Modeling of Common-mode Currents on Electric Ship

ArchitecturesMississippi State University

Department of Electrical and Computer Engineering

Michael Mazzola and Maryam Rahmani

Presented by Michael Mazzola This work was supported by the Office of Naval Research as part of the Electric Ship Research and Development Consortium under Grant N00014-08-1-0080.

Michael MazzolaAngela Card

Student:Maryam Rahmani

Grounding Team

Lukas Graber (lead)Mischa SteurerJozef Kvitkovic

Student:Patrick Breslend

Steve Pekarek

Students:Aaron Brovont

External Collaboration: W. Blake, B. Hood, K. Watts

310 Aug 2014

Concentrated and Distributed Models

G ~=

==

=~ M

Ship hull≥ 5-port

Super ground(e.g. sea water, port connection)

Concentrated Models

Distributed Models

• Grounding models for power cables• Lumped element models (pi-sections)• Distributed models (PSCAD: freq. dep. phase model)• S-parameter models (ADS, MATLAB, Empirical)

• Grounding models for power electronics• DC-DC converter (S-parameter; MATLAB)• Inverter (not completed)

• Grounding models for rotating machines• Lumped element models (T-model; SimPowerSystems, PLECS)• S-parameter models (ADS)

• Ship hull (ADS)

Common-Mode Current on the Hull and Bulkheads

• Demonstrate behavioral modeling tools for hull and interconnected grounded conductors derived from physics based simulation. – Many grounded conductors bonded to hull and forming interconnected

network on which common-mode current is impressed (e.g., cable sheaths)– Model with multi-port system based on, or derived from, S-parameters– ADS computes S-parameters for hull & bulkhead geometries with N bonds– Network analyzer measures three-terminal S-parameters for cables– Synchronizing reference potential requires careful thought

S-Parameters of Open-Form Conductor Systems

•Reference plane•Air = 50 mm•“Steel” = 25.4 mm•“Paint” = 1 mm•“Seawater” = 100 mm

Physics based calculation of S-parameter model of a four-port square block in Agilent ADS• Finite element analysis with auto-generated mesh• Frequency range is zero to 10 MHz

Physics based calculation of S-parameter model of elementary rectangle in ADS• Finite element analysis with auto-generated mesh• Edge ports to interconnect elementary rectangles to form

a single square• Frequency range is zero to 10 MHz

Comparison of equivalent S-parameters in ADS formed from a single block and a composite block made of two elementary rectangles

1 2 3 4 5 6 7 8 90 10

-22.8

-22.6

-22.4

-22.2

-23.0

-22.0

freq, MHz

dB(S

(2,1

))dB(_

11port

_A

ir50m

m_H

exagon_A

ppEdge_4_cacaded_FEM

..S(2

,1))

1 2 3 4 5 6 7 8 90 10

-1.0

-0.9

-0.8

-0.7

-1.1

-0.6

freq, MHz

dB(S

(1,1

))dB(_

11port

_A

ir50m

m_H

exagon_A

ppEdge_4_cacaded_FEM

..S(1

,1))

Discrete

Continuous

Verification of numerical four-port model with solution to parallel line-charge electrostatic solution

Network Analyzer connected to cable ends through removable coaxial terminations

S-Parameters of CablesEmpirically Derived

Cable

Are the ports the center conductor or

the shield?

• For power system the ports are the center conductor.• For the safety grounding system the ports are the sheaths.

S-Parameters of CablesEmpirically Derived

Cable

S-parameter model is symmetrical

• Measure at center conductor.• Reference third terminal at: • Hull potential in power system

simulation• Power bus potential in hull

system simulation.

center conductor

shield conductor

Summary• Ship power systems are evolving in complexity to the

point where design automation is essential.• Simulation and modeling of a large open-form

conductor system (ship) using finite element analysis too cumbersome for early stage design.

• Problem can be solved by converting to behavioral models derived from physics-based modeling supplemented with empirical data.

• “Arbitrary” open-form conductor systems built up from elementary behavioral models.