7th Harmonics Research Articles

Design and analysis of novel optimal harmonic elimination strategy based on MOPSO to obliterate low‐order harmonics of odd‐nary cascaded transformers‐based multilevel inverter

Creating a high‐step staircase sinusoidal voltage taking into account of low number of switches is recognized as a significant challenge ahead of inventors of power electronics. This paper suggests a maiden cascaded transformer‐based multilevel inverter to effectively develop and solve the abovementioned challenge. Hence, via appending the bidirectional switches to the capacitors of submultilevel inverter as well as low‐frequency transformers, the proposed inverter structure can flexibly operate as so‐called “odd‐nary asymmetrical multilevel inverter.” From the perspective of low‐order harmonics produced by all inverter structures, apart from inverter type, it is essential that an effective strategy to be implemented to eliminate these harmonics. Toward this subject, kerf‐style Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) has been scheduled as an optimization problem. Because of nature of multiobjective state of the problem, application of the multiobjective optimization technique is inevitable. Considering significant performance of Multi Objective Particle Swarm Optimization (MOPSO) for solving the nonlinear objectives, the elimination of fifth, seventh, and 11th harmonics is formulated by relevant fitness functions based on MOPSO. Putting it all together, the relevant analytical study accompanying both the simulation and experimental results has transparently verified the performance of the proposed multilevel inverter. Furthermore, elimination of all three designated low‐order harmonics, ie, fifth, seventh, and 11th harmonics using MOPSO‐based kerf‐style SHEPWM strategy has been well confirmed.

Operating performance analysis on wind turbines with the speed regulating differential mechanism

In this paper, a hybrid transmission system is presented for variable-speed constant-frequency wind turbines (WTs). This approach employs an electrically controlled speed regulating differential mechanism (SRDM) so that the synchronous generator is able to rotate at a stable speed and, thus, generate electricity in constant frequency regardless of the changing wind rotor speed. In order to find out the operating performance of the proposed SRDM-based WT, a detailed 1.5 MW simulation model is established by which the speed-regulating accuracy, the electrical harmonic pollutions, and the system low-voltage ride-through (LVRT) capability are all studied in depth and then compared with those of the existing direct-drive or double-fed wind power systems. Simulation results indicate that, under various wind conditions, SRDM can efficiently regulate the output power frequency with satisfactory deviations by using a low-power (less than 262 kW) permanent magnet synchronous motor. Compared to the existing WTs, the 5th, 7th, 11th, and 13th current harmonics of the proposed WT are all ideally reduced to 0.4% of the fundamental current. Moreover, around 0.45 p.u., reactive power can be provided for the rapid recovery of the grid during severe voltage sags. The output power quality, system transient stability, and LVRT capability are all improved. Theoretical analysis and case studies give good verifications of the feasibility and superiority of the proposed SRDM-based WT.

EMI Reduction Methods in Wireless Power Transfer System for Drone Electrical Charger Using Tightly Coupled Three-Phase Resonant Magnetic Field

Wireless power transfer (WPT) technology is a promising way for convenient and safe battery charging without any electrical contact, which may cause an unwanted electric spark or deliver dangerous electric current to the users. When transferring power from the source to the battery, strong electromagnetic fields (EMFs) are generated. Moreover, the inverter output contains a wide range of harmonics. Therefore, it is important to reduce the EMFs and electromagnetic interference (EMI) in a WPT system. For the first time, in this paper, we propose a new tightly coupled three-phase resonant magnetic field (TC-TPRMF) charger for a drone operating at 60 kHz, which can completely eliminate the third harmonic and its integer multiples in the output voltage. Furthermore, to reduce the selective EMI, the conduction angle control is proposed for the WPT charging system. Through a series of measurements, we verified that the proposed TC-TPRMF with the conduction angle control can reduce the seventh and 11th harmonics of the Tx current by 6.08 and 11.84 dBμA, respectively. The coil-to-coil power transfer efficiency and total system power transfer efficiency are maintained at 91% and 72%, respectively.

Photonic Generation of Frequency-Multiplied Microwave Signals With Constant Amplitudes

This letter presents a photonic scheme to generate frequency-multiplied microwave signals with nearly constant amplitude. Optical injection locking and an optical fiber active loop filter are utilized to generate a frequency-multiplied microwave signal and equalize its amplitude, respectively. The significance of the scheme is that optical injection locking and nonlinear modulation are simultaneously implemented by a semiconductor distributed feedback laser, making this system compact and low-cost compared with other similar photonic implementations. Corresponding experiments display the effects of amplitude equalization for 10th and 11th harmonics with an initial frequency of 1.5 GHz and an 18th harmonic with an initial frequency of 1 GHz, respectively. The harmonic suppression ratios reach over 20 dB, and the SSB phase noises (<−92 dBc/Hz at 10 kHz offset frequency) are somewhat decreased with respect to the conventional optical injection locking.

Selective Harmonic Elimination With Optimal DC Sources in Multilevel Inverters Using Generalized Pattern Search

This paper presents the computation of optimal dc sources and switching angles using the generalized pattern search (GPS) optimization method for harmonic elimination in a cascaded multilevel inverter. The goal is to solve nonlinear equations for eliminating low-order harmonics and reaching desired fundamental component. For case study, 5- and 7-level inverters are chosen. The 7-level inverter with equal dc sources and 5- and 7-level inverters with an optimal dc source are applied to eliminate fifth and seventh harmonics. To obtain this goal, MATLAB software is used. Considering simulation results, cost, and simpler implementation, 5-level inverter with an optimized dc source is more effective in all modulation indexes in comparison with 7-level inverter. Also, results demonstrate the superiority of GPS over genetic algorithm (GA) in attaining accurate global minima. For better evaluation of optimizing more dc sources and GPS performance in comparison with GA, 7-level inverter with two optimal dc sources is applied to eliminate fifth, seventh, 11th, and 13th harmonics. Finally, to validate the accuracy of the 5-level inverter with an optimal dc source and GPS performance, the experimental results are provided for a 5-level cascaded H-bridge inverter.

Chirp-control of resonant high-order harmonic generation in indium ablation plumes driven by intense few-cycle laser pulses.

We have studied high-order harmonic generation (HHG) in an indium ablation plume driven by intense few-cycle laser pulses centered at 775 nm as a function of the frequency chirp of the laser pulse. We found experimentally that resonant emission lines between 19.7 eV and 22.3 eV (close to the 13th and 15th harmonic of the laser) exhibit a strong, asymmetric chirp dependence, with pronounced intensity modulations. The chirp dependence is reproduced by our numerical time-dependent Schrödinger equation simulations of a resonant HHG by the model indium ion. As demonstrated with our separate simulations of HHG within the strong field approximation, the resonance can be understood in terms of the chirp-dependent HHG photon energy coinciding with the energy of an autoionizing state to ground state transition with high oscillator strength. This supports the validity of the general theory of resonant four-step HHG in the few-cycle limit.

Modeling of the GPS satellite clock error and its performance evaluation in precise point positioning

The different functions, which include the polynomial and the harmonics based functions, are used to model and extrapolate the GPS satellite clock for simplifying the service mode and real-time application. The modeling accuracy decreases with the increasing modeled time, when the polynomial functions are used. The 4th order harmonics based function is used to model the one-year single day satellite clocks. The results indicate that the accuracies of the modeled Rb clocks are better than 0.30 ns, while that of the Cs clocks just are better than 0.79 ns. Meanwhile, we noticed that the daily fitted amplitudes for 16 Block IIF and Block IIR-M Rb clocks vary regularly with a 6 months periodicity. This is mostly visible for the harmonics of 6 and 12 h periods. However the initial phases of these 12 and 6 h harmonics have obvious linear variation for the 16 Block IIF and Block IIR-M Rb clocks. Additional periods of 8 h, 4.8 h, 3.43 h and 2.67 h are noticed by analyzing the modeling residuals of 4th order harmonics based function. The modeling of 8th order harmonics based function is implemented and the modeled accuracy is improved. The extrapolated results of the 4th and 8th order harmonics based functions are better than that of the broadcast ephemerides and the predicted parts of International GNSS Service (IGS) Ultra-Rapid (IGU) products. The performances of the modeled clocks in precise point positioning (PPP) show that the results of 4th and 8th order harmonics based functions reach centimeter level although their convergence times are slower than that of the IGS clock series product.

Machine learning enabled acoustic detection of sub-nanomolar concentration of trypsin and plasmin in solution

We demonstrate a machine learning enabled low-cost acoustic detection of protease which may find application in assuring quality and safety of dairy products, drug screening, molecular profiling, and disease diagnostics. A hydrophilic SiO2-coated quartz crystal microbalance (QCM) acts as a substrate to assemble α-, β-, and ĸ-casein layers (protease reporters) and as a transducer for measuring changes in frequency as casein is removed by protease. We demonstrate that α-, β-, and ĸ-caseins can form stable assembly on SiO2 from phosphate-buffered solution (PBS) solution. Exposure to protease results in cleaving of casein which changes the frequency of the 1st–11th odd harmonics of QCM. Monitoring β-casein cleavage allows ∼0.2 nM detection of trypsin and ∼0.5 nM detection of plasmin and enables differentiation between trypsin and plasmin after <2 min of protease exposure. The casein-coated QCM allows sub-nanomolar detection and classification of protease.

Detecting molecular changes in UV laser-ablated oil/diterpenoid resin coatings using micro-Raman spectroscopy and Laser Induced Fluorescence

Naturally occurring diterpenoid resins were extensively applied, mainly as oily mixtures, through the ages as protective and decorative coatings on paintings, metals and wood artifacts. When these coatings age, tend to generate tougher films than triterpenoid resins, completely insoluble, increasingly subject to darkening, and then very hard to remove using conventional methods. In this regards, laser sub-micrometric ablative techniques are being increasingly used in the cultural heritage field also for the treatment of synthetic and natural polymer coatings. Here, in the wake of the positive outcomes achieved on triterpenoid resin films, the present approach has been applied and extended to diterpenoid resin coatings, which have never been thoroughly studied yet. In detail, colophony, sandarac and Manila copal resin films, prepared as solvent and linseed oil formulations, were subject to light-ageing and then systematically irradiated at various exposure conditions using the 4th (266 nm) and 5th (213 nm) harmonics of a Q-Switched Nd:YAG laser. UV–Vis absorption spectroscopy was used as preliminary characterization of the films optical properties. The assessment of physico-chemical modifications induced by artificial light-ageing and ns UV laser irradiation were assessed non-invasively by μ-Raman spectroscopy, Laser Induced Fluorescence (LIF) and microscopic examination.The results underlined that, due to the presence of a polymer network, sandarac and copal resin coatings showed higher Fth than those composed of colophony. Morphologically, all the coatings were subject to bubbling upon 266 nm irradiation, while damage-free at 213 nm. At molecular level, irradiation at 266 nm produced minor changes to ν(CH3)/ν(CH2), ν(CO) and ν(CC) modes, thus confirming an ablation mechanism mainly driven by photo-thermal bond-breaking through the ejection of gaseous by-products. Raman background fluctuations along with shifting and broadening of LIF maxima were supportive in the assessment of laser-induced surface modifications. Finally, the work performed indicates that the 213 nm wavelength is the most indicated for the treatment of aged solvent and oil diterpenoid-based coatings, as no side effects occurred. This outcome, corroborated by the previous results obtained in triterpenoid resin films, may have important implications in the field of cultural heritage conservation, as it extends the application range of solid-state Nd:YAG lasers to all types of protective and decorative terpenoid coatings.

APPROACH TO DETERMINATION OF NO LOAD CURRENT OF THREE-PHASE POWER TRANSFORMERS WITH PLANE RODS MAGNETIC SYSTEMS

Purpose. Development a new effective approach for determining the open-circuited transformer parameters by implementing a combination of a schematic and spatial mathematical model of nonstationary electromagnetic fields in three-phase transformers, taking into account the constructive structure of the active part, the nonlinearity of the magnetic properties of electrical steels providing high accuracy and computational efficiency.Methods. The researches were carried out using the methods of the electromagnetic field theory, the theory of electrical circuits, the theory of power transformers, mathematical physics, the finite element method, regression analysis methods.Results. Theoretical researches of electromagnetic processes based on numerical realization of a three-dimensional mathematical model of a power three-phase transformer in open-circuited operation are carried out. An approach is proposed for improving the field simulation efficiency of the open-circuited operation, which consists in reducing the dimension of the computational domain and the transition to 2D models. It allow reducing the computing resources cost more than 2.8 times, time resources more than 250 times at a weighted average discrepancy of not more than 3.6%. The regularities of the distribution of flux density and the energy of the magnetic field for the active part of the transformer in open-circuited operation are determined. Their quantitative ratio value for the rods of different phases, which determining the ratio of the currents and resistances of the forward and reverse sequences of the transformer are calculated. A new approach to determine the open-circuited parameters of three-phase transformers with flat rod magnetic systems, based on the methods of circuit and 3D modeling, harmonic analysis and symmetrical components is realized. It characterized by high efficiency of numerical realization and accuracy for transient processes in switching moment of the three-phase transformer without loads. System of phase idle currents, characterized by non-sinusoidality and asymmetry, is proved. The harmonic composition of these currents is dominated by the 1st, 5th and 7th harmonics, but the first harmonic component predominates. The parameters of the forward and reverse sequence of the phases of the first harmonic for open-circuited operation, based on symmetrical components method were determinated. A corrective technique, which clarifies the traditional engineering approach, is proposed. The use of parameter correction for the researched ratios of the currents of the forward and reverse sequences will been increase the accuracy of calculation of the idle current by 12-14% and the idle losses by 9-11% in comparison with the generally known engineering design techniques.Originality. An approach is proposed for improving the efficiency of field simulation of the open-circuited operation, which consists in reducing the dimension of the computational domain and the transition to 2D models. A new approach of determination of the open-circuited parameters of three-phase transformers with flat rod magnetic systems based on the methods of circuit and 3D modeling, harmonic analysis and symmetrical components is realized. It characterized by high efficiency of numerical realization and accuracy for transient processes in switching moment of the three-phase transformer without loads.Practical value. The approaches and techniques allows to reduce the cost of computing resources by more than 2.8 times, time resources more than 250 times, with a weighted average discrepancy of not more than 3.6%, and increasing the accuracy of calculation of idle currents by 12-14% and losses of idling by 9-11% in comparison with the well-known engineering methods of designing.

The evolution of free and bound waves during dispersive focusing in a numerical and physical flume

Since the introduction of the NewWave theory (Lindgren, 1970), focused wave groups are used in physical and numerical studies to investigate the interaction of marine structures and ships with extreme waves. The propagation of such wave groups is associated with high order nonlinearities that can cause considerable deviations from linear and 2nd order predictions. Consequently, nonlinear numerical models or laboratory tests are needed to accurately describe the evolution of focused wave groups. In the present study, we validate a widely used two-phase Reynolds Averaged Navier-Stokes (RANS) solver realised in OpenFOAM with experimental results for the propagation of steep focused wave groups, using a newly developed methodology based on the separation of harmonics. This approach allows for accurate focusing of wave groups and in-detail examination of the individual evolution of the high order terms, as well as identifying the source of discrepancies between experiments and numerical models. The wave groups comprise long-crested broadbanded Gaussian spectra of increasing steepness propagating in intermediate water depth. The contribution of the nonlinear harmonics to the crest height and overall shape of the wave are also discussed, together with the effect of nonlinear wave interactions on the free-wave spectrum. The rapid growth of 3rd and 4th harmonics near focusing as well as the evolution of the free-wave spectrum, cause departures of up to 29% and 22% from analytic linear and 2nd order predictions. The present results demonstrate that RANS-VoF solvers constitute accurate models to propagate nearly breaking waves.

Vlasov simulations of electron acceleration by radio frequency heating near the upper hybrid layer

It is shown by using a combination of Vlasov and test particles simulations that the electron distribution function resulting from energization due to Upper Hybrid (UH) plasma turbulence depends critically on the closeness of the pump wave to the double resonance, defined as ω ≈ ωUH ≈ nωce, where n is an integer. For pump frequencies, away from the double resonance, the electron distribution function is very close to Maxwellian, while as the pump frequency approaches the double resonance, it develops a high energy tail. The simulations show turbulence involving coupling between Lower Hybrid (LH) and UH waves, followed by excitation of Electron Bernstein (EB) modes. For the particular case of a pump with frequency between n = 3 and n = 4, the EB modes cover the range from the first to the 5th mode. The simulations show that when the injected wave frequency is between the 3rd and 4th harmonics of the electron cyclotron frequency, bulk electron heating occurs due to the interaction between the electrons and large amplitude EB waves, primarily on the first EB branch leading to an essentially thermal distribution. On the other hand, when the frequency is slightly above the 4th electron cyclotron harmonic, the resonant interaction is predominantly due to the UH branch and leads to a further acceleration of high-velocity electrons and a distribution function with a suprathermal tail of energetic electrons. The results are consistent with ionospheric experiments and relevant to the production of Artificial Ionospheric Plasma Layers.

Cancellation of selected stator harmonics in BLDC by using an adaptive feedforward controller

This paper proposes an adaptive feedforward controller (AFC) for the cancellation of selected low order harmonics from the stator currents of a brushless DC motor (BLDC) with a non-sinusoidal flux distribution. Under proper tuning, the AFC can track selected harmonic orders of the motor back-EMF and counter-modulate the stator voltage to cancel the induced harmonic currents. The proposed AFC is combined with a field-oriented controller (FOC), which regulates the motor speed, in order to provide supplemental modulation action to the stator voltages at the selected harmonic frequencies. Experimental results are presented in the paper, where the AFC was designed to cancel the 5th and 7th harmonics. The results obtained verify the operation of the proposed controller and demonstrate its effectiveness in achieving significant improvement in the stator current waveform.

하이브리드 변압기의 2차측 위상각 변화에 따른 고조파 저감 효과 분석

The phase shifts in the Zig-Zag windings can be used in reducing the harmonic components. To obtain the optimum hybrid transformer design, it is required to analyze the harmonic reduction rate over phase shifts in Zig-Zag windings. The photovoltaic systems are used as a harmonic source in analyzing the harmonic reduction effects of the hybrid transformer. Each phase shifts in the secondary windings of the hybrid transformer is set to 15°, 30°, 45°, 60°. From the results, it was found that the reduction rates of the hybrid transformer has maximum values when the phase shifts is 60° and has minimum values when the phase shifts is 30°. By comparing the case of 60° phase shift with the 30° phase shift, it can be seen that the reduction rates in 5th, 7th, 11th, and 13th harmonics increases by 0.84%, 1.98%, 4.12%, and 5.9% respectively. It was also found that the reduction rates increases as the order of the harmonics increases.

Effect of Context on the Contribution of Individual Harmonics to Residue Pitch

There is evidence that the contribution of a given harmonic in a complex tone to residue pitch is influenced by the accuracy with which the frequency of that harmonic is encoded. The present study investigated whether listeners adjust the weights assigned to individual harmonics based on acquired knowledge of the reliability of the frequency estimates of those harmonics. In a two-interval forced-choice task, seven listeners indicated which of two 12-harmonic complex tones had the higher overall pitch. In context trials (60 % of all trials), the fundamental frequency (F0) was 200 Hz in one interval and 200 + ΔF0 Hz in the other. In different (blocked) conditions, either the 3rd or the 4th harmonic (plus the 7th, 9th, and 12th harmonics), were replaced by narrowband noises that were identical in the two intervals. Feedback was provided. In randomly interspersed test trials (40 % of all trials), the fundamental frequency was 200 + ΔF0/2 Hz in both intervals; in the second interval, either the third or the fourth harmonic was shifted slightly up or down in frequency with equal probability. There were no narrowband noises. Feedback was not provided. The results showed that substitution of a harmonic by noise in context trials reduced the contribution of that harmonic to pitch judgements in the test trials by a small but significant amount. This is consistent with the notion that listeners give smaller weight to a harmonic or frequency region when they have learned that this frequency region does not provide reliable information for a given task.

Experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum tube

We report the experimental demonstration of a 5th harmonic mm-wave frequency multiplying vacuum electronic device, which uses an over-moded spherical sector output cavity. In this device, a pencil electron beam is helically deflected in a transverse deflecting cavity before entering the output cavity. No magnetic field is required to focus or guide the beam. We built and tested a proof-of-principle device with an output frequency of 57.12 GHz. The measured peak power was 52.67 W at the 5th harmonic of the drive frequency. Power at the 4th, 6th, and 7th harmonics was 33.28 dB lower than that at the 5th harmonic.

Effects of square-wave magnetic fields on synchronization of nonlinear spin precession for sensitivity improvement of MX magnetometers

Optically pumped atomic magnetometers have found widespread application in biomagnetic studies. Most of the studies utilize MX gradiometers as sensitive and simple arrangements. One the sensitivity improvement methods in the MX configurations is detection of magnetic resonance at higher harmonics due to nonlinear precession of spin polarization. To enhance the harmonic components, we have proposed square wave RF magnetic fields with various duty cycles as substitute for sinusoidal fields. Our results revealed that detection of the 5th harmonic of a 10% duty cycle square wave magnetic field, improved the magnetometer sensitivity by a factor of 4.5 respect to the first harmonic which could be a reliable option to generate high sensitivity MX magnetometers in the MCG applications.

Harmonic dissipative soliton resonance square pulses in an anomalous dispersion passively mode-locked fiber ring laser

We demonstrate the generation of dissipative soliton resonance square pulses from a co-doped Er:Yb double-clad fiber ring laser operating in an all anomalous dispersion regime. The obtained pulses have a repetition rate of 672 kHz and a pulse energy of 409 nJ. By carefully adjusting the polarization controllers while increasing the pump power, the square pulse can split into a series of identical equally spaced smaller square pulses up to the 13th harmonic of the fundamental repetition frequency. The average output energy of the square pulses follows a scaling law versus the harmonic order.

A Wilkinson Power Divider with Harmonics Suppression and Size Reduction Using Meandered Compact Microstrip Resonating Cells

AbstractIn this paper, a novel compact Wilkinson power divider with harmonics suppression using meandered compact microstrip resonating cells (MCMRC) at 2 GHz is proposed. In the design structure an open stub is used to suppress 2nd harmonic and two proposed MCMRC units are inserted into quarter wavelength lines of the conventional power divider to suppress 3rd–7th harmonics. The proposed power divider reduces the size over 65 % compare to the conventional one and impressively suppresses the harmonics (2nd–7th) with high level of attenuation. The proposed resonator and power divider are fabricated and measured. The measured and simulated results are in good agreements. The overall dimensions of the resonators and proposed power divider are only about 1.56 mm×9.2 mm (0.013 λg×0.08 λg) and 9.1 mm×13.1 mm (0.08 λg×0.11 λg) respectively.‎

Control of a Uniform Step Asymmetrical 13-Level Inverter Using Particle Swarm Optimization

Harmonic Elimination Strategy (HES) has been a widely researched alternative to traditional PWM techniques. This paper presents the harmonic elimination strategy of a Uniform Step Asymmetrical Multilevel Inverter (USAMI) using Particle Swarm Optimization (PSO) which eliminates specified higher order harmonics while maintaining the required fundamental voltage. This method can be applied to USAMI with any number of levels. As an example, in this paper a 13-level USAMI is considered and the optimum switching angles are calculated to eliminate the 5th, 7th, 11th, 13th and 17th harmonics. The HES-PSO approach is compared to the well-known Sinusoidal Pulse-Width Modulation (SPWM) strategy. Simulation results demonstrate the better performances and technical advantages of the HES-PSO controller in feeding an asynchronous machine. Indeed, the harmonic distortions are efficiently cancelled providing thus an optimized control signal for the asynchronous machine. Moreover, the technique presented here substantially reduces the torque undulations.