Cascaded Common Nodal Point Multi-level Inverter Topology

Recent trends in the multi-level inverter (MLI) technology demand reduced number of switches, driver circuits, isolated DC sources, peak inverse voltage (PIV), appreciable number of voltage level, and lower total harmonic distortion. This paper presents an improved cascaded MLI configuration. Each module comprises ten switches, two isolated DC sources, and two capacitors; it can generate a maximum of 9-level output voltage waveform. Optimized switching sequence is developed that ensures minimum switching transitions and is implemented through single-carrier pulse width modulation for the control of the proposed topology. The classical cascaded H-bridge inverter and some recently developed MLI configurations were compared with the proposed inverter circuit. Results show that the proposed inverter configuration generates high number of output voltage levels with reduced number of power switches and PIV. It also has a lower per-unit power loss profile. Unit capacitor voltage balancing scheme is developed, which ensures proper control of the unit step voltage level in each of the cascaded modules, at extreme loading condition. For two cascaded inverter modules, simulation and experimental verifications are carried out on the proposed inverter for an R–L load. Simulation results of the output voltage waveforms and its harmonic spectrum are in conformity with experimental results.     

Sinusoidal Pulse-width Modulated Three-phase Multi-level Inverter Topology

Abstract—This article presents a sinusoidal pulse-width modulated three-phase multi-level inverter topology. In this configuration, the basic two-level, three-phase inverter is modified to synthesize higher voltage levels by the insertion of two auxiliary switches per phase leg. The multi-level inverter configuration generates output voltage levels similar to the corresponding well-known conventional diode-clamped flying capacitors and cascaded H-bridge inverters but with fewer power circuit components and more simplicity. For output voltage and frequency variations demanded by such applications as variable-speed drives, active power filters, photovoltaic power conversions, etc., the sinusoidal pulse-width modulation technique is employed in the generation of the gating signals for the proposed three-phase multi-level inverter. A balanced three-phase R-L load is applied at the inverter output terminals, and the inverter performance is compared with that of other sinusoidal pulse-width modulated conventional multi-level inverter configurations. The validity of the proposed multi-level inverter topology and the modulation scheme are verified through simulations and experiments.     

Cascaded Multilevel Inverters Using Proposed Series Sub-multilevel Basic Blocks with Reduced Switching Devices

In this paper, a novel configuration of the cascaded multilevel inverters using series connection of new sub-multilevel basic blocks is presented. The basic structure of the proposed sub-multilevel inverter is made of three isolated batteries and eight unidirectional power switches. Hereby, by changing the polarity of one of such batteries and two power switches, two different modules of sub-multilevel inverters can be extracted that each of them is able to be incorporated into two different cascaded structures as the series basic blocks. Contemporary, to determine the suitable magnitudes of the integrated batteries, two different algorithms for each topology along with their relevant mathematical analysis have been also given. In this study, a complete comparison between the proposed topologies and several recently presented structures has been conducted. The compiled comparisons can prove the fact that both the proposed cascaded inverters are capable of generating a higher number of output voltage levels with less number of switching counts. Other advantages of these structures are reduction of voltage sources numbers, DC sources variety, value of total blocking voltage, and also conducting losses. In order to demonstrate the correct operation of the proposed structures and presented algorithms, some experimental results will be also shown.     

新型混合级联多电平逆变器拓扑及调制策略

为解决现有非对称级联多电平逆变器存在低压单元电流倒灌和输出电平数少的问题,提出一种基于开关电容电路的混合级联多电平逆变器。首先,在两单元非对称级联H桥型逆变器的低压单元中嵌入一个开关电容电路,有效避免了低压单元电流倒灌,且输出电平数得以增加。然后,为减少所提方案应用于三相系统时所需直流电源的数量,提出了用三电平中点箝位型或T型逆变器电路作为高压单元的三相混合级联多电平逆变器拓扑。之后,针对所提逆变器拓扑的特性,提出了含有移相载波和层叠载波的混合调制策略,在满足逆变器输出高质量正弦脉宽调制电压波形的同时,有效减小了开关电容电压纹波和开关器件的切换频率及开关应力。最后,通过实验验证了所提混合级联多电平逆变器拓扑及调制策略的可行性。     

Staircase Control of Hybrid Cascaded Multi-level Inverter

A cascaded multi-level inverter consists of H-bridge modules that can generally be divided into one with the same DC bus voltage and another with different DC bus voltages. By using the same power device as a standard 7-level 3H-bridge converter, the proposed converter operates with 15-level resolution with separate DC voltage sources of voltage ratio 4:2:1. The analysis of this hybrid cascaded converter with staircase control shows that this proposal can be applied in many power conversion applications, such as flexible alternative current transmission systems, uninterruptible power supply, and electric power conversion, transmission, and storage of renewable energy sources. Simulation results are presented with the proposed 15-level cascaded H-bridge inverter for a low distortion, near-sinusoidal stepped-voltage output, and a laboratory prototype of a 15-level insulated gate bipolar transistor-based cascaded H-bridge inverter is designed and implemented on a digital signal processor. The total harmonic distortion is proved less than 5%.     

基于最大延伸定理的级联多电平控制策略分析

近年来,多电平变换器在高压、大功率领域的应用越来越广泛,因而其相应的PWM控制策略也成为一个研究热点。本文提出一种按照最大延伸定理来分配不同电压比的控制策略,在相同输出电平数量情况下,可以减少独立直流电压源数量,即在相同直流电压源的情况下,可以增加输出电压电平数量,因此采用这种控制策略可以提高波形质量,减少谐波,降低高压时输出波形的du/dt,从而降低电磁干扰。同时,分析了各单元取不同电压比时的优缺点以及解决方法。最后通过仿真加以验证。     

级联型电力电子变压器电压与功率均衡控制方法

对于模块级联型电力电子变压器,如果整流级直流输出电压不均衡或各双有源DC-DC变换器(DAB)模块传递的功率不均衡,可能导致开关器件电压或电流应力分配不均。因此提出在整流级采用电压均衡控制,在DAB级采用功率均衡控制来解决整流级输出电压的不均衡问题和因各DAB模块参数不匹配导致的功率不均衡问题。对于该功率均衡控制,是利用各整流模块占空比的有功分量作为反馈量来调节各DAB模块占空比实现的。电压均衡控制与功率均衡控制共同作用,以使系统达到整流级直流输出电压均衡和各DAB模块功率均衡的目的。此外,该功率均衡控制可以很容易由DSP实现,且不需要任何电流传感器。该控制方法已得到仿真验证,并在模块级联型电力电子变压器实验平台上得到实验验证。     

基于载波自由度的改进载波移相PWM技术

载波移相(CPS-PWM)应用于级联H桥型(CHB)多电平逆变器时,虽然各级联单元具有功率均衡的特点,但输出电压的直流电压利用率较低,且低调制度时谐波性能比较差.针对这2个问题,提出一种改进的CPS-PWM调制技术,该调制技术基于载波形状自由度,利用改进的载波代替原CPS-PWM中的三角形载波进行调制,通过状态空间平均...     

混合四电平电压源逆变器及其中点电位控制

针对传统多电平逆变器结构较复杂的缺点,提出了一种混合四电平三相三桥臂电压源逆变器的拓扑结构及其中点电位控制方法,该拓扑结构将直流侧三个分压电容的电压调整为1∶2∶1的比例,利用相与相之间的电压差来实现与传统五电平结构相同的输出线电压电平数。与传统NPC型五电平逆变器相比,该结构所需开关器件更少,具有更高的经济效益。针对拓扑结构提出的中点电位控制方法,能够实现直流侧电容电压的平衡。通过在给定条件下的MATLAB/Simulink仿真验证,仿真结果为中频逆变电源的开发研制提供了一定的参考依据。     

直流电压不等级联型逆变器一维矢量调制研究

H桥级联型多电平逆变器由于具有良好的输出波形得到广泛运用,对直流电压相等的H桥级联型逆变器,当H桥直流电压由于功率元器件差异或运行过程中负载瞬时突变等出现不等或波动时可能引起输出电压、电流波形变化,各H桥输出功率不等,严重时甚至损坏变频器.对于H桥级联型多电平逆变器传统的控制方式都是建立在H桥直流电压相等的前提下,研究了H桥直流电压不等的情况,提出了适合直流电压不等的一维矢量调制技术和直流电压不等时实现H桥等功率输出的一维矢量调制.提出的方法在两单元级联型变频实验装置上进行了验证.     

电容钳位H桥级联多电平逆变器功率均衡控制方法

针对电容钳位H桥级联多电平逆变器载波层叠SPWM调制方法中存在功率不均衡的问题,对该逆变器各个级联单元的有功功率输出进行理论分析,提出了一种改进载波层叠方式的功率均衡控制方法。该方法在不影响逆变器输出电压波形质量的前提下,通过保证该逆变器各个单元输出电压波形的基波幅值相等的方式,可以在一个输出周期内实现各个级联单元的输出功率均衡。以两单元电容钳位H桥级联多电平逆变器为例,进行了仿真分析和对比研究,详细给出了改进功率均衡控制法与传统控制方法下输出电压谐波失真(total harmonic distortion,THD)和输出功率的对比曲线,以及两种方法下逆变器输出的电压波形及其频谱图,结果验证了该控制方法的可行性与优越性。     

A Single-phase Hybrid Multi-level Inverter

This article presents a single-phase 17-level hybrid multi-level inverter. The cascaded unit is made up of two five-level inverter configurations: a diode-clamped inverter and an inverter constituted of a main inverting H-bridge leg and level-clamping half-bridge circuit. The asymmetrically cascaded inverters have a separate DC input ratio of 1:3 that affects reduction in the power circuit component count in the single-phase multi-level inverter system. The operational principles, modulation schemes, and switching functions have been analyzed in detail. Fast fourier transform analysis of the output voltage waveform was carried out, and a low total harmonic distortion value of 7.61% was obtained. The validity of the proposed hybrid multi-level inverter is verified through simulation and experimental results.     

Cascaded Multi-level Inverter Topology Developed from a Modified H-bridge

In this paper, a single-phase cascaded multi-level inverter topology is proposed. It is basically developed from a modified H-bridge module. This topology reduces the switch count, the gate drive requirement, and voltage stress. The significant advantages of the proposed inverter are modular structure, simpler control, and lower number of switches. The Nearest Level Control algorithm is employed to generate the gating signals for the power switches. To verify the performance of the proposed structure, simulation results are carried out by MATLAB (The MathWorks, Natick, Massachusetts, USA)/SIMULINK. Experimental results are presented to validate the simulation results.     

Double input Z-source inverter applicable in dual-star PMSG based wind turbine

This paper proposes a new double-input Z-network for application in wind energy conversion system (WECS) which is composed of two same DC voltage sources as input sources, two inductors and one capacitor. As a result, the presented structure requires less capacitor number compared to traditional Z-network and it will be able to deliverer energy of both DC sources to local load or grid. The proposed inverter is applicable in dual-star PMSG based WECS, since it requires two DC voltage sources in same value. Besides, dynamic modeling of dual-star PMSG is presented to analyze proposed WECS connected to grid which employs dual-star PMSG and double-input Z-source inverter. The proposed dual-input Z-source inverter controls maximum power point tracking (MPPT) and delivering power to the grid. Therefore, other DC–DC chopper is not required to control two sets of rectified output voltage of generator in view of MPPT. As a result, the proposed topology requires less power electronic switches and the suggested system is more reliable against short circuit. The ability of proposed WECS with dual-star PMSG and double-input Z-source inverter is validated with simulation results and experimental tests using PCI-1716 data acquisition system.     

A new generalized switched diode multilevel inverter topology with reduced switch count and voltage on switches

This article presents a new multilevel inverter topology with reduced power switches. The proposed topology composes of several series connection of basic unit for obtaining a required output voltage level. The proposed topology can operate in symmetric condition. The proposed topology is connected in a cascaded structure to produce a higher number of output voltage levels. The proposed cascaded structure is optimized with the minimum number of components for the maximum number of levels. To prove the superiority of the proposed multilevel inverter topology, different technical parameter comparisons are carried out with recently developed multilevel inverter topologies from the literature. The calculation of total standing voltage is examined for the proposed topology. The operation of the proposed topology is tested and verified for nine-level output voltage. The simulated results are carried out, and it is strengthened by the real-time prototype results.     

基于级联多电平的有源滤波器直流侧电压平衡控制

为了减小电网中非线性负载带来的谐波电流对电网质量的影响,针对基于H桥的有源滤波器装置中直流电容电压问题,提出一种新的控制方法。将控制模块分成模块均值电压控制器和直流母线电压控制器两个部分,通过调节每个H桥之间的有功功率交换和有源滤波器同电网间有功功率的交换来实现直流电容电压的平衡控制。利用该方法对八个单元H桥级联的并联型有源滤波装置进行Matlab/Simulink仿真,并基于FPGA+DSP实验平台搭建了三单元H桥级联样机。仿真和实验结果表明,基于级联多电平的有源滤波器直流侧电压平衡控制方法是有效和实用的。     

A Home-type (H-type) Cascaded Multilevel Inverter with Reduced Device Count: Analysis and Implementation

Abstract

Multilevel inverter (MLI) is increasingly recognized as a low distorted wave synthesizing power converter built using recent power semiconductor devices. However, MLIs suffer from the requirement of higher device count. In this paper, a 15-level Home-type (H-type) inverter topology is proposed to address this concern. The H-type inverter topology is cascaded to synthesize a higher number of levels in output voltage. Voltage ratings of the dc sources are designed to generate a large number of uniform steps in output voltage. Analysis of the proposed method is presented for required number of switches, dc voltage sources, driver circuits and blocking voltage of switches. Comparative study demonstrates that the suggested topology requires reduced device count compared to the similar topologies reported in the literature. Simulation and experimental studies have been carried out to validate the performance of proposed MLI topology.     

Improvement of power conversion efficiency of soft‐switching inverter in range of low output power by adjustable dead time control

The power conversion efficiency of soft‐switching inverters can be improved by using loss‐less snubber commutation; however, the main switches of the inverter fail in zero‐voltage turn‐on when the output current is small. As a solution to this problem, adjustable dead time control in a loss‐less snubber commutation according to the magnitude of output current has been proposed. Adjustable dead time control achieves zero‐voltage turn‐on of the inverter main switches in a loss‐less snubber commutation in the range of low output current; however, waveforms of the output current of the inverter become distorted. In this paper, we propose a scheme for adjustable dead time control with dead time compensation for soft‐switching inverters. The effectiveness of the proposed control scheme is verified by experiments. Experimental results demonstrate that when the proposed control scheme is adopted, the power conversion efficiency in the range of low output power improves up to about 3% and the THD is improved within 3%. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(1): 57–64, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21282     

输入串联输出等效并联多逆变器驱动的高压大功率无线电能传输系统研究

提升逆变器输入侧直流电压源的电压等级,是实现更大功率无线电能传输的可行方案之一。但单个开关器件的额定电压有限,满足不了更高输入电压的需求。为此,文章设计了一种输入串联输出等效并联多逆变器驱动的高压大功率无线电能传输系统。该系统采用多个逆变器串联以承担较高的输入直流电压,同时每个逆变器驱动一个独立的发送线圈向同一个接收线圈发送功率。文章在考虑多个发送线圈之间互感的情况下对该系统的谐振电路参数进行了设计,分析在零相差(Zero Phase Angle,ZPA)及非零相差两个条件下系统的电流和功率输出能力,发现了运行角频率及互感的乘积对系统输出能力具有重要影响。开发出由三个逆变器串联驱动的无线电能传输样机,在750 V直流输入条件下获得最大38. 4 kW的无线电能传输功率,效率达88. 7%。     

三电平H桥级联型逆变器

级联型多电平变频器输出电压谐波含量小,易于实现模块化,适用于高压大功率场合.本文主要针对三电平H桥级联型逆变器的拓扑结构和控制方式的相关问题进行分析与研究.级联个数不同,对控制方法也有不同的要求.提出了基于载波层叠调制和载波移相调制的混合载波调制方法,三电平桥臂内采用反相层叠载波调制,级联单元间及桥臂间均采用载波移相调...