The use of shaft generators in marine applications makes it possible to operate the main engine more efficiently and to provide additional power to the electrical system. This paper develops a dynamic model and controller for a hybrid marine propulsion system that operates efficiently in both mechanical and hybrid modes such as power take-off (PTO). A simplified electric power system model with a shaft generator and a battery set is introduced into the ship propulsion system. The corresponding control and switching logics are also described and are proved with simulations.
Nowadays, hybrid ship propulsion systems are of great interest and the application of shaft generators (SGs) has developed rapidly. The operation mode of a hybrid ship propulsion system can include power take-in (PTI), power take-off (PTO), and boost mode (Sui, de Vos, Stapersma, Visser, and Ding, 2020). In this paper, we investigate the use of optimal combinator curves for the control of a hybrid ship propulsion system driven by an engine with and without a shaft generator.
For marine applications, the main propeller can be driven by the engine, and the shaft generator can be engaged to charge the battery set and/or power the electric bus (PTO mode). Using the shaft generator system to charge the battery is more efficient than starting auxiliary engines (Liu, Xue, and Ye, 2007; Prousalidis, et al., 2012; Sarigiannidis, Kladas, Chatzinikolaou, and Patsios, 2015). Fig. 1 shows an overview of the proposed propulsion system, which consists of a main diesel engine (DE), a controllable pitch propeller, and a shaft generator (SG) connected to the electric system (EL).
Since many combinations of shaft speed and propeller pitch can produce the same thrust, the propulsion control problem with controllable pitch propeller (CPP) (Carlton, 2018) can be formulated as the optimization of a cost function. For example, many marine propulsion control systems focus on reducing fuel consumption and avoiding cavitation at the propellers. The combinator curve set used in this report is optimized for maximizing efficiency. The optimal setpoints of propeller pitch and shaft speed are chosen from the optimal combinator curve and are controlled independently.