Torque Control Of Permanent Magnet Brushless DC Motor

Permanent magnet brushless DC motor(BLDCM)has received extensive attention in industrial applications owing to its simple structure,high efficiency,high power density and high stability.Electromagnetic torque is one of the most important indexes for high performance motor drive.This paper takes the torque control of BLDCM as the research object,and deeply studies a series of problems such as parameter variation,external disturbance and torque ripple caused by currents commutation.BLDCM mainly operates in the normal conduction region with two phases of windings energized.As the existence of winding inductance and the limitation of the dc-link voltage,the commutation region with three phases of windings energized occurs in every 60° of commutation process.In this paper,the mathematical model of BLDCM is firstly established for the different working regions,where the common pulse width modulation(PWM)techniques and there selection rules are also introduced.According to the control purpose in the different operation regions,three control strategies are further designed to improve the torque control performance.In normal conduction region,a switched gain adaptive current controller is proposed to reduce the influence of motor parameters variation and external disturbances on torque control performance in the complex operating conditions and harsh environments.The controller consists of a continuous control component based on model reference adaptive control(MRAC)and a switching control component based on integral sliding mode control(ISMC).In order to enhance the robustness of the current controller and improve its tracking performance,the adaptive regulation mechanism of switching gain is further constructed.In commutation region,a commutation torque ripple suppression method considering back EMFs' variation is proposed for the high speed range.This paper firstly reveals the influence mechanism of back EMFs' variation on the torque ripple suppression in the traditional method.Then,a new commutation torque ripple suppression method is designed by reconstructing the torque smoothing mechanism.The proposed method can effectively suppress commutation torque ripple,while broaden the speed range of commutation torque ripple suppression.In order to reduce commutation torque ripple with a unify control strategy and shorten the time of commutation process in full speed range,a commutation torque ripple suppression strategy with the added non-inductance boost converter is further studied in this paper.They are firstly explained that the operation principle of the non-inductance boost converter and the selection mechanism of the switching vector.Then,the voltage regulation mechanism of the non-inductance boost converter in normal conduction process and the commutation torque ripple suppression method are designed respectively.Finally,the boost capability of the proposed method is analyzed.In order to verify the feasibility of the robust current controller and the two commutation torque ripple suppression methods,a set of high reliability BLDCM drive system is built.The experimental results prove the correctness of the theoretical analysis and the effectiveness of the proposed method.