Research On Key Technology Of Current Loop For High Precision Voice Coil Motor

In recent decades,with the rapid development of space-to-Earth observation technology,the optical observation index of space satellite system is getting higher and higher.Optical loads are more and more sensitive to the micro-vibration environment brought by the normal operation of spaceborne moving parts.As the key actuator of vibration isolator of satellite platform,the output accuracy of voice coil motor directly affects the vibration isolation performance of the whole satellite platform.In the position,speed and current loop of voice coil motor,the current accuracy of current loop is directly related to the output accuracy of motor.At the same time,as the inner loop of the three-loop control,the property of the current loop directly determines the performance of the whole control system.Therefore,high-precision current loop control technology has become one of the key technologies for developing high-performance vibration isolation system.The application background of vibration isolator on satellite platform requires high thrust of voice coil motor,which is reflected in high rated current in current ring,making the traditional current control scheme based on analog devices difficult to use.Based on the switching scheme,this paper establishes a theoretical model of the current loop of voice coil motor.Through analysis,the realization of high-precision current control technology is divided into three parts: high-precision current sampling under strong EMI environment,ripple suppression of output current,and external suppression of current loop disturbance.In the aspect of current feedback,considering the volume constraints brought by high precision and spacecraft background,the shunt method is adopted as the current sampling scheme.This paper analyses and compares the influence of different access positions of shunt resistors on current detection accuracy,establishes the current detection error model of shunt and subsequent devices,and divides the error into compensable static error and dynamic error which is difficult to compensate.The shortcomings of small current error in shunt method are pointed out.Aiming at compensatable static error,the compensation function is designed by combining the measured value of high precision digital ammeter with the least square method,and the effectiveness of static error compensation is verified by experiments.Aiming at the disadvantage of large small current error in shunt method,a feedback loop gain switching logic based on sampling current and its derivatives is proposed,which uses high gain to suppress small current error and avoid the influence of frequent switching gain on current detection.In order to suppress the influence of high frequency sampling noise and provide current conductance value for gain switching logic,TD tracking differentiator in sampling ADRC method is used as current filter.Its filtering performance,response speed and ability of eliminating false values are analyzed by simulation and experiment.In the aspect of ripple suppression,in order to reduce the output current ripple,this paper establishes the output current ripple model based on bipolar PWM modulation.After analysis,two methods are adopted to reduce the output current ripple: increasing the switching frequency and changing the effective duty cycle.In order to improve the switching frequency,the new device GaN is used in high switching frequency environment to replace the traditional Si MOSFET as a power device.In order to solve the problem of narrow safe range of gate-level driving voltage and misleading communication caused by common-mode source inductance in high-frequency GaN devices,the driving loop area optimization method and bus capacitor configuration method based on flux cancellation method were designed to suppress parasitic inductance.The oscillation voltage suppression ability before and after optimization was compared through experiments.At the same time,the additional common-mode source inductance caused by parasitic inductance of shunt resistor is designed to isolate parasitic inductance of shunt resistor from common-mode source inductance.In the aspect of disturbance compensation,through the analysis of current loop model of voice coil motor,the disturbance source of current loop under high switching frequency is located as dead-zone disturbance.In this paper,a dead-zone model of current loop of voice coil motor is established.Based on the existing PI regulator,the influence of dead-zone on current is located as distortion near the zero-crossing point of current.In order to solve the problem of step-type dead-time compensation of average voltage and current oscillation when PI regulator is used together,this paper presents a gradual-type dead-time compensation method of average voltage.The validity of current polarity is judged by the current derivative value obtained by TD tracking differentiator,which enlarges the dead-time compensation range,solves the phenomenon of current oscillation and plays a certain role in the dead-time effect suppression.A high performance current loop driver for voice coil motor is developed,and its key hardware circuit and software workflow are designed.The correctness and validity of the theoretical analysis are further verified by the experimental study of the proposed scheme.