ABSTRACT

Cascaded multilevel inverters have been increasingly used in industrial applications. However, the quality of the output voltage of these inverters depends highly on the modulation techniques. One of the factors affecting the quality of the inverter output voltage is the existence of common mode voltage. This affects the life of three-phase electric motors connected to the inverter. This paper presents a method of modulating the carrier frequency for cascaded multilevel inverters to reduce common mode voltage and harmonics. In the proposed method, the carrier frequency modulator is considered an adaptive controller and the carriers are completely controlled by the control signal. Changes of control signals such as amplitude, frequency, and phase angle make the carrier frequency vary accordingly. In addition, the ability to reduce common mode voltage also helps increase the amplitude of the inverter output voltage. Moreover, an algorithm for reduction of switching commutations is also proposed to reduce the switching loss. The simulation and experiment results based on a cascaded 5-level three-phase inverter system with an induction motor load have confirmed the performance of the proposed method compared to that of the methods using unmodulated carriers through the comparison of output harmonics and number of switching commutations.

摘要

级联多电平逆变器已越来越多地用于工业应用。然而，这些逆变器的输出电压质量很大程度上取决于调制技术。影响逆变器输出电压质量的因素之一是共模电压的存在。这会影响连接到逆变器的三相电动机的寿命。本文提出了一种调制级联多电平逆变器的载波频率以降低共模电压和谐波的方法。在所提出的方法中，载波频率调制器被认为是一个自适应控制器，并且载波完全由控制信号控制。幅度、频率、相位角等控制信号的变化，使载波频率发生相应的变化。此外，降低共模电压的能力也有助于增加逆变器输出电压的幅度。此外，还提出了一种减少开关换向的算法，以降低开关损耗。基于具有感应电机负载的级联五电平三相逆变器系统的仿真和实验结果通过比较输出谐波和开关换向次数证实了所提方法与使用未调制载波的方法相比的性能.