Voltage balancing control method for multi-level modular converter

Abstract

The invention relates to a voltage balancing control method for a multi-level modular converter, which is characterized by comprising the following steps of: 1) judging whether the current direction of a bridge arm is a positive direction or a negative direction; 2) searching for a sub-module with the highest capacitor voltage amplitude value from the sub-modules in an output state, and simultaneously searching for the sub-module with the lowest capacitor voltage amplitude values from the sub-modules in a bypass state; and 3) judging whether to use or bypass the sub-modules or not. By the method, sub-module switching randomness is completely avoided, and the switching frequency of the sub-module is reduced; and the sub-module capacitor voltage balancing control method is more applicable in the field of high-voltage high-capacity converters with a great number of sub-modules.

Description

technical field [0001] The invention relates to a control method, in particular to a voltage equalization control method of a converter. Background technique [0002] The differences in the charge and discharge, loss and capacitance value of the neutron modules of each bridge arm of the modular multilevel converter will make the capacitor voltage unbalanced, which will endanger the normal operation of the converter. In order to ensure the modular multilevel converter The normal operation of the device, the traditional sub-module capacitor voltage equalization control method is: [0003] (1) Quickly monitor and sort the capacitor voltage values ​​of the sub-modules; (2) Monitor the current direction of each bridge arm to determine the charging and discharging of the bridge arm sub-modules; (3) When triggering the control action, if the bridge arm current makes the To charge the sub-modules, input the corresponding number of sub-modules in the order of capacitor voltage from ...

AI Technical Summary

Problems solved by technology

If a sub-module in the phase unit is cut off, the same number of sub-modules must be put in at the same time to maintain a constant total DC voltage; due to the differences in the switching characteristics of power electronic devices and the introduction of dead time, the technology of different sub-modules in and out It is impossible to be completely at the same time, which will cause the total DC voltage to fluctuate; the more sub-modules that need to change the switching state, the more severe the fluctuation of the total DC voltage

[0006] Secondly, the switching frequency of sub-modules is too high, which makes the switching frequency and switching loss of power electronic devices larger, which reduces the efficiency of the modular multilevel converter type DC transmission system

[0007] Thirdly, due to the large number of bridge arm sub-modules in the modular multi-level converter type DC transmission system, it takes a lot of time to monitor and sort the capacitor voltages of the sub-modules, which will introduce a large delay in the trigger control , to reduce the speed of the converter to track the modulating wave

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