Showing papers on "Harmonic published in 2020"
TL;DR: A constant switching frequency multiple-vector-based FCS-MPCC scheme for multi-phase motor schemes that selects optimal V3s and their duty ratios in two orthogonal subspaces without time-consuming enumeration-based state predictions and cost function calculations is proposed.
Abstract: Most of the existing finite-control-set model predictive current control (FCS-MPCC) schemes for multi-phase motor suffer from heavy computational burden, inevitable low-order harmonic currents, and variable switching frequencies. Some virtual voltage vector (V3)-based FCS-MPCC schemes can effectively suppress harmonic current by zeroing the harmonic subspace voltage on average during one sampling period. However, they fail when the motor has a nonsinusoidal back electromotive force. In order to solve the aforementioned issues, this paper proposes a constant switching frequency multiple-vector-based FCS-MPCC scheme. Unlike the traditional FCS-MPCC schemes, the proposed scheme selects optimal V3s and their duty ratios in two orthogonal subspaces. Thus, it can simultaneously track the references in both orthogonal subspaces. In this approach, the optimal V3s and their duty ratios are directly obtained from the principle of deadbeat current control without time-consuming enumeration-based state predictions and cost function calculations. In addition, the obtained optimal V3s and their duty ratios are adopted to rearrange the pulse sequence to obtain constant switching frequency and can be simply synthesized by carrier-based pulsewidth modulation. Furthermore, a discrete time disturbance observer is designed to improve the robustness of the proposed FCS-MPCC against parameter mismatch. Finally, comparative experiments with traditional MPCC schemes for five-phase surface-mounted permanent magnet synchronous machine are carried out to verify the effectiveness of the proposed scheme.
100 citations
TL;DR: A novel multiple enhanced sparse decomposition (MESD) method is proposed to address multiple feature extraction for gearbox compound fault vibration signals and the simulation and engineering signals of the gearbox validate the performance of the proposed MESD method.
Abstract: The vibration monitoring of gearboxes is an effective means of ensuring the long-term safe operation of rotating machinery. A gearbox may have more than one fault in actual applications. Therefore, gearbox compound fault diagnosis should be investigated. In this paper, a novel multiple enhanced sparse decomposition (MESD) method is proposed to address multiple feature extraction for gearbox compound fault vibration signals. Through this method, a novel MESD algorithm is utilized to simultaneously separate and extract the harmonic components and transient features of the gear and bearing from the compound fault signal. Three subdictionaries are specially constructed according to the gearbox failure mechanism to accurately extract each feature component. Meanwhile, the generalized minimax concave (GMC) penalty is used as sparse regularization to further ensure the accuracy of sparse decomposition. The simulation and engineering signals of the gearbox validate the performance of the proposed MESD method.
91 citations
TL;DR: This paper presents a Hybrid Shunt Active Power Filter (HSAPF) optimized by hybrid Particle Swarm Optimization-Grey Wolf Optimization (PSO-GWO) and Fractional Order Proportional-Integral-Derivative Controller (FOPIDC) for reactive power and harmonic compensation under balance and unbalance loading conditions.
Abstract: This paper presents a Hybrid Shunt Active Power Filter (HSAPF) optimized by hybrid Particle Swarm Optimization-Grey Wolf Optimization (PSO-GWO) and Fractional Order Proportional-Integral-Derivative Controller (FOPIDC) for reactive power and harmonic compensation under balance and unbalance loading conditions. Here, the parameters of FOPID controller are tuned by PSO-GWO technique to mitigate the harmonics. Comparing Passive with Active Filters, the former is tested to be bulky and design is complex and the later is not cost effective for high rating. Hence, a hybrid structure of shunt active and passive filter is designed using MATLAB/Simulink and in real time experimental set up. The compensation process for shunt active filter is different from predictable methods such as (p-q) or (i
d
-i
q
) theory, in which only the source current is to be sensed. The performance of the proposed controller is tested under different operating conditions such as steady and transient states and indices like Total Harmonic Distortion (THD), Input Power Factor (IPF), Real Power (P) and Reactive Power (Q) are estimated and compared with that of other controllers. The parameters of FOPIDC and Conventional PID Controller (CPIDC) are optimized by the techniques such as PSO, GWO and hybrid PSO-GWO. The comparative simulation/experiment results reflect the better performance of PSO-GWO optimized FOPIDC based HSAPF with respect to PSO/GWO optimized FOPIDC/CPIDC based HSAPF under different operating conditions.
82 citations
TL;DR: In this article, a modified second-order generalized integrators (mSOGI) is proposed for a fast estimation of all harmonic components of arbitrarily distorted single-phase signals, such as voltages or currents in power systems.
Abstract: This article proposes modified second-order generalized integrators (mSOGIs) for a fast estimation of all harmonic components of arbitrarily distorted single-phase signals, such as voltages or currents in power systems. The estimation is based on the internal model principle leading to an overall observer consisting of parallelized mSOGIs. The observer is tuned by pole placement. For a constant fundamental frequency, the observer is capable of estimating all harmonic components with prescribed settling time by choosing the observer poles appropriately. For time-varying fundamental frequencies, the harmonic estimation is combined with a modified frequency locked loop (mFLL) with gain normalization, sign-correct antiwindup, and rate limitation. The estimation performances of the proposed parallelized mSOGIs with and without mFLL are illustrated and validated by measurement results. The results are compared to standard approaches such as parallelized standard SOGIs (sSOGIs) and adaptive notch filters (ANFs).
78 citations
TL;DR: In this article, a dc impedance model of an MMC is developed by harmonic transfer function method that considers the internal dynamics and typical controls of MMCs, while typical controls consist of dc voltage control, positive-negative sequence separation-based phase current control, circulating current control and some other linear controls.
Abstract: The dc impedance model of a modular multilevel converter (MMC) is the basis for analyzing harmonic resonances of MMC-based dc systems. As an MMC typifies a multiple harmonic response system, its internal dynamics and controls significantly influence its external characteristics. In this paper, a dc impedance model of an MMC is developed by harmonic transfer function method that considers the internal dynamics and typical controls of MMCs. The internal dynamics mainly include capacitor voltage fluctuation and multi-harmonic response characteristics, while typical controls consist of dc voltage control, positive–negative sequence separation-based phase current control, circulating current control, and some other linear controls. As a result, the proposed impedance model can be used not only to analyze the harmonic stability of an MMC-based dc system, but also to investigate the influence of additional controls in an MMC on system stability. Furthermore, the proposed model makes up for the deficiencies in harmonic stability analysis of MMC-based dc systems. The results of both the hardware-in-the-loop RT-LAB digital simulation and the physical experimentation validate the proposed impedance models and analyses.
68 citations
TL;DR: In this paper, a real-time detection algorithm of decaying dc component is first developed for a generic single-phase distorted ac signal, and fast and robust elimination of both decaying dc transient and harmonics can be performed simultaneously in three-phase grids, by adoption of moving average filters in $d$ − $q$ frame and subsequent calculations.
Abstract: Active power filters are conventionally utilized to compensate steady-state harmonic currents and reactive power in the utility, yet their capabilities are usually limited if the elimination of undesirable effects associated with decaying dc components during transients is the target, especially under the weak grid condition. In this letter, active cancellation of the typical first-order decaying dc-mode transients is explored. To this end, a real-time detection algorithm of decaying dc component is first developed for a generic single-phase distorted ac signal. Furthermore, fast and robust elimination of both decaying dc transient and harmonics can be performed simultaneously in three-phase grids, by adoption of moving average filters in $d$ – $q$ frame and subsequent calculations. Hardware-in-the-loop experiment results verified the effectiveness of the proposed technique.
65 citations
TL;DR: An adaptive linear neuron based current harmonics suppression method for permanent magnet synchronous motors with nonsinusoidal back electromotive force (EMF) is presented, with due account for dead-time effect.
Abstract: In this article, an adaptive linear neuron based current harmonics suppression method for permanent magnet synchronous motors with nonsinusoidal back electromotive force (EMF) is presented, with due account for dead-time effect. The current harmonics can be well-suppressed by feedforwarding a self-tuning compensation voltage. The proposed method does not rely on the knowledge of back-EMF harmonic components and dead-time effect. Moreover, the proposed method is easy to implement, since it does not need the process to extract the current harmonics. The effectiveness of the proposed method is verified by both simulation and experimental results without requiring additional hardware.
65 citations
TL;DR: A current harmonic suppression strategy based on an extended state observer (ESO) that works well when considering other factors that may cause harmonic distortion, such as magnetic circuit saturation, saliency ratio, over-modulation of the inverter, the voltage drop caused by electric devices, and dead time is proposed.
Abstract: Dual three-phase (DTP) permanent magnet synchronous machines (PMSM) have been utilized in many applications due to their outstanding performance. However, large stator current harmonics limit the further application of the DTP-PMSM due to the low impedance in the harmonic subspace. To solve this problem, this article proposes a current harmonic suppression strategy based on an extended state observer (ESO). A detailed analysis is carried out to demonstrate the disturbance rejection ability and robustness of the proposed method. The theoretical analysis also shows that the ESO strategy outstands the conventional proportional-integral controller and advanced proportional resonance (PR) controller in terms of harmonic reduction. The advantages are verified by simulation and experimental results under different operating conditions. The proposed strategy still works well when considering other factors that may cause harmonic distortion, such as magnetic circuit saturation, saliency ratio, over-modulation of the inverter, the voltage drop caused by electric devices, and dead time. Meanwhile, some limitations are also pointed out. The proposed strategy can also be easily applied to other multiphase PMSM types.
62 citations
TL;DR: An airgap-harmonic-orientated design method is proposed, where the airgap harmonics are newly acted as the effective bridge between the three key elements of permanent magnet sources, modulators, or armature windings and the motor performances.
Abstract: In this article, an airgap-harmonic-orientated design method is proposed, where the airgap harmonics are newly acted as the effective bridge between the three key elements of permanent magnet sources, modulators, or armature windings and the motor performances. In the proposed design method, the airgap harmonics play couple roles of design objectives and variables, which are not only served as the design variables for the motor performances, but also considered as the objectives for design parameters. For extensive investigation, a V-shape flux-modulated permanent-magnet (V-FMPM) motor is selected as a design example, which has a potential application for the electrical vehicles. In the optimization process, the sensitivity analysis of different airgap harmonics on the torque performance is conducted to select the leading airgap harmonics. Meanwhile, the sensitivity degrees of the design parameters on the leading harmonics are calculated to pick out the sensitive design parameters. Then, the performances of the V-FMPM motor are evaluated for validating airgap-harmonic-orientated design method. Finally, a prototype motor is built and tested. Both the theoretical analysis and experimental results verify the effectiveness and reasonability of the proposed design method and the V-FMPM motor.
61 citations
TL;DR: This paper proposes a transformer integrated filtering system (TIFS) for harmonic suppression in the industrial dc supply system that has the merits of lower transformer loss, stronger ability in harmonic elimination, and higher integration of the electric equipment in the high-power industrial applications.
Abstract: This paper proposes a transformer integrated filtering system (TIFS) for harmonic suppression in the industrial dc supply system. Designed for the electric environment with large current and severe harmonic contamination and the installation space with restricted planning area, the proposed TIFS has the merits of lower transformer loss, stronger ability in harmonic elimination, and higher integration of the electric equipment in the high-power industrial applications. The winding arrangement of the inductive filtering transformer with integrated reactor is introduced. Considering the influence of the residual weak coupling, the electromagnetic decoupling model of TIFS is established. Then, the interaction between the zero-impedance designed filtering winding and the decoupled winding is analyzed to determine the restricted range of the design parameter. The control strategy together with the transformer design method is further illuminated. At last, the prototype of TIFS is established in the laboratory. The experimental results verify the feasibility and effectiveness of the proposed filtering method.
57 citations
TL;DR: In this article, the authors demonstrated that the MXene V2CTx, which has a strong modulation depth (nearly 50%), can serve as an excellent saturable absorber (SA) in passively mode-locked (PML) fiber lasers.
Abstract: Abstract MXene as a novel two-dimensional (2D) material exhibits a lot of advantages in nonlinear optics. However, the common MXene, Ti3C2Tx and Ti2CTx nanosheets, easily suffer from degradation under ambient conditions, greatly limiting their practical applications. Here, we demonstrated one of MXene compounds, V2CTx, which has a strong modulation depth (nearly 50%), can serve as an excellent saturable absorber (SA) in passively mode-locked (PML) fiber lasers. More importantly, 206th harmonic order has been successfully generated in Er-doped mode-locked fiber laser, exhibiting maximum repetition rate of 1.01 GHz and pulse duration of 940 fs, which to the best of our knowledge, is the highest harmonic mode-locked fiber laser from the MXene SA so far. In addition, the high harmonic order mode-locked operation can maintain at least 24 h without any noticeable change, suggesting MXene V2CTx nanosheets have excellent stability in this mode-locked fiber laser. It is anticipated that the present work can pave the way to new design for MXene-based heterostructures for high-performance harmonic mode-locked lasers.
TL;DR: A model predictive control for a six-phase permanent magnet synchronous machine (PMSM) with a reduced-dimension cost function where only the variables in the harmonic subspace are included into the cost function, while the energy conversion related variables are excluded.
Abstract: This paper presents a model predictive control for a six-phase permanent magnet synchronous machine (PMSM) with a reduced-dimension cost function. Only the variables in the harmonic subspace are included into the cost function, while the energy conversion related variables are excluded. This is achieved by using the deadbeat direct torque and flux control method to obtain a reference voltage vector and then to track the torque and stator flux properly in the energy conversion related subspace. Then, according to the position of the reference vector, the appropriate prediction vectors can be determined. Subsequently, a reduced-dimension cost function including only the harmonic constraints is defined to evaluate the feasible prediction vectors. In this way, the predictive model and the cost function are simplified without redundant constraints. Meanwhile, the torque and flux can be regulated satisfactorily, and the harmonic currents are suppressed effectively. Finally, experimental results of the proposed method and the conventional model predictive torque control are presented in this paper to verify the validity of the proposed method.
TL;DR: The teeth chopping effect is proposed and demonstrates that the slot number order radial force is the root of the zeroth-mode vibration of the motor.
Abstract: For the integer slot permanent-magnet (PM) driving synchronous motor, the zeroth-mode slot frequency vibration and noise play a significant vibroacoustic role in the low-frequency domain. For conventional analysis in literature, it is usually assumed that the zeroth-mode vibration is caused by the zeroth-order radial force harmonic. But in this paper, the genuine reason for zeroth-mode vibration is proposed and discussed in detail, which is different from the conventional analysis. The teeth chopping effect is proposed and demonstrates that the slot number order radial force is the root of the zeroth-mode vibration of the motor. After the analysis of the zeroth-mode vibration in existing research work is presented, the teeth chopping effect is introduced and described. The amplitudes of the zeroth-order and slot number order forces are compared with an analytical method, while their amplitudes and caused deformations of these forces are calculated with the finite-element method (FEM). Finally, to validate the analytical and FEM results, a 6-pole 36-slot PM driving motor is manufactured and tested, and the results are in good agreement with those of the FEM results.
TL;DR: In this article, a harmonic-domain single-input single-output (SISO) equivalent modeling technique for the impedance modeling and stability analysis of a single-phase grid-connected voltage-source converter (VSC) is presented.
Abstract: This article presents a harmonic-domain single-input single-output (SISO) equivalent modeling technique for the impedance modeling and stability analysis of a single-phase grid-connected voltage-source converter (VSC). The basis is a conversion technique that transforms a harmonic transfer function (HTF)-based model into a SISO equivalent model while preserving all the information of frequency couplings. The proposed SISO modeling concept is useful for understanding the meaning and consequence of SISO impedance measurement of an interconnected system with frequency couplings, which further enables a simpler impedance measurement and impedance-based analysis. Applications of this method for the VSC model reduction and stability characteristic analyses are presented. From these results, useful conclusions regarding the accuracy of three types of reduced-order VSC impedance models and the stability effects of the VSC control with and without compensation for dc voltage variation are obtained. The presented examples of applications demonstrate how the proposed SISO modeling technique facilitates a simpler and efficient impedance-based analysis. Finally, experimental results verify the validity of the proposed VSC-SISO admittance and corresponding analyses.
04 May 2020
TL;DR: Experimental results show that a simple convolutional neural network back-end with the proposed front-end outperforms state-of-the-art baseline methods in automatic music tagging, keyword spotting, and sound event tagging tasks.
Abstract: We introduce a trainable front-end module for audio representation learning that exploits the inherent harmonic structure of audio signals. The proposed architecture, composed of a set of filters, compels the subsequent network to capture harmonic relations while preserving spectro-temporal locality. Since the harmonic structure is known to have a key role in human auditory perception, one can expect these harmonic filters to yield more efficient audio representations. Experimental results show that a simple convolutional neural network back-end with the proposed front-end outperforms state-of-the-art baseline methods in automatic music tagging, keyword spotting, and sound event tagging tasks.
TL;DR: A multi resonant component-based grid-voltage-weighted feedforward scheme is proposed, which introduces a series of quasi-resonant components into the grid voltage full feedforward path so that only the background harmonics in the grid Voltage are fed forward.
Abstract: The grid voltage full feedforward scheme is an effective method to improve the injected grid current quality of the grid-connected inverter. However, due to the digital control delay, the suppression of the injected grid current harmonics is weakened, and the inverter output impedance has an additional negative phase shift, which deteriorates the system stability under weak grid. In this article, a multi resonant component-based grid-voltage-weighted feedforward scheme is proposed, which introduces a series of quasi-resonant components into the grid voltage full feedforward path so that only the background harmonics in the grid voltage are fed forward. By properly designing the quasi-resonant components, the phase lag due to the digital control delay is compensated and the feedforward weights at different harmonic frequencies are introduced in the grid voltage feedforward path. Thus, the suppression of the injected grid current harmonics and the system stability is improved. The experimental results from a 6-kVA prototype are provided to verify the effectiveness of the proposed grid-voltage-weighted feedforward scheme.
TL;DR: A controlled wide-bandwidth impedance measurement approach is presented in this paper, in which, a butterfly-type disturbance circuit and chirp pulsewidth modulation signal model are incorporated to generate the desired controlled-band width harmonics with a high aggregation as well as the average amplitude.
Abstract: The accurate information of the wide-bandwidth impedance versus the frequency is urgently needed for evaluating the system resonances, instabilities, and operations of the railway traction power system (TPS), and to avoid/control the harmonic resonance and oscillation issues. As the system topology and detailed parameters of the TPS are not fully known even timely varying, we have to obtain the detailed wide-bandwidth impedance information through exciting the harmonic disturbance into the system, and then, calculating the response information. Therefore, a controlled wide-bandwidth impedance measurement approach is presented in this paper, in which, a butterfly-type disturbance circuit and chirp pulsewidth modulation signal model are incorporated to generate the desired controlled-bandwidth harmonics with a high aggregation as well as the average amplitude. Impedance measurement results of the proposed approach have been validated through both simulation and experiment. Considering the measured errors, the proposed method is efficient in testing the wide-bandwidth impedance of the single-phase railway traction system.
TL;DR: This paper enhances the IARC scheme by proposing a 3rd harmonic elimination approach by adopting a current reference generation method using the symmetric sequence components concept, which complies with the grid code requirements by injecting the requested reactive current.
Abstract: This paper proposes a new control scheme to eliminate the 3rd harmonic in the output currents of grid-following inverters under unbalanced grid conditions. Unbalanced grids adversely affect the performance of grid-following inverters due to the oscillations appearing on the DC-link voltage with a frequency twice the line frequency. The paper is based on instantaneous active reactive control (IARC) technique due to its advantages over other existing methods. However, the presence of severe asymmetrical 3rd harmonic distortions in the inverter output currents is the main challenge with IARC method, which impairs the power quality requirements. This paper enhances the IARC scheme by proposing a 3rd harmonic elimination approach by adopting a current reference generation method using the symmetric sequence components concept. Furthermore, the proposed scheme complies with the grid code requirements by injecting the requested reactive current. Finally, the proposed approach is evaluated by theoretical and simulation analysis and validated experimentally using a hardware setup.
TL;DR: A bilinear recursive least squares (BRLS) adaptive filter is proposed and integrated into a sliding-mode position observer to suppress the dominant harmonic components in the estimated back EMF and as a result, the accuracy of the estimated rotor position can be greatly improved.
Abstract: In the back electromotive force (EMF)-based sensorless control of interior permanent magnet synchronous motor (IPMSM), the inverter nonlinearity and flux linkage spatial harmonics will possibly give rise to (6 k ± 1)th harmonics in the estimated back EMF, especially the fifth and seventh harmonics. Those harmonics will consequently introduce (6 k )th harmonic ripples to the estimated rotor position, especially the sixth harmonic component. In order to solve this problem, a bilinear recursive least squares (BRLS) adaptive filter is proposed and integrated into a sliding-mode position observer to suppress the dominant harmonic components in the estimated back EMF and as a result, the accuracy of the estimated rotor position can be greatly improved. A unique feature of the BRLS adaptive filter is its ability to track and suppress the specified harmonic components in different steady state and dynamic operational conditions. The proposed method can compensate for harmonic ripples caused by the inverter nonlinearity and machine spatial harmonics at the same time; this method is also robust to machine parameter variation, and the BRLS algorithm itself is machine parameter independent. The implementation of the proposed BRLS filter in the sensorless control of IPMSM is explained in details in this paper. The enhanced drive performances using the BRLS filter have been thoroughly validated in different steady state and dynamic operational conditions on a 1.5-kW IPMSM sensorless drive.
20 Dec 2020
TL;DR: In this article, a mean-field theory for active cavities analogous to the Lugiato-Lefever equation was proposed, which describes both fundamental FM combs and harmonic states.
Abstract: In many laser systems, frequency combs whose output is frequency-modulated (FM) can form, producing light whose frequency sweeps linearly. While this intriguing result has been replicated experimentally and numerically, a compact description of the core physics has remained elusive. By creating a mean-field theory for active cavities analogous to the Lugiato–Lefever equation, we show that these lasers are described by a nonlinear Schrodinger equation with a potential proportional to the phase of the electric field. This equation can be solved analytically and produces a field with quasi-constant intensity and piecewise quadratic phase. We refer to these nondispersive waves as extendons, and they describe both fundamental FM combs and harmonic states. Our results apply to many lasers, explaining the ubiquity of this phenomenon, and our new theory unifies many experimental observations.
TL;DR: In addition to their strong nonlinear optical response, transition metal dichalcogenides (TMDCs) possess a high refractive index in the visible and infrared regime as mentioned in this paper.
Abstract: In addition to their strong nonlinear optical response, transition metal dichalcogenides (TMDCs) possess a high refractive index in the visible and infrared regime. Therefore, by patterning those T...
TL;DR: The model analysis results demonstrate that the MMC impedance is coupled with the grid impedance due to the internal harmonics, and the proposed model not only consists of the ac current and the circulating current control, but also incorporates dc voltage outer loop and PLL with a clear physical meaning.
Abstract: Harmonic state space (HSS) is seen as an effective impedance modeling method to precisely characterize the internal harmonic features of the modular multilevel converter (MMC). However, the existing MMC impedance models assume the ideal grid, ignoring the grid impedance, and they also do not incorporate the widely used dual-loop control and phase-locked loop (PLL). In this article, a complete MMC impedance model based on HSS is proposed to reveal the grid impedance coupling effect of MMC. The model analysis results demonstrate that the MMC impedance is coupled with the grid impedance due to the internal harmonics. This coupling causes MMC to be affected by the grid impedance and may cause instability. On the other hand, the proposed model not only consists of the ac current and the circulating current control, but also incorporates dc voltage outer loop and PLL with a clear physical meaning. Based on the proposed model, this article illustrates the factors that will enhance the coupling, which shows that the proposed model has to be used to improve the accuracy of the analysis. Finally, effectiveness of the proposed model is verified by simulation and experimental results.
TL;DR: In this article, the authors explore novel photoelectric functional materials via chemical substitution-oriented design, which can be expanded to the discovery of high-performance UV nonlinear optica.
Abstract: Exploring novel photoelectric functional materials via chemical substitution-oriented design is an effective strategy, which can be expanded to the discovery of high-performance UV nonlinear optica...
TL;DR: The modeling and analysis of the inverter-based MGs under harmonic conditions and the dynamic behavior of the microgrid is investigated via small-signal analysis, observing that the virtual impedance for harmonic compensation brings inter-inverter oscillations on harmonic domain.
Abstract: Microgrids (MGs) operate under harmonic conditions due to the integration of nonlinear loads. The autonomous harmonic compensation control of inverter-interfaced DG has been proposed to successfully mitigate the harmonics. However, the small-signal analysis of harmonic compensation controls has not been investigated in the microgrid with multiple inverters. This paper develops the modeling and analysis of the inverter-based MGs under harmonic conditions. The concept of dynamic phasor (DP) is used to describe the fundamental and harmonic components of an ac waveform via dc variables. The developed model consists of droop-controlled distributed generators (DGs), diodes rectifiers (working as nonlinear load) and resistance loads. Virtual impedance control is considered in the droop-controlled DGs for the autonomous harmonic compensation. Based on the developed DP model, the dynamic behavior of the microgrid is investigated via small-signal analysis. It is observed that the virtual impedance for harmonic compensation brings inter-inverter oscillations on harmonic domain. Participation and eigenlocus analysis are performed to investigate the influence of parameter tuning of harmonic compensation on microgrid stability. Numerical simulations are carried out to validate the effectiveness of the proposed modeling method and the analysis results.
TL;DR: A novel real-time detection scheme for incipient stator inter-turn short circuit fault in voltage sources inverter-fed induction machines is proposed and the competency of the proposed algorithm is validated using simulation and verified by hardware with VSI- fed induction motor drive.
Abstract: This work proposes a novel real-time detection scheme for incipient stator inter-turn short circuit fault in voltage sources inverter-fed induction machines. Both non-sinusoidal input voltage and the short circuit fault causes harmonics in the motor stator current and these combined harmonic components complicate the spectral analysis-based diagnosis in inverter-fed motors. Aim of the analysis is to identify the effect of inverter fundamental/switching frequency on early detection and classification of the inter-turn fault. Discrete wavelet transform based analysis is performed on stator current using daubechies1 wavelet and statistical parameter L2 norm has been computed for the detailed and approximate coefficients at different decomposition levels to obtain the most precise feature of fault. Support vector machine-based learning algorithm is used for the accurate classification of the incipient fault. The proposed method is independent of switching and fundamental frequency, the modulation index and mechanical load. Real-time detection is possible even with infinitesimal fault current of 350 mA by the proposed method. The competency of the proposed algorithm is validated using simulation and verified by hardware with VSI-fed induction motor drive.
TL;DR: A control method that combines a vector resonant controller and an active disturbance rejection control controller is proposed in this article for suppressing the current harmonics of permanent magnet synchronous linear motors.
Abstract: A control method that combines a vector resonant controller and an active disturbance rejection control controller is proposed in this article for suppressing the current harmonics of permanent magnet synchronous linear motors. First, the resonant controller is improved by changing its transfer function so that it can suppress current harmonics better. Then, an active disturbance rejection control (ADRC) is designed to suppress the parameter disturbance of motors, which will adversely affect the improved resonant controller. The parameter disturbance is estimated by an extended state observer, and linear feedback control is used for disturbance compensation. The ADRC and the improved resonant controller work together to not only suppress harmonics but also improve resistance against system disturbance. Finally, a linear motor control platform is built, and experimental results are presented to verify the significance and correctness of the proposed approach.
TL;DR: A distributed control system is proposed which uses the Conservative Power Theory (CPT) and a consensus algorithm to share imbalance and harmonics between different converters in three-phase four-wire droop-controlled Microgrids (MGs).
Abstract: A distributed control system is proposed which uses the Conservative Power Theory (CPT) and a consensus algorithm to share imbalance and harmonics between different converters in three-phase four-wire droop-controlled Microgrids (MGs). The CPT is used to identify the balanced, unbalanced and distorted components of the currents and powers in the system. Control loops based on virtual impedance and implemented in the stationary a-b-c frame are then used to distribute these components between the various converters in the MG. The magnitudes of the virtual impedances are adaptively calculated using a novel consensus-based distributed control scheme with the aim of sharing imbalances and harmonics according to the residual VA capacity of each converter whilst regulating the imbalance and distortion at their output to meet the appropriate IEEE power quality standards. Extensive simulations show that the proposed distributed control has excellent performance, and experimental validation is provided using a laboratory-scale 4-wire MG.
TL;DR: In this article, the crystal harmonic spectra of MgO from an ultrashort mid-infrared laser pulse are shown to exhibit the Cooper minimum characteristic, which could potentially be useful for retrieving the band information of solid materials and all-optical reconstruction of the band structure through high-order harmonic generation.
Abstract: The crystal harmonic spectra of MgO from an ultrashort midinfrared laser pulse are shown to exhibit the Cooper minimum characteristic. This study could potentially be useful for retrieving the band information of solid materials and all-optical reconstruction of the band structure through high-order harmonic generation.
TL;DR: This paper aims to investigate the elimination of harmonics in a solar fed cascaded fifteen level inverter with aid of Proportional Integral, Artificial Neural Network and Fuzzy Logic based controllers to provide output voltage regulation in terms of maintaining voltage and frequency at the inverter output end in compatible with the grid connection requirements.
Abstract: The presence of harmonics in solar Photo Voltaic (PV) energy conversion system results in deterioration of power quality. To address such issue, this paper aims to investigate the elimination of harmonics in a solar fed cascaded fifteen level inverter with aid of Proportional Integral (PI), Artificial Neural Network (ANN) and Fuzzy Logic (FL) based controllers. Unlike other techniques, the proposed FLC based approach helps in obtaining reduced harmonic distortions that intend to an enhancement in power quality. In addition to the power quality improvement, this paper also proposed to provide output voltage regulation in terms of maintaining voltage and frequency at the inverter output end in compatible with the grid connection requirements. The simulations are performed in the MATLAB / Simulink environment for solar fed cascaded 15 level inverter incorporating PI, ANN and FL based controllers. To exhibit the proposed technique, a 3 kWp photovoltaic plant coupled to multilevel inverter is designed and hardware is demonstrated. All the three techniques are experimentally investigated with the measurement of power quality metrics along with establishing output voltage regulation.
TL;DR: This work demonstrates that frequency-domain method can be used for oscillator-based converters in the high-frequency range, specifically, for harmonic mitigation in the converter output current, and proposes a virtual impedance-based selective harmonic current suppression method.
Abstract: Virtual oscillator control (VOC) is a nonlinear grid-forming controller that simultaneously achieves the functionality of output voltage control and primary control layers in a power electronics interfaced distributed generation (DG) unit. Unlike conventional phasor-based primary control methods such as the droop control and virtual synchronous machine control, VOC is a time-domain controller that can guarantee almost global asymptotic synchronization. However, the high-frequency dynamics has largely been ignored in the analysis of VOC in prior art; as a result, VOC-based DGs fail to suppress harmonic current in the presence of harmonic distortion in the network-side voltage. In this work, we demonstrate that frequency-domain method can be used for oscillator-based converters in the high-frequency range, specifically, for harmonic mitigation in the converter output current. We propose a virtual impedance-based selective harmonic current suppression method, and demonstrate that it is better to use the network-side current feedback rather than that of the converter-side current for VOC implementation with virtual impedance control. Established harmonic rejection strategies for grid-following and conventional grid-forming converters are compared with the proposed method for VOC. Through impedance-based analysis, we demonstrate that the proposed method augments the passivity range of the converter terminal response with a much simpler implementation. The proposed harmonic suppression strategy is validated through hardware experiments using a single-phase inverter prototype.