针对"状态变量多、阶数高"给多换流器并联直流系统暂态稳定性分析带来的困难,提出计及多换流器动态交互的等值单机非线性模型,简化大扰动稳定性分析及控制参数设计复杂度.首先,对每台换流器下垂双环控制中的所有状态变量做等效变换,建立直流系统的等值单机非线性模型;其次,基于等值单机的Takagi-Sugeno(TS)模糊模型刻画出最大估计吸引域,分析系统控制参数设计不合理导致的"小扰动稳定、大扰动失稳"问题;然后,提出基于等值单机的直流系统控制参数整定方法,通过等值单机设计推导系统中每台换流器的控制参数,降低了直流系统控制参数设计的难度,最后,RT-BOX硬件在环实验平台验证等值单机非线性模型及理论分析的准确性.

合适的等效降阶模型能够为中压直流(MVDC)配电系统的稳定性分析及控制参数设计提供便利.首先,基于所提出的开闭环逐步等效降阶建模方法,建立了MVDC配电系统的等效降阶电路模型,并据此建立了计及换流器间动态交互的开环等效降阶模型.在不增加开环等效降阶模型阶数的前提下,基于泰勒展开的状态反馈控制方法为系统振荡频率及阻尼比的精准设计创造了有利条件.然后,基于所建立的计及换流器间动态交互的闭环等效降阶模型,并结合所提出的MVDC配电系统控制参数设计方法,实现了系统振荡频率及阻尼比的精准设计.最后,硬件在环实验结果验证了理论分析的合理性.

For medium-voltage DC (MVDC) distribution system, the MVDC bus voltage is prone to instability owing to the dynamic interaction among source, constant power load and cable. Based on the equivalent model of MVDC distribution system, the input and output impedance considering the cable are established in detail. In addition, the voltage closed-loop transfer function of the equivalent model is also established. Then, the instability mechanism of system oscillation caused by cable can be revealed intuitively. To address this oscillation issue, the input filter capacitor of constant power load is further increased, thus the oscillation instability of the system is suppressed effectively. Finally, PLECS based simulation verification have been provided.

Voltage stability in medium-voltage DC (MVDC) power systems is a key design goal. Based on Norton’s Theorem and Thevenin’s Theorem, the equivalent circuit model of MVDC power system is established. Furthermore, the supercritical reduced-order circuit model is established by ignoring the line parameters, and it is found that the negative impedance characteristic of CPL is the main reason for the oscillation instability of MVDC power system. Therefore, a state feedback control algorithm based on Taylor expansion for generation-side converters is proposed in this paper, which compensate for the negative incremental resistance of CPL in MVDC power systems. Obviously, the control strategy could be conveniently implemented in decentralized controller, which is the most simple and desirable control structure in MVDC power system. Numerous simulation results verify the rationality of the supercritical reduced-order model and the effectiveness of the proposed control algorithm.

用阴、阳离子表面活性剂分别对炭黑(CB)、碳纳米管(CNTs)进行表面修饰,使其分别带负电荷和正电荷,并采用超声波分散仪对其进行分散处理.探讨了添加几种不同分散剂超声分散的效果.利用相反电荷相互吸引原理,将带有负电荷的CB和正电荷的CNTs,进行静电组装形成具有优良性能的CB/CNTs导电材料.结果表明:表面活性剂可以使CB、CNTs表面附有相应电荷,可以有效分散CB、CNTs.利用静电组装法制得CB/CNTs复合材料,且导电性能得到良好改善.

用表面活性剂分别对炭黑、碳纳米管进行表面修饰，并采用超声波分散仪对其进行分散处理。探讨了添加几种不同分散剂超声分散的效果。利用相反电荷相互吸引原理，将带有相反电荷的炭黑和碳纳米管，静电组装成CB/CNTs导电材料。实验结果表明：表面活性剂可使炭黑、碳纳米管表面附有相应电荷，有效分散炭黑、碳纳米管。且静电组装法制得CB/CNTs复合材料，导电性能得到良好改善。