Converting method for modularized multi-level converter working in quasi-two-level mode

Abstract

The invention provides a commutation method for a modularized multi-level converter working in a quasi-two-level mode. The method comprises the following specific execution steps: judging the current commutation stage; and calculating and judging the magnitude of the sum to determine whether the bridge arm sub-module needs to be directly bypassed (or inserted) or not to act at the current moment. And repeating the step 2 until the commutation process is finished. And whether the current sub-module should be bypassed (or inserted) or not to act can be easily judged in a way of adding'one delay '. Besides, the method can quickly complete the commutation process, and as a delay always occurs in the early stage of the commutation process as much as possible, the change of the circulating current is maximized, and the circulating current reaches a reference value as soon as possible to complete the commutation process.

Description

technical field [0001] The invention relates to a commutation method for a modular multi-level converter working in a quasi-two-level mode, and belongs to the technical field of medium-voltage driving and power electronic energy conversion. Background technique [0002] Modular multilevel converters have received extensive attention in the field of medium voltage motor drives due to their modularity and easy expansion. However, due to the inherent defects of the topology, when the modular multilevel converter drives the motor at low speed, it will cause large capacitor voltage fluctuations, which will lead to the unstable operation of the system. The traditional solution is to inject high-frequency circulating currents and common-mode voltages. However, when the system works at low speed and large load, this method cannot effectively suppress the capacitor voltage fluctuation. A more effective way of suppressing voltage fluctuations is to make the modular multilevel conver...

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Problems solved by technology

[0004] ①Inner loop high-frequency pulse width modulation method: This method cannot guarantee that the commutation will be completed in the fastest way, and this will cause large fluctuations in the capacitor voltage during the commutation process

Because it is an open-loop control, this method cannot be adjusted in real time according to the current bridge arm current during the commutation process, which will lead to a decrease in system control performance

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