Patent ID: 8079825

Claim:
A method of protecting a cylinder of a compressor comprising a piston, a linear permanent magnet (PM) having a coil and a magnet, and a sensor-less control of the PM for moving the piston in and out of the cylinder, the cylinder having a discharge valve and the piston being coupled to a spring, the compressor achieving a maximum compression ratio when the piston reaches a Top Dead Point near zero, the method comprising the steps of: receiving a reference position of the piston from a temperature control loop, the reference position indicating a compression ratio; deriving a compensation voltage and a load spring effect information from a current through the coil, wherein said compensation voltage is derived by comparing a first actual current from the compressor and a second estimated current of the compressor; providing a model input voltage to a model of a mechanical structure of the compressor for predicting position of the piston, the model input voltage comprising a first voltage derived from the reference position; providing a compressor input voltage to the compressor, the compressor input voltage comprising the first voltage plus the compensation voltage; and using a position control loop to recognize when the maximum compression ratio is desired and controlling the piston to achieve maximum compression ratio without causing damage to the discharge valve.