Model predictive control of a free piston compressor/expander with an integrated linear motor /alternator

摘要

Linear positive displacement machines are becoming increasingly more attractive for applications that are normally known as unconquerable niches of rotary and scroll machines.Free-piston machines are characterized by the absence of a crank mechanism,since there is a direct transformation of electrical energy into the piston movement.From the point of view of manufacturing,these machines benefit from a higher robustness and reliability because of less mechanical components involved and reduced frictional losses associate with a conventional crank mechanism.However,the major challenge in replacing the rotary machines by linear ones is a lower efficiency at lower speeds which is unavoidable because of the nature of linear motion:continuous operation means a reciprocating movement within a stroke length with significantly long periods of acceleration and deceleration when the speed is far from its optimal value.However,the advantage of free-piston machines is the fact that the motion profile is freely configurable within physical constraints,which provides a possibility to optimize the speed given the efficiency map of particular linear motor.While the methods and results of the efficiency assessment for rotary machines are widely available,there is a lack of these analyses for linear machines.The current study provides in-depth analyses of a double-coil iron core linear motor also acting as a generator.