交直流混联系统对变压器保护性能的影响及解决措施

在交直流混联系统中,直流偏磁和换相失败都会对变压器差动保护产生不利影响.以西北电网交直流混联系统为分析对象,分别研究了变压器差动保护在这2种情况下的运行性能.仿真数据表明:直流偏磁严重的变压器发生区内弱故障时,差动电流中的2次谐波将会引起变压器差动保护拒动;直流系统换相失败时,交流系统电流可以看成一个谐波源,此时发生内部故障时,变压器差动保护也会由于差动电流中2次谐波的存在而使保护拒动.为了解决这些问题,文中采用了基于故障分量综合阻抗的保护方案.理论分析和仿真验证都表明新方案在变压器直流偏磁或换相失败时仍然具有很高的灵敏度和可靠性.     

单相AC-DC变换电路设计及试验

该单相AC-DC变换电路以有源功率因数控制器UCC28019为核心,STM32F103做主控芯片,采用主控芯片片上DAC调节UCC28019电压误差放大器反馈端,控制输出电压稳定输出;设计功率因数测量电路、输出保护电路、功率因数调整电路等电路模块。经测试,系统输入电压为24 V时,输出2 A电流时可稳定输出36 V电压,负载调整率为0.02%,电压调整率为0.028%,功率因数测量最大误差为0.02,过流保护动作电流为2.54 A,交流输入侧功率因数校正后最高达99.9%,转换效率达96.7%,功率因数在0.8¹.0稳定可调。     

交直流接点转换器的应用

介绍了交 直流信号转换器在实际中的应用 .实践表明 ,多粉尘强振动环境下应用这种转换器可使PLC和继电接触器控制系统的运行十分可靠 .     

交直流电力集成技术

建立了新型电机的数学模型，为解决关键技术问题提供了理论基础。查明了发电机整流系统特有的低频功率振荡的机理，得出了稳定判据及解决稳定问题的技术措施；通过合理设计，可控制直流电压的浮动范围；综合治理整流过程引起的交流谐波和直流脉动，提高了系统的EMC性能；巧妙地处理了系统的强非线性，从而得出了直流短路和交直流同时短路的冲击电流解析式；提出了根据整流装置输入、输出电压波形进行实时在线故障诊断的原理和方法。在此基础上，将定子3相绕组、12相绕组、整流装置、励磁系统、励磁调节器等集于一体，功研制出性能优良的交直流发电机，能同时提供高品质交直流电源，为独立电力系统的集成化奠定了基础。     

LED照明中TRIAC调光电路的研究与设计

本文阐述了TRIAC调光原理,并对LED照明中TRIAC调光存在的问题进行了分析,然后结合NS的LED驱动芯片LM3445调光实现方式,设计出TRIAC调光具体电路,最后通过仿真对该电路进行了验证。本文通过合理的电路设计解决了LED照明中TRIAC维持电流IIH不足,TRIAC导通瞬间输入电流振荡等问题,最终满足了TRIAC调光器在LED室内照明中的应用需求。     

Switching frequency determination of a bidirectional AC-DC converter to improve both power factor and efficiency

This paper investigates the possibility to optimize both the efficiency and the power factor of energy conversion systems which include power electronic converters. The values of these important power quantities depend on different parameters, such as the switching technique and the switching frequency of the power electronic elements. Comparing the already known and used switching techniques with each other we can conclude that the sPWM method offers the highest values of the efficiency and the power factor simultaneously. However, when using this technique the basic current harmonic lags as to the voltage in case of ohmic inductive loads resulting in the decrease in the power factor. In the present work a new sPWM switching technique is suggested in order to achieve higher power factor and efficiency compared to the traditional sPWM method. The aforementioned switching technique is a modified sPWM method based on an appropriate shifting of the input current to the grid voltage. But, the following question is raised: Is there a switching frequency value in a given converter topology by which both the efficiency and the power factor gain optimal value? Thus, the main aim of the present paper is determine this specific switching frequency value. This is achieved by using a simple method based on a criterion suggested in this work. In order to demonstrate how this specific frequency value can be found, a bidirectional AC-DC converter composed of a single phase bridge and two switching elements at the DC side is used. This proposed converter topology excels in that the total number of the switching elements is minimal. The study of this subject is carried out through Matlab/Simulink simulation and experimentation.     

交直流复合电压下的油纸绝缘局部放电统计图谱研究(英文)

The converter transformer is one of the most critical equipments in high-voltage direct current transmission systems.Valve-side windings have to withstand complex stresses combined of AC,DC,and pulsed voltages.Partial discharges(PDs) can thus easily occur in oil-impregnated paper insulation.The current paper presents the statistical phase-resolved distributions of partial discharges in oil-paper insulation under combined AC and DC voltage stress.First,the voltages in the converter transformer were analyzed.In the experiments,four artificial insulation defect models were designed to generate PD signals under AC-DC combined voltage stress detected by a Rogowski coil sensor.Histograms including the φ-q-n data of these PD signals were created.The variations of φ-q-n data generated by PDs in different insulation defect models were analyzed while increasing the test voltage.Experimental results showed that the PD phase-resolved distributions of different insulation defect models were different from one another.The findings of the current study are useful in further research on the mechanism and pattern recognition of PDs in converter transformers.     

Impact of selection of DC base values and DC link control strategies on sequential AC-DC power-flow convergence

This paper demonstrates the convergence of the integrated AC-DC power-flow algorithm as affected by the selection of different base values for the DC quantities and adoption of different control strategies for the DC link. For power-flow modeling of integrated AC-DC systems, the base values of the various DC quantities can be defined in several ways, giving rise to different sets of per-unit system equations. It is observed that different per-unit system models affect the convergence of the power-flow algorithm differently. In a similar manner, the control strategy adopted for the DC link also affects the power-flow convergence. The sequential method is used to solve the DC variables in the Newton Raphson (NR) power flow model, where AC and DC systems are solved separately and are coupled by injecting an equivalent amount of real and reactive power at the terminal AC buses. Now, for a majority of the possible control strategies, the equivalent real and reactive power injections at the concerned buses can be computed a-priori and are independent of the NR iterative loop. However, for a few of the control strategies, the equivalent reactive power injections cannot be computed a-priori and need to be computed in every NR iteration. This affects the performance of the iterative process. Two different per-unit system models and six typical control strategies are taken into consideration. This is validated by numerous case studies conducted on the IEEE 118-bus and 300-bus test systems.     

应用于能量收集中的接口电路的设计

针对从周围环境中收集能量的微型发电机输出功率和电压非常小,无法直接应用的问题。文中设计了一种超低输入电压、低功耗且高效的接口电路。该接口电路包含两级,第一级是无源级和仅由一个有源二极管组成的第二级。为降低有源二极管的功耗,采用一个工作在亚阈值区的衬底输入比较器用来驱动MOS开关。设计采用TSMC 018 μm 标准CMOS工艺,使用Cadence Spectre在室温的条件下进行仿真。结果表明,在输入电压为500 mV（100 Hz）,负载电阻为50 kΩ时整流器的电压转换率为977%,能量转换率为913%。整流器能够在输入电压振幅为320 mV以上实现高效整流。     

运算放大器和电压比较器测试技术的实践应用

针对半导体集成电路运算放大器失效模式指出了其测试方法,通过分解半导体集成电路运算 (电压)放大器、电压比较器测试电原理图,说明了该类器件的一些主要性能参数测试原理,介绍了在生产实践中测试技术应用方法和注意事项,提出了生产单位怎样建立完整的运算放大器IC测试系统的构想.