Specific Harmonic Order Research Articles

All-optical spatiotemporal phase-matching of high harmonic generation using a traveling-grating pump field

We demonstrate spatiotemporal phase-matching of high harmonic generation both theoretically and experimentally utilizing a pump field in the form of a traveling intensity grating. Such an arrangement has the potential to enable selective enhancement of specific harmonic orders while fine-tuning their frequency by controlling the spatial and temporal parameters of the pump.

Vibration Suppression of a Specific Harmonic Component by Teeth Flux Density Control Using Multi-Phase MATRIX Motor

In recent years, progress in power semiconductor switching devices has created more additional advantages that can be realized using multi-phase inverter-fed motors. The authors propose a MATRIX motor to realize electric motors with higher functionalities than conventional electric motors. Since the MATRIX motor is driven by H-bride inverters connected with each phase winding, it has a high degree of freedom in control. Moreover, these inverters can change their connections to different phase coils to realize a wide operating range. The voltage equation of each mode can be expressed using the transformation matrix when the winding connection is changed. Therefore, we call the proposed motor MATRIX motor. In addition, since motors are being applied to various applications that operate within proximity of people, further quietness of the motor is required. In this paper, we propose a method to suppress vibration caused by a specific harmonic order radial direction electromagnetic force via teeth flux density control using the MATRIX motor. The specific order radial force and vibration are suppressed by utilizing two features of the MATRIX motor. One is a high degree of freedom of current control owing to multi-phase drive and the other is local flux density observation. The effectiveness of the proposed method was clarified using experimental results.

High-Intensity Harmonic Generation with Energy Tunability Produced by Robust Two-Color Linearly Polarized Laser Fields

By using the numerical solution of the time-dependent Schrödinger equation, we theoretically explored the high-order harmonic generation process under the interaction of high-intensity two-color ultrashort driving laser pulses with atoms. The symmetry of the electric field of the laser pulse will be broken. The producing electric field was controlled at the subcycle level by an IR laser and its second harmonic, which has the unique characteristic that two sequential half-cycles become distinct, rather than merely opposite in sign. Compared with the case of the atom in the fundamental laser pulse, the harmonic efficiency showed an increase of 1∼2 orders of magnitude at specific harmonic order with this combined pulse action. Through the theoretical analysis with the “three-step model”, it was demonstrated that the enhancement of the harmonic intensity is due to the fast ionization of electrons at the ionization moment and the short time from ionization to recombination of ionized electrons. In addition, effects of the peak field amplitude ratio, the full width at half maximum, the phase delay of the two-color pulses, the laser intensity and ionization probability on the harmonic efficiency enhancement were also investigated.

Adaptive Polynomial Harmonic Distortion Compensation in Current and Voltage Transformers Through Iteratively Updated QR Factorization

Measuring current and voltage harmonics has paramount importance for improving the power quality of distribution grids. However, the achieved accuracy strongly depends on the adopted instrument transformer. The present paper proposes an adaptive technique that enables an effective compensation of both the filtering behavior and the harmonic distortion introduced by current and voltage transformers, namely the strongest nonlinear effect at low-order harmonics. The approach is based on a flexible, linear in the parameters polynomial modeling of harmonic distortion in the frequency domain. Model complexity can be different from one harmonic to the other, and it is selected through an automatic iterative process to suit the nonlinear behavior at each specific harmonic order, while avoiding overfitting. In particular, the number of parameters is increased by progressively updating the QR factorization of the regressor matrix trough Householder reflections, until a convergence condition is reached. Experimental tests performed on an inductive VT and CT highlight the effectiveness of the approach.

A synchronization technique for single-phase grid applications

The utility grid disturbances like dc offset and harmonic components can severely affect the estimated variables from the phase-locked loop (PLL), resulting in poor performance of the system relying on it. Therefore, there is an emerging need for well-designed PLL algorithms ensuring robust response against different operating conditions. This paper proposes a simple single-phase PLL algorithm with inherent dc offset and specific harmonic orders rejection capability. Utilizing adaptive time-delay fictitious signal generation. A full mathematical model of the proposed PLL has been provided. The proposed PLL is compared with other filter-based single-phase PLLs, to validate its simplicity and excellent performance.

Investigation and Analysis of Novel Skewing in a 140 kW Traction Motor of Railway Cars That Accommodate Limited Inverter Switching Frequency and Totally Enclosed Cooling System

This study facilitated the improvement of no-load back electromotive force (back-EMF) wave form, total harmonic distortion (THD) of back-EMF, and torque ripple using a novel skew angle formula, considering the specific order of a no-load THD. In real usage environments, it is taken into consideration for the fully enclosed cooling system and limited inverter switching frequency of urban railway car traction motors. Since the most railway car traction motors use high-withstand voltage rectangular wires in slot-open structure, a no-load back EMF waveform includes large space slot harmonics, which should be smaller as possible. For 6-step control, the no-load back EMF waveform is important because switching for motor control is performed once after the rotor position is determined. To improve the no-load back EMF waveform and THD, two-dimensional and three-dimensional finite element analysis (FEA) were performed using a novel skew angle formula considering specific harmonic order reduction, while the fundamental amplitude was minimally reduced. A prototype with the novel skew was fabricated and verified. In addition, it was designed by calculating a low current density for a fully enclosed cooling system. A temperature saturation experiment was also performed, and successfully verified. Therefore, we suggest that the no-load back EMF characteristics and torque ripple are improved by applying the novel skew angle instead of a traditional skew angle.

A model for calculating losses in transformer related to orders and harmonic amplitude under analysis of joule effect, eddy current and hysteresis

AbstractThe electrical transformer is one of the most used equipment in electrical power systems. The non-linear electrical loads are increasing, mainly in the electrical distribution system, and the electrical power transformer is inserted in this scenario, supplying these loads. Consequently, the increasing non-linear loads affect the electrical transformers and their factors directly, like in the dependency between temperature and harmonic increase. Therefore, to study the influence of harmonics in the transformer’s temperature, one should understand how it will behave with these changes in the electrical power system. For this reason, in this article, numeric simulations and tests were performed to predict the transformer temperature behavior. The proposal is a numeric technique for coupling two equations, thermal and electromagnetic, of an electrical transformer, considering heat sources regarding joule, eddy current, and hysteresis effect. To evaluate the numeric simulation and understanding the electrical transformer behavior in real-life, tests with specific harmonic orders (3rd, 5th, and 7th) and their combinations and a test with less than 10% total harmonic distortion, according to IEEE 519 standard were performed. It is verified that the electrical transformer temperature rises with the increase in harmonic amplitude and its orders. Results show that the industry must be aware of the effects of the increasing non-linear loads when designing the next generation of transformers concerning their durability and lifetime.

Improved Model Predictive Control for High-Power Current-Source Rectifiers Under Normal and Distorted Grid Conditions

This article proposes an improved model predictive control (MPC) method for high-power current-source rectifiers (CSR). Instead of introducing the virtual impedance based active damping notion into MPC framework, the predefined cost function directly takes grid-side current and capacitor voltage as the regulating objectives to suppress the $LC$ resonance and grid current distortions. The relationship and differences between the proposed cost function and its form with active damping function are analyzed in detail under normal grid conditions. Moreover, the number of discrete candidate vectors during each predictive horizon in the proposed scheme is reduced from nine to five by considering the constraint of switching states transition. Therefore the computational burden is relieved compared with conventional MPC under normal grid conditions. Finally, in order to keep sinusoidal grid current for CSR even working under severe distorted supply voltage, specific harmonic orders of grid current suppression items are added into the proposed cost function subsequently. The performance of proposed methods at low switching frequency ( $\leq$ 1 kHz) under normal and distorted grid conditions are tested through both simulation and experiments. For the implementation of all MPC methods, capacitor voltage is estimated by an observer to save hardware expense instead of using transducers.

Designing Passive Harmonic Filter on Dynamic Positioning Vessel's Electrical System Affected using Electrical Thruster

Ship with a dynamic positioning system has the ability to maintain her position dynamically. To be able to maintain the position, generally, ship with a dynamic positioning system have several thrusters located at bow or stern of the ship. Based on the propulsion system, there are 2 types of thruster which are mechanical thruster and electrical thruster. In electrical type, the thruster is driven by an electric motor supplied from the generator. In addition, on dynamic positioning vessel equipped with the electrical thruster, there are also VFD or Variable Frequency Drive to control the speed of motor thruster. The use of VFD components in the system may cause harmonic interference. Harmonic itself can be regarded as distortion in the sinusoidal waves due to the interference of other waves that have integer frequency multiples of their fundamental frequency due to the operation of non-linear thruster motor. Some of the most affected components of this distortion are the communications equipment and the components used for measurement. This research conducted an analysis of harmonic disturbance arising from the operation of 2 units bow thruster on DP Ship by simulating 6 scenarios of generator configuration using simulation software . The results from this research were total harmonic distortion value or VTHD of the system that complies with standards and rules, also the specification of a passive harmonic filter to reduce the VTHD value at the specific harmonic order.

Designing Passive Harmonic Filter of Electric Propulsion System on Tanker Ship

Harmonic is a frequency defect that have some negative effect to the electrical network system. In a ship, electrical network system are interconnected to each other to another electrical consumer device. The effect will impact all the device that connected to the electrical network system. This can be reducing the consumer devices reliability. This research analyzed and simulate the effect of harmonic when there is no harmonic filter condition and with a passive harmonic filter for each operating condition on this ship. This research also includes the comparison diagram between no filter and with a passive harmonic filter condition, and some simulation report from the software. The research results were VTHD value are need to be comply with the classification standards and rules. Passive harmonic filter can reduce the VTHD value by reducing a specific harmonic order and the impact from reducing specific harmonic order can reduce the other harmonic order. Besides that, passive harmonic filter also can gain a higher power factor (PF) value

Mechanism of equivalent electric dipole oscillation for high-order harmonic generation from grating-structured solid-surface by femtosecond laser pulse

We theoretically study high-order harmonic generation (HHG) from relativistically driven overdense plasma targets with rectangularly grating-structured surfaces by femtosecond laser pulses. Our particle-in-cell (PIC) simulations show that, under the conditions of low laser intensity and plasma density, the harmonics emit principally along small angles deviating from the target surface. Further investigation of the surface electron dynamics reveals that the electron bunches are formed by the interaction between the laser field and the target surface, giving rise to the oscillation of equivalent electric-dipole (OEED), which enhances specific harmonic orders. Our work helps understand the mechanism of harmonic emissions from grating targets and the distinction from the planar harmonic scheme.

Optimal-control theory of harmonic generation

Coherent control of harmonic generation was studied theoretically. A specific harmonic order was targeted. An optimal control theory was employed to find the driving field where restrictions were imposed on the frequency band. Additional restrictions were added to suppress undesired outcomes such as ionization and dissociation. The method was formulated in the frequency domain. An update procedure for the field based on relaxation was employed. The method was tested on several examples demonstrating generation of high frequencies from a driving field with a restricted frequency band.

Parallel-Connected Shunt Hybrid Active Power Filters Operating at Different Switching Frequencies for Improved Performance

This paper proposes a combination of low- and high-frequency hybrid active power filter (APF) to operate in parallel for better performance. The individual hybrid APF is a series combination of L-C filter with the corresponding voltage source inverter. The dc links of both the inverters are connected in parallel, and the voltage of the dc link is maintained by the low-frequency inverter (LFI). The low- and high-frequency inverters eliminate lower order and higher order harmonics, respectively. In addition, it is possible to design the LFI such that it can also compensate the reactive power of the load. The individual L-C filter of the hybrid topology is designed to take care of specific order of harmonics that are predominant in the load. A combination of feedforward and feedback controller is designed for the proposed conditioner. The performances of the proposed topology and the controller are first examined by MATLAB/SIMULINK-based simulation. An experimental prototype is also designed to confirm the usefulness of the proposed system.

Vibration Analysis and Measurements Through Prediction of Electromagnetic Vibration Sources of Permanent Magnet Synchronous Motor Based on Analytical Magnetic Field Calculations

This study is devoted to the analysis of the vibration characteristics of a permanent magnet synchronous motor (PMSM) through investigation into its electromagnetic vibration sources. For this purposed, we derive analytical solutions for the magnetic fields generated by permanent magnets (PMs) in terms of a magnetic vector potential and a two-dimensional (2-D) polar coordinate system. A 2-D permeance function is also introduced in order to consider slotting effects. The electromagnetic vibration sources such as torque ripple, cogging torque, and radial force density are analyzed using these solutions. The analytical results are validated extensively with finite element (FE) analyses. The fast Fourier transformation (FFT) analysis is employed for investigating the specific harmonic orders of the electromagnetic vibration sources that affect the vibration of the PMSM. Finally, mechanical modal analysis results and test results such as vibration measurements are obtained to confirm the validity of the analysis methods presented in this paper.

Harmonic compensation of a six-pulse current source controlled converter using neural network-based shunt active power filter

Active power filter (APF) performance is affected by the system delay introduced in the reference signals and/or the actual injected current. This study introduces an artificial intelligent-based technique using a neural network control strategy for a shunt APF. The proposed system is capable of mitigating specific harmonic orders and consequently achieves low harmonic factor and reduced current total harmonic distortion (THD). In addition, the delay time introduced when extracting the harmonic reference current and when controlling the filter current is minimised. The control technique presented in this study is assessed on a medium voltage 6-pulse current source converter where the mains current dominant harmonics (5th, 7th, 11th and 13th) are compensated. The proposed system is simulated using MATLAB/SIMULINK. A prototype system is used to experimentally validate the proposed APF performance.

Multilevel inverter using cascaded 3-phase transformers with common-arm configuration

In multilevel inverter development for 3-phase applications, total number of transformer in the circuit can be reduced by using of cascaded 3-phase transformer circuit instead of single-phase transformer circuit. In the scheme, total number of switching components in the circuit is still a drawback to achieve lower cost and smaller size of the inverter compared with conventional multilevel inverter. This paper includes a challenging method to reduce total switching components in the multilevel inverter by adopting common-arm structure. The proposed inverter has been operated by two control schemes, Newton–Raphson and Equal-area method. After theoretical and experimental comparison of the methods, we found that Newton–Raphson method is useful to eliminate a specific harmonic order. However, the method has a shortcoming in real time operation which is performed by iterative calculation of the nonlinear equations. With Equal-area method, we can easily find the switching angles by calculating a trigonometric function. It can sufficiently minimize Total Harmonic Distortion (THD) of output voltage in real time operation of Digital Signal Processor (DSP).

Comparative analysis of the high-order harmonic generation in the laser ablation plasmas prepared on the surfaces of complex and atomic targets

We analyzed high-order harmonic generation from the plasma plumes prepared on the surfaces of complex targets. The studies of In-Ag targets showed that the characteristics of the high-order harmonics from the double-target plume were the same as those from the single-target plasmas. For the chromium-tellurium plasma, the enhancements of the 29th and 27th harmonics were obtained, thus indicating the appearance of the enhancement properties from both components of the double-target plasma. These comparative studies also showed higher enhancement of a single harmonic in the case of atomic plasma (Sb) with regard to the molecular one (InSb). The additional component can only decrease the enhancement factor of the medium, due to the change of the oscillator strength and spectral distribution of the transitions involved in the resonance enhancement of the specific harmonic order. The theoretical calculations have shown the enhancement of specific harmonics for the Sb, Te, and Cr plasmas in the double-target configurations.

Phase-matching control of high-order harmonic generation in a two-color laser field

The phase-matching condition of high-order harmonic generation driven by intense few-cycle pulses could be controlled by adding second-harmonic pulses to change the ionization fraction of the gaseous medium. The harmonic generation efficiency could be improved by moving the phase-matching point with an all-optical control of the ionization fraction or a proper change of the confocal parameter. A specific order of harmonics could be easily controlled to reach phase matching at a fixed higher gas pressure by adding second-harmonic pulses with a suitable intensity. Such an all-optical phase-matching control was demonstrated to be dependent upon the temporal delay between the fundamental-wave and second harmonic pulses.

A novel-type tunable and narrowband extreme ultraviolet radiation source based on high-harmonic conversion of picosecond laser pulses

At the Laser Centre Vrije Universiteit a table-top size, tunable and narrowband laser-based source of extreme ultraviolet radiation was developed using high-harmonic generation of powerful laser pulses of 300 ps duration and Fourier-transform limited bandwidth. The generated radiation has unprecedented spectral purity of λ / Δ λ > 2.5 × 1 0 5 at wavelengths covering the entire tunability range of 40–100 nm. The process of high-order harmonic generation was investigated in different gases (Ar, Kr, Xe, N 2) uncovering resonance phenomena for the conversion efficiency of specific harmonic orders.

Design of an extreme-ultraviolet monochromator free from temporal stretching.

High-order harmonic generation in gases by use of femtosecond lasers is a source of ultrashort pulses in the extreme-ultraviolet (XUV). For many applications it is necessary to select radiation of only one specific harmonic order without affecting the duration of the ultrashort pulse. A three-grating monochromator that meets this demand has been designed and modeled by ray tracing as well as by wave-optical simulations. The only remaining temporal stretching of an XUV pulse is due to distortion of the pulse front on the gratings and is predicted to be approximately 1 fs. The design has been successfully tested in the near infrared. Finally, the monochromator is also capable of eliminating any existing linear chirp in the harmonic pulses, thus compressing them to shorter durations.