Fast model predictive control of power amplifiers for nanometer precision motion systems

This paper deals with the design of a fast MPC algorithm for the current control of a power amplifier utilized for nanometer precision positioning systems within lithography machines. In order to achieve nanometer precision positioning, the internal power amplifier must accurately track a current reference in a very short time (tens of microseconds). Classical industrial control solutions based on transfer functions do not take duty-cycle limits into account and suffer from limited bandwidth, which in turn limits the achievable positioning precision. We design a fast gradient based MPC algorithm that can accurately track the dynamic current reference while satisfying constraints. Simulations show that the MPC-controlled amplifier results in at least 2x better nanometer positioning precision for specific metrics employed in the lithography industry, compared to an industrial loop-shaping controller and an LQR controller.