Duty ratio control of a rotary PWM valve with periodic measurement error

The focus of this paper is on estimating system states in the presence of repetitive measurement noise. This estimation technique is applied to a novel self-spinning high speed rotary on/off valve that is being developed for pulse width modulating (PWM) fluid flow. The PWM duty ratio is determined by the valve spool´s axial position. Unfortunately, the optical position measurement is corrupted by a repetitive noise, induced by the spool´s rotary motion. Two models are developed to represent the periodic noise: one discrete time time invariant model based on internal model principle and a continuous time model that uses a set of periodic basis functions. Kalman filters are designed to estimate the spool position and the periodic noise. This estimates are used with a PI with feed-forward controller for the spool position reference tracking. Simulation and experimental results indicate the usefulness of estimating the periodic noise.