Joint Space Disturbance Rejection Control of Hybrid Platform for Active Wave Compensation with Improved Sliding Mode

In harsh sea conditions, the shipborne hybrid platform constructed by a Stewart platform and gangway can provide active wave compensation to increase the offshore operation time. But most of the existing studies analyze the Stewart platform and gangway independently. This paper proposes a joint space disturbance rejection control method for the hybrid platform by considering the Stewart platform and gangway simultaneously. This method combines the extended state observer (ESO) with the improved sliding mode control (ISMC). The ESO is responsible for suppressing the main disturbances, while the ISMC is tasked with suppressing the disturbances that exceed the compensation range of the observer. Additionally, an improved reaching law is introduced in the ISMC to reduce the chattering at the output of the controller. The simulation results demonstrate an excellent disturbance rejection capability, and the improved reaching law effectively reduces the output chattering of the ISMC.