Sensorless Optimal Commutation Steady Speed Control Method for a Nonideal Back-EMF BLDC Motor Drive System Including Buck Converter

For the low inductance brushless dc motor with nonstandard trapezoidal waveform and asymmetric three-phase back-EMF, this article first analyses the influence of nonideal back-EMF on the position of the detected commutation point when sensorless method is applied. Then, the fluctuations of electromagnetic torque driven by square wave current are compared when commutating according to several different commutation points, and the optimal commutation control method is proposed. In addition, for the low inductor motor with nonideal back-EMF and buck front-end drive circuit structure, an integrated nonlinear model of motor and buck drive circuit including precise back-EMF parameters is established. Based on the nonlinear model, the feasibility of model linearization is analyzed. The linearization method based on input-output feedback method is proposed, and a steady-state controller based on linearization model is designed. Finally, experimental results verify the effectiveness of the proposed optimal commutation control and steady speed controller.