MIT ESRDC YEAR 2010 WORK PLAN
ESRDC Year 2010 Work Plan
Franz Hover
Structural Design of Power Distribution Systems
We will address foundational design issues for power distribution systems, with specific
application to the MVDC objectives in the AES.
We have been focusing on design of robust distribution systems based on specification of
structural parameters (such as degree distribution), rather than individual realizations, because
structural design is truly scalable whereas design of a realization is not. To set up the problem,
we model the DC power system as an undirected flow graph, and then identify the most robust
classes of networks for AES operating conditions, employing optimization and random graph
theory techniques.
For example, such an approach can quantify how much connectedness is necessary to prevent
islanding of components following a failure, while also minimizing exposure to damage in other
parts of the ship and maintaining an acceptable level of efficiency. Although we do take a global
network view in the problem statement, the objective is not to generate entirely random
interconnections, but rather to understand what topology modifications could be made to an
existing baseline design, to improve performance. Geographical considerations can be
embedded in the graph structure. By making the foundational power system layout as robust and
efficient as possible we minimize the burden on higher level control measures, because these
good properties are intrinsic to the design.
ESRDC Year 2010 Work Plan
Steven B. Leeb
Combat Power Monitor
Proposed Effort
1. During the proposed work, we will continue to develop such models and to use them to return
immediate value to active vessels. The simulation models that we create, which are VTB
compatible, are intended to be of use to the entire ship design community. During the coming
year we intend to focus on models for diagnostic indication and pathology detection in electrical
distribution and generation plans, and also HVAC systems. During the current performance
period, we have successfully demonstrated the NILM as a field capable platform using data
collected from the USCGC Seneca and USCGC Escanaba and preliminary data from the DDG-51
LBES facility at the Philadelphia Navy Yard. For instance, we have already created models that
have allowed the NILM to diagnose impending failures in both Auxiliary Sea Water (ASW) and
waste-disposal systems [2], [3]. During the proposed effort, we will collaborate to develop modelbased diagnostic indicators for critical shipboard mechanical systems, including cycling pump
systems, liquid cooling systems, air handlers and HVAC systems, water purification systems,
generation, and other mission critical electromechanical loads.
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2. During the proposed performance period, we will develop a hardware emulator for the electrical
generation aboard a ship. We will develop a minimum-two generator testbed with a zonal
distribution architecture. We will emulate the control system on-board the USCGC Escanaba, but
will also compare relevant dynamics and time constants of the testbed with those of a typical
DDG-51 plant. The hardware emulator will support scale experiments with both ac and dc power
distribution at scale levels. A simulation model of the generator will be developed. The goal of
this work is to support the “Red Team” challenge activity. It is also intended to provide a
hardware testbed for deploying the CBM as part of the zonal protection system on different
NGIPS platforms.
ESRDC Year 2010 Work Plan
James Kirtley, Chrys Chryssostomidis
Contra-Rotating Propulsion Motor
In anticipation that a pair of propellers rotating in opposite directions may be more efficient than a single
propeller, thought must be given to building a propulsion motor that is compatible with contra-rotating
shafts. At first, this seems to be a good option: electric machines are torque producing devices and so
produce power roughly in proportion to their rotational speed. A contra-rotating system should produce
an air-gap velocity that is twice that of either shaft alone, and therefore twice the power. It seems
reasonable that a single machine, sized for the same torque, could do the same job as each machine of
two, each one driving one propeller of a contra-rotating pair.
The implementation of such a system, however, has some interesting features. It involves at least one
bearing between the inner and outer of two concentric shafts and either a seal between shafts or a ‘can
seal’ motor. It also requires the ‘stator’ to be made rotatable and a set of slip rings and brushes to carry
motor power to the ‘stator’. There must be structure for the additional rotating element.
This study has two parts. One is an experimental element which would consist of modifying a
commercial, off the shelf induction motor, mounting the stator on bearings and supplying slip rings and
brushes, and providing bearings and, likely, a seal between the two shafts, mating this up with an
experimental contra-rotating propeller pair and testing it in a water tunnel or tow tank. The other part
consists of estimating the size and efficiency advantage of the drive motor, taking into account the
additional structure required slip rings, etc.
MIT ESRDC Year 2010 Work Plan
Michael Triantafyllou
Power System Modeling, Simulation, and Validation
Over the next year, we plan to fully develop the electric ship models and then proceed to use
them for applications in design, control, and reconfiguration:
(a) We will continue the development of comprehensive propeller models so as to assess the
feasibility of using high-speed propellers with high speed motors. Issues of hydrodynamic
performance and cavitation will be addressed, while full-system simulation will exhibit the
benefits of the new system configuration.
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(b) We will verify the maneuvering equations through extensive testing. We will include
comprehensive models for rough seas so as to combine sharp-maneuvering with seakeeping, and
we will assess the performance in a stochastic sea environment. In particular, we will develop a
nonlinear wave induced force model, parameterized by heading angle, so as to combine
maneuvering with sea excitation and we will assess stability issues.
(c) We will impose transient loads simultaneously with maneuvering and will provide a
probabilistic assessment of performance. We will continue our work on developing effective
control schemes at the system level.
(d) We will continue our work of compact representation of stochastic sensitivity, including
sensitivity to large amplitude perturbations, and we will apply the methodology to control system
design and reconfiguration.
MIT ESRDC Year 2010 Work Plan
Mirjana Milosevic Marden, George Karniadakis, James Kirtley
An End-to-end MVDC Simulator for the AES Integrated Power System
The first phase of the work will involve the development of computer models to allow trading off
different, integrated-power-system scalable architectures at the early stages of ship design. Our focus
will be on the MVDC architectures. Specifically, we will consider two levels of power, namely the Purple
team design (small scale) and also the Red Team design (full scale).
To this end, we will first consider the generation system assuming a hypothetical load consisting of a
resistor. Subsequently, we will model the propulsion system assuming an ideal DC voltage source. After
we verify and validate these two sub-models we will integrate them in order to create an end-to-end
MVDC simulator that also includes a detailed turbine model as well as detailed hydrodynamics. This
integrated simulator will be similar to the AC end-to-end simulator already developed at MIT in the past
years.
The new technical challenges are the design of robust controllers for power electronics interface
(converters, inverters & rectifiers) using detailed models. Sensitivity analysis will be performed both at
the component but also at the system levels using polynomial chaos methods. A key issue related to
stability in the MVDC system is the use of “energy storage” to maintain power balance; a possible
solution is the use of additional generator(s). In the case of multiple power sources (generators & storage
devices), control of parallel connected rectifiers that interfaced the power generation unit with the DC bus
becomes challenging. Specific tasks will include resolution of such performance and stability issues and
validation, when possible, with measurements available from the Red and Purple teams.
ESRDC Year 2010 Work Plan
Julie Chalfant, Chrys Chryssostomidis, James Kirtley
Architectural Model to Enable Power System Tradeoff Studies
One project is the continued development of an overall architectural model for an all-electric
ship including a fully-integrated simulation of electrical, hydrodynamic, thermal, and structural
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components of the ship operating in a seaway. The goal of this architectural model is to develop
an early stage design tool capable of performing tradeoff studies on concepts such as AC vs. DC
distribution, frequency and voltage level, inclusion of reduction gears, energy and power
management options, and effect of arrangements and topology. The results of the tradeoffs will
be presented in standard metrics including cost, weight/stability, volume, efficiency/fuel
consumption, reliability and survivability. We will specifically look at the hull, mechanical and
electrical (HM&E) systems that support the ship and its missions; specifically, the electrical
generation and distribution system, propulsion equipment, fresh- and saltwater pumping and
distribution, control systems, and structural components.
To date we have created a basic design tool which uses hullform, drive train particulars, and
operational employment of the vessel to determine resistance, powering and fuel usage. Our
next planned step is to include a detailed electrical distribution system to more completely
analyze the effects of changes (e.g. frequency, voltage level) in terms of the metrics described
above. This analysis will include not only the connection diagrams of the system components
but also the location, weight and volume of the components and the interconnecting cabling.
Indeed, the cost, weight, volume, efficiency, electrical load, thermal load, and reliability of every
piece of equipment is included in the analysis as applicable. The zonal placement of the
equipment and the interconnections will contribute to the survivability of the systems in face of
damage.
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