Direct Self-Control for BLDC Motor Drives Based on Three-Dimensional Coordinate System

In this paper, a new control algorithm for brushless dc (BLDC) motor drives is presented. Direct self-control, which has been widely applied on induction motor drives in high-power low-frequency traction, is introduced to BLDC drives. The Cartesian coordinate system is selected with three coordinate axes X, Y, and Z mutually at right angle to each other with three phase axes a, b, and c being movable. A two-phase conduction scheme is selected with the axis of the exciting phase located in the X-Y plane or, otherwise, along the direction of the Z-axis during unexcited (i.e., the unexcited phase axis is always directed along the Z-axis). The tracks of stator flux and voltage vectors are all three-dimensional, as a result of a variable voltage of unexcited phase and commutation every 60 electrical degrees. However, projections on the X-Y plane of these three-dimensional tracks are concise. The projection of flux vector is a hexagonal path, whereas the voltage vector projections are six active vectors. The projection of stator flux is controlled by the projections of voltage vectors. The newly proposed algorithm can be implemented with relatively low cost hardware and concise software, presenting fast torque transient response in 0.1 ms. The sensorless control is also implemented by flux estimation once in one sector. The validity and effectiveness of the proposed scheme are verified with simulated and experimental results.