A Dual Carrier Modulation Method for Modular Multilevel Converter

Abstract

The invention discloses a double-carrier-wave modulation method of a modular multilevel converter. The method comprises two parts, i.e., double-carrier-wave modulation and a voltage balance control method. First of all, according to reference voltages of upper legs and lower legs, quantities of submodules needing to be invested for the upper legs and the lower legs are respectively obtained through the double-carrier-wave modulation, a submodule change quantity needing to be invested at a current control period is further obtained, and then capacitance voltage balance is realized through the capacitance voltage balance control method. An operation condition is determined according to an absolute value of the invested submodule change quantity, only submodules needing switching operation or removal are calculated, the computation complexity is further reduced on the basis that a switch frequency is reduced, and the performance of a control system is improved. The method provided by the invention has the advantages of easy realization, good harmonic wave characteristics, low switch loss and the like.

Description

technical field [0001] The invention relates to a modular multilevel converter, in particular to a dual-carrier modulation method for a modular multilevel converter. Background technique [0002] Modular Multilevel Converters (MMC) have the characteristics of high modularity, easy expansion, easy redundancy, high efficiency, good harmonic characteristics, and four-quadrant operation. The most attractive multi-level topology in the field has broad application prospects in flexible DC transmission, motor drive, power quality management and other fields. [0003] Multilevel modulation technology and capacitor voltage balance control method are the key technologies for the stable and efficient operation of modular multilevel converters. At present, the modulation technology of MMC mainly includes specific harmonic elimination method, space vector modulation, nearest level approximation modulation, carrier phase shift modulation, and carrier in-phase stack modulation. Among the...

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Problems solved by technology

The traditional capacitor-voltage balance control method needs to sort all sub-modules from large to small, and then perform switching operations on the corresponding number of sub-modules according to the number of input sub-modules, voltage magnitude and current direction, which requires a large amount of calculation and switching loss Higher; the capacitor voltage balance control method to reduce the switching frequency only operates on the sub-modules that have been put into operation or the sub-modules that have not been put into operation according to the change in the number of input sub-modules, which reduces the switching frequency, but reduces the capacitance of the switching frequency The voltage balance control method still needs to sort the sub-modules from large to small. When the number of sub-modules is large, the amount of calculation is still large, which affects the performance of the control system.

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