Modeling of Electric Ship Power Systems

A. Ouroua, B. Murphy, J. Herbst, and R. HebnerUniversity of Texas at Austin

ShipServices

Power Generation Power Conditioning & Distribution Power Conversion Power Consumption

Prime Movers Generators

Synchro./Sep. Exc.

Synchro./PM

Super-conductive

Homo/hetero Polar

Diesel Engine

Gas Turbine

Nuclear Power Plant

Fuel Cells

G2

G3

G4

G1

Fuel

Optional Energy Storage

Gear

Synchro./Sep. Exc.

Synchro./PM

Super-conductive

Homo/hetero Polar

Variable Reluctance

M2

M4

M3

M5

M6

M1Induction

Motors

Direct Drive

Propeller

Podded Propulsion Non-podded Propulsion

Motor + propellerin single unit

Motor on board

Transformers Converters

Propulsion

Ship Services

PWM

Synchro

Cyclo

Rectifier

AC or DC Transmission?

Loads

PulseLoads

Power system option summary

Power system option summary

General system description leads to circuit model

• Captures key components• Permits prediction of

• Stability• Load flow• Transient responses• Switching surges• • •

ShipServices

Power generation Power conditioning and distribution Power conversion Power consumption

Prime movers Generators

Synchro./Sep. Exc.

Synchro./PM

Super-conductive

Homo/hetero polar

Diesel engine

Gas turbine

Nuclear power plant

Fuel cells

G2

G3

G4

G1

Fuel

Optional Energy Storage

Gear

Synchro./Sep. Exc.

Synchro./PM

Super-conductive

Homo/hetero polar

Variable Reluctance

M2

M4

M3

M5

M6

M1Induction

Motors

Direct drive Propeller

Podded propulsion Non-podded propulsionMotor + propellerin single unit

Motor on board

Transformers Converters

Propulsion

Ship services

PWM

Synchro

Cyclo

Rectifier

AC or DC transmission? Loads

Sample component selection

System model

Pulsed loadsSimulink, ACSL, VTB

Non-circuit behaviors can also be critical and must be modeled separately

Morton Effect

• Thermo-hydrodynamic effect

• Positive feedback between shaft temperature distribution and vibration• Noise • Bearing failure• Machine failure

DC test grid

•Entire Grid• About 0.5 MW

•Upper Half• About 1 MW

Focus of dc test grid

• Response to transients• Ground faults• Series faults• Step load changes

• Response of particular interest• Surge generation due to stray inductance and filter capacitance• Transient circuit representation of faults• Transient circuit representation of capacitors• Power transients exceeding steady-state source ratings

• Interest due to surge effects• Insulation • Power electronics

Fault study approach

• Physics-based model of breakdown•Pre-breakdown•Post-breakdown

• Develop equivalent circuit from physics-based model• Integrate fault circuit model into power circuit model• Validate results using test grid

Complete

To be done

Model of breakdown

Computations• Laplace’s Eq. on rectangular grid• 483 to 10,243 grid points• 32 processers, 1 hour maxAssumptions• Stochastic• Available electronPredictions• Breakdown initiation• Shape• Free path• Transition

Simulation predicts experimental shapes

Excellent correlation with a wide range of experimental results

Experiment Simulation

Computation of potential distribution

16

14

12

10

8

6

4

2

0

24222018161412108

0.94 0.94 0.92 0.9 0.88 0.86 0.84 0.82 0.8 0.78

0.76 0.74

0.72 0.7 0.68 0.66

0.64

0.62 0.6

0.58 0.56

0.54 0.52

0.5 0.48 0.46

0.44 0.42

0.4 0.38

0.36 0.34 0.32

0.3 0.28

0.26 0.24

0.22

0.2 0.18 0.16

0.14

0.1

2

0.12 0.1 0.08 0.06 0.04

0.02

Electric field structure becomescomplex during discharge propagation

Equivalent circuits

Post-breakdown

Pre-breakdown

Notional temporal behavior

Time

Magnit

ude

Pre-breakdown Post-breakdown

Circuit models can generate “experience base”

Insulation example Knowledge of insulation medium

Knowledge of an insulation component

Evaluation of a way to give a design criterion

Insulation Design StepsInsulation Design Steps

Material evaluationStatistical analysisHigh voltage testingDischarge phenomena researchMeasurement (aging, space charge, dielectric, partial discharge, etc.)

Supporting TechnologySupporting Technology

DesignStress

Evaluation of voltages applied to apparatus

E50 (Area, thickness, volume effect)==

x

Evaluation of influential factorson insulation performance

Database of ;

Insulation medium evaluation parametersResults of insulation component model and mock up model tests

Experiences and past records

Insulation coordinationElectromagnetic field computationElectromagnetic transient analysis

(1 - ns)

Deterioration factor

Temperature factor

Safety factor

Transients are critical

• Capacitors fail due to time at operating voltage• Other insulation fails under transient conditions

• Land-based• Switching surges• Lightning

• MVDS for ships• Likely switching surges• Expect switching surges to be different

• Lower inductance, higher capacitance, tighter connection to generators

Simulation of switching surges in ac ship systems

In ac systems, transients can be large. Likely smaller in MVDC, but power electronics have low tolerance for voltage spikes.

Test grid needed to validate modeling for future ships

• Response to transients• Ground faults• Series faults• Step load changes

• Response of particular interest• Surge generation due to stray inductance and filter capacitance• Transient circuit representation of faults• Transient circuit representation of capacitors• Power transients exceeding steady-state source ratings

• Interest due to surge effects• Insulation • Power electronics

Conclusions

1. Physics-based modeling of breakdown through air and across surfaces can provide necessary parameters for circuit simulations

2. Circuit simulations are critical to identify the sources, size, and occurrence frequency of transients in future ship power systems

3. Validations of simulations can be performed on model systems of sufficient complexity

4. The knowledge of the distribution of transients leads toa) Minimum cost and weight of insulation with predictable

reliabilityb) Appropriate protection for power electronic devices

5. Much more work is needed