Line Power Factor Research Articles

Novel Current-Mode AC/AC Converters With High-Frequency AC Link

A novel circuit-topology family of the current-mode AC/AC converter with high-frequency AC link, based on a Flyback converter, is proposed. These circuit topologies, which can transfer one unregulated sinusoidal voltage with high total harmonic distortion (THD) into another regulated constant-frequency sinusoidal voltage with low THD, are composed of input cycloconverter, high-frequency storage transformer, and output cycloconverter. The circuit-topology family includes single four-quadrant power switch mode, push-pull mode, half-bridge mode, and full-bridge mode circuits. The single four-quadrant power switch mode and push-pull mode converters are suitable for low input voltage fields, but the half-bridge mode and full-bridge mode converters are suitable for high input voltage fields. The operational mode, steady principle, and transient voltage feedback control strategy of the kind of converter are investigated. The output characteristic curve, its relation to internal resistance, and the design criteria for the key circuit parameters are given. The theoretical analysis and the test result of the 500 VA 220 V 15% 50 HzAC/220 V 50 HzAC prototype have shown that the converters have advantages such as high-frequency galvanic isolation, simple topology, two-stage power conversion [low frequency alternating current (LFAC)/high frequency alternating current (HFAC)/LFAC], bidirectional power flow, high efficiency, high power density, low THD of the output voltage, strong adaptability to various loads, higher line power factor, low audio noise, etc.

Model Reference Adaptive Control Design for a Shunt Active-Power-Filter System

In this paper, model reference adaptive control (MRAC) is proposed for a single-phase shunt active power filter (APF) to improve line power factor and to reduce line current harmonics. The proposed APF controller forces the supply current to be sinusoidal, with low current harmonics, and to be in phase with the line voltage. The advantages of using MRAC over conventional proportional-integral control are its flexibility, adaptability, and robustness; moreover, MRAC can self-tune the controller gains to assure system stability. Since the APF is a bilinear system, it is hard to design the controller. This paper will solve the stability problem when a linearization method is used to solve the nonlinearity of the system. Moreover, by using Lyapunov's stability theory and Barbalat's lemma, an adaptive law is designed to guarantee an asymptotic output tracking of the system. To verify the proposed APF system, a digital signal controller (dsPIC30F4012) is adopted to implement the algorithm of MRAC, and a 1-kVA laboratory prototype is built to test feasibility. Experimental results are provided to verify the performance of the proposed APF system.

A DSP-based modified slip energy recovery drive using a 12-pulse converter and shunt chopper for a speed control system of a wound rotor induction motor

This paper introduces a modified slip energy recovery drive system for speed control of a wound rotor induction motor offering improvement of drive performance, particularly line power factor and overall system efficiency. A 12-pulse line commutated thyristor converter operating in an inverter mode in conjunction with an additional IGBT shunt chopper is employed to transfer slip energy back to ac mains supply via three phase transformers. This approach offers motor speed control by varying the duty cycle of the chopper instead of changing the inverter firing angle. As a consequence, supply power factor can be improved. The servo state feedback designed by linear quadratic regulator (LQR) with observer is also included in order to keep motor speed to be constant over a certain range of operating conditions by using the estimated dc link current derived from motor speed. The advantage of this technique is absence of current transducers for current feedback control loop. The overall control system is implemented on DSP, DS1104’TMS320F240 controller board. Experimental results are illustrated in order to validate performance of the proposed system.

The uni-polarity phase-shifted controlled voltage mode AC–AC converters with high frequency AC link

A circuit configuration and circuit topological family of voltage mode ac–ac converters with high frequency ac links, which are based on forward converters, and a uni-polarity phase-shifted control strategy are proposed and deeply investigated. These kinds of converters consist of a input cycloconveter, a high frequency transformer, an output cycloconverter, input and output filters, and can transfer an unsteady ac voltage with a high harmonic into steady same-frequency ac sinusoidal voltage with a low harmonic. By using uni-polarity phase-shifted control strategy, output filtering inductance current is naturally commutated, and zero voltage switching of the output cycloconverter is realized. The converters’ averaging model, the output characteristic curve, and design criteria for the key circuit parameters are given. The theoretical analysis and test result of 1 kVA 220 V ± 10% 50 Hz ac/110 V 50 Hz ac prototype have shown that the converters have such advantages as high frequency electrical isolation, simple topology, two-stage power conversion (LFAC/HFAC/LFAC), bidirectional power flow, uni-polarity synchronized pulsewidth modulation waveform, high efficiency, high power density, high steady precision, low total harmonic distortion of the output voltage, strong adaptability to various loads, high line power factor, and low audio noise etc.

Power factor correction technique based on artificial neural networks

This paper presents a novel technique based on artificial neural networks (ANNs) to correct the line power factor with variable loads. A synchronous motor controlled by the neural compensator was used to handle the reactive power of the system. The ANN compensator was trained with the extended delta-bar-delta learning algorithm. The parameters of the ANN were then inserted into a PIC 16F877 controller to get a better and faster compensation. The results have shown that the proposed novel technique developed in this work overcomes the problems occurring in conventional compensators including over or under compensation, time delay and step changes of reactive power and provides accurate, low cost and fast compensation compared to the technique with capacitor groups.

Single-Phase Operation of a Three-Phase Induction Generator Using a Novel Line Current Injection Method

By using two capacitances and a current injection transformer, a three-phase induction generator can operate with good phase balance and line power factor while delivering power to a single-phase power grid. This paper presents a systematic analysis on this novel induction generator configuration. The solution of the system's inspection equations using the method of symmetrical components enables the steady-state generator performance at any speed to be computed. The conditions for achieving perfect phase balance are deduced from the phasor diagram. It is shown that the capacitances that result in perfect phase balance depend on the generator admittance, power factor angle, as well as the turns-ratio of the current injection transformer. Where possible, the computed results are verified by experiments conducted on a 2-kW induction machine. An experimental investigation on the system waveforms and harmonics is also carried out.

Fuzzy Logic Control of an Active Power Line Conditioner

Fuzzy logic and active power line conditioners (APLC) are two tools that are being increasingly applied to power quality problems. In this paper, a switch-mode APLC that uses fuzzy logic to control the semiconductor switches is described. Frequency-domain analysis is used to determine the desired compensation current, and a rule-based piecewise-linear fuzzy proportional-integral controller (FPIC) provides the appropriate switching pattern of the APLC to generate the actual compensation current. MATLAB simulations and experimental measurements on a low-power (700 VA), digital signal processor-based, hardware prototype show that the APLC produces excellent results despite the use of a relatively low switching frequency, which is necessary to minimize semiconductor switching losses. The simulations and measurements are in good agreement and show that the APLC/FPIC system can significantly improve line current total harmonic distortion and power factor during both steady-state and transient operating conditions.

Single-phase operation of a three-phase induction generator with the Smith connection

Single-phase operation of a three-phase induction generator with the Smith connection (SMIG) is analyzed using the method of symmetrical components. It is shown that, despite the asymmetrical nature of the winding connection, balanced currents can be made to flow in the three-phase stator winding. The conditions for achieving perfect phase balance are carefully deduced. With the aid of a phasor diagram, expressions for the line power factor and line current under perfect phase balance are also obtained. The effect of the phase-balancing capacitances on the generator performance is investigated. A simple dual-mode control scheme is also proposed with a view of minimizing the phase imbalance over the practical operating speed range. Experiments conducted on a 2.2 kW induction machine confirm the validity of the theoretical analysis and feasibility of the control method.

Single-Phase Operation of a Three-Phase Induction Generator with the Smith Connection

Single-phase operation of a three-phase induction generator with the Smith connection (SMIG) is analyzed using the method of symmetrical components. It is shown that, despite the asymmetrical nature of the winding connection, balanced currents can be made to flow in the three-phase stator winding. The conditions for achieving perfect phase balance are carefully deduced. With the aid of a phasor diagram, expressions for the line power factor and line current under perfect phase balance are also obtained. The effect of the phase-balancing capacitances on the generator performance is investigated. A simple dual-mode control scheme is also proposed with a view of minimizing the phase imbalance over the practical operating speed range. Experiments conducted on a 2.2-kW induction machine confirm the validity of the theoretical analysis and feasibility of the control method.

The Effects of Nonideal Voltage and Winding Conditions on the Performance of Induction Motors

This paper investigates the effects of over-voltage, under-voltage, unbalanced voltage, and unbalanced windings on the performance of induction machines in terms of line currents, power factors, and efficiencies. A set of three motors of 50 hp, 100 hp, and 300 hp, respectively, has been tested. Of these, the 100-hp, 4-pole motor was specially prepared by connections that enable either regular balanced-phase windings or unbalanced windings by the removal of one coil per phase. The performance (i.e., phase currents, power factor, and efficiency for balanced operation over a range of loads from 0 to 150% of rated) was established. This was compared to the performance at three different voltage conditions: 10% overvoltage, 10% undervoltage, and 2.5% voltage unbalance. This entire range of commonly encountered, nonideal voltage conditions was then repeated with the 100-hp motor with the windings deliberately unbalanced. The test results show how the different motors behave similarly in terms of line current and power factor and differently in terms of efficiency when subject to the particular voltage conditions.

Characteristics of fixed-frequency hybrid resonant converter operating on the utility line

A single-phase single-stage AC-to-DC controlled rectifier using a high-frequency transformer isolated hybrid parallel series resonant converter bridge, operating on the utility line, is described. A fixed-frequency phase-shift control scheme is used to achieve high line power factor with reduced line current harmonic distortion. Based on both approximate AC and state-space analysis, design curves are obtained. A design example for a 150 W converter is presented. The converter performance is evaluated with SPICE simulation (without active control) and by measurements on the 150 W broadband model. The line power factor is greater than 0.95 with harmonic distortion of 16.5% (at full load), even without active control. A simple active line current control technique has been used for waveshaping the line current waveform close to sinusoid, and to reduce the line current total harmonic distortion.

High power factor operation of resonant converters on the utility line

Operation and characteristics of resonant converters on the utility line are presented. Series-parallel (LCC-type) resonant converter operating with discontinuous current mode and continuous current mode (variable frequency control as well as fixed-frequency) are considered. Design examples are presented. SPICE simulation and experimental results obtained for the designed converters (rated at 150 W) are presented to verify the theory. It is shown that high line power factor (>0.95) and line current total harmonic distortion (THD) of <25% are obtained for the LCC-type converter for a wide load range (from full load to 10% rated load) without any active control, and the switch peak current decreases with the load current. With active line current control, low distortion and zero voltage switching for the entire cycle are realized.

On-line utility tie power factor control

Large industrial operations with internal electrical generation capabilities and parallel utility ties have always worked to control watt and VAr flows across their tie lines. In today's economic climate, the ability to control tie line operation can significantly impact a facility's bottom line. In a power system expansion, Union Camp Corporation's Savannah pulp and paper mill installed a tie line power factor control system that has proven to be reliable and effective. It uses load tap changers on two pairs of utility tie transformers to maintain control within the guidelines of the utility contract. It is implemented by a programmable logic controller (PLC) and other nonproprietary hardware. An analysis of this project illustrates how this scheme can be implemented on simple or complex power systems.

A fully software-controlled PWM rectifier with current link

A fully-software-controlled pulse-width-modulated (PWM) rectifier with a current link is presented. The rectifier uses six switches to connect the three-phase source of the load directly. Line power factor is controlled while maintaining DC current. The input filter of the rectifier is analyzed, showing that unity power factor is achieved by the lagging of the input current of the rectifier with respect to the source voltage. The PWM technique is developed using a space vector modulation, and its implementation is carried out with a minimal control hardware structure based on a 16 b single-chip microcomputer. It is shown experimentally that the scheme gives good performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rectifier for minimum line-current harmonics and maximum power factor

Rectifier line current harmonics interfere with proper power system operation, reduce rectifier power factor, and limit the power available from a given service. The rectifier's output filter inductance determines the rectifier line current waveform, the line current harmonics, and the power factor. Classical rectifier analysis usually assumes a near-infinite output filter inductance, which introduces significant error in the estimation of line current harmonics and power factor. A quantitative analysis of single and three-phase rectifier line current harmonics and power factor as a function of the output filter inductance is presented. For the single phase rectifier, one value of finite output filter inductance produces maximum power factor and a different value of finite output filter inductance produces minimum line current harmonics. For the three phase rectifier, a near-infinite output filter inductance produces minimum line current harmonics and maximum power factor, and the smallest inductance that approximates a near-infinite inductance is determined. >

High-efficiency single-phase motor

A three-phase induction motor was supplied from a single-phase public utility using a new and unique reconnection of the machine windings and three power capacitors to provide balanced currents and voltages in all of the windings and the corresponding three-phase high efficiency. Zero-crossing solid-state relays changed the capacitor values in response to load changes so that the single-phase efficiency was within 3% of the three-phase efficiency for all shaft loads between 20% and 120%. The single-phase power line power factor was near unity for a wide range of powers. This method is applicable to both high efficiency and standard three-phase motors without motor modifications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microprocessor Based Power Factor Improvement of Induction Motor

This paper describes the design of a microprocessor controller for a fixed-capacitor, thyristor controller reactor (FC-TCR) compensator to achieve on line and fast power factor improvement of a dynamic load. The microprocessor system monitors the power factor of the load and uses a look-up table to adjust the FC-TCR compensator to give a unity supply power factor. The results show that under all loading conditions, the power factor of almost unity is achieved automatically. The response time of the system is very fast.

Power Factor Improvement of Induction Motor Using Microprocessor Controlled FC-TCR Compensator

This paper describes the design and implementation of a scheme using a microprocessor to achieve on line and dynamic power factor improvement of a single phase induction motor subjected to variable load. The proposed scheme employs an FC-TCR type of power factor compensator along with associated control circuits. The results show that, under all loading conditions, the power factor of almost unity is achieved automatically. Furthermore, the waveform of supply curent can be kept almost sinusoidal. The response time of the proposed scheme to motor load changes is very fast.

A novel chopper for the power control of DC loads

Abstract When AC lines are used to supply DC loads, conventionally a rectifier and a DC chopper or a controlled rectifier are used. In many cases, a transformer is available for isolation purposes and also for matching the maximum DC load voltage requirements. When the conventional methods are used for the power control, line power factor deteriorates. A new chopper to improve the line power factor and which is free from commutation problems is developed and is presented in this paper. Experimental verification of the basic principles involved are carried out.

A force commutated solid state synchronous tap-changer for R-L loads

Abstract Whenever the required load voltage variation is over a limited range, it is preferable to use tap-changers to supply power to inductive loads. This improves the line power factor over the conventional phase control scheme. This paper shows that further improvement in the power factor is possible when force-commutation is used for such a purpose. This paper also suggests a suitable force commutated, trouble-free power circuit for the implementation of the suggested method.