Abstract
This paper presents the theoretical analysis and experimental verification of a direct fault harmonic identification approach in a converter-fed electric drive for automated diagnosis purposes. On the basis of the analytical model of the proposed real-time direct fault diagnosis, the fault-related harmonic component is calculated using recursive DFT (RDFT) and Goertzel DFT (GDFT), applied instead of the full spectrum calculations required in the most popular FFT algorithm. The simulation model of an inverter sensorlessly controlled induction motor drive is linked with the induction machine rotor fault model for testing the sensitivity of the GDFT- and RDFT-based fault diagnosis to state variable estimation errors. According to the presented simulation results, the accuracy of the direct identification of a fault-related harmonic is sensitive to the quality of fault harmonic frequency estimation. The sensitivity analysis with respect to RDFT and GDFT algorithms is included. Based on the experimental setup with a sensorlessly controlled induction motor drive with the investigated rotor fault, fault diagnosis algorithms were implemented in the microprocessor by integration with the control system in one microcontroller and experimentally verified. The RDFT and GDFT approach has shown accurate and fast direct automated fault identification at a significantly decreased number of arithmetical operations in the microcontroller, which is convenient for the frequency-domain fault diagnosis in electric drives and supports fault-tolerant control system implementation.
Highlights
Increasing requirements are formulated for converter-fed variable-speed drives with respect to their control quality, reliability and safety
The most popular method in recent years for diagnosing induction motor drives was the Motor Current Signature Analysis (MCSA), with reasoning based on the harmonic analysis using the Fast Fourier Transform (FFT) [1,2,3,4,5]
DFT harmonic culation and analysis of the microprocessor computing time and memory availability, the calculation and analysis of the microprocessor computing time and memory availability, the modified control system including fault algorithms was implemented in a microprocessor modified control system including fault algorithms was implemented in a microprocessor as an application in C++ language, providing real-time fault diagnosis
Summary
Increasing requirements are formulated for converter-fed variable-speed drives with respect to their control quality, reliability and safety. The fault diagnosis in the frequency domain is usually based on a known mathematical model applied for specified harmonic frequencies of the fault-related symptom and their amplitude identification and analysis [13,14,15,16,17,18,19]. Considering the high computational load of the control unit in modern electrical drives, the integrated real-time diagnostic methods need to be optimized due to the increasing switching frequency of inverter transistors in many applications, e.g., in SIC MOSFET transistors, which implies decreased TADC , and the feasibility of additional diagnosis algorithms [27]. The application of Fast Fourier Transform is not efficient in this case because it requires computing the full spectra of the harmonics, which is unnecessary assuming that the mathematical equations for specified fault-related symptom harmonics are known.
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