Showing papers on "Power factor published in 1999"

Power System Oscillations

Abstract: 1. Introduction. 2. The Nature of Power System Oscillations. 3. Modal Analysis of Power Systems. 4. Modal Analysis for Control. 5. Power System Structure and Oscillations. 6. Generator Controls. 7. Power System Stabilizers. 8. Power System Stabilizers - Problems and Solutions. 9. Robust Control. 10. Damping by Electronic Power System Devices. A1. Model Data Formats and Block Diagrams. A2. Equal Eigenvalues. Index.

Hybrid multilevel power conversion system: a competitive solution for high power applications

Abstract: Use of multilevel inverters is becoming popular in recent years for high power applications. Various topologies and modulation strategies have been investigated for utility and drive applications in literature. Trends in power semiconductor technology indicate a trade-off in the selection of power devices in terms of switching frequency and voltage sustaining capability. New power converter topologies permit modular realization of multilevel inverters using a hybrid approach involving integrated gate commutated thyristors (IGCT) and insulated gate bipolar transistors (IGBT) operating in synergism. This paper is devoted to the investigation of a hybrid multilevel power conversion system typically suitable for high performance, high power applications. This system designed for 4.16 kV, /spl ges/100 hp load comprises of a hybrid seven-level inverter, a diode bridge rectifier and an IGBT rectifier per phase. The IGBT rectifier is used on the utility side as a real power flow regulator to the low voltage converter and as a harmonic compensator for the high voltage converter. The hybrid seven-level inverter on the load side consists of a high voltage, slow switching IGCT inverter and a low voltage, fast switching IGBT inverter. By employing different devices under different operating conditions, it is shown that one can optimize the power conversion capability of entire system. A detailed analysis of a novel hybrid modulation technique for the inverter, which incorporates stepped synthesis in conjunction with variable pulse width of the consecutive steps is included. In addition, performance of a multilevel current regulated delta modulator as applied to the single phase full bridge IGBT rectifier is discussed. Detailed computer simulations accompanied with experimental verification are presented in the paper.

Method and apparatus for multi-power source for power tools

Abstract: Method and apparatus for providing multi-power source for power tools. The apparatus includes (a) a multi-functional power block capable of being powered from multiple energy sources including, but not limited to, AC mains, DC power or fuel cell, and (b) a multi-functional battery module capable of receiving power from the multi-functional power block and fit into the recess in the tool which receives the power pack. The multi-functional power block includes an AC to DC converter, a voltage input selector, a DC to DC converter, an auto voltage selector, and a solid state power monitor which automatically sets the voltage and current to be delivered to power connectors integral to the multi-functional power block. The multi-functional battery module includes batteries, a battery charger which uses power from the multi-functional power block to recharge the battery, a power distributor, and a power monitor which monitors operation of the tool's motor so that the power distributor can automatically deliver the required voltage and current to the tool's motor from one or a combination of battery power and the multi-functional power block to produce the required operational driving torque. The apparatus also includes an AC mains plug and a first flexible line running from the AC mains plug to the multi-functional power block, a DC connector and a second flexible line running from the DC connector to the multi-functional power block, a third flexible line with attached DC plugs at both ends, and a series of adapters designed to fit into recesses in the multi-functional power block and in the tool.

Power supply and methods for limiting power in electrosurgery

Abstract: A high frequency power supply for applying electrical energy to a target site on or within a patient's body includes an electrical output driver, an output current sensor detecting the current output from the driver, and a power limiting device coupled to the current sensor during normal conditions, the power limiting device operates on a continuous basis. When current output exceeds a predetermined threshold level, the power limiting device is adapted to reduce power on the output driver to a standby mode. The power limiting device operates on a periodic detection or duty cycle when in the standby mode. The power limiting device switches into the stand-by mode to prevent excessive power drains. The power supply operates at a low power, pulsatile manner when an attached probe is in conductive or isotonic fluid but is not engaging body tissue or near a high impedance source. In this pulsatile mode, the power supply operates in a cyclical manner, typically at a predetermined duty cycle.

Effects of unbalanced voltage on the operation performance of a three-phase induction motor

Abstract: This paper uses a real load test to investigate the effects of an unbalanced voltage supply on an induction motor's performance. Based upon various experiments, including: (1) cases with the same unbalance voltage factor but different unbalanced voltages; (2) cases with only one unbalanced voltage but different degrees of unbalance; and (3) cases with the same positive-sequence voltage but different negative-sequence voltages, the importance of the positive-sequence voltage in the motor's apparent performance and of the negative-sequence voltage in the hidden damage are pointed out. Finally, it is strongly suggested that the related regulations, and a motor's derating factor and temperature rise curves should be based on not only a voltage unbalance factor, but also the magnitude of the positive-sequence voltage.

The theory of instantaneous power in three-phase four-wire systems: a comprehensive approach

Abstract: This paper describes a holistic approach to the theory of instantaneous power in three-phase four-wire systems, focusing on the original theory created in 1983 and a modified theory presented in 1994. The two theories are perfectly identical if no zero-sequence voltage is included in a three-phase three-wire system. However, they are different in the instantaneous active and reactive power in each phase if a zero-sequence voltage and current are included in a three-phase four-wire system. Theory and computer simulations in this paper lead to the following conclusions: an active filter without energy storage components can fully compensate for the neutral current even in a three-phase four-wire system including a zero-sequence voltage and current, when a proposed control strategy based on the original theory is applied. However, the active filter cannot compensate for the neutral current fully, when an already-proposed control strategy based on the modified theory is applied.

Adaptive SVM to compensate DC-link voltage ripple for four-switch three-phase voltage-source inverters

Abstract: An adaptive space vector modulation (SVM) approach to compensate the DC-link voltage ripple in a B4 inverter is proposed and examined in detail. The theory, design, and performance of this pulsewidth modulation (PWM) method are presented, and the method effectiveness is demonstrated by extensive simulations and experiments. High-quality output currents are guaranteed by this approach even with substantial DC-voltage variations that might be caused by an unbalanced AC supply system, the diode rectification of the line voltages, and circulation of one output phase current through the split capacitor bank. The application of this approach to induction machine drives is also discussed. It is concluded that the DC-voltage ripple effect on the B4 inverter output can be minimized by an adaptive SVM algorithm with the advantage of improving the response of the DC-link filter and the output quality of the inverter becoming high.

Full-bridge isolated current fed converter with active clamp

Abstract: The full-bridge isolated current fed converter with active clamp advantages are in its ZVS capability and its well-clamped operation devoid of voltage overshoot on the converter switches and the rectifier diodes. Another relative advantage is that the isolation transformer magnetising current does not have a DC component. An analysis defines the converter voltage transfer ratio taking into consideration the switches' parasitic capacitance and the transformer leakage and magnetizing inductance. The analysis defines the selection criteria for power stage component values. Two breadboard models were built and tested utilizing the current fed full bridge topology. One model was realized as a DC/DC and the other as a single stage PFC. The models' experimental data confirmed calculations.

AEP unified power flow controller performance

Abstract: The installation of the world's first unified power flow controller (UPFC) has been completed and a series of commissioning tests were conducted at the Inez Substation of American Electric Power (AEP) in eastern Kentucky. The project is a collaborative effort between AEP, the Westinghouse Electric Corporation, and the Electric Power Research Institute (EPRI). Comprising two /spl plusmn/160 MVA voltage-sourced GTO-thyristor-based inverters, this installation is the first large-scale practical demonstration of the UPFC concept, and its completion is a significant milestone in the progress of power electronics technology for flexible AC transmission system (FACTS). This paper briefly reviews the main features of the Inez installation and discusses the operation of the equipment. A collection of measured performance characteristics is presented to illustrate the unique capabilities of the UPFC. These dynamic measurements were made in the course of commissioning, and they graphically illustrate the ability of the UPFC to independently control the real and reactive power on a transmission line, while also regulating the local bus voltage. The results include a demonstration of the series inverter at Inez, operating in stand-alone mode. This test constitutes the first practical large-scale demonstration of the static synchronous series compensator (SSSC) concept.

Tracing active and reactive power between generators and loads using real and imaginary currents

Abstract: In a competitive environment, usage allocation questions must be answered clearly and unequivocally To help answer such questions, this paper proposes a method for determining how much of the active and reactive power output of each generator is contributed by each load This method takes as its starting point a solved power flow solution All power injections are translated into real and imaginary currents to avoid the problems arising from the nonlinear coupling between active and reactive power flows caused by losses The method then traces these currents to determine how much current each source supplies to each sink These current contributions can then be translated into contributions to the active and reactive power output of the generators It is also shown that the global contribution of a load can be decomposed into contributions from its active and reactive parts This decomposition is reasonably accurate for the reactive power generation To determine the contributions to active power generation, the previously-described method based on the active power flows is recommended

Uninterruptible power supply

Abstract: An electronic circuit, such as a UPS, interfaces a main ac power source and at least one secondary power source to a load. The secondary power source(s) may include one or more auxiliary generators, a flywheel motor generator or microturbine with high speed motor generator, and/or any of a variety of dc storage devices. The electronic circuit includes a dc bus, a first uncontrolled rectifier in combination with a first filter for coupling the main ac power supply to the dc bus, one or more additional uncontrolled rectifier(s) and filter(s) for coupling the auxiliary generator(s) to the dc bus, and a dc-to-ac inverter (between the dc bus and the load) for providing ac output power to the load. The advantages of reduced parts count, increased compatibility between the generator(s) and the electronic circuit, and a simpler method for paralleling many storage and generation devices with a very high power factor to the sources, regardless of the load power factor, are provided.

The instantaneous power theory on the rotating p-q-r reference frames

Abstract: This paper proposed the rotating p-q-r reference frames where one instantaneous active power p, and two instantaneous reactive powers q/sub q/, q/sub r/ were defined in 3-phase 4-wire systems. The three power components are linearly independent, so that compensating for the two instantaneous reactive powers leads to control the two components of the current space vector independently. With the theory, this paper shows that the neutral current of a 3-phase 4-wire system can be eliminated by only compensating for the instantaneous reactive power using no energy storage element. Simulation results verify the theory very well.

A new phase detecting method for power conversion systems considering distorted conditions in power system

Abstract: In this paper, a new phase detecting method is proposed for PWM rectifiers and active filters considering distorted utility conditions. The accurate phase angle information of utility voltage is essential to the active power conversion systems tied to the utility line. The angle information can be easily corrupted by the distorted utility voltage such as voltage unbalance and harmonics in the waveform. Thus, large harmonics may be caused in the current or voltage reference signal whose phase angle is based on the detected voltage phase angle. First, focusing on the distorted utility condition, effects of the several phase angle detecting methods on the operation of PWM rectifiers and active filters are investigated. Then a new voltage phase angle detector is proposed using voltage sequence detector and PI controller. The proposed method does not cause harmonics in the reference signal by adequately eliminating unbalance components and high-order harmonic terms in the utility voltage. The basic principle of the proposed method is described in detail. Experimental results prove the feasibility of the proposed strategy compared with the conventional method.

An instantaneous reactive volt-ampere compensator and harmonic suppressor system

Abstract: A novel control method for a reactive volt-ampere compensator and harmonic suppressor system is proposed. It operates without sensing the reactive volt-ampere demand and nonlinearities present in the load. The compensation process is instantaneous, which is achieved without employing any complicated and involved control logic. The compensator is operated in cycle-by-cycle reference-current-controlled mode to achieve the instantaneous compensating feature. A mathematical model of the scheme is developed. Detailed analysis and simulation results are presented. A laboratory prototype of the compensator is developed to validate the results.

A new soft-switched quasi-single-stage (QSS) bi-directional inverter/charger

Abstract: A new soft-switched quasi single-stage (QSS) bidirectional inverter/charger topology is proposed in this paper. It realizes seamless four-quadrant operation in inverter mode, and rectifier operation with unity power factor in charger mode. Single stage power conversion, standard half-bridge connection of devices, soft-switching for all the power devices, low conduction loss, simple center-aligned PWM control, and high efficiency are among the salient features. The principles of circuit operation, PWM control and synthesis, and topological extension are discussed in this paper. The experimental results on a 3 kVA prototype (12 V DC to and from 110 V AC) are also presented.

New approach to photovoltaic arrays maximum power point tracking

Abstract: The present trend for commercial telecommunication and scientific satellites is the utilization of standard platform, characterized by a high level of flexibility and reduced nonrecurring costs. One of the areas where flexibility is mandatory is the electrical primary power subsystem, due to the impact on solar array configuration and dimensions and on power conditioning unit. Use of the maximum power point tracker (MPPT) concept allows optimization of the above mentioned subsystem, maximizing the power transfer from the photovoltaic generator. The purpose of the paper is to present a new MPPT approach that allows minimization of the drawback caused by the intrinsic capacitance of the photovoltaic array (generally neglected) giving the possibility of operation with a large degree of freedom, independent from the converter topology and photovoltaic power generator, electrical network and technology.

The dynamics of a PWM boost converter with resistive input

Abstract: This paper investigates the large- and small-signal response issues and, in particular, the inner loop gain and outer loop response of an indirect control method for active power-factor correction. The control scheme is based on sensing the average inductor current and generating a D/sub OFF/ (the complement of the switch duty cycle) which is proportional to the current. The method is demonstrated by considering the performance of a boost-type active power-factor corrector (APFC) that does not need to sense the input voltage. Theoretical and experimental results confirm the validity of the approach and demonstrate that the proposed method can be useful in the design of robust APFC with low total harmonic distortion. The indirect control method investigated in this paper is also compared to the classical direct APFC control method, pointing to the differences between the two.

Volt/VAr control at distribution substations

Abstract: This paper proposes new methods to improve the performance of the current volt/VAr control schemes at distribution substations. The approach makes use of the new measurement and computer resources that are now available at the substations. The paper shows that new supervisory type control schemes can be developed to improve the performance of both the voltage regulator controllers and also the substation capacitor controllers that are used at the substations for volt/VAr control. The new voltage regulator controller makes use of the voltage drop characteristics of the feeders it regulates. The capacitor controller uses local real and reactive power measurements for power factor control at the substation.

A new configuration of single-phase symmetrical PWM AC chopper voltage controller

Abstract: With the increased availability of power MOSFETs and insulated gate bipolar transistors, a new generation of simple choppers for AC inductive loads is foreseen. These new power semiconductors ease the use of forced commutations of thyristor switches to improve the supply power factor, even with highly inductive loads. The AC controllers with thyristor technology can be replaced by pulsewidth modulation (PWM) AC chopper controllers which have important advantages. In this paper, a symmetrical PWM AC chopper designed to operate with single-phase inductive loads with a reduced number of controlled switches is described. The operation as a variable voltage source of this converter is evaluated. This includes the conversion characteristics, harmonic generation, harmonic distortion factor, and input power factor. By digital simulation, these characteristics are investigated theoretically, and to correlate the measurements with theory, an experimental setup is presented to confirm the analytical analysis.

A power re-use technique for improved efficiency of outphasing microwave power amplifiers

Abstract: An improved power re-use technique is introduced for application to outphased microwave power amplifiers. The technique allows a significant portion of the wasted out-of-phase components of the signal to be returned to the power supply, resulting in substantial improvements in overall power-amplifier efficiency. A peak re-use RF-to-DC efficiency of 63% was obtained at 1.96 GHz.

A line-voltage-sensorless synchronous rectifier

Abstract: A line-voltage-sensorless control for three-phase pulsewidth-modulated (PWM) synchronous rectifiers is presented. A line synchronization and unity power factor control are described. Indirect synchronization without sensing the line voltage allows a standard vector-controlled inverter to be used as a synchronous rectifier without requiring any additional hardware. Furthermore, the line synchronization can be properly operated under line voltage distortion or notching and line frequency variation. All control functions are implemented with a single-chip microcontroller. It is shown via experimental results that the proposed controller gives good performance for the synchronous rectifier.

Low power synthesis of dual threshold voltage CMOS VLSI circuits

Abstract: The use of dual threshold voltages can significantly reduce the static power dissipated in CMOS VLSI circuits With the supply voltage at 1 V and threshold voltage as low as 02 V the subthreshold leakage power of transistors starts dominating the dynamic power Also, many times a large number of devices spend a long time in a standby mode where the leakage power is the only source of power consumption We present a near-optimal approach to synthesize low static power CMOS VLSI circuits with two threshold voltages that reduces power consumption compared with a previous approach by up to 2945% Also, presented is a technique which finds static power optimal configurations for CMOS VLSI circuits when an arbitrary number of threshold voltages are allowed

Effects of nonsinusoidal voltage on the operation performance of a three-phase induction motor

Abstract: This paper uses a real load test to investigate the effects of each order of harmonic from 2 to 13 under various voltage distortion factors (VDF) on the performance of a three-phase induction motor. The investigation includes input current, power factor, efficiency, temperature rise and their impacts on the consumers and utility companies. Since the life span of the motors is dramatically affected by the temperature rise, a new derating factor is proposed in this paper. Besides, the impacts of harmonics on electricity energy, consumers and the life span of a motor are also discussed, respectively. Finally, it is strongly suggested that even order harmonics and harmonics having an order below 5 should be considered in related regulations of harmonics control and limits.

Sliding-mode control of boost-type unity-power-factor PWM rectifiers

Abstract: A robust sliding-mode controller, suitable for the output voltage control of voltage-sourced unity-power-factor three-phase pulsewidth modulation (PWM) rectifiers, presenting no steady-state errors, is described. This "just-in-time" switching controller controls the output voltage and the line input currents, while providing bidirectional power flow, near-unity-power-factor operation, low harmonic content, fast dynamic response of the output voltage, and minimum switching frequency due to a new /spl alpha/-/spl beta/ space-vector current regulator. The voltage controller performance is compared with the behavior of the conventional proportional integral output voltage control, aided by PWM current-mode modulators, and with the nonrobust fast and slow manifold sliding-mode approach. The comparison shows that the proposed controller confers faster dynamics and does not present steady-state errors. Test results confirm that the performance of the controller is independent of system parameters and load and exceeds the performance of existing hysteretic current-mode control systems.

VIENNA rectifier II-a novel single-stage high-frequency isolated three-phase PWM rectifier system

Abstract: Based on an analysis of basic realization possibilities, the structure of the power circuit of a new single-stage three-phase boost-type pulsewidth modulated (PWM) rectifier system (VIENNA Rectifier II) is developed. This system has continuous sinusoidal time behavior of the input currents and high-frequency isolation of the output voltage, which is controlled in a highly dynamic manner. As compared to a conventional two-stage realization, this system has substantially lower complexity and allows the realization of several isolated output circuits with minimum effort. The basic function of the new PWM rectifier system is described based on the conduction states occurring within a pulse period. Furthermore, a straightforward space- vector-oriented method for the system control is proposed which guarantees a symmetric magnetization of the transformer. Also, it makes possible a sinusoidal control of the mains phase currents in phase with the associated phase voltages. By digital simulation, the theoretical considerations are verified and the stresses on the power semiconductors of the new converter system are determined. Finally, results of an experimental analysis of a 2.5-kW laboratory prototype of the system are given, and the direct startup and the short-circuit protection of the converter are discussed. Also, the advantages and disadvantages of the new converter system are compiled in the form of an overview.

Apparent power definitions for three-phase systems

Abstract: It is shown that currently used apparent power definitions, namely the arithmetic VA, S/sub A/ and the vector VA, S/sub V/, both lack an important property: the system power losses are not a linear function of the apparent power squared, S/sub A//sup 2/ or S/sub V//sup 2/. The only apparent power definition known today, that holds this property for all the possible situations-balanced, unbalanced, sinusoidal or nonsinusoidal-has the mathematical expression suggested by F. Buchholz; and explained by W. Goodhue. This paper gives a set of basic examples meant to emphasize the merit of Buchholz-Goodhue approach.

A thermoelectric converter for energy supply

Abstract: A thermoelectric power generator in silicon technology is used for the energy supply of low power systems. An application is described generating an electrical power of 1.5 μW with a temperature difference of 10°C. With the generated electrical power it is possible to operate a small preamplifier and a sensor control system. For complexer applications a generator with a power in the region of 20 μW would be desirable.

A fuzzy-controlled active front-end rectifier with current harmonic filtering characteristics and minimum sensing variables

Abstract: A control strategy which allows conventional voltage-source current-controlled (VSCC) pulsewidth modulation (PWM) rectifiers to work simultaneously as active power filters is presented. The proposed control strategy also allows compensating the system power factor and compensating unbalanced loads. The measurement and/or calculation of the harmonics and reactive power are not required, making the proposed control scheme very simple. The active front-end rectifier acts directly on the mains line currents, forcing them to be sinusoidal and in phase with the mains voltage supply. To improve the dynamic of the system, the amplitude of the current is controlled by a fuzzy system, which adjusts the DC-link voltage of the PWM rectifier. The strategy is based on connecting all the polluting loads between the PWM rectifier and their input current sensors. The main advantages of this approach are the following: (1) there is no need to install a specially dedicated active power filter; (2) it also works simultaneously as a power factor compensator; and (3) no special and complicated calculations are required for harmonic elimination. The viability of the proposed active front-end rectifier is proved by simulation and with experimental results obtained from a 2 kVA PWM prototype.

Intelligent electrical devices

Abstract: An electronic circuit for use with an exhaustible power source and load such as a light bulb, a radio or motor, includes a microchip with an input that transmits a signal to the microchip when the load is activated or deactivated. The input does not form a serial link between the power source and the load. The power switch, by on/off switching, controls energy flow from the power source to the load. The electronic circuit has an automatic delayed shut-off function for the load and, a find-in-the-dark indicator and a power source level indicator which are active when the load is not energized and the power source is not being charged. The input to the microchip acts as an activation/deactivation user interface. The microchip allows the user to select specific functions based on the time duration of activation signals, the time duration between activation signals and the number of activation signals at the input.

High power factor rectifier with reduced conduction and commutation losses

Abstract: This paper presents a high power factor rectifier with reduced conduction and commutation losses for telecommunication applications. The reduced conduction losses are obtained through the use of a single converter, instead of the conventional configuration, composed of a four-diode front-end rectifier followed by a boost converter. A nondissipative snubber is responsible for the reduction in the commutation losses. A prototype rated at 1.6 kW, operating at 25 kHz with IGBTs has been implemented in laboratory.