A motion observer with on-line parameter estimation for moving-coil based digital valves in digital displacement machines

In this paper, a method is developed to estimate the parameters and motion of a moving coil actuator in the digital valves of Digital Displacement machines. The parameter estimation is carried out using three simple distinctive schemes from which certain electrical and magnetic parameters may be estimated. The parameter estimation method uses simple adaptation laws to update the moving coil actuator parameters used to estimate the valve plunger motion in an observer. The observer estimates the velocity using the back electro-motive force (back-emf) induced when moving the coil based on current and voltage measurements, but without any mechanical sensors. The valve movement of digital valves is confined by mechanical end-stops enabling estimating the valve position through integration of the estimated velocity relatively accurate. The observer depends on precise knowledge of the electrical dynamics to accurately estimate the valve motion. When the parameters are converged through adaptation the observer proves to be capable of tracking the valve motion relatively accurate, however some deviation occur at the mechanical end-stops of the valve. The parameter estimation method and the observer is implemented and tested off-line when using experimental data obtained from a newly developed digi-valve prototype which uses a moving coil actuator as the force producing element.