Research on resonance fault caused by dc magnetic biasing in ultra high voltage transformer with parallel static var compensator

For dealing with the resonance fault of ultra-high voltage transformers(UHVTs)with the parallel thyristor controlled reactor(TCR)+the filter compensator(FC)type static var compensator(SVC)caused by dc magnetic biasing,a simulation model of UHVT with parallel SVC for the frequency analysis of the impedance characteristics and a magnetic-field coupling model for UHVT based on classic Jiles-Atherton hysteresis theories are constructed based on the MATLAB/Simulink platform.Both the theoretical and simulation results prove that the resonance fault is caused by the resonance point on the low-voltage side of the transformer,which will approach the 4th harmonic point under magnetic biasing.Based on the fault analysis,a new resonance control method is proposed by adding reactance with by-pass switches in series with FC branches.Under dc magnetic biasing,the cutoff of the by-pass switch will increase the series reactance rate of the FC branches and change the resonance point.In order to avoid the 7th harmonic increasement caused by this method,the firing angle of the TCR branches is locked between 130°and 180°.The effect of the proposed method is validated by the simulation model of a 750 kV UHVT and the results show that the mechanism analysis of the resonance fault is correct and the resonance control method is valid.

Carbon decorated Li_(3)V_(2)(PO_(4))_(3) for high-rate lithium-ion batteries:Electrochemical performance and charge compensation mechanism

Fast charging and high-power delivering batteries are highly demanded in mobile electronics,electric vehicles and grid energy storage,but there are full of challenges.The star-material Li_(3)V_(2)(PO_(4))_(3) is demonstrated as a promising high-rate cathode material meeting the above requirements.Herein,we report the carbon decorated Li_(3)V_(2)(PO_(4))_(3) (LVP/C) cathode prepared via a facile method,which displays a remarkable high-rate capability and long-term cycling performance.Briefly,the prepared LVP/C delivers a high discharge capacity of 122 mAh g^(-1)(-93% of the theoretical capacity) at a high rate up to 20 C and a superior capacity retention of 87.1% after 1000 cycles.Importantly,by applying a combination of X-ray absorption spectroscopy and full-range mapping of resonant inelastic X-ray scattering,we clearly elucidate the structural and chemical evolutions of LVP upon various potentials and cycle numbers.We show unambiguous spectroscopic evidences that the evolution of the hybridization strength between V and O in LVP/C as a consequence of lithiation/delithiation is highly reversible both in the bulk and on the surface during the discharge-charge processes even over extended cycles,which should be responsible for the remarkable electrochemical performance of LVP/C.Our present study provides not only an effective synthesis strategy but also deeper insights into the surface and bulk electrochemical reaction mechanism of LVP,which should be beneficial for the further design of high-performance LVP electrode materials.

Simultaneous Multimode Oscillation of Stress-Compensated Cut Quartz Resonator with Narrow-Band Wide Variable-Range Quartz Crystal Oscillator

A multimode-quartz-crystal oscillator was developed to excite stable dual-mode resonance at different frequencies: The oscillation of the 3rd harmonic resonance of the principle C-mode and an additional resonance B-mode of SC-cut crystal. Harmonic combinations of the 3rd and fundamental mode of B-mode with the 3rd harmonics of C-mode are demonstrated. The measurement of the temperature dependence of the oscillation frequency is demonstrated along with the stability determined by root Allan variance. Dependence on the open conductance of the active circuit and the dependence on the coupling capacitors are discussed.

Bifurcation analysis for an SMIB power system with series capacitor compensation associated with sub-synchronous resonance

In this paper,an introduction to the bifurcation theory and its applicability to the study of sub-synchronous resonance (SSR) phenomenon in power system are presented. The continuation and bifurcation analysis software AUTO97 is adopted to investigate SSR for a single-machine-infinite-bus power system with series capacitor compensation. The investigation results show that SSR is the result of unstable limit cycle after bifurcation. When the system exhibits SSR, some complex periodical orbit bifurcations, such as torus bifurcation and periodical fold bifurcation, may happen with the variation of limit cycle. Furthermore, the initial operation condition may greatly influence the ultimate state of the system. The time-domain simulation is carried out to verify the effectiveness of the results obtained from the bifurcation analysis.

Compensation Control and Parameters Design for High Frequency Resonance Suppression of MMC-HVDC System

Large time delay is one of the inherent features of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system and is the main factor leading to the unfavorable’negative resistance and inductance’characteristic of MMC impedance.Research indicates that this characteristic interacting with the capacitive characteristics of an AC system is the cause of high frequency resonance(HFR)in the Yu-E HVDC project.As the current controller is one of the main factors that affects the MMC impedance,a compensation control to imitate the paralleled impedance at the point of common coupling(PCC)is proposed.Therefore,the structure and parameter design of the compensation controller are core to realizing HFR suppression.There are two potentially risky frequency ranges of HFRs(around 700 Hz and 1.8 kHz)in the studied AC system within 2.0 kHz.The core concept of HFR suppression is to make the phase angle of MMC impedance smaller than 90◦in the two risky frequency ranges according to impedance stability theory.Hence,the design parameters aim to coordinate the phase angle of MMC impedance in the two risky frequency ranges.In this paper,three types of compensation controller are studied to suppress HFRs,namely,first-order low pass filter(LPF),second-order LPF,and third-order band pass filter.The results of parameter design show that the first-order LPF cannot suppress both HFRs simultaneously.The second-order LPF can suppress both HFRs,however,it introduces a DC component into the current control loop.Therefore,a high pass filter is added to form the recommended third-order controller.All parameter ranges of the compensation controller are derived using analytical expressions.Finally,the correctness of the parameter design is proofed using time-domain simulations.

Transmission line realization of subwavelength resonator formed by a pair of conventional and LHM slabs

In this paper, the authors present the transmission line (TL) realization of one-dimensional subwavelength resonator formed by a pair of conventional right-handed material (RHM) and left-handed material (LHM). In such resonator, a novel reso- nant mode with the resonant frequency depending on the length ratio of the RH/LH TL sections occurs as a consequence of the full phase compensation due to the backward wave in the LH TL section. The theoretical circuit-model analyses are supported by simulation and experimental evidence on resonators with different RH/LH length ratios.

Effects of Material and Dimension on TCF,Frequency,and Q of Radial Contour Mode AlN-on-Si MEMS Resonators

This paper investigates the effects of material and dimension parameters on the frequency splitting,frequency drift,and quality factor(Q)of aluminium nitride(AlN)-on-n-doped/pure silicon(Si)microelectromechanical systems(MEMS)disk resonators through analysis and simulation.These parameters include the crystallographic orientation,dopant,substrate thickness,and temperature.The resonators operate in the elliptical,higher order,and flexural modes.The simulation results show that i)the turnover points of the resonators exist at 55°C,-50°C,40°C,and-10°C for n-doped silicon with the doping concentration of 2×1019 cm-3 and the Si thickness of 3.5μm,and these points are shifted with the substrate thickness and mode variations;ii)compared with pure Si,the modal-frequency splitting for n-doped Si is higher and increases from 5%to 10%for all studied modes;iii)Q of the resonators depends on the temperature and dopant.Therefore,the turnover,modal-frequency splitting,and Q of the resonators depend on the thickness and material of the substrate and the temperature.This work offers an analysis and design platform for high-performance MEMS gyroscopes as well as oscillators in terms of the temperature compensation by n-doped Si.

An Equivalent Fundamental and Odd Harmonic Resonators Controller for a Single-phase Dynamic Voltage Restorer

为提高单相动态电压恢复器（dynamic voltage restorer,DVR）的补偿性能,提出一种基于等效基波及奇次谐波谐振器组的数字控制方法。采用可等效为一组谐振器的延时模块,能够有效抑制电网基波和谐波扰动。给出一种包含两个控制参数和一组零相移陷波滤波器的结构及其设计方法,使系统在保证稳定性的同时,获得较大的谐振增益。其中,延时环节衰减系数可增加谐振器组鲁棒性;控制器比例增益可解决零相移陷波器中使用延时带来的问题;零相移陷波器组既能对消LC谐振峰,也能解决等效谐振器组高增益在高频处的稳定性问题。同时,引入电源电压和负载电流双前馈来保证响应速度,增加了对扰动的抑制能力。所提控制策略结构简单,谐波补偿能力强,动态响应快,易于实现。在2kW单相DVR实验装置上的实验结果验证了该控制方法的正确性。

基于双补偿下垂—MQPR的直驱式风电机组并网控制

为了实现直驱式永磁风力发电系统安全稳定并网,提出一种基于双补偿下垂与多重准比例谐振(multiple quasi proportional resonance,MQPR)相结合的并网控制策略。该策略源于传统下垂控制,在电压控制环节引入直流电压补偿量,能快速调节直流母线电压达到稳定;在电流控制环节引入电容电流补偿量,能有效减小滤波电容造成的电流误差影响;同时,设计出MQPR控制器替代内环电流的PI控制器,可以滤除系统中多次谐波电流。通过建立仿真模型,与双闭环PI和传统下垂控制策略进行对比,验证所提控制策略的有效性。

一种基于锁相放大的谐振式密度传感器谐振频率测量系统设计

谐振式密度传感器测量密度的关键在于谐振频率的测量。现有的测频法、测周期法、FFT法等谐振频率测量方法因噪声、脉冲误差等因素限制了其精度。为了解决该问题,设计了一种以锁相放大器为核心的谐振频率测量系统,其检测电路将交流振动信号的测量转换为直流恒定电压的测量。利用实验中发现的谐振区域内该直流电压与激励频率呈近似线性关系,基于扫频思想提出并实现了一种谐振频率自动测量算法。在(20±0.05)℃环境下进行了密度标定实验,对密度传感器进行了温度补偿。实验结果表明,在密度为700 kg/m^(3)~1000 kg/m^(3)的测量范围内,测得谐振频率稳定性可达到0.002%,传感器的密度测量最大误差为0.48 kg/m^(3),最大综合测量误差为0.069%,验证了所提谐振频率测量方法的有效性、精确性。

建筑电气节能系统的谐振抑制方法研究

文章建立谐振拓扑模型,提出整流电路、逆变电路以及无线电能传输系统线圈的设计方案,并对线圈传输效率进行分析。结果表明,系统整体性能受耦合线圈参数值的影响较大。因此,需要调整品质因数与耦合系数值来提高系统整体性能,通过仿真验证实验电路的可靠性和可行性。

电容补偿型硬标签质检技术设计与实现

合格的硬标签是电子商品防盗系统(Electronic Article Surveillance,EAS)可靠工作的基础。此类标签电路由线圈和电容串联而成,其组成的LC谐振频率F是硬标签关键参数。在研制全自动硬标签生产设备中,对其在线质检技术尤为关键。针对现有单、双线圈检测标签F存在的不足,设计了电容补偿型非接触单线圈式硬标签F检测技术。基于Proteus软件频率分析功能,对此检测方法的等效电路模型进行仿真,验证了方法的可行性。同时,设计MSP430F149处理器为核心的硬标签F测量的软硬件,对其信号处理单元电路的功能也进行Proteus仿真验证,达到预期效果。此检测技术的实测效果表明,测量硬标签F误差在±15 Hz内,为下一步将此技术用于全自动标签生产设备中提供了技术支持。

基于FPGA的硅微陀螺数字测控和温补技术研究

硅微陀螺仪由陀螺结构和测控电路组成,随着模拟接口电路的日臻完善,陀螺仪性能的提升主要靠数字电路中的测控和补偿算法;目前硅微陀螺测控电路正在向芯片化方向发展,为了加速硅微陀螺测控电路芯片化进程,用Verilog硬件描述语言设计了AGC和PLL对陀螺幅度和相位进行闭环控制,科氏力平衡进行闭环检测;对因加工造成的正交误差,设计了正交校正闭环;根据温度对陀螺仪的影响,对标度因数进行线性补偿,对零偏进行了BP神经网络补偿;实验结果表明,该控制系统下AGC相对稳定性为124 ppm,PLL相对稳定性为79.1 ppm,常温零偏稳定性为2.9°/h;在0~65℃内补偿前零偏稳定性为17.7°/h,补偿后零偏稳定性为9.1°/h,标度因数温度灵敏度降低1个数量级,不仅提升了硅微陀螺仪的性能,也为陀螺ASIC设计奠定了良好基础。

低温度敏感度谐振式压力传感器设计与仿真

为降低材料杨氏模量温度漂移和热应力对谐振式压力传感器温度漂移的影响,该文设计了一种基于Si-SiO 2复合H形谐振梁和双谐振器结构的低温度敏感度谐振压力传感器。通过有限元仿真软件COMSOL对传感器进行仿真验证。结果表明,在0~350 kPa内传感器灵敏度可达21.146 Hz/kPa,-50~125℃内零点温度漂移低至0.2 Hz/℃。与全硅结构相比,灵敏度温度漂移由339×10^(-6)/℃降低至14.1×10^(-6)/℃,可适应工作温度范围较高的环境。

单侧并联储能变流器并网谐振机理分析及抑制方法

为解决单侧并联储能变流器并网谐振问题,对谐振机理进行分析,设计抑制方法。通过研究系统待机与运行工况下的幅相参数,获取谐振特性。将谐振成因分为内因与外因,内因为并联系统输出电流随并机叠加,在并网阻抗上产生谐波压降,导致的电压谐波放大。外因为网侧所含背景电压谐波与并联系统阻抗频率在某些频段重叠。随并机数量增加,系统谐振点频率将降低。采用设计的电压谐波补偿单元进行功率解耦及动态多比例谐振控制器进行控制解耦两种方法,实现谐振抑制。通过仿真验证了谐振成因机理及抑制方法有效性。

三相LCL-LC型仅网侧反馈的改进时滞抑制

LCL-LC电压源型逆变器仅网侧电流反馈的有源阻尼相比于电容电流反馈下的有源阻尼减少了检测元件的使用,能有效抑制LCL-LC逆变器产生的谐振峰。但由于数字电路里存在控制延时影响,因此电网阻抗的变化会引起谐振频率fr偏移,当fr处于采样频率fs的16附近时系统将会失稳。为了解决LCL-LC有源阻尼逆变器仅网侧反馈时控制延时对逆变器的影响,研究了在数字域下电网阻抗的变化对系统稳定性的影响,并提出了一种新的延时补偿方法,即在控制回路的前向通路中加入改进型延时补偿,将有源阻尼的等效正电阻从原有的fs 6扩展到0.4965fs,补偿后的有缘阻尼在fr发生偏移时由于等效正电阻的扩宽使得系统在fs 6附近不会失稳,从而极大地提升了系统的稳定性。仿真和实验验证了理论的正确性。

直驱风电场并网对火电机组次同步谐振影响

直驱风电场(D-DWF)接入火电经串补外送系统后,其对火电机组的次同步谐振(SSR)影响机理尚不明确。针对风火打捆经串补点对网型系统,采用适用于模块化建模的状态变量消去方法,建立模块化的耦合小信号模型;利用特征值分析法研究D-DWF接入后系统的SSR情况;结合特征值分析结果阐释SSR机理,并针对D-DWF及串补线路参数进行阻尼分析。研究结果表明:D-DWF会引入与SSR频率相近并引起“共振”的一个新模态,使得“机电谐振”与“模态频率接近”的振荡机理耦合共存。在跟网型风机的控制策略及参数下,D-DWF并入会导致SSR模态阻尼大幅降低,恶化系统的SSR。随着D-DWF的容量、风速和系统串补度降低,系统阻尼将提高,SSR的风险将降低。基于PSCAD/EMTDC平台的电磁暂态仿真,验证了机理分析的正确性。

基于梯度线圈和双光束反向补偿的NMRG主磁场匀化方法

核磁共振陀螺气室磁场梯度导致的核自旋横向弛豫率是制约陀螺角度随机游走性能提升的重要因素。提出了基于梯度补偿线圈和双光束反向补偿的主磁场匀化方法。建立了气室原子系综Rb电子自旋极化、核自旋极化和泵浦光场传播的多场耦合动力学模型,结合有限元分析方法获得了方形气室磁场梯度与Xe核自旋横向弛豫的量化关系,分别对梯度线圈补偿环境磁场梯度、反向传播双光束均匀泵浦的Rb极化等效磁场匀化方案进行了研究。结果表明:梯度线圈将5×5×5mm^(3)气室的^(129)Xe_(T_(2))由3.6s提升到5.7s;Rb原子极化均匀性在纵向和横向都得到了显著改善,Rb原子极化等效磁场的一阶梯度得到抑制,残留的二阶等效磁场梯度导致的Xe核自旋横向弛豫率降低到约10^(-4)·s^(-1)量级。

基于OTC改进的半桥LLC变换器软启动控制

目前传统指数降频的轨迹优化控制方法有效减少了谐振电流峰值,但存在空载或轻载时输出电压超调,软启动时间长等问题。此处基于轨迹优化控制(OTC)提出了一种改进的软启动方法,解释了空载和满载下输出电压稳态调节的频率不同,引入线性补偿解决输出电压超调的问题,分析了LLC谐振变换器在启动过程中的阻抗特性和电流冲击特性,提出平方降频函数实现快速软启动。最后搭建了一台功率为185W用于半导体激光器供电电源的实验样机,验证了所提方法的可行性和有效性。实验结果表明,相比于传统指数降频的轨迹优化控制,所提出的方法在启动过程中实现了输出电压的快速响应和稳态调节。

Comprehensive Review and Analysis of Two-element Resonant Compensation Topologies for Wireless Inductive Power Transfer Systems

Wireless power transfer(WPT)is gaining much attention for battery charging of electric vehicles(EVs).Resonant WPT systems play a crucial role in achieving efficient power transfer from source to load.An overview of two-element resonant compensation techniques and their characteristics under various operating conditions are presented.Also the converter and control strategies used for different topologies are reviewed.The behavior of the performance factors are evaluated against the operating conditions and compared for the different topologies.