Multilevel DC-link inverter

This paper presents a new class of multilevel inverters based on a multilevel dc link (MLDCL) and a bridge inverter to reduce the number of switches, clamping diodes, or capacitors. An MLDCL can be a diode-clamped phase leg, a flying-capacitor phase leg, or cascaded half-bridge cells with each cell having its own dc source. A multilevel voltage-source inverter can be formed by connecting one of the MLDCLs with a single-phase bridge inverter. The MLDCL provides a dc voltage with the shape of a staircase approximating the rectified shape of a commanded sinusoidal wave, with or without pulsewidth modulation, to the bridge inverter, which in turn alternates the polarity to produce an ac voltage. Compared with the cascaded H-bridge, diode-clamped, and flying-capacitor multilevel inverters, the MLDCL inverters can significantly reduce the switch count as well as the number of gate drivers as the number of voltage levels increases. For a given number of voltage levels m, the required number of active switches is 2/spl times/(m-1) for the existing multilevel inverters but is m+3 for the MLDCL inverters. Simulation and experimental results are included to verify the operating principles of the MLDCL inverters.     

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.     

多电平高压变频器的拓扑结构分析与研究

分析比较了高压变频器的几种主电路拓扑结构,包括普通双电平,三电平电压源型,单元串联型多电平.通过对几种类型高压变频器主电路拓扑结构进行比较确定了单元串联型多电平高压变频器的拓扑结构的优越性.     

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.     

五电平逆变器窄脉冲补偿方法的研究

以五电平逆变器为例对多电平逆变器窄脉冲补偿方法进行了研究,分析了窄脉冲的各种情形,基于多电平载波PWM方法,提出了一种综合的处理方法--多电平零序电压注入(Multilevel Zero-sequence Vohage Injection,即MZSVI)补偿方法,即注入同符号零序电压、取三相中零序电压的极值以及两倍最小脉宽零序电压注入方法.仿真结果表明,采用MZSVI补偿方法后提高了输出电压,输出电压总谐波含量THD也大大减小.MZSVI方法可以推广到任意电平的逆变器的控制,可以有效地进行控制更高电压的中压大功率变流器,而且这种方法也适用于其它类型的多电平逆变器的窄脉冲补偿.     

一种光伏发电用高增益多电平逆变器

针对传统的多电平逆变器存在有源器件数量较多、电容电压不平衡、结构复杂以及电压增益低的问题,提出一种降低器件数量且可扩展的多电平逆变器。该逆变器由开关电容单元和两个半桥组成,使用1个直流电源、3个电容、13个开关管,实现4倍电压增益和九电平交流输出电压。该逆变器通过2个半桥代替后端H桥转换输出电压极性,可以有效降低开关管总电压应力。在所提逆变器的扩展结构中,电容逐级充电的工作方式进一步提高了电压增益和输出电平数。首先,详细阐述了所提逆变器的工作模式、调制策略、电容分析、电压应力计算和电路参数设计。然后,与其他类似多电平逆变器进行了比较。最后,通过仿真与实验验证了所提逆变器的可行性和理论分析的正确性。     

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.     

Reduced common-mode modulation strategies for cascaded multilevel inverters

This paper presents modulation strategies for cascaded multilevel inverters that substantially eliminate common-mode voltage on the output phases. The paper begins by developing generic multilevel inverter reference waveforms that use only "allowed" space vectors to achieve reduced common-mode voltage. A graphical technique is then proposed that allows various carrier disposition modulation strategies for a diode-clamped inverter to be converted to equivalent modulation of a cascaded inverter for any fundamental reference waveform. This graphical technique is confirmed for both alternative phase opposition disposition and phase disposition equivalent modulation of a cascaded inverter, and is then used to create reduced common-mode modulation strategies for cascaded inverters from their equivalent counterparts for diode-clamped inverters under both continuous and discontinuous switching conditions. The strategies have been confirmed by both simulation and experimental results obtained using a cascaded five-level inverter.     

二极管钳位型双Buck三电平逆变器输入均压解耦控制

输入电容均压是多电平逆变器的关键问题,多电平调制与输入均压耦合,造成多电平变换器电路结构与控制繁杂、调节速度慢。利用双Buck电路包括2个Buck桥臂、并按电流半周期工作的特点,提出一种二极管钳位双Buck多电平结构,在任一时刻,由其中一个Buck桥臂实现逆变,而另一个Buck桥臂工作于逆向Boost状态,对输入分压电容充电,逆变控制与钳位电压均衡控制可完全解耦。在电平数较多的情形下,该方法有助于减少器件数量,降低系统复杂度,提高可靠性。对三电平情形进行了仿真与实验验证。     

PWM控制下多电平混合逆变电路的脉宽调制及拓扑分析

PWM和多电平变换是在高压大功率电力电子变换中应用较多的两种技术 ,本文在试验一种新型混合逆变电路的基础上 ,通过分析PWM控制下的多电平混合逆变电路调制方法 ,提出了一种混合单元间电压比取值的方法 ,理论上试图涵盖可能出现的混合逆变电路拓扑     

An algorithm for controlling a multilevel voltage inverter

A vector algorithm for the control of a multilevel voltage inverter is presented. The algorithm is characterized by high efficiency and does not depend on the number of levels in the inverter; it is of methodical importance for understanding the principles based on which multilevel inverters operate.     

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。     

三相四桥臂混合五电平逆变器及其3D-SVPWM算法

混合型多电平逆变器可以用较少的开关器件输出更多的电平,常被应用于中频逆变器领域,与传统逆变器相比,具有体积小、成本低和效率高等优点。一种新型的三相四桥臂混合式五电平逆变器拓扑及其abc坐标下的空间矢量脉宽调制（SVPWM）优化算法被提出,通过将直流端3个电容器的电压按1∶2∶1的比例调整,可实现输出线电压的9个电压等级,精简了电路结构,降低开关管应力。最后,所提结构和3D-SVPWM算法的仿真和实验结果验证了该方法的性能。     

Novel multilevel inverter carrier-based PWM method

The advent of the transformerless multilevel inverter topology has brought forth various pulsewidth modulation (PWM) schemes as a means to control the switching of the active devices in each of the multiple voltage levels in the inverter. An analysis of how existing multilevel carrier-based PWM affects switch utilization for the different levels of a diode-clamped inverter is conducted. Two novel carrier-based multilevel PWM schemes are presented which help to optimize or balance the switch utilization in multilevel inverters. A 10 kW prototype six-level diode-clamped inverter has been built and controlled with the novel PWM strategies proposed in this paper to act as a voltage-source inverter for a motor drive     

Multilevel inverter modulation schemes to eliminate common-mode voltages

It is well known that conventional two-level pulsewidth modulated (PWM) inverters generate high-frequency common-mode voltages with high dv/dt. Similarly, commonly used multilevel inverter modulation schemes generate common-mode voltages. Common-mode voltages may cause motor shaft voltages and bearing currents and conducted electromagnetic interference (EMI). Premature motor bearing failures and electronic equipment malfunctions have been reported to be directly related to bearing currents and EMI. In this paper, approaches to eliminating common-mode voltage when using multilevel PWM inverters are presented. It is shown that inverters, which have an odd number of levels, will generate zero common-mode voltage by switching among certain states. Therefore, motor bearing currents will be eliminated and conducted EMI will be reduced. Both sinusoidal PWM and space-vector modulation (SVM) schemes are discussed and detailed comparative simulation results between conventional and novel modulation schemes are provided. The value of the proposed technique is demonstrated experimentally by applying the novel SVM approach to a conventional multilevel inverter.     

采用主从型逆变器结构的静态同步补偿器

针对6kV中压电网三相平衡负载的无功功率补偿，结合二极管箝位多电平逆变器和H桥级联多电平逆变器的特点，提出了一种能够直接并入电网的新型主从式逆变器结构：主逆变器采用二极管箝位三电平逆变器，从逆变器采用3个H桥(即全桥)逆变器。主逆变器和H桥逆变器采用级联的形式连接，构成一个五电平的混联逆变器。H桥逆变器负责产生一个方波电压，构成输出正弦电压的基本成分；主逆变器产生输出电压的补偿部分并负责消除低次谐波。最后通过仿真结果证明了所提出的这种主从型逆变器STATCOM结构在消除谐波方面的优越性。     

Multilevel invertors of traction motors

The peculiarities of using multilevel (three-level) voltage inverters for traction purposes are studied. It is shown that a three-level inverter allows one to achieve economical voltage control in traction motors which reduces losses in both devices and a traction drive in general.     

Investigation into spectral characteristics of multilevel semiconductor inverters

Calculation of spectral characteristics is investigated, and the harmonic distortion of the output voltage of a single-phase three-level voltage inverter is determined. It is shown that the application of multilevel inverters makes it possible to decrease the harmonic distortion over the entire control region of the output voltage compared with a single-level inverter.     

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 multilevel voltage-source inverter with separate DC sources forstatic VAr generation

A new multilevel voltage-source inverter with separate DC sources is proposed for high-voltage, high-power applications, such as flexible AC transmission systems (FACTS) including static VAr generation (SVG), power-line conditioning, series compensation, phase shifting, voltage balancing, fuel cell, and photovoltaic utility systems interfacing, etc. The new M-level inverter consists of (M-1)/2 single-phase full bridges in which each bridge has its own separate DC source. This inverter can generate almost sinusoidal waveform voltage with only one time switching per cycle as the number of levels increases. It can solve the size-and-weight problems of conventional transformer-based multipulse inverters and the component-counts problems of multilevel diode-clamp and flying-capacitor inverters. To demonstrate the superiority of the new inverter, an SVG system using the new inverter topology is discussed through analysis, simulation, and experiment