Fuzzy logic controller for three-level shunt active filter compensating harmonics and reactive power

In this paper, the three-level inverter is used as a shunt active power filter, making use of the multilevel inverter advantages of low harmonic distortion, and reduced switching losses. This PWM inverter is employed as shunt APF compensating reactive power and suppresses harmonics drawn from a nonlinear load. Most previously reported three-phase active power filters are based on two-level inverters with conventional controllers requiring a complex and a complicated mathematical model. In order to overcome this problem a fuzzy logic controller applied and extended to a three level shunt APF is proposed.     

多馈入直流系统中逆变站滤波器投切对谐波电流的影响

基于大型电力系统分析软件NETOMAC,提出了机电暂态和电磁暂态混合时域仿真法。该方法主要研究南方电网2008年多馈入直流系统各个逆变站由于滤波器投切产生的谐波电流的交互影响。对时域仿真得到的谐波电流进行傅里叶变换,仿真和分析结果表明某逆变站退出或投入任意类型的一组交流滤波器会使逆变站流入交流母线的对应谐波电流增大或减小,多个换流站的不同类型滤波器进行组合投切时,不同逆变站之间由于电气距离较近所产生的谐波交互影响可能造成投切效果和预期不同、甚至相反。     

多重化技术的几种拓扑结构和控制策略

近年来，多电平大功率变频器在电力传动领域越来越受到重视，因为它具有良好的输出波形，谐波少、开关损耗小。本文将介绍几种多重化拓扑结构和控制策略，其中某些拓扑结构通过优化配置H桥中间直流电源比率，输出端就可以得到最大数量的输出电平，从而提高波形质量；另外一些拓扑结构致力于电压等级和容量的提高，减少谐波。最后给出了几种拓扑结构的仿真波形。     

DIGITAL SIGNAL PROCESSOR BASED VOLTAGE FED INSULATED GATE BIPOLAR TRANSISTOR INVERTER DESIGN

ABSTRACT

A Digital Signal Processor (DSP) based voltage-fed Insulated Gate Bipolar Transistor (IGBT) inverter that drives a three-phase induction motor is presented. The selected DSP, a TMS320C14 chip by Texas Instruments, controls the PWM operation of the inverter. A host IBM PC is connected to the DSP through an RS-232 serial interface for data communications to and from the DSP. IGBTs are used in the inverter because of their characteristically low conduction losses, small switching delays and simplified gate drive circuit. A harmonic elimination scheme is adopted as the PWM strategy to eliminate four low-order harmonics in the inverter output.

The inverter performance is tested using a 1 HP, three-phase induction motor. The output waveforms are recorded and the harmonic spectra are developed using a FLUKE 41 power harmonics analyzer and the results show decidedly suppressed low-order harmonics. The design also highlights the simplicity and cost effectiveness of the DSP based modulator and IGBT based inverter design.     

Fuzzy logic controller for three‐level shunt active filter compensating harmonics and reactive power

In this paper, the use of a three‐level inverter as a shunt active power filter is carried out, taking advantage of the benefits of multi‐level inverter, namely, the reduction both in the overall switching losses and in total harmonic distortion. The main focus of this article is to investigate the potentialities of the inverter employed as shunt active power filter on the compensation of the reactive power and the mitigation of harmonics drawn from a nonlinear load and unbalanced sources. The most previously reported three‐level inverter‐based shunt active power filters have been controlled and monitored through conventional controllers, which require a complicated mathematical model. In order to overcome this problem, an extended intelligent controller is proposed for a three‐level shunt active power filter. The aim of the proposed fuzzy logic control algorithm is to improve the behavior of voltage across the floating capacitors in steady/dynamic states and to minimize the switches commutations by taking into account the references of the harmonic currents injected in the network. The proposed control strategy has been simulated, and the obtained results prove that it is very successful. Copyright © 2015 John Wiley & Sons, Ltd.     

Variable frequency inverter with sinusoidal voltage outputs using rotating coordinate transformation

An ideal inverter should have sinusoidal voltage and current outputs. Generally, output voltages of a voltage-source PWM inverter contain high-level switching frequency harmonies due to the PWM operation, while output currents are kept nearly sinusoidal. High-level harmonics contained in output voltages of a voltage-source inverter cause acoustic noises, iron losses and electromagnetic interferences. An LC filter was used to suppress the switching frequency harmonics; however, there is a danger of resonance in the LC filter. Accordingly, to remove harmonics of the LC filter resonance frequency, the authors add a voltage feedback loop. A conventional system can operate without difficulty within 50 Hz. However, with accompanying increases in the output frequency, output voltages are largely delayed and reduced by a high-pass filter inserted in the feedback loop. These problems are caused by a high-pass filter inserted in the feedback loop. Accompanied by the inverter output frequency, a high-pass filter cannot remove the fundamental component perfectly. As a result, a small fundamental component is fed back, which causes a delay and decrease in output voltage. This paper proposes the application of coordinate transformation to a high-pass filter inserted in the feedback loop. As a result, the proposed system realizes an ideal filter which can suppress fundamental frequency components perfectly, and improves the characteristics of the inverter with sinusoidal voltage outputs greatly. Theoretical analyses, simulations and experiments showed satisfactory results. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (4): 94–102, 1997     

矩阵式电力变换器的控制策略综述

对矩阵式电力变换器的几种控制策略进行了比较，分析了直接变换法、间接变换法和滞环电流跟踪法的基本原理和电压传输比。把矩阵变换器等效成一个虚拟的整流器和一个虚拟的逆变器，以虚拟逆变器为例，介绍了电压空间矢量脉宽调制(VSVPWM)技术的控制策略，并进一步探讨了实现这些控制策略的安全换流问题、开关损耗问题和谐波抑制问题。     

一种新的降低三相三线有源滤波器开关损耗的方法

随着用户电力技术的发展，有源滤波器逐渐趋于实用化，由于补偿谐波次数较高，逆变器开关频率很高，由此造成了较大的开关损耗，给APF的直流电压控制以及散热带来一定困难，提出一种用于三相三线有源电力滤波器的3次谐波注入PWM方法，用该方法控制逆变器，可以在不影响APF补偿效果的前提下，将有源滤波器开关损耗降低33％，仿真和实验结果证明，该方法是有效的。     

A power parallel active filter with higher efficiency

A new approach to expanding the suppression band and reducing the power losses in a parallel active filter by incorporating an additional corrective linear link into its structure, taking into account a delay in the interface filter, and minimizing the switching frequency of inverter power keys is developed. An algorithm of controlling the corrective link that allows increasing the performance of AF and improving the suppression of higher harmonics is proposed.     

异步电机低开关损耗的模型预测直接转矩控制

提出一种新颖的异步电机低开关损耗的模型预测直接转矩控制方法。通过建立异步电机离散时间预测模型,对不同开关矢量作用下的系统输出矢量进行轨迹外推,形成长预测范围的输出轨迹。同时分析三电平逆变器在开关切换时产生的开关损耗,以逆变器的平均开关损耗为价值函数,对不同开关矢量作用的输出轨迹进行在线评估,得到最优的开关矢量并将其作用于逆变器,从而有效降低了逆变器的开关损耗。仿真结果表明,基于该方法的驱动系统逆变器的开关损耗低,电机转矩和磁链动静态性能良好。     

低功耗三相电压空间矢量调制的逆变器特性研究

为了提高直流电压利用率,减少谐波,在三相逆变器中采用电压空间矢量调制技术取代SPWM技术,合理放置零矢量,选择恰当的开关频率,降低开关损耗。采用双重傅里叶变换对输出谐波进行了定量分析,在Matlab环境下对空间电压矢量调制和SPWM进行频谱对比分析,结果表明,电压空间矢量调制下直流电压利用率提高了15%,谐波含量减小,谐波幅值也大大降低。     

An optimal selective harmonic mitigation technique for high power converters

In medium-voltage medium- and high-power inverters, which are most likely to connect distributed generation systems to grids, it is of great importance to reach high quality waveforms using the least possible number of switching transitions. The power quality is also important to be kept as high as possible. Both inverter output harmonics and grid pre-existing distortions affect the power quality. The well-known selective harmonic elimination pulse width modulation (SHEPWM) method is able to totally eliminate some specific harmonics. But the recently introduced selective harmonic mitigation pulse width modulation (SHMPWM) method can mitigate a higher number of harmonics using the same switching frequency. In this paper, implementation of an optimal selective harmonic mitigation (OSHM) method using the least possible switching frequency to satisfy three grid codes EN 50160, CIGRE JWG C4.07 and IEC 61000-3-6 is presented. In the proposed method, also a technique is employed to minimize the individual harmonics as much as possible. Using the proposed method, there is no need to the bulky and heavy line side filters. Some simulations as well as experimental investigations are carried out to prove the claim and also compare the OSHM method with the conventional SHEPWM method using the same switching pattern to confirm its better performance over SHEPWM.     

采用波形合成法的级联型多电平逆变器谐波控制

为改善级联型多电平逆变器输出电压波形质量,对通过控制逆变单元开关角实现级联多电平逆变器谐波控制的方法进行了分析研究。针对解方程组法消除特定谐波中高次多变量方程组难于求解的问题,提出了一种波形合成消除特定谐波的方法。利用此方法可通过简单的三角公式递推计算获得实现特定谐波消除的开关角。依据理论计算结果进行的例证演示列出了开关角所有可能的取值情况,说明通过逆变器开关角的选择可同时实现输出电压中特定谐波的消除及基波幅值的调节。仿真与实验结果验证了该方法的可行性。     

遗传算法应用于多电平最优化阶梯波技术

最优化阶梯波是多电平逆变器常用的控制策略,其核心就是求解一组非线性方程组,但因不能得到解析解,而用迭代法获得数值解的难度仍然很大,故提出了应用遗传算法来进行求解的思想,通过评价函数来最小化主要的低次谐波,然后编写了相应的MATLAB程序,求解了在评价函数<0.5%的解的轨迹。最后的仿真和实验也证明了该方法的实用性。     

城市路况下电动汽车驱动器最优开关频率选择探讨

新能源汽车在城市路况上低速行驶时，由于此时电机输出功率较低，电机驱动器将会运行在低调制比工况下，此时脉冲宽度调制（PWM）带来的谐波会与非理想开关过程带来的谐波对电机工作效率与性能的影响会增加。为了在这种工况下获得良好的电机性能，需要选择合适的电机驱动器开关频率最大程度的降低两种谐波的影响。通过综合考虑两种谐波的表达式，提出了一种开关频率的优化选择方案，并在MATLAB中对方案进行了计算和仿真验证。     

基于RB-IGBT的三电平光伏并网逆变器的效率分析

笔者分析了1种基于RB-IGBT的新型三电平光伏并网逆变器在不同的开关频率下工作时的开关损耗和导通损耗,并介绍了相关损耗的计算方法,通过MATLAB软件的计算得出数值,并与NPC三电平逆变电路和两电平逆变电路在同等情况下运行时的损耗进行了对比,从而得出此逆变电路应用在光伏并网逆变器中可以提高逆变器的效率。     

Novel Pulse-width Modulation Strategy to Minimize the Switching Losses of Z-Source Inverters

This article proposes a novel pulse-width modulation strategy to minimize switching losses of the Z-source inverter. The Z-source inverter has different pulse-width modulation patterns unlike the conventional voltage source inverter. Shoot-through states have been inserted within the zero states of the traditional pulse-width modulation patterns of a voltage source inverter to boost DC input voltage. Thus, the Z-source inverter has six active states, two zero states, and additional shoot-through states differentiating the Z-source and conventional voltage source inverters. The currents flowing through the switches of the Z-source inverter are larger than those of the conventional voltage source inverter, because Z-network currents must flow through the switches during the shoot-through states. Therefore, shoot-through currents increase the total switching losses of the Z-source inverter. In this article, switching losses of the Z-source inverter with the existing pulse-width modulation strategy are analyzed in detail. Then, new modulation signals of the Z-source inverter are introduced to produce unique pulse-width modulation patterns that minimize the switching losses of the Z-source inverter. The switching losses of the Z-source inverter with both pulse-width modulation strategies are simulated and compared. In addition, an experimental system has been built and tested to verify the effectiveness of the proposed strategy.     

混合级联型七电平变频调速装置的研究

介绍了一种适用于中高压变频调速场合的混合级联型七电平变频调速装置,分析了这种装置的主电路拓扑结构及其特点,研究了主电路的开关逻辑关系,给出了基于低次谐波最小原则的控制策略,并给出输出电压波形的谐波分析,实验结果证明其有很好的输出波形,输出谐波含量少,具有较高的性能价格比。     

单极性SPWM调制方式下逆变器效率对比

全桥逆变器的单极性SPWM调制方式有单臂斩波、带同臂互补的单臂斩波、双臂斩波、带同臂互补的双臂斩波4种方式。通过分析逆变器的损耗组成,对比研究了4种调制方式下逆变器在开关次数、开关软硬动作状态和导通状态方面的异同,理论计算了采用不同调制方式时损耗的变化,分析得到:在小功率状态下加入同臂互补以后,开关损耗不变,导通损耗减少,此时,利用加入同臂互补斩波驱动的逆变器效率更高。最后搭建了实验平台,通过实验结果对比验证了理论分析的正确性。     

LCL滤波并网逆变器的控制策略

把LCL滤波器作为电压源型并网逆变器与电网的接口已受到广泛关注。与单电感L滤波器相比,利用电感值较小的LCL滤波器对入网电流的高次谐波具有显著的衰减效果,特别是在低开关频率的大功率并网逆变系统应用中更具明显优势,但是仅采用直接入网电流控制时,LCL滤波器接口的并网逆变器系统存在稳定性问题。该文采用电网侧电感电流和逆变侧电感电流双闭环控制策略对并网电流进行直接控制,电网侧电感电流作为外环更容易抑制并网电流的谐波因素,且可以直接控制入网电流的单位功率因数,采用逆变器侧电感电流作为内环可以增加系统阻尼,从而可抑制系统振荡,增加系统稳定性。对该方案进行系统建模,并深入分析了滤波器参数、控制器参数及系统稳定性之间的精确量化关系。仿真和实验结果表明,该控制策略既可有效抑制入网电流谐振和实现进网电流的高功率因数运行,同时又具有良好的稳态和动态性能。