Semi-closed Loop Based on Predictive Current Control for SPMSM Drives during Servo Stamping

Nonlinear factors in industrial servo press currently, including mechanisms for force amplification, installed clearances, gears backlash, and variations in rotational inertia, are commonly not considered during the control process. They would impact the control accuracy of the actuator's crank and slide and even affect the quality of material forming. So the conventional linear control method, field-oriented control based on the mini-closed loop of the electrical machine position utilizing kinematics, can not follow the trajectory smoothly and accurately. This study proposes a solution to address these issues by introducing a semi-closed loop control approach. This method fully accounts for the Lagrangian approach for the dynamic model of the servo press. The torque reference of the computed torque algorithm is implemented by model predictive current control. A comprehensive and comparative trial and analysis of the impacts of critical parameters are conducted. The proposed method is practically tested on a 1600 kN press equipped with a dual-core DSP servo drive. Experimental results demonstrate the effectiveness of this control approach, which significantly enhances the control accuracy of crank position and speed while also reducing the switching frequency and losses of the servo press drive.