H桥级联型多电平逆变器调制策略对比分析

针对H桥级联型多电平逆变器,对比分析了传统的多电平PWM调制策略,指出其存在的输出电压谐波性能问题。提出一种改进的调制策略,不仅抑制了直流母线电压波动引起的低次谐波含量,而且有效地降低了高、次谐波含量。最后通过对比实验,验证了所提出方法的正确性与有效性。     

H桥级联多电平逆变器相移SVPWM技术的研究

载波相移SPWM调制法是级联型逆变器的主流控制方法,其等效载波频率高、谐波特性好、功率单元之间输出功率平衡。而空间矢量法谐波特性好、电压利用率高、控制方法简单便于数字实现。文中针对H桥级联型多电平逆变器的结构特点,综合采用载波移相SPWM法和空间矢量法,并用一种新的空间矢量算法取代传统的方法。该算法中无需三角函数和无理数计算,计算过程非常简单,节约了计算时间,结果更为准确。最后通过系统仿真验证该算法的正确性和有效性。     

Control of a Single-Phase Cascaded H-Bridge Multilevel Inverter for Grid-Connected Photovoltaic Systems

This paper presents a single-phase cascaded H-bridge converter for a grid-connected photovoltaic (PV) application. The multilevel topology consists of several H-bridge cells connected in series, each one connected to a string of PV modules. The adopted control scheme permits the independent control of each dc-link voltage, enabling, in this way, the tracking of the maximum power point for each string of PV panels. Additionally, low-ripple sinusoidal-current waveforms are generated with almost unity power factor. The topology offers other advantages such as the operation at lower switching frequency or lower current ripple compared to standard two-level topologies. Simulation and experimental results are presented for different operating conditions.     

级联型多电平逆变器中多载波PWM控制方法的改进

级联型多电平逆变器由于其模块化结构、便于生产高度、更换容易等特点，受到电力电子工程技术人员的广泛关注。本文通过对于级联型多电平逆变器几种典型的控制方法的分析比较，提出了一种改进多载波PWM控制方法。该方法通过改变载波的幅值，使级联逆变器的各个逆变单元开关规律相同，并使所有的开关器件的损耗一致，有利于逆变单元的统一设计和可靠运行。     

一种新型的级联型多电平逆变器研究

本文提出一种新的级联型多电平逆变器拓扑结构，通过负载将两个电压型三相逆变器级联在一起，该逆变器能作为一个三电平或四电平逆变器运行。本文对这种逆变器的基本结构和控制原理进行了分析。     

自举式三相半桥级联型多电平逆变器

本文提出了一种新型的三相四线制多电平逆变器,它在常规六开关三相全桥逆变输出上,再级联一级半桥,并加入自举电路,负载中线与输入电源正极相连.在纹波跟踪分段式SPWM(Sinusoidal Pulse Width Modulation)调制下,级联的半桥电能由自举电路工作时得到.该电路拓扑结构及其控制方法,减少了多电平逆变的独立直流电源数,提高了逆变输出电压.文章用逐段计算法分析了规则采样SPWM调制法的自举电容的纹波和电流,以及产生的谐波.通过分析和实验表明,自举电容的电容量、充电回路电阻、负载和调制度等,均对自举电容的纹波和电流有影响.     

混合逆变器改进调制算法的研究

目前,在混合级联型逆变器的研究领域中,改变串联单元的母线电压比是一种比较典型的方法。但是,该类拓扑结构存在着不同电压比例母线之间的“能量回流”问题,在不同的调制比下运行,可能会出现导致母线电压不平衡的情况。针对该问题,本文在分析“能量回流”问题产生机理的基础上,提出了一种纯软件算法的解决方案,该方案针对不同的调制比,实时的改变主逆变器的导通比较电压,且同时动态的调整从逆变器的零序分量,从而实现了全调制比范围内克服“能量回流”的问题,并且改善了输出电压谐波性能等目标。最后,本文对所提出的控制算法进行了仿真和实验的验证。     

一种新型混合非对称多电平逆变器的研究

提出了一种新型混合非对称多电平逆变器,该逆变器的突出优点是在输出相同电平的条件下,电路所需的开关元器件和其他元器件比传统的多电平逆变器要少的多,简化了电路结构和控制,降低了成本。对逆变器主电路的结构和工作原理进行了详细阐述,并采用消谐波脉宽调制（Subharmonic Pulse Width Modulation,简称SHPWM）进行控制。最后给出了仿真结果,验证了理论分析。     

Hybrid Cascaded H-Bridge Multilevel-Inverter Induction-Motor-Drive Direct Torque Control for Automotive Applications

This paper presents a hybrid cascaded H-bridge multilevel motor drive direct torque control (DTC) scheme for electric vehicles (EVs) or hybrid EVs. The control method is based on DTC operating principles. The stator voltage vector reference is computed from the stator flux and torque errors imposed by the flux and torque controllers. This voltage reference is then generated using a hybrid cascaded H-bridge multilevel inverter, where each phase of the inverter can be implemented using a dc source, which would be available from fuel cells, batteries, or ultracapacitors. This inverter provides nearly sinusoidal voltages with very low distortion, even without filtering, using fewer switching devices. In addition, the multilevel inverter can generate a high and fixed switching frequency output voltage with fewer switching losses, since only the small power cells of the inverter operate at a high switching rate. Therefore, a high performance and also efficient torque and flux controllers are obtained, enabling a DTC solution for multilevel-inverter-powered motor drives.      

串联H桥高压变频器共模电压的研究

由电网供电，输出到电机的三相中性点可浮动的变频器驱动系统中，其负载端往往存在共模电压。对于串联H桥高压变频器来说，虽然其共模电压很小，但本质上共模电压仍然存在。由于此结构中存在变压器，且每相由多个H桥单元串联而成，拓扑结构复杂，为共模电压的分析增加了难度。本文首先给出共模电压的一般定义，然后提出一种串联H桥多平变频器共模电压的分析方法，并给出仿真结果。仿真结果和参考文献中的实际测量结果非常接近，验证了所提出方法的有效性。     

Cascaded Multilevel Inverter Employing Three-Phase Transformers and Single DC Input

This paper proposes an isolated cascaded multilevel inverter employing low-frequency three-phase transformers and a single dc input power source. The proposed circuit configuration can reduce a number of transformers compared with traditional three-phase multilevel inverters using single-phase transformers. It controls switching phase angles to obtain an optimal switching pattern identified with the fundamental frequency of the output voltage. Owing to this control strategy, harmonic components of the output voltage and switching losses can be diminished considerably. To verify the performance of the proposed approach, we implemented computer-aided simulations and experiments using a prototype.      

Cascaded Multilevel Inverter With Regeneration Capability and Reduced Number of Switches

Multilevel converters are a very interesting alternative for medium and high power drives. One of the more flexible topologies of this type is the cascaded multicell converter. This paper proposes the use of a single-phase reduced cell suitable for cascaded multilevel converters. This cell uses a reduced single-phase active rectifier at the input and an H-bridge inverter at the output side. This topology presents a very good performance, effectively controlling the waveform of the input current and of the output voltage and allowing operation in the motoring and regenerative mode. The results presented in this paper confirm that this medium voltage inverter effectively eliminates low frequency input current harmonics at the primary side of the transformer and operates without problems in regenerative mode.     

A Single-Phase Active Filter Using an H-Bridge PWM Converter With a Sampling Frequency Quadruple of the Switching Frequency

This paper presents a digital current regulator for H-bridge pulsewidth modulation (PWM) converters, whose sampling frequency equals quadruple of the switching frequency. The current regulator detects the ac current and manipulates the voltage reference not only at the upper and lower peaks of the PWM triangle carrier but also at its zero crossings. This paper theoretically discusses the switching sequence of the H-bridge PWM converter, and reveals the amount of the voltage error and the condition where the voltage error occurs. A modified deadbeat current regulator is proposed to suppress the current oscillation induced by the voltage error, based on the theoretical analysis. Experimental results are shown to verify the control performance of the proposed current regulator. Moreover, a proposed current regulator is applied to a single-phase active power filter to demonstrate the effectiveness in harmonic compensation.     

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。     

ARCP软开关逆变器控制方式比较

随着逆变器开关频率和效率的提高,软开关逆变器会比传统硬开关拓扑显得更具优势。辅助谐振极（ARCP）就是一种典型的ZVT型软开关逆变器拓扑,其辅助开关的控制方式会影响逆变器的可靠性和效率。本文比较了变时间和定时间两种控制方式的特点,给出了ARCP逆变器不同控制下的软开关区域和损耗分析,并在一台2 kW实验样机上进行了验证。     

一种光伏并网级联逆变器的研究

在一种混合控制的光伏并网级联逆变器的基础上,提出了一种在梯形波叠加方式下单元逆变器导通角的简易算法,计算不同位置时单元逆变器的输出功率,提出采取逆变器轮流工作方式解决电池模块输出功率不平衡问题,并对各级联单元光伏电池如何配置进行了分析和计算,通过仿真证明其正确性。     

Predictive Current Control for Multilevel Active Rectifiers With Reduced Switching Frequency

In this paper, a new low-frequency predictive current control is proposed for a single-phase cascaded H-bridge multilevel rectifier. The control method has been fully investigated with theoretical analysis, simulation, and experiments on a laboratory prototype with five series-connected H-bridges. However, the analysis and technique are valid for any general level structure. The simulations and experimental results presented demonstrate the excellent performance of the predictive control in terms of AC current waveform quality, power factor, and reduced switching frequency of each bridge, in comparison to traditional control schemes.     

A Novel Switching Sequence Design for Five-Level NPC/H-Bridge Inverters With Improved Output Voltage Spectrum and Minimized Device Switching Frequency

This paper presents a novel switching sequence design for the space-vector modulation of high-power multilevel converters. The switching sequences are optimized for the improvement of harmonic spectrum and the minimization of device switching frequency. Compared to other commonly used switching sequences, the output spectrum of the proposed design shows higher inverter equivalent switching frequency. Meanwhile, the device switching frequency is reduced by using a flexible switching pattern. The proposed switching sequence has been simulated and experimentally tested on a 5-level neutral point clamped H-bridge based inverter. The results from both simulations and experiments consistently verify the above-mentioned features.     

A Modular Strategy for Control and Voltage Balancing of Cascaded H-Bridge Rectifiers

In this paper, a new strategy for voltage balancing of distinct dc buses in cascaded H-bridge rectifiers is presented. This method ensures that the dc bus capacitor voltages converge to the reference value, even when the loads attached to them are extracting different amounts of power. The proposed method can be used for an arbitrary number of series H-bridges, different voltage levels, and different power levels in unidirectional or bidirectional rectifiers. To reduce the current harmonics and distortion, the input current is programmed to be sinusoidal and in phase with the input voltage; however, it is possible to adjust the input power factor to control both the active and reactive powers. In the proposed approach, both the low frequency (stepped modulation) and high frequency [pulse-width modulation (PWM)] switching methods are utilized to improve the performance of the rectifier. Using theoretical analysis, the acceptable load power limits for a rectifier with N-H-bridge cells are derived. The validity of the proposed method is verified by simulation and experimental results.      

Switching Characterization of Cascaded Multilevel-Inverter-Controlled Systems

In this paper, the method of triangular carrier switching control of two-level inverters is extended to cascaded multilevel inverters using phase-shifted multicarrier unipolar pulsewidth modulation (PWM). The condition for smooth modulation is obtained using the Bessel's function representation of the PWM output and the switching condition of the multilevel-inverter-controlled system. A method is proposed for the determination of the minimum amplitude of the triangular carrier for smooth modulation at fixed switching frequency. It is shown that the multilevel modulation based on the phase-shifted carriers significantly reduces the ripple magnitude in the switching function and allows the use of a smaller carrier amplitude under closed loop. This increases the forward gain and, hence, improves the tracking characteristics. The proposed cascaded multilevel inverter control is implemented for the operation of a distribution static compensator (DSTATCOM) in the voltage control mode. The experimental verification of the theoretical and simulation results is provided through a field-programmable gate array (FPGA) based control of a laboratory model of a single-phase DSTATCOM.