The effects of system voltage on electric machine design

Marine propulsion is essentially a variable speed - variable torque application. In the early days of the transition from purely mechanical drive trains to electrical versions, the only variable speed equipment available was powered by direct current. As the general understanding of power electronics and the successful development and deployment of technology has progressed, so too has the breadth of its applicability. Now, with systems capable of delivering usable alternating current from rectified sources over a wide range of frequencies, both synchronous and induction designs are making inroads into areas once thought to be the sole province of direct current machines. Modern power electronics systems are available that can deliver high current, high voltage, or both. The purpose of this paper is to present the case for choosing between the myriad of options so that the complexity of the rotating equipment connected to the output shaft is minimized, and that overall system reliability is not compromised.