Dynamic behavior of cycloconverter system

The dynamic behavior of a multiprocessor-based 12-pulse circulating current cycloconverter is discussed. This type of cycloconverter can provide a high output to input frequency ratio for fixed and variable-frequency applications. Waveform level simulation of the cycloconverter indicates that both feedback and feedforward techniques can be used to minimize the tracking error of the circulating current controller. The lab prototype is used to test the response of the 12-pulse, single-phase cycloconverter system. The control is implemented by a total of six 16-b microprocessor cards and additional input and output cards resident in a single card cage     

谐波对集合式并联电容器内部故障保护的影响

集合式并联电容器在实际运行中发现其内部故障保护的误动率较普通电容器高,并且容量越大,保护误动率越高.根据集合式电容器内部结构特点,基于内部故障保护动作整定值设置的基本法则,从高次谐波对内部元件最大允许故障率的影响角度阐明了误动率高的原因;同时分别针对单星形、双星形和桥形等不同接线形式,通过数学解析方法定量分析了谐波对保护动作值影响的程度,发现大容量双星形或桥形集合式电容器在高幅值的合闸暂态谐波涌流作用下,内部元件最大允许故障率大幅降低,致使内部保护的实际动作值严重低于整定值,从而易导致误动的发生;依据分析结果提出了相应的预防措施.     

交-交变频器系统谐波特性仿真研究

基于Matlab/Simulink环境,建立了交-交变频器的仿真模型。根据仿真结果,分析了交-交变频器谐波的分布规律,讨论了各种因素对交-交变频器动态特性及谐波的影响,为交-交变频装置的设计和谐波治理提供了一定的依据。     

交流背景谐波对MMC多端直流的影响分析及抑制策略

连接弱交流系统是基于模块化多电平换流器(MMC)的多端直流输电系统的重要应用场景之一。然而,弱交流系统更易受到谐波扰动的影响,该交流系统中的非线性设备可能形成总谐波畸变率偏高的背景谐波电压,这些背景谐波电压将在MMC的三相桥臂中产生正序、负序及零序电压分量及相应的电流分量。在一些极端情形下,某些频率的谐波将会引起直流网络的谐振,导致直流网络的谐波含量显著增大,并通过直流网络传播到其他互联的交流系统中。因此,本文首先从理论上分析了交流系统电压背景谐波对MMC桥臂电压的影响,获得了谐波传递规律;在此基础上,设计了利用MMC子模块储能能力的抑制直流侧谐波的附加控制策略。在PSCAD/EMTDC中的仿真表明,本文所提出的控制策略能有效阻断背景谐波向直流网络的传播,避免直流网络由于背景谐波产生谐振现象。     

三相高频链周波变流器的控制方法研究

由于高频链电路与周波变流器相结合，可以使功率双向流动，以及使装置体积小，重量轻，因此该电路拓扑适用于需要电气隔离的场合。但是。当高频变压器次级出现开路时，漏感中的储能没有放电回路。会导致较高的电压尖峰。因此，本文提出了一种新的控制方法来解决这个问题，在高频变压器原边采用全桥移相控制方式。产生周期性及相当稳定的电压过零区间；在高频变压器副边采用电流控制的脉冲密度调制方式，实现零电压开通和关断。并且，针对三相异步电动机负载进行了实验。从而证明该控制方法的正确性。     

含分数次谐波环境下提取整数次谐波信息的新方法

提出了一种在含有分数次谐波环境下,以一定的规律逐渐降低的频率序列依次作为基频,利用傅里叶级数展开电力系统中实际的电压、电流信号,再通过迭代算法从中提取出工频量及其整数次谐波分量信息的新方法。该方法回避了现有的加窗DFT算法中选取窗函数困难的问题。新方法的原理进行了详细的数学推导和说明,并给出程序框图。为了验证方法的正确性,利用程序对一实际信号进行了分析。实例结果表明,与传统的FFT算法比较,新方法在富含间谐波和次谐波环境下依然能够提出基波和整数次谐波的幅值和相角,且精度满足工程需求。同时,该方法还具有实现简单等优点,易于在工程实际中应用。     

基于DSP的三相交-交变频器控制系统

研究了基于DSP的三相交 -交变频控制系统 ,并设计了相应的零电流检测电路 ,同步信号检测电路和I/O扩展电路。实验结果表明该方案是可行、正确的     

Synthesis of cycloconverter and current-source-inverter for high power high performance drives

Contents Cycloconverters and current-source-inverters both have proved performance for drives in the MW-range. They operate best in combination with a synchronous motor. The cycloconverter drive has very low torque ripple from zero start-up until a relatively small frequency, while the current-source-inverter causes high torque ripple disturbing only at low frequencies and its maximum frequency is much higher than that of the cycloconverter. This paper describes the synthesis of both systems.

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Synthese aus Direktumrichter und Stromzwischenkreis-Umrichter für hochdynamische Großantriebe

Übersicht Direktumrichter und Stromzwischenkreis-Umrichter haben sich beide bei Antrieben im MW-Bereich bewährt. Sie werden am günstigsten mit Synchronmotoren kombiniert. Der Direktumrichter-Antrieb erzeugt vom Stillstand bis zu relativ kleinen Frequenzen sehr kleine Rüttelmomente. Dies ist der Drehzahlbereich, in dem sich die vom Stromzwischenkreis-Umrichter erzeugten hohen Rüttelmomente störend bemerkbar machen. Dafür ist die Maximalfrequenz dieses Umrichters jedoch wesentlich höher. In diesem Aufsatz wird die vorteilhafte Kombination beider Systeme behandelt.

     

Prediction control for a cycloconverter of a power distortioncompensation system

Control methods of a flywheel mechanical energy storage system composed of a flywheel-synchronous machine and a current-controlled cycloconverter are described. Improvements to the current control abilities of the cycloconverter, applying modern control and information theories, are discussed. To obtain good current follow characteristics, both deadbeat control and prediction control are applied. The dead-beat scheme possesses one sample delay in its controlled signal which can compensate by predicting reference signals of the next sample time. To predict the load currents at the next sample time, two prediction methods are used. One of the predictions, which has learning ability for repetitive waves using correlation functions of the current, is composed of 256 digital filters. The weighting coefficients of the filters are determined instantaneously to minimize RMS (root mean square) errors. The other prediction, which has a high-frequency response, is applied to compensate random components and high-frequency components. The system is controlled by two digital signal processors for prediction of the currents, and a 16-bit microprocessor for control of the cycloconverter. Experimental results show excellent compensation abilities, not only for repetitive harmonics but also for high-frequency random components