Guaranteeing the Fault Transient Performance of Aerospace Multiphase Permanent Magnet Motor System: an Adaptive Robust Speed Control Approach

To enhance the fault transient performance of aerospace multiphase permanent magnet synchronous motor(PMSM)system,an adaptive robust speed control is proposed regardless of the phase open-circuit(OC)and short-circuit(SC)fault in this paper,which can be applied for both the redundant motor system and fault tolerant motor system.For aerospace multiphase PMSM system,besides external load disturbance and system parameter perturbation,there inevitably exists the electromagnetic torque ripple in fault transient process,which can degrade the system performance and even cause the system instability.To cope with this issue,the electromagnet torque ripple of the multiphase PMSM system in fault transient process is first analyzed.Then,by considering the electromagnet torque fluctuation caused by fault transient as a system uncertainty,a novel adaptive robust speed control scheme is proposed,while the adaptive law is constructed to emulate the total system uncertainty bound,which include the load disturbance,the parameter variation,and the electromagnetic torque fluctuation due to fault transient.The resulting control can ensure the speed control performance even in fault transient process regardless of the uncertainty,in which no prior estimation of the uncertainty bound is required.In addition,the proposed adaptive robust speed control is demonstrated by a six-phase PMSM experimental platform.The novelty of this research is to explore a novel adaptive robust speed control to strengthen the fault tolerance performance of multiphase PMSM system even in fault transient process,which requires no prior estimation of the uncertainty bound.

Tunnel effect of fractal fault and transient S-wave velocity rupture (TSVR) of in-plane shear fault

Transient S wave velocity rupture (TSVR) means the velocity of fault rupture propagation is between S wave velocity α and P wave velocity β . Its existing in the rupture of in plane ( i.e . strike slip) fault has been proved, but in 2 dimensional classical model, there are two difficulties in transient S wave velocity rupture, i.e ., initialization difficulty and divergence difficulty in interpreting the realization of TSVR. The initialization difficulty means, when v ↑ v R (Rayleigh wave velocity), the dynamic stress strength factor K 2(t) →+0, and changes from positive into negative in the interval ( v R, β ). How v transit the forbidden of ( v R, β )? The divergence difficulty means K 2(t) →+∞ when v ↓ β . Here we introduce the concept of fractal and tunnel effect that exist everywhere in fault. The structure of all the faults is fractal with multiple cracks. The velocity of fault rupture is differentiate of the length of the fault respect to time, so the rupture velocity is also fractal. The tunnel effect means the dynamic rupture crosses over the interval of the cracks, and the coalescence of the intervals is slower than the propagation of disturbance. Suppose the area of earthquake nucleation is critical or sub critical propagation everywhere, the arriving of disturbance triggers or accelerates the propagation of cracks tip at once, and the observation system cannot distinguish the front of disturbance and the tip of fracture. Then the speed of disturbance may be identified as fracture velocity, and the phenomenon of TSVR appears, which is an apparent velocity. The real reason of apparent velocity is that the mathematics model of shear rupture is simplified of complex process originally. The dual character of rupture velocity means that the apparent velocity of fault and the real velocity of micro crack extending, which are different in physics, but are unified in rupture criterion. Introducing the above mentioned concept to the calculation of K 2 (t) , the difficulty of initialization can be overcome, and the integral equation of triggering the initialization of TSVR is given quantitatively. By solving this integral equation, the lower limit of TSVR is 1.105 3 β , not β , and the divergence difficulty is overcome. TSVR is unstable solution, and may degenerate to sub Rayleigh wave velocity rupture immediately where the non critical condition can be measured. The results of this paper show that the initialization and continuum depends on the condition of earthquake nucleation in seismogenic area.

Transient Fault Locating Method Based on Line Voltage and Zero-mode Current in Non-solidly Earthed Network

为解决配电网小电流接地故障时故障点定位困难的问题，提出一种基于线电压和零模电流暂态分量的故障定位新方法。该方法借助馈线自动化（feeder automation，FA）系统实现，不需要额外增加设备。馈线终端检测线电压和零模电流信号，利用暂态线电压的希尔伯特变换与暂态零模电流的乘积计算故障方向参数，FA主站根据故障点前后方向参数极性相反的特征确定故障点所在的线路区段。介绍基于线电压的小电流接地故障检测和接地故障相确定的算法。数字仿真与试验结果表明该方法是正确可行的。

Transient and Permanent Fault Injection in VHDL Description of Digital Circuits

The ability to evaluate the testability of digital circuits before they are actually implemented is critical for designing highly reliable systems. This feature enables designers to verify the fault detection capability of online as well as offline testable digital circuits for both permanent and transient faults, during the design stage of the circuits. This paper presents a technique for transient and permanent fault injection at the VHDL level description of both combinational and sequential digital circuits. Access to all VHDL blocks a system is straight forward using a specially designed single fault injection block. This capability of inserting transient and permanent faults should help in evaluating the testability of a digital system before it is actually implemented.

Enhancement of Transient Stability of the Nigeria 330 kV Transmission Network Using Fault Current Limiter

The dynamic responses of generators when subjected to disturbances in an interconnected power system have become a major challenge to power utility companies due to increasing stress on the power network. Since the occurrence of a disturbance or fault cannot be completely avoided, hence, when it occurs, control measures need to be put in place to limit the fault current, which invariably limit the level of the disturbances. This paper explores the use of Superconductor Fault Current Limiter (SFCL) to improve the transient stability of the Nigeria 330 kV Transmission Network. During a large disturbance, the rotor angle of the generator is enhanced by connecting a Fault Current Limiter (FCL) which reduces the fault current and hence, increases transient stability of the power network. In this study, the most affected generator was taken into consideration in locating the SFCL. The result obtained reveals that the Swing Curve of the generator without FCL increases monotonically which indicates instability, while the Swing Curve of the System with FCL reaches steady state.

A Transient Enhancement Method for Two-Stage Helicopter Gearbox Fault Diagnosis Based on ALE

Periodical impulse component is one of typical fault characteristics in vibration signals from rotating machinery. However, this component is very small in the early stage of the fault and masked by various noises such as gear meshing components modulated by shaft frequency, which make it difficult to extract accurately for fault detection. The adaptive line enhancer (ALE) is an effective technique for separating sinusoidals from broad-band components of an input signal for detecting the presence of sinusoids in white noise. In this paper, ALE is explored to suppress the periodical gear meshing frequencies and enhance the fault feature impulses for more accurate fault diagnosis. The results obtained from simulated and experimental vibration signals of a two stage helical gearbox prove that the ALE method is very effective in reducing the periodical gear meshing noise and making the impulses in vibration very clear in the time-frequency analysis. The results show a clear difference between the baseline and 30% tooth damage of a helical gear which has not been detected successfully in author’s previous studies.

Transient Model for Shafting Vibration of Hydro Turbine Generating Sets

The shafting vibration is closely related to the rotational angular speed.The angular speed of hydro turbine generating sets(HTGS)is rapidly change in fault transient,it maybe reduce the shafting damage.By means of energy analysis,the differential equation of shafting vibration for the HTGS is derived,in which include the equation of generator rotor and hydro turbine runner,it can be applied to transient analysis.Shafting model is transformed into first order differential equation groups,and is combined with the motion equation of HTGS to build integrated model.Various additional forces of shafting are taken as input inspire in proposed model,the generality of model is good.At last,the shafting vibration in emergency stop transient is simulated.

高比例新能源送端系统暂态电压运行风险分析

针对交、直流故障下的高比例新能源送端系统暂态电压演化传播机理及运行风险尚不明晰的问题,首先,基于交直流系统间的无功电压交互作用机理分析,明确了交、直流系统故障下的暂态电压特性及主导影响因素,阐明了高比例新能源送端系统电力电子设备主导的暂态电压演化传播路径。其次,从“交直流故障强耦合作用持续加强,暂态无功功率成分复杂”、“新能源比例不断提升,暂态电压问题凸显”及“故障承载与调节能力下降,连锁脱网风险增大”三方面系统地阐述了暂态电压运行风险。然后,基于DIgSILENT/PowerFactory建立了实际高比例新能源多直流外送系统仿真模型,不同新能源占比、不同故障工况下的仿真结果验证了暂态电压运行风险分析的正确性。最后,从增强耦合运行特性机理认识、提升新能源涉网性能、增加多尺度协同控制策略、加强交流网架结构等方面提出了应对暂态电压运行风险的技术展望。

中性点柔性接地配电网故障相恢复电压暂态时域特征分析

配电网接地故障过零熄弧后的电压暂态恢复特性决定了系统过电压水平及电弧重燃特性,目前,中性点柔性接地配电网故障熄弧后暂态恢复电压变化机理尚不明确,为此建立柔性接地配电网接地故障暂态等值电路,理论解析故障过零熄弧后故障恢复电压的时域表达式。在此基础上,对比分析配电网谐振接地与柔性接地方式下,系统参数变化对故障相恢复电压暂态峰值与恢复速度的影响,揭示暂态时间尺度下故障相恢复电压特征随注入零序电流值与电流注入时机的变化规律,阐明通过中性点注入可控零序电流抑制故障暂态过电压的机理。在PSCAD/EMTDC仿真环境与10 kV真型配电网实验场中模拟各种运行和故障工况,仿真与真型实验结果均验证柔性接地配电网故障相恢复电压时域解析特征与变化规律的正确性。

A Fast Extraction Method in the Applicaton of UHV Transmission Line Fault Location

To aim at the distribution parameter characteristics of UHV transmission line, this paper presents a fast extraction method (FE) to extract the accurate fundamentals of current and voltage from the UHV transmission line transient process, and locates the fault by utilizing two-end unsynchronized algorithm. The simulation result shows that this method has good performance of accuracy and stability, and has better location precision by comparing with results of one cycle Fourier algorithm. Therefore the method can efficiently improve the precision of fault location during the transient process, and makes the error of location results less than 0.5%.

含跟网和构网型新能源发电单元的混联电力系统暂态同步稳定分析

在新能源发电单元与同步发电机共同接入的混联电力系统中,不同同步方式新能源间,新能源与同步发电机间耦合复杂,深刻影响系统的暂态同步稳定性。为揭示电网对称短路故障下不同发电单元间的动态耦合机理及其对系统暂态同步稳定性的作用机制,该文首先建立故障条件下混联系统的暂态稳定分析数学模型。随后,利用空间矢量图示法与相平面法分析跟网型新能源发电单元注入电流、锁相环参数以及构网型新能源发电单元有功控制环参数等因素对混联系统内各发电单元暂态同步稳定性的影响规律,并据此给出系统控制器参数的设计原则。最后,通过不同工况下的仿真验证理论分析的正确性。

一种可选择中断的混合式直流断路器拓扑

传统的混合式直流断路器应对瞬时性故障时必须先切断故障电流,再进行重合闸,会造成短暂性的电能供应中断。对此,提出一种适用于中压直流的可选择中断混合式直流断路器拓扑。该断路器可根据不同的故障类型选择运行方式,在与主导通支路串联的桥式结构中增加电容和限流电感抑制故障的电流上升,并储存能量,通过释能电阻对能量进行释放。对所提出的拓扑进行工作过程和理论分析。在单端直流等效系统中进行仿真验证,该结构在应对永久性短路故障时,可在9 ms内切除故障;应对瞬时性故障时,可使系统在不中断电流的情况下恢复正常运行,并释放故障时产生的能量。仿真结果验证了该拓扑的优越性。

VSC输出电流反馈型虚拟同步控制技术

基于输出功率反馈的虚拟同步机(VSG)技术在网侧故障时,难以保持电压源暂态特性并实现精准暂态冲击电流限制,同时极易出现暂态同步失稳问题。为解决上述问题,提出一种基于电压源型变流器(VSC)输出电流反馈型VSG技术。外环控制直接采用VSC输出电流作为反馈控制量,不仅能实现构网和电压/频率主动支撑功能,还能保证在故障状态下外环控制具备稳定平衡点,降低暂态同步失稳风险,同时还能实现稳态下的电流限幅控制。电压内环采用基于相量分析的虚拟阻抗自适应选取方法,依赖就地量测信息进行虚拟阻抗快速自适应调整,以抑制故障瞬间暂态冲击电流。在PSCAD/EMTDC中搭建详细电磁暂态仿真模型,并构建相应的物理验证平台,仿真和实验结果表明,所提方法可以较好地抑制故障瞬间暂态冲击电流。

动力学耦合分析下反应堆被动容错可靠性控制

反应堆长时间、高负荷的运转,使内部各设备出现不同程度磨损,易发生故障。由于反应堆变量复杂,导致其控制难度较大。为此,提出动力学耦合分析下反应堆被动容错可靠性控制方法。根据差分格式、因子分解理论求解反应堆相关变量,即密度、能量、位置及其运动方向等,按照燃料与冷却剂的温度、密度求解每个区域的截面,确定反应堆运行状态;运用事件触发机制设计反应堆被动容错控制程序,使用故障分布矩阵分析每个设备故障程度,检测出故障位置,通过控制率重组理念修改正常状态反馈回路增益,使修改后系统与正常系统性能一致。实验结果表明,所提方法故障检测结果与实际情况一致,且控制误差小,有效提升了反应堆被动容错控制的可靠性。

The Impact of the Offshore Wind Farm Switching Transient Operation on Power System

In this paper, a practical method to establish Doubly Fed Induction Generator (DFIG) based wind farm equivalent model for switching transient analysis is demonstrated. In order to verify this method, a 3.6MW equivalent wind farm model is built. The steady state results and load switching results are verified with those of detailed models of four 0.9MW generators. Using this method, a model of 40MW wind farm, representing the capacity for a proposed South Carolina offshore wind farm is established. To study large wind farm switching transient impacts on a system, different switching operations such as cable energizing and three phase faults at different locations in wind farm are investigated and their impact on system are analysed. Finally, conclusions based on the switching cases are presented.

考虑暂态过电压特性的架空输电线路雷击故障时空预警方法

针对运行环境复杂多变,故障率持续居高不下,雷击故障占比较大,并具有随机性与无法预知性的问题,提出考虑暂态过电压特性的架空输电线路雷击故障时空预警方法。深入解析雷击机理与雷电流,确定雷击(感应雷与直击雷)输电线路暂态过电压计算方式,通过小波多分辨率分解算法处理输电线路暂态信号,评估暂态过电压在信号频段中的能量比,识别累计故障,判断雷击点与故障点是否一致,利用单端检测确定雷击点的位置,完成架空输电线路雷击故障的时空预警。实验数据显示,在不同实验组别背景下,当阈值pΔ取值为9.3时,雷击故障识别精度达到最大值92%,雷击点定位精度高达80%。可以获得精准的雷击故障识别结果与雷击点定位结果,充分证实了提出方法具备较好的雷击故障时空预警效果。

基于复域暂态解析的柔性直流输电线路单端故障测距方法

输电线路的精确故障测距能降低巡线的难度、缩短修复时间,提升柔性直流输电线路单端故障测距方法的精度具有重要意义。文中基于故障时域暂态波形相似度特征模型,以柔性直流输电系统复域故障暂态解析计算模型作为特征拟合工具,通过故障录波与解析结果的波形相似性评价特征拟合程度,将故障测距问题转化为余弦相似度、平均绝对差两个评估指标的优化问题进行求解;提出了基于复域暂态解析拟合的柔性直流输电线路故障测距方法。最后,通过PSCAD/EMTDC仿真验证了所提故障测距方法的有效性。所提方法耐受过渡电阻能力强,无须依赖大量仿真与训练来提高测距精度。

基于变压器故障量的分布式小电流接地选线方法

提出并分析了一种基于变压器工频故障量的分布式选线方法和一种基于变压器暂态故障量的分布式选线方法。分析表明,工频故障量选线方法可用于中性点经消弧线圈接地系统欠补偿状态的一部分场景;暂态故障量选线方法比较的是变压器负荷侧暂态故障参考量与被保护线路暂态故障量,这两个暂态故障量具有近距离串行的电流关系,两者的幅值与波形变化都很小,因此具有受干扰小和可靠性高的优点。

灵活接地系统小电阻退出暂态特征及对暂态故障选线方法影响

灵活接地系统发生高阻接地故障时,中性点小电阻并联阶段保护往往拒动,仍需考虑小电阻退出时的暂态特征对已有暂态故障选线方法的影响。并联小电阻退出时伴随一定的暂态过渡过程,文中针对此过程建立灵活接地系统单相接地故障暂态等值电路。分析了并联小电阻退出时系统各暂态电气量特征、不同故障情况对暂态电气量幅值的影响、暂态零序电流与暂态零序电压的约束关系,明确并联小电阻退出后暂态量对暂态故障选线方法稳定性的影响。当灵活接地系统高阻接地故障小电阻退出时,产生的暂态电气量将导致暂态幅值比较法、暂态极性选线法、暂态功率方向法误动,但暂态零序电流投影法选线正确,仿真验证了分析结果的正确性。