Showing papers on "Harmonics published in 2013"
TL;DR: The improved repetitive control scheme with a special designed finite impulse response (FIR) filter with a traditional delay function can effectively reduce the tracking error and compensate harmonics of the inverter systems.
Abstract: The power quality of grid-connected inverters has drawn a lot of attention with the increased application of distributed power generation systems. The repetitive control technique is widely adopted in these systems, due to its excellent tracking performance and low output total harmonic distortion (THD). However, in an actual system, the ratio of the sampling frequency to the grid frequency cannot always maintain an integer, and then, the resonant frequencies of the repetitive control technique will deviate from the real grid fundamental and harmonic frequencies. This will degrade the performance of the system, particularly when the grid frequency varies. Even if the ratio is a fixed integer, the auxiliary function for stabilization in the conventional repetitive control technique will also increase the steady-state tracking error and THD of the system. In this paper, an improved repetitive control scheme with a special designed finite impulse response (FIR) filter is proposed. The FIR filter cascaded with a traditional delay function can approximate the ideal repetitive control function of any ratio. The proposed scheme varies the FIR filter according to varied grid frequency and maintains its resonant frequencies matching the grid fundamental and harmonic ones. Finally, the simulation and experimental results show that the improved repetitive control scheme can effectively reduce the tracking error and compensate harmonics of the inverter systems.
232 citations
TL;DR: A selective harmonic detection system based on the three-phase cascaded delayed signal cancellation phase-locked loop that can be flexibly configured to detect any individual harmonic from the source with various background harmonics and offers excellent adaptability under small and considerable frequency variations.
Abstract: Fast and accurate selective harmonic detection has crucial value for many power system harmonic compensation systems. The existing detection methods are known to have a few drawbacks, such as long delay time, sensitivity to grid frequency variation, and difficulty to achieve zero steady-state error. In order to overcome these drawbacks, this paper proposes a selective harmonic detection system based on the three-phase cascaded delayed signal cancellation phase-locked loop. The system can be flexibly configured to detect any individual harmonic from the source with various background harmonics. It also features very short transient and excellent adaptability under small and considerable frequency variations, as verified by comprehensive experimental results. Finally, this paper provides guidance on how to tailor the detection system for different applications and a solution to address the practical implementation issues.
219 citations
TL;DR: In this article, the operation of the MMC using the multilevel selective harmonic elimination pulsewidth modulation (MSHE-PWM) technique is presented, which offers tight control of the low-order harmonics and the lowest switching frequency for the power semiconductors among all modulation techniques.
Abstract: The modular multilevel converter (MMC) is the state-of-the-art for multilevel converter topologies. This study presents the operation of the MMC using the multilevel selective harmonic elimination pulse-width modulation (MSHE-PWM) technique. MSHE-PWM offers tight control of the low-order harmonics and the lowest switching frequency for the power semiconductors among all modulation techniques. A comprehensive analysis of the modulation methods for the MMC leads to two different modulation patterns for MSHE-PWM. A method for selecting the number of sub-modules in the phase-legs of the converter is also proposed in this study. Simulation results for both patterns are provided and verified through matching experimental results from a single phase 11-level laboratory prototype.
183 citations
TL;DR: In this paper, a design procedure for the mains side LCL filter of an active three-phase rectifier is introduced, based on a generic optimization approach, which guarantees a low volume and/or low losses.
Abstract: Inductive components such as line filter inductors or transformers occupy a significant amount of space in today's power electronic systems, and furthermore, considerable losses occur in these components. A main application of inductive components is EMI filters, as, e.g., employed for the attenuation of switching frequency harmonics of power factor correction (PFC) rectifier systems. In this paper, a design procedure for the mains side LCL filter of an active three-phase rectifier is introduced. The procedure is based on a generic optimization approach, which guarantees a low volume and/or low losses. Different designs are calculated to show the tradeoff between filter volume and filter losses. The design procedure is verified by experimental measurements. Furthermore, an overall system optimization, i.e., an optimization of the complete three-phase PFC rectifier, is given.
182 citations
TL;DR: A three-phase cascaded multilevel inverter that uses five-level transistor-clamped H-bridge power cells that provides higher output quality with relatively lower power loss as compared to the other conventional inverters with the same output quality.
Abstract: This paper presents a three-phase cascaded multilevel inverter that uses five-level transistor-clamped H-bridge power cells. Multicarrier phase-shifted pulse-width modulation method is used to achieve balanced power distribution among the power cells. A new method to balance the midpoint capacitor voltage in each cell is developed and tested. The analysis of the output voltage harmonics and the total power losses covering the conduction and the switching power losses are carried out and compared with the cascaded neutral-point-clamped and the conventional cascaded H-bridge inverters. For verifications, the proposed inverter is experimentally tested on an induction motor. From the results, the proposed inverter provides higher output quality with relatively lower power loss as compared to the other conventional inverters with the same output quality.
179 citations
TL;DR: This paper first analyzes the limitations of the standard resonant current control operating under abnormal grid conditions and then introduces a control scheme that improves the current harmonic distortion in such adverse conditions without increasing the computational load of thestandard current control.
Abstract: The resonant current control has been extensively employed to reduce the current harmonic distortion in a wide range of grid-connected distributed generation applications, including photovoltaic (PV) inverters, wind and water turbines, and fuel-cell inverters. However, the performance of these systems is deteriorated when the utility grid voltage experiences abnormal conditions such as voltage harmonics and imbalances. Several advanced control solutions have been recently introduced to cope with this problem but at the cost of a significant increase in the control computational load. This paper first analyzes the limitations of the standard resonant current control operating under abnormal grid conditions and then introduces a control scheme that improves the current harmonic distortion in such adverse conditions without increasing the computational load of the standard current control. This theoretical contribution is validated by means of selected experimental results from a three-phase PV inverter.
179 citations
TL;DR: In this paper, a sliding-mode control (SMC) scheme via multiresonant sliding surface for single-phase grid-connected voltage source inverter with an LCL filter is presented to eliminate the grid current tracking error as well as suppress its total harmonic distortion (THD).
Abstract: This paper presents a sliding-mode control (SMC) scheme via multiresonant sliding surface for single-phase grid-connected voltage source inverter with an LCL filter to eliminate the grid current tracking error as well as suppress its total harmonic distortion (THD). In general, the design of SMC leads to a sliding surface that is a linear combination of the system state variables and the generated references. The sliding surface would drift while the system parameters change or external disturbance exists, which affects the tracking error and THD of system output seriously. Moreover, for ac tracking system, integral SMC can reduce, but not fully alleviate the sinusoidal tracking error and has limited ability to suppress the grid current harmonics, especially for high-order harmonics. In order to fully eliminate the grid current tracking error and suppress its THD effectively, multiple resonant terms of the grid current error are added to the sliding function. It is used for the first time in the SMC. This method can be used for an arbitrary ac tracking system. Simulation and experimental results on a 5-kVA single-phase grid-connected inverter prototype show the effectiveness of the proposed control strategy. The tracking precision of the grid current is about 0.91% and the THD of the grid current is 0.76%.
178 citations
TL;DR: In this paper, a novel strategy has been developed for analysis of wavelength-scanned, wavelength modulation spectroscopy (WMS) with tunable diode lasers (TDLs).
Abstract: A novel strategy has been developed for analysis of wavelength-scanned, wavelength modulation spectroscopy (WMS) with tunable diode lasers (TDLs). The method simulates WMS signals to compare with measurements to determine gas properties (e.g., temperature, pressure and concentration of the absorbing species). Injection-current-tuned TDLs have simultaneous wavelength and intensity variation, which severely complicates the Fourier expansion of the simulated WMS signal into harmonics of the modulation frequency (fm). The new method differs from previous WMS analysis strategies in two significant ways: (1) the measured laser intensity is used to simulate the transmitted laser intensity and (2) digital lock-in and low-pass filter software is used to expand both simulated and measured transmitted laser intensities into harmonics of the modulation frequency, WMS-nfm (n = 1, 2, 3,...), avoiding the need for an analytic model of intensity modulation or Fourier expansion of the simulated WMS harmonics. This analysis scheme is valid at any optical depth, modulation index, and at all values of scanned-laser wavelength. The method is demonstrated and validated with WMS of H2O dilute in air (1 atm, 296 K, near 1392 nm). WMS-nfm harmonics for n = 1 to 6 are extracted and the simulation and measurements are found in good agreement for the entire WMS lineshape. The use of 1f-normalization strategies to realize calibration-free wavelength-scanned WMS is also discussed.
177 citations
TL;DR: With the proposed full-feedforward schemes, the injected grid current harmonics and unbalance caused by grid voltages can be greatly reduced.
Abstract: This paper investigates the feedforward schemes of grid voltages for a three-phase LCL-type grid-connected inverter. The full-feedforward functions of grid voltages are derived for the stationary α- β frame, synchronous d - q frame, and decoupled synchronous d - q frame-controlled three-phase LCL-type grid-connected inverters. The derived full-feedforward functions mainly consist of three parts which are proportional, derivative, and second derivative parts. The use of the traditional proportional feedforward function in the three-phase LCL -type grid-connected inverter will result in the amplification of the high-frequency injected grid current harmonics. With the proposed full-feedforward schemes, the injected grid current harmonics and unbalance caused by grid voltages can be greatly reduced. The effectiveness of the proposed feedforward schemes is verified by the experimental results.
177 citations
TL;DR: In this article, a single-phase, single-stage current source inverter-based photovoltaic system for grid connection is proposed, where the maximum power point is maintained with a fuzzy logic controller, and a proportional-resonant controller is used to control the current injected into the grid.
Abstract: In this paper, a single-phase, single-stage current source inverter-based photovoltaic system for grid connection is proposed. The system utilizes transformer-less single-stage conversion for tracking the maximum power point and interfacing the photovoltaic arrays to the grid. The maximum power point is maintained with a fuzzy logic controller. A proportional-resonant controller is used to control the current injected into the grid. To improve the power quality and system efficiency, a double-tuned parallel resonant circuit is proposed to attenuate the second- and fourth- order harmonics at the inverter dc side. A modified carrier-based modulation technique for the current source inverter is proposed to magnetize the dc-link inductor by shorting one of the bridge converter legs after every active switching cycle. Simulation and practical results validate and confirm the dynamic performance and power quality of the proposed system.
170 citations
TL;DR: The model shows that efficient power transfer between the fundamental and higher-order modes of the fiber can be induced by a nonlinear interaction mediated through the thermo-optic effect, leading to transverse mode instability in high-power rare-earth doped fiber amplifiers.
Abstract: We present a simple theoretical model of transverse mode instability in high-power rare-earth doped fiber amplifiers. The model shows that efficient power transfer between the fundamental and higher-order modes of the fiber can be induced by a nonlinear interaction mediated through the thermo-optic effect, leading to transverse mode instability. The temporal and spectral characteristics of the instability dynamics are investigated, and it is shown that the instability can be seeded by both quantum noise and signal intensity noise, while pure phase noise of the signal does not induce instability. It is also shown that the presence of a small harmonic amplitude modulation of the signal can lead to generation of higher harmonics in the output intensity when operating near the instability threshold.
TL;DR: The potential for using photovoltaic (PV) interfacing inverters to compensate the residential system harmonics is explored and in-depth analysis and comparison of different compensation schemes based on the virtual harmonic damping impedance concept are carried out.
Abstract: The increased non-linear loads in today's typical home are a growing concern for utility companies. This situation might be worsened by the harmonic resonance introduced by the installation of capacitor banks in the distribution network. To mitigate the harmonic distortions, passive or active filters are typically used. However, with the increasing implementation of distributed generation (DG) in residential areas, using DG systems to improve the power quality is becoming a promising idea, particularly because many DG systems, such as photovoltaic (PV), wind and fuel cells, have DG-grid interfacing converters. In this paper, the potential for using photovoltaic (PV) interfacing inverters to compensate the residential system harmonics is explored. A system model including the residential load and DG is first developed. An in-depth analysis and comparison of different compensation schemes based on the virtual harmonic damping impedance concept are then carried out. The effects of the capacitor banks in the system are also studied. The effectiveness of the harmonic compensation strategies under different conditions is verified through analysis and simulations.
TL;DR: The proposed hybrid voltage and current control method allows the coordinated closed-loop control of the DG unit fundamental voltage and line harmonic currents and guarantees smooth transition during the grid-connected/islanding operation mode transfer.
Abstract: This paper presents a hybrid voltage and current control method to improve the performance of interfacing converters in distributed generation (DG) units. In general, current-controlled methods have been widely adopted in grid-connected converters nowadays. Nevertheless, in an islanded system, the voltage control of DG units is desired to provide direct voltage support to the loads. Due to the absence of closed-loop line current controller, the voltage control scheme can hardly regulate the DG unit's line current harmonics. Furthermore, if not addressed properly, the transfer between the grid-connected operation and autonomous islanding operation will introduce nontrivial transient currents. To overcome the drawbacks of voltage- and current-controlled DG units, this paper develops a hybrid voltage and current control method (HCM). The proposed method allows the coordinated closed-loop control of the DG unit fundamental voltage and line harmonic currents. With the HCM, local harmonic loads of the DG unit can even be compensated without using harmonic current extraction. In addition, the HCM guarantees smooth transition during the grid-connected/islanding operation mode transfer. Simulated and experimental results are provided to verify the feasibility of the proposed approach.
TL;DR: Experimental results obtained from induction motors show that the proposed diagnosis algorithm is capable of detecting BRB faults with an accuracy that is superior to the zoom-based MUSIC algorithm.
Abstract: The classical multiple signal classification (MUSIC) method has been widely used in induction machine fault detection and diagnosis. This method can extract meaningful frequencies but cannot give accurate amplitude information of fault harmonics. In this paper, we propose a new frequency analysis of stator current to estimate fault-sensitive frequencies and their amplitudes for broken rotor bars (BRBs). The proposed method employs a frequency estimator, an amplitude estimator, and a fault decision module. The frequency estimator is implemented by a zoom technique and a high-resolution analysis technique known as the estimation of signal parameters via rotational invariance techniques, which can extract frequencies accurately. For the amplitude estimator, a least squares estimator is derived to obtain amplitudes of fault harmonics, without frequency leakage. In the fault decision module, the fault diagnosis index from the amplitude estimator is used depending on the load conditions of the induction motors. The fault index and corresponding threshold are optimized by using the false alarm and detection probabilities. Experimental results obtained from induction motors show that the proposed diagnosis algorithm is capable of detecting BRB faults with an accuracy that is superior to the zoom-based MUSIC algorithm.
TL;DR: In this article, the applicability of each part of the overall control in a weak grid case with the use of a stability criterion is evaluated, and a recommendation for system design has been presented.
Abstract: For grid-connected inverters, switching harmonics can be effectively attenuated through an LCL-type filter. In order to suppress resonance and guarantee good performance, many strategies (e.g. active damping (AD), harmonic resonant control, repetitive control and grid feedforward) have been proposed. However, the wide variation of grid impedance value challenges system stability in practical applications. The aforementioned methods need to be investigated. This study evaluates the applicability of each part of the overall control in a weak grid case with the use of a stability criterion. It has been demonstrated that the feedback-based AD control can work well in a wide range of grid conditions. However, the resonant and repetitive control methods meet constraints. The grid feedforward method brings in an extra positive feedback path, and consequently results in high harmonics or even instability. Finally, a recommendation for system design has been presented. Simulations and experiments have been provided to verify the analysis.
TL;DR: This work demonstrates experimentally the key influence of the steepness of the plasma-vacuum interface on the interaction, by measuring the spectral and spatial properties of harmonics generated on a plasma mirror whose initial density gradient scale length L is continuously varied.
Abstract: High-order harmonics and attosecond pulses of light can be generated when ultraintense, ultrashort laser pulses reflect off a solid-density plasma with a sharp vacuum interface, i.e., a plasma mirror. We demonstrate experimentally the key influence of the steepness of the plasma-vacuum interface on the interaction, by measuring the spectral and spatial properties of harmonics generated on a plasma mirror whose initial density gradient scale length L is continuously varied. Time-resolved interferometry is used to separately measure this scale length.
03 Jun 2013
TL;DR: In this article, the authors proposed an algorithm to calculate the optimal amplitude and phase of the harmonic current components that can be injected in the circulating currents of a modular multilevel converter (MMC) to minimize the capacitor voltage fluctuations.
Abstract: This paper proposes an algorithm to calculate the optimal amplitude and phase of the harmonic current components that can be injected in the circulating currents of a modular multilevel converter (MMC) to minimize the capacitor voltage fluctuations. An optimal second harmonic component and an optimal set of second and fourth harmonic components are proposed. Simulation results are obtained in MATLAB/Simulink environment to study the effectiveness of the calculated optimal currents. Selected experimental results have been obtained from an MMC laboratory prototype, testing the effects of the circulating currents. The reported results demonstrate the effectiveness of using a fourth harmonic component in the circulating current, which improves the effect of the second harmonic on reducing the capacitor voltage fluctuations.
TL;DR: In this paper, the reactive power compensation and active filtering capability of a wind energy conversion system (WECS) was improved by a back-to-back AC-DC-AC PWM converter.
TL;DR: A new control strategy for fault-tolerant operation of the R-FSPM motor drive considering the capability limitation of the power converter by injecting harmonic currents, the so-called remedial injected-harmonic-current (RIHC) operation mode is proposed.
Abstract: Redundant flux-switching permanent-magnet (R-FSPM) motors are a new class of brushless machines having magnets in the stator, offering high power density, simple and robust rotor structure, and good thermal dissipation conditions. This paper proposes a new control strategy for fault-tolerant operation of the R-FSPM motor drive considering the capability limitation of the power converter. The key is to operate the R-FSPM motor in the remedial mode by injecting harmonic currents, the so-called remedial injected-harmonic-current (RIHC) operation mode. Moreover, the motor losses at the existing and the proposed remedial operations are compared for evaluation. Both cosimulation and experimental results are presented, confirming that the proposed RIHC operation can offer good steady-state and dynamic performances while reducing the motor losses and the capability requirements of the power converter during fault.
TL;DR: In this article, the authors present a linear multi-harmonic analysis method to evaluate the performance of digitally controlled dual RF-input power amplifiers (PAs) in a complex design space involving two independent inputs.
Abstract: This paper presents a linear multi-harmonic analysis method to evaluate the performance of digitally controlled dual RF-input power amplifiers (PAs). The method enables, due to its low computational cost, optimization of PA efficiency and bandwidth in a complex design space involving two independent inputs. Under the idealized assumption of short-circuited higher harmonics, the analysis is used to prove the existence of a Doherty-outphasing continuum, featuring high average efficiency over 100% fractional bandwidth. With this result as a foundation, a combiner incorporating microwave transistor parasitics is analyzed without assuming short-circuited higher harmonics, showing that high average efficiencies are also achievable under more realistic conditions. A PA is straightforwardly designed from these calculation results using two 15-W GaN HEMTs. The simulated layout-ready (large-signal transistor model) PA average drain efficiency exceeds 50% over 1.1-3.7 GHz for a 6.7-dB peak-to-average power-ratio WCDMA signal. The measured PA has a maximum output power of 44 ±0.9 dBm and a 6-dB output power back-off (OPBO) power-added efficiency (PAE) of 45% over 1-3 GHz. After applying digital pre-distortion, excellent linearity is demonstrated when transmitting the WCDMA signal, resulting in an adjacent channel leakage power ratio lower than -57 dBc with corresponding average PAE of 50% and 40% at 1.2 and 2.3 GHz, respectively. This is, to the authors' knowledge, the most wideband OPBO efficiency enhanced PA reported to date, proving the effectiveness of employing linear multi-harmonic analysis in dual-input PA design.
TL;DR: The objective of this paper is to make a clear and rigorous characterization and classification of the harmonics present in a healthy cage rotor induction motor spectrum as a starting point for diagnosis.
Abstract: Before applying current-signature-analysis-based monitoring methods, it is necessary to thoroughly analyze the existence of the various harmonics on healthy machines. As such an analysis is only done in very few papers, the objective of this paper is to make a clear and rigorous characterization and classification of the harmonics present in a healthy cage rotor induction motor spectrum as a starting point for diagnosis. Magnetomotive force space harmonics, slot permeance harmonics, and saturation of main magnetic flux path through the virtual air-gap permeance variation are taken into analytical consideration. General rules are introduced giving a connection between the number of stator slots, rotor bars, and pole pairs and the existence of rotor slot harmonics as well as saturation-related harmonics in the current spectrum. For certain combinations of stator and rotor slots, saturation-related harmonics are shown to be most prominent in motors with a pole pair number of two or more. A comparison of predicted and measured current harmonics is given for several motors with different numbers of pole pairs, stator slots, and rotor bars.
TL;DR: In this article, a simple single-phase grid-connected photovoltaic (PV) inverter topology consisting of a boost section, a low-voltage single phase inverter with an inductive filter, and a step-up transformer interfacing the grid is considered.
Abstract: In this paper, a simple single-phase grid-connected photovoltaic (PV) inverter topology consisting of a boost section, a low-voltage single-phase inverter with an inductive filter, and a step-up transformer interfacing the grid is considered Ideally, this topology will not inject any lower order harmonics into the grid due to high-frequency pulse width modulation operation However, the nonideal factors in the system such as core saturation-induced distorted magnetizing current of the transformer and the dead time of the inverter, etc, contribute to a significant amount of lower order harmonics in the grid current A novel design of inverter current control that mitigates lower order harmonics is presented in this paper An adaptive harmonic compensation technique and its design are proposed for the lower order harmonic compensation In addition, a proportional-resonant-integral (PRI) controller and its design are also proposed This controller eliminates the dc component in the control system, which introduces even harmonics in the grid current in the topology considered The dynamics of the system due to the interaction between the PRI controller and the adaptive compensation scheme is also analyzed The complete design has been validated with experimental results and good agreement with theoretical analysis of the overall system is observed
TL;DR: In this article, the selection of primary shear-horizontal (SH) and Rayleigh-Lamb (RL) ultrasonic wave modes that generate cumulative second harmonics in homogeneous isotropic plates is analyzed by theoretical modeling.
TL;DR: In this paper, the potential for using the power spectrum, cepstrum, bispectrum, and neural network as a means for differentiating between healthy and faulty induction motor operation is examined.
TL;DR: The proposed control system (implemented digitally) provides superior performance over the conventional multiple proportional-integral and proportional-resonant control methods due to the absence of the PARK's transformation blocks as well as phase lock loop requirement in the control structure.
Abstract: In this paper, a novel current control technique, implemented in the a-b-c frame, for a three-phase inverter is proposed to control the active and reactive power flow from the renewable energy source to a three-phase generalized microgrid system. The proposed control system not only controls the grid power flow but also reduces the grid current total harmonic distortion in the presence of typical nonlinear loads. The control system shapes the grid current taking into account the grid voltage unbalance, harmonics as well as unbalance in line side inductors. The stability of the control system is ensured by the direct method of Lyapunov. A SRC is also proposed to improve the performance of the current controller by estimating the periodic disturbances of the system. The proposed control system (implemented digitally) provides superior performance over the conventional multiple proportional-integral and proportional-resonant control methods due to the absence of the PARK's transformation blocks as well as phase lock loop requirement in the control structure. A new inverter modeling technique is also presented to take care of unbalances both in grid voltages and line side inductors. Experimental results are provided to show the efficacy of the proposed control system.
TL;DR: In this paper, a control design approach for optimum dynamic response in single-phase grid-connected renewable converters with minimum energy storage components is presented, which is a crucial matter in realizing compact and robust converters without use of bulky and sensitive electrolytic capacitors.
Abstract: This paper presents a control design approach for optimum dynamic response in single-phase grid-connected renewable converters with minimum energy storage components. This is a crucial matter in realizing compact and robust converters without use of bulky and sensitive electrolytic capacitors. Nonoptimum dynamic response results in undesired interruptions of the maximum power point tracking and reduction of the overall efficiency of the system. Common practice is to select a large dc-bus size in order to reduce the double-frequency ripples that cause harmonics and to slow down the dynamic response to avoid large fluctuations on the bus caused by random input power jumps. This paper shows that both problems can be addressed to a great extent by improving the control system and without need to excessively increase the size of the bus component. This paper proposes a control system to achieve these goals and provides an analytical design method to optimize both dynamic response and output current harmonics. The proposed method succeeds to reduce the size of bus component several times without compromising the system performance. Details of the proposed method, mathematical modeling of the bus control and current control systems, simulations, and experimental results are presented and discussed.
TL;DR: A novel adaptive neuro-fuzzy control approach for the renewable interfacing inverter to achieve smooth bidirectional power flow and nonlinear unbalanced load compensation simultaneously, where the conventional proportional-integral controller may fail due to the rapid change in the dynamics of the highly nonlinear system.
Abstract: Power electronics plays an important role in controlling the grid-connected renewable energy sources. This paper presents a novel adaptive neuro-fuzzy control approach for the renewable interfacing inverter. The main objective is to achieve smooth bidirectional power flow and nonlinear unbalanced load compensation simultaneously, where the conventional proportional-integral controller may fail due to the rapid change in the dynamics of the highly nonlinear system. The combined capability of neuro-fuzzy controller in handling the uncertainties and learning from the processes is proved to be advantageous while controlling the inverter under fluctuating operating conditions. The inverter is actively controlled to compensate the harmonics, reactive power, and the current imbalance of a three-phase four-wire (3P4W) nonlinear load with generated renewable power injection into the grid simultaneously. This enables the grid to always supply/absorb a balanced set of fundamental currents at unity power factor even in the presence of the 3P4W nonlinear unbalanced load at the point of common coupling. The proposed system is developed and simulated in MATLAB/SimPowerSystem environment under different operating conditions. The digital signal processing and control engineering-based laboratory experimental results are also provided to validate the proposed control approach.
TL;DR: In this article, a new detection method based on anticonjugate harmonic decomposition and cascaded delayed signal cancellation is proposed, which uses constant zero as the quadrature signal, and has a completely open-looped structure.
Abstract: Single-phase grid-connected converters are widely used in many applications such as photovoltaics, fuel cells, active power filters, etc. An important topic for the development of their control schemes is ac signal detection, such as grid phase detection for grid-interfacing inverters, and harmonic detection for harmonic compensation devices. Since only one signal is available, the task is more difficult than in three-phase systems. Among the existing methods, the frequency-domain ones are known to have a one-cycle delay and heavier computational burden. Meanwhile, the time-domain methods often rely on phase-locked loop, quadrature signal generation, and complex filtering techniques; the resulted multiple-looped system may suffer from slow transients and stability issues. This paper proposes a new detection method based on anticonjugate harmonic decomposition and cascaded delayed signal cancellation. The method uses constant zero as the quadrature signal, and has a completely open-looped structure. The resulted detection system is very simple and robust. The fundamental and harmonic detection transients can be as short as 0.47 cycle in most cases, or 1.5 cycles for cases with considerable frequency variations. Meanwhile, zero steady-state error can be guaranteed in complicated harmonic scenarios, including all typical single-phase system harmonics. The performance of the proposed detection method is verified by experiments.
TL;DR: Results show that the FFRENV response is dominated by peripheral auditory channels responding to unresolved harmonics, although low-frequency channels driven by resolved harmonics also contribute, demonstrating the utility of the PLV for quantifying the strength of FFRenV across conditions.
Abstract: Two experiments, both presenting diotic, harmonic tone complexes (100 Hz fundamental), were conducted to explore the envelope-related component of the frequency-following response (FFRENV), a measure of synchronous, subcortical neural activity evoked by a periodic acoustic input. Experiment 1 directly compared two common analysis methods, computing the magnitude spectrum and the phase-locking value (PLV). Bootstrapping identified which FFRENV frequency components were statistically above the noise floor for each metric and quantified the statistical power of the approaches. Across listeners and conditions, the two methods produced highly correlated results. However, PLV analysis required fewer processing stages to produce readily interpretable results. Moreover, at the fundamental frequency of the input, PLVs were farther above the metric's noise floor than spectral magnitudes. Having established the advantages of PLV analysis, the efficacy of the approach was further demonstrated by investigating how different acoustic frequencies contribute to FFRENV, analyzing responses to complex tones composed of different acoustic harmonics of 100 Hz (Experiment 2). Results show that the FFRENV response is dominated by peripheral auditory channels responding to unresolved harmonics, although low-frequency channels driven by resolved harmonics also contribute. These results demonstrate the utility of the PLV for quantifying the strength of FFRENV across conditions.
TL;DR: A novel scheme based on using below-threshold harmonics, generated in a “seeding cell”, to boost the HHG process in a "generation cell" placed further downstream in the focused laser beam, enhances the conversion efficiency of HHG, opening the path for the realization of robust intense attosecond XUV sources.
Abstract: High-order harmonic generation (HHG) in gases has been established as an important technique for the generation of coherent extreme ultraviolet (XUV) pulses at ultrashort time scales Its main drawback, however, is the low conversion efficiency, setting limits for many applications, such as ultrafast coherent imaging, nonlinear processes in the XUV range, or seeded free electron lasers Here we introduce a novel scheme based on using below-threshold harmonics, generated in a "seeding cell", to boost the HHG process in a "generation cell", placed further downstream in the focused laser beam By modifying the fundamental driving field, these low-order harmonics alter the ionization step of the nonlinear HHG process Our dual-cell scheme enhances the conversion efficiency of HHG, opening the path for the realization of robust intense attosecond XUV sources