Detection Technique for Stator Inter-Turn Faults in BLDC Motors Based on Third-Harmonic Components of Line Currents

Among the methods for detecting stator inter-turn faults, the techniques that use the harmonic characteristics have been researched in induction motors with distributed windings. However, it is questionable that the techniques are available to apply in permanent magnet machines with concentrated windings and different control methods. First of all, this study analyzes the harmonic components of line current in a brushless dc (BLDC) motor, including the issues such as supply imbalance and inherent structural asymmetry, through the developed finite-element analysis and experiment under different operating conditions. As a result, the third harmonic in negative frequency (-3f) is suitable as a fault detector because it is free from those issues. Finally, in BLDC motors with 120° conduction in a six-step operation, the faults can be detected by determining whether or not the third harmonics exist at the incipient state.