Higher order harmonics suppression in extreme ultraviolet and soft x-ray

The extreme ultraviolet and soft x-ray sources are widely used in various domains. Suppressing higher order harmonics and improving spectral purity are significant. This paper describes a novel method of higher order harmonics suppression with single order diffraction gratings in extreme ultraviolet and soft x-ray. The principle of harmonic suppression with single order diffraction grating is described, and an extreme ultraviolet and soft x-ray non-harmonics grating monochromator is designed based on the single order diffraction grating. The performance is simulated by an optical design software. The emergent beams of a monochromator with different gratings are measured by a transmission grating spectrometer. The results show that the single order diffraction grating can suppress higher order harmonics effectively, and it is expected to be widely used in synchrotron radiation, diagnostics of laser induced plasma, and astrophysics.

MINIATURIZED MICROSTRIP BRANCH-LINE COUPLER WITH GOOD HARMONIC SUPPRESSION PERFORMANCE

This paper presents a miniaturized microstrip branch-line coupler with good harmonic suppression performance. The proposed coupler consists of four branch-line sections, each of which is loaded by open-circuit stubs both at the center and the two ends. This type of loading can realize size reduction and harmonic suppression. As an example, a proposed branch-line coupler operating at 1.0 GHz is designed, fabricated and measured. The results show that the proposed branch-line coupler occupies 67% size of a conventional one and has better than 20 dB suppression from 1.9 to 5.8 GHz. Furthermore, the high slop of the transition band ensures good selectivity of the coupler.

Reactive Power Compensation and Harmonic Suppression for Power Supply System of HT-7U Superconductive Tokamak

In this paper, a strategy for the reactive power compensation and harmonic suppression of the power supply system in HT-7U superconductive Tokamak is proposed. The optimized approach is given in the parameters design for passive filter. Also a controlling method with fast response time and good accuracy is put forward for the compensator, which is more suitable for the dynamic load.

Verification of Existence of Harmonic Suppression in Error Separation by Prony Spectrum Analysis

Prony spectrum analysis is employed in this paper to analyze the harmonics of estimation of radial runout of axis in error separation. The result of analysis verifies the existence of harmonic suppression in multi-step method, thereby advancing the study of harmonic suppression which stayed at the theoretical level for years.

Costless-Function Model Predictive Current Control of Seven-Phase PMSM to Improve Dynamic Performance and Suppress Harmonics of Marine Electric Propulsion System

In order to improve the dynamic performance and suppress current harmonic for seven-phase PMSM(permanent magnet synchronous motor),this paper proposed an MPCC(mode predict current control)scheme based on SVPWM(space vector pulse width modulation)technique.By this scheme,the 14 virtual voltage vectors are first calculated based on the principle:the voltage vector synthesized in the 3rd harmonic subspace and the 5th harmonic subspace should be zero,in each sampling period,the optimal voltage vector is directly selected from the 14 virtual voltage vectors to achieve the best output current performance of seven-phase PMSM.In addition,no cost function related calculations are required in the MPCC scheme,reducing the calculation time and improving the dynamic response of the system.The simulation model of the seven-phase PMSM vector control system is established by using the Simulink tool of MATLAB,and the effectiveness of the scheme will be presented.

A Designated Harmonic Suppression Technology for Sampled SPWM

Sampled SPWM is an excellent VVVF method of motor speed control, meanwhile the harmonic components of the output wave impairs its applications in practice. A designated harmonic suppression technology is presented for sampled SPWM, which is an improved algorithm for the harmonic suppression in high voltage and high frequency spectrum. As the technology is applied in whole speed adjusting range, the voltage can be conveniently controlled and high frequency harmonic of SP WM is also improved.

Quantitative Measurement of the Proportions of High-Order Harmonics for the 4B7B Soft-X-Ray Source at Beijing Synchrotron Radiation Facility

A transmission grating coupled with an X-ray charge coupled device （CCD） is used to quantitatively measure the proportion of high-order harmonics of the soft-X-ray source of beam line 4B7B. The results show that the monochromatic X-ray has third-order and second-order harmonics. The proportion of second-order harmonic of 4B7B is less than 9.0% and the third- order harmonic is below 0.7% when no suppressing method is applied. When suppression methods are used, the proportion of second-order harmonic is less than 1.7% and the third-order harmonic is ignorable.

多功能一体化装备高灵敏度侦察的虚假频率抑制技术研究

高灵敏度侦察系统由于侦察灵敏度高,当侦察环境中出现大功率信号时,会给系统引入工作带宽内的虚假频率。而在一体化装备中,系统本身就会产生大功率信号,对侦察造成了无意干扰并引入虚假频率。当大功率信号频率在带外时,使用宽开接收机侦收大功率信号,将侦收到的脉冲引入到窄带高灵敏度系统,在窄带接收机中,通过比较脉冲的时序关系,将大功率信号的频率作为参考频率写入到窄带接收机产生的脉冲描述字参数中。当大功率信号频率在带内时,直接比较带内产生的脉冲的时序关系进行参考频率打标。对具有参考频率的脉冲描述字,使用基于统计的脉冲串虚假频率抑制方法,在信号级对虚假频率进行滤除,能够有效地抑制一体化装备中高灵敏侦察面临的虚假频率问题。

柔性直流输电系统中高频振荡研究综述

近年来,国内外多个电压源型柔性直流输电工程中发生了中高频振荡现象,影响系统的安全稳定运行。针对柔性直流输电系统出现的中高频振荡问题,阐述了柔直换流站阻抗模型和状态空间模型的建立方法,交流系统数学模型建立方法。对使用阻抗分析法、特征值法进行系统稳定性分析的原理、方法进行了说明。基于换流器阻抗模型,分析了电压前馈、电流内环、锁相环、环流控制等因素对换流器阻抗特性的影响。归纳总结了现有中高频振荡抑制策略及其对柔性直流输电系统动态性能的影响,介绍了谐波保护方法。对中高频振荡问题的抑制措施研究进行展望,给出了未来研究方向建议。

Vibration harmonic suppression technology for electromagnetic vibrators based on an improved sensorless feedback control method

To realize low harmonic distortion of the vibration waveform output from electromagnetic vibrators,we propose a vibration harmonic suppression technology based on an improved sensorless feedback control method.Without changing the original driving circuit,the alternating current(AC)equivalent resistance of the driving coil is used to obtain high-precision vibration velocity information,and then a simple and reliable velocity feedback control system is established.Through the study of the effect of different values of key parameters on the system,we have achieved an effective expansion of the velocity characteristic frequency band of low-frequency vibration,resulting in an enhanced harmonic suppression capability of velocity feedback control.We present extensive experiments to prove the effectiveness of the proposed method and make comparisons with conventional control methods.In the frequency range of 0.01-1.00 Hz,without using any sensors,the method proposed in this study can reduce the harmonic distortion of the vibration waveform by about 40%compared to open-loop control and by about 20%compared to a conventional sensorless feedback control method.

Simulation of a kind of active harmonic reduction 18-pulse rectifier

To solve the input current harmonic pollution of the high power rectifier system,18-pulse rectifier based on a kind of active harmonic suppression technique at dc side is proposed in this paper.The pulse rectifier employs three-phase diode bridges,each of them followed by a boost converter.Unlike the conventional three-phase unity-power-factor diode rectifier,the ideal sinusoidal main currents of circuit topology are obtained by control its output current or input currents of three boost converters for approximately triangular modulation.The theoretical of modulation strategy and characteristics of input and output currents about the proposed rectifier are analyzed in detail.Simulation results by Matlab/Simulink demonstrate that the proposed rectifier draws nearly sinusoidal current and power quality index is improved.The correctness of the theoretical analysis is validated.

Harmonics suppression effect of the quasi-periodic undulator in SASE free-electron-laser

In this paper, the harmonics suppression effect of quasi-periodic undulators （QPUs） in self-amplified spontaneous emission free-electron laser （SASE FEL） is investigated. The numerical results show that the harmonics power is reduced by using QPUs, but the fundamental radiation power also has a pronounced decrease as the saturation length gets very long. The cases of employing QPUs as parts of undulators are studied. The calculations show that if the fraction of QPUs and their offgap are appropriate in an undulator system, the harmonics radiation could be suppressed remarkably, meanwhile the fundamental saturation length does not increase too much.

谐波干扰抑制下的低压配电网母线电压自动控制系统

母线电压的平稳程度,直接影响低压配电网的运行安全,因此设计谐波干扰抑制下的低压配电网母线电压自动控制系统。该系统以配电网调度系统的控制需求为前提,在系统无功补偿层引入抗谐波干扰无功发生器获取母线电压的无功补偿量,母线无功控制需求整定层依据该计算结果和母线电压控制指令,结合母线实时运行电压结果,对比判断母线实际电压结果和参考电压之间的差距,确定母线电压所需的无功补偿量,完成电压控制。测试结果显示:该系统能够有效控制母线电压谐波,谐波畸变率低于4.4%;能够保证电压的稳定,电压控制的偏差结果均在±1.5 V之间,母线在相位阶跃和稳态两种情况下的相位误差结果均低于0.075。

基于几何约束优化的重复控制器及PMSM电流谐波抑制应用

重复控制器凭借其具有多个谐振峰而广泛应用于电流谐波抑制领域,然而在实际电机控制系统中,由于系统采样频率固定而电流谐波频率随电机转速而变化,会导致重复控制器中出现分数阶延时环节,而该环节在实际控制器中无法实现。对此,该文针对现有分数阶处理方法进行讨论,分析了插值逼近方法中插值系数对重复控制器整体频率特性的作用,据此提出基于几何约束优化的分数阶重复控制器,通过优化各插值系数,电机在全转速范围内都可以保证谐振频率和电流谐波频率相吻合,并且谐振峰值更符合电机谐波组成规律;还分析了滤波器所处反馈回路位置对频率特性的影响,作为组合滤波器设计依据;为保证系统稳定,对包含PI、重复控制器以及离散电机模型的电流控制系统进行稳定性分析,并作为控制参数选取依据。最后,通过台架实验验证了该文所提出的方法的谐波抑制性能是更优的。

用于并网逆变器的频率自适应复合重复控制

针对电网频率波动时重复控制(repeat control,RC)难以准确跟踪谐波分量和周期性干扰的问题,提出一种频率自适应复合重复控制策略(frequency adaptive PRC,FAPRC)。采用基于幂级数的滤波器实现分数延时。电网频率发生波动时,只需要输入频率比值的小数部分就能在基频和各次谐波频率处产生高增益,对实际电网频率进行准确跟踪,从而增强了系统在频率波动时的无静差跟踪能力和谐波抑制能力,实现频率自适应。在电网频率变化情况下对该控制策略进行仿真分析,与复合重复控制策略相比,所提策略更具优越性。

基于虚拟电压矢量模型预测转矩的船舶推进电机控制研究

针对船舶电力推进系统中六相永磁同步电机所采用传统直接转矩控制技术(DTC)仅采用最外围电压大矢量,会产生较大谐波电流并导致转矩波动大的问题,提出基于虚拟电压矢量合成的模型预测转矩控制策略(V-MPTC),利用α-β子空间中同向的大矢量和中矢量与z_(1)-z_(2)子空间中反向的小矢量和中矢量恰好对应原理,通过适当地调节一个PWM周期内大矢量和中矢量的占空比,可以使z_(1)-z_(2)子空间中的合成电压矢量幅值为0,实现对电机谐波电流和转矩脉动的抑制。同时为了便于硬件系统实现,进行电压矢量中心化以及采取提前2步的预测方法。仿真结果表明,采用V-MPTC控制策略使系统响应速度有所提高,启动转速超调降低,转矩脉动从0.15 N·m降至0.04 N·m,谐波畸变率从68.92%降至10.85%,验证了该方法在船舶电力推进系统中可提高其控制性能。

基于基准频率自适应谐波准谐振控制器的宽变频逆变电源控制研究

360~800 Hz宽变频交流电源系统是多电飞机电力系统的主要发展方向之一。为实现宽变频中频逆变电源在包括带整流型非线性负载等工况下的宽范围谐波抑制,保证其任意基准频率下的输出电压质量,提出一种基于频率基准自适应谐波准谐振控制器的控制策略。基于滤波电感电流反馈,设计了包含数字控制延迟补偿的有源阻尼方案,以抑制输出滤波器的谐振尖峰,对电压控制器的被控对象进行校正使系统得到简化;设计并采用积分与准比例谐振相结合的基波追踪控制器以消除基波频段的稳态误差;提出基准频率自适应的补偿角度设计方法以实现谐波准谐振控制在电压环控制带宽之外的谐波抑制。在理论分析的基础上,搭建了一台300~800 Hz/600 W单相逆变器样机并进行实验测试,结果表明,采用该控制策略的逆变器能够实现宽基波频段内任意基准频率下的宽范围谐波抑制,且具有良好的稳态和动态输出特性。

绝对式纳米时栅传感器栅尺污染误差分析与抑制方法研究

针对服役状态下油污降低位移传感器精度和可靠性的问题,本文基于绝对式纳米时栅传感器,开展了栅尺油污污染误差分析与抑制方法研究。首先阐述了绝对式纳米时栅传感器测量原理;其次建立了栅尺油污污染的数学理论模型和电场仿真模型。通过理论和仿真分析表明:均匀油污污染对传感器没有影响,非均匀油污污染主要引入一次谐波误差,并且误差随着污染油污的厚度和宽度的增加而增加;最后搭建实验平台验证了以上理论分析的正确性。同时提出差动结构,有效抑制了一次谐波误差,提高了传感器抗污能力。研究油污造成的误差影响对提高传感器环境适应性有重要意义,同时也为提高传感器长期可靠性和增强环境适应性提供了理论基础。