Showing papers on "Total harmonic distortion published in 2001"

Harmonic sources and filtering approaches

Abstract: This article presents 22 configurations of power filters for the harmonic compensation of nonlinear loads. Some of these configurations are novel and result from the newly discovered characteristics of nonlinear loads and circuitry duality, while the others are well known and used in practice. Nonlinear loads can be characterized into two types of harmonic sources: current-source nonlinear loads and voltage-source nonlinear loads. These two types of harmonic sources have completely distinctive and dual properties and characteristics. Based on their properties and characteristics, the current-source nonlinear loads and voltage-source nonlinear loads have their own suitable filter configurations, respectively.

Grid Power Quality with Variable-Speed Wind Turbines

Abstract: Grid connection of renewable energy sources is essential if they are to be effectively exploited, but grid connection brings problems of voltage fluctuation and harmonic distortion. In this paper, appropriate modeling and simulation techniques are discussed for studying the voltage fluctuation and harmonic distortion in a network to which variable speed wind turbines are connected. Case studies on a distribution network show that the voltage fluctuation and harmonic problems can be minimized with the proposed power electronics interface and control system while the wind energy conversion system captures the maximum power from the wind as wind speed varies. The studies have also demonstrated the ability of the advanced converter to assist the system voltage regulation.

A novel current-tracking method for active filters based on a sinusoidal internal model [for PWM invertors]

Abstract: A new current control method based on the internal model principle in control theory is proposed. It introduces a sinusoidal internal model into the control system. It does not use any coordinate transformations. The method can be used for tracking an arbitrary number of harmonics: a DC component or fundamental frequency component signal. It is applied to a single-phase pulsewidth modulation inverter and active filter. The validity is confirmed by simulation and experimental results.

Torque density improvement in a six-phase induction motor with third harmonic current injection

Abstract: The use of six-phase induction motor for industrial drives presents several advantages over the conventional three-phase drive such as improved reliability, magnetic flux harmonic reduction, torque pulsations minimization and reduction on the power ratings for the static converter. For these reasons, six-phase induction motors are beginning to be a widely acceptable alternative in high power applications. A typical construction of such drives includes an induction machine with a dual three-phase connection, where two three-phase groups are spatially shifted thirty electrical degrees, a six-leg inverter and a control circuit. By controlling the machine's phase currents, harmonic elimination and torque ripple reduction techniques could be implemented. This paper describes a technique of injecting third harmonic zero sequence current components in the phase currents, which greatly improves the machine torque density. Analytical, finite element and experimental results are presented to show the system operation and to demonstrate the improvement on the torque density.

Understanding Power System Hannonics

Abstract: Harmonics – Past to Present Power systems are designed to operate at frequencies of 50 or 60Hz. However, certain types of loads produce currents and voltages with frequencies that are integer multiples of the 50 or 60 Hz fundamental frequency. These higher frequencies are a form of electrical pollution known as power system harmonics. Power system harmonics are not a new phenomenon. Concern over harmonic distortion has ebbed and flowed during the history of electric power systems. Steinmetz published a book in 1916 that devoted considerable attention to the study of harmonics in three-phase power systems. His main concern was third harmonic currents caused by saturated iron in transformers and machines, and he was the first to propose delta connections for blocking third harmonic currents. Later, with the advent of rural electrification and telephone service, power and telephone circuits were often placed on common rights-of-way. Harmonic currents produced by transformer magnetizing currents caused inductive interference with open-wire telephone systems. The interference was so severe at times that voice communication was impossible. This problem was studied and alleviated by filtering and by placing design limits on transformer magnetizing currents. Today, the most common sources of harmonics are power electronic loads such as adjustable-speed drives (ASDs) and switch-mode power supplies. These loads use diodes, silicon-controlled rectifiers (SCRs), power transistors, and other electronic switches to chop waveforms to control power or to convert 50/60Hz AC to DC. In the case of ASDs, the DC is then converted to variable-frequency AC to control motor speed. Example uses of ASDs include chillers and pumps. Due to tremendous advantages in efficiency and controllability, power electronic loads are proliferating and can be found at all power levels – from low voltage appliances to high voltage converters. Hence, power systems harmonics are once again an important problem.

Synchronous-frame harmonic control for high-performance AC power supplies

Abstract: In order to achieve the reduction of voltage distortion in AC power supplies (ACPSs), this paper describes an implementation of synchronous-frame control for selected frequencies in the output voltage. The regulation of the fundamental output voltage, as well as that of some low-order harmonics, is achieved using a synchronous-frame controller for each selected frequency in addition to a conventional control. The conventional part conserves good dynamic performance under load changes, while rotating-frame controllers allow a slow, but very precise compensation of the residual errors within the assumption that the harmonics produced by distorting load are slowly varying. Moreover, motivated by a fixed-point implementation, a set of refinements and modifications of the original scheme is proposed, allowing a reduction of signal processing requirements and a new control algorithm structure less sensitive to quantization and rounding errors. This solution is particularly effective for high-power fully digitally controlled ACPSs, where the voltage loop bandwidth is usually not large enough to provide regulation at harmonic frequencies. The proposed control scheme has been implemented using a fixed-point single-chip digital signal processor (ADMC401 by Analog Devices). Experimental results on a 3-kVA three-phase converter prototype show the effectiveness of the proposed approach.

Power Systems Harmonics: Fundamentals, Analysis and Filter Design

Abstract: Contents: Introduction - Fundamentals of Harmonics - Causes of Harmonics in Power Systems - Effects of Harmonic Distortion on Power Systems - Mitigation of Power System Harmonics - Limits of Harmonic Distortion - Modelling of System Components for Harmonic Studies -Transformer Modelling - Modelling of Transmission Lines / Cables - A Simple Approach to Power System Harmonic Studies - Bibliography - Appendix A: A Review of Transformation and Symmetrical Components - Appendix B: Phase and Sequence Admittance Matrices for Three-Phase Transformers - Appendix C: Transmission Matrices for Three-Phase Transformers - Index.

Digital repetitive learning controller for three-phase CVCF PWM inverter

Abstract: In this paper, a plug-in digital repetitive leaning control scheme is proposed for three-phase constant-voltage constant-frequency (CVCF) pulsewidth modulation inverters to achieve high-quality sinusoidal output voltages. In the proposed control scheme, the repetitive controller (RC) is plugged into the stable one-sampling-ahead-preview-controlled three-phase CVCF inverter system using only two voltage sensors. The RC is designed to eliminate periodic disturbance and/or track periodic reference signal with zero tracking error, The design theory of plug-in repetitive learning controller is described systematically and the stability analysis or overall system is discussed. The merits of the controlled systems include features of minimized total harmonic distortion, robustness to parameter uncertainties, fast response, and fewer sensors. Simulation and experimental results are provided to illustrate the effectiveness of the proposed scheme.

A 10-bit 200-MS/s CMOS parallel pipeline A/D converter

Abstract: This paper describes a 10-bit 200-MS/s CMOS parallel pipeline analog-to-digital (A/D) converter that can sample input frequencies above 200 MHz. The converter utilizes a front-end sample-and-hold (S/H) circuit and four parallel interleaved pipeline component A/D converters followed by a digital offset compensation. By optimizing for power in the architectural level, incorporating extensively parallelism and double-sampling both in the S/H circuit and the component ADCs, a power dissipation of only 280 mW from a 3.0-V supply is achieved. Implemented in a 0.5-/spl mu/m CMOS process, the circuit occupies an area of 7.4 mm/sup 2/. The converter achieves a differential nonlinearity and integral nonlinearity of /spl plusmn/0.8 LSB and /spl plusmn/0.9 LSB, respectively, while the peak spurious-free-dynamic-range is 55 dB and the total harmonic distortion better than 46 dB at a sampling rate of 200 MS/s.

Considerations of a shunt active filter based on voltage detection for installation on a long distribution feeder

Abstract: This paper deals with a curious phenomenon referred to as the "whack-a-mole" that may occur in a long-distance distribution feeder having many capacitors for power-factor correction. The idea of whack-a-mole is that installation of an active or passive filter on the feeder makes voltage harmonics increase on some buses, whereas it makes voltage harmonics decrease on other buses, especially at the point of installation. The distributed-parameter representation is applied to a simplified feeder, thus making it possible to perform analysis of the whack-a-mole. As a result, this analysis yields such a basic way as to avoid the whack-a-mole. Moreover, both theory and experiment clarify that installation of the active filter acting as a harmonic terminator on the end bus of the feeder can damp out harmonic propagation throughout the feeder without causing any whack-a-mole.

A three-phase line-interactive UPS system implementation with series-parallel active power-line conditioning capabilities

Abstract: This paper presents a three-phase line-interactive uninterruptible power supply (UPS) system with series-parallel active power-line conditioning capabilities, using a synchronous reference frame (SRF) based controller, which allows an effective power factor correction, load harmonic current suppression and output voltage regulation. The three-phase UPS system is composed of two active power filter topologies. The first one is a series active power filter, which works as a sinusoidal current source in phase with the input voltage. The other is a parallel active power filter, which works as a sinusoidal voltage source in phase with the input voltage, providing to the load a regulated and sinusoidal voltage with low total harmonic distortion (THD). Operation of a three-phase phase-locked loop (PLL) structure, used in the proposed line-interactive UPS implementation, is presented and experimentally verified under distorted utility conditions. The control algorithm using SRF method and the active power flow through the UPS system are described and analytically studied. Design procedures, digital simulations and experimental results for a prototype are presented to verify the good performance of the proposed three-phase line-interactive UPS system.

A low-power reconfigurable analog-to-digital converter

Abstract: A low-power CMOS reconfigurable analog-to-digital converter that can digitize signals over a wide range of bandwidth and resolution with adaptive power consumption is described. The converter achieves the wide operating range by (1) reconfiguring its architecture between pipeline and delta-sigma modes; (2) varying its circuit parameters, such as size of capacitors, length of pipeline, and oversampling ratio, among others; and (3) varying the bias currents of the opamps in proportion to the converter sampling frequency, accomplished through the use of a phase-locked loop (PLL). This converter also incorporates several power-reducing features such as thermal noise limited design, global converter chopping in the pipeline mode, opamp scaling, opamp sharing between consecutive stages in the pipeline mode, an opamp chopping technique in the delta-sigma mode, and other design techniques. The opamp chopping technique achieves faster closed-loop settling time and lower thermal noise than conventional design. At a converter power supply of 3.3 V, the converter achieves a bandwidth range of 0-10 MHz over a resolution range of 6-16 bits, and parameter reconfiguration time of twelve clock cycles. Its PLL lock range is measured at 20 kHz to 40 MHz. In the delta-sigma mode, it achieves a maximum signal-to-noise ratio of 94 dB and second and third harmonic distortions of 102 and 95 dB, respectively, at 10 MHz clock frequency, 9.4 kHz bandwidth, and 17.6 mW power. In the pipeline mode, it achieves a maximum DNL and INL of /spl plusmn/0.55 LSBs and /spl plusmn/0.82 LSBs, respectively, at 11 bits, at a clock frequency of 2.6 MHz and 1 MHz tone with 24.6 mW of power.

Linearity error compensator

Abstract: In one aspect, the present invention is directed to a compensator for compensating linearity errors, such as harmonic distortion and intermodulation distortion, in devices. The compensator includes a means for phase-shifting and a means for exponentiation to generate a compensation signal such that the linearity error distortion signals are canceled in the system output while maintaining the desired fundamental signal. Another aspect of the invention is directed to methods for calibrating the linearity error compensator. Another aspect of the invention is directed to a modeling linearity errors in a device.

A new space-vector-based control method for UPS systems powering nonlinear and unbalanced loads

Abstract: In this paper, a new real-time space-vector-based control strategy is presented for three-phase uninterruptible power supply systems powering nonlinear and unbalanced loads The proposed control strategy generates the inverter reference and gating signals in closed loop and guarantees high-quality output voltages at the load terminals The approach, which is implemented on a digital signal processor, adapts to a wide variation of nonlinear and unbalanced load conditions without specific knowledge of the output filter (L-C) component values Analysis and experimental results on a 10-kVA prototype are presented The results show that the output voltage is restored at heavy nonlinear and unbalanced load

A vector control technique for medium voltage multilevel inverters

Abstract: This paper presents a switching strategy for multilevel cascade inverters, based on the space vector theory. The proposed switching strategy generates a voltage vector with very low harmonic distortion and reduced switching frequency. This new control method is an attractive alternative to the classic multilevel PWM techniques considering the following aspects: (i) voltage and current THD, (ii) range of linear operation, and iii) number of commutations.

Power Systems Harmonics : Computer Modelling and Analysis

Abstract: Deregulation has presented the electricity industry with many new challenges in power system planning and operation. Power engineers must understand the negative effect of harmonics on an electrical power network resulting from the extensive use of power electronics-based equipment. Serving as a complete reference to harmonics modelling, simulation and analysis, this book lays the foundations for optimising quality of power supply in the planning, design and operation phases. Features include: MATLAB function codes to aid the development of harmonic software and provide a hands-on approach to the theory presented; Insight into the use of alternative, increased efficiency, harmonic domain techniques; Examination of the harmonic modelling and analysis of FACTS, along with conventional and custom power plant equipment; Clear presentation of the basic analytical approaches to harmonic theory and techniques for the resolution of harmonic distortion. Advanced undergraduate and postgraduate students in electrical engineering will benefit from the unique combination of practical examples and theoretical grounding. Practising power engineers, managers and consultants will appreciate the detailed coverage of engineering practice and power networks world-wide.

The effect of voltage distortion on ageing acceleration of insulation systems under partial discharge activity

Abstract: This paper focuses on the features of harmonic distortion which may affect significantly the reliability of typical ac-power network equipment, such as low-voltage self-healing capacitors used for reactive power and harmonic compensation. Moreover, the effect of high-frequency pulse-like voltage generated by Adjustable Speed Drives (ASD) on electrical machine insulation is also investigated, resorting to life tests carried out on different insulating materials of the standard and "corona resistant" type, at electrical field levels able to incept partial discharges (PD).

An eighth-order CMOS low-pass filter with 30-120 MHz tuning range and programmable boost

Abstract: A CMOS low-pass filter with programmable boost is presented. The architecture is a G/sub m//C type with the G/sub m/ value controlled through a resistor servo approach. The transfer function has been optimized in order to reduce the sensitivity to component parameter variations. The 1:4 tuning range is achieved by exploiting a dual-loop control over a degenerated differential pair. At the nominal output voltage swing of 200 mV/sub pp/ differential, a THD better than 40 dB is guaranteed. The high-frequency boost is programmable between 6 and 14 dB. This filter, realized as a cascade of biquad and first-order cells, is implemented in a 0.25-/spl mu/m 2.5-V CMOS technology. It dissipates 120 mW with f/sub c/=120 MHz and has a die area of 0.23 mm/sup 2/.

The analysis of conduction and switching losses in multi-level inverter system

Abstract: The multi-level inverter system is very promising in AC drives, when both reduced harmonic content and high power are required. But, as the output voltage level increase, the number of using the semiconductor device is increased. In case of multi-level inverter system, the loss of semiconductor devices cannot be analyzed by conventional methods. The reason is that the loss of each the semiconductor device is different from one another unlike 2-level and the diode clamped inverter system needs extra clamping diode. In this paper, a simple and accurate method of computing conduction and switching loss is proposed for multi-level inverter system. The validity of the proposed method is proven for 3-level and 4-level diode clamped inverter system.

An optimal and flexible control strategy for active filtering and power factor correction under non-sinusoidal line voltages

Abstract: This paper gives a new insight into the concept of load compensation under distorted voltages. Achieving both unity power factor (UPF) and perfect compensation of current harmonics are not possible where competition will arise between these two important factors. Through evaluating the present control strategies, a generalized, optimal, and flexible control strategy (OFC) for harmonic compensation of utility lines is proposed. The proposed control strategy, which provides a unified and highly flexible compensation framework has the ability of programming for perfect current harmonics compensation, or (UPF) accomplishment, or other newly defined objectives such as maximizing the power-factor subject to some adjustable constraints on the level of current harmonics and unbalancing via an on-line optimization algorithm. The strategy can fulfill the IEEE-519 standards requirements, while guaranteeing the best achievable power factor and optimum required rating for the compensator. Theoretical concepts and practical features of the proposed control strategy have been shown through extensive simulation studies using MATLAB/SIMULINK programs.

Low distortion line dimmer and dimming ballast

Abstract: A line dimmer has a limited maximum firing angle to limit a total harmonic distortion within a powering signal. A dimming ballast generates a pulse width modulated signal based on a firing angle of the powering signal, generates a dimming command signal based on the pulse width modulated signal, and dims a lamp based on the dimming command signal. The maximum firing angle may be limited to 30 degrees, 25 degrees, or 20 degrees, for example, to limit a resulting total harmonic distortion.

Three-phase PWM boost-buck rectifiers with power-regenerating capability

Abstract: Three-phase pulsewidth-modulated (PWM) boost-buck rectifiers with power-regenerating capability are investigated. The converters under consideration are capable of: (1) both voltage step-up and step-down; (2) bidirectional power processing; and (3) almost unity-power-factor operation with nearly sinusoidal AC current. Expected advantages are: (1) applicability to lower voltage applications, e.g., direct retrofit to replace diode or thyristor rectifiers; (2) switching loss reduction in the inverter load; (3) low-order harmonic control in the inverter load output voltage; (4) blanking time effect mitigation in the inverter load; and (5) a modest level of voltage sag/swell compensation. In this paper, firstly, a step-by-step power stage derivation process is described. Then, taking the Cuk-Cuk realization as an example, its operating principle and modulation scheme are described. A steady-state model and dynamic model for controller design are also described. Representative results of circuit simulations and hardware experiments are presented. Through these procedures, the feasibility of the presented three-phase PWM boost-buck rectifier with power-regenerating capability is demonstrated.

Integration of optimized low-pass filters in a bandpass filter for out-of-band improvement

Abstract: In this paper, we discuss the control and suppression of spurious resonances commonly encountered with distributed bandpass filters. The basic idea consists of introducing low-pass structures within bandpass topologies. By adjusting low-pass filter cutoff frequencies, harmonic resonances are attenuated, while maintaining in-band performances. In addition, transmission losses may be reduced as the insertion technique leads to optimum designs in terms of overall size. The approach described here is based upon the combination of classical synthesis techniques and optimization procedures provided by conventional computer-aided-design tools. Experimental results are obtained in the case of /spl lambda//sub g//4 shunt-stub filters implemented in classical semilumped low-pass architectures. Then, we investigate alternative integration technologies and techniques to improve the out-of-band rejection over very wide operating bandwidth. To overcome some design limitations, i.e., workable characteristic impedance value, we propose and validate a multilayer solution. Finally, new low-pass topologies are suggested to improve low-pass filter band rejection.

Method of using cascaded sweeps for source coding and harmonic cancellation

Abstract: A method of seismic surveying using one or more vibrational seismic energy sources activated by sweep signals The highest order harmonic that has sufficient strength to cause significant harmonic distortion of a sweep segment is determined A number of sweep segments in excess of the number of sources is selected Initial phase angles are selected for each sweep segment of each seismic energy source so that substantially all harmonics up to and including the highest order harmonic are suppressed Using cascaded sweeps, seismic data are acquired and processed to substantially attenuate harmonics upto the selected order

The first low voltage, low noise differential silicon microphone, technology development and measurement results

Abstract: The first differential silicon microphone is presented. This capacitive working device consists of two backplates with a membrane in between. Due to the balanced arrangement the air gap can be minimized. Thus, a higher electrical field and sensitivity can be achieved for low voltages. A dedicated process sequence has been developed in order to get the optimum mechanical and electrical properties for all structural layers. Furthermore, a sandwich structure has been developed to achieve a reproducible, very sensitive microphone membrane with a thickness of only 0.5 /spl mu/m and a stress of 45 MPa. The total sensitivity for a bias of 1.5 V was measured to be 13 mV/Pa and the A-weighted equivalent input noise was measured to be 22.5 dB SPLA. The upper limit of the dynamic range has been determined to be 118 dB SPL and the total harmonic distortion at 80 dB SPL is below 0.26%.

Distortion compensation apparatus

Abstract: A distortion compensation apparatus for compensating for the distortion occurring in an amplifier with high precision is provided. Distortion generating devices generate a distortion of amplitude or phase on a signal to be provided for an amplifier. A signal level detecting device detects a level of the signal provided for the amplifier, and a distortion amount control system controls the amount of distortion generated by the distortion generating devices on the basis of the level detected by the signal level detecting device, and at this time, a control timing adjusting system adjusts the timing for controlling the distortion amount by a distortion amount control system (D/A converters) so that the distortion occurring in the amplifier maybe compensated sufficiently.

A new generalized direct matrix converter

Abstract: In this paper, the authors attempt to introduce a new modulation algorithm for matrix power converters, with an alternative PWM strategy, regardless of type of input and output (AC or DC), and also the number of input and output phases, by using suitable toggling matrix switches, such that favorable output patterns are achieved (with variable amplitudes and frequency). The switch functions in such a converter ensure that the switches do not short-circuit the voltage sources, and do not open-circuit the current sources, thus yielding continuous currents at output terminals. Also if the number of input-phases are equal or less than the number of output-phases, then continuous current is available at input terminals. The advantage of this approach is that it can be developed for any kind of matrix converter. It is illustrated that, even under unbalanced and highly distorted input voltage waveforms, the output waveforms are reasonably clean and balanced. Here, the topology of a DC to single-phase AC power converter and single-phase to three-phase AC/AC power converter are presented.

Trends in Power Quality Monitoring

Abstract: This letter introduces two Pade/spl acute/ approximation schemes that, when combined, enable the ABCD parameters of multiconductor transmission lines to be accurately and efficiently evaluated directly in the phase domain for application to harmonic analysis studies. Since the solution is obtained directly in the phase domain, modal decompositions are completely avoided.

Time-Varying Harmonics: Part II-Harmonic Summation and Propagation

Abstract: This paper represents the second part of a two-part article reviewing the state-of-the-art of probabilistic aspects of harmonics in electric power systems. It includes tools for calculating probabilities of rectangular and phasor components of individual as well as multiple harmonic sources. A procedure for determining the statistical distribution of voltages resulting from dispersed and random current sources is reviewed. Some applications of statistical representation of harmonics are also discussed.

Antidistortion method for wavelet transform filter banks and nonstationary power system waveform harmonic analysis

Abstract: A method is presented for eliminating the effect of imperfect frequency response of the filters in wavelet transform (WT) filter banks, and a WT-based algorithm for harmonic analysis of nonstationary power system waveforms. The method recovers the signal magnitude, which is distorted due to the imperfect response of filters. The WT-based algorithm is then developed. The algorithm is incorporated with the above antidistortion method to give accurate harmonic magnitudes. The power and practicality of the algorithm are illustrated through its application for the diagnosis of a motor-starting problem, which occurred in the Western Australia power system.