Static voltage balancing control method for capacitor of MMC sub-module in start of off-network inverter circuit

Abstract

The invention discloses a static voltage balancing control method for a capacitor of an MMC sub-module in the start of an off-network inverter circuit. The alternating current side of the inverter circuit is an off-network type load, that is to say, charging can only be completed via a bus voltage of the direct current side, when the capacitor of the MMC sub-module is pre-charged. The method comprises the steps of firstly, performing uncontrolled pre-charging with a first preset time length on all the MMC sub-modules; then sorting all the MMC sub-modules according to the capacitor voltages, and according to a certain rule, performing controllable pre-charging with a second preset time length on all the sub-modules; and at last, switching the system back to a normal inversion working condition, thus completing the integrated start of the system. By the abovementioned method, the problems that security of the MMC system is affected and the voltage balancing control of the capacitors of the MMC sub-modules during the normal operation process is not facilitated due to the fact that the voltages of the capacitors are not consistent due to inconsistent rated standard parameters of the capacitors of the MMC sub-modules and the relatively large surging current occurs on the direct current side when the inverter circuit is in normal operation are mainly solved.

Description

technical field [0001] The invention relates to the technical field of power electronics, in particular to a static equalization control method for capacitor voltages of MMC sub-modules during startup of an off-grid inverter circuit. Background technique [0002] Modular Multilevel Converter (MMC) has been favored in recent years because of its advantages of high modularity, strong expandability, high output power quality, less voltage harmonic content, and low voltage distortion rate. The extensive attention of foreign scholars and engineers, especially in the field of high-voltage direct current transmission (HVDC), the research results on MMC are quite rich, and it has been applied in some demonstration projects at home and abroad. In addition, as the research on the inverter circuit of the MMC structure continues to deepen, it has reference significance for future applications in power quality control, high-power frequency conversion speed regulation systems, and energy ...

AI Technical Summary

Problems solved by technology

[0004] In view of this, the object of the present invention is to provide a static equalization control method for the capacitor voltage of the MMC sub-module in the start-up of an off-grid inverter circuit, to solve the problem of the capacitance of the MMC sub-module when the pre-charging is completed due to the error of the capacitor parameter of the MMC sub-module. The problem of voltage inconsistency is to avoid the problem of large surge current on the DC side when the inverter circuit is put into normal operation, so as to avoid affecting the safety of the MMC system and the voltage balance control of the capacitance of the MMC sub-module during normal operation. And other issues

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