Boundary Layer Using Dithering in Sliding Mode Control

Practical issues in the implementation of sliding mode control systems, such as finite switching frequency, time delays and unmodelled dynamics, determine the state to belong to a neighborhood of the sliding manifold (the boundary layer) instead of lying on it. Dithering is here proposed as a technique for the regulation of the boundary layer when the actuator has a natural on-off behaviour. It is proved that dithering maintains the state of the system close to the ideal sliding manifold and that state error and practical stability depend on the dither amplitude, period and shape. Simulations on DC/DC power converters show that dither can play an important role for stability and robustness by using sliding mode control. Copyright c ©2005 IFAC