可控避雷器晶闸管阀串联均压方法

可控避雷器晶闸管阀主要由反并联晶闸管对串联而成,为保证各个晶闸管承受电压的一致性,必须采取适当的均压措施。根据晶闸管阀串联均压的技术要求,利用电力电子系统设计程序,对传统RC均压方法的可行性进行了计算分析。研究得出RC均压方法可能严重破坏可控避雷器的静态电位分布,不适用于晶闸管阀。提出采用晶闸管与金属氧化物电阻片一对一并联的均压方法,利用金属氧化物电阻片良好的非线性伏安特性限制晶闸管的过电压,并对电阻片的均压效果进行了仿真计算。结果表明,合理选择电阻片的串、并联数和尺寸参数,可以将串联晶闸管的开通过冲电压均限制在要求的范围内。

适合于柔性高压直流输电系统的模块化多电平变流器的自适应均压方法

提出一种模块化多电平变流器(modular multilevel converter,MMC)的自适应均压方法。在每个控制周期中,根据桥臂电流绝对值的大小选择不同个数的功率模块进行轮换。此外,还推导并计算了采用该自适应均压方法的功率器件平均开关频率的解析表达式。通过160 k V/400 MVA的MMC仿真系统验证了所提出的自适应均压算法的有效性和平均开关频率计算的正确性。最后,在RT-LAB实时仿真实验平台中搭建了350 k V/1000 MW的MMC背靠背系统,对上述方法进行了实验验证。实验结果表明,采用所提出的自适应均压方法能够在保证功率模块电容电压均衡的前提下降低开关频率,提高系统效率。

10kV固态切换开关中串联晶闸管阀均压分析

针对10kV固态切换开关中晶闸管阀串联电压不均问题,分析了串联电压不均原因和串联均压技术要求及均压方法,研究了晶闸管阀两端并联静态均压电阻Rp和动态均压电路RC。运用Saber软件搭建仿真电路,验证了均压方法的有效性和均压参数计算的准确性。

MMC-MTDC系统协调启动控制策略

为快速平稳的启动基于模块化多电平换流器的多端柔性直流输电系统(modular multilevel converter-multi-terminal direct current,MMC-MTDC),避免各站启动时序配合不当引起大的电气冲击甚至启动失败,提出了MMC-MTDC系统协调启动控制策略。首先,指出MMC存在交流侧、直流侧和交直流侧混合3种预充电方式,基于其充电机理,设计了预充电方式识别方法,提出了可将子模块充电至额定电压的闭环均压充电策略;其次,研究了多端系统启动时序的有效配合方案,提出了基于直流电压斜坡控制方式的并联式MMC-MTDC系统协调启动控制策略;最后,通过Matlab/Simulink构建三端系统进行仿真。结果表明:闭环均压充电方法能自动适应MMC 3种预充电方式,使子模块平稳充电至额定值;协调启动策略则能很好的实现多端系统平稳解锁。

Online model identification of lithium-ion battery for electric vehicles

In order to characterize the voltage behavior of a lithium-ion battery for on-board electric vehicle battery management and control applications,a battery model with a moderate complexity was established.The battery open circuit voltage (OCV) as a function of state of charge (SOC) was depicted by the Nernst equation.An equivalent circuit network was adopted to describe the polarization effect of the lithium-ion battery.A linear identifiable formulation of the battery model was derived by discretizing the frequent-domain description of the battery model.The recursive least square algorithm with forgetting was applied to implement the on-line parameter calibration.The validation results show that the on-line calibrated model can accurately predict the dynamic voltage behavior of the lithium-ion battery.The maximum and mean relative errors are 1.666% and 0.01%,respectively,in a hybrid pulse test,while 1.933% and 0.062%,respectively,in a transient power test.The on-line parameter calibration method thereby can ensure that the model possesses an acceptable robustness to varied battery loading profiles.

Estimating Average Reservoir Pressure： A Neural Network Approach with Limited Data

Insight into average oil pressure in gas reservoirs and changes in production （time）, play a critical role in reservoir and production performance, economic evaluation and reservoir management. In all practicality, average reservoir pressure can be conducted only when producing wells are shut in. This is regarded as a pressure build-up test. During the test, the wellbore pressure is recorded as a function of time. Currently, the only available method with which to obtain average reservoir pressure is to conduct an extended build-up test. It must then be evaluated using Homer or MDH （Miller, Dyes and Huchinson） valuation procedures. During production, average reservoir pressure declines due to fluid withdrawal from the wells and therefore, the average reservoirpressure is updated, periodically. A significant economic loss occurs during the entire pressure build-up test when producing wells are shut in. In this study, a neural network model has been established to map a nonlinear time-varying relationship which controls reservoir production history in order to predict and interpolate average reservoir pressure without closing the producing wells. This technique is suitable for constant and variable flow rates.

Variable Universe Fuzzy Control for Battery Equalization

In order to avoid the overcharge and overdischarge damages, and to improve the lifetime of the lithium-ion batteries, it is essential to keep the cell voltages in a battery pack at the same level,i.e., battery equalization. Based on the bi-directional modified Cuk converter, variable universe fuzzy controllers are proposed to adaptively maintain equalizing currents between cells of a serially connected battery pack in varying conditions. The inputs to the fuzzy controller are the voltage differences and the average voltages of adjacent cell pairs. A large voltage difference requires large equalizing current while adjacent cells both with low/high voltages can only stand small discharge/charge currents. Compared with the conventional fuzzy control method, the proposed method differs in that the universe can shrink or expand as the effects of the input changes. This is important as the input may change in a small range. Simulation results demonstrate that the proposed variable universe fuzzy control method has fast equalization speed and good adaptiveness for varying conditions.

Outcome of surgical treatment of type Ⅳ capitellum frac- tures in adults

Objective： Fractures of the capitellum and trochlea constitute less than 1% of all elbow fractures and a shear fracture involving the capitellum and extending medially into most of the trochlea is rarely reported. Type Ⅳ capitellum fracture is still controversial in regard to its ra- diographic appearance, surgical approach and osteosynthesis. We report 10 cases of type Ⅳ capitellum fracture with a view to elucidating its clinical features and treatment outcome. Methods： We treated 10 patients of type Ⅳ capitellum fracture with a mean age of 32 years. A uniform surgical approach and postoperative rehabilitation were followed. Results： Nine patients presented to us after a mean of 4 days of injury and one patient was nonunion after 6 months of injury who had been treated conservatively by a bone setter. Double arc sign was absent in 6 cases. Intraopera- tively 6 capitellotrochlear fragments were devoid of soft tissue attachments. By Mayo Elbow Performance Score evaluation, 7 patients got excellent, 2 good and 1 fair results. One patient with associated elbow dislocation developed heterotopic ossification. There was no case of avascular necrosis, osteoarthrosis or fixation failures. Conclusions： Type Ⅳ capitellum fractures are rare and belong to complex articular injuries. A good functional out- come can only be achieved with open reduction and stable internal fixation followed by early mobilization. Preopera- tive radiographic assessment and computed tomography help surgeons in choosing the right surgical approach and implants. Good surgical technique and stable internal fixa- tion are the keys to early mobilization and good functional outcome.