Showing papers on "Power factor published in 1995"

The unified power flow controller: a new approach to power transmission control

Abstract: This paper shows that the unified power flow controller (UPFC) is able to control both the transmitted real power and, independently, the reactive power flows at the sending- and the receiving-end of the transmission line. The unique capabilities of the UPFC in multiple line compensation are integrated into a generalized power flow controller that is able to maintain prescribed, and independently controllable, real power and reactive power flow in the line. The paper describes the basic concepts of the proposed generalized P and Q controller and compares it to the more conventional, but related power flow controllers, such as the thyristor-controlled series capacitor and thyristor-controlled phase angle regulator. The paper also presents results of computer simulations showing the performance of the UPFC under different system conditions. >

Space vector modulated three-phase to three-phase matrix converter with input power factor correction

Abstract: Analysis, design, and implementation of the space vector modulated three-phase to three-phase matrix converter with input power factor correction are presented. The majority of published research results on the matrix converter control are given an overview, and the one which employs simultaneous output-voltage and input-current space vector modulation, is systematically reviewed. The modulation algorithm is theoretically derived from the desired average transfer functions, using the indirect transfer function approach. The algorithm is verified through implementation of a 2 kVA experimental matrix converter driving a standard induction motor as a load. The switching frequency is 20 kHz. The modulator is implemented with a digital signal processor. The resultant output voltages and input currents are sinusoidal, practically without low-frequency harmonics. The input power factor is above 0.99 in the whole operating range.

Analysis Of A Micro-electric Generator For Microsystems

Abstract: Supplying power to remote microsystems that have no physical connection to the outside world is difficult, and using batteries is not always appropriate. A solution is offered by the device proposed in this paper, which generates electricity from mechanical energy when embedded in a vibrating medium. This micro-generator has dimensions of around 5x5x1mm. Analysis predicts that the power produced is proportional to the cube of the frequency of vibration, and that to maximise power generation the mass deflection should be as large as possible. Power generation of 1/spl mu/W at 70Hz and 0.1mW at 330Hz are predicted for a typical device, assuming a deflection of 50/spl mu/m.

Synchronous frame based controller implementation for a hybrid series active filter system

Abstract: This paper proposes a synchronous reference frame based controller for a hybrid series active filter system. A hybrid series active filter system has been designed, built and installed at Beverly Pump Station in New England Electric utility for 765 kVA adjustable speed drive load to meet IEEE 519 recommended harmonic standards. The series active filter is rated 35 kVA-4% of the load kVA, and is controlled by a synchronous reference frame based controller to act as a harmonic isolator between the supply and load. This paper discusses the basic synchronous reference frame controller structure and addresses its operation under nonunity controller loop gain conditions. Design trade-offs and implementation issues of the synchronous reference frame controller are discussed. Operation of the hybrid series active filter system under off-tuned passive filter conditions and its impact on the performance of the synchronous reference frame based controller is experimentally evaluated. Effectiveness of the series active filter to provide harmonic damping and the use of simpler and low cost power factor correction capacitors as passive filters, is demonstrated by laboratory experimental results. Field installation and laboratory experimental results demonstrate the practical viability of the synchronous reference frame based controller for hybrid series active filter to provide harmonic isolation of nonlinear loads and to comply with IEEE 519 recommended harmonic standards.

A three-phase active power filter operating with fixed switching frequency for reactive power and current harmonic compensation

Abstract: The performance and dynamic characteristics of a three-phase active power filter operating with fixed switching frequency is presented and analyzed in this paper. The proposed scheme employs a PWM voltage-source inverter and has two important characteristics. First, it operates with fixed switching frequency, and second, it can compensate the reactive power and the current harmonic components of nonlinear loads. Reactive power compensation is achieved without sensing and computing the reactive component of the load current, thus simplifying the control system. Current harmonic compensation is done in time domain. The principles of operation of the proposed active power filter along with the design criteria of the power and control circuit components are discussed in detail. Finally, experimental results obtained from a 5 kVA prototype confirm the feasibility and the features of the proposed system. >

Uninterruptible power system

Abstract: An uninterruptible power system has a transformer with a primary connected to input terminals, a secondary connected to output terminals, a static switch connected between the input terminals and the primary, and an auxiliary primary connected to an inverter which is supplied by a battery to provide output voltage to the output terminals when a main AC power system connected to the input terminals has failed. The primary has multiple taps at different voltage levels and a buck-boost winding. The taps of the transformer are switched and the buck-boost winding is controlled to provide either buck, boost, or pass-by to allow control of the output voltage from the transformer to within a few percent of a desired voltage level despite large changes in the input voltage. A battery charger coupled to the auxiliary primary operates as a boost converter to provide current to charge the battery at a current level which tracks the input voltage from the AC power system, thereby providing a substantially unity power factor to the AC power system. The voltage control of the output voltage also controls the voltage at the output of the auxiliary primary to which the battery charger is connected, whereby the voltage applied to the charger is substantially regulated and the output power of the charger itself is substantially regulated. The charger can be operated in programmable modes to provide a desired charge configuration for the battery. Detection of faults in the AC power system is enhanced by accurate detection of the zero crossings of the input voltage from the AC power system, and by comparison of the AC input power waveform with an adaptive reference.

Single-phase three-level boost power factor correction converter

Abstract: In many single-phase power factor correction (PFC) applications, the power level can reach several kilowatts; and in some situations, the input voltage can be quite high too. For high power and/or high voltage applications, the major concerns of the conventional boost PFC converter are the inductor volume and weight, and losses on the power devices, which will affect converter cost, efficiency, and power density. In this paper, a three-level boost converter is adopted for single-phase PFC, which uses a much smaller inductor and lower voltage devices than the conventional boost PFC converter does, yielding high power density, high efficiency, and low cost. >

VSI-PWM rectifier/inverter system with a reduced switch count

Abstract: A current-controlled VSI-PWM rectifier and inverter with capacitor DC link is regarded as one of the most important structures for three-phase to three-phase power conversion. This type of power converter normally requires twelve switches for the rectifier and an inverter composed of self turnoff switch such as a bipolar transistor or an IGBT with an anti-parallel diode. In this paper, a new three-phase to three-phase AC/AC power converter for AC motor drives is proposed. The proposed power converter employs only eight switches and has the capability of delivering sinusoidal input currents with unity power factor and bidirectional power flow. This paper describes the feasibility and the operational limitations of the proposed structure. A mathematical model of the system is derived using the generalized modulation theory and experimental results for steady-state and dynamic behavior are presented to verify the developed model.

Step-up DC power supply based on a switched-capacitor circuit

Abstract: A new step-up DC-to-DC power converter with high power density is presented. It contains no inductors or transformers. The controlled energy transfer from an unregulated voltage source to a regulated output voltage is realized through a switched-capacitor circuit. The operation of the switches in the power stage is dictated by a PWM-type feedback circuit. The new regulator is simulated by using an averaged state-space approach. The transient and steady-state waveforms, as well as the AC small-signal input-to-output and control-to-output transfer functions are obtained by both simulation and experiments. The power supply, implemented for a nominal power of 15 W, and input-to-output voltage ratio of 5/12, features high efficiency for this class of powers, small output voltage ripple, continuous input current, low weight and small size. >

AC/DC/AC PWM converter with reduced energy storage in the DC link

Abstract: The paper introduces the family of quasi-direct converters, i.e., forced-commutated AC/DC/AC power converters including small energy storage devices in the DC link. In particular, the case of the three-phase to three-phase quasi-direct power converter is considered. Since energy storage minimization calls for instantaneous input/output power balance, a proper control strategy is needed. The paper describes a simple and effective control technique which also provides high-power factor and small distortion of the supply currents. After a discussion of the general properties of quasi-direct power converters, design criteria of both power and control sections are given, and experimental results of a 2-kVA prototype are reported. >

Nonlinear-carrier control for high power factor boost rectifiers

Abstract: Novel nonlinear-carrier (NLC) controllers are proposed for high-power-factor boost rectifiers. In the NLC controllers, the switch duty ratio is determined by comparing a signal derived from the main switch current with a periodic, nonlinear carrier waveform. As a result, the average input current follows the input line voltage. The technique is suitable for boost power converters operating in the continuous conduction mode. Input voltage sensing, the error amplifier in the current-shaping loop, and the multiplier/divider circuitry in the voltage feedback loop are eliminated. The current-shaping is based on switch (as opposed to inductor) current sensing. The NLC controllers offer comparable or improved performance over existing schemes, and are well-suited for simple integrated-circuit implementation. Experimental verification on a 240 W rectifier is described. >

Performance investigation of a current-controlled voltage-regulated PWM rectifier in rotating and stationary frames

Abstract: Active front-end rectifiers with reduced input current harmonics and high input power factor will be required in the near future for utility interfaced applications. In order to meet the new and more stringent regulations with force-commutated switches, the voltage source inverter approach is superior to the conventional current source approach, in terms of number of components and control options. However, the straightforward power angle control of the rectifier is characterized by a slow response and potential stability problems. This paper proposes a current-controlled PWM rectifier as an alternative. It provides near sinusoidal input currents with unity power factor and a low output voltage ripple. Moreover, it produces a well-defined input current harmonic spectrum, exhibits fast transient response to load voltage variations, and is capable of regenerative operation. PWM pattern generation is based on a carrier technique and the current controller is implemented in the: (a) stationary (abc) frame; and (b) rotating (dqo) frame. The design and the performance of the two controller options are investigated and compared. >

Control system for three-phase active power filter which simultaneously compensates power factor and unbalanced loads

Abstract: The effectiveness of an active power filter depends basically on three characteristics: (a) the modulation method used; (b) the design characteristics of the PWM modulator; and (c) the method implemented to generate the reference template. For the last characteristic there are many methods, most of them complicated and hence difficult to implement and adjust. In this paper, a new method, which has simplicity at its main characteristic, is presented. The method is based on "sample and hold" circuits, synchronized with the peak value of the phase-to-neutral mains voltage. This method is useful for shunt active power filters and is capable to eliminate harmonics, compensate power factor, and correct unbalance problems simultaneously. It also has the ability to slow-down sudden transient changes in the load. Experimental results, with the reference template obtained with the method, are presented in the paper.

A survey of distribution system power quality-preliminary results

Abstract: This paper presents preliminary results from a national monitoring program designed to characterize power quality levels on electric distribution systems. The monitoring program is being sponsored by the Electric Power Research Institute. Initial stages of the project resulted in the development of a new power quality monitoring instrument (designated the PQNode). This instrument permits simultaneous monitoring of steady state quantities (RMS voltage and current, harmonic distortion levels, power factor, etc.) and disturbances (voltage sags, overvoltages, transients, etc.). Approximately 200 PQNodes have been installed on distribution systems of 24 different utility companies. Monitoring data is being compiled by Electrotek Concepts in Knoxville, TN. The paper describes the monitoring system and presents preliminary results of the monitoring effort. >

Evaluation of neural network based real time maximum power tracking controller for PV system

Abstract: This paper presents a neural network based maximum power tracking controller for interconnected PV power systems The neural network is utilized to identify the optimal operating voltage of the PV power system The controller generates the control signal in real-time, and the control signal is fed back to the voltage control loop of the inverter to shift the terminal voltage of the PV power system to its identified optimum, which yields maximum power generation The controller is of the PI type The proportional and the integral gains are set to their optimal values to achieve fast response and also to prevent overshoot and also undershoot Continuous measurement is required for the open circuit voltage on the monitoring cell, and also for the terminal voltage of the PV power system Because of the accurate identification of the optimal operating voltage of the PV power system, more than 99% power is drawn from the actual maximum power >

Design considerations for single-stage isolated power-factor-corrected power supplies with fast regulation of the output voltage

Abstract: The paper introduces a new family of single-stage isolated power-factor-corrected power supplies with fast regulation of the output voltage, and discusses the most-important design issues, including all of the following: storage-capacitor voltage, dual-range and wide-range operation, device RMS currents, and line harmonic currents. In addition to the theoretical analyses, experimental data are also provided. >

Apparatus and method for controlling power usage

Abstract: A power control circuit and corresponding technique for reducing power consumption by an electronic device and thereby increasing performance. The power control circuit comprises a controller, a clock generation circuit and a power supply circuit. The controller detects whether a condition exists to scale the voltage and frequency of the electronic device and in response, signals the clock generation circuit to perform frequency scaling on the electronic device and the power supply circuit to perform voltage scaling on the electronic device. The condition may include a situation where the temperature of the electronic device is detected to have exceeded a thermal band. The condition may also include a situation where the electronic device is detected to be idle for a selected percentage of its run time.

A new approach to enhance power quality for medium voltage drives

Abstract: A new approach to medium voltage, variable frequency, static AC motor drives offers improvements in power quality. Harmonic current injection into power lines is below the most severe requirements of IEEE 519-1992. The power factor of this new type of drive exceeds 94% at full load and is above 90% at 10% load. Motor voltage and current waveforms are improved so that torque pulsations are reduced. Peak voltage stress on motor insulation does not exceed peak input line voltage, and no zero sequence voltage is imposed. Drive efficiency exceeds 96%. This paper describes the new approach, and some of the results achieved.

Circuit topologies for PWM boost rectifiers operated from 1-phase and 3-phase AC supplies and using either single or split DC rail voltage outputs

Abstract: This paper provides a survey of PWM boost rectifier circuit topologies for controlling a nonisolated DC-rail voltage whilst drawing supply currents at a unity fundamental power factor and with a low total harmonic distortion. Rectifier-leg topologies are classified by the number of switches and by the PWM waveforms generated. Complete rectifier circuit topologies are described for operation off 1-phase and 3-phase AC supplies. Circuit analogies are made between rectifiers for 1 and 3 phases, rectifiers using either a single or a split DC-rail and between rectifiers using either AC or DC side inductors. The performances of the various circuits are assessed with reference to factors such as conduction losses, efficiency, switch count, semiconductor voltage stresses, 3-level and 2-level PWM voltage waveforms and, finally, bi-directional power conversion. >

On lossless switched-capacitor power converters

Abstract: This paper addresses the design of efficient switched-capacitor power converters. The discussion starts with a review of the fundamental limitation of switched-capacitor circuits which shows that the topology of such circuits and the "forced" step changes of capacitor voltages are the inherent attributes of power loss. Although the argument follows from a rather trivial result from basic circuit theory, it addresses an important issue on the maximum efficiency achievable in a switched-capacitor power converter circuit. Based on the observed topological constraint of switched-capacitor power converter circuits, the simplest lossless topology for AC/DC power conversion is deduced. Also discussed is a simple version of lossless topology that achieves isolation between the source and the load. Finally, an experimental AC/DC switched-capacitor power converter, based on the proposed idea, is presented which demonstrates an improved efficiency over other existing switched-capacitor power converters. The proposed AC/DC power converter contains no inductors and thus is suitable for custom IC implementation for very low power applications. >

High efficiency multiple power level amplifier circuit

Abstract: A high efficiency multiple power level amplifier circuit for reducing power consumption during low power operations. A plurality of power amplifier stages are cascaded to provide multiple levels of amplification. At least one power amplification stage includes a signal switching network to allow one or any combination of power amplifiers to be switched out when lower power operations are desired. The switched out power amplifiers are biased such that substantially no current is drawn from the power source.

Optimal reactive power planning and its spot-pricing: an integrated approach

Abstract: The paper presents an integrated framework to analyze the issues of reactive power planning along with reactive power pricing. The planning problem involves optimal placement and sizing of capacitors in a network such that operating and investment costs are minimum. A simple bus-wise cost-benefit analysis (CBA) scheme is proposed which involves solving a modified optimal power flow problem (OPF) iteratively. The proposed CBA incorporates detailed hourly loading conditions at a bus and achieves a fairly accurate estimate of the benefits from capacitor placement. The formulation is directly handled by the well known MINOS code and is solved efficiently. It obviates the need to introduce integer variables and is thus suitable for large system applications. A two-part reactive power spot-pricing scheme is formulated, by which the investment and operational costs can be recovered by the utility. The proposed reactive power price has two parts-a fixed part to account for the investment costs of new capacitor at a bus and a variable spot price to account for the operating costs incurred in supplying the additional reactive power from generating units.

Low voltage, high efficiency GaAs Class E power amplifiers for wireless transmitters

Abstract: A Class E power amplifier for mobile communications is presented. The advantages of Class E over Class B, Class C, and Class F power amplifiers in a low voltage design are discussed. A fully integrated Class E power amplifier module operating at 835 MHz is designed, fabricated, and tested. The circuit is implemented in a self-aligned-gate, depletion mode 0.8-/spl mu/m GaAs MESFET process. The amplifier delivers 24 dBm of power to the 50-/spl Omega/ load with a power added efficiency greater than 50% at a supply voltage of 2.5 V. The power dissipated in the integrated matching networks is 1.5 times the power dissipated in the transistor. >

Power supply circuit for use with a battery and an AC power adaptor

Abstract: A power supply circuit prevents, without the use of a series diode, the flow of reverse current from a battery to an AC power adaptor when the power adaptor is disconnected from its external power source. The circuit includes both voltage and current detectors to determine if the output voltage and current of the power adaptor are above or below predetermined reference levels. A summing circuit sums the outputs of the voltage and current detectors, and when both the detected voltage and current are below the reference levels, a switch disconnects the battery from the output terminal of the power adaptor, thereby preventing reverse current flow.

Efficient power conversion

Abstract: In a power conversion scheme, a power conversion apparatus consisting of boost conversion elements for effecting a boost conversion of power originating from a varying voltage source; additional conversion elements for also effecting conversion of power originating from the varying voltage source; and circuitry for selectively configuring the conversion elements with respect to delivery of power to a load to achieve greater conversion efficiency than if all of the power delivered to the load were constrained to flow through the additional conversion elements and at least some of the boost conversion elements In another aspect power is converted from a voltage source having a predetermined source voltage range, and delivered to a load via two sets of power conversion elements, each set for effecting conversion of power from the voltage source, at least one of the sets having an input operating voltage range narrower than the source voltage range The apparatus includes control circuitry for configuring and reconfiguring interconnections of the two sets with the voltage source and the load to provide an input operating voltage range for the apparatus which is greater than the input operating range of the set of power conversion elements having the narrower input operating voltage range In another aspect, the input voltage operating range is enhanced for a power conversion circuit which has two sets of power conversion elements arranged to share power delivered to a load The circuit is selectively configured with the two sets in series or not in series in a manner so that the input voltage operating range of the power conversion circuit is broader than the input voltage operating range of either of the sets of power conversion elements

Revenue and harmonics: an evaluation of some proposed rate structures

Abstract: IEEE Recommended Practice 519 sets specific limits on harmonic voltages and currents at the "point of common coupling", which is usually interpreted as the revenue meter. Although most electric utilities will employ these limits simply to persuade and encourage their customers to reduce harmonics (and vice versa), it is also possible to construct economic incentives to encourage both the utility and the consumer to remain within the limits described in IEEE 519. This paper discusses seven approaches to this challenge, and discusses the advantages disadvantages of each. It appears that "harmonic-adjusted power factor" approach is practical, justifiable, compatible with existing rate structures, and relatively easy to implement. >

Modular power supply system

Abstract: A modular power supply system (10) is provided for providing a multiplicity of output voltages from a plurality of respective converter modules (70a - 70n). Each of the converter modules (70a - 70n) has an input coupled to a DC high voltage bus (22) from which a respective output voltage is generated. The voltage supplied on DC bus (22) is generated by a power factor corrected boost converter circuit (20) which is coupled to an AC input source (12). Further, a battery backup module (40) is coupled to the high voltage DC bus (22) for supplying backup power whenever the bus voltage drops below a predetermined level.

Harmonic power flow analysis for the measurement of the electric power quality

Abstract: The number and power of loads that pollute, from an electric point of view, the electric network are constantly increasing. Their connection to the electric network causes a significant distortion in the line current and, when their overall power is no longer negligible with respect to the network power, also some distortion in the line voltage, thus deteriorating the electric supply quality. The paper proposes a method, based on the evaluation of the harmonic powers, to identify whether the source producing harmonic distortion in the line currents and voltages of a three-phase system is a polluting load connected after the metering section or is the distortion of the line voltages. Some parameters are also defined in order to quantify the effects of the polluting load on the power quality. A Virtual Instrument is also described, realized to implement the proposed method and to verify it experimentally. The instrument accuracy is discussed. >

Dynamically switchable power supply

Abstract: A power supply system of an electronic system is dynamically switchable upon fluctuating demand for operational power. The power supply is capable of providing multiple voltage values to an electronic system which is capable of utilizing multiple logical voltage values. The power utilized by the electronic system is further controlled by varying the frequency at which the electronic system operates. Power is conserved by operating at a lower voltage and frequency and is optimally utilized upon demand by dynamically switching to operate at higher voltages and frequencies for the duration of the increased power demand. Temporary peak power greater than average operational power may be attained.

A new method of harmonic power detection based on the instantaneous active power in three-phase circuits

Abstract: This paper presents a new method of harmonic power detection based on the instantaneous active power in three-phase circuits, and its applications to search for dominant harmonic sources in power systems. The proposed method requires only band elimination filters and a three-phase active power meter to detect the harmonic active power, and it is able to deal with harmonic power flow more easily and precisely than a conventional meter which is based on Fourier series of single-phase circuits. In addition, measurement errors of the harmonic power are discussed theoretically. The validity of the proposed method is demonstrated by digital simulation. >