Abstract: The electro-hydraulic control system based on switching control between meter in and meter out for the underwater towed heave compensation system is designed in order to compensate bad influence of the towed ship heave motion on the towed body depth and improve depth compensating accuracy. The general design scheme of heave compensation control system composed of external depth heave compensation control subsystem and inner position servo-control subsystem for the towed heave compensation system is proposed. The external subsystem measures the towed body depth and outputs target angular displacement of the towing winch, furthermore, the inner subsystem quickly tracks the target angular displacement without steady-state error under time-varying tension moment disturbance of the cable. Against inner subsystem features that mathematic model of the electro-hydraulic control system is built with error and parameters perturbation and it is disturbed by time-varying tension moment, the internal model control strategy is applied to inner controller design. Simulation and experiment results show that for the inner position servo-control subsystem the ability to resist disturbance is strong, and the demand for modeling precision is low, and the parameter setting is convenient, and it has good dynamic performance.

Key words: Heave compensation, Internal model control, Underwater towed system