Showing papers on "Total harmonic distortion published in 1999"

Opportunities for harmonic cancellation with carrier-based PWM for a two-level and multilevel cascaded inverters

Abstract: Pulsewidth modulation (PWM) strategies have been the subject of many years of research effort, and the merits of the various alternatives investigated have been argued extensively. In general, it is now accepted that natural or asymmetrical regular sampled PWM with a third harmonic injected or a space-vector centered reference waveform gives the best harmonic performance, with discontinuous modulation having some advantages for higher modulation ratios. This paper uses a general analytical solution for carrier-based PWM to mathematically identify the harmonic cancellation that occurs in various PWM implementations and converter topologies. This solution provides a formal justification for the superiority of natural and asymmetrical regular sampling techniques in eliminating half of their sideband harmonics simply by virtue of their phase leg switching. Then, the use of fundamental reference phase shifting between phase legs to create single- and three-phase 1-1 output voltages is reviewed, and the harmonic cancellation that occurs is identified. One significant result from this analysis is the realization that an odd/triplen carrier/fundamental ratio has no intrinsic harmonic benefit, contrary to the generally accepted wisdom. Finally, opportunities for harmonic elimination in multilevel cascaded inverter systems by carrier phase shifting are investigated, and the optimum phase shift is identified.

Distortion in elementary transistor circuits

Abstract: In this paper the distortion components are defined for elementary transistor stages such as a single-transistor amplifier and a differential pair using bipolar transistors or MOSTs Moreover, the influence of feedback is examined Numerical examples are given for sake of illustration

Large- and small-signal IMD behavior of microwave power amplifiers

Abstract: In this paper, large-signal intermodulation distortion (IMD) sweet spots in microwave power amplifiers are studied and predicted using a new mathematical basis. The variations in the IMD versus drive pattern with active bias point and the terminating matching networks are investigated. This nonlinear distortion model enabled the design of power amplifiers specially tailored to present a desired IMD versus drive-level pattern. For practical validation purposes, a MESFET case study and an illustrative application example are presented.

Adaptive repetitive control of PWM inverters for very low THD AC-voltage regulation with unknown loads

Abstract: An adaptive repetitive control scheme is proposed and applied to the control of a pulsewidth-modulated (PWM) inverter used in a high-performance AC power supply. The proposed control scheme can adaptively eliminate periodic distortions caused by unknown periodic load disturbances in an AC power supply. The proposed adaptive repetitive controller consists of a voltage regulator using state feedback control, a repetitive controller with tuning parameters and an adaptive controller with a recursive least-squares estimator (LSE). This adaptive repetitive controller designed for AC voltage regulation has been realized using a single-chip digital signal processor (DSP) TMS320C14 from Texas Instruments. Experimental verification has been carried out on a 2 kVA PWM inverter. Simulation and experimental results show that the DSP-based adaptive repetitive controller can achieve both good dynamic response and low total harmonic distortion (THD) under large-load disturbances and uncertainties.

A Norton approach to distribution network modeling for harmonic studies

Abstract: This paper presents a Norton approach for modeling distribution networks where the system configuration is not fully known. Traditionally harmonic studies use complex distribution networks modeled by harmonic current sources for specific frequencies. Although this approach has been proved to be adequate for some studies, this may not happen for other applications. When changing the operating condition of the supply-side system, the harmonic currents injected by the distribution network might change. This information is in this paper used to estimate a Norton model of the load-side distribution network. The estimated models can be used to analyze, for example, the effect of harmonic filters under different supply system configurations or operating conditions. The method of estimating the Norton models is illustrated on a test system, simulated on the well-known simulation program EMTDC. The performance of the estimated models is, for different configurations of the supply system, compared to the performance of the traditionally used "constant current" approach.

Comparison between CCM single-stage and two-stage boost PFC converters

Abstract: In this paper, the analysis of the major-component ratings of the continuous current mode (CCM) single-stage power-factor-correction (PFC) and the CCM boost two-stage PFC converters is given. The results of the analysis are summarized in a number of design plots generated for different output power levels. Finally, merits and limitations of these two approaches are discussed.

The dynamics of a PWM boost converter with resistive input

Abstract: This paper investigates the large- and small-signal response issues and, in particular, the inner loop gain and outer loop response of an indirect control method for active power-factor correction. The control scheme is based on sensing the average inductor current and generating a D/sub OFF/ (the complement of the switch duty cycle) which is proportional to the current. The method is demonstrated by considering the performance of a boost-type active power-factor corrector (APFC) that does not need to sense the input voltage. Theoretical and experimental results confirm the validity of the approach and demonstrate that the proposed method can be useful in the design of robust APFC with low total harmonic distortion. The indirect control method investigated in this paper is also compared to the classical direct APFC control method, pointing to the differences between the two.

A 12 b digital-background-calibrated algorithmic ADC with -90 dB THD

Abstract: The linearity of analog-to-digital converters (ADCs) is often limited by component mismatches. Trimming can be used to achieve high linearity but cannot track variations over time caused by component aging or by temperature and power-supply changes. Background calibration overcomes this limitation. However, previous background-calibration methods require complicated post processing, occupy some of the range of the analog signal under conversion, or are tailored for a specific type of converter. This ADC uses a queue-based architecture for creating calibration time slots without disturbing the sampling of the input signal. The digital background calibration uses an adaptive algorithm to improve linearity. The queue-based architecture for generating the calibration time slots and the digital-background-calibration method are independent and can be used separately.

Broad-band linearization of a Mach-Zehnder electrooptic modulator

Abstract: Analog optical-link dynamic range in excess of 75 dB in a 1-MHz band has been achieved using specially designed electrooptic modulators that minimize one or more orders of harmonic and intermodulation distortion. To date, however, such "linearized" modulators have only enabled improved link dynamic ranges at frequencies below 1 GHz. Additionally, linearization across more than an octave bandwidth has required precise balancing of the signal voltage levels on multiple electrodes in a custom modulator, which represents a significant implementation challenge. In this paper, a link linearization technique that uses a standard Mach-Zehnder lithium-niobate modulator with only one RF and one dc-bias electrode to achieve broad-band linearization is discussed, resulting in a dynamic range of 74 dB in 1 MHz across greater than an octave bandwidth (800-2500 MHz). Instead of balancing the voltages on two RF electrodes, the modulator in this new link architecture simultaneously modulates optical carriers at two wavelengths, and it is the ratio of these optical carrier powers that is adjusted for optimum distortion canceling. The paper concludes by describing a second analogous link architecture in which it is the ratio of optical power at two modulated polarizations that is adjusted in order to achieve broad-band linearization.

Effects of nonsinusoidal voltage on the operation performance of a three-phase induction motor

Abstract: This paper uses a real load test to investigate the effects of each order of harmonic from 2 to 13 under various voltage distortion factors (VDF) on the performance of a three-phase induction motor. The investigation includes input current, power factor, efficiency, temperature rise and their impacts on the consumers and utility companies. Since the life span of the motors is dramatically affected by the temperature rise, a new derating factor is proposed in this paper. Besides, the impacts of harmonics on electricity energy, consumers and the life span of a motor are also discussed, respectively. Finally, it is strongly suggested that even order harmonics and harmonics having an order below 5 should be considered in related regulations of harmonics control and limits.

A new approach for single-phase harmonic current detecting and its application in a hybrid active power filter

Abstract: In this paper, a new approach for single-phase harmonic current detection is presented. The approach was obtained through extending ideas of three-phase instantaneous reactive power theory and constructing a two-phase system from the existing single-phase circuit. By theoretical and simulation analysis, it is shown to be a precise approach, which can be easily realized and has the merits of better steady state and dynamic performance than conventional approaches that could be used in single-phase circuits. The approach was applied into a hybrid active power filter, which combines a series active filter and a shunt passive filter together and aims at solving the harmonics problem originated by high-power single-phase nonlinear load. Following the system configuration and basic principles of the hybrid active power filter, the overall detection and control algorithm, the PWM generating technique and the DC voltage stabilizing method are introduced in detail. The detection and control algorithm were then realized by a digital control circuit with DSP processor, and successfully employed in a prototype hybrid active power filter. Experimental results on the prototype verified the effectiveness of the new detecting approach, the performance of the control circuit and the filtering characteristics of the hybrid active power filter.

A 14 b 100 Msample/s CMOS DAC designed for spectral performance

Abstract: A 14-bit, 100-MS/s CMOS digital-to-analog converter (DAC) designed for spectral performance corresponding more closely to the 14-bit specification than current implementations is presented. This DAC utilizes a nonlinearity-reducing output stage to achieve low output harmonic distortion. The output stage implements a return-to-zero (RZ) action, which tracks the DAC once it has settled and then returns to zero. This RZ circuit is designed so that the resulting RZ waveform exhibits high dynamic linearity. It also avoids the use of a hold capacitor and output buffer as in conventional track/hold circuits. At 60 MS/s, DAC spurious-free dynamic range is 80 dB for 5.1-MHz input signals and is down only to 75 dB for 25.5-MHz input signals. The chip is implemented in a 0.8-/spl mu/m CMOS process, occupies 3.69/spl times/3.91 mm/sup 2/ of die area, and consumes 750 mW at 5-V power supply and 100-MS/s clock speed.

Improved intrinsic dynamic distortions in directly modulated semiconductor lasers by optical injection locking

Abstract: The effects of optical injection locking on the nonlinear distortions of directly modulated semiconductor distributed feedback (DFB) lasers are investigated experimentally. The second harmonic distortion (SHD) and third harmonic distortion (THD), as well as the third-order intermodulation distortion (IMD3), are measured as functions of modulation frequency for both the free-running and injection-locked lasers. Under strong injection locking with -8-dB injection ratio, the SHD and THD of the DFB laser have been suppressed by 15 dB from 2 to 4 GHz. Moreover, nearly 15-dB reduction in IMD3 has been observed from 1.4 to 3.0 GHz with the same injection conditions. We also found that the injection locking is not effective in reducing the low-frequency distortions.

A general technique for derivation of average current mode control laws for single-phase power-factor-correction circuits without input voltage sensing

Abstract: This paper presents a general technique to derive average current mode control (CMC) laws without input voltage sensing to achieve high power factor for single-phase topologies operating in continuous conduction mode (CCM). The control laws are derived based on the steady-state input-output voltage relationships and the CCM large-signal averaged pulsewidth modulation (PWM)-switch model. Using this methodology, average CMC laws with linear PWM waveforms are discovered for commonly used single-phase power stage topologies such as boost, flyback, SEPIC, and buck/boost. Conventional three-loop-controlled average CMC converters can now be controlled with a two-loop architecture. Hardware results for a boost power factor correction (PFC) and simulation results for flyback, SEPIC, and buck/boost topologies verify operation. The small-signal models of the current loop and voltage loop are derived for the boost topology and are used for control loop design. Input current harmonic distortion measurements demonstrate improved performance compared to the conventional three-loop control technique.

Modeling and simulation, and their validation of three-phase transformers with three legs under DC bias

Abstract: This paper proposes a new model for three-phase transformers with three legs with and without task under DC bias based on electric and magnetic circuit theory. For the calculation of the nonsinusoidal no-load currents, a combination of time and frequency domains is used. The analysis shows that (1) asymmetric three-phase transformers with three legs generate magnetizing currents with triplen harmonics not being of the zero-sequence type. (2) The wave shapes of the three magnetizing currents of (asymmetric) transformers are dependent on the phase sequence. (3) The magnetic history of transformer magnetization-due to residual magnetization and hysteresis of the tank-cannot be ignored if a DC bias is present and the magnetic influence of the tank is relatively strong, e.g., for oil-cooled transformers. (4) Symmetric three-phase transformers with three legs generate no-load currents without triplen harmonics. (5) The effects of DC bias currents (e.g., reactive power demand, harmonic distortion) can be suppressed employing symmetric three-phase transformers with three legs including tank. Measurements corroborate computational results; thus this nonlinear model is valid and accurate.

An analysis of three-phase low-harmonic rectifiers applying the third-harmonic current injection

Abstract: An analysis of the three-phase low-harmonic rectifiers applying passive third-harmonic current injection networks is presented in this paper Optimal amplitude of the injected current to minimize the input current total-harmonic distortion (THD) is derived as a function of the injected current phase displacement Power aspects of the third-harmonic current injection are analyzed, and it is shown that improvement in the input current THD could be obtained at the expense of the power taken by the current injection network In the case of optimal current injection, the power taken by the current injection network is shown to be equal to 8571% of the input power, resulting in the input current THD of 5125% Effects of unwanted higher order harmonics in the injected currents are studied for two previously proposed passive current injection networks The current injection networks are compared under the constraint that volt-ampere ratings of applied components are the same Analytically obtained results are experimentally verified

Harmonic sources and filtering approaches-series/parallel, active/passive, and their combined power filters

Abstract: This paper 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 are 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, 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. This paper reveals 22 basic configurations: active and passive, series and parallel, and hybrid and combined power filters. Among them are some novel filter configurations, and their advantages are discussed and demonstrated by analysis, simulation, and experiment. In addition, a comprehensive comparison of all configurations is made in terms of required ratings, costs, performance and controls.

A variable speed wind energy conversion scheme for connection to weak AC systems

Abstract: A three level control system for a variable speed wind energy conversion scheme (VSWECS) supplying a weak AC power system is presented. The objective of the control strategy is to maximize energy capture and simultaneously to support the voltage of the bus where the VSWECS is connected. Using an insulated gate bipolar transistor (IGBT) inverter, both control of active and reactive power supplied to the grid and reduction of harmonic distortion can be achieved. The response of the proposed scheme has been tested and evaluated in a test system using a developed computer program simulating in detail the system operation.

Identification of harmonic sources of power systems using state estimation

Abstract: With three test systems, the paper demonstrates the ability of system-wide harmonic state estimation (HSE) to identify remote harmonic sources and estimate load admittance of a power system, from a few synchronised, partial and asymmetric measurements. Implemented off-line or on-line, it turns multipoint measurements to system-wide measurements in a very economical way. System-wide HSE provides an efficient power quality tool for assessing the impact of hidden harmonic sources on the overall performance of power systems.

A power line conditioner based on flying capacitor multilevel voltage source converter with phase shift SPWM

Abstract: In this paper, a new power line conditioning system is proposed. This system is constructed by a flying capacitor multilevel VSC (voltage source converter) and two reactors. The phase-shift SPWM (sinusoidal pulse width modulation) switching scheme is applied to control the switching devices of this converter. Due to this multilevel VSC and the switching scheme applied to this converter, the system is applicable to distribution systems or industrial applications. The reactive power compensation, harmonic suppression and load balancing functions of the power line conditioner are analyzed. A novel and effective startup procedure is proposed to start up the system. System simulation is carried out to verify the theoretical analysis results.

Distortion analysis of MOS track-and-hold sampling mixers using time-varying Volterra series

Abstract: A time-varying theory of Volterra series is developed and applied in the sampled-data domain to solve for harmonic and intermodulation distortion of a MOS-based track-and-hold sampling mixer with a nonzero fall-time LO waveform. Distortion due to sampling error is also calculated. These results, when combined with the continuous-time solution, quantify harmonic and intermodulation distortion of a track-and-hold type mixer completely. Closed form solutions are obtained. As a practical consequence, it is shown that for certain fall-time, the distortion of track-and-hold mixers can be better than what would be predicted by a simple application of time-invariant Volterra series theory.

Deadbeat control method for single-phase UPS inverters with compensation of computation delay

Abstract: In existing deadbeat control techniques for single-phase UPS inverters, the pulse width of the inverter output voltage is limited by the computation time of the controlling processor. This limits the utilisation of the DC source voltage and slows the response of the control system. A deadbeat control technique is presented which eliminates these limitations by allowing the application of the newly computed pulse width with time delay. During this delay, the previously applied pulse width is preserved until it is updated by the new pulse width. This method requires the use of a load-dependent reference function for the inverter output voltage. However, the error in the load voltage caused by using a fixed reference function is shown to be negligible. Computer simulations are performed to verify the theoretical results and for comparison with existing methods. Experimental results are also presented to support the theoretical considerations.

Modelling of adjustable speed drives for power system harmonic analysis

Abstract: A three-phase equivalent circuit model is developed to model adjustable speed drives (ASD) for power system harmonic analysis. The validity and accuracy of the model were verified by comparing simulation results with lab test results. Sensitivity studies are then conducted to determine the key factors affecting the harmonic characteristics of ASDs. Guidelines on modelling ASDs for harmonic distortion assessment are developed based on the results.

Line current harmonics of VSI-fed adjustable speed drives

Abstract: Voltage source inverter (VSI)-fed adjustable speed drives are frequently used in energy saving applications like the speed regulation of pumps and fans. The power supply of the inverter consists of a diode rectifier feeding a large DC link capacitor. Thus, very high line current harmonics occur if no inductance is provided for current smoothing. Assuming AC choke inductance, this paper presents diagrams in order to predetermine easily the harmonic distortions of the line current. The parameters considered are AC reactance, DC capacitor and the actual drive loading. With this, a more detailed description of the injected current harmonics of VSI-fed drives is achieved in order to improve the accuracy of harmonic analysis purposes. Examples show the use of the proposed method and comparing measurements proves its validity in practical applications.

Indices for assessing harmonic distortion from power quality measurements: definitions and benchmark data

Abstract: For many years, electricity distribution companies have used sustained interruption indices as indicators of the reliability of service provided on their systems. Today, however, many electricity consumers are adversely affected by more subtle voltage disturbances such as harmonic distortion. In response to the increased sensitivity of end-use equipment, many utilities are implementing extensive monitoring systems to assess service quality levels. Such monitoring systems yield massive databases of service quality data. This paper presents indices developed to quantify system service quality with respect to measured harmonic distortion levels. Example benchmark values for the indices are calculated using data from a national distribution power quality data collection project.

A new PWM controller with one-cycle response

Abstract: This paper proposes a new nonlinear control technique that has one-cycle response, does not need a resetable integrator in the control path, and has nearly constant switching frequency. It obtains one-cycle response by forcing the error between the switched variable and the control reference to zero each cycle, while the on and off pulses of the controller are adjusted each cycle to ensure near constant switching frequency. The small switching frequency variation due to changes in the reference signal and supply voltage and delays in the circuit are quantified. Using double-edge modulation, the switching frequency variation is further reduced, thus, the associated signal distortion is minimized. An experimental 0-20 kHz bandwidth 95 W RMS power audio amplifier using the control method demonstrates the applicability of this control technique for high-fidelity audio applications. The amplifier has a power supply ripple rejection (PSRR) of 63 dB at 120 Hz. Additionally, the total harmonic distortion plus noise (THD+N) is less than 0.07% measured with a power supply ripple of 15%.

Output ripple analysis of multiphase DC-DC converters

Abstract: This paper presents an output ripple analysis of multiphase DC-DC power converters having an output LC filter. Analytical expressions for the output voltage ripple of two- and three-phase DC-DC power converters are derived. Influence of the coupling coefficient of the output filter inductor on the output ripple is investigated. Because the unique parameters of the LC filter cannot be determined solely based on the specified maximum output ripple, an additional criterion based on minimum energy storage is introduced. A comparative evaluation of single-phase, two-phase, and three-phase DC-DC power converters is presented. The validity of the proposed analysis method is verified by experimental results.

Effect of dead time on harmonic distortion in class-D audio power amplifiers

Abstract: A model is described for predicting the harmonic levels introduced by the use of dead time in class-D, PWM-driven audio power output stages. The model demonstrates that the harmonic levels are a function of load impedance, modulation depth, dead time and switching frequency. In addition, measurements show that, for audio applications, dead time is the dominant cause of power stage nonlinearity.

Bandwidth considerations for multilevel converters

Abstract: Multilevel converters can achieve an overall effective switch frequency multiplication and consequent ripple reduction through the cancellation of the lowest order switch frequency terms. This paper investigates the harmonic content and the frequency response of these multimodulator converters. It is shown that the transfer function of uniformly sampled modulators is a bessel function associated with the inherent sampling process. Naturally sampled modulators have a flat transfer function, but multiple switchings per switch cycle will occur unless the input is slew-rate limited. Lower sideband harmonics of the effective carrier frequency and, in uniform converters, harmonics of the input signal also limit the useful bandwidth. Observations about the effect of the number of converters, their type (naturally or uniformly sampled), and the ratio of modulating frequency and switch frequency are made.