Research On Auxiliary Resonant Snubber-Based Current-Controlled High-Precision Power Amplifier

Current-controlled power amplifier converts voltage to current to drive the actuators.In the lithography machine,the power amplifier is required to realize the requirements of high dynamic(bandwidth above thousands Hz)and high precision(current precision below few ten thousandth)so that the reticle stage and workpiece stage can achieve nanometer-positioning precision.Soft-switching technique can solve the problems of large switching losses and serious EMI noises at the condition of high switching frequency so that the power amplifier can achieve the requirement of high dynamic.After achieving the basic bandwidth,the current precision of power amplifier becomes the critical factor to achieve nanometer-positioning precision of reticle stage and workpiece stage.After the process technology of integrated circuit is reduced below 10 nm,the problem of inaccurate positioning precision caused by the inaccurate current of power amplifier becomes outstanding.Thus,this thesis takes the auxiliary resonant snubber-based current-controlled power amplifier(ARSCPA)as research object,the voice coil motor as load to research the influence factors and improving techniques of output current precision.Because LC filter is added to reduce the current ripple and clamping diodes are added to reduce the peak voltage,the operating principle of ARSCPA is changed.Therefore,the operating principle of ARSCPA is analyzed firstly.The parameters in different modes are calculated and the mode judging criteria is obtained.Then the overvoltage problem of auxiliary switches with single branch and split branches is analyzed.An overvoltage suppression method by adding clamping diodes is proposed.Finally,simulation and experiment are finished to verify the effectiveness of theoretical analysis.In the power amplifier,the nonlinear error is the domain error source of positioning precision of workpiece stage and reticle stage.In the ARSCPA,the output current ripple increases the current harmonic.Dead-time effect generates the output voltage error,which increases the output current error and harmonic.On resistance and junction capacitance of switches generate voltage drop and switching delay respectively,resulting in increasing output distortion.Therefore,the linearity of ARSCPA in terms of output current ripple,dead-time effect and switch nonlinear behavior is analyzed.Firstly,the characteristic of output current ripple is analyzed.Then dead-time effect of ARSCPA is analyzed and the voltage error is calculated with the conventional constant Ir_A control.A dead-time effect suppression method by controlling the auxiliary current is proposed to reduce the output harmonic distortion.Finally,the circuit model of ARSCPA considering on resistance and junction capacitance is built.The output voltage error caused by on resistance and junction capacitance is calculated.Auxiliary initial resonant current is the current to charge and discharge the resonant capacitors at the initial resonant time,which will influence the output voltage and current.In the ARSCPA,the auxiliary initial resonant current error exists due to the open-loop control of it.Besides,the conventional auxiliary current control neglects the filter inductor current ripple,resulting in auxiliary initial resonant current error.Therefore,the output linearity influenced by the auxiliary initial resonant current error is analyzed.Aiming to reduce the error,an improved auxiliary initial resonant current control method considering the filter inductor ripple is proposed.The output precision is improved and the peak auxiliary current is reduced by using the method.To achieve the goal of high-precision current output,the load current must be closed-loop controlled.To improve the positioning precision of reticle stage and workpiece stage,the load current must track the slope signal without any steady error during the scan motion.Besides,since the LC filter together with the load inductor forms LCL branch,a resonance peak occurs in the system,which will make the system unstable.Aiming to solve the problems above,a dual closed-loop control based on dual PI controller and filter capacitor current feedback is proposed.Dual PI control is used to eliminate the slope current steady error.The capacitor current feedback aims to stabilize the system.A dual closed-loop control design method is proposed,which can simplify the design complexity of control parameters.Finally,a prototype with 800 W output power and 10 A output current is developed.The performance of the prototype is listed below: 10 k Hz bandwidth,2.575 m A current error with DC output,current THD below 0.017% with 10 A peak output current and 92.5% efficiency with 10 A DC output current.The requirements of high dynamic and high precision are achieved.