Variable DC Voltage Shipboard Power System With Permanent Magnet Generator and Diode Front End

The application of dc power systems to microgrids, such as the power system for vessels and islands, is gradually increasing. The major advantage of the dc system over the conventional ac system is the reduced fuel consumption and emission, which is mostly due to the variable speed operation of the diesel engine. It has been reported that the efficiency of the dc system can be maximized if the generation unit comprises a permanent magnet generator (PMG) and a diode rectifier. However, the fatal disadvantage of this composition is that the optimal efficiency operation of the variable speed engine may not be always possible unless the parameter of the PMG, specifically per-unit stator inductance, is within a specific range. The dc system design method proposed herein allows for a large voltage variation (e.g., 40%), and it is possible to operate engine along its optimum efficiency operating point even if the generator per-unit stator inductance does not have a specific range. At light-load conditions, in particular, the proposed method can reduce power converter switching loss and diesel engine fuel consumption. The validity of the proposed method was verified using computer simulations and small-scale experiments.