Multilevel Inverters: Topologies, Modulation and Control Strategies
Multilevel inverters have been experienced, in terms of research and applications, a continuous and increasing growth during the last three decades. Distinctive features of multilevel converters are their capability to overcome the voltage limits imposed by the adopted power devices and to reduce voltage and current harmonics content, thus reducing power losses, heat, noise and increasing efficiency and reliability. The effort of the researchers and industry has led to a rapid development of different multilevel inverter topologies, modulation techniques and control strategies. In this presentation, the speech will focus on three different related subjects to multilevel inverters; Topologies, Optimization Methods, and Control Strategies. At the first part, the speech will try to introduce some sub-modules to rebuild the presented topologies at the literature and also presenting new topologies of multilevel inverters. Another important point about multilevel inverters is that in most cases for a given topology, it is possible to use different configuration to generate the same number of output levels but with different number of components. So, it is strongly required to find a solution to optimize the topology in a way that by using minimum number of components to generate more number of levels. This subject will be the topic of second part. The next important point about multilevel inverters is their control methods. There are different control methods for multilevel inverters. Among them, the Selective Harmonic Modulation techniques (SHE) usually operate at fundamental frequency and are capable to cancel or mitigate one or more frequencies from the outputs. In addition, in symmetric multilevel inverters, balancing the provided energy by different DC voltage sources is other concern in controlling the multilevel inverters. After a theoretical discussion on the fundamentals of modulation algorithms with analytical methods, the speech will introduce and discuss in detail the selective harmonic modulation and charge balance control methods for modulation of cascaded H-Bridge multilevel converters.