Modular multilevel converter loss balance control method under capacitor soft fault

Abstract

The invention relates to a modular multilevel converter loss balance control method under capacitor soft fault. The method comprises the following steps: a capacitance value Caui is calculated by using the external characteristics of a submodule capacitor; the fluctuation coefficient ki of a required capacitance voltage AC component is then calculated according to the capacitance value; according to the fluctuation coefficient ki and a capacitance voltage AC / DC component, virtual capacitance voltage u'caui is obtained; and through controlling balance of the virtual capacitance voltage, the equivalent modulation wave xer_aui of each submodule is similar, and the loss of each submodule is further balanced. In the method, through introducing the AC component fluctuation coefficient ki, the influences on the submodule equivalent modulation wave xer_aui by the capacitance value are cancelled, the loss of each submodule is balanced, and the loss of a power switching device at the same position in each submodule is balanced.

Description

technical field [0001] The invention belongs to the technical field of multilevel power electronic converters, and in particular relates to loss balance control of modular multilevel converters under capacitor soft faults. Background technique [0002] Modular Multilevel Converter (MMC) has the advantages of small output voltage harmonics and high energy transmission efficiency, so its application in medium, high voltage and high power fields has been more and more widely used. By optimizing the control of MMC, its average switching frequency can be reduced without affecting the power quality. Currently, due to its simple structure, convenient assembly, and flexible application, MMCs are widely used in various fields such as machine drives, electric railway supplies, and microgrids. [0003] MMC contains a large number of power switching devices and capacitors, and each device can be regarded as a potential fault point, and the parametric fault of capacitors is one of the m...

AI Technical Summary

Problems solved by technology

When the capacitor value decreases, the ability of the capacitor to suppress voltage fluctuations will be weakened, and the equivalent modulation wave (Equivalent Reference, ER) of each sub-module will be different, resulting in uneven power loss distribution of each sub-module on the same bridge arm. This will definitely affect the aging speed of power switching devices and the service life of sub-modules, reducing the reliability of MMC operation

At present, the existing research involves the balance of the sub-module loss, but there are still deficiencies as follows: on the one hand, the existing literature on the loss of each sub-module on the bridge arm is not comprehensive and in-depth; on the other hand, it does not involve the same Loss leveling of positional semiconductor devices

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