Control of a Fast Switching Valve for use in Digital Hydraulics

Nathan Sell

Nigel Johnston and Andrew Plummer

University of Bath

UKACC PhD Presentation Showcase

UKACC PhD Presentation Showcase Slide 2

Introduction

Pumps, motors and actuators >90% efficient. High flow, low loss valves. Very complicated and specialised circuits and

control.

But still get system efficiencies <50% common.

Premise of most hydraulic control is throttling, which is intrinsically dissipative.

UKACC PhD Presentation Showcase Slide 3

Digital Hydraulics

Uses fast switching “digital” valves so that fluid power produced tracks power requirements. Digital Cylinders Digital Pumps and Motors Digital Transformers

University of Bath has created a valve for use in a Switched Reactance Hydraulic Transformer. Allows the transformation of flow into pressure or visa-versa. Similar operating principal to a buck converter.

UKACC PhD Presentation Showcase Slide 4

Fast Switching Valve

Three stage valve 37.7mm2 flow area 0.2mm stroke Overlapped spool Three ports (HP, LP and service) Integrated position and velocity sensors

Switching at >100Hz Needs to rise quickly Overshoot less than 0.1mm Variable width and frequency PWM

UKACC PhD Presentation Showcase Slide 5

Controller Design

Utilises an Iterative Learning Control Passes error through inverse model to discover the “incorrect” input Subtracts this from the previous input Able to adjust for changes properties or inaccuracies in valve model

Inverse model (L(s)) Position sensor and accelerometer used with complimentary filters to

provide accurate position, velocity and acceleration estimates. These values are used to numerically implement a 2nd order inverse

model, along with a negative delay.

UKACC PhD Presentation Showcase Slide 6

Simulated Results

UKACC PhD Presentation Showcase Slide 7

Summary

Digital hydraulics offers large efficiency savings in a host of fluid power applications.

University of Bath has developed a valve with a view to create a SRHT.

ILC has been shown to be a powerful tool to control the required fast switching valve.

Valve model needs validating on test rig. Control scheme needs proving in real time.