Method and system for calculating DC short-circuit current of modular multilevel converter

Abstract

The invention discloses a DC short-circuit current calculation method and system for a modular multilevel converter, and the method comprises the steps: obtaining the DC current and DC voltage of a fault circuit at a fault moment; obtaining a plurality of bridge arm reference voltages and DC reference voltages of the fault circuit to calculate a DC modulation ratio; Obtaining a plurality of circuit parameters to calculate a fixed parameter of the fault circuit, and calculating a time-varying parameter of the fault circuit according to the fixed parameter of the fault circuit and the DC modulation ratio; and judging the state of the fault circuit according to the direct current, the direct current voltage, the direct current modulation ratio, the fixed parameters of the fault circuit and the time-varying parameters of the fault circuit, and calculating the direct current short-circuit current of the fault circuit. According to the method, the influence of the control behavior of the converter can be considered, the change of a fault circuit structure along with the change of the control behavior of the converter is embodied, and an accurate expression of the direct-current short-circuit current is correspondingly given.

Description

technical field [0001] The invention relates to the technical field of high-voltage and large-capacity power electronic converter analysis, in particular to a DC short-circuit current calculation method and system for a modular multilevel converter. Background technique [0002] MMC (Modular Multilevel Converter, Modular Multilevel Converter) is a voltage source power electronic converter, based on fully controlled power electronic devices such as insulated gate bipolar transistors and pulse width modulation technology, it can stably control active power and reactive power transfer between AC and DC systems. At present, the representative MMC DC short-circuit calculation methods considering the control behavior of the converter mainly include three types. The first one considers that the converter performs blocking control after the DC fault occurs, the pulses of all sub-modules are blocked, the capacitor discharge process of the sub-modules is completely prevented, the DC ...

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Problems solved by technology

Although the above three calculation methods can give relatively accurate DC short-circuit current calculation results, they are all aimed at a specific control behavior and cannot be generally extended to multiple control behaviors.

However, when MMC actively participates in DC protection, its control behavior is more complicated, such as actively limiting the rising speed of short-circuit current, etc.

Therefore, the existing calculation methods cannot uniformly consider the control behavior of the converter to give an accurate calculation method for the DC short-circuit current

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