一种混合级联型多电平逆变器拓扑结构

在交流电动机调速领域,大容量多电平变换器的应用越来越广泛,为了改善系统性能,各种各样的多电平拓扑结构被提出.本文提出了一种新颖的混合级联式多电平拓扑结构,该结构将传统的H桥逆变器(主逆变器)和二极管钳位型三电平逆变器(从逆变器)结合起来,串联为电动机供电,而这其中仅仅只有主逆变器需要电压源.这种新型的拓扑结构由于增加了从逆变器作为辅助单元用于能量存储,可以提高系统的效率,一定程度上实现电动机的四象限运行.相比传统的H桥逆变器,该拓扑可以减少输入电压源的数目;当电动机以稳定速度运行时,从逆变器可以为负载提供无功能量.该拓扑结构在电力机车和大型舰船推进系统等领域有着广泛的应用前景.     

一种具有高性价比的五电平逆变器拓扑

为了提高五电平逆变器的性价比,在分析传统五电平逆变器拓扑的基础上,重组H桥级联结构与中点电位结构,只增加一个功率开关管构成辅助开关,跨接一个H桥与两个直流电压源,提出一种新型五电平逆变器拓扑。通过不同的开关组合,进而得到五电平输出电压。对H桥级联型五电平拓扑与新型拓扑的结构及输出性能进行了对比分析,仿真与试验结果表明:在输出相同电平的情况下,新型拓扑单元性价比高,验证了新型拓扑的正确性与有效性。     

一种新型混合级联不对称多电平逆变器

提出一种新型混合级联不对称多电平逆变器,这种多电平逆变器由多个不对称四电平逆变器级联在一起构成,输出电压由其级联单元的输出叠加而成.相对于传统的级联多电平拓扑,在得到相同输出电平的情况下,该拓扑需要较少的开关器件,因此可以简化电路结构.但是该拓扑需要特定的独立直流电源.实验室构建了一台单相混合级联不对称七电平逆变器,并采用消谐波混合不对称调制方法对其进行控制,最后通过仿真和实验进行验证.     

一种新型的级联型多电平逆变器拓扑

本文介绍了一种新型级联型多电平逆变器拓扑结构,并对其PWM调制算法进行了仿真研究。该拓扑电路与传统的H桥级联型多电平逆变器相比,可以用相对较少的电力电子开关器件实现多电平的输出。该拓扑电路由一系列电平变换单元级联而成,可以减少开关器件的数目及其功率损耗、减小逆变电路的体积、提高逆变效率并具有相对简单的控制系统。最后基于Matlab/Simulink对该拓扑结构的PWM调制方法进行了仿真,仿真结果验证了该拓扑结构的正确性与优越性。     

带储能单元的新型多电平逆变器及其控制算法

为了提高高压大容量变频器的性能,各式新型多电平变换器拓扑结构纷纷被提出。本文将传统的二极管钳位型三电平结构(从逆变器)与H桥级联型结构(主逆变器)相结合,提出了一种带储能单元的新型混合多电平逆变器拓扑结构。在该拓扑中,只有主逆变器是需要电源供电的,而从逆变器则不需要电源供电,其母线直接连接在悬浮的超级电容上。从逆变器可以作为能量存储装置,实现电机制动能量的存储再利用,提高系统的效率;在动态过程中,悬浮电容的电压可以通过一定的控制算法始终保持稳定。本文通过仿真和初步的实验验证了该拓扑及其控制算法的可行性。该拓扑结构有着广泛的应用前景,尤其是在电力机车和舰船推进等需要频繁启制动的独立电源系统中。     

一种新型电压型逆变器拓扑结构及其PWM控制方法

多电平逆变器具有功率容量大、输出谐波小、传输损耗低等优点而得到越来越广泛的应用.其主要缺点是电路结构复杂、需要大量的功率元件、控制方法复杂.在传统H桥级联型逆变器基础上,提出了一种新型逆变器拓扑结构.通过采用辅助双向开关,在提高输出电压电平数的同时大量减少功率开关元件的数量,简化了电路结构.并根据新型逆变器拓扑结构的特点,提出了一种阶梯波PWM控制方法,采用特定谐波消除法(SHE-PWM)对逆变器输出电压的低次谐波进行抑制,同时进行了仿真.最后建立一套九电平电压型逆变器试验系统,对拓扑结构和PWM控制方法进行了验证.     

基于级联式电压源逆变器的静止同步补偿电压控制器的设计

为了提高静止同步补偿器的耐压水平和容量,尽量限制系统谐波失真,同时减少逆变器的附属设备,设计了一种新型级联式电压源逆变器构成的静止同步补偿电压控制器,并对该控制器的运行进行了研究。根据该级联式三相三电平电压源逆变器的拓扑结构,该静止同步补偿器可以在没有变压器的情况下运行,并可以限制谐波失真到一个非常小的值。同时,给出了由级联式多电平电压源逆变器构成的静止同步补偿器的运行原理。     

H桥多电平逆变器的混合载波交叠式PWM控制

为了增大逆变器的功率等级,改善输出电压的波形质量,提出了一种级联H桥多电平逆变器拓扑和与其相对应的PWM载波调制控制策略。该方法是根据传统混合频率载波调制策略,采用了同相的交叠式三角载波调制,结合了同相层叠式载波调制较好的消谐特点以及使高低压单元功率自然平衡的特点,使级联H桥多电平逆变器拓扑结构不仅可以输出多电平,还能解决混合调制下的功率环流现象,而且逆变器模块化比较简单,可以使逆变器在输出周期内功率达到自然平衡。以2个高低压单元为例,进行了仿真实验。实验结果验证了该逆变器结构和控制策略的可行性。     

级联式并联有源电力滤波器的控制

本文提出了一种新的级联式并联有源电力滤波器(CSAPF)的控制算法.传统的两电平拓扑结构的有源滤波器由于其功率开关耐压水平的限制,难以实现对高压大容量非线性负载的谐波补偿.在高压大容量传动系统中,H桥级联式逆变器得到了广泛的应用.然而,这种逆变器独立电容电压的不平衡问题限制了其在有源滤波领域的应用.本文针对这一问题设计了一种新的参考电流提取算法和电容电压平衡PWM算法.实验结果表明了所提出算法的正确性和有效性.     

半桥级联多电平逆变器拓扑结构及其调制方法

针对半桥级联多电平逆变器拓扑结构,提出了与之相适应的调制方法。该拓扑结构与传统的H桥级联多电平逆变器相比,在基本单元级联数目相同的条件下,具有输出更多电平等级,减少电力电子开关器件数目等优点。以对称的3个功率单元和非对称的两个功率单元为例,分别对两种不同的调制方法进行了理论分析和仿真验证。仿真结果验证了该拓扑结构的优越性及其调制方法的可行性。     

多电平逆变器分析与仿真

目前,多电平逆变器常采用电力电子开关器件串联的逆变器,或者功率单元串联叠加的级联式逆变器。两者不仅直流供电电源不同,电路的结构形式也不同。新型级联多电平逆变器不仅结构简单,而且在输出电平数相同时,所需开关管较少,具有良好的工业应用前景。通过分析典型逆变器结构,阐述其结构特点与联系,并通过软件仿真,比较各自的优缺点,为高电压大容量多电平逆变器的选择提供有益的参考。     

非对称结构功率单元串联多电平变频调速系统

介绍了一种非对称结构功率单元串联多电平变频调速系统,其主体结构采用单元串联级联方式,每个单元采用非对称结构的三电平方式构建,介绍了几种功率单元的几种拓朴结构以及整机的控制算法.采用此结构可以用低压器件解决高压变频问题,同时还可以使系统的结构大为简化,系统输出谐波减小.最后给出了系统实际运行的结果.     

A power line conditioner using cascade multilevel inverters fordistribution systems

In this paper, a power line conditioner using a cascade multilevel inverter is presented for voltage regulation, reactive power (VAr) compensation, and harmonic filtering. The cascade M-level inverter consists of (M-1)/2 H bridges, in which each bridge has its own separate DC source. This new inverter can: (1) generate almost sinusoidal waveform voltage with only one time switching per line cycle; (2) eliminate transformers of multipulse inverters used in the conventional static VAr compensators; and (3) make possible direct connection to the 13.8 kV power distribution system in parallel and series without any transformer. In other words, the power line conditioner is much more efficient and more suitable to VAr compensation and harmonic filtering of distribution systems than traditional multipulse and pulsewidth modulation inverters. It has been shown that the new inverter is especially suited for VAr compensation. This paper focuses on feasibility and control schemes of the cascade inverter for voltage regulation and harmonic filtering in distribution systems. Analytical, simulated, and experimental results show the superiority of the new power line conditioner     

Overdistention operation of cascaded multilevel inverters

In the past decade, the multilevel power converter has transitioned from an experimental concept to a standard product of many medium-voltage drive manufacturers. By utilizing small voltage steps, the multilevel topology offers higher power quality, higher voltage capability, lower switching losses, and improved electromagnetic compatibility over standard topologies. Recently, several researchers have focused on the cascaded multilevel inverter whereby two multilevel inverters are series connected to a motor load by splitting the neutral connection. The resulting performance is exceptional in terms of power quality since the overall number of voltage levels is effectively the product of the two cascaded inverters. This paper demonstrates that it is possible to extend this performance to an even higher number of voltage levels referred to as overdistended operation. This further improves the power quality that is significant in applications that have stringent total harmonic distorsion requirements, such as naval ship propulsion. A new control is introduced for overdistention operation and is validated with computer simulation and laboratory measurements.     

Unified power flow controller based on two shunt converters and a series capacitor

In this paper a novel configuration of unified power flow controller (UPFC) which consists of two shunt converters and a series capacitor is proposed. In this configuration, a series capacitor is used between two shunt converters to inject desired series voltage. As a result, it is possible to control the active and reactive power flow as same as the conventional configuration of UPFC. The main advantage of the proposed UPFC in comparison with the conventional configuration is injection of a series voltage waveform with a very low total harmonic distortion (THD). Also, using two shunt converters instead of a series and a shunt converters, results in reduction of design efforts and simplification of control, measuring and protection strategies. An optimal control strategy based on the discrete model of converters is applied to shunt converters. The proposed UPFC is simulated using PSCAD/EMTDC and MATLAB software and simulation results are presented to validate the effectiveness of the novel configuration of UPFC. Also, the experimental results which are obtained from an experimental set-up are presented.     

五电平双降压式全桥逆变器

该逆变器是在两电平双降压半桥逆变器基础上改进得到的,它保留了双Buck逆变器无桥臂直通、无体二极管反向恢复问题的优点和半周期工作模式,是一种和传统的飞跨电容型、二极管钳位型或级联型都不相同的多电平逆变器.同传统多电平逆变器相比,电路复杂性和器件数量降低,控制简单易实现,无桥臂直通隐患.理论分析和实验结果均表明了该逆变器的优异性能,同时实现了高效率和小的滤波器体积重量.     

Modified multilevel inverter employing half- and full-bridge cells with cascade transformer and its extension to photovoltaic power generation

For the use of stand-alone photovoltaic inverters, it presents a modified multilevel inverter employing a half- and full-bridge cells with a cascade transformer. The circuit configuration is based on a prior (3ⁿ⁻¹ + 2) level inverter. Among full-bridge cells employed in the prior inverter, one cell is substituted by a half-bridge cell. Owing to this simple alteration, the proposed inverter has three promising merits. First it can increase the number of output voltage levels resulted in high quality output voltages. Second, it can reduce two power switches by means of employing a half-bridge cell. Third, it can reduce power imposed on a transformer connected with the half-bridge unit. That is to say, most power is transferred to loads via transformers connected with low switching inverters, which are used to synthesize the fundamental output voltage levels whereas the output of a transformer linked to a high switching inverter is used to improve final output voltage waves; thus, it is desirable in the viewpoint of the improvement of the system efficiency. By comparing to the prior inverter, it assesses the performance of the proposed inverter as a stand-alone photovoltaic inverter. The validity of the proposed inverter is verified by computer-aided simulations and experimental results.     

A multilevel inverter based on cascade connection of submultilevel units with reduced switch count

In this paper, a multilevel inverter based on cascade connection of new submultilevel inverters is presented. The suggested submultilevel inverter is constructed using series connection of basic switching units. The proposed multilevel inverter uses fewer power switches in comparison with some similar topologies which results in reduction of switch gate drivers and also converter size and cost. The proposed multilevel inverter can be implemented in both symmetric and asymmetric configurations. The multilevel inverter configuration and operation principle are described in detail, and then, design methods of symmetric and asymmetric configurations are given. Determination of the optimal number of basic units and cascaded submultilevel inverters regarding criteria such as number of switches and total blocking voltage (TBV) of switches is studied. Power losses of the proposed multilevel inverter are calculated, and then, its symmetric and asymmetric configurations are compared with each other and also with similar cascaded multilevel inverters in various items. The validity of the suggested cascaded multilevel inverter is verified using both computer simulations and laboratory prototype implementation.     

Theoretical Analysis of Harmonics in PWM Output Waveform of Multilevel Inverters

Multilevel inverters have very attractive features, such as lower harmonics in the output, lower EMI, and reduction of the required voltage rating of power semiconductor devices. Among them, lower harmonics in the output can reduce the volume of the output harmonic filter and additional losses caused by the harmonics. Therefore, multilevel inverters are expected to realize higher power density and higher efficiency. In this paper, as a basis of the quantitative investigation of these features, the harmonics in the PWM output voltage of multilevel inverters are analyzed theoretically. As an application of the theoretical results, the usefulness of the theoretical results is verified by the prediction of the harmonic contents of the load current.     

混合级联27电平逆变器控制策略和谐波分析

级联多电平逆变器因其具有众多优点,在高压大功率应用场合受到了越来越多的关注。混合级联多电平逆变器是级联多电平逆变器的一种特殊形式,它可以采用尽可能少的功率器件和独立直流电压源,得到尽可能多的电平数。本文混合级联多电平逆变器的直流侧采用1:3:9的电压比例,控制策略采用最近电平逼近调制(NLM),得到了27个电平数的输出电压,推导出输出电压的Fourier级数表达式,计算了理论上基波、谐波特性。最后通过Saber的联合仿真功能,仿真验证了最近电平逼近调制方法的有效性和基波、谐波特性的正确性。