A Compensation of Commutation Angle in Hall-Sensor-Controlled Brushless DC Motors for Maximum Torque per Ampere Operation

Hall-sensor-controlled brushless dc (BLDC) motors are used in many simple and low-cost applications. In the typical 120° control, the motor phase currents are supposed to be aligned with their respective back emfs', which effectively results in a maximum-torque-per-ampere (MTPA) operation. However, due to the winding inductance and commutation process, the phase current delays, resulting in a sub-optimal operation that may be especially noticeable for motors with large inductance (and small resistance). This paper presents a simple and direct method to compensate for the operating-point-dependent commutation angle. It is shown that a simple PI-control can be used to regulate the averaged d-axis current to zero, which restores the MTPA operation and improves the torque-speed characteristic. The proposed method is verified with a typical industrial BLDC motor using the results of detailed simulations and experiments.