Electromagnetic Torque Calculation Method based on Motor Current Ridge and Its Application for System Identification

The precise identification of dynamic characteristics of an electromechanical system is critical for optimizing the control accuracy of servo system. However, as a key parameter for system identification, electromagnetic torque is challenging to measure in actual operating equipment. In this study, an electromagnetic torque calculation method based on motor current time-frequency (TF) ridge extraction is proposed. Firstly, the synchrosqueezing transform (SST) is applied to extract the TF ridge of motor current, and the electrical angle of the servo motor is derived through ridge integration. Then, the electromagnetic torque is calculated using the vector transformation formula. Finally, the system identification is performed on the robotic arm test bench. The results demonstrate that the electrical angle acquired by the proposed method offers the advantages of minimal error and synchronization with motor current, leading to the accurate calculation of electromagnetic torque. The calculated torque is utilized for system identification, which is able to identify the frequency response (FR) of the test bench and highlights the resonance characteristics.