Total Harmonic Content Research Articles

Active control strategy based on vector‐proportion integration controller for proton exchange membrane fuel cell grid‐connected system

Considering the influence of slow response characteristic of a high-power proton exchange membrane fuel cell (PEMFC) on a grid-connected system adequately, a 150 kW PEMFC grid-connected system, including a PEMFC power unit based on a Ballard Stack Modules-FCvelocity™ HD6 is developed in this study. Moreover, then an active control strategy with vector-proportion integration controller is proposed to regulate the cascade system actively and improve the performance of compensating low-order harmonics. The comparisons with conventional active/reactive power (PQ) control are carried out to verify the validity of the proposed method under different conditional tests. The results demonstrate that the proposed strategy can not only track the grid power demand quickly, but also prevent the unsteady phenomena which are aroused by PQ control method from the relatively slow response of high-power PEMFC power unit. Furthermore, the total harmonic distortion of grid-connected current is measured by means of the criterion of IEEE Std1547-2003 and the result of fast Fourier transform analysis testifies that the proposed strategy can decrease the total harmonic content of currents better. Therefore, this proposed method will be an optional effective technique for the design of advanced high-power PEMFC grid-connected control system.

Parametric Analysis and Design for Embedded Engine Inlets

The present paper demonstrates the aerodynamic feasibility of boundary-layer ingesting embedded-engine inlet designs with low total pressure losses and distortion harmonic content. The inlet was designed using a hierarchical multi-objective computational fluid dynamics optimization that combined global and local shaping. Global parameters including duct offset and length, wall curvature and shape, inlet aspect ratio, lip contour and thickness, and upstream airframe contour were used to identify optimal design space regions. Local inlet shaping optimization further reduced total pressure losses and harmonic distortion upstream of the fan. Coupled inlet/fan design iterations were carried out for selected inlet designs to assess the fan/engine stability and operability benefits. The resulting inlet design has the potential of achieving a 3–5% boundary-layer ingesting fuel burn benefit for NASA’s Generation-After-Next aircraft relative to a baseline high-performance pylon-mounted propulsion system. It shows significantly improved performance when compared with NASA’s “inlet A” reference geometry with a length-to-diameter ratio of 3. The new inlet was shortened to a length-to-diameter ratio of 0.6, total pressure losses were reduced by three times, dominant distortion harmonic amplitudes were reduced by 30–50%, and fan efficiency losses were reduced from 6 to 0.5–1.5%. No flow control was required.

An improved control technique of switching frequency modulated power factor correctors for low THD and high power factor

This paper deals with switching-frequency modulation (SFM) for conducted electromagnetic interference (EMI) suppression in active power factor correctors (PFCs) operating in discontinuous conduction mode (DCM). The effect of SFM on different performance characteristics of DCM PFC is studied in details. It is shown that the use of SFM in PFC with conventional control approach leads to significant increase in total harmonic distortion (THD) and harmonic content of input current. Moreover, SFM leads to noticeable increase in peak power components currents. In order to use SFM for EMI reduction more effectively without significantly worsening THD, power factor, and harmonic content of DCM PFC, an improved control technique and a control circuit are proposed and verified by simulations and experimentally. The technique is based on the use of specific time delay injection to power MOSFET control signal. As show simulations and experiments, SFM PFC with the proposed delay technique in comparison to PFC without SFM has noticeably lower conducted EMI and THD of input current, at the cost of slightly decreased efficiency and moderately increased peak currents.

Simplified space vector modulation technique for seven‐level cascaded H‐bridge inverter

A simplified space vector modulation (SVM) technique is proposed for the seven-level cascaded H-bridge (CHB) inverter. It is based on decomposing the seven-level space vector hexagon into a number of two-level space vector hexagons. The presented technique significantly reduces the calculation time and efforts involved in the SVM of a seven-level inverter; without any loss in the output voltage magnitude or increase in the total harmonic distortion content. A further simplified technique is also presented in this study, which significantly reduces the complexity and effort involved in the seven-level SVM. Simulation results for the seven-level CHB inverter using the proposed techniques are presented. The results are compared with results using sinusoidal pulse-width modulation (PWM) and third harmonic injection PWM to prove the validity of the proposed techniques. The proposed technique is perfectly general and can be applied to all types of multilevel inverters and extended to higher level inverters.

Total Harmonic Distortion and Content Rate of Spatial Modal Information for Haptic Parallel Motion Analysis

In this paper, two kinds of evaluation index for the haptic motion analysis in parallel multiple degrees—of—freedom (MDOF) system are proposed. At first, the spatial modal decomposition method based on discrete Fourier series expansion (DFS) is presented. Spatial modal information expresses a motion element that corresponds to a specific physical action. The spatial modal information can mathematically be defined by the Fourier coefficients. Then, this paper proposes the total harmonic distortion (THD) and the content rate of the haptic modal information as motion evaluation indexes. THD of the spatial modal information can evaluate the complexity of the human motion and/or the deformability of the contact environment. Content rate of the spatial modal information can evaluate the priority of motion element. Some experimental results on the bilateral motion control of a parallel five DOF haptic system are shown, in order to confirm the utility of the proposed indexes.

Single-Loop Digital Control of High-Power 400-Hz Ground Power Unit for Airplanes

In this paper, the influence of one-sample delay for sampling and computation in digital control on the bandwidth of the inner current loop of a 400-Hz ground power unit (GPU) is analyzed first. The results show that it is difficult and even impossible for high-power 400-Hz GPUs to maintain low total harmonic distortion content in the output voltage with the conventional proportional-integral-based double-loop control. To improve the performance, resonant controllers with parallel structure which are widely used in active power filters are applied to the single-loop control of the 400-Hz GPU. The parameter design criterion for the parallel resonant controllers is discussed in the discrete time domain. Meanwhile, adoption of proportional gain in the single-loop control is investigated. The results show that it can improve the performance little and may cause instability problems. Comparisons between different control methods for the 400-Hz GPU are also made, and the single-loop control method in this paper seems to be the most suitable one in terms of simplicity and performance. Experiments on a 16-b fixed-point DSP-controlled 90-kVA 400-Hz GPU prototype show satisfactory results of the single-loop method feeding linear/nonlinear and balanced/unbalanced loads.

Field simulation studies for a high temperature superconducting synchronous generator with a coreless rotor

A series of 2D and 3D modelling investigations have been undertaken to evaluate and optimise magnetic field distributions in a high temperature superconducting synchronous generator with a coreless rotor. Such design studies are essential to determine if the required air-gap flux density is achievable and at the same time maintaining the total harmonic voltage content within desirable limits. Moreover, due to the anisotropic properties of the superconducting tapes, the presence of carefully designed flux diverters is required in order to reduce the magnetic field normal to the broad face of the tape. It is therefore necessary to model and optimise the shape and position of the flux diverters to minimise the undesirable magnetic field components. Since a 2D model does not take into account the effect of the end leakage flux, a 3D model was used to confirm the effectiveness of the design changes.

ELF magnetic field exposure in a neonatal intensive care unit.

In this paper, the magnetic flux density (MFD) distribution in a neonatal intensive care unit is described and MFD values inside a few open infant warming systems and incubators are reported. Typical measured values of the magnetic flux density at power frequency (50 Hz) in the "general environment" (the rooms of the unit) were lower than 0.2 microT, while higher MFD values were detected close to medical equipment and inside the open infant warming systems. In both cases, the magnetic flux density quickly decreases with increasing distance, so that measured values are reduced to "background" (i.e., general environment) levels 20-30 cm away from the sources. The total harmonic content over the 100-800 Hz frequency range was also evaluated. In the general environment, measured values in this band were negligible, while this was not the case close to medical equipment. Field levels inside the open and closed incubators depend on the position of the electronic control system, of the heating power generator and its winding conductor, and of the 220 V main plug. The magnetic flux density was also monitored for a prolonged period of time in a few types of open infant warming systems and incubators under standard intensive care unit operation with premature newborn present.

Spectral impact of the modulation index upon internal log-domain currents

This brief investigates quantitatively the impact of the input-signal modulation index upon the spectral content of internal log-domain currents. A second-order log-domain topology is treated as an example circuit and the quantitative dependence of the harmonic contributions to the total harmonic content of current signals internal to the topology upon different levels of strength of applied input tones is illustrated. Subsequently, this frequency-domain information is correlated with the transition frequency of the active devices which carry the nonlinear currents providing a certain degree of quantitative design insight.

Triangle-to-sine wave conversion with MOS technology

A description is given of MOS circuit design techniques for nonlinear analog circuits that perform a triangle-to-sine wave conversion. These techniques may also be applied to synthesizing other functions. Design techniques for compensating the conversion for variations in temperature, processing, and triangle wave amplitude are also presented. Results from simulation and monolithic circuit fabrication are reported which show that a sinusoidal approximation with a total harmonic content of 0.2% at 1 kHz is practical. The test circuit is powered from /spl plusmn/5 V supplies and displays a bandwidth of 1.1 MHz.

A Comparison of PWM Strategies for Inverter-Fed Induction Motors

Several sophisticated or "optimum" modulation strategies have been suggested for voltage source pulsewidth modulated (PWM) inverters for ac motor control. These modulation strategies may suppress specific low-order harmonics or minimize total harmonic content and have been successfully implemented in practical drive systems. The effectiveness of these PWM techniques in minimizing harmonic losses and reducing torque pulsations is investigated analytically, and their performance is compared with that of the usual sinusoidal or subharmonic PWM approach. The influence of skin effect on rotor 12R copper loss is taken into consideration, and harmonic core losses are compared. Peak current is also an. important factor in inverter design, and the various modulation strategies are again compared on this basis. Fourier analysis techniques are used in order to allow skin effect phenomena to be taken into consideration, and performance criteria are developed to allow comparisons of waveform quality in respect of harmonic copper and iron losses.

A new technology for high-power IC

The paper describes a new fabrication technology for a monolithic high-power linear IC. It is based on a novel process for controlling the epitaxial growth of single crystal regions and very fine polycrystalline regions on an IC substrate essentially in accordance with the specified mapping of the IC pattern. Polycrystalline regions are used in areas of isolation and collector lead paths which must be diffused deeply, and contribute to the most important characteristics required for the high-power IC, i.e., higher breakdown voltage and lower saturation resistance. A power capability far beyond any known in this field has been achieved. A typical example of the output power rating for an IC designed for use in a low-frequency SEPP-type power amplifier is 20-watts rms continuous service, and the total harmonic distortion content is less than 8 percent at 1 kHz at 40-volts source voltage.

A Fundamental Suppression Type Harmonic Analyzer

The principles and design of an harmonic analyzer of novel form are described. The analyzer operates by suppressing the fundamental and passing the harmonics through an amplifier with a calibrated gain control to a cathode-ray oscillograph or vacuum tube voltmeter. The apparatus is designed for analysis of audio-frequency oscillations but could be used with frequencies of a much higher order if the curve of frequency against gain were plotted for the amplifier. The power required for operation is small, an input impedance of the analyzer being of the order of 500,000 ohms. In practice it was found that the instrument was capable of giving a fairly accurate estimate of the total harmonic content for values as low as 0.2 per cent. Using a cathode-ray oscillograph it is possible to separate two or more harmonics, but the instrument is chiefly useful for estimating total harmonic distortion of a wave. The instrument should be useful as a distortion meter for power supply systems, giving a reading of the total harmonic distortion with the aid of a vacuum tube voltmeter.

The Alternating Current Bridge as a Harmonic Analyser

A simple impedance bridge, and auxiliary apparatus, is described for the measurement of total harmonic content of an alternating electric current. Total harmonic content is defined as the ratio of the square root of the sum of the squares of the harmonic amplitudes to the amplitude of the fundamental. This quantity is determined, using this method, by a simple comparison of two resistances. The bridge may also be used conveniently for the determination of the amplitude of large individual harmonics of low order. Details are given showing the extent of its usefulness in this field and the way in which it should be manipulated.