基于模式和广义射线理论研究水平层状介质中面波模式的接触现象

在近地表面波勘探中,尤其对于典型沉积盆地的探测,基于观测数据得到的频率-相速度域的能谱中,通常可以观察到基阶和一阶模式的模式接触现象(Mode-kissing)。基于模式理论,频率域中面波模式对应由频散方程的根给出的一系列极点。基于广义射线理论,时空域的多径,造成了频率域中的多模。本文结合广义射线理论和简正模理论研究广义射线理论中P极和S极两个表面波极点贡献对频散曲线的影响,解释实际观测的模式接触现象。基于两层介质模型,分析下层半空间S波速度β^((2))变化时,随P极点在复射线参数平面变化,引起的基阶和一阶模式的频散曲线、本征位移和质点偏振的变化特征。研究发现,模式接触现象出现在复射线参数平面内,P极越过1/β^((2))表示的支点,基本进入简正模区域时。与该极点对应的一阶露能模式,其地表质点轨迹为顺进椭圆,但本征位移随深度的变换表现出经典表面波特征,能量主要集中在地表。

层状半空间中导波的传播

研究了在弹性层状半空间中传播的导波的频散及激发机制,分别在含有两层和三层介质情况下,详细分析了对称点源激发的所有可能存在的导波模式的传播特性以及它们与介质参数的相互关系,研究了表面波和能陷波的激发与传播机理。对于速度递增的介质,可存在多个模式,但对于速度递减的介质模型,至多只存在一个导波模式。在含有低速夹层情况下,存在沿低速层传播的能陷模式。能陷波和表面波的传播特性不仅与介质参数有关,而且还与声源频率有关。

Power Electronic Interface with Islanding Detection and Unbalanced Fault Ride-through Capability

Power electronic interface of dispersed generation plays a very important role in connecting a dispersed generation with utility grids. A power electronic interface not only adjusts the amount of active and reactive power injecting into a grid but also implements other importance duties as well. In this study, negative-sequence current injection has been fulfilled in three-phase power electronic interface for two important duties besides injecting reference power into utility grids. The first one is for islanding detection, and the other one is to enhance unbalance-fault ride-through capability of dispersed generation. This paper introduces a mechanism of negative-sequence injection based on controlling two separate coordinates of dq-control and explains the effect of negative-sequence injection in limiting the unbalanced currents generated from a dispersed generation. Using adaptive notch filter as a signal processing unit for the three-phase system, negative-sequence components are observed. The performance of entire control system is evaluated by time domain simulations, PSCAD/EMTDC （power systems computer aided design/electromagnetic transients including DC）.