In a three-dimensional Cartesian coordinate system, the deformation of the medium around a particle includes strain, translation, and rotation. Rotational motion is an important aspect of current seismological research. Seismologists have recognized the importance of rotational motion in dynamic response and damage of structures caused by certain earthquakes, through investigations into earthquake damage. In rapid earthquake intensity reports, it is essential to not only consider factors such as earthquake location, source depth, magnitude, and fault rupture model, but also to emphasize the analysis of the amplification effect of shallow media. We discuss the attenuation characteristics and difference between seismic translational and rotational components by medium viscoelasticity through two-dimensional numerical simulation, analyze the amplification effect of shallow viscoelastic low-velocity layer on ground motion by the reference site spectral ratio (RSSR), and discuss the difference of the amplification caused by different low-velocity layer factors. The results show that the seismic primary frequency decreases more with increasing viscoelasticity, and the energy of rotational component attenuates more significantly than that of translational component. The elastic low-velocity layer amplifies high-frequency signals of body waves greater than the viscoelastic low-velocity layer, especially in rotational component. When shallow low-velocity layers consist of multilayered sediments compared to a single sediment, the amplification of surface wave is stronger, particularly in rotation. We follow the research method used for seismic translation to discuss the amplification effect of shallow viscoelastic medium on seismic rotation, which is important for performance-based seismic design and earthquake damage analysis.

The multi-time scale transient process of power electronic equipment in new type power system is interwoven with large power grid, which makes the dynamic process of the system more complicated, and electromagnetic simulation is needed to accurately simulate and analyze the dynamic behavior of the system. At present, the modeling of electromagnetic simulation data at large power grid level is usually converted from electromechanical model data. AC transmission line is an important component of electromagnetic simulation. This paper proposes an automatic modeling method that considers traveling wave transmission and electromagnetic simulation integration step size to select line model, and generates electromagnetic model data based on parameter conversion and complement of transmission line electromechanical model data. If the propagation time of electromagnetic wave on the line is less than the integration step, the lumped parameter line model is selected, otherwise the distributed parameter line model considering traveling wave transmission is selected. This paper analyzes the conversion relationship between the parameters of line electromechanical model and electromagnetic model, and develops an automatic modeling tool for transforming BPA electromechanical model into ATP-EMTP electromagnetic model. Finally, the efficiency and accuracy of the automatic modeling method of transmission lines are verified by an actual power grid simulation example.

The strong uncertainty environment in which renewable energy is the main power grid has the possibility of sudden changes in power supply or topology, and there is a risk of mismatch of transient control strategies. Therefore, a fast evaluation method for online transient control strategy in strong uncertainty environment is proposed. First, based on the Extended Equal Area Criterion (EEAC), after the grid operation scenario changes rapidly, the difference in stability margin between different processing methods for grid time-varying factors is calculated to define the grid time-varying degree; Then, the key parameter matching index is established in combination with the key network characteristics of the power grid, which is matched with the examples in the historical database established offline, and the control measures are obtained according to the principle of conservatism; Finally, check and verify in the current grid mode, and send to the device for executing after the verification is passed. The simulation of the actual power grid online data shows that the proposed method can basically solve the situation that the online strategy is not suitable due to the rapid change of power flow or topology change in the power grid in a short time.

Low frequency high voltage ac (LF-HVac) transmission has been proposed as a bulk power transfer alternative to either the conventional 50/60 Hz HVac or the high voltage dc (HVdc) schemes. In LF-HVac transmission, the suggestion is to use fractional values of the conventional 50/60 Hz as the ac operating frequency. Doing so would considerably increase the power transfer capacity of a given transmission cable, extend the range, reduce losses, and improve voltage and dynamic stability of the system. Grid integration of remote offshore wind farms has been identified as the most promising potential application of LF-HVac. Thus, this paper presents a study on the electrical characteristics and performance of submarine cables with respect to the operating frequency. The findings indicate that LF-HVac operation of a cable system would achieve superior power handling capacity and efficiency when compared to HVac operation of the same cable system.

An aggregation method is proposed that transforms the multiple DFIGs into an equivalent DFIG model that retains the major collective dynamic characteristics of a group of DFIGs. It is intended for Electromagnetic Transients Simulation (EMT). The aggregated machine can take into account different speeds and parameters of each of the individual DFIGs and the connecting impedance of individual DFIGs. Starting with a State Variable (SV) model of an individual DFIG, aggregation is carried out recursively, by combining two DFIGs at a time and then reducing the order of the aggregate to match the state variable equations of a single DFIG so that the steady state performances are identical. Validation is carried out by comparing the detailed electromagnetic transient (EMT) simulation of the unreduced system with the reduced aggregate system. It is shown that the proposed aggregation method accurately matches the steady state response and also accurately reproduces the dominant transient response of the unreduced system. As the aggregate DFIG has the same number of state variables as a single DFIG, the overall wind farm's order is reduced significantly to increase the modelling and simulation efficiency.

串联型能量回收电路从电路结构上保证了异常条件下脉冲功率系统中充电电源的安全,但恒流充电电源经回收电感向储能电容充电时会引起回收电路的振荡,不仅会造成充电电源输出过压和回收电感损耗增加,还会导致充电电压一致性明显变差等问题.在分析了回收电路振荡特性的基础上,提出了在回收电感两端并接旁路开关和双路充电输入的电路结构以及相应的充电控制方法,不仅可以抑制回路振荡从而提高充电一致性,还可以消除回收电感和旁路开关的不必要损耗且控制方法也简单通用.对包含有串接型回收电路的600 V/400 A充电系统进行了电路仿真和实验验证,实验结果表明:在600 V重频条件下,回收电路的改进方案可将储能电容电压的充电一致性偏差由10 V降低到2.6 V,对应的相对偏差由1.7％降低到0.5％以内.

为解决输配电系统检测设备供电难题,设计了能够从输电线路架空地线取电系统电源电路.根据输电线路地线感应电压不稳定的特点,采用不可控整流桥和单端正激变换电路,结合闭环控制技术,设计并搭建了电路模型.通过分析在不同输入电压情况下电路的输出特性,验证了电路可行性,该电源电路实现了将9 V～100 V可变交流输入转换为12 V稳定直流输出,并且通过拟合不同负载情况下电路输出功率特性曲线,分析得出电源电路输出功率稳定.

In this work, a wind farm aggregation method for electromagnetic simulation model based on FDNE is proposed. Identical subsystems terminated with a same node operating in parallel can be aggregated with the same constraints. WTGs connected to the same feeder within a wind farm can be aggregated as one equivalent subsystem. And the wind farm aggregated model includes several aggregated subsystems based on the grouping criterion. And each aggregated subsystem model constitutes an aggregated WTG with a current amplifier to generate the same amount of real power, an equivalent impedance of collector system, and a FDNE component to adjust the aggregated model frequency characteristics. Wind farms based on DFIG and PMSG are used to validate the effectiveness of the proposed aggregation method. The simulation comparison results indicate that the proposed method can guarantee the consistencies of the power flow and transient responses during faults with high accuracy. And the computation time is shortened by 87% in the dome cases.

Low frequency AC (LFAC) is being proposed as an intermediate transmission technology between HVAC and HVDC. It could be attractive as a means for connecting offshore wind farms to the grid, in lieu of VSC-HVDC. Its single converter station could even be located onshore. Because it could operate at a fraction of 50/60 Hz frequency, LFAC could transfer significantly more power and for longer distances, without compensation, than HVAC. Unlike HVDC, LFAC could have the advantage of employing conventional AC circuit breakers for fault current interruption. Thus, it could be readily used for multi-terminal connections. This paper presents state space modeling of an ideal back-to-back VSC (frequency converter). Eigenvalues of the linearized model are used for stability and step response analysis of the converter. PSCAD/EMTDC simulations are then used to verify the accuracy of the derived model. This state space model could be applied in the analysis of LFAC systems.

The dead-time effect in a series multi-inverter generation system under carrier phase shift SPWM modulation is studied. First,the ideal output voltage of the generation system is deduced,and the mathematical model of dead-time in the generation system is established by the method of equal area approximation theory combined with Fourier analy?sis. Second,by adding the dead-time voltage to the ideal output voltage,the influence of dead-time effect on the output voltage from the generation system is analyzed when the modulation ratio or carrier ratio changes. On this basis,a dead-time compensation method based on the variation of carrier ratio is proposed. Finally,simulations are conducted based on MATLAB/ SIMULINK,and results show that this analysis method for dead-time effect is effective,and the pro?posed dead-time compensation method can effectively diminish the influence of dead-time on the output voltage and cur?rent from the series multi-inverter generation system.

There exists serious governor control instability in the islanded operation system of large capacity UHVDC with its matching hydraulic power generators. Ultra-low-frequency oscillations (ULFO) will happen because of the inconsistent control features between UHVDC and frequency regulation of generators. Using frequency domain analysis, there exists a frequency band of negative damping in the hydraulic turbine control system. The larger value of water starting time constant, the more serious negative damping exists in the frequency control system. And if the forward gain of governor becomes larger, the negative damping will be more remarkable. Effective frequency control strategies for UHVDC islanded system are proposed in this work by withdrawing a part of primary frequency control functions of generators or coordinating the hydraulic generator governors and UHVDC frequency limitation controller (FLC). Using the proposed strategies, islanded system frequency is mainly controlled by UHVDC FLC, which can successfully suppress the ULFO. Verification simulations are carried out and the simulation results prove the effectiveness of the proposed strategies.

In order to analysis the output dynamic characteristics of dc offshore wind farm, a multimachine representation dynamic equivalent method based on an improved fuzzy C-means (IFCM) clustering algorithm is proposed. First, characteristic variables which can characterize the dynamic characteristics of the input and state performance are researched. Second, an IFCM clustering algorithm is first put forward. Third, the dc offshore wind generators (DCOWGs) are divided into many groups by analyzing the characteristic variables data with the IFCM. Finally, DCOWGs in the same group are equivalent as one DCOWG to analyze the dynamic characteristics. Simulation results from MATLAB/SIMULINK verify the theoretical analysis.

特高压直流与大型水电机组配套电源采用送端孤岛运行方式,能有效消除由直流闭锁引起的潮流大范围转移、系统暂态功角失稳问题.但是,送端孤岛系统的频率稳定性是决定系统能否运行的关键因素之一.结合南方电网楚穗、普侨特高压直流孤岛的调试情况,研究了水电站与特高压直流送端孤岛系统超低频振荡的机理,提出了频率稳定控制策略;阐述了直流甩负荷导致部分机组调相运行的机理.机网协调控制RTDS试验平台的仿真结果以及特高压直流孤岛系统的现场调试结果表明了所提控制策略的有效性.

大容量特高压直流输电系统与配套大型水电站构成的直流送端孤岛运行系统存在着较严重的调速器控制稳定问题.云广特高压直流送端孤岛系统也存在水电机组调速器与直流控制不协调而出现的超低频振荡现象.分析了电网超低频振荡过程中所有机组的同调特征,提出了电网超低频振荡分析模型.基于频域分析法指出了水轮机调节系统在超低频范围内存在负阻尼频带,水轮机调节系统的时间常数越大、调速器前向通道增益越大,负阻尼越显著.提出了通过退出部分机组一次调频功能或协调机组一次调频与直流频率限制控制器(FLC)动作死区设置,以直流FLC调频为主的直流孤岛频率控制策略能有效抑制孤岛系统的超低频振荡.基于实时数字仿真器(RTDS)的机网协调控制实时仿真结果验证了该策略的有效性.

The inter-transmission of sub-synchronous electrical parameters between AC and DC sides of HVDC power transmission system is analyzed by switching functions of converter, and in term of sub-synchronous frequency the mechanism of sub-synchronous oscillations (SSO) in power grid caused by the control system of HVDC system is expounded. By use of complex torque coefficients in time-domain simulation the sub-synchronous damping characteristic of AC/DC power grid is researched in detail, and the principle of suppression SSO by supplementary sub-synchronous damping controller (SSDC) is emphatically discussed, then the design approach for the design of modal control-based SSDC is proposed. In allusion to an actual SSO occurred in a certain power grid in China, a modal control-based SSDC is designed. The correctness of the principle applied in the design of modal control-based SSDC and its effectiveness in suppressing SSO are verified by time-domain simulation.

With the increasing capacity of multi‐infeed DC for East China Power Grid, the risk of losing large‐capacity power supply is increasing, and the frequency security and stability situation in low load mode is worsening. Since the ‘9·19’ incident, the frequency characteristics of East China Power Grid have aroused wide concern. Actually, there is a big gap between simulation results and the actual measured values. This study analysed the key factors that affect the frequency response from the point of view of the turbine‐governor and drum boiler. On the basis of measured values, the parameters of primary frequency modulation and main steam pressure are identified. The results reflect the dynamic frequency response of ‘9·19’ incident successfully. According to the recognition results, recommendations are put forward to give the backbone to the security and stability of East China Power Grid.

With the increasing capacity of multi-infeed DC for East China Power Grid, the risk of losing large-capacity power supply is increasing, and the frequency security and stability situation in low load mode is worsening. Since the "9.19" incident, the frequency characteristics of East China Power Grid have aroused wide concern. Actually, there is a big gap between simulation results and the actual measured values. This paper analyzed the key factors which affect the frequency response from the point of view of the turbine-governor and drum boiler. On the basis of measured values, the parameters of primary frequency modulation and main steam pressure are identified. The results reflect the dynamic frequency response of "9.19" incident successfully. According to the recognition results, recommendations are put forward to give the backbone to the security and stability of East China Power Grid.

The valve commutation process during the converter commutation failure is studied on the microscale of electromagnetic transient and two equivalent circuits are proposed for the short circuit state and the DC-side state under long-time line-voltage respectively,based on which,the characteristics of DC voltage variation during the HVDC commutation failure are analyzed.Results show the inverter-side DC voltage during the HVDC commutation failure will decrease and even reverse.Simulation is carried out on RTDS real-time simulation platform including actual control and protection devices,which verifies the correctness of the proposed equivalent circuits.

Island operation mode formed by UHVDC and its matching power plants is getting more common in China these years. Moreover, AC tie-line N-2 faults can force to form UHVDC island operation mode. There are many stability issues of UHVDC isolated island operation grid. This paper summarizes the latest progress and research status about real-time simulation methods, voltage stability, frequency stability, over-voltage and sub-synchronous oscillations in UHVDC isolated island grid. The features and deficiencies of present simulation modeling methods are pointed out. The related research contents of the operational characteristics and stability control methods for UHVDC isolated island grid are put forward, which can be taken as references for future research on UHVDC isolated island system.

The level of fundamental frequency temporary overvoltage mathematical equation was derived for severe overvoltage problem of Yunnan-Guangdong UHVDC load shedding in islanded operation mode.The variation law of the overvoltage times in different effective short-circuit ratios (ESCR),and the influence of the power drop rate on the voltage variation under different ESCR conditions were analyzed.Blocking sequence control logic in pole control part and VDCL control logic optimization schemes based on the existing system were proposed.Verification simulation studies were carried out on the grid-unit coordination control real time simulation platform which connected with the real replicas of UHVDC control protection system and generator controls.The simulation results proved the effectiveness of the optimization schemes.