The transfer capability of thermal power bases under different installed capacities and transmission distances as well as its required fixed series compensation(FSC) are analyzed. By means of eigenvalue analysis the sub-synchronous resonance(SSR) that may cause by series compensation is evaluated. Analysis results show that the thermal power base will face with different extent of SSR risk while the installed capacity of thermal power base is more than 200MW,the transmission distance is longer than 400km and the series compensation ratio is between 30 percent and 50 percent. With the increment of installed capacity,transmission distance and series compensation level,the damage of SSR will be more serious.

Combined with six regional grids in China, the security and economy about the voltage levels,transmission,structure and interconnection of synchronized power system are analyzed. It is pointed out that,AC 500 kV synchronized power system can meet the demands of China’s economic development until 2020 year;HVDC and AC 500 kV transmission of independent power sources are its fundamental power supply modes;the branch - like network structure and the hot - standby dynamic reactive power are the solutions to its cascading faults and voltage instability;the regional grid interconnection could be optimized by choosing between controllable(ordinary or back - to - back HVDC) and uncontrollable (extra - high voltage AC) mode according to practical conditions.

The economy and security analysis of AC UHV in China is carried out in three applications:long-distance large-capacity transmission,regional grid interconnection and UHV network,which is compared among three schemes:DC high-voltage (including back-to-back),AC 500 kV and UHV. Combined with different views in some relative references,it is concluded that,compared with the other two schemes,the AC UHV has no superiority in both economy and security for all three applications. DC high-voltage scheme is the better choice for 600 km and above transmission distance while AC 500 kV for less than 600 km. For about 600 km distance and over 7 000 MW transmission capacity,comparative selection between 500 kV and 1 000 kV may take place. AC interconnection enlarges the synchronous power grid but lowers security,while DC back-to-back interconnection improves the security but increases investments. The economic effect of UHV network is nearly same as other interconnection modes. With the consideration of investment,it is recommended to adopt EHV network + DC and EHV transmission + back-to-back or EHV interconnection. It is suggested to carry out the research for improving the usage efficiency of EHV network in China.

The reliability level of STATCOM devices is an key issue concerned by all of designers, manufacturers and operators. An k-out-of-n: G system model of STATCOM and the basic analysis method for it are proposed in this paper. The k-out-of-n: G system can be used to quantify the reliability benefit of redundancy units in main circuit of STATCOM. Utilizing the basic relability indices of IGCT, GTO and IGBT provided by literatures, the reliability value and MTTF of an practical 50 MVA STATCOM device are evaluated. And the optimal amount of redundant units is analyzed basing on the indices obtained in forenamed study. Finally the dynamic model is proposed to evaluate the reliability of the k-out-of-n: G system when component failure induces higher failure rates in survivors.

There will he several DC lines parallel connected to the South China Power Grid in 2015.A severe fault,i.e.DC bipolar block is selected to go deep into the research by simulation.The transient stability problem caused by this severe fault is theoretically analyzed and the rationality of the analysis is proved by the simulation.A novel new strategy is proposed,in which the filter of the DC fault line at converter station is reserved to enhance the system transient voltage stability under this fault. Finally the feasibility of this approach is proved by simulation.

The power network connected to Yimin-Fengtun transmission line with thyristor controlled series compensation (TCSC) is simplified and simulated by use of the principle of equivalent simplification. The results from numerical simulation and steady state power flow calculation before and after the simplification and those from stability calculation with 45% series compensation added show that the systems before and after the simplification are entirely equivalent for Yimin- Fengtun transmission line. When permanent single-phase grounding fault and loss of synchronism occurs respectively in the simplified system, the power angle characteristics of the simplified system and the bus voltage waveform at the Fengtun side are basically coincided with those of the system before simplification during the critical stability time intervals before t is equal to 5.5 second and t is equal to 6.0 second respectively.

目的探讨腹腔镜联合手术的优越性和手术原则.方法回顾分析2001年6月至2003年6月56例8类腹腔镜联合手术的方法及结果.结果 63例均顺利完成联合手术,无并发症.结论腹腔镜联合手术创伤小,痛苦轻,多病联治,住院时间短.拓宽了腹腔镜手术领域.

目的探讨腹腔镜在阑尾切除术中的应用价值.方法回顾性分析我院开展腹腔镜阑尾切除术48例的诊治经过.结果完成手术48例.手术时间20～60min,平均30 min.术后平均2.5 d出院.无并发症发生.结论腹腔镜阑尾切除术具有创伤轻、痛苦小、恢复快、疤痕小等优点,是治疗阑尾炎安全、有效的方法.

采用Siemens公司的NETOMAC数字仿真计算程序详细分析了2005年广东电网的暂态电压稳定性,对广东电网可能存在的暂态电压稳定问题、电压薄弱环节、影响因素等进行了深入的研究,提出了在系统中装设STATCOM设备和利用直流系统的紧急功率调制功能等措施解决存在的问题.

The great scales nonlinearities and uncertainties in modern power systems mean that they are among the most intractable problems in dynamic control. In the present paper, direct neural dynamic programming (direct NDP) is introduced for a real time supplementary control application. Direct NDP is an on-line learning control paradigm that learns to improve system performance by following the computed gradient toward meeting the overall learning objective. As such the method makes use of on-line measurements to generate proper control actions. This feature is of critical significance when dealing with dynamic systems that are difficult to model or model precisely. In This work, a static VAr compensator (SVC) supplementary damping control in a 4-generator 2-area system is implemented using direct NDP. The self-learning and adaptive abilities of direct NDP are analyzed in the MATLAB environment. Simulation results demonstrate the advantages of direct NDP over conventional control.

A simple, fast, and generally applicable multilevel space vector modulation (SVM) algorithm is described in this paper. The complex reference voltage vector is decomposed into an offset vector and a two-level model. Thus a complicated multilevel SVM control problem is simplified into a simple two-level SVM problem. The zero-sequence reference voltage is used to determine the switching states and their duty cycle so the control issues can be easily simplified. The proposed algorithm was implemented using a DSP-based modulator for multilevel inverters. Test and simulation results show that the algorithm is very simple and computationally efficient.

病人:女,68岁.因右上腹疼痛1周入院.1周前出现原因不明的右上腹疼痛,呈持续性,阵发性加剧,右肩背牵涉痛,伴恶心、呕吐,不思饮食等症状.

Based on the zero-sequence component of the reference voltages, this paper comprehensively analyzes the neutral-point variation and balancing control for three-level neutral-point-clamped inverter. An analytical method is proposed to accurately calculate the injected zero-sequence voltage for NP balancing. Based on the analytical analysis, the limitation of NP balancing control is revealed and the NP-fully-controllable region is presented. A real-time NP balancing algorithm is proposed as well. The feasibility of the proposed method is verified using simulation results for a 6kV/1800kVA medium voltage drive.

目的探讨腹腔镜在乙状结肠镜检查中的应用价值.方法将电视腹腔镜置入硬质乙状结肠镜,通过监视器屏幕观察,完成乙状结肠镜检查46例.结果由于视野扩大,图像清晰,缩短了检查时间,减轻了患者的痛苦,46例均顺利完成检查,无并发症发生.结论利用电视腹腔镜完成乙状结肠镜检查是可行的,尤其在基层医院充分利用了现有的腹腔镜设备.

A new theory of reference voltage decomposition is proposed. Based on this theory the reference voltage vector of a multilevel VSI is divided into two parts: base vector and two-level vector. Then a new multilevel space vector modulation (SVM) method is presented. With the proposed method only the two-level reference vector needs to be synthesized using conventional two-level SVM methods. The computation of the proposed method is very simple and fast through simplification of the multilevel SVM issue into a two-level SVM issue. In addition some important allocation laws of multilevel space vectors are presented which are very useful to find out all redundant switching states. The proposed method is applicable for any number of levels and its feasibility is verified by simulation results.

When the single phase to grounding fault occurs, the respective influence of two different synchronizing signals, i.e., the line current i and capacitor voltage uc, on TCSC device are studied by the digital simulation, dynamic simulation and theoretical analysis. Taking the line current i as synchronizing signal, the serious DC component will appear in line current i and the line current i will be seriously distorted when single phase grounding fault occurs. Taking the capacitor voltage uc as synchronizing signal, there is not serious DC component in the power system, but serious low-order harmonics. So both the line current and the capacitor voltage are not suitable for being used as the synchronizing signal. It is more rational to take the fundamental component of the line current for being used as the synchronizing signal of TCSC. The advantage of this method is to eliminate the DC component and harmonic components and the starting point of the phase angle of the synchronizing signal will not be shifted, and it is helpful for the stable operation of the power system. In this paper an efficient control strategy is proposed and this strategy can reduce the adjusting time during the fault process and reduce the harmful effect from the fault and improve the control characteristics of power system transient stability.

The choice of the synchronizing signal has strong-impacts on the transient behaviors of TCSC (Thyristor Controlled Series Compensation). When the capacitor voltage is used as the synchronizing signal, both overshoot and oscillation occur. However, when the line current is employed, TCSC acts as a first-order lag element. This paper presents a mathematical model to explain this extraordinary phenomenon. Based on the model, the factors affecting transient response of TCSC are also discussed. The model can give advice to the design of TCSC controller. Rules of controller parameters adjustment are discussed. This model is verified by digital simulation results.

The significant capacitance effects of long transmission lines may cause self excitation in small generators connected to the main electric grid by such long lines in less populated areas such as western China. Numerical simulations of the Qinghai provincial grid using PSCAD/EMTDC code agreed with experimental results of a three -machines analogous system. The various phenomena were analyzed to understand the principle for self -excitation waveforms. And some measures, such as destroying the parameters of the resonance, improving the excitation system, alternation of the adapters of sub -transformers, and so on, were recommended to restraint the self -excitation waveforms via simulations and experiments.

TCSC is a FACTS device installed in a long transmission line to improve its power transmission ability. By simulations, this paper investigates the influence of the phase and amplitude of TCSC output on the power oscillation of a 2-area interconnected system. The result indicates, when the compensation degree of TCSC increases, its effect will reach a pink value just like a saturation phenomenon. When the compensation degree is suitable, the phase of TCSC output has a more significant impact on the oscillation than the amplitude. In order to improve the damping of the system, TCSC is found to be a better choice than traditional series compensation or two parallel lines.

在可控串补(TCSC)动模实验装置特性研究的基础上,进一步研究了TCSC基频等效阻抗与TCR基频电抗的关系.提出了TCSC电容支路的电容是随着控制角β的变化而变化的等效电容CT的观点,并且从理论上和动模实验上进行了分析和验证.同时研究了TCR回路的基频电抗XL的大小对TCSC谐振点和控制范围的影响,以及对TCSC回路的电压和电流波形及大小的影响.获得了相应仿真和动模实验结果,确定了XC与XL的比值关系及K值选择范围.