Hoerbiger (Austria)

The performance of a linear free piston gas compressor is investigated in this study. Two compressor pistons are mounted on a robust reciprocating cage mover, which is driven by a double-stator linear induction machine. Since the beginning of the 21st century, many permanent-magnet machines were investigated due to their high power density and efficiency. Less attention has been paid to linear induction machines (LIMs) that stand out through the fact that they do not require expensive rare-earth magnets, and moreover, they are insensitive to strong magnetic fields, high temperatures, and harsh working conditions. This enables them to be used with corrosive media, e.g., for a hydrogen compressor. Therefore, a prototype of a potentially more robust electromagnetic free piston gas compressor was built. It is evaluated on two test benches: First, the LIM is tested with a load motor that enables the measurement of the mechanical output power, and second, the free piston gas compressor is tested with ambient air and the discharge pressure and output flow rate are measured. The electrical power consumption, the mechanical output power of the linear motor, and the pneumatic output power of the free piston compressor are determined for various operating conditions. The measurement results are presented and the average cycle efficiencies are calculated. Moreover, the average cycle power losses of the LIM are analyzed.

Spring assisted oscillating actuators allow to reduce the energy consumption. The concept relies on springs that take and release energy into the system when required. Conventional mechanic springs impose some limitations on the system regarding mainly compactness, friction, material fatigue and failure. Magnetic springs show the potential to overcome these issues especially for long stroke high frequent operation. This paper investigates the integration of a magnetic spring into a linear oscillatory motor, without any changes to the permanent magnet arrangement on the mover. The focus lies on a compact design with maximum energy storage capacity. The proposed design guidelines are used as starting point for a finite-element based optimization. Moreover the investigation covers the expected losses and demonstrates that a correct choice of materials is crucial for an efficient operation. The results of the simulated spring characteristic as well as the losses are validated with measurements on a prototype of the linear oscillatory motor featuring the proposed integrated magnetic spring.

Model predictive control is a powerful method for controlling multivariable systems, in particular when constraints have to be taken into account. However, MPC also has negative attributes, like a high computational effort but also a non intuitive tuning. While the first issue can be addressed by use of numerically efficient optimizers, the non intuitive tuning still remains. To this end, an approach for efficient tuning of a MPC environment consisting of controller and state observer is proposed. The idea is to provide an automatic tuning strategy, such that even an unexperienced user can design a satisfactory controller within reasonable time. The proposed tuning of the state observer is done by a combination of multi model and adaptive estimation methods and for the weight tuning of the MPC objective function an additional optimization loop is applied which also accounts for the numerical condition. Finally an example is presented, where the proposed strategies were used to tune the MPC for controlling a pipeline compressor natural gas engine in a nonlinear simulation environment, yielding promising results.