Control of directly connected energy storage in diesel electric vessel drives

This paper focuses on the control developing for directly connected energy storage (ES) in diesel electric vessel drives and on analysis of the application benefits. The energy storage reduces load variations of diesel and generator. This can lead to fuel consumption savings, especially during dynamic positioning mode of offshore supply vessel. Energy storage can be connected to vessel AC power network by power electronics, which means additional losses on energy transfer upon charging and discharging. The other more effective way is to connect energy storage directly to the DC link of the propulsion drives. In this case, the DC link voltage level must be controlled to charge and discharge ES according to generator power and drive load. The aim of the control is to keep generation output in optimal fuel consumption range of the prime mover with keeping up the energy storage state of charge. The control is developed using power distribution network model of the offshore support vessel in MATLAB/Simulink environment. DC and AC power distribution network concepts with directly connected ES are evaluated. Gains and benefits of controlled and directly connected ES on variation of generation and diesel fuel consumption is discussed in the paper.