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Sensorless Sensing and Control Techniques of the Piston Stroke of Linear Compressor

A linear compressor with a free piston structure has paid attention to household refrigerator applications due to its high efficiency. The stroke of piston should be precisely estimated and controlled, in order to guarantee a high efficiency and reliability operations of the linear compressor. In this paper, the strategy to estimate precisely the piston stroke without any displacement sensor by using a cascaded high-pass filter and allpass filter based on back electromotive force (EMF) method is suggested. The methods of both the top dead center (TDC) detection and the piston stroke control are proposed to avoid striking the piston to the cylinder head. The performances of the newly developed sensorless estimation and control methods of a piston stroke are verified through experiments utilizing a linear compressor drive system.