LCL Filter Design and Implementation for Improving Transient Position Tracking Control Performance of Voice Coil Motor

Voice coil motor (VCM) is widely used in high precision position servo control for its merits of high linearity and no cogging-torque. There are two conventional driving modes: PWM chopper drive and analog drive. PWM chopper drive usually results in current ripples, which could affect position control precision. Acceptable current ripple limits the increase in the DC bus voltage and could not achieve faster response. On the other hand, analog drive uses power amplifiers, which does not suffer from current ripple but can result in high power loss. Such power loss could also affect precision or result in cooling difficulty, especially for thermal-sensitive applications such as semi-conductor lithography. In this paper, a VCM chopping drive with an LCL filter together with filter design method is proposed. Unlike conventional LCL filter design for grid inverter that only focuses on steady state current quality, the proposed LCL filter design in this paper aims at transient position control, which considers the current ripple, transient position tracking time and additional volume. With the designed filter, position tracking time can be shortened with acceptable current ripple. To compensate the delay caused by LCL filter, the DC drive voltage is increased. And under the same current ripple level, with LCL filter and higher DC voltage can get faster position response speed than without LCL filter and lower voltage. The results are validated by simulation and experimental results.