基于三次谐波注入的级联多电平逆变器

本文详细分析了调制波变换技术和三次谐波注入多电平逆变器的原理,以及三次谐波注入后逆变器的调制信与输入直流电压的关系。并且,分析了在级联多电平逆变器开环PWM控制下,一般SPWM与三次谐波注入的不同。提出三次谐波注入法能够在不影响负载电流电压的情况下实现载波调制的优化控制,提高电压利用率。在Matlab/Simulink环境下通过仿真,证实了理论的正确性。     

模块化多电平变换器关键问题研究综述

随着电力电子技术的快速发展,多电平变换器及其相关技术的研究正逐步成为高压大功率运用场合的热点问题.模块化多电平变换器（Modular Multilevel Converter,MMC）因其具有模块化的结构优势,弥补了传统多电平变换器的不足.相对于传统多电平变换器,MMC具有谐波含量少、开关损耗低、故障穿越能力强等特点.本文首先从MMC的拓扑结构和工作原理入手,分析了MMC的技术特点.其次,根据当前国内外的相关理论研究,对MMC主电路建模、参数设计、调制策略以及子模块电容均压策略等关键问题进行了对比分析.最后,本文对MMC的前景进行了展望.     

基于改进差分进化算法的时间调制阵列多波束优化形成

提出了一种基于时间调制阵列的数字多波束形成方法。时间调制阵列会产生基波分量和各次谐波分量,通过调整各个单元的控制时序,实现谐波分量的幅度和相位综合,可以在正负第一次谐波处实现期望方向的波束形成。同时采用改进差分进化算法来优化控制时序,进一步降低最大旁瓣电平,实现两个指向不同的数字波束的设计。最后通过与时间调制阵列波束形成和基于基本差分进化算法的时间调制阵列波束形成对比,验证了该算法在数字多波束形成中的可行性和有效性。     

模块化多电平换流器的技术研究综述

随着电力电子器件的发展,电压源换流器(VSC)广泛应用于高压直流输电领域。与传统的两电平或三电平VSC相比,模块化多电平换流器(MMC)具有电压等级控制灵活、谐波含量少、开关损耗低等特点,因此受到了科研工作者的广泛关注。本文从MMC的工作原理、调制策略以及电容电压均衡策略等方面综述了目前MMC的研究现状,并对其应用前景以及存在的问题作出了展望。     

混合型级联多电平逆变器的PAM调制和PWM调制

介绍了混合型级联多电平逆变器的PAM和PWM调制方法,在Matlab7．0中构建了基于这两种调制方法的多电平逆变器的仿真模型。仿真结果表明,混合型级联多电平逆变器能够有效减小谐波畸变率,改善输出电压波形。     

三电平SPWM波的改进算法研究与谐波分析

以提高正弦波脉宽调制（SPWM）供电质量为主要目的,SPWM脉宽调制法通常可分为两电平、三电平和多电平调制法,其中,三电平SPWM波比两电平SPWM波有更好的消除谐波特性。并且基于三电平的SPWM规则采样法是一种为简化SPWM波开关点计算衍生出来的计算方法,一定程度上可以替代比较调制算法。本文提出了一种三电平SPWM波开关点实时计算的方法,并且给出一般性计算公式。通过MATLAB编程,对计算结果进行了谐波分析,同时为了与实际应用相结合,提出了一种包含死区时间的三电平SPWM规则采样算法。在设计开关点算法时,把死区时间计算在内,分析了谐波含量,为工程应用作了铺垫。     

二极管箝位级联多电平变换器仿真研究

级联多电平变换器和二极管箝位多电平变换器是现今研究较多并且实用性较强的两种多电平拓年结构。本文将结合这两种拓扑结构，研究了一种新型的二极管箝位级联多电平变换器，其思想是将数个二极管箝位变换器模型串起来，其输出电压是通过合成每个二极管箝位变换器的输出电压而形成的。文中彩用了消谐波PWM法作种新型拓扑的调制策略，并用对这种变换器进行了住址研究。最后本文给出了相关分析结论。     

一种级联H桥多电平变频器改进型载波移相PWM调制策略

级联Ｈ桥多电平变频器已经广泛应用于光伏发电、电机调速等领域，但由于各单元独立直流电源参数差异，导致各单元直流电压不均衡， 在单元直流电压不均衡时，传统载波移相ＰＷＭ调制策略存在输出电压低频边带谐波无法消除的问题，从而影响输出电能质量，对传统载波移相ＰＷＭ调制策略下变频器输出电压进行了傅里叶分析，研究了一种可变移相角的改进型载波移相ＰＷＭ调制策略，根据不同工况实时改变移相角，从而消除输出电压的低频边带谐波，有效提高输出电能质量，最后，通过样机实验验证了改进型调制策略的有效性。     

一种特定谐波消除多电平RF-PWM方法

为消除射频脉宽调制（Radio Frequency Pulse Width Modulation,RF-PWM）的特定谐波,本文提出了一种适用于全数字发信机（All-Digital Transmitters,ADTx）的多电平RF-PWM方法.该方法利用多个自适应门限与相位调制信号实时比较,控制多个子脉冲的脉冲宽度,在基波分量加权之和正比于输入信号包络的前提下,使其特定谐波分量相互抵消.和现有技术相比,该方法可显著降低ADTx的输出滤波要求,提高其宽频段性能.以3次谐波消除为例,本文给出了对应5电平RF-PWM方案,并利用仿真和离线实验证明了该方案的有效性.     

混合型级联多电平变换器调制策略研究

多电平变换器的调制策略与其主电路拓扑密切相关。文章首先讨论了几种多电平变换器的拓扑特点,推荐了一种混合型多电平变换器,分析了它的几种调制策略和频谱特性,并进行了电路仿真,比较了它们之间的优劣,给出了连续调制方式下的频谱表达式,仿真验证了结果的正确性,最后总结了几点有用的结论。     

Single-phase integrated power quality compensator based oncapacitor-clamped configuration

A control scheme of an integrated power quality compensator, which employs an active rectifier to work simultaneously as an active power filter (APF) to decrease current harmonics, is proposed. The employed rectifier is based on a capacitor-clamped configuration to produce multilevel pulsewidth modulation waveforms which result in low voltage stress and low conduction loss on the power switches. The proposed active rectifier is controlled to track the supply current to be a sinusoidal wave with low current harmonics. The advantages of the proposed control scheme are high power factor, low current harmonics, no complicated calculations for current harmonics elimination, and no dedicated APF needed for harmonic elimination. The experimental results are used to verify the validity and effectiveness of the proposed control scheme     

A 3-D space vector modulation generalized algorithm for multilevel converters

A three-dimensional (3-D) space vector algorithm of multilevel converters for compensating harmonics and zero sequence in three-phase four-wire systems with neutral is presented. The low computational cost of the proposed method is always the same and it is independent of the number of levels of the converter. The conventional two-dimensional (2-D) space vector algorithms are particular cases of the proposed generalized modulation algorithm. In general, the presented algorithm is useful in systems with or without neutral, unbalanced load, triple harmonics and for generating 3-D control vectors.     

Optimum harmonic reduction with a wide range of modulation indexes for multilevel converters

This paper proposes a novel modulation technique to be applied to multilevel voltage-source converters suitable for high-voltage power supplies and flexible AC transmission system devices. The proposed technique can generate output stepped waveforms with a wide range of modulation indexes and minimized total voltage harmonic distortion. The main power devices switch only once per cycle, as is suitable for high-power applications. In addition to meeting the minimum turn-on and turn-off time requirements for high-power semiconductor switches, the proposed technique excludes from the synthesized waveform any pulses that are either too narrow or too wide. By using a systematic method, only the polarities and the number of levels need to be determined for different modulation levels. To verify the theory and the simulation results, a cascaded converter-based hardware prototype, including an 8-b microcontroller as well as modularized power stage and gate driver circuits, is implemented. Experimental results indicate that the proposed technique is effective for the reduction of harmonics in multilevel converters, and both the theoretical and simulation results are well validated.     

Multicarrier PWM With DC-Link Ripple Feedforward Compensation for Multilevel Inverters

Like most power converter topologies, multilevel inverters are controlled with modulation techniques that are conceptually based on nonlinear waveform synthesis assuming constant dc-link voltages. However, real applications have load and supply dependent dc-links that usually present important low frequency ripple, which is also modulated and transmitted to the load, generating undesirable low frequency voltage and current distortion. This paper introduces a simple but effective dc-link ripple feedforward strategy into traditional carrier-based modulation techniques. The dc-link ripples are measured and used to modify the carriers or the reference directly in the modulation stage. Simulation and experimental results show the accuracy of the proposed method, eliminating low order harmonics in the load current.     

Compact analytical solutions for determining the spectral characteristics of multicarrier-based multilevel PWM

Multilevel pulsewidth modulation (PWM) has become very important in high-power applications in recent years. Many different types of topology and control strategy have been developed to cater for the increasing need. One of the major concerns of the control strategy is to reduce the undesirable harmonics in order to improve the performance and efficiency. This paper presents the derivation of analytical solutions for determining the spectral characteristics of the multicarrier-based multilevel sinusoidal PWM. By decomposing the multilevel PWM into a series of sub-PWM and followed by using double Fourier series analysis, compact analytical solutions for any level with any carrier phase disposition have been obtained. Closed-form solutions have also been derived for double-sided multilevel PWM under certain specific carrier phase settings. The analytical solutions have been cross verified extensively with simulations and the results match with each other very well. It is shown that the proposed analytical solutions are by far the most compact reported in the literature.     

A Five-Level Symmetrically Defined Selective Harmonic Elimination PWM Strategy: Analysis and Experimental Validation

A five-level symmetrically defined multilevel selective harmonic elimination pulsewidth modulation (MSHE-PWM) strategy is reported in this paper. It is mathematically expressed using Fourier-based equations on a line-to-neutral basis. An equal number of switching transitions when compared against the well-known multicarrier phase-shifted sinusoidal PWM (MPS-SPWM) technique is investigated. For this paper, it is assumed that the four triangular carriers of the MPS-SPWM method have nine per unit frequency resulting in seventeen switching transitions for every quarter period. For the proposed MSHE-PWM method, this allows control of sixteen harmonics and the fundamental. It is confirmed that the proposed MSHE-PWM offers significantly higher converter bandwidth in the standard range of the modulation indices. Moreover, when the bandwidth is reduced to be equal with the one offered with the MPS-PWM, the modulation index can be increased resulting in a higher gain and at a reduced switching frequency overall. Selected solutions for the switching transitions are presented and verified experimentally in order to confirm the effectiveness of the proposed technique.     

Three-dimensional space-vector modulation algorithm for four-leg multilevel converters using abc coordinates

In this paper, a novel three-dimensional (3-D) space-vector algorithm for four-leg multilevel converters is presented. It can be applied to active power filters or neutral-current compensator applications for mitigating harmonics and zero-sequence components using abc coordinates (referred from now on this paper as natural coordinates). This technique greatly simplifies the selection of the 3-D region where a given voltage vector is supposed to be found. Compared to a three-level modulation algorithm for three-leg multilevel converters, this algorithm does not increase its complexity and the calculations of the active vectors with the corresponding switching time that generate the reference voltage vector. In addition, the low-computational cost of the proposed algorithm is always the same and it is independent of the number of levels of the converter.     

Implementation of a three-level rectifier for power factorcorrection

In this paper, a new single-phase switching mode rectifier (SMR) for three-level pulse width modulation (PWM) is proposed to achieve high input power factor, low current harmonics, low total harmonic distortion (THD) and simple control scheme. The mains circuit of the proposed SMR consists of six power switches, one boost inductor, and two DC capacitors. The control algorithm is based on a look-up table. There are five control signals in the input of the look-up table. These control signals are used to control the power flow of the adopted rectifier, compensate the capacitor voltages for the balance problem, draw a sinusoidal line current with nearly unity power factor, and generate a three-level PWM pattern on the AC side of adopted rectifier. The advantages of using three-level PWM scheme compared with two-level PWM scheme are using low voltage stress of power switches, decreasing input current harmonics, and reducing the conduction losses. The performances of the proposed multilevel SMR are measured and shown in this paper. The high power factor and low harmonic currents at the input of the rectifier are verified by software simulations and experimental results from a laboratory prototype     

On multilevel block modulation codes

The multilevel technique for combining block coding and modulation is investigated. A general formulation is presented for multilevel modulation codes in terms of component codes with appropriate distance measures. A specific method for constructing multilevel block modulation codes with interdependency among component codes is proposed. Given a multilevel block modulation code C with no interdependency among the binary component codes, the proposed method gives a multilevel block modulation code C' that has the same rate as C, a minimum squared Euclidean distance not less than that of C, a trellis diagram with the same number of states as that of C, and a smaller number of nearest neighbor codewords than that of C . Finally, a technique is presented for analyzing the error performance of block modulation codes for an additive white Gaussian noise (AWGN) channel based on soft-decision maximum likelihood decoding. Error probabilities of some specific codes are evaluated by simulation and upper bounds based on their Euclidean weight distributions     

Simple Unified Approach to Develop a Time-Domain Modulation Strategy for Single-Phase Multilevel Converters

Single-phase power converters are widely used in power applications as photovoltaics and fuel-cell power conditioners. In addition, multilevel converters are a well-known solution in order to achieve high-quality output waveforms in power systems. In this paper, a time-domain duty-cycle computation technique for single-phase multilevel converters named 1DM is presented. The proposed technique is based on geometrical calculations with outstanding simplicity and generality. The proposed modulation technique can be easily applied to any multilevel converter topology carrying out the necessary calculations. The most common multilevel converter topologies have been studied in this paper as examples to introduce the proposed modulation strategy. Any other multilevel converter topology could be studied, and the corresponding 1DM could be easily developed. In addition, the well-known optimized voltage balance strategy for voltage capacitor control using the redundant switching states of the system is applied working with the proposed 1DM method, showing that both techniques are compatible. Experimental and simulation results for several single-phase multilevel converters are shown to validate the proposed modulation technique.