A cascade first and second order sliding mode control approach for speed control of brushless DC motor

This paper proposes a novel scheme for high-performance speed control of brushless DC motor (BLDCM). A cascade dual closed-loop control scheme based on the first order sliding mode (FOSM) control and second order sliding mode (SOSM) control is presented. The stability of the system is proved by constructing Lyapunov functions. An FOSM is used in the inner loop for high dynamic performance torque control. The SOSM-based outer loop speed control provides a continuous chattering-free reference command for the inner torque control loop, while the strong robustness and quick rapidity of sliding mode control (SMC) can be maintained at the same time. Though a dual closed-loop structure is adopted, there are only two parameters need to be tuned in the implementation of the proposed approach. Besides, it does not need derivatives of any state variable or sliding mode surface, which avoids the adverse effects of derivative calculation and simplifies the sliding mode surface design. The feasibility and effectiveness of the proposed approach are validated through theoretical analysis and simulation. Compared with the traditional PI dual closed-loop control, the static and dynamic performance, and the robustness of the system are significantly improved.