Research On High Precision Driving Control Technique Of Magnetically Suspended Flywheel

The attitude control actuators with high performance,low power consumption and long life are urgently needed by China's high-resolution satellites at present.Compared with traditional mechanical flywheel,the magnetically suspended flywheel supports its high-speed flywheel rotor by magnetic bearing,which has inherent superior features such as adjustable bearing,low vibration,zero friction,longevity and high accuracy of output torque.It has been becoming the ideal solution for fast-response and high-precision attitude control for spacecraft.In order to achieve high-precision control performance,this dissertation focuses on the key control technologies of the flywheel working mode design,the suppression of brushless DC motor commutation torque ripple,control system design and implementation based on FPGA.The main contributions are listed as follows:(1)In order to suppressing resistance moment of the magnetic suspension flywheel during its operation,the flywheel control laws,both in torque mode and velocity mode,are designed.Firstly,combined with the performance requirements of attitude control system,the speed loop and current loop controllers in the velocity mode are designed as PI controllers.Then,the response of the control system to the step speed instruction is analyzed when flywheel is disturbed by the resistance moment.On this basis,aiming at the problem of ignoring the resistance moment in traditional torque control mode,a torque control mode based on speed feedback is proposed to realize the tracking of output torque to torque instruction.At the same time,the fuzzy adaptive PI controller is introduced in the speed loop to further improve the dynamic characteristics and anti-jamming ability of the flywheel control system.(2)The torque ripple suppression strategies are proposed respectively in high and low speed region to attenuate the undesirable torque ripple caused by commutation of brushless DC motor.Firstly,the characteristics of commutation torque ripple in the whole speed range are analyzed,and the control strategy of using PWM-ON modulation in low speed region and overlapping commutation in high-speed region to compensate torque drop is proposed.a prediction control strategy of phase current is proposed to solve the problem that the delay time of overlapping commutation under different rotational speeds is difficult to determine,which is prone to under-compensation or over-compensation.(3)In order to verify the above control strategy,the corresponding software control system and hardware control system are designed.Firstly,high frequency clock generator,the digital PI controller,high-precision PWM generator,Variable M/T digital tachometer and loop operation control module are designed.Then,power driving circuit and current sensor circuit,logic commutation circuit and linear energy consumption braking circuit in the control system are designed.Based on the above experimental platform,the designed control algorithms are verified.