Position And Speed Compound Control Method For Unidirectional Speed-variable Constant Pump-controlled Differential Cylinder

Unidirectional speed-variable constant pump-controlled differential cylinder system is widely used in servo hydraulic press and other hydraulic systems,Due to its high energy efficiency.In the metal powder forming process,the quality of the products depends on The speed and position accuracy of the servo hydraulic press.In this paper,unidirectional speed-variable constant pump-controlled differential cylinder system was researched and analyzed the position and speed compound control strategy of the system.Based on the flow continuity equation and the force balance equation,a three-order state space model and transfer function model is proposed;Based on the operating principle and characteristic of compound control,established the system constraint equation.Then,the available PID controller and the model predictive controller(MPC)with improved optimization objective function is proposed.Compared to PID through simulation,the MPC controller is validated to be easier to adjust and feasible to complete the compound control of position and speed.In addition,based on moving least square(MLS)surface fitting method,a new testing method for low flow characteristic test of variable-speed pump is proposed to avoid the complicated regulating of loading valve.Based on the xPC target and the test platform,completed the flow characteristic test of pump and the experiment of speed and position compound control of the system respectively.The test results of pump flow characteristic show that,the new method based on MLS is verified to be practicable and effective.The experiment results of PID and MPC show that,the model predictive controller is more convenient and superior to the traditional PID controller in compound control.