A reduced order time-delay control for highly simplified brushless DC motor

A reduced-order time delay control (RTDC) has been derived and applied to the position control of a brushless DC motor (BLDCM) with a highly simplified hardware configuration: use of six-step commutation without current control unit. In addition, the closed-loop stability has been analyzed by using the singular perturbation method. Throughout simulation and experimental studies, RTDC has been observed to achieve a performance level approaching to that of a BLDCM adopting sinusoidal commutation with current control unit. More specifically, it has been observed that RTDC effectively compensates for parameter variations, nonlinearities, and the torque ripple caused by six-step commutation, which a conventional PID control cannot handle with adequate performances. This result shows that RTDC enables an economical design without compromising performance. More importantly, the example establishes a case that: a good control method can compensate for the hardware deficiency in a given plant; and as a result it even enables a simpler design of plants at the design stage.