Adaptive controller design based on input-output signal selection for voltage source converter high voltage direct current systems to improve power system stability

An input-output signal selection based on Phillips-Heffron model of a parallel high voltage alternative current/high voltage direct current(HVAC/HVDC) power system is presented to study power system stability. It is well known that appropriate coupling of inputs-outputs signals in the multivariable HVDC-HVAC system can improve the performance of designed supplemetary controller. In this work, different analysis techniques are used to measure controllability and observability of electromechanical oscillation mode. Also inputs–outputs interactions are considered and suggestions are drawn to select the best signal pair through the system inputs-outputs. In addition, a supplementary online adaptive controller for nonlinear HVDC to damp low frequency oscillations in a weakly connected system is proposed. The results obtained using MATLAB software show that the best output-input for damping controller design is rotor speed deviation as out put and phase angle of rectifier as in put. Also response of system equipped with adaptive damping controller based on HVDC system has appropriate performance when it is faced with faults and disturbance.

Impact of Ion Current on Total Electric Field Measurement Under HVDC Transmission Line

The total electric field(TEF) at ground level induced by high-voltage direct current(HVDC) overhead transmission lines is one of the important indexes for evaluating the lines' electromagnetic environment.Based on analyzing the existing TEF sensors and the measurement principle of ion-current density,the influence from ions on TEF measurements is quantitively studied.The results show that the ions generated by the corona from a HVDC transmission line in operation cause errors in the measurement of TEF.This error is determined through analyzing the component of total measuring current on the filed mill's sensing electrode: if no appropriate approach taken,the maximum measurement error reaches up to 4.3%.Furthermore,a method that can eliminate such error,and hence improve the accuracy of TEF sensors is designed.

HVDC送端系统振荡引发受端换相失败的机理分析

高压直流输电系统送、受端存在电气耦合及两端的控制配合,因此,送端振荡可通过系统控制逻辑、电气量及控制量变化等影响受端系统的运行状态,增加了受端换相失败的风险。现有工作主要研究了送端大扰动引发受端换相失败的现象与机理,通过对标准直流系统进行小信号分析,发现直流系统中存在低频频段的固有振荡频率,一旦交流系统发生相近频段的振荡,将可能诱发直流系统共振。在此基础上,首先分析共振引起系统电气量以及控制量的波动对换相失败的影响,通过HVDC的准稳态方程分析共振后直流电流上升导致关断角下降,进而引发首次换相失败的机理;然后从两端的控制系统出发,研究逆变侧控制切换引发后续换相失败的机理;最后对CIGRE直流输电标准测试系统进行验证,并结合换相失败发生机理对换相失败的抑制策略进行了初步讨论。

直驱风电场经MMC-HVDC并网送端系统稳定性分析及振荡抑制

基于模块化多电平换流器MMC(modular multilevel converter)的高压直流输电HVDC(high voltage direct current transmission)因具有无源网络支撑等优势而被广泛应用于大容量新能源外送消纳。受电力电子设备交互作用等因素影响,送端系统易发生振荡失稳现象。首先,建立了直驱风电场经MMC-HVDC并网送端系统的小扰动线性化模型,分析了风场有功输出对系统稳定性的影响。然后,建立了MMC及风机并网变流器交流侧dq阻抗模型,从阻抗角度揭示了送端系统振荡失稳机理。进一步,提出了基于MMC交流电压控制外环q轴附加阻尼的振荡抑制策略,可满足系统满功率范围内的运行稳定性要求。最后,基于全比例模型的仿真结果验证了所提振荡抑制策略的有效性。

不同锁相环对LCC-HVDC控制回路稳定性的影响

该文研究了电网换相换流器高压直流输电(line commutated converter high voltage direct current,LCC-HVDC)系统逆变侧采用不同锁相环时,锁相环控制回路比例–积分(proportional integral,PI)参数变化对直流控制回路稳定性的影响。首先,分别建立了逆变侧锁相环采用滑动平均滤波(mo ving average filter,MAF)和级联延时消去滤波(cascaded delayed signal cancellation,CDSC)的LCC-HVDC小干扰动态模型,并通过电磁暂态仿真验证了该模型的正确性。其次,基于拉普拉斯变换获得系统定电压控制回路的传递函数,利用奈奎斯特稳定判据以及稳定裕度指标分析不同锁相环对定电压控制回路稳定性的影响,并进行了机理分析,同时在PSCAD/EMTDC的电磁暂态模型上进行了验证。最后,进一步在LCC-HVDC工程模型上对该文所得结论的普适性进行了仿真验证。

New DDSCR structure with high holding voltage for robust ESD applications

A novel dual direction silicon-controlled rectifier(DDSCR)with an additional P-type doping and gate(APGDDSCR)is proposed and demonstrated.Compared with the conventional low-voltage trigger DDSCR(LVTDDSCR)that has positive and negative holding voltages of 13.371 V and 14.038 V,respectively,the new DDSCR has high positive and negative holding voltages of 18.781 V and 18.912 V in a single finger device,respectively,and it exhibits suitable enough positive and negative holding voltages of 14.60 V and 14.319 V in a four-finger device for±12-V application.The failure current of APGDDSCR is almost the same as that of LVT-DDSCR in the single finger device,and the four-finger APGDDSCR can achieve positive and negative human-body model(HBM)protection capabilities of 22.281 kV and 23.45 kV,respectively,under 40-V voltage of core circuit failure,benefitting from the additional structure.The new structure can generate a snapback voltage on gate A to increase the current gain of the parasitic PNP in holding voltage.Thus,a sufficiently high holding voltage increased by the structure can ensure that a multi-finger device can also reach a sufficient holding voltage,it is equivalent to solving the non-uniform triggering problem of multi-finger device.The operating mechanism and the gate voltage are both discussed and verified in two-dimensional(2D)simulation and experiemnt.

新能源基地经LCC-HVDC送出系统振荡机理分析与抑制策略(二):阻抗特性与振荡机理分析

该文基于系列文章1建立的电网换相换流器型高压直流(line commutated converter-based high voltage direct current,LCC-HVDC)阻抗模型,开展新能源基地经LCC-HVDC送出系统阻抗特性和振荡机理分析。首先,研究LCC-HVDC送端交流端口阻抗与阀本体交流阻抗、交流滤波器阻抗间的构成关系,分析直流线路、受端换流站、受端电网强度对送端换流站阀本体交流阻抗的主导影响;然后,研究送端换流站直流电流环对阀本体交流阻抗的重叠效应,分析送端换流站交流端口阻抗次/超同步频段负阻尼特性形成机理,并论述受端换流站和受端电网强度对送端交流端口阻抗特性的交互影响;接下来,建立新能源基地经LCC-HVDC送出系统等值模型,研究送端系统振荡边界条件,阐明LCC-HVDC对新能源并网点阻抗特性影响的变化规律,揭示直驱风机(permanent magnet synchronous generator,PMSG)、双馈风机(doubly-fed induction generator,DFIG)、光伏(photovoltaic,PV)不同类型新能源基地经LCC-HVDC送出系统次/超同步振荡机理;最后,不同类型新能源基地经LCC-HVDC送出系统仿真结果验证了该文提出的次/超同步振荡机理的正确性和通用性。

分网接入方式下LCC-HVDC系统运动方程模型及交互振荡模式的阻尼特征(一):扰动传递路径分解

与常规直流相比,永富直流逆变站存在功率全送和功率分送运行方式,而其处于分网接入方式时电网换相换流器高压直流输电(line commutated converter based high voltage directcurrent,LCC-HVDC)系统的交互振荡模式及特征尚不明确。针对这一特殊运行方式,采用模块化建模的思路建立可以反映系统电气/控制回路间交互耦合路径的运动方程模型。在此基础上,依据系统整流侧-逆变侧、正极-负极间的交互耦合路径分解得到影响系统主导模式稳定性的3条扰动传递路径,即整流侧内部自稳性路径、逆变侧内部自稳性路径、双极交互作用致稳性路径。最后,设置不同工况下的案例,量化评估不同作用路径提供的阻尼大小,并通过仿真验证运动方程模型及扰动传递路径分析结果的正确性,为后续研究分网接入方式下LCC-HVDC系统交互振荡模式的阻尼特征提供模型基础。

分网接入方式下LCC-HVDC系统运动方程模型及交互振荡模式的阻尼特征(二):交互振荡模式研究

为研究分网接入方式下电网换相换流器高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)系统的交互振荡模式及阻尼特征,基于系统的状态空间模型及系列文章(一)建立的运动方程模型,提取了表征逆变侧电气与控制环节强耦合特性的多个弱阻尼交互振荡模式,研究了不同短路比工况下交互振荡模式的变化特征。在此基础上,通过复转矩系数法量化评估了整流侧/逆变侧内部自稳性路径及双极交互作用致稳性路径对主导交互振荡模式阻尼特性的贡献度。结果表明:1)不同短路比工况下交互振荡模式的阻尼比会进行重新分配;2)当逆变侧正负极短路比相差较大时,双极交互作用较弱,正负极系统的稳定性由2个交互振荡模式各自主导,且稳定性特征有所差异;3)当逆变侧正负极短路比相近时,双极间动态交互加强,交互振荡模式会同时主导参与系统两极的稳定性,正负极稳定性特征相似。

DRU-HVDC系统并联风机无功环流的分析与抑制

基于二极管整流器单元的高压直流输电(DRU-HVDC)具有多重优势从而受到了广泛关注,但是线路阻抗不匹配会使并联风机之间无功功率分配不均,产生无功环流。与传统的P-f,Q-U控制不同,基于DRU构网型风机采用P-U和Q-f控制,分析了此背景下阻抗不匹配时风机间无功环流产生的机理,提出了一种基于自适应频率补偿的无功环流抑制策略。该策略是在使用全局统一参考坐标系的基础上,对各台风机的无功控制环加入自适应频率调节,以此来实现风机间的无功环流抑制。仿真结果与实验结果表明所采用的策略提高了无功功率分配精准度,无需线路阻抗信息即可抑制风机间的无功环流,确保了风机组稳定运行。

Hybrid Simulation of ±500 kV HVDC Power Transmission Project Based on Advanced Digital Power System Simulator

In order to effectively imitate the dynamic operation characteristics of the HVDC （high voltage direct current） power transmission system at a real ±500kV HVDC transmission project, the electromechanical-electromagnetic transient hybrid simulation was carried out based on advanced digital power system simulator （ADPSS）. In the simulation analysis, the built hybrid model＇s dynamic response outputs under three different fault conditions are considered, and by comparing with the selected fault recording waveforms, the validities of the simulation waveforms are estimated qualitatively. It can be ascertained that the hybrid simulation model has the ability to describe the HVDC system＇s dynamic change trends well under some special fault conditions.

Fault analysis method of integrated high voltage direct current transmission lines for onshore wind farm

Voltage source converter(VSC) based high voltage direct current(HVDC) transmission is most suited for the wind farm as it allows flexibility for reactive power control in multi-terminal transmission lines and transmits low power over smaller distance. In this work, a new method has been proposed to detect the fault, identify the section of faults and classify the pole of the fault in DC transmission lines fed from onshore wind farm. In the proposed scheme, voltage signal from rectifier end terminal is extracted with sampling frequency of 1 k Hz given as the input to the detection, classification and section discrimi-nation module. In this work, severe AC faults are also considered for section discrimination. Proposed method uses fuzzy inference system(FIS) to carry out all relaying task. The reach setting of the relay is 99.9% of the transmission line. Besides, the protection covers and discriminates the grounding fault with fault resistance up to 300 Ω.Considering the results of the proposed method, it can beused effectively in real power network.

VSC-HVDC系统中IGBT阀保护方案研究

针对电压源换流器的高压直流输电(VSC-HVDC)系统,首先分析正常运行情况下电压源换流器两侧交、直流电流之间满足的平衡关系。然后将换流器的5种开关模式按照桥臂导通状态分为两类工作状态,分析不同工作状态下全控型电力电子器件绝缘栅双极晶体管(IGBT)阀短路和阀开路的电流流通路径,研究故障后交流侧电流幅值和直流侧电流的变化及其相互关系。在此基础上,提出一种能够反应IGBT阀短路和阀开路的保护方案,将交流侧三相电流采样值分别与各自导通状态函数相乘并求和,并与直流侧电流采样值构成差动电流,利用该差动电流反应阀短路和阀开路故障,并给出保护的整定原则。最后,基于仿真平台搭建双端VSC-HVDC系统模型,验证了该保护方案的有效性。

Steady-state Voltage Security-constrained Optimal Frequency Control for Weak HVDC Sending-end AC Power Systems

Due to the fact that a high share of renewable energy sources(RESs)are connected to high-voltage direct current(HVDC)sending-end AC power systems,the voltage and frequency regulation capabilities of HVDC sending-end AC power systems have diminished.This has resulted in potential system operating problems such as overvoltage and overfrequency,which occur simultaneously when block faults exist in the HVDC link.In this study,a steady-state voltage security-constrained optimal frequency control method for weak HVDC sending-end AC power systems is proposed.The integrated virtual inertia control of RESs is employed for system frequency regulation.Additional dynamic reactive power compensation devices are utilized to control the voltage of all nodes meet voltage security constraints.Then,an optimization model that simultaneously considers the frequency and steady-state voltage security constraints for weak HVDC sending-end AC power systems is established.The optimal control scheme with the minimum total cost of generation tripping and additional dynamic reactive power compensation required is obtained through the optimization solution.Simulations are conducted on a modified IEEE 9-bus test system and practical Qing-Yu line commutated converter based HVDC(LCC-HVDC)sending-end AC power system to verify the effectiveness of the proposed method.

知识图谱框架下基于深度学习的HVDC系统故障辨识

为加快电力系统数字化转型,保证高压直流输电(high voltage direct current,HVDC)系统高质量安全运行,有必要通过智能技术充分挖掘、提炼HVDC系统日常调控、运维等阶段积累的海量数据和丰富管理经验,从而构建知识图谱辅助工作人员对故障进行诊断和处理。提出了一种基于小波变换和深度学习的HVDC系统故障诊断方法。首先,采用小波变换将换流站的故障录波数据(单相接地、相间短路和阀组短路)转换为二维时频图像,并采用数据增强技术来进一步扩充样本数据集。然后,利用ResNet50网络来实现HVDC系统的故障诊断。根据实验结果,所提方法在训练集的分类精度为93%,在测试集的分类精度为82%,证明了该方法的有效性,为HVDC系统的故障诊断提供了一种新的可行性路线。为了进一步验证所提方法,将其与GoogleNet、VGG16、AlexNet、SVM、决策树和KNN等方法进行对比,对比实验结果表明,所提方法在HVDC系统故障诊断中的表现更加出色。