Abstract
Reliability is one of the critical issues for a modular multilevel converter (MMC) since it consists of a large number of series-connected power electronics submodules (SMs). In this paper, a complete control strategy including fault detection, localization, and tolerant operation is proposed for the MMC under an insulated gate bipolar transistor (IGBT) open circuit fault. According to the output characteristics of the SM with the open-circuit fault of IGBT, a fault detection method based on the circulating current and output current observation is used. In order to further precisely locate the position of the faulty SM, a fault localization method based on the SM capacitor voltage observation is developed. After the faulty SM is isolated, the continuous operation of the converter is ensured by adopting the fault-tolerant strategy based on the use of redundant modules. To verify the proposed fault detection, fault localization, and fault-tolerant operation strategies, a 900 kVA MMC system under the conditions of an IGBT open circuit is developed in the Matlab/Simulink platform. The capabilities of rapid detection, precise positioning, and fault-tolerant operation of the investigated detection and control algorithms are also demonstrated.
Highlights
Owing to the superior characteristics of the modular design, high efficiency, low harmonic output, and so forth, modular multi-level converters (MMCs) are widely applied in the application of high voltage and power ratings, especially for high-voltage direct current (HVDC) transmission systems [1,2,3]
In Reference [17], a fault detection method based on the output current and the circulating current observers and a fault localization method based on the faulty SM capacitor voltage exceeding the set threshold were proposed
To precisely locate and bypass the faulty SM, a fault localization method based on the capacitor voltage difference observation has been proposed
Summary
Owing to the superior characteristics of the modular design, high efficiency, low harmonic output, and so forth, modular multi-level converters (MMCs) are widely applied in the application of high voltage and power ratings, especially for high-voltage direct current (HVDC) transmission systems [1,2,3]. All SM capacitor voltages in the same faulty arm would increase simultaneously when the MMC adopts the common carrier lamination modulation strategy with a sort-selection algorithm In this situation, the fault localization method based on the faulty SM capacitor voltage exceeding the set threshold would make it hard to discriminate the faulty SM from normal SMs. Two fault detection methods named the Clustering Algorithm based method and Calculated Capacitance (CC) based method were proposed in Reference [21], in which the clustering algorithm was used to detect and locate the faulty SMs by identifying the pattern of the 2-D trajectories of the SM characteristic variables, and the CC-based method was based on the nominal SM capacitance calculation and comparison.
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