An Improved Second-Order Sliding Mode Control for an Interception Guidance System without Angular Velocity Measurement

It is well-known that the successful implementation of current sliding-mode guidance laws relies on two key points: one is the prior knowledge of the upper bound of the target’s maneuver, and the other is the accurate measurement of motion information. The truth maneuver is usually difficult to acquire and can only be roughly estimated. Measurements are often affected by noise and physical limitations of the onboard sensor. This paper presents an improved second-order sliding-mode guidance law that can handle these two problems simultaneously while addressing the chattering phenomenon, which inherently exists in the sliding mode-based controller. We achieve this by using the estimation from an extended state observer (ESO) and tracking differentiator (TD). In light of the employed ESO, which is utilized to give an estimation of the external disturbance, prior knowledge of the target’s maneuver is not required. Most interestingly, we show that the motion information can be estimated efficiently from the ESO in real time. A TD filter can be further embedded to remove unwanted noise from the detected signal. A series of simulations has been conducted, clearly demonstrating that the estimation accuracy of the ESO is sufficient for the guidance law to implement accurate interception. The TD filter not only removes noise but also avoids the phase-loss problems associated with conventional filters. Moreover, the chattering phenomenon is completely eliminated in the control channel.