Control Strategy Research Of Secondary Regulation Active Heave Compensation System Based On Friction Compensation

The active heave compensation system can compensate the heave motion caused by wave interference,and ensure the safety and operation efficiency of offshore hoisting.Secondary regulation technology is a kind of hydrostatic driving technology with high response and high efficiency,which has a great application prospect in the field of active heave compensation.However,the friction in the secondary regulation system is nonnegligible,which will cause the system to crawl at low speed and discontinuous movement during reversing,thus restricts the improvement of heave compensation accuracy.In this paper,the active heave compensation system with secondary regulation is taken as the research object.Aiming at the nonlinear friction torque in the system,a friction parameter identification and compensation control scheme is proposed to improve the heave compensation accuracy,which is verified by experiments.The main work of this paper is as follows:(1)An active heave compensation experimental platform with a secondary unit being the driver and a Beckhoff industrial PC being the system controller is taking as the object.The working principle of the active heave compensation system with secondary regulation and its three loops(variable cylinder piston position loop,secondary unit speed loop and load position loop)control mode are introduced.Using Stribeck model as the description form of the system friction torque,the system mathematical model considering friction torque is established.(2)The parameter identification scheme of friction model is designed.Taking the sine sweep signal as the excitation signal of the system,an improved least square algorithm under relaxed excitation condition is introduced to identify the key parameters of the system model.Then,by fitting the discrete friction torque data in the sense of least square,the numerical law of the friction torque of the secondary regulation active heave compensation system with the secondary unit speed is obtained.(3)The compound control strategy of friction feedforward compensation and closed-loop feedback control is constructed.Through the obtained friction model,the feedforward control is set to compensate the friction torque of the system.The piston position loop of the variable cylinder is simplified as a first-order inertia element.The speed loop of the secondary unit adopts PI control to realize speed tracking without static error.The load position loop is controlled by a nonlinear PID controller with tracking differentiator and variable gain,which can suppress the measurement noise and improve the control performance.(4)Experimental research is carried out by compiling control program.The friction identification experiment is carried out,and the friction model parameters such as Coulomb friction torque,static friction torque,Stribeck velocity and viscous friction coefficient are obtained.The experiment of heave compensation control shows that the control strategy proposed in this paper significantly improves the control accuracy of heave compensation compared with the control strategy previously adopted by the research group.The experimental results verify the accuracy of friction identification results,the effectiveness of friction feedforward compensation and the superiority of the control strategy proposed in this paper.