Observation and estimation study for sensorless control of linear vapor compressors.

Linear vapor compressors have become widely investigated for refrigeration applications due to their high efficiency in comparison to the more common rotary type compressors. However, the nature of the linear compressor adds complexity to the control of these machines. The unconstrained motion of the piston in a linear compressor allows for continuous modulation of the compressor output, but requires knowledge of the mechanical dynamics to effectively control the compressor and prevent collision of the piston with the cylinder head. This control is made more difficult by the highly nonlinear nature of the force of gas compression acting against the piston. As this gas force changes so does the resonant frequency of the system. Efficient control of the compressor requires knowledge and tracking of this resonant frequency in addition to other objectives. Sensorless control of the system is preferred for reliability, ease of production, and cost effectiveness. To this end a series of nonlinear observers and a combination of controllers have been developed for the linear vapor compressor