Harmonic Amplification Research Articles

Research on active filter control strategy for 5th background harmonic amplification at Jinhua station

Research on active filter control strategy for 5th background harmonic amplification at Jinhua station

Analysis of active impedance characteristics and harmonic deterioration of multiple grid connected inverters considering nonlinear factors

AbstractThe harmonic problems caused by non‐linear factors of the grid connected inverter (GCI) system are more complicated, including both non‐characteristic harmonics emitted by the dead‐time and the changes in harmonic impedance characteristics. Harmonics interact with the changing impedance, and even cause harmonic amplification and resonance. The harmonic deterioration of the multiple GCIs system is serious. To analyse the mechanism and way of harmonic deterioration in grid‐connected system caused by nonlinear factors, the active impedance models of single inverter and multiple GCIs system including dead‐time effect and digital control delay are established first. In view of this, the influence mechanism of non‐linear factors on system stability is explored. The improved modal analysis method is used to traverse the network series parallel resonance caused by nonlinear factors. The results show that both the dead‐time effect and digital control delay reduce phase margin of the system, resulting in the resonant frequency shift and the resonant peak increase. When the harmonic excitation source interacts with the complex network under the influence of nonlinear factors, it will lead to further deterioration of harmonics. Finally, based on the MATLAB and RT‐LAB hardware‐in‐the‐loop simulation platforms, a multiple GCIs system model is built to verify the correctness of the established active impedance model and harmonic deterioration analysis.

An improved derivative‐based phase‐locked loop for single‐phase grid synchronization under abnormal grid conditions

SummaryGenerating a quadrature signal in a single‐phase system using a second‐order generalized integrator (SOGI) requires accurate frequency information. The standard SOGI phase‐locked loop (PLL) includes frequency feedback to the SOGI. However, during grid abnormalities such as voltage sag/swell and phase angle jumps, the SOGI‐PLL faces frequency disturbances that propagate to the phase detector (PD) and affects the quadrature signal generator (QSG). Furthermore, the SOGI‐PLL having two loops dependent on each other creates loop coupling phenomena; either a change in phase or frequency affects each other. SOGI‐PLL is tuning sensitive, as the SOGI block has a gain that needs to be adjusted, increases the complexity, and affects the performance of the system. There is a trade‐off between SOGI gain and PLL parameters that needs to be considered for adequate parameter design to provide accurate grid synchronization while maintaining the stability of the system. To attain better performance, researchers have proposed derivative‐based PLL (DPLL). The conventional DPLL faces challenges to noise and harmonics amplification. This paper presents an improved DPLL for single‐phase grid synchronization under adverse grid conditions. The improved derivative‐based PLL (IDPLL) comprises two improved derivative‐based quadrature signal generator (IDQSG) blocks to extract the phase‐error information for accurately estimating phase and frequency. The detailed mathematical modeling and bode plot for the IDQSG and IDPLL are presented. The proposed IDQSG eliminates the requirement of gain tuning, hence reducing complexity. Moreover, there is no interdependent loop in the IDPLL, which significantly improves the dynamic performance. A hardware setup is developed to evaluate the performance of the system in real‐time. The experimental results are obtained using an field programmable gate array (FPGA)‐based controller.

Active filter parameter tuning method for harmonic voltage mitigation in wind power plants

It is challenging to determine the active filter control factors in wind power plants (WPP) to obtain effective harmonic voltage mitigation and avoid over-modulation or system instability problems caused by overlarge feedforward or feedback gains. To address this issue, an active filter tuning (AFT) method is proposed in this paper to offer a common parameter tuning and stability assessment strategy for both current-controlled and voltage-controlled harmonic impedance reshaping (HIR) methods by introducing a coordination factor including different weight coefficients for system stability margin, wind turbine (WT) harmonic suppression, and grid harmonic mitigation. The superiority of the proposed method is verified in a 20 MW WPP with four cases considering both WT harmonic voltage amplification and grid voltage amplification. Compared to previous methods, the AFT-based HIR method achieves a more flexible balance between system stability and harmonic voltage mitigation, obtaining better performance in WT harmonic suppression, grid harmonic suppression, system robustness, and transient response.

Self-enhanced coherent harmonic amplification in seeded free-electron lasers

High-intensity, ultrashort, fully coherent X-ray pulses hold great potential for advancing spectroscopic techniques to unprecedented levels. Here, we propose a novel scheme for generating high-brightness and femtosecond-scale soft X-ray radiation within a seeded free-electron laser (FEL) operating at MHz repetition rates. This scheme relies on the principles of self-modulation and superradiance. A relatively weak energy modulation of the pre-bunched electron beam is significantly amplified by the coherent radiation emitted in the self-modulator. Consequently, a coherent signal at ultra-high harmonics of the seed is achieved, and this signal is further amplified in the subsequent radiator through the fresh bunch and superradiant processes. Based on the parameters of the Shanghai soft X-ray FEL facility, three-dimensional simulations have been performed. The simulation results demonstrate that an electron beam with a laser-induced energy modulation as small as 2.3 times the slice energy spread can generate ultrashort coherent radiation pulses of around 2 GW within the water window spectral range. Moreover, the experimental results demonstrate that self-enhanced coherent energy modulation enables the production of coherent signals up to the 15th harmonic of a 266-nm seed laser. These findings indicate that the proposed scheme promises to generate ultrashort and coherent soft X-ray pulses at MHz repetition rates.

Converter induced resonances in microgrids due to high harmonic distortion

This paper describes the resonance introduced by harmonics amplification and adverse interaction of electronic converters. An observation of undamped oscillation leading to instability in a microgrid is described. The term “converter induced resonances” is proposed to describe this phenomenon. The amount of distributed generation, active loads, FACTS and battery energy storage systems are expected to increase in future Smart Grids. All these resources will be interfaced with electronic converters. The potential impact of converter induced resonances in such grids is described. A coordinated design of the control systems of all converters is in practice not feasible. Each device will be independently tested to fulfil grid codes and have its own converter control implemented that can include functionality to modify voltage and /or current waveform.

A novel programmed hybrid modulation for electromagnetic interference mitigation and current ripple control in miniaturised synchronous machine drives

AbstractA novel programmed hybrid spreading spectrum modulation method to mitigate electromagnetic interference (EMI) emission and bearing current in the context of miniaturised and lightweight synchronous machine drives is proposed. The proposed method adopts the combination of conventional pulsewidth modulation (PWM) and low common mode voltage PWM. The offline look‐up table for switching frequency is acquired by analysing the root mean square voltage values at different modulation indices and angles. By adjusting the switching frequency according to this table, the spectrum can be spread into the sidebands of the switching frequency, and the harmonic spike can be suppressed. To address the challenge of increased current ripple and harmonic distortion in high torque density motors under overload conditions, a motor model that considers the cross‐saturation and slotting effect is presented. This motor model is used to derive the switching frequency correction factors, aiming to mitigate the influence of saturation and slotting effect on harmonic amplification. The proposed method is well‐suited for controlling synchronous motors using three‐phase two‐level voltage source inverters. The simulation and experimental results validate the effectiveness of the proposed method, showcasing its advantages in terms of computational complexity reduction and significant attenuation of peak EMI currents.

Network impedance reconstruction method for high-frequency resonance mitigation in cabled distribution systems

The increasing proportion of cables and power electronic equipment leads to frequent high-frequency resonance in distribution systems. To address this issue, this paper proposes a network impedance reconstruction method for high-frequency resonance mitigation. The main contributions and improvements of this study include: (i) introducing a passive damping scheme from the network side to achieve resonance mitigation by reconstructing the utility impedance characteristics and disrupting the network parameter conditions, (ii) establishing multiple assessment criteria of the network side, such as the harmonic current amplification factor, Bode plot of the system function, and root locus, to comprehensively evaluate the efficacy of resonance mitigation, and (iii) presenting several technical and economic indexes for the multi-objective optimization of passive damping parameters to promote the resonance mitigation effect. Moreover, the performance of the proposed method is verified by a field case study of an industrial park distribution system. The results demonstrate that the proposed method enables the resonance frequency shift and resonance peak reduction, thereby effectively mitigating high-frequency resonance.

Tubular cubic polynomial sonotrode for green and sustainable ultrasonic welding technology

Ultrasonic Welding has emerged as a sustainable, green, and efficient manufacturing technology. This technique joins unique and advanced materials quickly, with good welding quality through high-intensity vibrations. Ultrasonic welding uses relatively low energy and incurs lower costs compared to various conventional welding systems. One of the key aspects to ensure high welding quality and strength, along with the transmission of high forces, is the design of an efficient ultrasonic sonotrode. This research study is aimed at proposing, evaluating, and testing the design of a tubular cubic polynomial sonotrode using finite element analysis. This novel ultrasonic welding sonotrode operates with low stresses and high displacement amplification. The performance of the proposed ultrasonic welding sonotrode design was compared with the commercially popular sonotrode, as well as cubic Bezier, exponential, and conical designs. This comparison was done in terms of harmonic excitation response, stresses, axial stiffness, displacement amplification, and factor of safety. The performance characteristics were also evaluated along the sonotrode length. The proposed sonotrode was found to be superior in terms of high vibration amplification and axial stiffness within safe stress limits. The benefits of the flexible design as per requirement to attain a higher displacement amplitude at the output end; consequently, lower welding forces were also realized. The proposed design is an improvement towards an efficient and green manufacturing technology involving reduced cost, energy consumption, use of consumables, effort, waste generation, and harm to the environment.

Quantitative Harmonic Amplification Analysis in Electric Railway Traction Power Supply Systems

Background: Harmonic resonance is one of the apprehensive power quality problems in electric railway traction power supply systems. Harmonic resonances result in big harmonic voltage distortions or harmonic currents. Different harmonic resonance frequencies existing in a power system possess varying propagation areas and amplification levels. The frequency scan analysis technique and the resonance mode analysis technique are the two most commonly used methods. The frequency scan analysis technique can reveal whether resonance exists and determine the resonance frequency. Resonance mode analysis technique can further identify the location where a resonance can be most easily initiatedand observed. However, there are still few studies on the quantitative analysis of harmonic propagation and resonance amplification in traction power supply systems. Methods: The model of the all-parallel autotransformer-fed system in the high-speed railway is built accurately, then a quantitative analysis method based on harmonic electrical distance is used to study the harmonic propagation characteristics and propagation severities caused by electric trains, and analyses in detail the influence of the number of lines, the number of trains, and the location of the train on the severity of resonance amplification. Results: The results of case studies reveal the traction power supply system harmonic propagation characteristics and amplification severities and system parameter sensitivities in a quantitative way, validating the effectiveness and superiority of the quantitative analysis method. Conclusion: Compared with the resonance mode analysis method and the frequency scan analysis method, at a harmonic resonance frequency point, the quantitative analysis method can quantitatively reveal the harmonic propagation area and amplification level at each bus of the traction power supply system. Meanwhile, it is simple and practical.

Research on Step-down Resonance Suppression and Filtering Device

In recent years, offshore wind farms have developed rapidly, and their installed capacity is getting bigger and bigger, and the offshore distance is getting farther and farther. In order to meet the needs of large-capacity and long-distance offshore wind power transmission, the AC submarine cable has the characteristics of long distance, high voltage and large cross-section. Along with the significantly improved transmission capacity, its equivalent capacitance is also increasing, which further reduces the resonance frequency of the offshore wind power AC transmission system. If the parallel resonance frequency of the offshore wind power transmission system is close to the main harmonic current frequency band of wind turbines, it will cause harmful system resonance and harmonic amplification, significantly increasing the harmonic current of grid-connected lines and the voltage distortion rate of nodes in nearby power grids, and seriously affect the safety of equipment and the safe and stable operation of offshore wind power transmission system. A step-down resonance suppression filtering device applied to the offshore wind power transmission system is proposed. The AC cable is connected to the low-voltage 35 kV side of the compensation winding of the centralized control center to eliminate the resonance risk of the 220 kV system and filter out the harmonic current. Compared with the existing technical scheme, the device has the advantages of simple control, reliable operation, stable resonance suppression effect, low operation loss and the like, and has great engineering popularization value.

Research on harmonic resonant fault mechanism and suppression measures of oilfield power grid based on fast mode analysis method

In recent years, with the use of electric drilling rig, electric fracturing pump, and other equipment, the harmonic resonance problem of oilfield power grid is becoming more and more serious. In view of the high time and space complexity and long calculation time of the traditional harmonic resonance analysis method, the improved power iteration method is combined with the traditional modal analysis method, and the harmonic resonance problem of the oilfield power grid is analyzed by the fast modal analysis method. At the same time, a new set of harmonic resonance amplification index is derived and verified, and the harmonic content amplification times in the resonant influence region and different busbars are revealed. And then a passive filter is used to suppress harmonic resonance, and the effectiveness of the scheme is verified by field tests. The results show that, in the frequency range of 0–1000 Hz, the resonant frequency points in the oil field are mainly related to the rectifier pulse number of the drilling rig and the frequency conversion device for fracturing. The proposed fast modal analysis method has the advantages of fast convergence speed and memory saving, which is helpful to accurately detect the harmonic resonance region caused by the multi-pulse frequency conversion device, and the harmonic resonance can be effectively suppressed by installing a filter at the main excitation bus of the resonant frequency.

Role of Gas Pressure in Quasi-Phase Matching in High Harmonics Driven by Two-Color Laser Field

The results of a study on the effect of pressure in a medium consisting of a set of gas jets separated by vacuum gaps, interacting with two-color laser fields formed by the fundamental and the second harmonics of a laser, are presented herein. It has been demonstrated that a decrease in pressure leads to a shift in the region of harmonics where quasi-phase matching (QPM) occurs towards shorter wavelength radiation, accompanied by an increase in the efficiency of amplification of these harmonics. A feature of this process is the identical power-law character of the shift in the region and the increase in the efficiency of harmonic QPM amplification. Additionally, the study presents the results of the effect of inaccurately setting the width of the gas jets on the shape of the spectrum of harmonic QPM amplification.

Parameter analysis on the harmonic amplification for offshore wind power plants: A case study in the Netherlands

Parameter analysis on the harmonic amplification for offshore wind power plants: A case study in the Netherlands

Amplification and ellipticity enhancement of high-order harmonics in a neonlike x-ray laser dressed by an IR field

In Khairulin et al. [Sci. Rep. 12, 6204 (2022)] we proposed a method for amplifying a train of sub-femtosecond pulses of circularly or elliptically polarized extreme ultraviolet radiation, composed by high-order harmonics of an infrared (IR) laser field, in a neonlike active medium of a plasma-based x-ray laser, additionally irradiated with a replica of a fundamental frequency laser field used to generate harmonics. Here we present the analytical theory and numerical study of an amplification process of an individual harmonic with either preservation of its polarization state or ellipticity enhancement. We also analyze in detail the spectral-temporal and polarization properties of a sub-femtosecond pulse train formed by a set of elliptically or circularly polarized harmonics during the propagation through the medium. We discuss also the possibility of an experimental implementation of the suggested technique in an active medium of an x-ray laser based on neonlike ${\mathrm{Ti}}^{12+}$ ions irradiated by an IR laser field with a wavelength of 3.2 \textmu{}m.

Research on A Fast Recognition System for Abnormal Harmonic Amplification Caused by Centralized Connection of Multiple Wind Power Plants

This paper introduces the abnormal harmonic current amplification phenomenon that occurred in the electric transmission lines, which is caused by the centralized join-up of multiple wind farm plants, by collecting and analysing the voltage, current, and active power indicators data of harmonic amplification phenomenon, to realize the classification and statistics of abnormal indexes variation trend during the harmonic amplification phenomenon. In this paper, the abnormal indexes are classified by different working conditions, such as normal operating state and harmonic amplification phenomenon, thus the recognition index of harmonic amplification is compared and summarized. After screening the most obvious changed part of the index under two kinds of working conditions, nine feature indexes are chosen to be embraced into the recognizing system. Finally, this method is used to analyse the harmonic amplification events in other moments of transmission lines, and all the harmonic amplification phenomena are identified successfully, which proves the feasibility and accuracy of this method.

Simulation and Analysis of Harmonic High Voltage Filters for Wind Farm

With the rapid development of the wind power industry, the total installed capacity of wind power has increased dramatically worldwide, and a large number of wind power installations need to be connected to the grid. In wind turbines, voltage flicker due to output power fluctuations caused by wind speed changes, and the application of a Voltage Source Converter (VSC) cause harmonic richness and other power quality problems to become more and more prominent. In this regard, the research is focused on the harmonic and reactive current distribution, impedance frequency characteristics, and voltage distortion rate of several offshore wind farm access systems, including the establishment of a harmonic current simulation model of the offshore wind farm delivery system, simulation analysis of network impedance frequency characteristics, simulation analysis of harmonic currents, and proposed a preferred filtering scheme. Taking into full consideration the characteristic harmonics of the wind farm, the system resonance generated by the submarine cable and the background harmonic level of the power grid, combined with the simulation results of the harmonic voltage, harmonic current, and network impedance frequency characteristics of each node, the technical solution of adding a direct-mounted high-voltage filtering device to the 220 kV bus at the metering station is proposed, which can destroy the system resonance conditions of the 3rd to 6th times of the submarine cable. Various wind farms and system operating conditions are able to form a stable harmonic absorption point to avoid the problem of harmonic amplification.

Harmonic Resonance Suppression With Inductive Power Filtering Method: Case Study of Large- Scale Photovoltaic Plant in China

Taking actual engineering as a case study, this article provides a novel scheme of applying the inductive power filtering method (IPFM) to resolve the harmonic resonance issues in large-scale photovoltaic (PV) plant. By using IPFM's special structure and dual zero-impedance design, the impedance network of large-scale PV plant is reshaped while the performance of power filters is improved, so that the harmonic resonance due to the interaction between the inverters and the power grid is suppressed. First, the topology and components of the IPFM-based large-scale PV plant are introduced. The three-phase mathematical model in harmonic domain is then established. Based on the deduced transfer matrix, the simplified circuit of the studied large-scale PV plant is obtain-ed. Moreover, the IPFM's resonance damping mechanisms on resonant frequency shift and harmonic amplification mitigation are analyzed. Both simulation and engineering tests verify the feasibility of the proposal.

Analysis of harmonic resonance amplification caused by AC submarine cable integration of offshore wind farm

Offshore wind power plants (WPPs) using AC submarine cables connected to the power grid may experience harmonic resonance and harmonic amplification that are not common in onshore wind farms under the action of the distributed capacitance of submarine cables, which seriously threatens the safe and reliable operation of offshore WPPs. To investigate the influencing factors of harmonic amplification in offshore WPPs, a scalable state space-based modeling method for large-scale offshore WPPs were established. Moreover, the root locus method was used to study how the factors including that grid short-circuit capacities, cable parameters and the number of wind turbine generators (WTGs) affect the resonance modes. Finally, an offshore WPP in Jiangsu was built on the MATLAB/Simulink simulation platform, and the analysis results verify the correctness of the theoretical analysis.

Research on High Harmonic Amplification of 10kV Series Static Var Generator

With the continuous development of power electronic devices and science and technology, cables and rectifiers, inverters, DC transmission equipment, and other nonlinear loads have been widely used in power systems. However, this causes harmonic pollution and large capacitive reactive power, which can affect the safe and stable operation of the power system. Based on the analysis of the reasons for the use of static var generator in the power grid and the existing conditions of even harmonic, the impedance analysis method was used to analyze the abnormal noise event of a transformer in a substation. Firstly, the equivalent impedance model diagram is drawn by the equivalent circuit method, and the equivalent impedance value of the system is calculated. A number of harmonic amplifications and the positions of the resonance point are calculated by MATLAB software. Secondly, the correctness of the above theoretical analysis is verified by field test and simulation model built in ETAP software. Finally, because of the abnormal noise of the transformer in a substation caused by harmonic amplification, three harmonic suppression measures are given.