A non-invasive fault location method for modular multilevel converters under light load conditions

TL;DR

This paper introduces a non-invasive fault location method for modular multilevel converters that effectively operates under light load conditions by injecting a second-order circulating current to improve fault detection accuracy.

Contribution

It presents a novel approach of injecting second-order circulating current to enhance fault location in MMCs under light load, addressing limitations of existing methods.

Findings

Fault location time reduced to one-sixth of previous methods.

Method effectively detects faults under light load conditions.

Simulation results validate the approach's effectiveness.

Abstract

This paper proposes a non-invasive fault location method for modular multilevel converters (MMC) considering light load conditions. The prior-art fault location methods of the MMC are often developed and verified under full load conditions. However, it is revealed that the faulty arm current will be suppressed to be unipolar when the open-circuit fault happens on the submodule switch under light load. This leads to the capacitor voltage of the healthy and faulty submodules rising or falling with the same variations, increasing the difficulty of fault location. The proposed approach of injecting the second-order circulating current will rebuild the bipolar arm current of the MMC and enlarge the capacitor voltage deviations between the healthy and faulty SMs. As a result, the fault location time is significantly shortened. The simulations are carried out to validate the effectiveness of the proposed approach, showing that the fault location time is reduced to 1/6 compared with the condition without second-order circulating current injection.