Research And Design On Control System Of Permanent Magnet Brushless DC Motor

Permanent magnet brushless DC motor(PMBLDCM)has the clear advantages of rapidity,controllability,reliability,small,light in weight,energy saving,high efficiency,survivability in environment,economical efficiency,simpler control system compared with the induction motor,and so on.However,PMBLDCM has large ripple which reduces system's serve life and stability.Thus,the research on the suppression method of PMBLDCM's torque ripple restraining has realistic significance on improving the equipment's operating service life and quality.Permanent magnet brushless DC motor(PMBLDCM),using electronic commutation instead of DC motor's mechanical commutation,not only has DC motor's advantages such as high running efficiency,good speed regulation performance,but also has AC motor's series advantages such as simple structure,reliable operation,easy maintenance.The rotor of is excited by permanent magnet,without excitation loss.The appearance and development of high performance permanent magnetic materials,such as Nd Fe B,has greatly promoted the production and application of PMBLDCM.The ideal BEMF waveform of BLDCM is trapezoid with 120° platform width.In the 120° conduction mode,the stator current is not ideal due to the stator inductance,and the torque ripple occurs.Firstly in this paper,the basic structure and working principle of PMBLDCM are introduced;the phase-commutation logic controlling principle of six-phase asymmetrical PMBLDCM is explained;the mathematical model is derived and builded,including voltage equation,back EMF equation,electromagnetic torque equation and motion equation,and so on,and the dissertation presents principle of commutation torque ripple caused by the PWM modes.The conclusion is reached,the commutation torque ripple varies with the rotor speed.In consideration of different ripple performance when motor running in low middle speed and high speed,two restraining strategies are presented,non-commutation phase current hysteresis control based on pwm-on-pwm and overlapping commutation control.Through simulation,the correctness and availability of two strategies is demonstrated.Finally,on the basis of the above theory and simulation,PMBLDCM controller based on DSP&CPLD is designed,including hardware circuit design,software program design and Labview program design of principal computer.On this basis,the experiment is conducted on the speed and current dual-closed-loop control system.The experimental result validates effectiveness and feasibility of the six-phase asymmetric permanent magnet brushless DC motor control system.