Chattering reduction of a digital variable structure BLDC motor speed control system using a look-ahead law

For digitally implemented variable structure controllers, the switching between controller structures cannot be conducted instantaneously. This is due to a finite time delay in obtaining the system states and to compute the command for switching. This time delay, corresponding to the sampling period, introduces an enlarged chattering amplitude as compared to the continuous variable structure controllers. Here, a look-ahead control law is proposed to minimise the chattering where the corrective action is issued on a predicted system representative point in one sampling period ahead. This algorithm needs a minimum additional computational overhead, which amounts to only one multiplication, one subtraction, one sign operation and a comparison Simulation results with an application to a brushless DC motor velocity control system demonstrate the effectiveness of this control law.