A Novel Resonant Frequency Tracking Control for Linear Oscillatory Machine Based on Variable Exponential Terminal Sliding Mode Observer

For linear oscillatory machine (LOM), it is necessary to simultaneously implement the resonant frequency tracking and the position sensorless piston stroke control to obtain the maximum output efficiency and guarantee the safe and reliable operation of the whole system. Since the existing position sensorless resonant frequency tracking control method has problems of severe oscillation and low tracking accuracy, this article investigates a novel resonant frequency tracking control method based on variable exponential terminal sliding mode observer (VETSMO) to improve the frequency tracking performance. First, a double cross-correlation function ratio (DCFR) method is proposed to track the system resonant frequency, which not only can improve the antiinterference performance by directly controlling the phase of the stroke and current signals, but also reduce the computational complexity. In addition, by introducing the second-order nonsingular terminal sliding surface and the variable exponential reaching law, a VETSMO with second-order generalized integrator is designed to provide the more accurate piston stroke observation signal, thereby improving the frequency tracking accuracy of DCFR method. Finally, experimental results demonstrate the effectiveness and superiority of the proposed method.