浅谈解决三相变压器直流电阻不平衡率的问题

通过对三相变压器直流电阻不平衡率实例的分析,总结出了解决三相变压器直流电阻不平衡率的方法。     

三相异步电动机的滚动轴承装配工艺

介绍了三相异步电动机的滚动轴承结构和装配工艺,尽量避免了滚动轴承装配不正确导致的电机振动及噪声问题。     

浅谈三相交流变频电动机的设计

综合考虑三相交流变频电动机的特点,分析了恒压恒频供电的常规电机与由变频电源供电的变频电机在设计方面的区别,就变频电机设计原则和设计过程应注意的问题进行了探讨。     

Hydrodynamic studies on three-phase fluidized bed using CFD analysis

Three-phase fluidization refers to fluidization of solid particles by co-current, upward flow of gas and liquid-phases for the purpose of bringing three-phases in contact in a single operation. Due to complications in understanding hydrodynamics of three-phase fluidized bed, CFD analysis is used to predict the hydrodynamics of it. In this study, liquid-phase is water which flows continuously, where as the gas phase is air which is distributed discretely throughout the bed. Ceramic particle of 1 mm diameter, density of 2650 kg/m³ is used as a solid phase. Excellent mixing, heat and mass transfer rates are the unique features of three-phase fluidized bed. The selection of distributor plays an important role in the quality of fluidization [1]. CFD model is created as the realistic representation of actual fluidized bed. The liquid and solid flow is represented by the mixture model. The air is injected from the bottom of the fluidized by means of discrete phase method (DPM). Simulation results are obtained by using porous jump and porous zone model to represent the distributor. It is found that porous zone model is best applicable in the industries, since stability of operating conditions is achieved even with non-uniform air, water flowrates and with different bed heights(100 mm, 200 mm, 300 mm, 400 mm and 500 mm).Simulated Pressure drop values of the fluidized bed have good agreement with the experimental findings. As the gas flowrate increases, the pressure drop in the column is decreases, provided the initial bed height, diameter of the column, and liquid flowrate are constant. This is due to decrease in density of the fluid medium in the bed by means of more gas hold up. The approach of the simulated values to the experimental values can be reduced with better understanding the nature of the fluidized bed.     

数码发电机整流开关控制电路设计

对现有数码发电机中整流开关控制电路存在的不足作了讨论,设计了一种新型的整流开关控制电路。在保证控制性能的前提下,利用一路触发电路同时控制三相半控整流电路中三只晶闸管的导通与关断,不需要同步电路,简化了电路结构,减小了电路的体积和重量,降低了数码发电机的成本。     

不换位输电线路产生的不对称问题及解决方法

在线路负荷较轻或系统黑启动的初始阶段,由不换位超高压输电线路参数不对称产生的负序电流可能导致发电机负序保护动作,引起发电机跳闸或阻止发电机并网运行而造成大面积停电,或损坏系统中的一些用电设备.文章利用三相潮流计算程序对不同输送功率和不同线路长度情况下的由输电线路参数不对称引起的负序电压和电流进行了计算和分析,并对通过合理设置线路串补元件及线路两端无源无功补偿元件参数来减小负序分量的方法的可行性进行了探讨.计算分析结果表明,该方法能够有效抑制由线路参数不对称产生的负序电流和电压.     

三相四线制电力有源滤波器的滑模变结构控制

设计了一种基于滑模变结构控制的三相四线制有源滤波器装置,介绍了该装置的原理及滑模变结构控制方法,并对滑动模态的存在性、可达性和稳定性进行了分析;指出滑模控制的本质是一种等速趋近律,并对其优缺点进行了分析,仿真结果表明该控制方法具有良好的谐波抑制性能,且易于实现.     

Flutter of delaminated three-phase nano-composite beam-plates

ABSTRACT

In this article the supersonic flutter instability of delaminated carbon nanotube reinforced three-phase composite plate is investigated. The classical laminate plate theory and piston aerodynamic theory are developed to construct the governing equation of delaminated three-phase nano-composite plates. The effective material properties are obtained using Halpin-Tsai relation and rule of mixture. The effects of different parameters including carbon nanotubes (CNTs) weight percentage, fiber volume fraction, CNTs aspect ratio and different fiber orientation on flutter pressure of delaminated reinforced composite plates are considered. According to the results, appending small amount of CNTs (4% wt) into the matrix epoxy can improve the flutter critical pressure by 33% in comparison to the neat matrix epoxy.     

Adaptive nonlinear control of three-phase shunt active power filters with magnetic saturation

The problem of controlling three-phase shunt active power filters (SAPF) is addressed in presence of nonlinear loads. Previous works generally design control for SAPF based on standard models that assume the involved magnetic coil to be linear. In reality, the magnetic characteristics of these components are nonlinear (especially in the presence of large magnetic flux density in the ferromagnetic core). In this paper, a new oriented control model for SAPF-load system, taking into account for the nonlinearity of coil characteristics, is developed. The control objective is twofold: (i) compensating for the current harmonics and the reactive power absorbed by the nonlinear load; (ii) regulating the inverter DC capacitor voltage. To this end, based on the new model, a nonlinear controller is developed, using the backstepping technical design. It is therefore able to ensure good performances over a wide range of variation of the load current. Moreover, the controller is made adaptive for compensating the uncertainty on the switching loss power. The performances of the proposed adaptive controller are formally analyzed using tools from the Lyapunov stability and the averaging theory. The supremacy of the proposed controller with respect to standard control solutions is illustrated through simulation.     

基于PIC12C508的三相电源相序测试仪的设计

三相电路作为实际工程中整个电力系统的驱动部分,在实际应用中有其特殊的意义,因此对其进行正确的利用和测试尤为重要。本文从测试入手,利用PIC12C508单片机实现了对三相电源相序测试。