Voltage balancing control method applicable for sub-module capacitor voltage hierarchy of high-level MMC (Modular Multilevel Converter)

Abstract

The invention discloses a voltage balancing control method applicable for sub-module capacitor voltage hierarchy of a high-level MMC (Modular Multilevel Converter). The voltage balancing control method comprises the following steps of: determining a voltage hierarchical container according to the maximum and minimum of capacitor voltages placing the capacitor voltages of all sub-modules in the voltage hierarchical container isolated at an equal voltage, placing the sub-modules in corresponding voltage hierarchical container according to the values of the capacitor voltages; optimizing and sequencing according to the current direction of a bridge arm and the total number of the sub-modules needed to be thrown into the bridge arm; and introducing a criterion whether the voltage hierarchical container is required to be layered again. With the adoption of the method, the sequencing rate of sub-module capacitor voltages of the high-level MMC can be improved, the complexity of a sequencing algorithm is reduced, a certain voltage balancing control effect can be guaranteed, and the switching-off frequency of the sub-module IGBT (Insulated Gate Bipolar Transistor) is reduced.

Description

technical field [0001] The invention belongs to the technical field of power system operation and control, and relates to a voltage equalization control method suitable for sub-module capacitor voltage stratification of high-level MMC. Background technique [0002] Modular multilevel converter (MMC), as the latest achievement of HVDC transmission technology in the direction of high voltage and high power, has received a lot of attention since it was proposed. The modular multilevel converter adopts the superposition of modular sub-modules to achieve flexible changes in output voltage and power level. It has the advantages of strong scalability, small output voltage harmonics, and low switching frequency. With the increase of the number of levels of the modular multilevel converter and the improvement of the transmission power, the number of sub-modules connected in series on the bridge arm is increasing, which brings great challenges to the voltage equalization control of th...

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Problems solved by technology

[0004] However, with the increase of the number of levels, the complexity of sub-module voltage equalization control is greatly increased. Especially in actual engineering, the MMC system with high level number needs to sort the capacitor voltages of sub-modules arranged in scattered series, and the voltage equalization Control has become an unavoidable problem

Moreover, sorting all sub-modules and changing the operating status of all sub-modules frequently will easily cause the switching frequency of the IGBT of the sub-modules to be too high, which will greatly increase the switching loss of the sub-modules

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