Design of PI controllers for achieving time and frequency domain specifications simultaneously

This paper deals with the design of PI controllers which achieve the desired frequency and time domain specifications simultaneously. A systematic method, which is effective and simple to apply, is proposed. The required values of the frequency domain performance measures namely the gain and phase margins and the time domain performance measures such as settling time and overshoot are defined prior to the design. Then, to meet these desired performance values, a method which presents a graphical relation between the required performance values and the parameters of the PI controller is given. Thus, a set of PI controllers which attain desired performances can be found using the graphical relations. Illustrative examples are given to demonstrate the benefits of the method presented.     

Overshoot Graded Layers for Mismatched Heteroepitaxial Devices

We have studied the use of overshoot graded layers for the control of the dislocation density in mismatched heteroepitaxial layers. Graded ZnS _y Se_1–y structures were grown on GaAs (001) by photoassisted metalorganic vapor-phase epitaxy (MOVPE) and characterized by high-resolution x-ray diffraction (HRXRD). All samples had a uniform top layer of ZnS_0.014Se_0.986, and various graded layers were incorporated between the substrate and the uniform top layer; these included forward-graded (FG) and reverse-graded (RG) buffers. Some structures incorporated overshoot at the interface with the uniform top layer (FGO and RGO buffers). Among the FG samples, those with overshoot exhibited better crystal quality and lower dislocation densities than those without. This is expected because the mismatched interface between the graded layer and the top ZnS_0.014Se_0.986 can affect the bending over of threading dislocations for the production of misfit dislocations, indirectly promoting annihilation and coalescence reactions. An overshoot interface with 0.1% mismatch was found to remove 2 × 10⁸ cm⁻² dislocations from the top device layer. Overshoot did not reduce the dislocation density in RG structures, but this may be because the sign of the overshoot caused the generation of new dislocations rather than interactions between existing ones. For growing a high-quality device layer with minimal defect density, it appears that steep forward-graded layers with overshoot may be best in this material system.     

大功率变流器系统H桥低感叠层母线排设计

针对80kVA/400A变流器H桥母线排的设计要求,使用ANSOFT MAXWELL有限元分析软件比较了不同设计原则下杂散电感参数的变化,并提出了一种新型的优化母线排结构,较少了IGBT模块的关断过冲电压,并优化了高频电流的分布。通过仿真和实验分别证实了新型母线排的良好测试结果,最后给出了系统结构和实验波形。     

新型可内置软启动电路的设计及其应用

提出了一种基于BiCMOS工艺设计的芯片内置软启动电路,用于避免启动过程中浪涌电流及输出电压过冲对电子系统造成损害.该电路结构简单,无需使用外部软启动电容,可完全集成在芯片内,有效节省了应用电路板空间和元件成本.经HSPICE仿真验证,证明该电路仅使用一个10pF的小电容即可实现1ms的软启动时间.该电路可应用于各种开关电源中.     

复合阻尼对锥阀压力特性的影响

针对独立阻尼调压锥阀工况适应能力差等问题,提出一种复合阻尼调压锥阀,利用AMESim平台搭建系统仿真模型,与普通锥阀进行对比分析,并分析了复合阻尼调压锥阀减振调压的影响。结果表明:在一定结构参数条件下,复合阻尼调压锥阀具有更好的静态特性且动态特性得到优化;半锥角、孔径对复合阻尼调压锥阀减振调压能力有重要影响。     

Performance characteristics of air-breathing anion-exchange membrane direct ethanol fuel cells

An air-breathing direct ethanol fuel cell (DEFC) with an anion-exchange membrane (AEM) and Pt-free electrodes is designed and investigated. Particular attention is paid to studying the performance characteristics of the air-breathing AEM DEFC. Experimental results reveal that this air-breathing AEM DEFC yields a peak power density as high as 38 mW cm⁻² at room temperature, which is comparable to the conventional Pt-based proton exchange membrane direct methanol fuel cells (PEM DMFCs). The overshoot/undershoot behaviors of both the cell voltage and cell temperature are avoided in the air-breathing AEM DEFC due to the use of ethanol-tolerant cathode catalyst. It is also found that the cathode water flooding behavior occurs in this air-breathing AEM DEFC, thus lowering the cell performance.     

Experimental investigation of dynamic performance and transient responses of a kW-class PEM fuel cell stack under various load changes

The dynamic performance is a very important evaluation index of proton exchange membrane (PEM) fuel cells used for real application, which is mostly related with water, heat and gas management. A commercial PEM fuel cell system of Nexa module is employed to experimentally investigate the dynamic behavior and transient response of a PEM fuel cell stack and reveal involved influential factors. Five groups of dynamic tests are conducted and divided into different stage such as start-up, shut-down, step-up load, regular load variation and irregular load variation. It is observed that the external load changes the current output proportionally and reverses stack voltage accordingly. The purge operation benefits performance recovery and enhancement during a constant load and its time strongly depends on the operational current level. Overshoot and undershoot behaviors are observed during transience. But the current undershoot does not appear due to charge double-layer effect. Additionally, magnitudes of the peaks of the voltage overshoot and undershoot vary at different current levels. The operating temperature responds fast to current load but changes slowly showing an arc-like profile without any overshoot and undershoot events. The air flow rate changes directly following the dynamic load demand. But the increased amount of air flow rate during different step-change is not identical, which depends on the requirement of internal reaction and flooding intensity. The results can be utilized for validation of dynamic fuel cell models, and regarded as reference for effective control and management strategies.     

Set invariance and performance analysis of linear systems via truncated ellipsoids

The objective of this paper is to develop numerically simple and effective methods for system analysis using truncated ellipsoids. The paper studies linear time-invariant systems subject to persistent disturbance and state constraint. The maximal output under a set of initial conditions and the overshoot under a given step input are estimated. Attempts are also made to detect an invariant set, as large as possible, within state constraint. The results are based on the set invariance condition for the truncated ellipsoid, and a characterization of the set where the output possibly reaches a local extrema. The analysis problems are converted into optimization problems whose constraints become linear matrix inequalities when a few variables are fixed. Numerical examples demonstrate the effectiveness of the truncated ellipsoid and the proposed methods.     

大型重载平台支撑液压缸过冲力学分析

大型重载平台在支撑液压缸下降或调平时会出现过冲情况,严重影响平台的正常功能。通过对大型重载平台支撑液压缸下降或调平过冲进行力学分析,建立大型重载平台支撑液压缸载荷、电磁换向阀功率极限和系统压力设定之间的关系,对后续系统设计具有指导意义。     

一种改进的数字PID控制算法及其在励磁系统中的应用

文章在普通ＰＩＤ调节算法的基础上提出一种新的改进算法。由此算法支持的微机励磁调节器在实验及生产运行中表明：此算法大大改善了调节特性,超调量下降,振荡次数减少等。