abstract: This paper deals, both from the Fourier analysis and the circuit design point of view, with a large family of electronic power converters which synthesize the assigned slow-varying waveforms via highfrequency switching, thereby needing very little reactive elements. A general condition for high-frequency synthesis applicability is given, together with a method which allows direct converter design from the desired input-output characterizations. Furthermore, a general model is introduced for high-frequency synthesis converters; as a consequence, they are characterized as two-port, multipole, time varying, linear circuit elements. Finally, as a major application example, a new AC-AC, three-to-three phase converter is introduced. The new converter displays several attractive features: sinusoidal waveforms, bidirectionality, separate control over amplitude, frequency, phase, and power factor. Moreover, depending on which side is taken as an input, it can either step up or step down the voltage. For these reasons the new converter can be regarded to as a generalized transformer.

Optimal Control of Reactive Power flow for Improvements in Voltage Profiles and for Real Power Loss Minimization

Abstract: A mathematical formulation of the optimal reactive power control (optimal VAR control) problem and results from tests of the algorithm are presented in this paper. The model minimizes the real power losses in the system. The constraints include the reactive power limits of the generators, limits on the load bus voltages, and the operating limits of the control variables, i.e., the transformer tap positions, generator terminal voltages and switchable reactive power sources. Real power economic dispatch is accomplished by standard techniques.

Excitation System Models for Power System Stability Studies

Abstract: Excitation system models suitable for use in large scale system stability studies are presented in this paper. With these models, most of the excitation systems currently in widespread use on large, system connected generators in North America can be represented.

Unity power factor switching regulator

Abstract: A single or multiphase boost chopper regulator operating with unity power factor, for use such as to charge a battery is comprised of a power section for converting single or multiphase line energy into recharge energy including a rectifier (10), one inductor (L 1 ) and one chopper (Q 1 ) for each chopper phase for presenting a load (battery) with a current output, and duty cycle control means (16) for each chopper to control the average inductor current over each period of the chopper, and a sensing and control section including means (20) for sensing at least one load parameter, means (22) for producing a current command signal as a function of said parameter, means (26) for producing a feedback signal as a function of said current command signal and the average rectifier voltage output over each period of the chopper, means (28) for sensing current through said inductor, means (18) for comparing said feedback signal with said sensed current to produce, in response to a difference, a control signal applied to the duty cycle control means, whereby the average inductor current is proportionate to the average rectifier voltage output over each period of the chopper, and instantaneous line current is thereby maintained proportionate to the instantaneous line voltage, thus achieving a unity power factor. The boost chopper is comprised of a plurality of converters connected in parallel and operated in staggered phase. For optimal harmonic suppression, the duty cycles of the switching converters are evenly spaced, and by negative coupling between pairs 180° out-of-phase, peak currents through the switches can be reduced while reducing the inductor size and mass.

Maximum power control for a solar array connected to a load

Abstract: An analog and a digital control is provided which causes a dc to ac inverter operated in the constant power mode to supply sinusoidal current to a utility while drawing maximum power from a solar array. The current drawn from the array is forced to be proportional to the array voltage by a variable gain amplifier so that the inverter presents a resistive load to the array which remains statically stable under rapid changes of insolation while using a perturb-and-observe method of maximum power tracking. The perturb-and-observe method adjusts the gain of the variable gain amplifier to achieve maximum power output from the solar array.

Microprocessor controlled voltage regulating transformer

Abstract: A voltage regulating transformer utilizing a microprocessor and a versatile multipurpose set of hardware modules and software modules it is described. A standard tap changing mechanism is driven in response to an analog control signal to change the output voltage of the transformer in response to digitally sampled values of voltage and current which have been transformed from the time domain to the frequency domain through a software program using Fourier transform techniques. The output current is also transformed and digitally processed to determine the power factor and the direction of power flow through the transformer. By inserting the digital values of the line characteristics to the load, line drop compensation is provided for. The difference in voltage across the input and output transformers is transformed to a digital signal and internally processed to provide an indication of the position of the tap changing mechanism without relying upon mechanical devices. The various software and hardware modules are designed so as to be readily utilizable in other electrical distribution controls.

Class E tuned power amplifier with shunt inductor

Abstract: The `class E tuned power amplifier with a shunt inductor' is presented It offers a DC-to-RF power conversion efficiency approaching 100 percent The proposed circuit of the amplifier uses a shunt inductor instead of a shunt capacitor The conditions for optimum operation are formulated and discussed The following are determined: the waveforms, the fundamental-frequency components, the peak values of the collector current and voltage, the output power, and the values of the load network elements Experimental results are also presented The proposed amplifier circuit minimizes the power dissipated during the on-to-off transition, even if the switching time is an appreciable fraction of the signal period

Optimum Input and Output Filters for a Single-Phase Rectifier Power Supply

Abstract: The ``optimum'' output filter inductance Lf and the input filter capacitor Ci for a single-phase uncontrolled bridge rectifier employed for low power de-to-dc converters or inverters is established. The filter Ci is optimized to obtain maximum input power factor, minimum filter inductance, and minimum output dc voltage regulation. A design example is provided and theoretical results have been verified on an experimental model.

Method of and apparatus for controlling loads on an electrical power supply

Abstract: To enable a consumer of electrical energy to effect control of total energy consumption by various individual appliances and loads, each individual load (12, 13, 14 or 60, 61, 62) has a control unit (40 or 63), conveniently in a plug top, which responds to pulses broadcast on the power supply wiring in the form of short duration interruptions of the waveform. At each appliance a microprocessor unit (43) including a counter (45) counts the number of successive pulses in a predetermined time interval and operates an electronic switch (41) if the received count reaches a predetermined number, which may be different for different loads thereby enabling selective control of the loads. Provision is made for automatic restoration of supply if the overall energy consumption falls. Provision can also be made for automatic resumption of supply after a predetermined time interval.

Inverter for interfacing advanced energy sources to a utility grid

Abstract: A transistor is operated in the PWM mode such that a hlaf sine wave of current is delivered first to one-half of a distribution transformer and then the other as determined by steering thyristors operated at the fundamental sinusoidal frequency Power to the transistor is supplied by a dc source such as a solar array and the power is converted such that a sinusoidal current is injected into a utility at near unity power factor

Hybrid D.C. power controller

Abstract: A hybrid D.C. power controller of the relay/circuit breaker type that uses a hybrid arrangement of hard contacts (4) and power FET's (18, 20) in cooperative functional combination as the arc quenching means for 270 volt D.C. power systems in low atmospheric pressure environments such as at 80,000 feet altitude in aircraft applications. Also, the relay is provided with arc horns (44c, 48b, 48c, 46c), magnetic field amplifiers (60, 62) looped stationary contacts (44, 46), arc splitters (64, 66), and gas ablating insulating members (60b, 62b, 72, 74, 64b, 66) to enable the relay to interrupt the power circuit if necessary without the help of the power FET's. The power FET's are controlled in both opening and closing the power circuit to afford arcless contact operation in normal load make-break situations. Current and voltage sensing (28, 32) and sampling (CS, VS) circuits determine when to turn the power FET's on after contact arcing has provided the required values. The power contacts (4) can be closed and opened by manual switch (TS) control and opened automatically under overload or short circuit conditions by instantaneous trip detector (ITD) control. Isolation contacts (2) in the power circuit are controlled by delay means (MMV4, MMV8) to close last and open first with respect to the power contacts.

Bi-lateral four quadrant power converter

Abstract: A power converter which supplies AC or positive or negative DC output voltage with positive or negative current while isolating the output voltage from the input power source This converter includes a pulse width modulator converts power amplitude signals to pulses of proportionate width A power driver circuit applies these pulses to a sychronous demodulator and low pass filter via a pulse transformer A low output impedance is presented to all output disturbances such that the converter can source or sink current in true four quadrant operation, including the passing of power from output to input when a load voltage exceeds the intended supply voltage

Electronic ballast for gaseous discharge lamps

Abstract: An electronic ballast for energizing one or more gaseous-discharge lamps and for regulating the power consumed thereby, the ballast including a power supply for providing a source of DC power between a pair of outputs, a pair of transistors connected as switches in series between the power-supply outputs, the transistors for selectively coupling to the juncture thereof positive and negative potentials, a voltage-conditioning and current-limiting network for energizing the lamp from the potential developed between the transistor juncture and a power-supply common, and a pulse generator for developing pulses for driving each of the transistors in turn whereby a potential is developed at the transistor juncture which alternates as positive-going and negative-going pulses each separated by a dead time, the pulse generator for monitoring the power consumption level of the lamp and responsive thereto operative to vary the frequency and/or the width of the transistor driving pulses whereby the lamp consumption is regulated. Also included is a third harmonic trap for coupling the power supply to the AC power line to improve the power factor.

Measurement and Modeling of Pacific AC Intertie Response to Random Load Switching

Abstract: In recent years spectral analysis of system response to random load changes has become a standard engineering tool at the Bonneville Power Administration. Analysis of random fluctuations in power on the Pacific AC Intertie has provided information about the influence of system operating conditions upon the effectiveness of Pacific HVDC Intertie modulation, and about dynamic behavior of the western power system generally. This technique has also been used to estimate the required size for a superconducting electromagnetic storage device which will provide backup to HVDC Modulation, and has detected a major system mode 6 months before it was first observed in a transient disturbance

Forced load sharing circuit for inverter power supply

Abstract: A power supply system that utilizes a plurality of inverter power supplies connect in common to drive a common load with control circuitry for forcing the power supplies to share the load equally is described. Control circuitry associated with each inverter power supply senses the current level provided to the load and compares to the average current provided by all other power supplies in the system. The control circuitry includes circuitry for controlling the pulse width modulator circuitry in response to the sensed condition that the power supply is supplying more than its equal share of the load and causes it to adjust the duty cycle of power switches in the power supply downward to reduce the output current level.

Class E high-efficiency switching-mode tuned power amplifier with only one inductor and one capacitor in load network-approximate analysis

Abstract: A class E high-efficiency switching-mode tuned power amplifier can be realized with only one inductor and one capacitor in the load network; previously published class E circuits contained at least two inductors and two capacitors. Switch conduction duty ratio and network loaded Q cannot be chosen independently as they can in the circuits published previously. This simplified circuit is appropriate for applications in which the harmonic content and the phase-modulation noise of the output are not important criteria, e.g. in providing RF energy for heating, for generation of sparks, arcs, or plasmas, for communications jamming, or for input drive to a higher power stage; or to a rectifier so that the entire circuit functions as a high-efficiency DC/DC converter. Experimental results and an approximate analysis are given; the two are in good-to-fair agreement.

Induction generator system with switched capacitor control

Abstract: An electric power generator system including a switched capacitor controlled induction generator adapted to provide power at a regulated voltage and frequency. The system is adapted for autonomous operation for delivery of power with unity power factor to an external power grid.

High power vector summation switching power amplifier development

Abstract: A time sequence of square waves is summed to provide minimum distortion high power voltage sinusoids. The phase difference is varied to control the resultant summed amplitude. Frequency and phase modulation is achieved through digital control of the individual square waves.

Control of electric power systems

Abstract: commercial and industrial type. It must withstand with reasonable security the capricious forces of nature. In an age of high energy costs it is called upon to transform the prime energy resources into electric form with an optimum overall efficiency. The control functions are obviously many and varied. Some control and decision processes, exemplified by the optimal utilization of the controlled flow of river systems involve dynamics with month-long time constants. Other phenomena, like the transients on the transmission lines following lightning strikes, run their course in a few milliseconds. The slower control processes are normally handled by computer-assisted human operators. The faster control functions are trusted to fully automatic control systems of either open or closed-loop nature. The objective of this article is first to outline briefly the basic functional features of a power system and, secondly, describe some of the more important controls required for its satisfactory operation. Finally some of the more relevant research and development areas are identified and discussed. Fig. 1 shows a one-fine diagram of a section of a larger system. The electric power is produced in the generators. transformed to an appropriate voltage level in the transformers and then via the buses sent out on the transmission fines for final distribution to the loads. Via tie-lines the system is connected to neighboring systems belonging to the same pool. Fig. 1 does not show the low-voltage distribution portion of the system, which contains the majority of the load objects. For most important system studies it is sufficient to use lumped or composite representations of the loads. The load symbols in Fig. 1 are of the latter type. The circuir breakers permit the tripping of faulty components and also sectionalizing of the system. High voltage dc (HVDC) is being used in special cases. However, the vast majority of the world's electric power is being generated, transformed, transmitted and distributed as high voltage ac (HVAC) of the threephase variety. Collectively the generators, transformers, buses, lines and loads constitute the power network or grid.

Power factor controller

Abstract: A power factor controller for an AC induction motor which controls the input power to the motor commensurate with the loading on the motor so as to improve efficiency. The circuit provides a signal representative of the phase difference between the current through the motor and the voltage across it. The phase difference varies with motor loading and accordingly is utilized to control the input power to the motor. The improvement in efficiency is displayed in terms of the percent savings provided by the controller. The circuit provides an immediate response to initial energization of the motor to enable the motor to reach full speed in minimum time.

Generalized theory of electric power

Abstract: The paper presents the generalized theory of electric power, which makes it possible to estimate the operation of complex electric circuits. Use has been made of the correlation analysis and new definitions have been found for various kinds of power occurring in such systems. It has been shown that both the active and the reactive power depend on the voltage-current correlation of the system. A new definition has been found for the distortion power, together with the condition which leads to its minimization.

Power factor correction system

Abstract: A discrete-time, closed loop power factor corrector system controls the coupling of a delta-connected switched capacitor array to a 3- or 4-wire power line which may have time-varying, unbalanced, inductive loads. For inductive loads that cannot be exactly compensated with a delta-connected capacitance, the corrector system minimizes the total RMS reactive current drawn from the power line.

Low Voltage Bulk Power System Restoration Simulation

Abstract: Time is the crucial element in restorative state control for electric power systems. One method for reenergizing large portions of a blacked out electric power system with a minimum of switching and thus time to restoration, is described. Results of a simulated system restart utilizing actual power system facilities are compared to power flow studies. The simulation tests were performed on the Los Angeles Department of Water and Power (LADWP) system in order to verify the concept of utilizing generation operating at extremely low voltage to energize as large a part as possible of the unloaded bulk power transmission system located within the service area.

Finite Element Modeling of Large Turbine Generators; Calculations Versus Load Test Data

Abstract: In support of EPRI Program 1288-1, Improvement in Accuracy of Prediction of Electrical Machine Constants, generator parameters at load have been calculated by the finite element method, in two dimensions. These calculated parameters are compared with test data obtained under EPRI Program RP 997-2, Determination of Synchronous Machine Stability Study Constants. An iterative procedure was used to match the calculated terminal voltage with the test value, for a given armature current and power factor. The test/calculated values for field current, the various angles, and Xq are then compared. Good agreement in all the above parameters is obtained for six diverse load points. Reactances are also compared. Considerable saturation effect is found, and is confirmed by test data in the case of X4. The results of this systematic comparison are judged to be a confirmation of the power of the finite element method.

Parallel resonant induction cooking surface unit

Abstract: A parallel resonant induction cooking surface unit comprises a voltage fed inverter which drives a load circuit, comprised of a main induction drive coil, a tuning capacitor coupled in parallel with the main induction drive coil, and an inductor coupled in series with the main induction drive coil, with a square wave voltage, causing the main induction drive coil to generate a time variant magnetic field resulting in eddy currents being induced in the surface of a metallic, food-containing utensil positioned adjacent to the main induction drive coil, and hence, utensil heating. By tuning the load circuit to resonance at or near the square wave frequency, reactive currents therein are minimized, resulting in improved power factor. Moreover, resultant main induction drive coil voltage and current are nearly sinusoidal, thereby achieving reduced electromagnetic interference radiation at frequencies greater than the square wave frequency.

Motor power factor controller with a reduced voltage starter

Abstract: A power factor type motor controller in which the conventional power factor constant voltage command signal is replaced during a starting interval with a graduated control voltage. The present invention adds to the three-phase system of pending application Ser. No. 199,765, filed Oct. 23, 1980, means for modifying the operation of the system for a motor start-up interval of 5 to 30 seconds. The modification is that of providing via ramp generator 174 an initial ramp-like signal which replaces a constant power factor signal supplied by potentiometer 70. The ramp-like signal is applied to terminal 40 where it is summed with an operating power factor signal from phase detectors 32, 34, and 36 to thereby obtain a control signal for ultimately controlling SCR devices 12, 14, and 16 to effect a gradual turn-on of motor 10. The significant difference of the present invention over prior art is that the SCR devices are turned on at an advancing rate with time responsive to the combination signal described rather than simply a function of a ramp-like signal alone. The added signal, the operating power factor signal, enables the production of a control signal which effectively eliminates a prior problem with many motor starting circuits, which is that of accompanying motor instabilities.

Apparatus and methods for controlling induction motors

Abstract: When induction motors are lightly loaded, their powerfac- tors and efficiency are poor but in the arrangement power factor is controlled regardless of load. An induction motor (10) is connected by way of a triac (12) to a supply (11). The voltage across the triac (12) is monitored by a comparator (21) for voltage steps which correspond to current turn-off and a signal is developed at the output of an amplifier (19), which represents error from required phase lag. A comparator (17) and trigger pulse generator (16) trigger the triac (12) in accordance with the error. An override circuit (31) overrides the control system during starting. A number of further induction motors (28, 29) may be connected in parallel with the motor (10). Additional circuits deal with problems arising when a three-phase induction motor is connected by three wires only.

Capacitive energy source and circuitry for powering medical apparatus

Abstract: An electric power supply operates to supply electrical energy to an electronic device implanted within a living body. The electric power supply has a capacitor which is used as the principal power source. A voltage regulator, overvoltage inhibitor, and a diode are cooperatively arranged to couple the capacitor with an induced voltage source used to charge the capacitor. The diode prevents the capacitor from discharging through the charging circuit when capacitor charging is not taking place. A regulator is used to control the electrical energy that flows to the electronic device. In one form of the electric power supply, a make-before-break switch unit is used to alternately connect the electric device with a charged capacitor or a battery power source so as to provide continuous electrical energy to the electronic device.

Self start flyback power supply

Abstract: A switching regulator power supply operates at a variable high frequency with low power dissipation and a minimum of complexity. The transformer primary windings are included as part of a self starting circuit which starts a pulse generator having a fixed pulse width and variable frequency. During a first cycle of operation, the self starting circuit in response to the input rectified AC power after a predetermined period of time applies sufficient voltage which enables the pulse generator to begin generating a first output pulse of fixed pulse width. This causes the primary windings to store energy and feedback energy to the self starting circuit which increases the voltage applied to the generator causing it to begin normal operation at maximum frequency. An error circuit coupled to the secondary winding compares the output DC supply voltage to a reference voltage and generates an error signal which is applied through a DC coupling circuit for adjusting the frequency of the pulse generator to existing line and load conditions.