Abstract
Multilevel converters have gained popularity in both medium voltage and low voltage applications. To find out the connections between various multilevel voltage-source converter topologies and to reveal how to obtain new topologies, this paper has presented four methods to derive multilevel converter topologies. Many existing topologies as well as new topologies can be derived with the methods presented in this paper. The fundamental characteristics of the multilevel converters which determine their usability such as dc-link neutral point voltage balancing and flying capacitor voltage control are also investigated in this paper with a mathematical model and an example. It is expected that more new topologies will be invented based on the work in this paper for emerging applications.
Highlights
M ULTILEVEL converters have superior characteristics over the standard two-level converter such as reduced output harmonics, lower dv/dt, and switching loss
Another advantage to obtain the topology through the derivation process is that it is easy to understand in some topologies why certain devices need to block higher voltages, e.g., T5 and T6 in Fig. 4(c) need to block twice the voltage of other devices because they replaced two devices in series
The four-level diode neutral point clamped (NPC) converter shown in Fig. 2(b) is not a good cell choice given its dc-link capacitor voltages cannot be balanced under high modulation indices and high power factors
Summary
M ULTILEVEL converters have superior characteristics over the standard two-level converter such as reduced output harmonics, lower dv/dt, and switching loss They are widely used in high or medium voltage (>3 kV) power conversion systems due to their capability to handle higher voltage and higher power [1]. This paper attempts to answer the above questions based on the work in [23]–[27] It has been found out though it is not possible to derive all the topologies from a single unified topology, there are several generic topologies and building blocks that can be used to derive many topologies. This paper presents four methods to derive multilevel converters, in the hope that these can inspire researchers to identify more useful topologies, which may find application in emerging areas
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