小电流接地系统中非稳定电弧接地故障选线方法

小电流接地系统广泛应用于我国35KV及以下的配电网中,由于单相接地故障的复杂性,接地电流存在着大量高频谐波。不同于常规的利用傅立叶变换分离出基波和谐波,本文采用自适应陷波滤波器对故障信号进行分析,提取线路零序电流的5次谐波分量,利用故障线路的相位与非故障线路的相位相反,幅值是所有非故障线路幅值之和这个特征进行接地故障选线,以改善小电流接地系统中非稳定电弧接地故障选线的效果。     

基于Matlab的p-q法与ip-ip法仿真分析

针对p-q法和ip-iq法的谐波电流检测效果的比较,由于两种检测方法都是首先检测出原电流基波分量,再与原电流做差得到原电流谐波分量,因此可以通过计算检测出的基波电流中的谐波含量或畸变率来比较两种方法的检测性能.在接有非线性负载的系统中,通过控制电压源的电压波形,在(0.8-0.9)s时间段内产生标准正弦电压,在(0.9-1.0)s时间段内产生的畸变电压,利用p-q法和ip-ip法分别对同-检测点进行谐波电流检测.通过Matlab软件仿真试验,在(0.8-0.9)s时间段内利用p-q法和ip-ip法测得的基波电流的畸变率分别为1.72％和2.04％,在(0.9-1.0)s时间段内利用p-q法和ip-iq法测得的基波电流的畸变率分别为32.73％和4.39％.从而得出结论:在检测点处电压无畸变时,两种方法的检测性能都比较好,基波电流畸变率低,误差小;当电压发生畸变时,p-q法检测性能变差,基波电流畸变率变高,而ip-ip法检测性能无明显变化,适用范围更广.     

基于BP神经网络和全相位快速傅里叶变换的电力系统谐波检测技术研究

在分析现有谐波检测方法的基础上,研究了基于全相位快速傅里叶变换和人工神经网络的谐波和间谐波检测算法。针对谐波检测精度不高的问题,提出了一种基于全相位快速傅里叶变换和BP神经网络的谐波检测方法,同时采用全相位快速傅里叶变换和自适应神经网络的谐波检测方法,进一步提高了谐波检测的精度。通过虚拟仪器软件开发平台Lab Windows/CVI,设计了基于全相位快速傅里叶变换和自适应神经网络的谐波检测软件。软件实现了谐波幅值和相位的检测以及总谐波畸变率的计算,并能够在总谐波畸变率超标的情况下给出警报。     

谐波和无功电流检测方法分析

谐波、无功和负序电流的准确与快速检测是决定配电网静止同步补偿器性能的关键因素之一。文章对p-q法、ip-iq法、改进ip-iq法的检测性能进行了理论和仿真分析,并在TMS320LF2407A实验系统中对它们进行了实验研究。结果表明,只有当三相电压对称无畸变时,p-q法才能准确检测谐波、无功和负序电流分量;不管电网电压是否对称畸变,改进的ip-iq法都能精确检测正序基波有功电流,但计算量大;即使电网电压不对称且畸变,ip-iq法也能准确检测谐波电流,而对谐波、无功和负序电流的检测精度取决于锁相环对正序基波电压相位的检测精度,但该法的计算量小,更易于数字化实现。     

凹球面自聚焦声场非线性效应的研究

用球束方程(SBE)研究了声源参数和媒质特性对凹球面自聚焦声场非线性效应的影响。结果表明,谐波的最大幅值出现在声焦点附近,基波与线性声场的分布类似,而高阶谐波的聚焦性能更好。超声频率、声源表面初始声压幅值或非线性参数越大,即平面波冲击间断形成距离越短,声的非线性效应越明显。声衰减会使非线性效应减弱,而凹球面曲率半径增大会使谐波和基波最大值的位置偏离更明显。     

基于基波磁通补偿的大容量串联型有源电力滤波器

提出了一种基于基波磁通补偿的大容量有源滤波器，在串联变压器的二次侧设计多个绕组，每个绕组都配置一个PWM逆变器单元，每个单元向相应的二次侧注入幅值相同，相位相同的基波电流(跟踪一次侧电流中的基波，并与之反相位)，在补偿系数等于1或略大于1时，在串联变压器一次侧对基波呈近似为零的阻抗，而对谐波呈现高阻抗。     

基于谐波测量的改进余弦窗函数

电网电压监测设备在监测运行设备的电流电压波形时通常采用谐波分析法,针对传统FFT谐波分析法在电网频率波动时谐波测量会产生栅栏效应和频谱泄漏的问题,在研究余弦窗特性的基础上提出了一种改进3项余弦窗。通过频谱衰减曲线与传统余弦窗对比,采用基于数据样本的非线性拟合方法,拟合出了改进窗插值算法的谐波幅值相位修正系数,使改进窗插值算法能实际应用于谐波测量。通过谐波测量仿真对比,验证了加改进余弦窗的谐波测量准确度更高。     

基于虚拟阻抗控制策略的微电网功率分配研究

针对孤岛型微电网的功率分配问题,文中提出了一种增强型微电网分布式发电(DG)虚拟阻抗控制方法。运用DG线路电流和公共耦合点(PCC)电压馈电来调节基波和谐波频率的虚拟阻抗,实现了更好的无功功率和谐波功率分配。通过减小DG装置等效谐波阻抗可以减小PCC谐波电压,无需提取基波和谐波分量即可实现精确的功率分配和PCC谐波电压补偿。通过单相微电网的实验分析,验证了所提出的虚拟阻抗控制方法的可行性。     

基于DSOGI-PLL与ANF-LPF的ip-iq三相谐波检测方法

随着分布式电源大规模接入电网,电力系统中频率波动、电压不平衡以及谐波畸变等问题日益严重。在这样不平衡和失真的电网条件下,传统i_p-i_q谐波检测法已不能满足工程需要。为解决这一问题,文中提出一种基于DSOGI-PLL与ANF-LPF的i_p-i_q三相谐波检测方法。一方面,采用DSOGI-PLL提高复杂电网下提取基波相位的能力;另一方面,采用一种具有选择性谐波滤波能力的改进结构LPF,来提高谐波检测的抗干扰能力。结果表明,所提方法能够在复杂电网条件下完成三相谐波检测。     

基于小波变换和FFT的电能质量检测的研究

傅立叶变换可以精确确定出平稳波形中各次谐波的幅值;它只能检测基波和整数倍于基波的谐波,傅立叶变换算法存在着频谱泄漏和栅栏现象,从而使检测出谐波的幅值、相角和频率均存在较大的误差。小波变换可以准确确定发生突变的时刻,滤除干扰信号,但出现各次谐波频段混叠现象。故此文中采用基于小波变换和FFT相结合分析电能质量信号的方法。用小波变换检测电能质量信号的突发信号,对各次谐波混叠的信号采用FFT进行频谱分析,并进行了计算机仿真,取得了较满意的结果。     

基于滑动积分的电压故障的检测

电压暂降、暂升、中断和电压谐波是目前电压质量的主要问题,对于这些问题的抑制与治理,检测是关键。本文提出一种基于滑动积分器的方法,通过简单的计算和判断,以较高的精度快速的检测出任意时刻发生的电压故障—电压暂降、暂升、中断的基波幅值、相位和电压谐波。与其他的检测方法相比,该方法无需添加低通滤波器,具有算法简单、容易实现,运算速度快,精度高等优点。仿真分析验证了该方法的正确性。     

PTF-based control algorithm for three-phase interleaved inverter-based SAPF

In this paper, modelling and hardware implementation of three-phase interleaved inverter-based shunt active power filter (SAPF) is proposed to mitigate current harmonics, reactive power for ensuring unity power factor and load balancing without shoot-through effect. Shoot-through effect is one of the hazardous issues in conventional voltage source inverters such as damage of power electronic switches, electromagnetic interference, ringing in the power circuitry. The present power system has inevitable non-linear loads which create large variations in the supply voltage distortions. Therefore, the compensation capability and efficiency of the SAPFs degrades. A novel predictive tuned filter is proposed in this paper to estimate the variations in the amplitude of supply voltage, frequency and harmonics for extracting the fundamental voltage signal. The fundamental extracted signal is further processed for reference current generation using generalized p-q theory. The performance of the proposed system is simulated using MATLAB®/Simulink environment and tested under different supply voltage conditions. The simulation results have been validated by developing a prototype in the laboratory by using a dSPACE1104 controller. It is found from the simulated and experimental results that the proposed system is fast, robust and accurate which improves the power quality without shoot-through problem.     

Frequency tracking techniques of power systems in coloured noises

A technique for tracking the frequency of power systems in sine noises using numerical differentiation is presented. A voltage or current sinusoidal signal corrupted by sine noises and white noises is considered. For the signal corrupted by one or two sine noises, a central numerical differentiation-based method is proposed. For the signal corrupted by multiple sine noises and white noises, a hybrid method of numerical differentiation and a digital finite impulse response (FIR) filter are proposed. The digital FIR filtering algorithm is used to remove the white noises and the sine noises, and the numerical differentiation algorithm is used to estimate the fundamental frequency of power systems when the fundamental component is decomposed out of the signal. The proposed algorithm shows an advantage in time and speed when compared with other existing techniques and shows better dynamics and higher accuracy in frequency estimation. Carried out in Matlab, the simulation results are satisfactory     

A Single-Phase DG Generation Unit With Shunt Active Power Filter Capability by Adaptive Neural Filtering

This paper deals with a single-phase distributed generation (DG) system with active power filtering (APF) capability, devised for utility current harmonic compensation. The idea is to integrate the DG unit functions with shunt APF capabilities, because the DG is connected in parallel to the grid. With the proposed approach, control of the DG unit is performed by injecting into the grid a current with the same phase and frequency of the grid voltage and with an amplitude depending on the power available from renewable sources. On the other hand, load harmonic current compensation is performed by injecting into the alternating current system harmonic currents like those of the load but with an opposite phase, thus keeping the line current almost sinusoidal. Both detection of the grid voltage fundamental and computation of the load harmonic compensation current have been performed by two neural adaptive filters with the same structure, one in a configuration ldquonotchrdquo and the other in the complementary configuration ldquoband.rdquo The ldquonotchrdquo filter has been used to compute the compensation current by eliminating only the contribution of the fundamental of the load current, whereas the ldquobandrdquo configuration is able to extract the fundamental of the coupling point voltage. Furthermore, because the active power generation and the APF features require current control of components at different frequencies, respectively, a multiresonant current controller has been adopted. The methodology has been tested successfully both in numerical simulation and experimentally on a suitably devised test setup. The stability analysis of the proposed control approach has been performed in the discrete domain.     

A series active power filter based on a sinusoidalcurrent-controlled voltage-source inverter

A series active power filter working as a sinusoidal current source, in-phase with the mains voltage, has been developed and tested. The amplitude of the fundamental current in the series filter is controlled through the error signal generated between the load voltage and a pre-established reference. The control allows an effective correction of power factor, harmonic distortion and load voltage regulation. Compared with previous methods of control developed for series active filters, this method is simpler to implement because it is only required to generate a sinusoidal current, in-phase with the mains voltage, the amplitude of which is controlled through the error in the load voltage. The proposed system has been studied analytically and tested using computer simulations and experiments. In the experiments, it has been verified that the filter keeps the line current almost sinusoidal and in-phase with the line voltage supply. It also responds very quickly under sudden changes in load conditions, reaching its steady-state in about two cycles of the fundamental     

一种改善PFC变换器输入电流过零畸变的方法

功率因数校正（PFC）变换器普遍存在输入电流在输入电压过零点附近发生畸变的现象。文中详细分析了PFC变换器输入电流在输入电压过零点附近产生畸变的原因,指出了Boost PFC变换器的输入电流超前于输入电压是导致位移因数不为1和输入电流过零畸变的主要原因;提出了根据输入电流在输入电压过零时刻的值实时修正参考输入电压的初相角,以改善PFC变换器输入电流过零畸变的数字控制方法。仿真结果证明了文中所提出的方法的有效性,特别是在400Hz输入电压下有很好的效果。     

Hysteresis describing method for control of an active power filter

A hysteresis describing method is proposed to control and design an active power filter. The describing function used to develop this method consists of the linearisation of the non-linear current control loop. The linearisation is done by deriving the hysteresis complex describing function to find the stability condition of the closed-loop current. Under this condition, the frequency and amplitude values of the error signal correspond to the maximum switching frequency and the current ripple, respectively. The proposed method permits calculation of these parameters in a simple algebraic equation as a function of the hysteresis band, dc bus voltage and inductive filter value. Moreover, the compromise between the dc bus voltage and inductor value can be evaluated easily as a function of both switching frequency and ripple requirements. Two design examples are worked out. Experimental results validate the theory.     

UPQC检测控制方法研究

介绍了一种综合型的电能质量补偿装置UPQC的功能和结构,分析了它的检测控制策略.并在此基础上,提出利用瞬时无功功率理论中的同步坐标变换来提取电网电压基波正序相位的检测方法,它简单易行,实时性好,避免了大量对三的相量计算,且无须相不对称且畸变电压进行锁相和滤波.并介绍了根据UPQC内部功率平衡来实现的串连和并联有源滤波器的综合控制方法.仿真结果验证了上述检测控制方法的正确性.     

相角裕度和幅值裕度的一种估算方法

相角裕度和幅值裕度是自动控制系统中反应系统的相对稳定性的重要指标。本文提出了求解相角裕度和幅值裕度一种估算方法,首先介绍了截止频率的一种估算求法,再利用相角裕度定义求出相角裕度;其次是先通过劳斯判据求出系统临界稳定时的开环增益,再利用幅值裕度的含义求出,最后用估算法求出穿越频率。这些估算方法简单实用,实例证明它们有较高的计算精度。