Research On Performance Optimization Of Direct Torque Control Of Two-phase Conduction Brushless DC Motor

Brushless DC motors are widely used due to its high power density?simple control?and good dynamic performance.However,the brushless DC motor itself also has a prominent problem of large torque ripple,which greatly reduces the control performance of the system,and brings serious problems such as vibration and resonance.In severe cases,it even reduces the life of the motor.At the same time,because the brushless DC motor The ideal back EMF is a trapezoidal wave with a flat top portion occupying 120°.The 120° continuity control method is often used to obtain the maximum torque output.At present,the torque performance of two-phase conduction brushless DC motors under direct torque control Optimization is the focus of research on brushless motors.This paper takes the direct torque control of two-phase conduction brushless DC motors as the research content,and focuses on the aspects of torque ripple suppression from the zero-voltage vector transmission scheme,pulse width modulation strategy and torque ripple suppression scheme during commutation the study.1.Firstly,the different non-zero vector modulation modes in two-phase conduction mode are briefly introduced.Secondly,the definition of the zero voltage vector and the influence of the motor current and torque performance under the zero voltage vector selection scheme are studied and analyzed,and a new voltage vector modulation scheme is obtained.In the experiment,the torque performance of different voltage vector schemes is analyzed,and the proposed voltage vector scheme is proved to be effective in suppressing torque ripple.2.Aiming at the problem of large torque ripple during commutation of two-phase brushless DC motors,this paper proposes a torque ripple suppression strategy suitable for commutation.Firstly,by analyzing the circuit state during commutation,a new duty cycle calculation method based on current prediction is proposed for the calculation of the duty cycle of voltage vector modulation.By predicting the current change in the next cycle,combined with The moment-invariant control idea has obtained the calculation formula of the required duty cycle.Secondly,for high-speed operation,the limitations of the two-phase conduction mode,that is,during the high-speed phase,due to the short commutation time,the off-phase current drops extremely fast,and even if the duty cycle of non-zero voltage vector reaches the upper limit of 1,it cannot compensate for the problem of torque drop,a modulation strategy is proposed that incorporates the shutdown phase into the control.The above theoretical scheme is analyzed and tested in detail through simulation.Finally,the experimental verification is performed on the motor experimental platform.The experimental results prove that the proposed control method has a significant suppression effect on torque ripple.