Showing papers on "Power factor published in 2003"

A review of single-phase improved power quality AC-DC converters

Abstract: Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

Leakage current: Moore's law meets static power

Abstract: Off-state leakage is static power, current that leaks through transistors even when they are turned off. The other source of power dissipation in today's microprocessors, dynamic power, arises from the repeated capacitance charge and discharge on the output of the hundreds of millions of gates in today's chips. Until recently, only dynamic power has been a significant source of power consumption, and Moore's law helped control it. However, power consumption has now become a primary microprocessor design constraint; one that researchers in both industry and academia will struggle to overcome in the next few years. Microprocessor design has traditionally focused on dynamic power consumption as a limiting factor in system integration. As feature sizes shrink below 0.1 micron, static power is posing new low-power design challenges.

Modeling and control of a wind turbine driven doubly fed induction generator

Abstract: This paper presents the simulation results of a grid-connected wind driven doubly fed induction machine (DFIM) together with some real machine performance results. The modeling of the machine considers operating conditions below and above synchronous speed, which are actually achieved by means of a double-sided PWM converter joining the machine rotor to the grid. In order to decouple the active and reactive powers generated by the machine, stator-flux-oriented vector control is applied. The wind generator mathematical model developed in this paper is used to show how such a control strategy offers the possibility of controlling the power factor of the energy to be generated.

Single phase power factor correction: a survey

Abstract: New recommendations and future standards have increased the interest in power factor correction circuits. There are multiple solutions in which line current is sinusoidal. In addition, a great number of circuits have been proposed with nonsinusoidal line current. In this paper, a review of the most interesting solutions for single phase and low power applications is carried out. They are classified attending to the line current waveform, energy processing, number of switches, control loops, etc. The major advantages and disadvantages are highlighted and the field of application is found.

Predictive digital current programmed control

Abstract: This paper explores predictive digital current programmed control for valley, peak or average current. The control laws are derived for the three basic converters: buck, boost, and buck-boost. It is found that for each variable of interest (valley, peak or average current) there is a choice of the appropriate pulse-width modulation method to achieve predictive digital current control without oscillation problems. The proposed digital control techniques can be used in a range of power conversion applications, including rectifiers with power factor correction (PFC). Very low current distortion meeting strict avionics requirements (400-800 Hz line frequency) is experimentally demonstrated on a digitally controlled boost PFC employing predictive average current programmed control.

Genetic algorithm based design of the active damping for a LCL-filter three-phase active rectifier

Abstract: The use of a LCL-filter mitigates the switching ripple injected in the grid by a three-phase active rectifier. However stability problems could arise in the current control loop. In order to overcome them a damping resistor can be inserted, at the price of a reduction of the efficiency. On the contrary the use of the active damping seems really attractive but it is often limited by the use of more sensors respect to the standard control and by the complex tuning procedure. This paper introduces a new active damping method that does not need the use of more sensors and that can be tuned using genetic algorithms. It consists of adding a filter on the reference voltage for the converter's modulator. The tuning process of this filter is easily done, for a wide range of sampling frequencies, with the use of genetic algorithms. This method is used only for the optimum choice of the parameters of the filter and an on-line implementation is not needed. Thus the resulting active damping solution does not need new sensors or complex calculations. Moreover, in the paper particular attention is devoted to the dynamics of the system due to the introduction of the active damping.

Power supply rail controller

Abstract: A power supply rail controller operates on an analog component having a signal input, a power input and a signal output. A voltage controller provides a control output responsive to the signal output. A power supply generates a voltage for the power input, where the voltage is responsive to the control output. The voltage is reduced in magnitude to reduce power dissipation and increased in magnitude to avoid signal distortion.

Implementation and control of grid connected AC-DC-AC power converter for variable speed wind energy conversion system

Abstract: 30 kW electrical power conversion system is developed for a variable speed wind turbine system. In the wind energy conversion system (WECS) a synchronous generator converts the mechanical energy into electrical energy. As the voltage and frequency of generator output vary along the wind speed change, a DC-DC boosting chopper is utilized to maintain constant DC link voltage. The input DC current is regulated to follow the optimized current reference for maximum power point operation of turbine system. Line side PWM inverter supply currents into the utility line by regulating the DC link voltage. The active power is controlled by q-axis current whereas the reactive power can be controlled by d-axis current. The phase angle of utility voltage is detected using software PLL (phased locked loop) in d-q synchronous reference frame. Proposed scheme gives a low cost and high quality power conversion solution for variable speed WECS.

Improving passive filter compensation performance with active techniques

Abstract: This paper presents the performance analysis of a hybrid filter composed of passive and active filters connected in series. The analysis is done by evaluating the influence of passive filter parameters variations and the effects that different active power filter's gain have in the compensation performance of the hybrid scheme. The compensation performance is quantified by evaluating the attenuation factor in a power distribution system energizing high-power nonlinear loads compensated with passive filters and then improved with the connection of a series active power filter. Finally, compensation characteristics of the hybrid topology are tested on a 10-kVA experimental setup.

Analysis and design of direct power control (DPC) for a three phase synchronous rectifier via output regulation subspaces

Abstract: In this paper, the authors present a controller that directly regulates the active and instantaneous reactive power in a synchronous three-phase boost-type rectifier. The controller ensures a good regulation of the output voltage, and guarantees the power factor close to one. The controller builds upon the ideas of the well known direct torque control (DTC) for induction motors. In their case, the active and reactive powers replace the torque and flux amplitude used as the controlled outputs in DTC, thus motivating the name DPC-control. They show that a simple modification to the original algorithm makes the selection of the control inputs more accurate. To formalize this technique, they utilize the concept of output regulation subspaces. A modification is added to the basic controller to deal with disturbances such as unbalance and distortion in the source voltage. Finally, the proposed controller was tested both in simulations and experimentally, and illustrative results are presented.

Digital repetitive controlled three-phase PWM rectifier

Abstract: In this paper, a digital repetitive control (RC) strategy is proposed to achieve zero tracking error for constant-voltage constant-frequency (CVCF) pulse width modulation (PWM) converters. The proposed control scheme is of "plug-in" structure: a plug-in digital repetitive controller plus a conventional controller (e.g., PD controller). The design of the plug-in repetitive learning controller is systematically developed. The stability analysis of overall system is discussed. A repetitive controlled three-phase reversible PWM rectifier is given as an application example. Near unity power factor and constant output DC voltage are ensured under parameter uncertainties and load disturbances. Simulation and experimental results are provided to testify the effectiveness of the proposed control scheme.

High current inductive coupler and current transformer for power lines

Abstract: There is provided an inductive power line data coupler (10). The coupler (10) includes (a) a magnetic core (105) having a high magnetic permeability at a data communication frequency and being configured to allow a power line (100) to serve as a primary winding, (b) a data signaling circuit that provides a secondary winding (115) through the magnetic core (105) for coupling a data signal between the power line (100) and a communication device (130), and (c) a choke coil (135) coupled to the data signaling circuit for creating a flux-canceling power frequency current opposite in direction and comparable in magnitude to a power frequency current. The coupler (10) may also include a circuit for sensing a level of current in the power line (100).

Power line carrier system

Abstract: The power line carrier system provides with a filter in a power branch apparatus removable from an external power line. The filter passes a power line carrier signal in a signal mode for the external power line, and interrupts another power line carrier signal which is in a signal mode different from the mode for the external power line.

On the feasibility of four-switch three-phase BLDC motor drives for low cost commercial applications: topology and control

Abstract: The main purpose of this paper is to describe a low cost four-switch brushless DC (BLDC) motor drive for commercial applications. For effective utilization of the developed system, a novel direct current controlled PWM scheme is designed and implemented to produce the desired dynamic and static speed-torque characteristics. Also, the feasibility of the four-switch converter is extended to two-phase BLDC motor drives and the six-switch converter for power factor correction and speed control. The operational principle of the four-switch BLDC motor drive and the developed control scheme are theoretically analyzed and the performance is demonstrated by both simulation and experimental results.

Electrical power distribution control methods, electrical energy demand monitoring methods, and power management devices

Abstract: Electrical power distribution control methods, electrical energy demand monitoring methods, and power management devices are described. In one aspect, an electrical power distribution control method includes providing electrical energy from an electrical power distribution system, applying the electrical energy to a load, providing a plurality of different values for a threshold at a plurality of moments in time and corresponding to an electrical characteristic of the electrical energy, and adjusting an amount of the electrical energy applied to the load responsive to an electrical characteristic of the electrical energy triggering one of the values of the threshold at the respective moment in time.

Method of determining battery power limits for an energy storage system of a hybrid electric vehicle

Abstract: A method of providing closed-loop control of power flowing into and out of an energy storage system (ESS), wherein the ESS comprises a battery is provided. The method may be implemented as a computer control algorithm for determining the charge and discharge limits for the ESS in a hybrid electric vehicle (HEV), wherein the ESS comprises a battery pack or array. The method comprises determining charge and discharge power limits during each of a plurality of control loops, comparing these limits during each of the plurality of control loops, and providing a charge power limit output and a discharge power limit output for use in a subsequent control loop which are based upon the charge power limit and the discharge power limit. The charge power limit output and discharge power limit output are set equal to the discharge power limit and charge power limit, respectively, when the discharge power limit is greater than the charge power limit; and are selected from the group consisting of the charge power limit, the discharge power limit and zero when the discharge power limit is less than or equal to the charge power limit.

Grid-connected power systems having back-up power sources and methods of providing back-up power in grid-connected power systems

Abstract: A grid-connected power system includes a primary power source, a back-up power source, a DC/AC inverter and a DC/DC converter. Direct current from the primary power source is supplied to the DC/AC inverter to obtain an alternating current output supplied to a utility grid when power from the utility grid is available to power a load. The output of the inverter is supplied to a selected portion of the load when power from the utility grid is unavailable to the load. Direct current from the back-up power source is supplied to the inverter through a DC/DC converter when power from the utility grid is unavailable to the load. The DC/DC converter converts the voltage of direct current from the back-up power source to direct current having a voltage compatible with the voltage of the primary power source and the inverter. The back-up power source may be charged by the primary power source or by the utility grid. Methods of providing back-up power include converting the voltage of direct current from a back-up power source to direct current of converted voltage and supplying the direct current of converted voltage to a DC/AC inverter.

Concurrent and simple digital controller of an AC/DC converter with power factor correction based on an FPGA

Abstract: Nowadays, most digital controls for power converters are based on DSPs. This paper presents a field programmable gate array (FPGA) based digital control for a power factor correction (PFC) flyback AC/DC converter. The main difference from DSP-based solutions is that FPGAs allow concurrent operation (simultaneous execution of all control procedures), enabling high performance and novel control methods. The control algorithm has been developed using a hardware description language (VHDL), which provides great flexibility and technology independence. The controller has been designed as simple as possible while maintaining good accuracy and dynamic response. Simulations and experimental results show the feasibility of the method, opening interesting possibilities in power converters control.

LED driving device

Abstract: A LED driving device includes a plurality of LEDs, a voltage detecting circuit, and a current switching circuit When the voltage detecting circuit detects the different voltage level of power source without coupling to a filtering capacitor, it sends a signal to the current switching circuit and then the current switching circuit is automatically activated to electrically rearrange the configuration of LEDs with a predetermined current value by lighting the greatest number of LEDs that improving the power factor and efficiency

Power converter system

Abstract: A power converter system advantageously employs a modular, bi-directionally symmetrical power converter assembly in a readily customizable configuration to interconnect a direct current power source to a three-phase alternating power grid. Connections external to the power converter assembly are selected to optimize the power converter system for a specific application, such as interconnecting a photovoltaic array to the three-phase electrical power grid. The electrical interconnections of various elements including isolation transformers, voltage sensors, and control switches are optimized to improve efficiency and reliability.

Conditioning circuit for a power supply at the maximum power point, a solar generator, and a conditioning method

Abstract: The invention relates to a conditioning circuit that measures operating points of a power supply to deduce therefrom the current-voltage characteristic thereof and to determine directly the voltage corresponding to its maximum power point, without using any kind of tracking algorithm that causes the operating point of the power unit to oscillate about the maximum power point The maximum power point voltage VMPP is supplied to a controller which regulates a power cell by slaving it to the input voltage until the output voltage of the supply is equal to the maximum power point voltage V MPP The invention also relates to a solar generator and an associated conditioning method One particular application is to high-power satellites

Active power filter control using neural network technologies

Abstract: A method for controlling an active power filter using neural networks is presented. Currently, there is an increase of voltage and current harmonics in power systems, caused by nonlinear loads. The active power filters (APFs) are used to compensate the generated harmonics and to correct the load power factor. The proposed control design is a pulse width modulation control (PWM) with two blocks that include neural networks. Adaptive networks estimate the reference compensation currents. On the other hand, a multilayer perceptron feedforward network (trained by a backpropagation algorithm) that works as a hysteresis band comparator is used. Two practical cases with Matlab-Simulink are presented to check the proposed control performance.

Three-phase unity-power-factor star-connected switch (VIENNA) rectifier with unified constant-frequency integration control

Abstract: A unified constant-frequency integration (UCI) controller for a three-phase star-connected switch three-level rectifier (VIENNA) with unity-power-factor-correction is proposed. One of advantages of this rectifier is that the switch voltage stress is one half of the total output voltage. The proposed control approach is based on one-cycle control and features great simplicity and reliability: all three phases will be power factor corrected using one or two integrators with reset along with several flips-flops, comparators and logic and linear components. It does not require multipliers to scale the current reference according to the output power level as used in many other control approaches. In addition, the input voltage sensor is eliminated. It employs constant switching frequency modulation that is desirable for industrial applications. The proposed controller can operate by sensing either the inductor currents or the switching currents. If the switching currents are sensed, the cost is further reduced because switching currents are easier to sense comparing with inductor currents. The proposed approach is supported by experimental results.

Stability margin monitoring for DC distributed power systems via perturbation approaches

Abstract: In multi-module power electronics systems, especially DC distributed power systems, the small-signal stability issues are often dealt with by employing Middlebrook's impedance criterion. However, for on-line system stability margin monitoring, directly measuring impedance of the source and load subsystems then making quantitative comparisons is too complicated and difficult. This paper proposes practical and simple methods, which involve applying current or voltage perturbation to the dc side of distributed power systems then only measuring the amplitude of two currents or voltages in order to monitor the stability margin. For both methods (current perturbation and voltage perturbation), an implementation approach that does not employ external voltage or current perturbation source is also presented. All these methods and approaches are equivalent to the impedance measuring and comparing method based on the impedance criterion with different forbidden regions. A comparative evaluation of each method and its corresponding implementation approach is provided.

Delivering clean and pure power

Abstract: There are two approaches to the mitigation of power quality problems. The first approach is called load conditioning, which ensures that the equipment is made less sensitive to power disturbances, allowing the operation even under significant voltage distortion. The other solution is to install line-conditioning systems that suppress or counteract the power system disturbances. Among the different new technical options available to improve power quality, active power filters have proved to be an important and flexible alternative to compensate for current and voltage disturbances in power distribution systems. Power filter topologies are discussed including shunt active filter, series active filters, series-shunt active filters, and hybrid active filters. New topologies using multilevel inverters are also discussed.

Nonlinear dynamics of power-factor-correction converter

Abstract: The boost power-factor-correction (PFC) converter with average-current-mode control is a nonlinear system due to the effects of the multiplier and a large variation of the duty ratio. Although its stability analysis must be studied depending on a nonlinear model, most prior research attempted to make some assumptions to force this nonlinear system to be linear. As a result, the practical dynamics and the nonlinear phenomena were disregarded. In this paper, two kinds of nonlinear phenomena are detected under the conditions that are considered to be stable by the prior criteria: one is period-doubling bifurcation and the other is chaos. Stability maps and phase-plane trajectories are introduced at different loads to clarify the power factor and also the instability regions. It is clear that the output storage capacitor is a main contributing parameter on the system stability, therefore, bifurcation maps are developed to determine the accurate minimum output capacitance value that assures the system stability under all operating conditions. Also, PFC converter stability is explained and judged by comparing the consequence of charging and discharging energy in the output capacitor.

A passivity-based multilevel active rectifier with adaptive compensation for traction applications

Abstract: The control of a single-phase multilevel H-bridge rectifier suitable for traction applications is considered. Such a converter often presents instability problems making difficult its design and uncertain its behavior. In this paper the use of a passivity-based controller is experimentally investigated. Such a controller achieves stability, unity power factor, good balancing between the two DC links, and satisfactory behavior even in the presence of load changes. A right choice of the damping parameters allows the fulfilling of system requirements in terms of DC-link voltage error and grid current distortion.

Vernier hybrid machines

Abstract: The vernier hybrid machine is a member of the family of variable-reluctance permanent-magnet machines. It develops high specific torque by means of a magnetic gearing effect but it suffers from low power factor. The construction of the machine is simple. Analytical formulae are derived for specific torque and power factor. The formulae may be used to find a suitable compromise between the desire for high specific torque and for good power factor. Static torque tests taken from a small laboratory machine are in satisfactory agreement with theory.

Design Simulation and Experimental Investigations, on a Shunt Active Power Filter for Harmonics, and Reactive Power Compensation

Abstract: This paper presents complete design, simulation, and experimental investigations on a 3-phase shunt active power filter to compensate harmonics and the reactive power requirement of nonlinear loads. The paper describes the complete design aspects of power circuit elements and control circuit parameters. The compensation process is based on sensing line currents only, an approach different from conventional methods that require the harmonics and reactive volt-ampere requirement of the load. Various simulation results are presented to study the performance during steady-state and transient conditions to validate the design. A laboratory prototype has been developed to verify the simulation results. The control scheme is realized on a dedicated micro-controller-based system. PWM pattern generation is based on carrierless hysteresis-based current control to obtain the switching signals. Based on simulation and experimental results it can be concluded that the compensation process is simple and easy to impleme...