Abstract
The modular multilevel converter offers benefits for medium and high voltage power conversion due to indirect series connection of devices. The drawback is a large amount of capacitance that has to be installed in each module, often prohibiting its use in cost sensitive applications. This letter proposes a new operation mode of modular multilevel topologies that allows reducing the capacitance by at least an order of magnitude. To achieve this, the multilevel operation is sacrificed, but many advantages of indirect series connection, such as proper voltage sharing, small voltage steps, limited voltage slopes, modularity, and scalability remain.
Highlights
T HE greatest drawback of modular multilevel topologies, i.e., modular multilevel converter (MMC) and modular multilevel matrix converter, is the energy variation at the module capacitors, which determines the required module capacitance
The output voltage includes the additional frequency used for energy balancing, which has to be suppressed by passive filters
It is visible that the gray branch reference voltage is partly below zero, or eventually higher than the maximum available voltage. As these voltages cannot be synthesized by the branches, the reference voltage signals need to be clipped, which leads to a distortion of the output voltage
Summary
T HE greatest drawback of modular multilevel topologies, i.e., modular multilevel converter (MMC) and modular multilevel matrix converter, is the energy variation at the module capacitors, which determines the required module capacitance. Several approaches were presented in order to reduce the energy variation at low output frequencies [1]–[3]. These methods do not affect the phase-to-phase output voltage. They do not reduce the size of capacitors to a level where they are not dominant any more. The output voltage includes the additional frequency used for energy balancing, which has to be suppressed by passive filters. Another approach is presented in [5].
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