三端星型柔性直流配电系统的启停、协调控制

为实现三端星型柔性直流配电系统定直流电压端、定功率端、直流变压器端有序启动,首先设计了系统的启动控制策略,同时设计了功率可控端功率按既定斜率下降的停运控制策略。其次,提出了柔性直流配电系统的协调控制策略,在直流变压器低压侧的不同元件投切时,利用储能装置抑制功率波动,以实现元件的平滑投退。最后,通过RTDS仿真,结果表明所提控制策略能实现柔性直流配电系统的有序启动、协调运行和平滑停运。     

直流微电网孤岛运行控制策略研究

针对湖北黄石地区楼宇建筑直流微电网孤岛运行场景,提出一种光伏和储能电池的协调控制策略。基于直流微电网系统的实时状态,根据直流母线电压数值对微电网的运行模式进行划分,并设置变流器动作阈值,微电网内的各变流器根据母线电压所处的区间范围,执行相应的控制策略,满足微电网的能量平衡及电压稳定性需求。考虑微电网内部储能电池状态的一致性要求,针对电池变流器提出一种基于电池荷电状态(State of Charge,SOC)的协调控制策略,在电池的充放电过程中,根据不同电池组之间的容量差异进行功率分配,避免相同的充放电效率导致过充或过放现象。最后通过Matlab/Simulink对所提控制策略进行仿真验证分析。     

基于模型预测控制的直流微网混合储能能量管理策略

为有效增强直流微网安全性、稳定性及其经济运行能力,基于模型预测控制理论,提出了一种直流微网混合储能系统(HESS)优化控制策略。根据超级电容与蓄电池的特性、系统安全工作需求及各种约束条件,建立含混合储能直流微网的预测模型。通过定义其优化指标,设计能量优化管理策略,并将其转化为二次规划问题进行求解,实现了直流微网中功率的合理调度。此外,提出了系统脱离约束情况下的功率控制方法。仿真实验验证了所提优化管理策略的可行性和有效性。     

适用高比例新能源系统广域消纳的输电技术研究综述

针对特高压直流输送新能源存在的频率稳定、电压稳定和连锁反应等问题,本文分析研究了几种研究较多、有可能在我国纳入规划的技术的原理、应用场景和案例。从替代技术角度,提出了半波长交流输电替代特高压直流输电和构建立体电网的应用场景;分析了柔性直流利于组网的特点,提出了用于新能源接入及构建直流电网的应用场景。以单位容量年费用法比较了两类替代技术的经济性,得出了柔性直流输电技术更优的结论,研究了其经济输电范围。从辅助技术角度,分析了虚拟同步机改善新能源调频特性,并提出可应用于新能源高渗透率送受端电网的场景;分析了调相机的动态无功调节能力,并提出了可应用于新能源基地的输电系统。以四类替代技术及辅助技术的发展轨迹及我国电网发展历程、未来形态的变化,讨论、预测未来四类技术的发展趋势及其对未来电网形态的影响。     

雁门关直流接地极附近地表电位分布研究

超高压直流输电系统采用单极大地回线方式运行时,直流入地电流会造成接地极附近地表电位发生变化。不同地区由于土壤结构的差异,地表电位分布并不相同。为了研究雁门关换流站单极运行时地表电位变化规律,采用Wenner四电极法实测雁门关直流接地极附近土壤视在电阻率,建立了3层大地土壤水平分层模型,用CDEGS计算了接地极在额定电流下附近100Km范围内变电站、风电场、输气管道的电位分布,并定量给出了地表电位随距离变化的函数关系式。最后研究了注入电流、土壤电阻率、埋地金属管道对地表电位分布的影响。     

直流微电网电源系统混合储能电机回路控制方法研究

直流微电网电源系统混合储能电机回路控制能够有效平稳电路,以往大多以人为调整参数的形式进行控制,控制效率低下且调整过程中存在误差值,导致控制精度下降。提出一种新的直流微电网电源系统混合储能电机回路控制方法,先详细分析直流微电网电源系统混合储能电机回路详情,通过基于回路的正向响应控制策略与基于回路的反向响应控制策略,实现直流微电网电源系统混合储能电机回路控制。研究结果验证了所提方法有效性,且与其他控制方法相比,该方法在并网与离网两种状况控制下,直流微电网电源系统各方面数值标准性均高于95%,并能够在短时间内将直流微电网电源系统混合储能功能稳定性控制在期望标准中,控制性能显著。     

一种混合开关电感和开关电容的高增益DC/DC变换器

针对传统Z源DC/DC变换器存在的输入电流不连续、输出电压增益不够高和功率器件电压应力较高等不足,利用开关电感和开关电容技术,提出了一种混合开关高增益DC/DC变换器。该变换器主电路中只用到1个储能电容,结构简单,与现有典型的高增益阻抗源DC/DC变换器相比,所提出的混合开关电感和开关电容的DC/DC变换器可以实现更高的输出电压增益,同时电容和开关器件的电压应力较低。详细分析了所提变换器的工作原理,通过在实验室中所建立的输入电压16～40 V、输出电压26～107 V和输出功率7～114 W的原型验证了其性能。     

Revisited generalized substitution theorem and its consequences for circuit analysis

The Substitution Theorem (ST) is generally perceived as a mere theoretical curiosity. In this paper, a formerly derived generalized ST (GST) is carefully revised, which leads to both a Weak Revisited GST (RGST) and a Strong RGST (characterized by noticeably relaxed hypotheses with respect to the GST). Then, despite the common opinion about the ST, such RGSTs are showed to be powerful analytical tools to generalize, make rigorous and rigorously prove several classic results of Circuit Theory, namely: the Substitution Theorem for Multiterminal Circuits, the Source‐Shift Theorem, the Thévenin–Norton Theorem, the Miller Theorem alongside its Dual, and the Augmentation Principle. More specifically, the Substitution Theorem for Multiterminal Circuits is extended to an arbitrary set of sources, possibly including nullors. The Source‐Shift Theorem is rigorously derived, and possible related ambiguities are removed. Also, all possible hybrid forms of the Thévenin–Norton Theorem for multiports are individuated, and a precise operative procedure for calculating the relevant entities is provided for all cases. Furthermore, the Miller Theorem and its Dual are extended to an arbitrary number of variables and to multiports. As to the Augmentation Principle, the constraint regarding the linearity of the augmenting resistors is removed. Finally, thoroughly worked examples are given in which the aforementioned noteworthy consequences of the RGSTs are proved to be efficient tools for analysis by inspection of linear and nonlinear circuits. Among the other things, systematic pencil‐and‐paper procedures for DC‐point and input‐output (or driving‐point) characteristic calculation in nonlinear networks are derived and applied to circuits with considerably complex topology. Copyright © 2016 John Wiley & Sons, Ltd.     

Coordinated Control of Wind Farms and MTDC Grids for System Frequency Support

This paper proposes a coordinated control strategy to provide system frequency support for separated main grids from offshore wind farms (WFs) that are integrated through multi-terminal DC (MTDC) system. The control strategy consists of two control loops including the MTDC frequency regulation loop (FRL) and the automatic WF power regulation loop (AWFPRL). In events of AC main grid disturbances, the former can re-dispatch MTDC grid power flow to support system frequency, while the latter can adjust wind power output accordingly through the variable frequency control of WF-connected converters. Inertia energy stored in wind turbines can be utilized to stabilize system frequency via MTDC grids. Moreover, wind power fluctuations can also be smoothed by the proposed control. An expression of frequency response coefficient is calculated, which is used to quantify the contribution of frequency support from offshore WF-connected MTDC system. Case studies have been conducted to demonstrate the effectiveness of the proposed control strategy using a four-terminal DC grid.     

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.