适用于次同步振荡分析的直驱式风电场等值方法

为解决大规模直驱式风电场阻抗建模困难和数值仿真节点限制的问题,基于阻抗分析法的核心原理,以等值前、后直驱式风电场外阻抗特性相一致为目标,提出了适用于次同步振荡分析的直驱式风电场等值方法。该方法包括基于阻抗灵敏度分析的分群聚合和基于遗传算法的等值降阶2个步骤。分别以风电场含相同型号直驱风机和不同型号直驱风机为例,对等值前、后的直驱式风电场外阻抗特性进行对比分析。结果表明,所提方法能够实现大规模直驱式风电场模型的等值降阶,等值前、后的直驱式风电场外阻抗特性较为接近,其等值误差能够被量化。     

一种实时自适应前沿消隐电路

基于正激变换器结构,设计了一种实时自适应前沿消隐电路。通过振荡时间消隐和振荡幅度消隐,对最优消隐时间进行追踪,实现实时自适应的前沿消隐,在保证消隐可靠性的基础上降低了系统体积与成本,并确保不限制电路高频化发展。设计的前沿消隐电路能获得消除尖峰振荡的输出电流信息,保证系统能对输出负载变化做出快速响应。基于0.18 μm BCD工艺,对电路进行设计。仿真结果表明,该电路在没有其它额外限流功能条件下,启动过冲电压只有50 mV,负载切换时的下掉电压与过冲电压分别为519 mV和578 mV。     

一种宽带注入锁定三倍频器

文章提出了一种宽带注入锁定三倍频器。在传统注入方式基础上,倍频器采用了推-推差分对输入信号进行二倍频,并将产生的二次谐波通过变压器耦合至注入管的源极共模点,增强了注入管源极共模点二次谐波。由于注入电流是由注入信号与源极共模点二次谐波进行混频而产生,因此注入电流也被增强,从而增大了锁定范围。除此之外,三倍频采用了四阶谐振器,谐振阻抗的相位在过零点被平坦化,锁定范围进一步被增大。采用标准CMOS 65 nm工艺设计三倍频,芯片面积为720×670 μm²,1.2-V供电时的功耗为15.2 mW。0 dBm注入功率下三倍频的锁定范围为19.2~27.6 GHz,对应的基波抑制比大于25 dB,二次谐波抑制大于35 dB。注入锁定三倍频器可满足5G收发机中本振源的要求。     

An improved strategy for out-of-step oscillation separation devices based on apparent impedance angle applied to a series compensated line

Out-of-step oscillation separation devices based on apparent impedance angle trajectory are widely used in the power grid in China, and their reliability is of great importance. In this paper, the influence mechanism of series compensation on apparent impedance angle trajectory is analyzed. It reveals that series compensation capacitors reduce the equivalent impedance angle and consequently the apparent impedance angle cannot pass through all four zones, resulting in the risk of failure for the separation devices. A revised method of apparent impedance angle based on compensation principle is discussed, and then an improved out-of-step oscillation detection criterion is proposed. In view of the fact that the apparent impedance angle at the moment of maximum current is equal to the equivalent impedance angle during an oscillation process, a practical algorithm based on the compensated apparent impedance angle is proposed. RTDS tests are conducted to verify the effectiveness of the new criterion, considering transmission lines with a high series compensation level.     

直驱风电场和串补之间的次同步振荡风险

随着电网规模的持续扩大,串补长距离输电系统引发的次同步振荡现象频现。因此,如何探析串补输电系统失稳的深层原因是当前系统稳定性分析发展方向之一。本文基于开环模式谐振理论,提出了一种串补输电线路引发次同步振荡的开环模式谐振分析方法,文章首先建立了直驱风电场外接串补输电线路的小信号模型,并通过开环模式谐振分析方法研究了串补线路和直驱风电场之间的动态交互作用。结果表明串补主导的开环次同步振荡模式与风电场主导的开环次同步振荡模式在复平面靠近时,系统的闭环稳定性将会下降,并运用残差指标成功预测了开环模式谐振条件下闭环模式的位置,而改变风机参数或调整串补度可以规避动态交互的发生。本文通过算例系统验证了上述理论分析的正确性,证明直驱风电场通过串补输电线路进行输电时存在一定的失稳风险,能在一定程度上为串补输电系统的参数整定提供借鉴。     

Simulation of rotating stall in a whole stage of an axial compressor

Aerodynamic instabilities that naturally occur in compression systems, such as surge and rotating stall, largely reduce the life duration and performance of system components. The prediction of the compressor operating range is thus a key parameter for the design of gas turbines. This paper investigates the ability of an unsteady flow solver to simulate the rotating stall phenomenon in the full annulus of an axial compressor stage. A comparison with experimental data indicates that the simulation correctly estimates the stability limit. However the rotating stall flow patterns are different. While measurements show only one full span rotating stall cell (40 Hz), the simulation shows first a part span stall with 10 cells (790 Hz) that evolves then towards a full span stall with three cells (170 Hz). A spectral analysis based on numerical results underlines the role of rotor-stator interactions in the development of rotating stall. The effects of downstream volumes and inlet distortions are also discussed, showing the necessity to consider the whole geometry to correctly predict the rotating stall frequency.     

微小尺度射流流量传感器的设计与仿真分析

在许多新型传感器和微系统中均存在微量流体自动、精确地驱动和控制问题,而这有赖于微小尺度下对流量的精确测量。基于射流振荡原理设计了一种新型的无反馈通道微小尺度流量传感器,采用计算流体动力学(CFD)方法对该流量传感器的测量特性进行了仿真研究。通过观测振荡腔内部流场,分析了振荡器内部流动形态和射流振荡过程。通过对监测点压力变化曲线的分析,获得了不同入口速度下流体振荡频率,建立了流体流速与振荡频率的函数关系。研究结果表明,该微小尺度射流振荡器振荡平稳,主射流切换灵活,在较宽的流速范围内,流速与振荡频率具有线性关系,具有0.3%的较低的相对压力损失并可达到较小的测量下限,易于加工成型。     

Globally conservative high-order filters for large-eddy simulation and computational aero-acoustics

In computational aero-acoustics, large-eddy simulations (LES) or direct numerical simulations (DNS) are often employed for flow computations in the source region. As part of the numerical implementation or required modeling, explicit spatial filters are frequently employed. For instance, in LES spatial filters are employed in the formulation of various subgrid-scale (SGS) models such as the dynamic model or the variational multi-scale (VMS) Smagorinsky model; both in LES or DNS, spatial high-pass filters are often used to remove undesired grid-to-grid oscillations. Though these type of spatial filters adhere to local accuracy requirements, in practice, they often destroy global conservation properties in the presence of non-periodic boundaries conditions. This leads to the incorrect prediction of the flow properties near hard boundaries, such as walls. In the current work, we present globally conservative high-order accurate filters, which combine traditional filters at the internal points with one-sided conservative filters near the wall boundary. We test these filters to remove grid-to-grid oscillations both in a channel-flow case and in 2D cavity flow. We find that the use of a non-conservative filter leads to erroneous predictions of the skin friction in channel flows up to 30%. In the cavity-flow simulations, the use of non-conservative filters to remove grid-to-grid oscillations leads to important shifts in the Strouhal number of the dominant mode, and a change of the flow pattern inside the cavity. In all cases, the use of conservative high-order filter formulations to remove grid-to-grid oscillations lead to very satisfactory results. Finally, in our channel-flow test case, we also illustrate the importance of using conservative filters for the formulation of the VMS Smagorinsky model.     

基于支持向量机的高频振荡回路性能评价

提出了基于支持向量机(SVM)高频振荡回路性能的评价方法。以高频并联振荡电路为实验研究对象,通过将由高精密仪器设备采样信号分析与基于SVM的性能的评价分析相对比,证明了此评价方法的可靠性与精确性。该方法采用径向基核函数和合适的ε、C参数,有效地对高频振荡电路的通频带等参数进行测定、分析误差,是值得推广与研究的高频振荡回路性能评价的一种新方法。实验表明,该方法可推广到通信网络的相关参数的评价当中。