Free Piston Controller for Natural Gas Compressor

Under CEM's Department of Energy ARPA-E award, researchers at CEM recently completed and demonstrated a controller for their free piston linear motor compressor.

free piston

The team's compressor concept aims to increase reliability and lower the cost of home refueling appliances for natural gas vehicles.  The compressor design results in a single moving part (the free piston) and reduces part count considerably when compared to traditional reciprocating compressors driven by a rotary motor. 

With the team's aggressive compressor cost target of $500, it is critical that every element of the design be optimized for efficiency.  Leveraging prior motor/generator design experience and tools, CEM performed a detailed linear motor trade study early in the project to identify the most efficient and suitable motor design for the compressor application.  Prior to choosing a compressor motor design, CEM conducted trade studies evaluating cost versus performance, on six motor designs.

CEM also leveraged experience in modeling and controls to develop dynamic simulations of the linear motor coupled to the reciprocating compressor.  As a result of this effort, the CEM researchers were able to quantify the dependency of the overall compressor efficiency on several factors, such as physical attributes of the compressor and accuracy of the motor control systems.     Understanding how each element of the design affects the compressor efficiency is critical in developing a compressor that allows for efficient residential natural gas vehicle refueling. 

CEM has recently completed building and testing a small bench-top mock-up of a linear motor.  The simple motor as shown in the video is constructed from off the shelf components.  Although the mock-up varies greatly from the team's current design, the system has served to verify sensor elements and the motor control system accuracy.  Proving out the motor control system, which plays a critical role in the compressor efficiency, is a key step in moving forward with the overall linear motor and compressor design. In the coming months, the researchers will focus on novel seals and coatings aimed at increasing compressor life and durability.  Testing of the initial prototype compressor, or proof-of-concept, is scheduled to begin late Summer 2014.  

free piston vid

MP4 version of the demonstration video can be viewed here.

WMV version of the demonstration video can be viewed here.

Additional Information: Mike Lewis

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