Zhengru Ren

Modeling and Control of Crane Overload Protection During Marine Lifting Operation Based on Model Predictive Control

This paper deals with a nonlinear model predictive control (NMPC) scheme for a winch servo motor to overcome the sudden peak tension in the lifting wire caused by a lumped-mass payload at the beginning of a lifting off or a lowering operation. The crane-wire-payload system is modeled in 3 degrees of freedom with the Newton-Euler approach. Direct multiple shooting and real-time iteration (RTI) scheme are employed to provide feedback control input to the winch servo. Simulations are implemented with MATLAB and CaSADi toolkit. By well tuning the weighting matrices, the NMPC controller can reduce the snatch loads in the lifting wire and the winch loads simultaneously. A comparative study with a PID controller is conducted to verify its performance. INTRODUCTION Due to the oil crisis in 1973-74 and anti-nuclear sentiment, wind farm industry was motivated and started to grow in the late 1970s. At the beginning stage, investment subsidy, tax-free policy, CO2 bonus, and long-term policy goals stimulated the industry, while it is meanwhile blocked by local protests, siting difficulties, and the inner resistance in the power company [1]. In recent years, there is a significant development of offshore wind farms with an increasing rated power per turbine. Large amounts of newly built offshore wind farms, e.g. in United Kingdom, Denmark, and Germany, have sparked an increasing requirement for safe and cost-and-time efficient installation schemes. Lifting is one of the most common operations during wind turbine installation. Due to the great mass of the payload, sudden wire rope tension at the initial stage of the lifting off and the lowering operation is crucial to the marine installation safety [2]. As largely depending on pragmatic experiences, marine operations ordinarily follow the criteria from guidance documents and confidential data from decades of experience. For example, alpha factor, which is a correction factor on the operational limit in terms of significant wave height, is used to modify the operational criteria and contributes to the decision making process, e.g., when to start a specific operation based on the weather forecasts. To reduce the environmental influence and to provide a stable platform for lifting crane operations, a jackup is the most widely applied scheme. Such methods can merely reduce the risk; however, they are insufficient to satisfy strict deadlines and limitations in operational time windows. The vessel may wait for quite a long period until a calm and long enough weather window for positioning of the jackup rigs. Such operations can only be conducted during 1 Copyright c