Modular Distributed Linear Actuation for Reciprocating Piston Compressors: an innovative revival of an old technology.

The ever-growing energy demand worldwide, makes efficiency key in a world where industrial machines operate around the clock. This translates into a necessity of reliable supply of com- pressed air and gas to ensure production continuity, resulting in the fact that the majority of compressors should be designed for 24-hour-a-day operation, year after year. To limit downtime, maintenance should be limited to a minimum, making reliability a top priority of current and next generation of compressors. This can be seen in current evolution towards smaller machines with a significant reduction of mechanical losses in the system, to obtain a compact, efficient and reliable device.
This dissertation presents the investigation of linear motor technology specifically fitted on pis- ton compressor applications to significantly reduce the overall footprint of the machine and to provide a hermetic, oil-free solution for the compression of inert and special gasses. More specifi- cally, the linear motor actuation principle is combined with a mechanical link to limit the motion of the motor and piston to avoid collision with the cylinder at any cost. The kinematically linked linear motor principle allows to combine the advantages of the more efficient, compact and oil- free linear compressors together with the increased reliability and high volumetric efficiency of traditional reciprocating compressors. The concept is tackled in three subsequent steps where 20%, 80% and eventually 100% of the power is provided by a linear motor. For the first two cases, the linear motor works together with the central rotary motor, while for the 100% case, the compression cycle is completely driven by the linear motor.
The first concept (20%), denoted as Rod Load Assist, focuses on boosting current generation reciprocating compressors. The idea is that by providing an additional 20% of the nominal power of the compressor, a wider range of customer’s requirements can be met with a single add-on device. The concept allows for an investigation of the electromagnetic and thermodynamic fun- damentals in a first step of this research.
In the second concept (80%), denoted as Power Assist, the linear motor becomes the main power source of the system (80%) and the remaining 20% is still provided by a rotary motor. This in- termediate step allows to increase the complexity of the linear motor while maintaining a rather simple control strategy, since any (small) error of the controller can be counteracted by the in- duction motor guaranteeing the position over the full cycle.
Eventually the full power (100%) is provided by the linear motor in the third concept, denoted as Power Transfer. By maintaining a kinematic link, in contrary to current generation linear compressors, the controller complexity can be reduced to a minimum and a mechanical fail-safe during operation is guaranteed. This final step allows to investigate innovative control strategies and design rules associated with this hybrid configuration.
The concepts are evaluated virtually and experimentally on a low power academic set-up (300 W) and afterwards on a high power industrial case (75 kW).