Brushless DC Motor Sliding Mode Variable Structure Control Program - Using Variable Speed PVC Strategy

Sliding Mode Control (SMC) represents a robust control methodology for nonlinear systems, particularly suitable for brushless DC motors (BLDC) that experience parameter variations and external disturbances. When combined with a Variable Speed Pulse Width Control (PVC) strategy, it further enhances system dynamic response and disturbance rejection capabilities.

The core concept involves designing a sliding surface to force the system state trajectory to converge to this surface within finite time and maintain sliding mode motion. The innovation of the variable speed PVC strategy lies in dynamically adjusting PWM frequency based on speed error - employing low-frequency PWM in high-speed regions to reduce switching losses, while switching to high-frequency PWM in low-speed regions to improve torque ripple.

Key implementation aspects include three-level design: 1) Sliding surface design based on motor model, typically selecting an integral form of speed error; 2) Frequency switching logic for variable speed PVC, requiring appropriate hysteresis bands to prevent frequent switching; 3) Control law design incorporating sign functions, with attention to using saturation functions or observers to mitigate chattering phenomena.

Compared to traditional PI control, this scheme demonstrates advantages including insensitivity to motor parameter variations, approximately 40% reduction in recovery time during load transients, and no requirement for precise motor mathematical models. In practical applications, attention must be paid to the impact of current sampling noise on sliding mode observation, with recommendations to incorporate moving average filters.