Showing papers on "Power factor published in 1982"

Reactive Power Control In Electric Systems

Abstract: Theory of Load Compensation. Theory of Steady--State Reactive Power Control in Electric Transmission Systems. Reactive Power Compensation and the Dynamic Performance of Transmission Systems. Principles of Static Compensators. Design of Thyristor Controllers. An Example of a Modern Static Compensator. Series Capacitors. Synchronous Condensers. Reactive Compensation and the Electric Arc Furnace. Harmonics. Reactive Power Coordination. Selected Bibliography. Index.

Harmonic Power Flow Studies Part I - Formulation and Solution

Abstract: The conventional Newton-Raphson power flow study has been reformulated to permit the inclusion of nonlinear loads. These loads give rise to harmonic signals which propagate throughout the power system. The reformulation is based on the reduction to zero of the mismatch active power and reactive voltamperes, the imbalance current at harmonic frequencies, and the mismatch apparent Voltamperes. Conclusions on the existence of positive, negative, and zero sequence signals are made for harmonic frequencies. The harmonic power flow study formulation is illustrated for a three phase full wave bridge rectifier. A companion paper presents a discussion of the actual computer implementation and several practical examples.

Uninterruptible power supplies

Abstract: A power train of an uninterruptible power supply selectively transforms its load from a primary source of power to a reserve source of power under control of a stored program control operating in real time. A microprocessor operating in conjunction with a prioritized interrupt controller and a plurality of external counters monitors and responds to signal conditions existing at various points of the power supply. In particular, the amplitude of a primary AC voltage source is sampled at precise angles of the sinusoidal waveform in response to a comb pulse waveform generated to conform to the actual period of the primary AC voltage. The frequencies range is determined by comparing a count interval to the period of the primary AC voltage. Relative power flow from the primary AC voltage source and a reserve AC voltage signal is controlled by relative phasing of the two signals. The reserve AC voltage signal is adjusted in phase during normal operation when all power is supplied by the primary AC voltage source by comparison to an AC output signal of the power supply to either null power dissipation in the generator of the reserve AC voltage signal or to supply charging current to its energizing DC voltage source.

Boost power supply having power factor correction circuit

Abstract: A boost power supply having a full-wave rectifier driving an inductor, diode, and the parallel combination of a filter capacitor and load. A shunting switch connected between the inductor and diode is periodically closed to draw current through the inductor, thereby charging the inductor. The switch is then opened so that the inductor, while discharging, generates a relatively high voltage which is applied to the load and filter capacitor through the diode. The shunting switch is opened and closed in a manner which causes the input current to follow a sinusoidal waveform in phase with the input voltage with an amplitude that maintains the output voltage of the power supply constant. Specifically, a harmonically pure sinusoidal waveform is multiplied by a voltage inversely proportional to the output voltage. An offset is then added and subtracted to this waveform to generate respective positive and negative reference waveforms which are both in phase with the input voltage but differ slightly in magnitude from each other. A signal indicative of the input current is compared to the positive and negative reference waveforms to open the shunting switch when the input current reaches the level of the positive reference waveform and to close the shunting switch when the input current falls to the level of the negative reference waveform. In order to maintain the operating frequency of the switch constant, the difference between the positive and negative reference waveforms may be varied throughout the sinusoidal cycle so that the time for the inductor to charge to the positive reference waveform and discharge to the negative reference waveform is constant.

Multiloop control of a unity power factor fast switching AC to DC converter

Abstract: A new three-phase ac to de converter is proposed for inductive loads such as de machines or current fed inverters. The converter consists of a set of fast electronic switches and a small three-phase LC-filter. It permits the control of the load current while maintaining almost sinusoidal currents at zero phase displacement in the mains. An analysis of the circuit leads to the definition of a complex transfer vector k which governs the interaction between the ac side and the de side. During operation the modulus and the argument of the transfer vector are varied using a special amplitude and angle modulation technique for complex quantities. To facilitate closed loop control the state variables of the system are subjected to a coordinate transformation. The transformed variables are processed in a multiloop control system so as to maintain the desired operating conditions.

Phase modulated switchmode power amplifier and waveform generator

Abstract: A phase modulated DC-to-AC or a DC-to-DC power converter utilizes input terminals connected to a source of power and output terminals connected to a suitable load. The transfer of power between the power source and the load or from the load back to the power source is accomplished by electronic switching that is phase displaced controlled in all four quadrants.

Dimmable electronic gas discharge lamp ballast

Abstract: A two-wire electronic dimming ballast arrangement for one or more gas discharge lamps is disclosed which includes an inverter driven by a variable pulse width electric power and a control system for modulating the pulse width of the variable pulse width square wave electric power driving the inverter A unique distortion suppression system is provided for suppressing current abberations and achieving substantially a unity power factor

Direct AC converter for converting a balanced AC polyphase input to an output voltage

Abstract: A direct AC converter for converting a polyphase AC input supply into an output DC or single or polyphase AC supply of amplitude, phase, frequency or power factor which is different from the input supply using a matrix of bidirectional switches having contiguous width modulated conduction periods in cycles which synthesize the output supply voltage or voltages from samples of the input supply voltages taken cyclically at a much higher frequency than the supply frequency or frequencies. The switches are operated so that the or each output supply conductor is connected to only one of the input supply conductors at a time. The width modulation may be effected in response to phases of a sinusoidal oscillation to produce a frequency change. The output may have a "negative" frequency so that a phase displacement between current and voltage due to a reactive load appears in the opposite sense in the input supply. Width modulation may alternatively be effected by a combination of two sinusoidal oscillations so that the output frequency has equal positive and negative values to eliminate phase displacements in the input supply due to a reactive load. Motor speed control and generator output frequency control applications are described.

High power factor switching-type battery charger

Abstract: A switching-type charging circuit is described wherein the power factor of the circuit has been optimized. The switching-type charging circuit utilizes a dual loop feedback system to control the input and output current of the circuit. The dual feedback loop system utilizes a sinusoidal voltage reference in conjunction with a pulse width modulation circuit to force the input impedance of the circuit to appear substantially purely resistive.

AC Motor-starting for aircraft engines using APU free turbine driven generators

Abstract: The invention is an electric starting system for starting aircraft jet engines (32), (34) and (36) using an APU (10) free turbine driven generator (12) The operating power factor of the starter-generator (12) is controlled during start mode operation of the APU (10) by monitoring the line current via a current transformer (58) Contactors (14) and (16) connect the generator (12) into the aircraft's ac power system and ac starting system, respectively A master start relay (22) is provided, and is closed in the `start` mode such that a power electronics inverter (24) may be powered from external power via contactors (18) The variable-voltage/variable-frequency output of inverter (24) is controlled via a logic controller (26) and can be applied sequentially to the three engine driven generators (32), (34) and (36) via start relays (42), (44) and (46) to start the engines (32), (34) and (36) respectively An alternative embodiment of the APU generator/power electronics/starter-generator start system is the utilization of a separate induction motor starter than can operate with or without the use of power electronics

Control Algorithm for a Static Phase Shifting Transformer to Enhance Transient and Dynamic Stability of Large Power Systems

Abstract: A robust control algorithm for the control of a static phase shifting or quadrature boost transformer has been developed and tested. This algorithm utilizes the inherent stabilizing ability of a phase shifter to rapidly return the power system to a stable operating point following severe transients. Under normal operating conditions, the controller minimizes power flow deviations and slip fluctuations due to random power demand changes. The control commands are generated using only local measurements (voltage and complex power at the transformer), specified power flow, and imprecise values of equivalent impedances of the power system.

Rectifier control system for a DC power plant system

Abstract: A DC power plant system has the operation of its individual rectifiers controlled by a stored program control system for the purpose of optimizing power efficiency. Load power requirements are compared with rated capacities of operating rectifiers of the system and individual rectifiers are turned on or off so that the plant efficiency is always maximized. Rectifiers are selected for turn on and off in the basis of their rated power capacity and their accumulated operating times.

An AC to DC converter with high quality input waveforms

Abstract: An ac to dc converter which draws sinusoidal and in phase current waveforms from the ac power source is described. Harmonic and power factor measurements obtained from an FET converter operating at 45 kHz for a single phase and a three phase connection are presented. A stability analysis and design methodology is given.

Control system for an electronically commutated motor

Abstract: A circuit for controlling the energization of an electrical load from an AC source. The circuit has a pair of DC lines, and means is provided for rectifying the AC output of the source to apply a DC voltage across the DC lines in the form of a full wave rectified sinusoidal signal. Signal switching means for connection between the DC lines and the load establishes a conductive path therebetween during a variable time interval when the voltage applied by the full wave rectified sinusoidal signal exceeds the voltage across the load, and means including the switching means is provided for chopping the full wave rectified sinusoidal signal to apply pulses to the load during the variable time interval at a frequency which is high with respect to the frequency of the signal. Means connected to the chopping means for modulating the width of the pulses is responsive to an externally derived signal representative of the desired operation of the load, and means is responsive to the load current for modifying the externally derived signal to maintain the amplitude of the load current below a predetermined level whereby a high power factor is presented to the AC source during a predetermined range of operation of the load. A laundering apparatus, a method of operating a laundry machine, a control system for an electronically commutated motor, and a method of operating an electronically commutated motor are also disclosed.

Power factor controller

Abstract: In a computer controlled power factor control system switches are activated and deactivated in a predetermined order so that each capacitor is electrically connected to the power distribution system for substantially the same total time throughout the life of the capacitors.

A quantitative analysis of induction motor performance improvement by SCR voltage control

Abstract: Minimum input power and maximum efficiency operation occur at characteristic slip values which can be realized for any induction motor operating at part load by properly adjusting the amplitude of the applied stator terminal voltages. It is shown that these two criterion yield perceptibly different results when the motor is driven from an SCR voltage controller. In addition, it is demonstrated that a constant power factor controller results in an operating regime which is substantially poorer than operation at either minimum input power or maximum efficiency. It is further shown that minimum stator current and minimum power factor angle criterion yield results which are closer to the ideal than the constant power factor controller.

Control Design of an Active and Reactive Power HVDC Modulation System with Kalman Filtering

Abstract: This paper discusses results of an EPRI contract on control design for an ac/dc transmission system to increase power transfers limited by dynamic stability. The control is acbieved by modulating the rectifier dc current or power and the inverter dc voltage. Coordinated active and reactive power modulation is accomplished by Linear Quadratic (LQ) control design. Improved performance is realized by utilizing reactive power coupling between dc and ac networks to modulate dc and ac active power. For the demonstration system, power modulation with coordinated voltage modulation is shown to be about ten times more effective than power modulation alone. Control interactions between electromechanical modes of oscillation are eliminated by Kalman filtering. Filtering permits excellent control performance with a minimum of system measurements. Modern control technology is applied within realistic system constraints, such as measurements.

Motor-generator system providing prolonged uninterrupted power supply to a load

Abstract: The present invention relates to a generator system connected to an external A.C. power source for supplying electrical A.C. power to a load for prolonged periods when the external electrical A.C. power source fails. The system comprises a main A.C. generator unit capable of generating an A.C. potential at a selected frequency and voltage for the load, and an auxiliary A.C. generator is connected to the main generator for generating A.C. at a high frequency. This high frequency A.C. is conveyed to a relatively small high speed motor and flywheel unit in a sealed chamber, which unit at full speed can store large amounts of rotational kinetic energy. The high speed motor has a stator armature with a power winding and an excitation coil, and a cooperating rotor of soft magnetic material having a cylindrical surface with a layer of magnetizable permanent magnet material thereon. When energized with the high frequency A.C., the power winding causes the rotor to rotate as a hysteresis motor. When the external electrical A.C. power source fails, the excitation coil is energized with high frequency A.C. to magnetize the layer of permanent magnet material into a pattern of north and south magnetic poles which will enable the rotational kinetic energy of the rotor and flywheel to generate high frequency A.C. of constant frequency in the power winding which is supplied to the auxiliary generator to cause it to function as a synchronous motor to drive the main A.C. generator so that it will keep on producing the A.C. potential to the load.

New solar cell power supply system using a boost type bidirectional DC-DC converter

Abstract: New solar cell power supply system is presented, in which the boost type bidirectional dc-dc converter and the simple control circuit with a small monitor solar cell are employed to track the maximum power point of the solar array. It is confirmed by the experiment that the new system has the sufficiently precise tracking operation performance and the satisfactorily high power efficiency. Also, a comparison of the power efficiencies is made with theoretically as well as experimentally on the new and the conventional solar cell power supply systems. As a result, it is revealed that the new system is superior to the conventional one in the power efficiency.

DC To AC power inverter

Abstract: The DC to AC power inverter is of the class B, C, D or E type and includes a battery, at least one power SCR and associated capacitor circuitry, at least one input winding on a main transformer core and at least one output secondary winding on the transformer core. Such inverter requires a quiescent current to establish operating current for capacitor commutation charge and includes a feedback loading circuit for feeding current generated by the quiescent current back to the battery. The inverter also includes a self-detecting load demand circuit coupled to a line from said output winding for cyclically energizing the inverter, for sensing a minimum AC load and for holding said inverter in an energized state until less than a minimum AC load is sensed during an energizing cycle. Further the invention includes automatic power factor correction circuitry for supplying full time leading power factor correction to a load, with the automatic power factor correction circuitry being sensitive to light reactive loads.

A Simple Multiple Pulsewidth Modulated AC Chopper

Abstract: A simple multiple pulsewidth modulated (MPWM) ac chopper using power transistors for 3-? power control is discussed. 120° chopping period is used for main transistors so that the circuit can accommodate resistive and lagging or leading power factor loads. Only 1-? sensing is used for 3-? control. An alternate economical power and control schemes for 3-? MPWM ac choppers suitable only for resistive loads is also suggested. The experimental results for 12 choppings per cycle are given.

Constant power switching power supply

Abstract: A power supply for a gaseous discharge lamp in which power adjustments are made automatically to insure that rated lamp power is delivered regardless of changes in lamp impedance or line voltage which may occur. A high D.C. voltage is delivered to a step down low hysteresis transformer and electronic switching is provided to obtain a high frequency pulsed flow to the primary of the transformer. Sawtooth waves are generated and peak current is utilized to regulate closely power input to the transformer. A feature is the use of a programming resistor to select the desired power level for the particular gas discharge lamp.

Asymmetrically Modulated AC Chopper

Abstract: The paper describes a current impulse-commutated ac triac chopper employed to obtain the optimum supply power factor correction for reactive loads. The resultant displacement and distortion factors of the supply and efficiency of the load are considered. Theoretical results are in excellent agreement with results obtained experimentally.

Semiconductor current regulator and switch.

Abstract: A semiconductor current regulating and switching apparatus is described wherein an NMOS enhancement mode power transistor is used in the positive lead to regulate the flow of current from a power source to a load. In order to achieve a low resistance on-state for the NMOS power transistor, the control gate must be biased to a voltage which exceeds the positive voltage of the power source. This bias voltage is generated within the apparatus.

Control apparatus for D.C. power transmission system

Abstract: This invention relates to an apparatus for controlling a D.C. power transmission system having a line-commutated converter which is connected between a first A.C. system and D.C. power transmission lines and which performs power conversion between A.C. power and D.C. power, and a forced-commutated converter which is connected between the D.C. power transmission lines and having a second A.C. system and which performs power conversion between A.C. power and D.C. power. In order to control transmission power in the two-terminal D.C. power transmission system wherein the two A.C. systems are associated by direct current, a control apparatus for a D.C. power transmission system according to this invention includes a voltage detector which detects a D.C. voltage of the D.C. power transmission lines, a first control circuit for comparing the output of the voltage detector with a voltage reference signal and for controlling ignition of the self-excited converter in accordance with the comparison, a detector which detects a current which is proportional to the conversion power of the line-commutated converter, and a second control circuit for comparing the output of the current detector with a power reference signal and for controlling ignition of the line-commutated converter in accordance with the comparison.

Method and means for feeding electric energy to a portable power tool

Abstract: A method and a means for feeding electric energy to a portable power tool is based on a principle according to which the brushless AC motor of the tool is individually supplied with power from a solid state inverter type power supply by which the amplitude and frequency of the AC current are automatically and individually adapted to the instantaneous load conditions experienced by the motor.

Current Harmonics, Voltage Distortion, and Powers Associated with Battery Chargers Part I: Comparisons Among Different Types of Chargers

Abstract: This report compares the performance of five types of battery chargers for use with electric vehicles. Chargers with and without controlled rectifiers for maintenance of constant charging current and with and without current-smoothing inductors are analyzed. Based on a typical electric vehicle battery pack and an 8 hour recharge cycle, current and voltage waveshapes, current harmonic levels, power, reactive and distortive volt-amperes, voltage distortion factor, and power factor are reported for each charger type.

Greatly prolonged period non-interruptible power supply system

Abstract: This invention relates to a power supply system having the capability of furnishing to a load sensitive to electrical faults and interruptions, electrical power for prolonged periods of time after a utility or other external power supply source thereto is interrupted. The system comprises a main A.C. generator furnishing A.C. potential at a selected frequency and a selected voltage to the sensitive load, an auxiliary A.C. generator connected operatively thereto and a driving means for the generators energized with electricity from the external power supply source which is subject to outages and faults. The auxiliary generator generates A.C. potential at a much higher frequency than from the main A.C. generator and this higher frequency A.C. is supplied to a high speed A.C. induction motor and a flywheel unit in a sealed chamber, which unit can store large amounts of kinetic energy at full speed. Upon interruption of electricity from the utility or other external power source, the high speed A.C. induction motor in the sealed casing will function as a generator and feed back A.C. potential to the auxiliary generator which begins to operate as a motor and drives the main A.C. generator. A relatively small A.C. motor and flywheel unit can store and supply power to keep the main A.C. generator operating for from 1 to 20 minutes so as to ride out practically all reasonably expected power line outages. Particularly good results are obtained if the main A.C. generator is the Roesel generator of U.S. Pat. No. 4,168,459.

Control circuit arrangement for a self-start 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 frequency and variable pulse width The self-starting circuit includes a control circuit network which connects to the transformer primary windings and a low voltage regulator circuit connects to the pulse generator and network The control circuit network provides the voltage regulator circuit with the desired current characteristics of high instantaneous current during a short turn-on time interval and a zero current during power supply operation The self-starting circuit in response to the input rectified AC power after the short turn-on period of time applies sufficient voltage which enables the pulse generator to begin generating a first output pulse 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 pulse width The output DC supply voltage is compared to a reference voltage for generating an error signal which is used to adjust the width of the pulse generator to existing line and load conditions during power supply operation

Switched mode power supply

Abstract: Switched mode power supplies have been disclosed for powering discharge lamps and other loads. In one example the line current is shaped, in response to a signal representing the load, or optionally the input, current to provide a suitably high power factor. The circuit, however, includes a switch breaking the input path which is found to be disadvantageous. The in­ vention provides a switching means (CT1) connected across the circuit to control the current without breaking the current path. A current sensing resistor (R1) in the input path senses the current and a potentiometer (6) senses the potential from the rectifier (1). These are compared in a comparator with hys­ teresis (7) the output of which controls the switching means (VT1). An FET (FET1) connected across part of potentiometer (6) varies the attenuation ratio thereof to maintain the output voltage constant.