Showing papers on "Harmonic published in 2011"
TL;DR: A new multiresonant frequency-adaptive synchronization method for grid-connected power converters that allows estimating not only the positive- and negative-sequence components of the power signal at the fundamental frequency but also other sequence components at other harmonic frequencies is presented.
Abstract: This paper presents a new multiresonant frequency-adaptive synchronization method for grid-connected power converters that allows estimating not only the positive- and negative-sequence components of the power signal at the fundamental frequency but also other sequence components at other harmonic frequencies. The proposed system is called MSOGI-FLL since it is based on both a harmonic decoupling network consisting of multiple second-order generalized integrators (MSOGIs) and a frequency-locked loop (FLL), which makes the system frequency adaptive. In this paper, the MSOGI-FLL is analyzed for single- and three-phase applications, deducing some key expressions regarding its stability and tuning. Moreover, the performance of the MSOGI-FLL is evaluated by both simulations and experiments to show its capability for detecting different harmonic components in a highly polluted grid scenario.
950 citations
TL;DR: In this paper, the most common multilevel inverter topologies and control schemes have been reviewed, and the selection of topology and control techniques may vary according to power demands of inverter.
574 citations
TL;DR: A multiple-complex coefficient-filter-based PLL is presented, and its unique feature lies in the accurate and rapid extraction of the positive and negative sequence components from the polluted grid voltage, and the harmonic components can also be estimated precisely.
Abstract: Synchronization with the utility networks is crucial for operating three-phase grid-interfaced converters. A challenge of synchronization is how to fast and precisely extract the fundamental positive and negative sequences under the distorted and unbalanced conditions. Many phase-locked loop (PLL) and synchronization techniques have been presented in the past decades. Most of them make a tradeoff between the accuracy and dynamic response under severe distorted and unbalanced conditions. In this paper, a multiple-complex coefficient-filter-based PLL is presented, and its unique feature lies in the accurate and rapid extraction of the positive and negative sequence components from the polluted grid voltage, and the harmonic components can also be estimated precisely, which has the potential use for selective compensation in active filter applications. Another advantage of the proposed method is its flexibility for simplifying its structure in some specified conditions. Results of continuous-domain simulations in MATLAB and discrete-domain experiments based on a 32-b fixed-point TMS320F2812 DSP are in good agreement, which confirm the effectiveness of the proposed method.
402 citations
TL;DR: In this article, the authors applied nearest level control (NLC) to the modular multilevel converter (MMC) and analyzed the voltage harmonics in order to select a proper sampling frequency, which significantly influenced the output voltage levels and voltage total harmonic distortions.
Abstract: This paper applies nearest level control (NLC) to the modular multilevel converter (MMC). Since there are a number of submodules (SMs) in high-voltage applications of MMC and all SM voltages are required to be measured and sorted, if the uniform sampling frequency is not high enough, the SM will not be triggered as quickly as possible. Thus, the converter-output voltage levels and voltage harmonics will be affected. A method to systematically analyze the voltage harmonics is presented, considering the uniform sampling frequency. In order to select a proper sampling frequency, two critical values, which significantly influence the output voltage levels and voltage total harmonic distortions, are calculated. Simulation results based on PSCAD/EMTDC proved the validity of the proposed modulation scheme and the importance of a properly selected sampling frequency.
386 citations
TL;DR: With conversion efficiencies similar to those of inorganic SHG crystals, these structures provide a promising approach for the design and fabrication of stable, synthetic second-order nonlinear optical materials tailored for specific wavelengths.
Abstract: Plasmonic nanostructures enable the generation of large electromagnetic fields confined to small volumes, potentially providing a route for the development of nanoengineered nonlinear optical media. A metal-capped hemispherical nanoparticle, also known as a nanocup, generates second harmonic light with increasing intensity as the angle between the incident fundamental beam and the nanocup symmetry axis is increased. Nanoparticle orientation also modifies the emission direction of the second harmonic light. With conversion efficiencies similar to those of inorganic SHG crystals, these structures provide a promising approach for the design and fabrication of stable, synthetic second-order nonlinear optical materials tailored for specific wavelengths.
290 citations
TL;DR: In this paper, a nonlinear sliding mode control (SMC) scheme is proposed to directly calculate the required converter's control voltage so as to eliminate the instantaneous errors of active and reactive powers without involving any rotating coordinate transformations.
Abstract: This paper proposes a new direct active and reactive power control (DPC) for the three-phase grid connected dc/ac converters. The proposed DPC strategy employs a nonlinear sliding mode control (SMC) scheme to directly calculate the required converter's control voltage so as to eliminate the instantaneous errors of active and reactive powers without involving any rotating coordinate transformations. Meanwhile, there are no extra current control loops involved, which simplifies the system design and enhances the transient performance. Constant converter switching frequency is achieved by using space vector modulation, which eases the design of the ac harmonic filter. Simulation and experimental results are provided and compared with those of the classic voltage-oriented vector control (VC) and conventional lookup table (LUT) DPC strategies. The proposed SMC-DPC is capable of providing enhanced transient performance similar to that of the LUT-DPC, and keeps the steady-state harmonic spectra at the same level as those of the VC scheme. The robustness of the proposed DPC to line inductance variations is also inspected during active and reactive power changes.
265 citations
TL;DR: In this paper, an impedance-based analytical method for modeling and analysis of harmonic interactions between the grid and aggregated distributed generation (DG) inverters is proposed, where impedance limits are specified and used as an extra design constraint for DG inverters in order to minimize the harmonic distortion impact on the grid.
Abstract: This paper proposes an impedance-based analytical method for modeling and analysis of harmonic interactions between the grid and aggregated distributed generation (DG) inverters. The root cause of harmonic interaction/resonance problems is the impedance-network quasi-resonance between the effective output impedance of the inverter and the equivalent grid impedance at the connection point. Starting with the output impedance modeling of an inverter, a Norton model of the inverter is derived. Comparing with the switching model and the average model of the inverter, simulation results show the effectiveness of the model. This paper proposes that impedance limits should be specified and used as an extra design constraint for DG inverters in order to minimize the harmonic distortion impact on the grid. Assuming the impedance models of individual inverters and local loads within a distribution grid are known, especially in the case of new grids under construction, harmonic interactions between the grid and a certain number of DG inverters can be preliminarily estimated.
259 citations
TL;DR: In this paper, an energy harvester consisting of a clamped-clamped piezoelectric beam bi-morph is considered and the shape of the harvesters' potential function is altered by applying a static compressive axial load at one end of the beam.
253 citations
TL;DR: The synthesis of simultaneous broadside sum and difference patterns, flat-top and narrow beam patterns, and steered multibeams is enabled as assessed by a set of selected results reported and discussed to show the potentialities of the proposed method.
Abstract: In this paper, the synthesis of simultaneous multibeams through time-modulated linear arrays is studied. Unlike classical phased arrays where the antenna aperture is usually shared to generate multiple beams, the periodic on-off sequences controlling the static excitations are properly defined by means of an optimization strategy based on the Particle Swarm algorithm to afford desired multiple patterns at harmonic frequencies to make practical application of these harmonic beams which are typically regarded as an undesirable effect in time-modulated arrays. The synthesis of simultaneous broadside sum and difference patterns, flat-top and narrow beam patterns, and steered multibeams is enabled as assessed by a set of selected results reported and discussed to show the potentialities of the proposed method. Comparisons with previously published results are reported, as well.
225 citations
TL;DR: In this article, a mathematical model of a doubly fed induction generator (DFIG) in the positive synchronous reference frame under distorted grid voltage conditions is presented, where the fundamental and the fifth and seventh-order components of rotor currents are directly regulated by the PI-R controller without sequential component decompositions.
Abstract: This paper presents a mathematical model of a doubly fed induction generator (DFIG) in the positive synchronous reference frame under distorted grid voltage conditions. The oscillations of the DFIG's electromagnetic torque and the instantaneous stator active and reactive powers are fully described when the grid voltage is harmonically distorted. Four alternative control targets are proposed to improve the system responses during grid harmonic distortions. A new rotor current control scheme implemented in the positive synchronous reference frame is developed. The control scheme consists of a proportional-integral (PI) regulator and a harmonic resonant (R) compensator tuned at six times the grid frequency. Consequently, the fundamental and the fifth- and seventh-order components of rotor currents are directly regulated by the PI-R controller without sequential-component decompositions. The feasibility of the proposed control strategy is validated by simulation studies on a 2.0-MW wind-turbine-driven DFIG system. Compared with the conventional vector control scheme based on standard PI current controllers, the proposed control scheme leads to significant elimination of either DFIG power or torque oscillations under distorted grid voltage conditions.
223 citations
TL;DR: In this paper, an approximate analysis of LLC resonant converter with capacitive filter operating above and below resonance is presented, and an equivalent ac resistance model of the rectifier valid for discontinuous as well as continuous conduction modes is proposed.
Abstract: This paper presents an approximate analysis of LLC resonant converter with capacitive filter operating above and below resonance. An equivalent ac resistance model of the rectifier valid for discontinuous as well as continuous conduction modes is proposed. The dc voltage conversion ratio is then obtained using the fundamental harmonic approximation analysis method. Based on the analysis, LLC converter design plots and guidelines are suggested. The theory is verified by simulation and experiment.
TL;DR: In this paper, an analytical theory of the nonlinear electromagnetic response of a two-dimensional (2D) electron system in the second order in the electric field amplitude is developed, and the second-order polarizability and the intensity of the second harmonic signal are calculated within the selfconsistent field approach both for semiconductor 2D electron systems and for graphene.
Abstract: An analytical theory of the nonlinear electromagnetic response of a two-dimensional (2D) electron system in the second order in the electric field amplitude is developed. The second-order polarizability and the intensity of the second harmonic signal are calculated within the self-consistent-field approach both for semiconductor 2D electron systems and for graphene. The second harmonic generation in graphene is shown to be about 2 orders of magnitude stronger than in GaAs quantum wells at typical experimental parameters. Under the conditions of 2D plasmon resonance the second harmonic radiation intensity is further increased by several orders of magnitude.
TL;DR: In this article, a number of predictive control concepts are rapidly emerging, and their characteristic hyperbolic tradeoff functions are derived, compared with each other, and benchmarked with respect to PWM and offline optimized pulse patterns (OPPs).
Abstract: Control and modulation schemes for ac electrical drives synthesize switched three-phase voltage waveforms that control the electrical machine. Particularly in medium-voltage applications, the aim is to minimize both the switching losses in the inverter and the harmonic distortions of the stator currents and the torque. For a given modulation scheme, lower switching losses usually imply higher distortion factors and vice versa. This tradeoff can be described by a hyperbolic function, as shown in this paper for pulsewidth modulation (PWM). A number of predictive control concepts are rapidly emerging. Their characteristic hyperbolic tradeoff functions are derived, compared with each other, and benchmarked with respect to PWM and offline optimized pulse patterns (OPPs). It is shown that predictive schemes with long prediction horizons shift the performance tradeoff curve toward the origin, thus lowering both the switching losses and the harmonic distortions. As a result, at steady-state operating conditions, these predictive schemes achieve a performance similar to OPPs, while providing a superior dynamic performance during transients.
TL;DR: A novel feedback mechanism for single-phase PLL phase detectors using the estimated phase angle is proposed that has the capability to eliminate the noise ripple entirely and, under extreme line distortion conditions, can reduce the ripple by at least half.
Abstract: A crucial component of grid-connected converters is the phase-locked loop (PLL) control subsystem that tracks the grid voltage's frequency and phase angle. Therefore, accurate fast-responding PLLs for control and protection purposes are required to provide these measurements. This paper proposes a novel feedback mechanism for single-phase PLL phase detectors using the estimated phase angle. Ripple noise appearing in the estimated frequency, most commonly the second harmonic under phase-lock conditions, is reduced or eliminated without the use of low-pass filters, which can cause delays to occur and limits the overall performance of the PLL response to dynamic changes in the system. The proposed method has the capability to eliminate the noise ripple entirely and, under extreme line distortion conditions, can reduce the ripple by at least half. Other modifications implemented through frequency feedback are shown to decrease the settling time of the PLL up to 50%. Mathematical analyses with the simulated and experimental results are provided to confirm the validity of the proposed methods.
TL;DR: In this article, an extended continuous class-F mode RF power amplifier (PA) is presented for the first time and experimental validation of this novel PA mode demonstrates a new design space over a wide band of frequencies.
Abstract: The extended continuous class-F mode RF power amplifier (PA) is presented for the first time. The introduction and experimental validation of this novel PA mode demonstrates a new design space over a wide band of frequencies. This paper will show that high output power and drain efficiency, equivalent to the class-F mode, can be maintained by varying the reactive components of fundamental and second harmonic impedances in accordance with the new formulation of the voltage waveform. Additionally it will be shown that, by varying both phase and magnitude of the fundamental and second harmonic impedances, a yet wider design space can be achieved, where the efficiency is maintained at a level greater than a certain target value. For the validation of this new theory, an experimental investigation was carried out on GaAs pseudomorphic HEMT devices and demonstrates that high output power and drain efficiency between 75%-83% can be achieved over a wide range of fundamental and second harmonic loads.
TL;DR: In this paper, a dual-mass vibration energy harvester with two masses connected in series with the energy transducer and spring is proposed and analyzed, and the optimal parameters for maximizing the power output in both the traditional and the new configurations are discussed in analytical form while taking the parasitic mechanical damping of the system into account.
TL;DR: In this article, a thorough analysis of the generalized delayed-signal cancellation (DSC) operator in both synchronous and stationary reference frames is first conducted, and the discretization error during digital implementation due to nonideal system sampling frequency and/or grid-frequency variation is quantified with the proposed concept of relative harmonic gain error.
Abstract: Phase-locked loop (PLL) is usually required to detect grid phase angle in grid-tied converters. Conventional PLL schemes have to compromise between steady-state accuracy and transient dynamics when grid voltage is polluted by unbalance and harmonics. To overcome this challenge, a generalized delayed-signal-cancellation (DSC) operator is proposed recently to form cascaded DSC (CDSC) operator to eliminate arbitrary harmonics. With the CDSC operator, the conditioned voltage can be used in PLL loop with very high bandwidth for fast tracking. However, for digital implementation, the CDSC operator may subject to delay-time error, which subsequently leads to residual distortions in the conditioned voltage. In this paper, a thorough analysis of the CDSC operator in both synchronous and stationary reference frames is first conducted. The discretization error during digital implementation due to nonideal system sampling frequency and/or grid-frequency variation is quantified with the proposed concept of relative harmonic gain error. An effective improvement method is then developed that is based on linear interpolation and is effective for all delay-based PLL schemes. Finally, experimental results are obtained to verify the harmonic elimination ability of CDSC in various scenarios and the effectiveness of the interpolation-based digital implementation scheme.
TL;DR: An enhanced predictive current control technique with fixed switching frequency is introduced for an asymmetrical dual three-phase ac drive and fast torque and current responses are achieved while favoring stator current harmonic suppression.
Abstract: The interest in predictive control approach and multiphase drives has been steadily growing during the last decade. Predictive control techniques have been recently introduced as a viable alternative to conventional PI controllers with carrier-based or space vector PWM techniques in the current regulation of multiphase power converters and drives. The developed schemes have demonstrated a good performance at the expense of a high computational cost, an unknown switching frequency, and the appearance of large undesirable stator current harmonic components. In this paper, an enhanced predictive current control technique with fixed switching frequency is introduced for an asymmetrical dual three-phase ac drive. Fast torque and current responses are achieved while favoring stator current harmonic suppression. The experimental results are provided to verify the benefits of the proposed control method when compared to the other existing predictive control methods.
TL;DR: To detect a stator winding fault caused by a short-circuited turn in a permanent magnet synchronous motor, a simple online fault detecting scheme is presented based on the monitoring of the second-order harmonic components in the q-axis current through harmonic analysis.
Abstract: To detect a stator winding fault caused by a short-circuited turn in a permanent magnet synchronous motor, a simple online fault detecting scheme is presented. The proposed scheme is based on the monitoring of the second-order harmonic components in the q-axis current through harmonic analysis. To verify the effectiveness of the proposed scheme, a test motor which allows an interturn short in the stator winding has been built, and the entire control system has been implemented using the DSP TMS320F28335.
TL;DR: A new dynamic harmonic estimator is presented as an extension of the fast Fourier transform (FFT), which assumes a fluctuating complex envelope at each harmonic, and is able to estimate harmonics that are time varying inside the observation window.
Abstract: A new dynamic harmonic estimator is presented as an extension of the fast Fourier transform (FFT), which assumes a fluctuating complex envelope at each harmonic. This estimator is able to estimate harmonics that are time varying inside the observation window. The extension receives the name “Taylor-Fourier transform (TFT)” since it is based on the McLaurin series expansion of each complex envelope. Better estimates of the dynamic harmonics are obtained due to the fact that the Fourier subspace is contained in the subspace generated by the Taylor-Fourier basis. The coefficients of the TFT have a physical meaning: they represent instantaneous samples of the first derivatives of the complex envelope, with all of them calculated at once through a linear transform. The Taylor-Fourier estimator can be seen as a bank of maximally flat finite-impulse-response filters, with the frequency response of ideal differentiators about each harmonic frequency. In addition to cleaner harmonic phasor estimates under dynamic conditions, among the new estimates are the instantaneous frequency and first derivatives of each harmonic. Two examples are presented to evaluate the performance of the proposed estimator.
TL;DR: One of the novelties of this paper is the fact that the diagnosis is carried out via the identification not only of the traditional lower sideband harmonic but also of the upper side band harmonic and four additional fault-related components.
Abstract: In this paper, a new induction motor diagnosis methodology is proposed. The approach is based on obtaining a 2-D time-frequency plot representing the time-frequency evolution of the main components in an electrical machine transient current. The identification of characteristic patterns in the time-frequency plane caused by many of the fault-related components enables a reliable machine diagnosis. Unlike other continuous-wavelet-transform-based methods, this work uses frequency B-spline (FBS) wavelets. It is shown that these wavelets enable an efficient filtering in the region neighboring the main frequency, as well as enable a high level of detail in the time-frequency maps. As a consequence, the evolution of the most important current components is precisely traced. These characteristics make it easy to identify the patterns related to the fault components. The technique is applied to the experimental no-load start-up current of motors in a healthy state and with broken bars; the FBS capabilities are revealed. One of the novelties of this paper is the fact that the diagnosis is carried out via the identification not only of the traditional lower sideband harmonic but also of the upper sideband harmonic and four additional fault-related components.
TL;DR: In this article, the effect of eddy-current loss reduction by the magnet segmentation in synchronous motors with concentrated windings is investigated, and the effect depends on the types of the rotors, for instance, interior and surface permanent magnet rotors.
Abstract: In this paper, we investigate the effect of eddy-current loss reduction by the magnet segmentation in synchronous motors with concentrated windings in order to understand appropriate segmentation methods. The loss-reduction effects in each harmonic eddy current in the magnets are analyzed by both the theoretical solution and the three-dimensional finite-element analysis with Fourier transformation. The basic experiments using magnet specimens are carried out in order to support the calculated results. It is clarified that the loss-reduction effect varies with the harmonic orders and that the effect depends on the types of the rotors, for instance, interior and surface permanent-magnet rotors.
TL;DR: In this paper, a new control strategy of effective fifth and seventh harmonic elimination in the stator output voltage at the point of common coupling for a stand-alone doubly fed induction generator (DFIG) feeding a three-phase diode rectifier was proposed.
Abstract: This paper proposes a new control strategy of effective fifth and seventh harmonic elimination in the stator output voltage at the point of common coupling for a stand-alone doubly fed induction generator (DFIG) feeding a three-phase diode rectifier. This load regularly causes such harmonic distortions, which harmfully affect the performance of other loads connected to the DFIG. In order to allow the DFIG to deliver a pure sinusoidal stator output voltage, these harmonics must be rejected. The proposed elimination method is investigated based on the rotor current controller employing a proportional integral and a resonant controller, which is implemented in the fundamental reference frame. In this frame, both positive seventh and negative fifth voltage harmonic can be eliminated by using only single resonant compensator tuned at six multiples of synchronous frequency in the rotor current controller. The control scheme is developed in the rotor-side converter for the control and operation of the DFIG. Simulations and experimental results with 2.2-kW DFIG feeding a nonlinear load are shown to verify prominent features of the proposed control method.
07 Jul 2011
TL;DR: In this paper, a modulation method for the modular multilevel converter is proposed based on a fixed pulse pattern, where harmonic elimination methods can be applied to the pulse pattern without measuring the capacitor voltages or using any other form of feedback control.
Abstract: This paper presents a new modulation method for the modular multilevel converter. The proposed method is based on a fixed pulse pattern where harmonic elimination methods can be applied. Modulation methods with harmonic elimination based on calculated pulse patterns have been presented for other multilevel topologies. However, similar modulation schemes have not yet been presented for the modular multilevel topology. In the proposed modulation method, the pulse pattern is chosen in such a way that the stored energy in each submodule remains stable. It is shown that this can be done at the fundamental switching frequency without measuring the capacitor voltages or using any other form of feedback control. Such a modulation scheme has not been presented before. The theoretical results are verified by both simulations and experimental results. The simulation results show successful operation at the fundamental switching frequency with a larger number of submodules. When a smaller number of submodules are used, harmonic elimination methods may be applied. This is verified experimentally on a converter with eight submodules per phase leg. The experimental results verify that stable operation can be maintained at the fundamental switching frequency while successfully eliminating the fifth harmonic in the ac-side voltage.
TL;DR: This Letter experimentally demonstrates the nonlinear-optical mirror effect in a bulk negative-index nonlinear metamaterial, along with two other novel phase-matching configurations, utilizing periodic poling to switch between the three phase- matching domains.
Abstract: Nonlinear metamaterials have been predicted to support new and exciting domains in the manipulation of light, including novel phase-matching schemes for wave mixing. Most notable is the so-called nonlinear-optical mirror, in which a nonlinear negative-index medium emits the generated frequency towards the source of the pump. In this Letter, we experimentally demonstrate the nonlinear-optical mirror effect in a bulk negative-index nonlinear metamaterial, along with two other novel phase-matching configurations, utilizing periodic poling to switch between the three phase-matching domains.
01 Nov 2011
TL;DR: In this paper, a desired second-order harmonic is intentionally induced in the circulating current in order to make the peak of the capacitor voltage coincide with the maximum requested voltage, aiming either to extend the limits of the instantaneous available voltage or avoid unnecessarily high capacitor voltages.
Abstract: The second-order harmonic in the circulating current of a modular multilevel converter (M2C) influences the capacitor voltage ripple. If no measures are taken to control it, it is not possible to operate the converter with unity modulation index. An open-loop method that precalculates the instantaneous values of the circulating current and the capacitor voltages is used, in order to control the circulating current. A desired second-order harmonic is intentionally induced in the circulating current in order to make the peak of the capacitor voltage coincide with the maximum requested voltage, aiming either to extend the limits of the instantaneous available voltage or avoid unnecessarily high capacitor voltages. A method for numerical estimation of the appropriate amplitude and phase of the induced second-order harmonic is described. The method is experimentally evaluated on a three-phase down-scaled laboratory prototype. From the experiments it was found that significantly improved operating conditions could be obtained.
TL;DR: A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD) to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity.
Abstract: A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). This numerical method is used to simulate propagation of a diagnostic ultrasound pulse through a measured representation of the human abdomen with heterogeneities in speed of sound, attenuation, density, and nonlinearity. Conventional delay-andsum beamforming is used to generate point spread functions (PSF) that display the effects of these heterogeneities. For the particular imaging configuration that is modeled, these PSFs reveal that the primary source of degradation in fundamental imaging is reverberation from near-field structures. Reverberation clutter in the harmonic PSF is 26 dB higher than the fundamental PSF. An artificial medium with uniform velocity but unchanged impedance characteristics indicates that for the fundamental PSF, the primary source of degradation is phase aberration. An ultrasound image is created in silico using the same physical and algorithmic process used in an ultrasound scanner: a series of pulses are transmitted through heterogeneous scattering tissue and the received echoes are used in a delay-and-sum beamforming algorithm to generate images. These beamformed images are compared with images obtained from convolution of the PSF with a scatterer field to demonstrate that a very large portion of the PSF must be used to accurately represent the clutter observed in conventional imaging.
TL;DR: A novel PLL scheme based on a real-time implementation of the discrete Fourier transform (DFT) is presented in this paper and can be considered to be a PLL in which phase detection is performed via a DFT-based algorithm.
Abstract: Phase-locked loop (PLL) algorithms are commonly used to track sinusoidal components in currents and voltage signals in three-phase power systems. Despite the simplicity of those algorithms, problems arise when signals have variable frequency or amplitude, or are polluted with harmonic content and measurement noise, as can be found in aircraft ac power systems where the fundamental frequency can vary in the range 360-900 Hz. To improve the quality of phase and frequency estimates in such power systems, a novel PLL scheme based on a real-time implementation of the discrete Fourier transform (DFT) is presented in this paper. The DFT algorithm calculates the amplitudes of three consecutive components in the frequency domain. These components are used to determine an error signal which is minimized by a proportional-integral loop filter in order to estimate the fundamental frequency. The integral of the estimated frequency is the estimated phase of the fundamental component, and this is fed back to the DFT algorithm. The proposed algorithm can therefore be considered to be a PLL in which phase detection is performed via a DFT-based algorithm. A comparison has been made of the performances of a standard PLL and the proposed DFT-PLL using computer simulations and through experiments.
Proceedings Article•
15 Sep 2011TL;DR: An efficiency optimized variable speed drive is presented which consists of the alternative 3-level T-type converter topology which is very efficient for low switching frequencies and a standard induction machine.
Abstract: In this paper an efficiency optimized variable speed drive is presented. It consists of the alternative 3-level T-type converter topology which is very efficient for low switching frequencies and a standard induction machine. The total system efficiency is optimized concerning the converter losses as well as fundamental and harmonic induction machine losses.
TL;DR: A vector network analyzer-based spectrometer is developed that supports the accurate measurement of both the absorbance and refractive index of solvated biomolecules over the corresponding gigahertz to terAhertz frequency regime, thus providing experimental information regarding their largest-scale, lowest frequency harmonic motions.
Abstract: Decades of molecular dynamics and normal mode calculations suggest that the largest-scale collective vibrational modes of proteins span the picosecond to nanosecond time scale. Experimental investigation of these harmonic, low-amplitude motions, however, has proven challenging. In response, we have developed a vector network analyzer-based spectrometer that supports the accurate measurement of both the absorbance and refractive index of solvated biomolecules over the corresponding gigahertz to terahertz frequency regime, thus providing experimental information regarding their largest-scale, lowest frequency harmonic motions. We have used this spectrometer to measure the complex dielectric response of lysozyme solutions over the range 65 to 700 GHz and an effective medium model to separate the dielectric response of the solvated protein from that of its buffer. In doing so, we find that each lysozyme is surrounded by a tightly bound layer of 165 ± 15 water molecules that, in terms of their picosecond dynam...