Showing papers on "Power factor published in 2000"

Steady-state analysis of an interleaved boost converter with coupled inductors

Abstract: Boost converters are widely used as power-factor corrected preregulators In high-power applications, interleaved operation of two or more boost converters has been proposed to increase the output power and to reduce the output ripple A major design criterion then is to ensure equal current sharing among the parallel converters In this paper, a converter consisting of two interleaved and intercoupled boost converter cells is proposed and investigated The boost converter cells have very good current sharing characteristics even in the presence of relatively large duty cycle mismatch In addition, it can be designed to have small input current ripple and zero boost-rectifier reverse-recovery loss The operating principle, steady-state analysis, and comparison with the conventional boost converter are presented Simulation and experimental results are also given

Control of parallel inverters in distributed AC power systems with consideration of line impedance effect

Abstract: The authors have developed a new control technique which allows paralleled inverters to share linear or nonlinear load in a distributed AC power supply system. This technique does not require control interconnections and automatically compensates for inverter parameter variations and line impedance imbalances. Experimental results are provided in the paper to prove the concept.

An improved control algorithm of shunt active filter for voltage regulation, harmonic elimination, power-factor correction, and balancing of nonlinear loads

Abstract: This paper deals with an implementation of a new control algorithm for a three-phase shunt active filter to regulate load terminal voltage, eliminate harmonics, correct supply power-factor, and balance the nonlinear unbalanced loads. A three-phase insulated gate bipolar transistor (IGBT) based current controlled voltage source inverter (CC-VSI) with a DC bus capacitor is used as an active filter (AF). The control algorithm of the AF uses two closed loop PI controllers. The DC bus voltage of the AF and three-phase supply voltages are used as feedback signals in the PI controllers. The control algorithm of the AF provides three-phase reference supply currents. A carrier wave pulse width modulation (PWM) current controller is employed over the reference and sensed supply currents to generate gating pulses of IGBTs of the AF. Test results are presented and discussed to demonstrate the voltage regulation, harmonic elimination, power-factor correction and load balancing capabilities of the AF system.

Phase-locked loop for grid-connected three-phase power conversion systems

Abstract: Analysis and design of a phase-locked loop (PLL) is presented for the power factor control of grid-connected three-phase power conversion systems. The dynamic characteristics of the closed loop PLL system with a second order are investigated in both continuous and discrete-time domains, and the optimisation method is discussed. In particular, the performance of the PLL in the three-phase system is analysed under the distorted utility conditions such as the phase unbalancing harmonics, and offset caused by nonlinear loads and measurement errors. The PLL technique for the three-phase system is implemented in software of a digital signal processor to verify the analytic results, and the experiments are carried out for various utility conditions. This technique is finally applied to the grid-connected photovoltaic power generation system with the current-controlled PWM inverter as a subpart for generating the current reference of the inverter. The experimental results demonstrate its phase tracking capability in the three-phase grid-connected operation.

DC-bus voltage control of three-phase AC/DC PWM converters using feedback linearization

Abstract: In this paper, a fast voltage control strategy of three-phase AC/DC pulsewidth modulation (PWM) converters applying a feedback linearization technique is proposed. First, incorporating the power balance of the input and output sides in system modeling, a nonlinear model of the PWM converter is derived with state variables such as AC input currents and DC output voltage. Then, by input-output feedback linearization, the system is linearized and a state feedback control law is obtained by pole placement. With this control scheme, output voltage responses become faster than those in a conventional cascade control structure. For robust control to parameter variations, integrators are added to the exact feedback control law. Since the fast voltage control is feasible for load changes, it is shown that the DC electrolytic capacitor size can be reduced. In addition, the capacitor current is analyzed for size reduction of the capacitor. As is usual with PWM converters, the input current is regulated to be sinusoidal and the source power factor can be controlled at unity. The experimental results are provided to verify the validity of the proposed control algorithm for a 1.5 kVA insulated gate bipolar transistor PWM converter system.

A new approach to load balancing and power factor correction in power distribution system

Abstract: This paper presents a new approach for generating reference currents for an active filter and/or a static compensator. It is assumed that the compensator is connected to a load that may either be connected in star or in delta. The load can be unbalanced and may also draw harmonic currents. The purpose of the compensating scheme is to balance the load, as well as make the supply side power factor a desired value. The authors use the theory of instantaneous symmetrical components to obtain an algorithm to compute three phase reference currents which, when injected to the power system, produce desired results. They also propose a suitable compensator structure that will track the reference currents in a hysteresis band control scheme. Finally, the feasibility of such a scheme is demonstrated through simulation studies.

Voltage instability: phenomena, countermeasures, and analysis methods

Abstract: A power system may be subject to (rotor) angle, frequency or voltage instability. Voltage instability takes on the form of a dramatic drop of transmission system voltages, which may lead to system disruption. During the past two decades it has become a major threat for the operation of many systems and, in the prevailing open access environment, it is a factor leading to limit power transfer. The objective of this paper is to describe voltage instability phenomena, to enumerate preventive and curative countermeasures, and to present in a unified and coherent way various computer analysis methods used or proposed.

The Electric Power Engineering Handbook

Abstract: Electric Power. Electric Power Utilization. Transformers. Transmission Systems. Substations. Distribution Systems. Electric Power Utilization. Power System Analysis and Simulation. Power System Protection. Power System Transients. Power System Dynamics/Stability. Power System Operation/Control. Power System Planning (Reliability). Power Electronics. Power Quality.

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

Abstract: A topological review of the single stage power factor corrected (PFC) rectifiers is presented in this paper. Most of reported single-stage PFC rectifiers cascade a boost type converter with a forward or a flyback DC-DC converter so that input current shaping, isolation, and fast output voltage regulation are performed in one single stage. The cost and performance of a single-stage PFC converters depend greatly on how its input current shaper (ICS) and the DC-DC converter are integrated together. For the cascade connected single-stage PFC rectifiers, the energy storage capacitor is found in either series or parallel path of energy flow. The second group appears to represent the main stream. Therefore, the focus of this paper is on this group. It is found that many of these topologies can be implemented by combining a 2-terminal or 3-terminal boost ICS cell with DC-DC converter along with an energy storage capacitor in between. A general rule is observed that translates a 3-terminal ICS cell to a 2-terminal ICS cell using an additional winding from the transformer and vice versa. According to the translation rule, many of reported single-stage PFC topologies can be viewed as electrically equivalent to one another. Several new PFC converters were derived from some existing topologies using the translation rule.

Three-stage large capacitive load amplifier with damping-factor-control frequency compensation

Abstract: A novel damping-factor-control frequency compensation (DFCFC) technique is presented in this paper with detailed theoretical analysis, This compensation technique improves frequency response, transient response, and power supply rejection for amplifiers, especially when driving large capacitive loads, Moreover, the required compensation capacitors are small and can be easily integrated in commercial CMOS process. Amplifiers using DFCPC and nested Miller compensation (NMC) driving two capacitive loads, 100 and 1000 pF, were fabricated using a 0.8-/spl mu/m CMOS process with V/sub tn/=0.72 V and V/sub tp/=-0.75 V. For the DFCFC amplifier driving a 1000-pF load, a 1-MHz gain-bandwidth product, 51/spl deg/ phase margin, 0.33-V//spl mu/s slew rate, 3.54-/spl mu/s settling time, and 426-/spl mu/W power consumption are obtained with integrated compensation capacitors. Compared to the NMC amplifier, the frequency and transient responses of the DFCFC amplifier are improved by one order of magnitude with insignificant increase of the power consumption.

Power supply and LED lamp device

Abstract: An LED lamp device of the invention includes a power supply unit ( 102, 103 ) supplied with an alternating-current power supply voltage, and an LED lamp ( 106 ) constituted by one or a plurality of serially connected LEDs connected to output terminals of the power supply unit ( 102, 103 ). The power supply unit ( 102 ) obtains a rectified wave of the alternating-current power supply voltage, admits electric power for only part of a time period in which the voltage of the rectified wave corresponding to each half period of the wave of the alternating-current power supply voltage is higher than or equal to a predetermined value, and uses the electric power as power for lighting the LED lamp ( 106 ).

Semiconductor memory device with a voltage down converter stably generating an internal down-converted voltage

Abstract: A comparison circuit compares a reference voltage Vref from a reference voltage generation circuit with an internal power supply voltage VCI on an internal power supply line to provide a signal according to the comparison result A drive transistor supplies current to the internal power supply line from an external power supply node according to the output signal of the comparison circuit A resistance element connected between the external power supply node and the output node of the comparison circuit and a resistance element connected between the output node of the comparison circuit and a ground node VSS suppresses the amplitude of an output signal of the comparison circuit Thus, overdrive of the drive transistor can be suppressed, and a current corresponding to an abrupt change of the internal power supply voltage can be supplied from the external power supply node to the internal power supply line by the amplitude limitation function Thus, an internal power supply voltage generation circuit is provided superior in high frequency response that can generate an internal power supply voltage stably

Analysis, design, and performance evaluation of droop current-sharing method

Abstract: The droop current sharing method is analyzed, and a general design procedure is proposed. It is shown that the current-sharing accuracy of N+1 power supplies is a function of the output-voltage set-point accuracy, the slope of the output-voltage droop, and gains of the control loop. It was found that to achieve a current sharing accuracy of 10% the output voltage of the paralleled power supplies needs to be set within 0.35%. The accuracy of the design procedure was compared against measured results of three power supplies operating in parallel.

Optimization of VDD and VTH for low-power and high speed applications

Abstract: Closed-form formulas are presented for optimum supply voltage (VDD) and threshold voltage (VTH) that minimize power dissipation when technology parameters and required speed are given. The formulas take into account short-channel effects and the variation of VTH and temperature. Using typical device parameters, it is shown that a simple guideline to optimize the power consumption is to set the ratio of maximum leakage power to total power about 30%. Extending the analysis, the future VLSI design trend is discussed. The optimum VDD coincides with the SIA roadmap and the optimum VTH for logic blocks at the highest temperature and at the lowest process variation corner is in the range of 0V~0.1V over generations.

A direction finder for power quality disturbances based upon disturbance power and energy

Abstract: While existing techniques are capable of automatically identifying and classifying various types of distribution-level power quality disturbances, they do not provide any information about the locations of the disturbance sources. This paper shows that it is possible to use sampled voltage and current waveforms to determine on which side of a recording device a disturbance originates. This is accomplished by examining the energy flow and peak instantaneous power for both capacitor energizing and voltage sag disturbances. The authors demonstrate the technique by testing it on both ATP-generated waveforms and actual field disturbance data. In both cases, they are able to accurately determine on which side of a recording device the disturbance originates. If enough recording devices are available in a network, the individual readings can be collectively used to pinpoint the locations of disturbance sources.

High efficiency power conditioner employing low voltage DC bus and buck and boost converters

Abstract: A power conditioner interfaces a load to a fuel cell 10 that produces a low voltage that varies with the load. A dc-to-ac inverter 16 operates with a low voltage input provided by a dc bus 14 . When a positive step load change occurs, a low voltage battery 22 provides power equal to the step change until the fuel cell 10 is able to provide enough power to support the entire load. The power from the battery 22 is supplied to the varying dc bus 14 through a boost converter 12 . When very large positive load step changes occur, the battery can feed power to the dc bus through diode D 1 , rather than through the boost converter. Diode D 1 does not need to be used, but its use allows the boost converter to be sized for common load changes rather than for the maximum possible load change (such as might be seen during a faulted output). A buck converter converts the variable voltage on the dc bus 14 to the appropriate float charging voltage of the battery. The buck converter also supplies power for auxiliary equipment when available from the fuel cell. If the fuel cell is unable to provide the auxiliary power (such as during startup or load transients), then the auxiliary power can come directly from the battery.

AC/AC power conversion based on matrix converter topology with unidirectional switches

Abstract: In this paper, a new type of AC/AC power converter is proposed. The proposed converter is capable of direct AC/AC power conversion and, except for a few small snubber elements, it does not require the use of any input inductors or a DC-link capacitor. In contrast to the matrix converter, which requires bidirectional switches, the proposed converter consists of only unidirectional switches such as insulated gate bipolar transistors. The converter has a unity input displacement power factor, and its input line current waveform is similar to that of a diode rectifier with a DC-link inductor. The proposed converter has been validated experimentally using an induction motor driven with field-oriented control.

Low power bus coding techniques considering inter-wire capacitances

Abstract: The power dissipation associated with driving data buses can be significant, especially considering the increasing component of inter-wire capacitance. Previous work on bus encoding has focused on minimizing transitions to reduce power dissipation. In this paper, it is shown that transition reduction is not necessarily the best approach for reducing power when the effects of inter-wire capacitance are considered. An electrical model for data buses designed with submicron technologies is presented and a family of coding techniques is proposed that can reduce the average power consumption of the bus by 40%.

Revenue meter with power quality features

Abstract: Power quality detection, monitoring, reporting, recording and communication in a revenue accuracy electrical power meter is disclosed. Transient events are detected by monitoring the wave shape of the electrical power and comparing deviations to a known threshold. Sags and Swells are detected by computing root mean square value over a rolling window and comparing the computed value with a known threshold. Harmonic frequencies and symmetrical components are quantified by a known algorithm and compared with a known threshold. Incoming waveforms are stored to memory. All recorded and computed data is moved to non-volatile storage via direct memory access transfer in the event that a power quality event jeopardizes the operating power of the meter. Further, the meter provides a power supply utilizing high and low capacitive storage banks to supply sufficient energy to survive short duration power quality events which jeopardize the meter's operating power.

Instantaneous phase-angle estimation algorithm under unbalanced voltage-sag conditions

Abstract: If a negative sequence is generated by voltage sag and/or unbalance, it appears as an oscillating error in a synchronous reference frame (SRF). In power conditioning equipment, the exact value of a positive sequence is needed to achieve the unity power factor and constant output voltage, whereas the exact value of a negative sequence is needed for unbalance compensation. To measure the positive sequence separately from the negative sequence, a low pass or notch filter having a narrow bandwidth is normally used. However, such a filter causes a lot of phase delay, thus the response time of the system tends to be lengthened. A method of estimating the positive- and the negative-sequence voltages separately is presented, without a significant delay, by utilising the weighted least-squares estimation (WLSE) method with the covariance resetting technique. A frequency update law is also proposed to accommodate the frequency varying environments. The authors demonstrate through simulation and experiment the superior performance of the proposed scheme in measuring the positive- and the negative-sequence voltages at the time of abrupt transition. This method can be applied to uninterruptable power supplies (UPS), pulsewidth modulation (PWM) AC/DC converters, active filters, AC voltage compensators etc.

Transformerless 3 phase power inverter

Abstract: The invention in the simplest form is an improved transformerless 3 phase power inverter topology and control method for power distribution systems. This 3 phase power inverter system provides the necessary output voltage and current waveform regulation, harmonic distortion rejection, very low output impedance, and ultra low DC offset of the output AC power, even when exposed to a high magnitude of the non-linear, single phase, or the unbalanced loading.

A novel approach to the design of a shunt active filter for an unbalanced three-phase four-wire system under nonsinusoidal conditions

Abstract: A new approach is presented for the design of a shunt active filter in a three-phase, four-wire distribution system with unbalanced, distorted sources and unbalanced loads. The purpose of the shunt active filter is to provide compensation currents such that the source needs to supply balanced (positive-sequence) fundamental source current at unity power factor even though the load consumes harmonic currents as well as positive, negative, and zero-sequence currents. A major feature of the proposed approach is that it does not require symmetrical component transformation to transform the three-phase voltages and currents to /spl alpha/-/spl beta/-o quantities. This makes practical implementation of the proposed method easier than the symmetrical component transformation approach. In addition, the power factor of the positive-sequence fundamental component is close to unity and only positive-sequence power is supplied by the source. The effectiveness of the proposed control algorithm is demonstrated by computer simulation and experimental results of a shunt active filter for a three-phase four-wire distribution system with distorted, unbalanced source voltages and unbalanced loads.

A multilevel converter-based universal power conditioner

Abstract: This paper presents the development of a control scheme for a multilevel diode-clamped converter connected in a series-parallel fashion to the electrical system such that it can compensate for deviations in utility voltage (sag, surge, and unbalance) and act as a harmonic and/or reactive current source for a load. New carrier-based multilevel pulsewidth modulation techniques are identified to maximize switch utilization of the two back-to-back diode-clamped inverters that constitute the universal power conditioner. An experimental verification for a six-level power conditioner is given.

Energy flow and power phenomena in electrical circuits: illusions and reality

Abstract: Common opinions respective to the nature of the reactive power, energy flow and oscillations, as well as the notion of the apparent power in single- and in three-phase systems are discussed in this paper. It is shown that some interpretations of powers and energy flow in linear, single-phase circuits are often generalized for more complex situations where these interpretations are not longer valid. Consequently, power phenomena in electrical systems are often misinterpreted. This relates to the reactive power which occurs in three-phase systems without energy oscillation between the supply source and the load, as well as it occurs in time-variant systems without energy storage capability. Also, it was demonstrated in the paper that the arithmetic and geometric apparent powers, commonly used in three-phase systems, do not characterize the supply loading correctly when the load is unbalanced.

Integral motor with driver and wireless transmission of power and information for autonomous subspindle drive

Abstract: This paper describes the novel technology of an integral motor with the associated driver and wireless transmission of power and information (WTPI), which is effectively applied to autonomous spindle drive for the sophisticated workpiece machining. The power supply to the integral motor is made by way of a separable WTPI coupling. In addition, calculation for variable voltage and variable frequency (VVVF) control is done at the primary side of the coupling, and then the frequency command is transmitted to the secondary side by an overlapped transmission of the data on the power transmission through the WTPI coupling. At the secondary side, direct power conversion from the induced high-frequency voltage to the motor terminal voltage is conducted using a bidirectionally controllable power switch. The amplitude of the terminal voltage is adjusted by changing the inverter voltage at the primary side. In this way, the VVVF drive is made through the WTPI coupling, thus providing the integral subspindle with the autonomy for sophisticated machining.

Efficiency optimized control of medium-size induction motor drives

Abstract: The efficiency of a variable speed induction motor drive can be optimized by adaptation of the motor flux level to the load torque. In small drives (<10 W), this can be done without considering the relatively small converter losses, but for medium-size drives (10-1000 kW) the losses cannot be disregarded without further analysis. The importance of the converter losses on efficiency optimization in medium-size drives is analyzed in this paper. Based on the experiments with a 90-kW drive, it is found that it is not critical if the converter losses are neglected in the control, except that the robustness toward load disturbances may unnecessarily be reduced. Both displacement power factor and model-based efficiency-optimizing control methods perform well in medium-size drives. The last strategy is also tested on a 22-kW drive with good results.

Control system for a PWM-based STATCOM

Abstract: The always-increasing switching frequency of modern solid-state power switches, together with the application of multi-converter topologies, make it possible to use pulse width modulation (PWM) in high power applications of STATCOMs (static synchronous compensators). This paper investigates the control system for a PWM-based STATCOM. First of all, a discrete-time model of the STATCOM is derived to take into account the discrete-time implementation of the controller. Secondly, the control algorithm is detailed. It ensures decoupled control of the real and reactive power exchanged between the power converter and the electric-energy system. This is necessary to control the DC capacitor voltage during transients of the exchanged reactive power. Finally, the control of the capacitor voltage is explained in detail. The controller is tailored to keep the capacitor voltage almost constant in spite of the fast control of the reactive power. This helps to reduce the capacitor size significantly. The main contributions are illustrated using a 15 kVA laboratory prototype.

Power reception circuits for a device receiving an AC power signal

Abstract: Power reception circuits employable in portable data devices (e.g., smart cards) to derive power and/or data from an input AC power signal (e.g., an ASK modulated carrier signal). In one embodiment, the power reception circuit comprises a power rectifier (120), a shunt rectifier (142) and a shunting element (132). The power rectifier (120) is adapted to rectify the input power signal, yielding a rectified output waveform. The shunt rectifier (142) is connected in parallel with the power rectifier (120). The shunting element (132) is connected to the shunt rectifier (142) and is operable to regulate an output voltage or current waveform produced at the output of the power rectifier (120). In another embodiment, the power reception circuit includes an analog circuit (610) for recovering data from a modulated carrier signal. A decoupling device (630) isolates the analog circuit (610) from impedance variations of a load. A shunt device (640) diverts undesired current from the load.

Operating a power converter at optimal efficiency

Abstract: A power converter control system is provided which combines a pulse train regulation control technique with a pulse train optimization technique, to control the output level of the power converter, while maintaining optimal performance for other power converter parameters. The power converter control system describe herein provides versatility not previously available in power converter control systems by providing features such as quasi-resonant mode control, discontinuous mode control, and/or power factor correction. A pulse optimizer adjusts or customizes, for example, the ON time, duty cycle or frequency of pulse train pulses output by a pulse generator. The adjusted pulses are gated by a pulse rate controller to selectively actuate a power switch, thereby regulating the output power level and optimize the overall performance of the power converter.

Electrical power extraction from mechanical disturbances

Abstract: A method of extracting power includes coupling a transducer that converts mechanical power to electrical power to a disturbance; coupling an electrical circuit to the transducer such that a peak voltage experienced by the transducer is greater than two times higher than any peak voltage of an open circuit transducer due to the disturbance alone; extracting power from the transducer using the electrical circuit, and storing extracted power. Power is extracted from the transducer and applied to the transducer during different intervals in the course of the disturbance. A system for extracting power includes a transducer, an electrical circuit, and a storage element for storing extracted power.