一种基于ip-iq法的三相4线制系统谐波检测改进方法

为了提高传统三相4线制电力系统谐波电流检测方法的精度,首先分析了传统的三相4线制中谐波电流检测存在的不足,并针对不足提出了基于瞬时无功功率理论的传统三相4线制谐波检测的两点改进方法,最后采用MATLAB仿真软件对改进方法进行了仿真,仿真波形显示,通过改进方法补偿后的三相电流获得了较好的改善.理论分析和仿真结果证明了这种改进方法的可行性和实时性.     

A survey of neutral currents in three-phase computer power systems

It is shown that the magnitude of the neutral current in three-phase computer power systems depends on the harmonic content and phase balance of the load currents. While very high neutral currents are possible due to the additive nature of triplen harmonic currents, a low percentage of data processing sites in the United States are actually experiencing neutral currents in excess of the rated phase current. However, trends in computer systems make high harmonic neutral currents more likely. Power system problems associated with high harmonic neutral currents include overloaded transformers, voltage distortion, and common mode noise. Whenever three-phase, four-wire power systems are used to supply power to computer systems or other similar electronic loads, the power system design should allow for the possibility of high harmonic neutral current to avoid potential problems     

提高开关电源功率因数的方法

开关电源是电源的发展方向，但开关电源功率因数很低。它的输入电流波形严重畸变，所含谐波对电网有干扰，故如何提高开关电源的功率因数，抑制谐波，减小对电网的干扰是一个重要课题。本文对抑制谐波、改善功率因数的三种常用方法──串联谐振滤波器、并联谐振滤波器和升压式变换器进行了试验研究。表明有源升压式变换器是提高开关电源功率因数的最好方法。     

Investigation of harmonic currents and power factor on power rectifier circuits with nonequi-PWM and equi-PWM control (inductive load)

Lately, on the power rectifier circuit with semiconductor switching device, PWM control is generally employed for the purposes of reducing the harmonic currents on the dc side and improving the power factor of fundamental wave. In this case, the analysis of the current waveform becomes fairly complex. However, we express the PWM controlled voltage waveform by the step function, and can easily analyze the current waveform. We reported formerly some results of analysis about the waveform and harmonics of the current. In this paper, on the power rectifier circuit to which the nonequi-PWM and equi-PWM control are applied, we exactly calculate the harmonic currents on the dc and ac side, and the power factor by the use of the above analytical results. The characteristics of both control methods are compared on condition that each controlled factor of the load voltage is equal. These results are shown in the calculated charts. The following items can be seen from these charts on the power rectifier circuit: (1) The nonequi-PWM control can let the harmonic currents on the dc side decrease more than the equi-PWM control. But on the contrary, the harmonic currents on the ac side increase. Consequently, when the nonequi-PWM control is applied, the total power factor decreases by the increase of distortion factor of the current on the ac side. (2) The difference between the harmonic currents on the dc and ac side to both of the nonequi-PWM and equi-PWM control increases with the increase of controlled factor of the load voltage. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 117–125, 1999     

Harmonic analysis for industrial customers

A power flow program is developed to analyze the harmonic distortion of a power system with various types of harmonic loads. The proposed program can be applied to solve the harmonic current flow, voltage harmonic distortion factor, resonance frequency, and current amplification factor at every bus in the system. In this study, a large metal factory is selected for the harmonic power flow analysis. The current waveforms at every bus are measured and analyzed to determine various orders of harmonic components. These harmonic currents are used in the computer simulation to determine the harmonic voltage distortion factor at the buses of the system, and the variations of resonance impedance and amplification factor with frequencies are investigated. Finally, the program is used to calculate the harmonic load flow when the metal factory is expanded by including a new plant in the power system, and proper filters are designed to alleviate the harmonic problems     

基于Laguerre多项式的电力机车谐波电流估计

提出利用Laguerre多项式的逼近函数进行电力机车谐波电流估计。根据机车不同的运行方式建立机车模型,通过随机变量矩的合成求出机车电流的k阶原点矩,利用Laguerre多项式展开拟合其概率密度函数PDF(ProbabilityDensityFunction)。根据机车谐波电流与负荷电流的比例关系,求得谐波电流的95%概率估计值。最后,对SS1型机车产生的谐波电流进行估计,证明了该方法的有效性。     

基于电路模型和神经网络的谐波电流检测方法

针对有源滤波器的谐波电流与无功电流检测建立了三相非线性负载的等效电路模型,提出了一种基于神经网络的检测方法.该方法使用神经网络对模型中的电阻负载进行逼近,得出相对应的电力系统中的基波有功电流,从而实现谐波电流的检测.仿真结果证明了该方法的有效性.     

非正弦供电十五相感应电机谐波电压确定

通过确定非正弦供电十五相感应电机的3次谐波注入电压,为电机PWM调制提供理论依据。把注入3次谐波电压的十五相感应电机气隙磁动势峰值下降幅度最大作为电机理想运行准则,得到基波磁动势与3次谐波磁动势之间空间位置关系与磁动势幅值间数值关系。以十五相感应电机基波等值电路与3次谐波等值电路为基础并从相应的激磁电流出发,计算基波电压与3次谐波电压有效值,求出3次谐波负幅值点与基波正幅值点间相位差,并通过电机空载实验对计算方法的准确性进行了验证。在额定基波电压下,计算了对应于不同给定转差率的基波激磁电流与3次谐波激磁电流,进而得到3次谐波电压有效值及磁动势波形间相位差,最终通过线性插值来获得任意转差率下的3次谐波电压。     

利用小波变换抑制数字相位测量中的噪声

本文研究了用小波变换降低噪声对正弦波间小相角差测量的影响。实际的正弦模拟信号经Ａ／Ｄ板采样后,会混入宽频带的随机噪声即所谓采集噪声,同时还会有直流、谐波等噪声信号混入。     

从一次变压器差动保护误动的联想

电力系统运行中继电保护误动的原因很多,其中谐波电流注入到系统中,会给电网运行造成一定的危害,并由此可能引发继电保护误动。在现场,对中频电炉产生的谐波电流进行了测试,对谐波电流造成的保护误动进行了分析。并联电容器对谐波有一定的放大作用,当系统参数符合电流谐振条件时系统将产生谐振,将严重影响继电保护的正确动作。为此,建议在谐波源处增设谐波治理装置或改变系统的LC参数避免谐振的出现,微机继电保护在原理设计上应避免谐波因素的影响。     

一种基于补偿电流的单相电路谐波电流检测算法

针对电网中谐波的危害和"污染"等问题,为了实现有源电力滤波器控制系统谐波电流检测的精确性、实时性,本文提出了一种单相电路谐波电流检测算法,该算法基于补偿电流最小检测原理,通过构造函数将谐波电流检测问题合理地转化为基波有功电流幅值问题,实验表明,新算法具有实时性好、计算量小、易于实现等优点。基于此算法的有源电力滤波器具有较好的动态响应性能,能实现有效的谐波电流补偿,仿真结果验证了该算法的有效性和正确性。     

Harmonic Filters for Six-Phase and Other Multiphase Motors on Voltage Source Inverters

Inverter-driven motors having five, six, or more phases have smaller torque pulsations and lower rotor I2R loss due to harmonics than do their three-phase counterparts. However, they generally have higher stator harmonic currents. For example, six-phase motors, supplied by a six step voltage source inverters have fifth and seventh harmonic currents which are from two to five times as large as in a comparable three-phase motor. If the motor has five or more phases, these currents can be substantially reduced by the harmonic filter described. The filter consists of transformer-like devices connected in the leads between the inverter and motor. The coils on these are interconnected in a prescribed way so that they add negligible impedance for fundamental currents, but they add considerable impedance for most harmonics. Since the filters do not affect fundamental current, they do not affect the speed-torque characteristic. These filters are described for any number of phases, and equations to determine their inductance values for the various harmonics are developed. Their effectiveness is demonstrated by experimental results.     

基于电压注入的高速永磁电机谐波电流抑制方法

针对高速永磁同步电机在运行过程中相电流谐波含量高这一问题,提出了一种基于电压注入的高速永磁同步电机谐波抑制方法。在考虑存在谐波电流的前提下建立了高速永磁电机数学模型,采用闭环谐波电流检测方法,提取5次和7次谐波电流,根据电机谐波数学模型计算谐波电压补偿量,在传统的双闭环系统上设计增加了谐波电流反馈环和谐波电压补偿环,通过注入谐波电压的方式来抑制高速永磁电机运行时相电流中的谐波分量。仿真和实验结果表明,基于电压注入的高速永磁同步电机谐波电流抑制方法可以有效抑制电机相电流中的谐波,验证了该方法的有效性。该方法易于实现,适应性强。     

不同工作模式下基于谐波电流有效值分级标准的CRT参数设计

控制绕组级数的减少对于提高变压器式可控电抗器(CRT)的工作效率、降低设计制造难度具有重要意义。基于国标GB/T 14549—93对谐波电流的要求,提出了更经济的CRT谐波电流有效值分级标准,在此基础上分析了3种典型单支路工作模式下控制绕组电流、控制绕组级数、谐波电流之间的关系,并以谐波电流为约束条件对CRT不同工作模式下的控制绕组级数和各级电流等参数进行设计,同时对3种工作模式的控制绕组级数大小进行比较分析。算例计算结果表明:在基于谐波电流有效值分级标准对CRT控制绕组参数进行设计时,控制绕组级数与第1级控制绕组电流、最大k次谐波电流和工作模式相关,不同工作模式下控制绕组级数不同,但注入电网的谐波电流均能满足要求,且第1级控制绕组电流分配相差不大时,固定单支路工作模式下谐波电流最小。     

用户层多谐波源的责任区分方法

为了区分公共耦合点处的用户谐波责任,论文提出了一种基于非正弦功率分解的谐波辨识方法。在分析用户谐波传播机理的基础上,以系统畸变电压为基,对馈线电流进行正交分解。引入非谐波电压、非谐波电流及谐波电流的概念,以此为基础计算负载线性度,实现用户层的谐波定位。采用多端口网络理论建立多谐波源的网络方程,以独立分量分析法对馈线谐波电流进行解耦。在不求解网络谐波参数和谐波源特性未知的情况下,以负熵为目标函数,通过分离观测量还原出用户发射的原始谐波电流,实现谐波责任量化。仿真算例验证了该方法的有效性,可实现谐波源定位、谐波全电流计算,是对用户层谐波责任估计的有益探索。     

三相电路的广义瞬时无功功率理论

基于瞬时无功功率理论发展起来的三相电路谐波电流的检测方法,以其精度高、实时性好、算法简单及硬件实现方便等优势,正逐渐应用于电力有源滤波器中。本文为使其能适用于电力系统更广泛的谐波电流检测场合需要,在仅能检测三相电路总谐波电流含量的瞬时无功功率理论基础上,进一步发展成为能检测三相电路任意次谐波电流的广义瞬时地无功功率理论。文中给出该理论及基于该理论的谐波电流检测方法。     

Development of a Modulation Strategy for a PWM Inverter Drive

When induction motors are driven by electronic inverters, the applied voltage waveforms are quite nonsinusoidal. The fundamental component of the current is controlled by the load. The harmonic currents are limited principally by the motor leakage inductance and are independent of load. These harmonic currents can lead to increased motor heating and to increased peak currents. In addition, the modulation technique can give rise to problems in the control. An analysis method was developed to predict the performance of an induction motor in response to inverter waveforms. The correctness of the method was verified by comparison to measurements made on an operating system. This tool was then used to aid in the development of a modulation strategy, to accurately evaluate the motor heating problem and to analyze a new method of transitioning from pulsewidth modulation to square wave operation.     

一种新型谐波与无功电流检测方法

谐波电流的快速精确检测是有源电力滤波器滤波性能的关键指标,现有的谐波检测方法并非很理想。文中提出一种适用于有源电力滤波器的补偿电流检测新方法,该方法通过瞬时有功功率计算出负载基波正序有功电流幅值,然后乘以单位电压幅值的电源波形,得到基波正序有功电流的瞬时值,进而分离出待补偿电流分量;建立了基于PSIM的仿真系统,针对不同负载性质和负载电流突变等情况进行了分析。仿真结果表明,该方法能够准确、快速地检测出负载电流中的谐波和无功电流分量。     

阵变换器-永磁同步电机矢量控制系统的新型电流控制方法

分析了基于电流滞环控制的矩阵变换器-永磁同步电机(MC-PMSM)系统的开关组合状态和存在的缺点:系统侧电流存在较大的5次和7次谐波分量.提出了一种改进电流控制方法,该方法采用电机电流双环控制,得出三相电机电流的6个电流控制信号,并将输入三相电压分成12个相区,根据电流控制信号和相区号的不同,选择不同的输入相与输出相连接,确定出矩阵变换器开关组合状态.在该方法中,每个输入相在整个周期内都参与调制,降低了系统输入电流的谐波分量,提高了系统输入电流的正弦度.     

含滤波器的多换流站谐波阻抗模型与谐波交互影响研究

当多个换流站位于相邻交流电网时,换流站之间电气距离较小,一些特定的交流滤波器组合投切方式可能会引发换流站之间谐波电流的交互影响。基于谐波阻抗方法定义了换流站谐波电流影响系数,用于计算换流站之间谐波电流的交互影响程度。以银川东站与灵州站构成的多换流站系统为例,搭建含有交流滤波器的谐波阻抗模型,针对特征谐波,计算谐波电流影响系数,分析了交流滤波器组合投切对银川东站、灵州站谐波电流交互作用的影响。结果显示11、13次谐波电流的交互影响较小,23、25次谐波电流的交互影响较大,且特定滤波器的投切会造成各换流站交流母线谐波电流的明显变化。最后,建立PSCAD电磁暂态仿真模型,对上述分析结果进行了验证。