Modular multi-level converter capacitor voltage fluctuation inhibition method under low-frequency working condition

Abstract

The invention relates to a modular multi-level converter capacitor voltage fluctuation inhibition method under a low-frequency working condition, and belongs to the technical field of power electronics and motor drive. The method comprises the following steps: the alternating-current side three-phase phase current which meets the low-frequency working need is obtained by performing closed-loop control on the modular multi-level converter alternating-current side three-phase phase current; loop current only contains a direct-current component and a high-frequency alternating-current component by closed-loop control of the three-phase loop current, and a bridge arm voltage contains a high-frequency zero sequence component by overlapping high-frequency voltage at the midpoint electric potential at the direct-current side; the amplitude values, the frequencies and the phases of the loop current high-frequency alternating-current component and the bridge arm voltage high-frequency zero sequence component are obtained by operation, so that the phase voltage and the phase current of the alternating-current side do not contain high-frequency harmonic waves, moreover, the cycles of charging and discharging submodules are shortened, and the effect of inhibiting the capacitor voltage vibration of the submodules is realized; the electrical quantity of each bridge arm is kept to be balanced by the balancing control on the bridge arm energy so as to guarantee that the modular multi-level converter runs symmetrically and stably.

Description

technical field [0001] The invention relates to a method for suppressing capacitor voltage fluctuations of a modular multilevel converter under low-frequency working conditions, and belongs to the technical fields of power electronics and motor transmission. Background technique [0002] High-voltage frequency conversion technology is a technology that realizes the control of AC power by changing the frequency. Because of its excellent energy-saving effect, high reliability, and high precision, the frequency conversion speed regulation system has great significance for saving energy and improving the level of industrial automation and product quality in my country. Significance. There are many ways to implement high-voltage frequency converters. Traditionally, it is realized through a "high-low-high" circuit. Two transformers are used on both sides to reduce the high voltage level outside the frequency converter to low voltage. The two transformers are connected to the low-vo...

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Problems solved by technology

However, this document does not limit the frequency and amplitude of the zero-sequence voltage. This method will cause the output phase voltage and phase current to contain high-frequency zero-sequence harmonics, and will cause electrical interference between the bridge arms of the modular multilevel converter. The asymmetry of the quantity affects the output characteristics and smooth operation of the modular multilevel converter

At the same time, this document does not perform closed-loop control on the superimposed high-frequency circulating current. When there is an error in the modulation link, the control effect is not good, and it is difficult to ensure effective control of the bridge arm current, which may even exceed the tolerance value of the device; In addition to the beneficial high-frequency components of voltage fluctuations, there are also double-frequency circulating currents, which cause large device losses

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