新型模块化多电平DC-DC变换器拓扑及其工作机理分析

针对目前模块化多电平DC-DC变换器拓扑结构及其主要采用的交流平衡控制方法所带来的问题,基于直流控制思想,提出了一种新型模块化多电平DC-DC变换器拓扑。通过重构一种全桥子模块结构,每个子模块电容同时包含两条充放电路径,相邻子模块间通过形成局部的并联支路实现电容间电能传递和电容电压自平衡,避免了子模块电容在单向直流电能变换导致的电压失衡。通过对变换器的平衡机理及其基本工作原理分析、仿真实验验证,结果表明所提出的变换器在直流控制方式下能够稳定运行,子模块电容电压具有自平衡能力,变换器电压变比范围大,具有适用于不同应用场合直流输配电的应用潜力。     

基于线性最优的MMC子模块电容电压均衡控制策略

为进一步优化模块化多电平换流器(MMC)子模块控制策略,尤其是能够兼顾子模块电容电压波动、桥臂环流二次谐波含量、子模块绝缘栅双极型晶体管(IGBT)投切次数和算法计算量四方面的性能,提出一种基于线性最优解的MMC子模块电容电压均衡控制策略。首先,阐述了子模块电容电压波动和子模块IGBT投切次数之间的相悖性,通过理论分析证明子模块电容电压波动与桥臂环流二次谐波含量之间也存在非线性关系,需寻找适当算法使其三者同时达到最优情况。然后,针对此目标,对传统算法进行优化,增加附加调节子模块功能,并结合子模块电容电压均衡控制策略,详细阐述了所述算法的控制流程及其优越性。最后,通过动模试验对传统控制策略、子模块电容电压均衡控制策略、所提控制策略及其他采用不同数量的附加调节子模块的控制策略进行对比。试验数据表明,所提策略可以在子模块电压波动、桥臂环流中的二次谐波含量和子模块IGBT投切次数三方面达到线性最优。     

纳秒脉冲触发的阵列微空心阴极放电特性

阵列微空心阴极(MHC)是一种在同一个阴极结构上加工多个微孔形成微孔阵列,实现大面积高电子密度的放电微等离子体结构。相比直流触发模式,纳秒短脉冲触发阵列微空心阴极,可以显著地减少直流触发时的电流热负荷效应,提高放电电流和放电能量。本文利用自行研制的纳秒脉冲电源,实现对阵列微空心阴极在氩气下进行脉冲放电,研究其脉冲条件下的放电特性;其次,研究其在纳秒脉冲下多孔阵列的同步放电问题,并通过加入预触发结构,有效改善其同步特性;最后,利用光纤式发射光谱仪进行氩气下氩发射光谱测量,并对纳秒放电等离子体进行光谱诊断。     

Modeling and Full Decoupling Control of a Grid-Connected Five-Level Diode-Clamped Converter

This paper presents a novel approach to deal with the regulation of the dc-link capacitor voltages and ac-side currents in a grid-connected five-level diode-clamped converter. Due to the controllability problems of this topology, guaranteeing a solid current control and, mainly, a correct dc-link voltage sharing, represents a complex technical challenge. With the purpose of coping with it, an averaged model that describes the system dynamics at both sides of the converter is presented, assuming that a modulation strategy is integrated in the system to generate the switching sequence. In order to derive the proposed model, no restriction concerning the use of only the three nearest vectors to the desired voltage reference is taken into account. Then, several changes of variables are carried out in the model equations to obtain control input decoupling for control purposes, while reducing the complexity of the model as well. Finally, the voltage and current controllers are designed separately using different control inputs in a straightforward way. Neither auxiliary hardware nor complicated mathematical calculations are required to achieve the control objectives. The effectiveness and good performance of the system under the proposed control approach are validated by simulation results, suggesting that the five-level diode-clamped converter can be a solid solution as an interfacing system connected to the utility grid for, e.g., industrial drives or renewable energy applications.     

Cascaded Multilevel Inverters Using Proposed Series Sub-multilevel Basic Blocks with Reduced Switching Devices

In this paper, a novel configuration of the cascaded multilevel inverters using series connection of new sub-multilevel basic blocks is presented. The basic structure of the proposed sub-multilevel inverter is made of three isolated batteries and eight unidirectional power switches. Hereby, by changing the polarity of one of such batteries and two power switches, two different modules of sub-multilevel inverters can be extracted that each of them is able to be incorporated into two different cascaded structures as the series basic blocks. Contemporary, to determine the suitable magnitudes of the integrated batteries, two different algorithms for each topology along with their relevant mathematical analysis have been also given. In this study, a complete comparison between the proposed topologies and several recently presented structures has been conducted. The compiled comparisons can prove the fact that both the proposed cascaded inverters are capable of generating a higher number of output voltage levels with less number of switching counts. Other advantages of these structures are reduction of voltage sources numbers, DC sources variety, value of total blocking voltage, and also conducting losses. In order to demonstrate the correct operation of the proposed structures and presented algorithms, some experimental results will be also shown.     

Parallel Simulation of Power Systems Transient Stability Based on Implicit Runge–Kutta Methods and W-transformation

This paper presents a novel parallel algorithm for power systems transient stability simulation based on fully implicit Runge–Kutta (IRK) method. The s-stage IRK method is used to convert the differential-algebraic system simultaneously at s different time points into a set of non-linear algebraic equations, and the algebraic system is then solved by Newton's method. By the use of the matrix factorization technique, the solution of the linear equations involved in Newton's process is divided into two parts: the first part is decoupled at s different time points, thus it is fully parallelizable in time, and the second part is solved by preconditioned generalized minimal residual method (GMRES) method, while a new preconditioning method has been proposed by using the W-transformation and double-parameters method. For test, the proposed algorithm is implemented on multiple-graphics processing units (GPUs) computing platform. The results show that the proposed algorithm is accurate and has good convergence. Moreover, the parallel algorithm implemented on multiple-GPUs computing platform achieves high parallel efficiency.     

交流背景谐波对MMC多端直流的影响分析及抑制策略

连接弱交流系统是基于模块化多电平换流器(MMC)的多端直流输电系统的重要应用场景之一。然而,弱交流系统更易受到谐波扰动的影响,该交流系统中的非线性设备可能形成总谐波畸变率偏高的背景谐波电压,这些背景谐波电压将在MMC的三相桥臂中产生正序、负序及零序电压分量及相应的电流分量。在一些极端情形下,某些频率的谐波将会引起直流网络的谐振,导致直流网络的谐波含量显著增大,并通过直流网络传播到其他互联的交流系统中。因此,本文首先从理论上分析了交流系统电压背景谐波对MMC桥臂电压的影响,获得了谐波传递规律;在此基础上,设计了利用MMC子模块储能能力的抑制直流侧谐波的附加控制策略。在PSCAD/EMTDC中的仿真表明,本文所提出的控制策略能有效阻断背景谐波向直流网络的传播,避免直流网络由于背景谐波产生谐振现象。     

多相并联的15 kW无线电能传输系统

设计了一种耦合电感的循环级联方法来实现多相逆变之间的电流平衡,并分析了耦合电感参数对系统性能的影响;对多相并联下系统主要的功率损耗进行了分析,以解释在大输出电流条件下多相系统具有较低损耗的原因,开发了6相D类半桥逆变并联的原型机对系统性能进行验证。实验表明该方法能够将相间电流不平衡控制在较好的范围之内。使用2个外边长90 cm×70 cm的4圈的平面矩形螺旋线圈,在距离20 cm时进行无线电能传输。当接收端整流桥后的6.87Ω负载上获得15 k W的功率时,测得发送端直流输入到接收端直流负载的DC-DC效率为94.7%。     

一种模块化级联H桥构造的三相—单相同相牵引供电系统

为解决高速、重载电气化铁路负序、谐波和无功等电能质量问题,依据三相对称补偿理论,并结合H桥构造,提出了基于模块化级联H桥的三相—单相同相牵引供电系统。分析了系统补偿特性及工作原理,研究了直挂型"!"联结的有源补偿装置(MMCHC)拓扑结构,推导了子模块参数确定方法,并给出了系统控制策略。通过直挂补偿装置将三相牵引变压器转换为单相供电,节省了匹配变压器的容量为补偿容量的2倍。仿真表明,补偿装置在牵引和再生制动工况下均具备良好的补偿特性和动态性能,消除了牵引负荷引起的负序、谐波和无功分量,且子模块电容电压稳定在2%以内。     

并联式自动加注机器人运动学标定

为解决并联式自动加注机器人在高精度运动学逆解建模的问题,以并联式自动加注机器人为对象,对其 运动学标定进行研究。采用矢量微分法建立位姿误差模型,对各误差源对动平台末端位姿的影响规律进行分析,寻 找合适的标定位置,并以位姿均方根误差最小为目标函数,使用粒子群算法对神经网络结构进行优化,最后通过仿 真试验对其进行验证。仿真结果表明：该方法能有效提高并联式自动加注机器人的精度,为后续实验应用提供了理 论依据。