The principal applications of Stirling coolers include infrared imaging systems and
superconductive electronics. Among the requirements these applications place on the
cooler are low vibration export, low power consumption and long operating life.
A linear twin-piston compressor of a cooler provides for inherently low vibration
levels and is a solution widely accepted in industry. As compared with rotary or
linear single-piston compressors, it produces less vibration due to the balanced
counter-motion of two oppositely reciprocating pistons. However, the vibration
resulting from the mismatch of opposite piston assemblies caused by manufacturing
errors and natural wear cannot be completely eliminated.
In the ultra-low vibration applications an active balancing of the twin-piston
compressors is often used. Such systems normally rely on using internal (e.g.
LVDTs) or external (e.g. accelerometers or load cells) sensors and sophisticated
controllers. This leads to an unacceptable increase of cooler price and the reduction
This thesis describes the development, implementation and test of an adaptive
control system for (i) quasi-sensorless balancing of the twin-piston compressor,
where the detection and synchronisation of the pistons' motion is based on the direct
measurement of motors' voltages and currents, and (ii) minimisation of the input
electrical power required to drive the cooler, while maintaining the cold tip
temperature at a required level by simultaneously varying the driving frequency and
Modelling of cooler and control system operation was performed using
Matlab/Simulink software. Based on the results of the modelling, developed control
algorithms were implemented using LabVIEW RT software running on a National
Instruments controller. The attainable performance of the developed control system
was evaluated through the full-scale tests performed on the Ricor's K535 linear twinpiston
Stirling cryogenic cooler.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.