Abstract
Commutation angle is a key design criterion when brushless DC (BLDC) motors sensorlessly operate based on the detection of back electromotive force(EMF) zero-crossing and must be designed significantly less than 30 electrical degree. The paper describes a detailed investigation on the commutation angle of brushless DC motors with 120° voltage source inverter. Analytic method is applied to analyze the influence factors. The proposed design principles can provide a clear guide for the adjustment of system parameters. Then two criteria and an estimation method based on approximate anlytical solution of commutation angle are presented with experimental validation.