Double-Ratio Based PI Parameters Design Method of Two-Mass Speed-Loop System

The conventional surface-mounted permanent magnet synchronous motor (SPMSM) speed servo drive typically adopts a dual closed-loop control architecture, comprising an inner current loop and an outer speed loop. In many cases, both loops can be approximated by first-order models with time delays, facilitating the application of classical control design techniques. One common approach is the zero-pole cancellation (ZPC) method, which employs a proportional-integral (PI) controller to cancel the plant's dominant time constant. While this strategy performs adequately in single-inertia systems, it proves insufficient when applied to more complex two-mass systems, where mechanical resonance introduces additional poles that the ZPC method cannot effectively handle. To overcome this limitation, a PI tuning method based on double ratios is proposed. This method leverages the characteristic ratios of system and time constants to reshape the closed-loop dynamics, effectively suppressing resonance peaks and reducing overshoot. Simulation studies have been conducted to assess the performance of the proposed method, and the results confirm its superiority in enhancing system stability and dynamic response compared to conventional ZPC-based approaches.