This paper presents a dual-loop P/PI control strategy for a DC servodrive, focusing on the modeling, analysis, and numerical demonstration of system performance. The control structure consists of two cascaded loops: the inner current loop, which ensures fast electromagnetic torque generation, and the outer velocity loop, responsible for dynamic tracking of motor speed. The inner loop is designed using a proportional (P) controller to obtain a fast current response, while the outer loop utilizes a proportional-integral (PI) controller to achieve zero steady-state error in speed control. A mathematical model of the DC motor is developed, including the electrical and mechanical subsystems, and the transfer functions for each control loop are derived. Stability and transient performance of the closed-loop system are evaluated based on classical control theory methods. Finally, a numerical example is provided to demonstrate the tuning approach and illustrate the effectiveness of the dual-loop P/PI control architecture. The results confirm that the cascaded control structure improves dynamic performance and robustness, making it suitable for industrial servodrive applications.

DC servodrive, cascaded control, PI current loop, P speed loop

Ogata, K. “Modern Control Engineering”, Prentice Hall.

Dorf, R.C., “Modern Control Systems”, Pearson.

Hughes, A. “Electric Motors and Drives”, Elsevier.

Wikipedia article: “DC motor speed control”.

MathWorks Documentation: “Cascade Control in Servodrives”.