A three-dimensional numerical calculation of the wind-driven thermohaline and tide-induced Lagrangian residual current in the Bohai Sea

On the basis of a three-dimensional weakly nonliear theory of Lagrangian residual current in the Baroclinic shallow seas, a diagnostic numerical calculation of wind-driven, thermohaline and tide-induced Lagrangian residual current in the Bohai Sea is made. The model involves the Richardson number in the eddy viscosity coefficient, wind, thcrmolialine and tidal effects in the focing terms. The runoff of the Huanghe River and a part of the Huanghai Warm Water coming from the Huanghai Sea through the Bohai Sea Strait is also considered. The velocity-splitting method is adopted. The wind-driven circu lation, thermohaline circulation and the tide-induced Lagrangian residual circulation are also obtained individually and analysed. The dynamics of the three main eddies in the Lagrangian mean circulation is discussed. Finally, the numerical result is partly verified with the observed data.

New Method for 3D Transient Eddy Current Field Calculation and Its Application in Magneto-Acoustic Tomography

A new method of 3D transient eddy current field calculation is proposed. The Maxwell equations with time component elimination （METCE） are derived under the assumption of magnetic quasi static approximation, especially for the sample of low conductivity. Based on METCE, we deduce a more efficient reconstruction algorithm of a 3D transient eddy current field. The computational burden is greatly reduced through the new algorithm, and the computational efficiency is improved. This new algorithm decompounds the space-time variables into two individual variables. The idea is to solve the spatial vector component firstly, and then multiply it by the corresponded time component. The iterative methods based on METCE are introduced to recover the distribution of conductivity in magneto-acoustic tomography. The reconstructed images of conductivity are consistent with the original distribution, which validate the new method.

Calculation of currents in Taiwan Strait during summerⅠ.Three-dimensional diagnostic calculation

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Numerical calculation of drift current in wind waves

-Drift current induced by wind and waves is investigated with phase-averaged Navier-Stokes equation in which the Reynolds stress is closed by k-ε model. The governing equations are solved by the finite volume method in a system of nonorthogonal coordinates which is fitted to the phase-averaged wave surface. The predicted drift current is fairly reasonable and the drag coefficient of sea-surface predicted with the newly developed interface conditions shows good agreement with previous measurements when breaking waves do not exist.

An Analysis of Observed Ocean Currents Data and Numerical Simulation in the Offshore Area of Jiaonan

Based on the diurnal consecutively observed data in the offshore area of Jiaonan in 2005, the paper tries to make a preliminary analysis of the specificity of ocean currents, tidal current property and residual current property in the area in observing dates. Then on the basis of observed data analysis and by employing the split-step method, the paper conducts a numerical simulation of the tidal current field, which can show the M2 tidal constituent tidal wave system, current ellipse distribution, maximum current velocity distribution and time-dependent current field. The calculated results agree well with the observed data, which can on the one hand reflect the basic specificities of temporal and spatial distribution of the M2 tidal constituent current field to some extent, and, on the other hand, offer more information about the hydrodynamic condition. So the paper would provide a scientific basis for the making of sea environment protection plans in the offshore area of Jiaonan under certain conditions.

Asymmetrical Fault Current Calculation Method and Influencing Factors Analysis of Droop-Controlled Inverters

Since the fault dynamic of droop-controlled inverter is different from synchronous generators (SGs), protection devices may become invalid, and the fault overcurrent may damage power electronic devices and threaten the safety of the microgrid. Therefore, it is imperative to conduct a comprehensive fault analysis of the inverter to guide the design of protection schemes. However, due to the complexity of droop control strategy, existing literatures have simplified asymmetric fault analysis of droop-controlled inverters to varying degrees. Therefore, accurate fault analysis of a droop-controlled inverter is needed. In this paper, by analyzing the control system, an accurate fault model is established. Based on this, a calculation method for instantaneous asymmetrical fault current is proposed. In addition, the current components and current characteristics are analyzed. It was determined that fault currents are affected by control loops, fault types, fault distance and nonlinear limiters. In particular, the influences of limiters on the fault model, fault current calculation and fault current characteristics were analyzed. Through detailed analysis, it was found that dynamics of the control loop cannot be ignored, the fault type and fault distance determine fault current level, and part of the limiters will totally change the fault current trend. Finally, calculation and experimental results verify the correctness of the proposed method.

Wave Transformation and Breaking in Diagonal Opposing Current

When waves propagate into diagonal opposing current from non-current area, not only the wave parameters but also the direction of wave propagation will change, that is, wave refraction will occur. The authors have calculated the changes of wave parameters, including wave refraction, by Linear Wave Theory, and have also done systematic study on wave transformation and breaking in opposing current by means of experimental analysis and theoretical calculation. In order to know the effect of wave refraction, computation is done in this paper about wave transformation and breaking on gentle slopes in diagonal opposing current.

Design of a Hardware-Implemented Phase Calculating System for Feedback Control in the LHCD Experiments on EAST

A fully hardware-implemented phase calculating system for the feedback control in the lower-hybrid current drive （LHCD） experiments is presented in this paper. By taking advantages of field programmable gate array （FPGA） chips with embedded digital signal processing （DSP） cores and the Matlab-aided design method, the phase calculating algorithm with a square root operation and parallel process are efficiently implemented in a single FPGA chip to complete the calculation of phase differences fast and accurately in the lower-hybrid wave （LHW） system on EAST.

Measurement and Simulation of Induced Voltage and Current on 110 KV Crossing Transmission Lines under UHV AC Transmission Lines

The induced electricity of 110 kV transmission lines which cross the UHV AC transmission lines may threaten personal safety of the maintenance staff. In this paper, field measurement of the induced voltage and induced current on a 110 kV crossing line inside Jinhua in Zhejiang province is performed. The electrostatic induced voltage on the measured line is 12.24 kV. The power frequency electromagnetic field simulation model is established, and the calculation results are consistent with the measured. Influence factors analysis shows that the electrostatic induced voltage on the 110 kV line is 12.78 kV, the electromagnetic induced voltage is 12.3 V, the induced current through ground wire is less than 1A when the UHV lines operate at full load. The induced voltage and current decrease while the crossing distance increases. Parallel lines induction is much higher than crossing lines. The electromagnetic induced voltage after ground knife-switch shut down would exceed the human safety voltage 36 V while the crossing angle is less than 30?, so the temporary ground wire must be hanged to ensure safety of the maintenance staff.

同轴多层筒式空心线圈自感和互感解析计算方法

在电磁耦合的无线电能传输系统中,准确获取线圈电感参数是设计和优化无线电能传输系统的重要理论依据。现有的无线电能传输系统研究大多针对平面板结构线圈,同轴多层筒式空心线圈相比于平面板线圈具有更高的传输功率和传输效率。因此,该文针对同轴多层筒式空心线圈,提出了一种考虑高频涡流效应的自感和互感解析计算方法。首先,将单匝线圈截面离散等效为数量众多、形状相同的网格带电圆环单元,采用离散等效求和法推导出单匝线圈的自感和线圈间互感的解析式;然后,基于筒式空心线圈的整体结构以及考虑高频涡流效应,推导出基于第一类、第二类完全椭圆积分和开尔文函数的一、二次线圈自感和总互感计算的理论解析式;最后,以两种不同排布方式的筒式空心线圈为例,对比解析计算、有限元计算和实验测量结果,验证了所提解析法的可行性,同时也为筒式空心线圈的设计提供参考依据。

脉冲晶闸管热网络模型及运行状态评估方法

针对脉冲晶闸管承受强流脉冲导致的瞬态电磁热力联合冲击产生的热疲劳累积突发性失效问题,提出了在脉冲晶闸管内布置温度传感器的状态监测方法,建立了脉冲晶闸管的高阶瞬态热阻抗网络模型,分析了强流脉冲作用下脉冲晶闸管内部不同层的温度分布规律,并通过理论计算验证了分析方法的有效性。计算结果表明,热网络模型计算相对偏差小于5%。可为脉冲晶闸管型强流开关的状态评估提供理论指导。

混合级联特高压直流功率损失计算方法研究

混合级联特高压直流(UHVDC)在降低直流换相失败风险的同时提升了直流输电的灵活性,但由于LCC与VSC混合拓扑导致不同阀组闭锁后健全阀组的功率传输能力存在不确定性,影响了直流功率损失准确计算。此处提出了一种适用于混合级联UHVDC的功率损失计算方法。直流控制系统以极为单位计算阀组闭锁后的直流功率并发送安控系统计算直流功率损失,设计了合理接口与数据处理方式保证阀组单次及相继故障直流功率损失计算的准确性。最后通过试验,验证了所提方法的正确性与有效性。

基于七阶NR法与Broyden方法的柔性直流系统潮流新算法

目的 为了解决当前柔性直流输电系统潮流算法求解效率低的问题,方法 首先提出基于七阶NR法的潮流算法,该算法相较于传统的潮流算法具有更高的收敛阶数,可以有效减少迭代次数,提高算法效率;其次,针对七阶NR法单步迭代计算量大的问题,提出基于七阶NR法与Broyden方法的改进算法,利用七阶NR法突出的收敛特性,减少迭代次数,同时保留Broyden方法单步迭代计算成本较低的优势,避免浪费计算能力,使计算效率得到较大提升;最后提出一种经验法则,以确定改进算法中高阶NR法的迭代次数。结果 使用经典和改进算法对修改后的IEEE标准算例进行仿真测试,结果表明:与经典NR法相比,交流和直流的改进算法潮流计算结果最大误差分别为1×10^(-8)和2×10^(-8);平均计算时间方面,在IEEE-14、IEEE-30、IEEE-57、IEEE-118共4种算例系统下,改进算法的平均计算时间比经典NR法的减少了约61%;当算例系统由双端变为三端和双馈入后,改进算法的迭代次数保持不变,计算时间分别增加0.352 ms和0.636 ms;在重负荷情况下,改进算法的计算效率最高,且预设迭代次数较简单,当负荷值达到2.992时,其计算时间仅为经典NR法的60%。结论 本文的改进算法具有与经典NR法相同的精确性,但在计算速度方面更有优势,且更有利于在重负荷等极端情况下使用。

双制式列车接地系统的车-地联合牵引供电计算

为研究双制式列车在不同供电制式区段下的车体环流和车体—轴端电位分布,针对某型双制式列车构建列车接地系统的链式电路模型,并提出车-地一体化的交、直流区段联合牵引供电计算方法;同时,建立列车接地保护电阻优化模型,并分析2种列车接地系统配置方案.以国内某条双制式线路为算例进行仿真验证,研究结果表明:方案1相较方案2,列车的车体—轴端电位最大值降低36.58%~41.04%,车体环流最大值降低18.49%~22.97%;并且在方案1中,头尾车保护电阻设置为20 mΩ,可使列车的车体—轴端电位最大值为1.15 V,车体电流最大值为50.30 A,达到抑制车体—轴端电位的最优效果.该车-地一体化的交、直流区段联合牵引供电计算方法可适用于单一供电制式或者多供电制式列车接地系统的分析.

一种分时段输电线路动态载流量计算时间点的确定方法

讨论了输电线路动态载流量计算的启动时间问题,基于影响输电线路载流量的2个主要因素——温度和风速,结合长序列的历史气象数据,通过对相邻时段风速的互信息分析,总结出不同季节条件下日内24 h风速的变化规律,根据这些变化规律,提出了在1条线路或1个区域内输电线路动态载流量日内计算时间点的设置方法。在某省1条220 kV输电线路的全年仿真验证中,验证了所提计算方法相对于静态环境算法对同一条输电线路载流量有较大的扩容能力。

含主动限流控制的MMC-HVDC电网直流短路故障电流解析计算

传统的MMC-HVDC电网直流短路故障电流计算一般采用等效RLC电路方法。但是该方法没有考虑主动限流控制(ACLC)对等效电路RLC参数的影响,因此无法直接用于含ACLC的MMC-HVDC电网的直流短路故障电流的解析计算问题。该文通过将ACLC的控制效果等效为虚拟阻抗产生的压降,建立了体现ACLC的控制影响的等效RLC电路,以包含电流变化率限流环节的典型ACLC算法为例,推导了直流双极短路故障条件下ACLC的控制参数与虚拟阻抗的映射关系以及相应的直流故障电流解析表达式。最后,以基于含ACLC的半桥型四端MMC-HVDC电网为例,建立PSCAD/EMTDC仿真模型,对采用ACLC的直流双极短路故障电流解析计算结果进行了验证。结果表明:故障后10ms内直流短路故障电流的PSCAD仿真结果与所提出的含ACLC的等效RLC电路解析计算结果的平均误差在8.29%以内,最大误差在10.99%。因此,使用所提出的方法具有工程实用性。

含逆变型分布式电源的不平衡配电网快速短路电流计算

为实现含逆变型分布式电源的不平衡配电网快速短路电流计算,首先建立计及故障穿越控制的逆变型分布式电源序等效受控电流源模型,通过引入虚拟线路和虚拟节点并结合广义Fortescue变换建立不平衡配电网的系统序导纳矩阵。在此基础上构建含逆变型分布式电源不平衡配电网的序节点电压方程,提出基于序分量的短路电流迭代计算方法。通过引入预条件处理的广义极小残余法可避免求解系统序阻抗矩阵,能够有效提升短路电流迭代计算的计算速度。最后,通过对含逆变型分布式电源的13节点、123节点和多个大型合成系统仿真结果对比,验证了所提方法的正确性和可行性。