Research on a Novel Inverter of VSC

In order to improve waveform performance of light HVDC system, a lot of switches which operate in high frequency are used, which causes large switching losses and results high cost. A new Buck type voltage source converter(BVSC) is proposed. The new BVSC comprises a dual-buck converter and a three-phase inverter operating in grid frequency. Only two high frequency switches are used, which results good output waveform performance. In order to reduce the high frequency switching losses, a novel improved double-frequency Buck type voltage source converter(DBVSC) is also proposed. An additional dual-Buck converter is added to the BVSC, the added dual-Buck converter deals with the fundamental power that operates in low frequency, and BVSC only deals with harmonic power that operates in high frequency. The output waveform is enhanced and the switching losses are reduced in DBVSC, and the power rating is also increased. The DBVSC is very suitable for large power rating application. The one cycle control theory is adopted to control the proposed DBVSC with analog circuit, which is very simple. The proposed DBVSC and control method are verified by simulation.     

An EOQ Model at Random when Average Demand Is a Linear Increasing Function

For certain types of inventory, the ordering cycle and demand may be random variants, which satisfy certain types distribution. The classical EOQ model usually neglects the fact. Based on the constant demand, under the hypothesis that the ordering cycle is a random variant which satisfies exponent distribution, average demand is a linear increasing function, this paper considers the effects of the time-value of capital and inflation on replenishment strategy of inventory system. Loosening the condition of basic economic order quantity model under deterministic state, the total cost function of the model is provided. The optimum order quantity and cycle are obtained. The application range of EOQ model under the constant demand is widened. The theoretical evidence is provided for the inventory system to make management decision.     

微山湖典型水域营养盐分布及富营养化评价

为了明确微山湖水体营养盐分布及其富营养化水平现状,笔者根据2010年4月对微山湖3个典型水域营养盐监测数据,分析了微山湖营养盐空间分布特征,并应用卡尔森营养状态指数法和潜在性富营养化评价模式对研究水域富营养化现状进行了评价。结果表明：总磷、磷酸盐、总氮、硝酸盐氮、氨氮、叶绿素a含量均表现为：入湖河道> 湖中航道>养殖区;透明度表现为：养殖区>入湖河道>湖中航道。入湖河道、湖中航道和养殖区的卡尔森营养状态指数均值分别为63.0、61.8和52.0,入湖河道和湖中航道为重度偏中度营养水平,养殖区为中度偏重度营养水平;潜在富营养化评价表明：除S1站位为富营养,S5站位为磷中等限制潜在性富营养外,其他站位均为磷限制潜在性富营养水平。     

Saturation and Parameter Variation Influence Precision of Observer

The authors analyze the influence in vector controlled induction machine caused by parameter variation and main flux saturation affects speed estimation of adaptive state observer. According to simulation of the modified scheme with saturated induction motor model, it is proved that when the vector control scheme operates in field weakening region, the main flux saturation will obviously influence precision of speed observer and bring great error of speed estimation. Thereby, the main flux saturation should be compensated to improve performance of the vector control system.     

水环境容量的研究

如何将人类活动控制在水资源、水生态环境的承受范围之内,已成为实现人类可持续发展的核心问题之一。阐述水环境容量的定义、内涵、基本特征和类型,系统分析国内外对水环境容量研究的现状,并介绍水环境容量的计算方法,为今后水环境容量的研究提供一定的理论依据。     

康平县农业机械能耗现状与节能减排措施

近年来康平县农业装备水平快速提高,农业机械节能减排问题越来越突出。介绍康平县农业机械能耗现状,分析农机能耗过大的主要原因,有针对性地提出农业机械节能减排技术措施,以推进康平县农业农村节能减排工作进程。     

智能切换的模型参考模糊自适应内模控制的研究

针对具有大惯性、大滞后特性的电厂主汽温对象,采用模型参考自适应控制的思想,结合模糊控制和内模控制方法,提出了一种模型参考模糊自适应内模控制方法:在相消法设计内模控制器的基础上,利用参考模型的系统误差及其变化率去调节控制器中的参数。并用带反馈校正的模型预测作系统输出预测,根据系统响应和系统预测值是否在给定误差范围内来共同决定控制量在限幅值与内模控制器输出值之间进行在线智能切换。并通过热工对象的仿真研究,证明其有效性。     

辽宁省水稻育插秧机械化发展研究

水稻是辽宁省主要作物,水稻机械化育插秧是水稻生产全程机械化中的薄弱环节。阐述辽宁省为提高水稻机械化栽植水平采取的一系列措施及取得的成效,分析水稻育插秧技术推广中存在的问题及主要原因,并提出对策与发展建议。     

起重机吊臂有限元模态分析

利用ANSYS软件对起重机吊臂进行了有限元模态分析,得出了各阶模态下吊臂的固有频率和振型,找到了吊臂振动中的危险区域,为产品设计和改进提供了理论依据。     

污水泵的研究现状与进展

研究固液两相流体在离心泵内的运动规律、完善其设计理论和设计方法一直是设计人员十分重视的课题。针对污水泵的研究情况,分别从污水泵理论研究、内特性研究、外特性研究、水力设计等几个方面对污水泵的研究现状进行了较为详细的阐述,指出加强泵内外特性研究、探求流动机理、开发适合水泵设计的专业化软件用于泵产品的计算机集成制造(CIMS),将是泵行业发展的重要方向。