Abstract
The circuit topology of a submodule (SM) in an modular multilevel converter (MMC) defines many of the functionalities of the complete power electronics conversion system and the specific applications that a specific MMC configuration can support. Most prominent among all applications for the MMC is its use in high-voltage direct current (HVDC) transmission systems and multiterminal dc grids. The aim of the paper is to provide a comprehensive review and classification of the many different SM circuit topologies that have been proposed for the MMC up to date. Using an 800-MVA, point-to-point MMC-based HVDC transmission system as a benchmark, the presented analysis identifies the limitations and drawbacks of certain SM configurations that limit their broader adoption as MMC SMs. A hybrid model of an MMC arm and appropriate implementations of voltage-balancing algorithms are used for detailed loss comparison of all SMs and to quantify differences among multiple SMs. The review also provides a comprehensive benchmark among all SM configurations, broad recommendations for the benefits and limitations of different SM topologies which can be further expanded based on the requirements of a specific application, and identifies future opportunities.
Highlights
Large-scale integration of renewable energy systems, predominantly through larger wind and solar farms, combined with the need for greater flexibility in operating electricity networks are among the key drivers of global growth in high-voltage direct current (HVDC)transmission systems [1]
Voltage-source converter (VSC) HVDC systems based on modular multilevel converters (MMCs) combine the system advantages of fast and independent active and reactive power control, passive network supply, black start capabilities, frequency support and power oscillation damping [2] with power electronics benefits such as scalable design [3], increased reliability, lower conversion losses and reduced filtering requirements, offering a commercially competitive solution
The popularity and commercial success of the modular multilevel converter and its flexible circuit topology using submodule (SM) structures has led to a substantial increase in the number of circuit topologies that have been proposed for use in the converter
Summary
Large-scale integration of renewable energy systems, predominantly through larger wind and solar farms, combined with the need for greater flexibility in operating electricity networks are among the key drivers of global growth in high-voltage direct current (HVDC)transmission systems [1]. Large-scale integration of renewable energy systems, predominantly through larger wind and solar farms, combined with the need for greater flexibility in operating electricity networks are among the key drivers of global growth in high-voltage direct current (HVDC). Voltage-source converter (VSC) HVDC systems based on modular multilevel converters (MMCs) combine the system advantages of fast and independent active and reactive power control, passive network supply, black start capabilities, frequency support and power oscillation damping [2] with power electronics benefits such as scalable design [3], increased reliability, lower conversion losses and reduced filtering requirements, offering a commercially competitive solution. From the perspective of power electronics conversion technology, the advantages of the modular design introduced by the MMC [11] have facilitated its use in other applications such as Static Synchronous Compensators (STATCOMs) [12], dc–dc conversion [4], battery energy storage systems (BESS) [13] and traction power supply systems [14]. The dynamic model is introduced to make the AC/DC current approach the reference value [10], and the average capacitance voltage control and capacitance voltage balance strategy are added [4]
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