Integrating a Hybrid Electric Drive Propulsion System With the Existing DDG 51 Class Machinery Control System

The destroyers of the USS Arleigh Burke Class all have 4 propulsion gas turbines and 3 gas turbine generators (GTGs). A typical at-sea “condition 3” operating profile consists of having 2 gas turbine generators running at approximately 50% capacity, and one propulsion gas turbine online at low to intermediate ship speeds. Having 2 GTGs online at all times at 50% load each provides the obvious advantage of maintaining all electric loads should one GTG shut down unexpectedly. This luxury does come at the cost of fuel efficiency, as gas turbines efficiency improves continuously as they move away from idle. On the propulsion end, a single gas turbine is capable of generating enough horsepower to propel the ship at speeds in excess of 20 knots. Depending upon the specific mission that the destroyer may be on, however, quite a bit of operating profile may be at speeds below 15 knots where the LM2500 is operating at less than 20% capacity. In this range of operation specific fuel consumption ratios are also relatively low. The proposed Hybrid Electric Drive (HED) system has the potential to address both of these inefficient ranges of operation. By installing one 2000 horsepower electric motor on each shaft, the electric motors can be used to propel the ship at speeds below 14 knots (projected) while running the GTGs up to 90% operating range where they are most efficient. The LM2500 is shut down completely at this range, and the potential fuel savings in this configuration is substantial. While there are many engineering challenges with installing such a HED system on board an in-service DDG, the focus of this paper is on how to integrate HED with the existing Machinery Control System (MCS). Such challenges include interfacing MCS to the HED supervisory controller, developing a new HED control interface for the propulsion control operator, integrating HED into the existing shaft speed control algorithm, transitioning to and from HED propulsion, and updating data logging to include HED. Managing the interface between current electric load, changing electric loads, and current available HED power will also be addressed.