为提高锁相环(phase-locked loop,PLL)的动态性能和锁相精确度,提出一种基于dq变换的改进锁相环,其通过平均值环节而不是延时信号消除(delayed signal cancellation,DSC)或低通滤波器(low pass filter,LPF)预先将负序与谐波分离出去,大幅缩短了暂态响应时间,同时亦消除了系统电压不平衡或畸变对锁相精确度的影响。详述了该PLL的工作原理;给出了关于负序与谐波分离方法的讨论;推导了控制环的线性化模型及其PI参数的整定方法。仿真与实验结果表明,由于采用平均值环节和不存在传统软件锁相环(soft ware phase-locked loop,SPLL)具有的耦合关系,该PLL可快速而准确地锁定系统电压中正序基波分量的相位,具有高动态性能和锁相精确度,适用于动态电压恢复器(dynamic voltage restorer,DVR)或统一电能质量控制器(unified power quality controller,UPQC)等对电压变化敏感的柔性交流输电系统(flexible AC transmission system,FACTS)。
A physical model of transport in an azimuthator channel with the sheath effect resulting from the interaction between the plasma and insulation wall is established in this paper. Particle in cell simulation is carried out by the model and results show that, besides the transport due to classical and Bohm diffusions, the sheath effect can significantly influences the transport in the channel.As a result, the ion density is larger than the electron density at the exit of azimuthator, and the non-neutral plasma jet is divergent, which is unfavorable for mass separation. Then, in order to improve performance of the azimuthator, a cathode is designed to emit electrons. Experiment results have demonstrated that the auxiliary cathode can obviously compensate the space charge in the plasma.
Based on particle-in-cell simulation, we studied the motions of ions and electrons. The results have shown that electrons are bounded by a magnetic field and only a small number of electrons can pass through the whirler channel. The plasma becomes non-neutral when it is emitted from the whirler, and the spatial charge leads to a beam divergence, which is unfavorable for mass separation. In order to compensate the spatial charge, a cathode is designed to transmit electrons and the quasi-neutral plasma beam. Experiment results have demonstrated that the auxiliary cathode can obviously improve the compensation degree of the spatial charge.
