变频器谐波分析与抑制对策

变频设备中的变频器产生大量6k±1次谐波,此特征谐波使电网电流波形严重畸变,THD超过国标（GB/T14549-93）限值。对此本文提出有效的谐波抑制方案,并给出了单调谐滤波器的详细设计过程,同时通过仿真分析验证了谐波抑制效果的明显性。     

智能电网中电动汽车充电站的谐波抑制方法研究

电动汽车的快速发展推动了电动汽车充电站的广泛建设,大量充电机的投入运行将对电网产生严重的谐波危害,12脉动整流变压器的应用将有效地降低充电站的谐波电流。先对现有的6脉动整流充电机的优缺点进行了分析,在此基础上以串联型12脉动整流充电机为例分析了电网侧电流的谐波,并对无源滤波器的原理进行简介,最后通过实验进行了6脉动整流、6脉动整流加无源滤波器、12脉动整流、12脉动整流加无源滤波器的电网侧谐波电流比较。通过实验验证,12脉动整流变压器加无源滤波器的形式谐波抑制效果较佳。     

基于附加电流控制的并网逆变器输出谐波抑制策略

针对并网逆变器（VSC）在间谐波电压下的谐波电流问题,提出一种基于附加电流控制的VSC输出谐波抑制策略。首先,建立VSC在电网电压畸变工况下的数学模型;然后,在传统矢量控制的基础上附加谐波电流反馈控制环路,形成基于附加电流控制的输出谐波抑制策略;最后,设计附加电流控制器的型式和参数,并基于VSC样机进行测试验证。实例分析表明,所提VSC控制策略可提升VSC入网电流对电网电压畸变的抗扰能力,同时抑制VSC整数次谐波和间谐波电流。     

应用并联型有源电力滤波器对空压机变频器进行谐波治理

针对山东中烟工业公司济南卷烟厂空压机变频器工作时产生的谐波电流导致厂内动力部分出现变压器温度过高、噪音增大、信号波动、通讯中断等故障现象,采用并联型有源电力滤波器进行谐波治理。对并联型有源电力滤波器的控制系统和主电路进行了介绍,给出现场谐波治理的方案。通过该滤波器现场运行效果表明,并联型有源电力滤波器具有理想的谐波补偿效果,同时降低了空压机运行的电流,实现节能降耗。     

电网畸变条件下基于LCL型滤波的STATCOM电流控制策略研究

在节约总电感用量的前提下,为了提高系统的滤波性能,选择LCL型滤波器作为配电网STATCOM(D-STATCOM)的输出滤波器。LCL型滤波器是一个三阶系统,采用直接入网电流控制时谐振峰的存在会影响系统的稳定性。为此,提出一种基于状态反馈的虚拟阻抗法用于抑制LCL型滤波器的谐振峰,从而避免无源阻尼法增大系统的损耗。由于电网电压中含有谐波含量会造成补偿电流畸变,从而不能准确跟踪其指令值,针对这一问题,提出一种多谐振比例谐振(PR)控制器,用于增大特定频率处电网电压对入网电流的输入阻抗,从而抑制电网谐波电压的扰动,优化补偿电流波形,提高电流追踪性能。仿真和实验结果证实了控制策略的有效性。     

基于补偿前馈电压控制的三电平逆变器研究

考虑到光伏并网逆变后存留的高频谐波对LCL滤波中参数固定的电容及电感产生谐振作用,该文引入三电平逆变器,一方面可在输出端保证谐波含量低、电压的波形更加接近正弦波以降低滤波器中电容和电感串联谐振的可能,另一方面也为可在电流进入电容前而对系统做出相应的动作。该文比较传统电流内环控制策略,改进电压前馈的控制策略,提取逆变器输出端输出的电流对电压进行补偿,通过设计滤波器参数搭建模型及进行仿真得到结果表明其有效的抑制谐振,并可同时提高电网电流和电压的稳定性,有效地抑制电网电压谐波对网侧电流的影响。     

并网矩阵变换器网侧谐波及稳定性分析

针对并网矩阵变换器PWM信号开关频率较低,输出电流中谐波含量较大的状况,在并网变换器中采用T型滤波器取代典型的电感滤波器以抑制谐波电流;然后对T型滤波器系统的稳定性进行了分析,提出采用电网电流和滤波电容电流双闭环控制策略来实现系统的稳定运行。最后通过仿真实验证明,采用该控制策略不仅能保证系统的稳定运行,而且还具有较好的正弦输出电流波形和较小的谐波含量。     

基于APF电动汽车充电站谐波放大效应及抑制措施

为提高电动汽车充电站并联有源滤波器的治理效果,文章研究有源滤波器在检测系统侧电流和负载侧电流两种控制方式下产生的谐波电流放大效应。搭建电动汽车充电机(站)的结构模型,分析充电站补偿系统等效电路,得到两种控制方式下充电站补偿系统谐波放大关系式和补偿效果。定义谐波放大程度系数、负载与系统间的阻抗比、APF治理因子等参数,提出抑制谐波放大效应措施。理论分析和算例仿真结果表明,所提方法能有效抑制谐波放大效应,提高APF补偿效率。     

变频器谐波干扰及解决办法

变频器作为电力电子设备,主要包含有电子元器件、计算机芯片等,易受到外界的一些电气干扰,同时,变频器本身输入侧是一个非线性整流电路,使电源的波形畸变,出现高次谐波;变频器输出侧电压、电流非正弦波或非完全正弦波也含有丰富的谐波,对输出电路也有影响.这就是说变频器投入运行后会产生高次谐波,它对与其相接的电网和用电设备会产生干扰,即通常所说的电磁兼容EMC(Electro-Magnetic Compatibility) . 　　……     

基于VC-综合赋权法的海上风电APF配置优化方法研究

大容量海上风电机组的接入改变了传统电力系统结构,给电网带来了谐波等问题,影响了电能质量。为抑制海上风电机组产生的低次谐波,文章首先建立了海上风电机组并网电流的低次谐波理论模型;然后,在仿真软件ETAP上搭建海上风电机组仿真模型,验证不同出力情况下风电场的输出谐波特性;最后,基于风电场输出谐波特性,提出变异系数（Variation Coefficient,VC）综合赋权法对风电场有源滤波器（APF）进行优化配置,提升了风电场谐波的治理效果。基于实际算例验证了所提方法的有效性。     

Power conditioning system for grid-connected photovoltaic system

This study develops a new control strategy for an expandable grid-connected photovoltaic (PV) system. The proposed system performs dual functions of a PV generation and an active power filter, or either one. To this end, the grid current, instead of output current of the converter, is shaped to be a sinusoidal current in phase (or opposite phase) with the grid voltage. Furthermore, its reference current is generated in multiplying the voltage loop controller output by the grid voltage waveform, and therefore non-active components analysis for harmonics elimination and reactive power compensation in the conventional design is not necessary. As a result, the algorithm is simple and easy to implement, and only one sensor for current detection plus two voltage sensors are required. Experimental results verified the effectiveness of the proposed method.     

电网频率波动时LCL并网逆变器重复控制研究

针对电网频率波动时,并网电流畸变和谐波较大的问题,提出了静止坐标系下LCL并网逆变器的重复控制策略,该策略可有效降低并网电流谐波畸变率;在静止坐标系下,LCL并网逆变器数学模型无耦合现象,省去了复杂的解耦运算,从而该控制策略简单易实现;在确定电路参数的基础上,对重复控制进行了参数设计,并通过仿真试验证明了理论分析的正确性。研究成果对于提高电能质量意义重大。     

Fault ride through of fully rated converter wind turbines with AC and DC transmission

Fault ride through of fully rated converter wind turbines in an offshore wind farm connected to onshore network via either high voltage AC (HVAC) or high voltage DC (HVDC) transmission is described. Control of the generators and the grid side converters is shown using vector control techniques. A de-loading scheme was used to protect the wind turbine DC link capacitors from over voltage. How de-loading of each generator aids the fault ride through of the wind farm connected through HVAC transmission is demonstrated. The voltage recovery of the AC network during the fault was enhanced by increasing the reactive power current of the wind turbine grid side converter. A practical fault ride through protection scheme for a wind farm connected through an HVDC link is to employ a chopper circuit on the HVDC link. Two alternatives to this approach are also discussed. The first involves de-loading the wind farm on detection of the fault, which requires communication of the fault condition to each wind turbine of the wind farm. The second scheme avoids this complex communication requirement by transferring the fault condition via control of the HVDC link to the offshore converter. The fault performances of the three schemes are simulated and the results were used to assess their respective capabilities.     

Hybrid control approach for PV/FC fed voltage source converter tied to grid

A hybrid and adaptive control approach for solar photovoltaic system and fuel cell fed voltage source converter (VSC) is presented in this work. Further maximum power from solar photovoltaic array is extracted by using incremental conductance (INC) based maximum power point tracking approach. This hybrid approach combines I cos ? technique and gradient descent back propagation learning (GDBP) neural network (NN) to extract fundamental components from load current for efficient harmonics compensation and provides power quality improvement and support the three-phase AC grid by supplying power to the grid and as well as connected loads. The proposed system includes photovoltaic (PV) array, a voltage source converter (VSC), ripple filter and combination of linear and non-linear loads. The proposed control approach provides a fast response during dynamic conditions as well. Results of the proposed control technique also compared with the other available control techniques for its superiority analysis. The developed control technique is demonstrated by using MATLAB/SIMULINK platform.     

Three-port single-phase three-wire power converter interface for micro grid

This paper proposes a three-port single-phase three-wire (TPSPTW) power converter interface integrating an isolated current-fed full-bridge power converter (ICFPC), a three-port power converter (TPPC), a fuel cell and a battery set for micro grid (MG).The ICFPC is used to control the output power of fuel cell and to step-up its output voltage to the voltage of high-voltage DC port of the TPPC. The TPPC can manage the power conversion between the fuel cell, the battery set, the loads and the utility. This power converter interface charges the battery set, outputs AC power and acts as an active power filter (APF) in the grid-connection mode, supplies uninterruptible power to the loads when it operates in the stand-alone mode. The fuel cell outputs a programmed power regardless of whether the power converter interface operates in the grid-connection mode or in the stand-alone mode. The programmed power outputted from the fuel cell is the average power of load under the stand-alone mode. The battery set is used to respond to the varied power of loads under the stand-alone mode. A prototype is developed to verify the performance of power converter interface, and the experimental results are as expected.     

直驱永磁风力发电系统电网侧变换器的模糊功率控制

针对基于储能的并网永磁直驱风力发电系统的运行特点,提出了一种对电网侧变换器的模糊功率控制策略,当电网发生电压瞬时跌落时使电网侧变换器运行在模糊功率控制模式,依据电网电压跌落深度及风机输出功率大小通过模糊控制器来确定发出无功电流的大小,从而使风电系统能够适度地向电网提供一定的无功功率来支撑电网电压。仿真结果表明,所提出的控制策略正确、有效。     

AC side harmonic and phenomena accompanying DC-injection of utility-interactive PV system

The experiments investigated phenomena related to direct contact between the DC output of a PV array and the AC power from the utility grid. The results show that the DC power flows through the distribution transformers (DC-injection) saturating their magnetic circuits. The saturation of magnetic circuits makes peak currents, incorporating a large portion of even harmonics, flow through the high-voltage side of the distribution transformer, adding the level of harmonic distortion of its exciting current. With the increase of injecting DC-current to the utility grid, peak currents at the primary side of distribution transformer increases the most, and even among the same effective (rms) values, the increase of primary side current is larger than that of the secondary side current.     

LCL filter design and robust converter side current feedback control for grid-connected Proton Exchange Membrane Fuel Cell system

Proton Exchange Membrane Fuel Cell (PEMFC) systems are environment-friendly systems that can be used as distributed power generation (DPG) system. As DPG units are usually utilized in weak power distribution systems, the grid inductance variations should be investigated during the control design stage of the grid-tied fuel cell systems. In recent years, LCL filter is broadly utilized to grid connection of DPG units, and the proper design of this filter is an important issue. In this paper, converter side current feedback (CSCF) method has been applied due to its innate damping feature to integrate PEMFC fuel cell system through LCL filter into weak power distribution system. The impact of delay should be considered as it limits the stability region of the resonance frequency of the CSCF control method especially, in the presence of wide variations of the grid inductance. Precise-tuned LCL filter design and consequently, the proper choice of the resonance frequency can remarkably affect the performance of the CSCF control. An adequate-tuned design procedure for LCL filter parameters has been proposed in this paper. Step-by-step tuning of the PR controller parameters has also been included to enhance the power quality. The grid-tied fuel cell system with modified-Y-Source inverter and LCL filter as an interface between inverter and grid has been simulated to analyze the quality of the injected power. Simulation results in MATLAB/Simulink environment verify the suitable performance of the proposed power conditioning system as well as its stable operation versus wide variation of weak grid inductance.