Adaptive Active Vibration Control For Cryocooler Compressor

As a part of satellite payload in space,cryocooler has been an integral part of space equipment.The vibration of the mechanical cryocooler is one of the critical threat during the application in sensitive instruments.Compressor as the power source of mechanical cryocooler,its vibration will affect the pointing accuracy and resolution of the target,and even cause the mechanical resonance of the platform.In order to reduce the vibration of the compressor and meet the general requirements of vibration force less than 0.2 N_RMS in sensitive aerospace applications,high-order active vibration control must be adopted.The vibration characteristics of the cryocooler compressor are analyzed and researched.Compressor adopts piston symmetry structure,the two pistons do reciprocating motion under the action of alternating electromagnetic thrust.Basing on the research of the compressor vibration mechanism,we can find the unequal of the motion equation of the single piston and the corresponding parameters of the compressor opposing piston cause the vibration.And the non-linearity of the driving signal,the spring,the damping and the aerodynamic force lead to the high frequency vibration.The test result of vibration shows that the vibration of the compressor is commonly several Newton's order,and it is mainly concentrated within 300 Hz.Vibration spectrum shows as a series of discrete harmonics,whose fundamental frequency is the drive frequency.The active vibration control scheme and the control algorithm of the compressor are researched.According to the linear superposition principle of the force and the vibration spectrum characteristic of the compressor,an adaptive narrowband notch filter which does not require transfer function model is adopted.The adaptive vibration control is realized by adjusting the driving signal.Compressor has two opposing motors,one of which also uses by a shock absorber.Since each order vibration is present only at a single frequency point,each order of vibration can be controlled separately by superimposing the various order of the vibration attenuating signal on the drive signal and adjusting the magnitude and phase of the vibration to attenuate signals of each stage.The anti-vibration force produced by each order of vibration attenuating signal is equal in size and opposite in direction with the compressor vibration,so that the anti-vibration force generated by vibration attenuating signal and the compressor vibration could cancelled out each other,so as to achieve the purpose of vibration.The control circuit and the software are designed,and the control system including the control software,the electronic circuit,compressor and the vibration sensor is set up to attenuate the vibration.The hardware circuit mainly includes the driving circuit,the signal conditioning circuit,the power supply circuit,and the overcurrent protection circuit.And the function and the reliability of the system are both considered when designing the circuit.Control software is written in the DSP,and the convergence rate and the computational complexity are also considered when designing the software algorithm.The Hilbert transform has been introduced to reduce the filter order,and the phase compensation has been considered by the delay effect of the motor response.The vibration test has been completed.The five order active vibration control has been tested to the 90 W driving power compressor by using the adaptive vibration control system.In the frequency range of 20²80 Hz,the vibration force is reduced from 0.68 N_RMS to 0.14 N_RMS by a factor of 13.46 dB.The power consumption is only1.26 W,and the converging time is only about 2 seconds.The same parameters for 60W and 105 W can also maintain good adaptive ability.