Showing papers on "Power factor published in 1998"

Self-powered signal processing using vibration-based power generation

Abstract: Low power design trends raise the possibility of using ambient energy to power future digital systems. A chip has been designed and tested to demonstrate the feasibility of operating a digital system from power generated by vibrations in its environment. A moving coil electromagnetic transducer was used as a power generator. Calculations show that power on the order of 400 /spl mu/W can be generated. The test chip integrates an ultra-low power controller to regulate the generator voltage using delay feedback techniques, and a low power subband filter DSP load circuit. Tests verify 500 kHz self-powered operation of the subband filter, a level of performance suitable for sensor applications. The entire system, including the DSP load, consumes 18 /spl mu/W of power. The chip is implemented in a standard 0.8 /spl mu/m CMOS process. A single generator excitation produced 23 ms of valid DSP operation at a 500 kHz clock frequency, corresponding to 11,700 cycles.

Characterization of double-layer capacitors (DLCs) for power electronics applications

Abstract: The double-layer capacitor (DLC) for power applications is a new device. A simple resistive capacitive equivalent circuit is insufficient to characterize its terminal behavior. Based on physical reasoning, an equivalent circuit is proposed to provide the power electronics engineer with a model for the terminal behavior of the DLC. The equivalent circuit model consists of three RC branches, one of them with a voltage-dependent capacitance. A method to identify the circuit parameters is presented. Measurements of carbon-based DLC's for power applications are presented, analyzed, and the equivalent circuit response is compared with experimental results.

Harmonic and reactive power compensation based on the generalized instantaneous reactive power theory for three-phase four-wire systems

Abstract: This paper presents harmonic and reactive power compensation based on a generalized theory of instantaneous reactive power for three-phase power systems. This new theory gives a generalized definition of instantaneous reactive power, which is valid for sinusoidal or nonsinusoidal and balanced or unbalanced three-phase power systems with or without zero-sequence currents and/or voltages. The properties and physical meanings of the newly defined instantaneous reactive power are discussed in detail. A harmonic and reactive power compensator based on the new theory for a three-phase harmonic-distorted power system with zero-sequence components in the load current and/or source voltage is then used as an example to show harmonic and reactive power measurement and compensation using the new theory. Simulation and experimental results are presented.

Residential photovoltaic energy storage system

Abstract: This paper introduces a residential photovoltaic (PV) energy storage system, in which the PV power is controlled by a DC-DC power converter and transferred to a small battery energy storage system (BESS). For managing the power, a pattern of daily operation considering the load characteristic of the homeowner, the generation characteristic of the PV power, and the power-leveling demand of the electric utility is prescribed. The system looks up the pattern to select the operation mode, so that powers from the PV array, the batteries and the utility are utilized in a cost-effective manner. As for the control of the system, a novel control technique for the maximum power-point tracking (MPPT) of the PV array is proposed, in which the state-averaged model of the DC-DC power converter, including the dynamic model of the PV array, is derived. Accordingly, a high-performance discrete MPPT controller that tracks the maximum power point with zero-slope regulation and current-mode control is presented. With proposed arrangements on the control of the BESS and the current-to-power scaling factor setting, the DC-DC power converter is capable of combining with the BESS for performing the functions of power conditioning and active power filtering. An experimental 600 W system is implemented, and some simulation and experimental results are provided to demonstrate the effectiveness of the proposed system.

An universal active power line conditioner

Abstract: The power circuit of a general active power line conditioner (APLC) is based on series and shunt power converters that share a single DC link. In the present paper, a generic control concept for these series and shunt converters is proposed. It is based on the instantaneous real and imaginary power theory. In fact, the resulting equipment deals with the custom power and FACTS concepts. This equipment incorporates not only the compensation functions at the fundamental frequency like a unified power flow controller (UPFC), but also provides active harmonic mitigation capabilities. For these reasons, the compensator proposed here is called the universal active power line conditioner (UPLC). Simulation and experimental results are presented to confirm that the new approach has better performance than those obtained by controllers based on traditional concepts of active and reactive power.

Active filter system implementation

Abstract: Adjustable speed AC drives with low input current THD are becoming increasingly important in industry. This article has detailed the implementation of a parallel active filter, which is integrated within a 450 kW adjustable speed drive to provide an overall system which conforms to IEEE 519, and which provides significant benefits on a system level. The design of the active filter is seen to be driven by overall system specifications which include input current THD, efficiency, displacement power factor, a high level of integration with the load converter, and cost targets. Active filter operation and control has been analyzed at a detailed level, and fundamental issues relating to current regulator topology and operation, limits on compensation capability, DC bus control, switching frequency ripple suppression, etc., have all been addressed, and have all been shown to be very important in terms of helping the system meet its performance objectives. The overall drive system including the active filter, meets IEEE 519 by reducing the supply current THD from 26.8% without the active filter to 4.1% with the active filter operating. This is achieved in presence of supply voltage THD of 2.3% and filter terminal voltage V/sub f/ unbalance of 1.3% and, includes an ASD load induced subharmonic component at 33 Hz. Further, individual harmonic limits are met up to the 35th harmonic.

Method and apparatus for supplying contactless power

Abstract: A method and apparatus for supplying contactless power. Electrical power is transferred from a power source (100) to a load (500) through a primary energy converter that can be connected to the power source, through a primary inductive loop connected to the magnetically coupled to the primary (200) inductive loop, and then to a secondary energy converter. The power factor for the transfer of electrical energy is one. Multiple loads can receive power from the power source end, where the loads are located in zones, collisions between the loads can be prevented.

A shunt active filter based on voltage detection for harmonic termination of a radial power distribution line

Abstract: This paper focuses on a shunt active filter based on the detection of harmonic voltages at the point of installation. The objective of the active filter is to attenuate harmonic propagation resulting from series/parallel resonance between capacitors for power factor correction and line inductors in a power distribution line. The active filter acts as a low resistor to the external circuit for harmonic frequencies, and it is installed on the end bus of the power distribution line, just like a 50 /spl Omega/ terminator installed on the end terminal of a signal transmission line. Therefore, the function of the active filter is referred to as "harmonic termination" in this paper. Experimental results obtained from a laboratory system rated at 200 V and 20 kW verify that the active filter for the purpose of harmonic termination has the capability of harmonic damping throughout the power distribution line.

Application of STATCOMs to wind farms

Abstract: Effective reactive power control in distribution networks can have an important influence on the level of embedded generation that is acceptable and on the costs of its connection. A comprehensive study was undertaken to investigate how STATCOMs could be used with fixed-speed wind turbines, which use induction generators, to improve both the steady-state and dynamic impact of a wind farm on the network. An optimal power flow model based on loss minimisation was developed and used to show that operation of a wind farm at unity power factor is unlikely to allow maximum penetration of wind energy into a weak distribution circuit. The results of the electromagnetic simulations showed that the use of a STATCOM improves the steady-state stability limits of the network. They also showed that the use of a STATCOM with an appropriately designed control strategy can prevent damaging overvoltages that may occur under islanding conditions. The results also demonstrated that a STATCOM can be used to mitigate voltage fluctuations at blade passing frequency, which may occur if the rotors of a number of wind turbines fall into synchronism.

Uninterruptible power supply with direction of DC electrical energy depending on predetermined ratio

Abstract: An uninterruptible power supply is disclosed in which the backup energy source is connected to the power supply of the protected computer by means of a bi-directional power converter. This converter operates without sensing circuitry, relays, or switches, operating continuously when a load is present in either charging or discharging the backup energy source. This uninterruptible power supply can be placed within the available space of a functioning standard computer power supply enclosure, and may be configured so that it may be replaced during normal computer operation (i.e. it is "hot swappable"). Methods are described to interface the uninterruptible power supply to the computer, providing mutual control and communication. The device may be also used to power devices requiring external DC power, which are commonly found in association with computer operations.

Comparison of basic converter topologies for power factor correction

Abstract: Basic types of DC-DC converters, when operating in discontinuous conduction mode, have self power factor correction (PFC) property, that is, if these converters are connected to the rectified AC line, they have the capability to give higher power factor by the nature of their topologies. Input current feedback is unnecessary when these converters are employed to improve power factor. In this paper, basic types of DC-DC converter topologies are studied to investigate their self-PFC capabilities. Their input characteristics are compared and their input line current waveforms are predicted.

A family of continuous-conduction-mode power-factor-correction controllers based on the general pulse-width modulator

Abstract: This paper presents a family of constant-switching-frequency pulse-width-modulated controllers for single-phase power-factor-correction (PFC) circuits that operate at continuous-conduction mode (CCM). Both trailing- and leading-edge pulse-width modulation (PWM) are used. These controllers do not require the multiplier and rectified-line-voltage sensor, which are needed by traditional control methods, and they can be implemented with a unified control circuit. Controller examples are analyzed and verified experimentally.

Low power radio frequency transmitter with controllable gain

Abstract: A low power transmitter useful for vehicle remote keyless entry systems, for example, includes a transmitter circuit portion and a gain control circuit portion. The gain control circuit portion preferably includes an inductive load that introduces a resonant frequency that provides radio frequency gain control. The transmitter circuit portion preferably includes a transistor having a collector node and an emitter node. The gain controller circuit preferably includes a capacitive load coupled between the emitter node and the collector node of the transistor. The inductive load preferably is coupled between the emitter node of the transistor and ground.

Control of parallel inverters in distributed AC power systems with consideration of the 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. Simulation results are provided in the paper to prove the concept.

A unity power factor converter using half-bridge boost topology

Abstract: A single-phase high-efficiency near-unity power-factor (PF) half-bridge boost converter circuit, which has been proposed earlier by other researchers, is presented with detailed analysis. This converter is capable of operating under variable PF. However, the focus of this paper is in achieving unity PF operation only. The efficiency of this circuit is high because there is only one series semiconductor on-state voltage drop at any instant. The existence of an imbalance in the voltages of the two DC-link capacitors, which was noted before, is confirmed here. The cause for the imbalance is analyzed using appropriate models, and a control method to eliminate it is discussed in detail. Analysis and design considerations for the power circuit using the fixed-band hysteresis current control (HCC) technique are provided. The analytical results are verified through simulation using switched and averaged circuit models of the scheme and also through experimental work. At 90-V AC input and 300-W 300-V output, the experimental prototype demonstrates an efficiency of 96.23% and a PF of 0.998. This converter, with its relatively high DC-output voltage, is well suited for the 110-V utility supply system. A circuit modification for universal input voltage range operation is also suggested.

Switched-mode high-efficiency microwave power amplifiers in a free-space power-combiner array

Abstract: A design-oriented analysis of the microwave transmission-line class-E amplifier is presented. Experiments and harmonic-balance circuit simulations verify the theoretical equations which predict class-E-amplifier output power, maximum frequency of operation, and dc-RF conversion efficiency. Experimental results at 0.5, 1,2, and 5 GHz are presented. At 0.5 GHz, 83% drain efficiency and 80% power-added efficiency (PAE) are measured, with an output power of 0.55 W, using the Siemens CLY5 MESFET. These results are compared to a class-A and class-F power amplifier using the same device. At 5 GHz, 81% drain efficiency and 72% PAE are measured, with an output power of 0.61 W, using the Fujitsu FLK052WG MESFET. Finally, the 5-GHz class-E power amplifier is successfully integrated into an active-antenna array, demonstrating power combining of four elements with an 85% power-combining efficiency. At 5.05 GHz, the class-E power-amplifier antenna array delivers a total of 2.4 W of output power, with a dc-RF conversion efficiency of 74% and a PAE of 64%.

Method and apparatus for providing uninterruptible power using a power controller and a redundant power controller

Abstract: A power supply system has a power input to receive input power from a power source, a power output to provide output power to a load, at least one battery module having a battery output that provides battery power, at least one power module coupled to the power input to receive the input power, coupled to the battery output to receive the battery power and coupled to the power output to provide the output power, a controller, coupled to the at least one power module, constructed and arranged to monitor and control the output power from the at least one power module, and a redundant controller, coupled to the at least one power module and to the controller, constructed and arranged to provide redundant monitoring and controlling of the output power from the at least one power module.

A new scheme for generating and measuring active, reactive, and apparent power at power frequencies with uncertainties of 2.5/spl times/10/sup -6/

Abstract: A new method for generating and measuring active, reactive, and apparent power at power frequencies has been devised. It makes use of digital signal synthesis and discrete Fourier transform (DFT) evaluation based on a single master clock. This results in a significant reduction of synchronizing errors and thus in an uncertainty of only 2.5/spl times/10/sup -6/ (k=1).

Control strategy for grid-connected DC-AC converters with load power factor correction

Abstract: The paper presents the modelling, analysis and design of a pulse width modulation voltage source inverter (PWM-VSI) to be connected between a DC source, which is supplied from a photovoltaic (PV) array and the AC grid. The control algorithm of the PWM-VSI applies the concepts of the instantaneous p-q (real-imaginary) power theory. The objective is to show that, with an adequate control, the converter can transfer the DC energy from PV array and improve the power factor (and the power quality) of the electrical system. Some design considerations are also discussed. A digital simulation and measurements on a small prototype model verified the feasibility of the proposed control method.

An economical single-phase passive power-factor-corrected rectifier: topology, operation, extensions, and design for compliance

Abstract: This paper describes a novel passive power-factor correction circuit that ensures the compliance of the capacitively filtered single-phase rectifier with the EN61000-3-2 norm at a cost much lower than the known solutions The circuit can be used to about 300 W The additional components are a small inductor, a small capacitor and a diode

Power supply and methods for electrosurgery in conductive fluid

Abstract: A high frequency power supply (28) for applying electrical energy to a target site on or within a patient's body in the presence of electrically conductive fluid. In one embodiment, the power supply (28) includes an electrical output driver (342), an output current sensor (302) detecting the current output from the driver, and a power limiting device (330) coupled to the current sensor. During normal conditions the power limiting device (330) operates on a continuous basis. When current output exceeds a predetermined threshold level, the power limiting device (330) is adapted to reduce power on the ouput driver to a standby mode. The power limiting device (330) operates on a periodic detection or duty cycle when in the standby mode. The power limiting device (330) switches into the standby mode to prevent excessive power drains.

Nonlinear-carrier control for high-power-factor rectifiers based on up-down switching converters

Abstract: In this paper, nonlinear-carrier (NLC) control is proposed for high-power-factor rectifiers based on flyback, Cuk, Sepic, and other up-down power converters operated in the continuous conduction mode (CCM). In the NLC controller, the switch duty ratio is determined by comparing a signal proportional to the integral of the switch current with a periodic nonlinear-carrier waveform. The shape of the NLC waveform is determined so that the resulting input-line current follows the input-line voltage, as required for unity power factor rectification. A simple exponential carrier waveform generator is described. Using the NLC controller, input-line voltage sensing, error amplifier in the current-shaping loop, and multiplier/divider circuitry in the voltage feedback loop are eliminated. The simple high-performance controller is well suited for integrated-circuit implementation, Results of experimental verification on a 150 W flyback rectifier are presented.

DC voltage control and stability analysis of PWM-voltage-type reversible rectifiers

Abstract: A PWM voltage rectifier has useful characteristics on its DC and AC sides. On its DC side, a DC-link unidirectional voltage is obtained and bidirectional power transfer capability is possible by reversing the flow direction of the DC-link current. On its AC side, near sinusoidal current waveforms and AC four-quadrant operation can be obtained, leading to high-quality power being exchanged between the power converter and the mains. The use of AC filters becomes unnecessary. The rectifier DC voltage must be regulated to a constant value. In this paper, three solutions for the DC voltage control are presented. In the first solution, the DC voltage is controlled by acting upon the quadrature component of the power converter fundamental Park's voltages with relation to the mains voltages. Slow responses are necessary because of stability reasons. Also, load power variations produce both active and reactive power variations in the power converter AC side. To improve the DC voltage response, a second control solution is presented. The power converter currents in Park's coordinates must be controlled. The DC voltage is controlled by controlling the direct Park's current component and, thus, acting only on the active power of the converter AC side. Faster responses are achieved. In this case, load power variations do not produce reactive power variations in the converter AC side. The third control solution is a simplified version of this last one. Experimental results from a 2 kVA IGBT-based prototype showing good system dynamic performance are presented.

Power factor correction method and apparatus

Abstract: A method and apparatus for controlling a boost converter, which offers improved power factor correction by compensating for the distorting effects of parasitic capacitance and parasitic oscillations. By precise adjustments to the closing time of the boost switch, the effects of parasitic capacitance can be reduced or eliminated. A zero current detector capable of detecting both forward and reverse zero current points facilitates the compensation. The method and circuit of the present invention are well-suited to integration with an inexpensive digital controller such as a microprocessor, and a method of dithering to enhance the time resolution of clocked digital circuits is presented.

The use of matrix converters in direct torque control of induction machines

Abstract: In this paper a new control method for matrix converters is proposed which allows, under the constraint of unity input power factor, the generation of the voltage vectors required to implement the direct torque control (DTC) of induction machines. Using this control method it is possible to combine the advantages of matrix converters with the advantages of the DTC schemes. Some numerical simulations are carried out showing the effectiveness of the proposed method in steady-state and transient conditions.

Dynamics of a buck converter with a constant power load

Abstract: The dynamic properties of the buck converter with a constant power load are studied in this paper. The line-to-output and control-to-output transfer functions are derived, for voltage mode control and current mode control, in continuous conduction mode and discontinuous conduction mode. A comparison with the case of a resistive load is made in each case.

State variable decoupling and power flow control in PWM current-source rectifiers

Abstract: Pulsewidth modulated (PWM) current-source rectifiers (CSR), among other alternatives, offer marked improvements over thyristor line-commutated rectifiers as a source of variable DC power. Advantages include reduced line current harmonic distortion and complete displacement power factor control, including unity displacement power factor operation. However, due to nonlinearities of the PWM-CSR model, their control has usually been carried out using direct line current control in a three-phase stationary frame (abc). This paper proposes the application of a nonlinear control technique that introduces more flexibility in the control of the rectifier and results in a more straightforward approach to controller design. The proposed technique is based on a nonlinear state variable feedback approach in the rotating frame (dq). The approach allows the independent control of the two components of the line current (active and reactive) with the same dynamic performance, regardless of the operating point. The control strategy also eliminates the need for input damping resistors and rejects the effect of supply voltage variations. Furthermore, a space vector modulation (SVM) technique is used to maximize the supply voltage utilization. This paper includes a complete formulation of the system equations and a controller design procedure. Experimental results on a 2 kVA digital-signal-processor-controlled prototype confirm the validity of theoretical considerations.

Grid interface options for variable-speed, permanent-magnet generators

Abstract: The authors survey the many forms of DC/AC converter which may be applied to permanent magnet generators, examine their potential to meet the waveform, power factor, cost and efficiency requirements and consider their features in relation to the special environment of a wind turbine system. Feasible options are identified and compared. The control needed to achieve maximum energy capture from the wind is described. Inverters have been selected which are able to effect the necessary power control whilst providing controllable reactive power and causing minimal harmonic pollution of the network. Device cost and overall efficiency have been assessed for each option.

Pitfalls of electric power quality indices

Abstract: Several indices are in common use for the quantification of electric power quality. These indices are convenient for condensing complex time and frequency domain waveform phenomena into a number. However, a variety of commonly encountered circumstances are not readily accommodated (e.g. quasiperiodic and aperiodic signal components and noninteger multiples of the power frequency). Also, the power acceptability curves have been used as convenient measures of power quality and these curves do not capture three-phase detail of power quality problems. In this paper, the general subject of pitfalls of power quality indices is discussed and suggestions for alleviating these problems are made.

New dynamic flip-flops for high-speed dual-modulus prescaler

Abstract: A fast pipeline technique using single-phase, edge-triggered, ratioed, high-speed logic flip-flops and D flip-flops is introduced and analyzed. The circuits achieve high speed by reducing the capacitive load and sharing the delay between the combination logic blocks and the storage elements. Also it is suitable for realizing high-speed synchronous counters. A divide-by-128/129 and 64/65 dual-modulus prescaler using the proposed flip-flops is measured in 0.8 /spl mu/m CMOS technology with the operating clock frequency reaching as high as 1.8 GHz.