Abstract
Fault detection can increase the reliability and efficiency of power electronic converters employed in power systems. Among the converters in the power system, a Neutral Point Clamped (NPC) three-level inverter is most commonly used to drive electric motors. In this paper, a new approach for open-circuit fault detection and location of the NPC three-level inverter for a shifting process using a constant voltage-to-frequency ratio is proposed. In order to diagnose open-circuit fault in as short a time as possible, an adaptive electrical period partition (AEPP) algorithm is proposed to pick single electrical periods from real-time three-phase current signals. The Maximal Overlap Discrete Wavelet Transformation (MODWT) and Park’s Vector Modulus (PVM) are used for feature analysis and normalization of electrical period signals. The statistical characteristics of the electrical period signals are extracted, and a random forest model is constructed to realize the state classification. Compared with the traditional fault diagnosis method, the proposed algorithm finds fault locations quickly and accurately. The effectiveness and accuracy of the proposed algorithm are verified by experiments.
Highlights
As the key device that converts DC signals into AC signals, inverters are widely used in electrical power control devices, such as mine hoists and belt control systems
The electrical period is decomposed by three-level Maximal Overlap Discrete Wavelet Transformation (MODWT), and Park’s Vector Modulus (PVM) is used to normalize the low-frequency approximation component which is retained for fault diagnosis during the shifting process
The electrical period is decomposed by three-level MODWT, and only the low-frequency approximation component is retained for normalization using PVM
Summary
As the key device that converts DC signals into AC signals, inverters are widely used in electrical power control devices, such as mine hoists and belt control systems. A large number of fault diagnosis methods have been proposed by researchers for open-circuit faults These methods can be classified into voltage-based and currentbased methods. Current-based open-circuit fault diagnosis methods based on the output current change trend and direction of the power switches [10] are mostly used in inverters. In [12], an open-circuit fault diagnosis method based on the normalized mean current Park’s Vector Modulus (PVM) and angle was proposed. [17] put forth a three-phase voltage source inverter (VSI) current sensor and open circuit fault diagnosis algorithm based on adaptive threshold. The proposed fault diagnosis method in this paper, on the other hand, is used to diagnose open-circuit fault during the shifting process of the NPC inverter.
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