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Online Detection of Irreversible Demagnetization Fault with Non-excited Phase Voltage in Brushless DC Motor Drive System

Existing methods for irreversible demagnetization fault (IDF) diagnosis in a motor have fatal weaknesses such as offline and necessity of additional hardware. A method to overcome these disadvantages should be needed in wide and various applications, especially for brushless DC (BLDC) motors. A novel IDF detection technique for a permanent magnet (PM) type BLDC motor is proposed. The main idea of this technique is to utilize three features of the voltage drop/back-EMF at the non-excited phase of a BLDC motor operated by 120-degree conduction control with pulse width modulation. Since the IDF precisely reduces the back-EMF of the machine, the suggested method is easy to implement and subject to detecting IDF by using back-EMF of the machine. The proposed technique is also appropriate for sensorless BLDC motor drive system without additional hardware. The suggested algorithm for IDF detection is verified based on simulation and experiment with a 400-watt BLDC motor.