Session 3 – Ship Electric Power Systems 10 of the Topics at UT Austin Prof. Mack Grady, ECE Dept.

Topic 1. Load Modeling for Stability Studies Every time there is a thunderstorm, you get voltage sags on the transmission grid The power electronic loads on nearby feeders momentarily drop out, giving us a chance to determine their net MW and observe their response to voltage deviations We have carefully studied field data, plus lab-created experiments, and now have load models for nonlinear loads that are suitable for traditional power grid stability studies. Voltage sag Extracted power electronic load current component Key Findings: On utility feeders, the net single-phase power electronic load is 5-15% For PSSE stability simulations of the UT Austin 80MW system, we find that the impact of these loads is “stability friendly” for 3-cycle disturbances, but “stability unfriendly” for 6-cycle or longer disturbances. Extracting the power electronic load

Topic 2. Harmonics Testing Station and Nonlinear Load Modeling 5% V7, Peaky 5% V7, Flattened Precision voltage waveform control with feedback. Portable. LabView based 1kW inverter provides (or eliminates) the harmonic distortion, while the 60Hz building voltage provides the bulk of the load power. Thus, a compact design. Real-time synching with the grid frequency is part of the Jacobian-based feedback. Can produce practically any complex voltage waveform – single or multiple harmonics, or sinusoidal. Repeatedly. The interaction between harmonic voltage and load current can be analyzed. Results – Touted Norton-based models for nonlinear loads do not work. Better to assume simple harmonic current injection. Feedback Inverter output summed with building voltage

Motivation –Copious amounts of interharmonics generated by nonlinear multi-frequency power electronic devices, e.g., adjustable speed drives (ASDs) –Small amplitude interharmonics can be harmful to the shipboard system. Objective –Assess interharmonic-related PQ problems in a more quantitative way Approach –Utilize higher-order-statistical (HOS) signal processing Excitation of a 14 Hz natural frequency of an offshore platform turbine-generator by a 14 Hz interharmonic current frequency From M. Hernes, SINTEF Energy Research, September 2003 Achievements –Developed robust detection methods for interharmonics generated by ASDs –Developed ASD condition monitoring methods based on the unique interharmonic signatures of ASDs –Developed interharmonic-caused light-flicker assessment methods for LEDs and CFLs Topic 3. Interharmonic Detection and Analysis

 Motivation As machines degrade, they often tend to become progressively more nonlinear Classical power spectra can not quantify the multi-frequency phase coupling associated with nonlinear interactions  Objective To provide new nonlinear signatures of and physical insight into the degradation of rotating machines  Approach Higher-Order Spectral (HOS) Analysis  Achievements Improve conventional HOS approach by utilizing the bicoherence Discriminate between intrinsic nonlinearities of a healthy machine and fault-induced nonlinearities Resolved several practical issues related to applying HOS to condition monitoring of rotating machines Quantify the strength of the nonlinear interactions by estimating complex coupling coefficients Topic 4. Machine Condition Monitoring Diagnostic Experimental setup used to evaluate the effectiveness of our new HOS-based approach (Induction motor)(DC generator) Accelerometer Variable Resistor

Topic 5. Impact of Pulse Loads on Electric Ship Power Systems, With and Without Flywheel Energy Storage Systems FESS reduces disturbances on the generator and propulsion motor during pulse load operation Initial Results * PSCAD/EMTD model

 Architecture of shipboard NGIPS Generators Breakers Propulsion Transformers Rectifiers Filter Motor Drive Propulsion Motor Energy storage Ship Electric Power System UT Activities: Topic 6 AC distribution model (as built in Matlab/Simulink) GOAL Re-build AC and DC models with independent solvers Conduct analyses using multi-processor machines Status: Started work on solutions of component models DC distribution model

Ship Electric Power System UT Activities: Topic 7  Prime power generation studies  Prime mover type Gas turbines Diesel engines  Coupling method Gear boxes Direct  Electric generator type Wound-field Permanent-magnet Superconducting  Power conversion  DC output  Variable AC output MT30 LM2500 LM1600 MT5 Fuel consumption during 24-h mission for DDG MW genset System performance System size Analyses 24 possible topologies Analyzed 1 possible topology Plan to select and analyze other topologies

Ship Electric Power System UT Activities: Topic 8  Ship IPS components: Electric machine models + pλdpλd LmdLmd RkdRkd L kd RfRf LfLf LlLl LmqLmq RkqRkq L kq + - pλqpλq VfVf idid ifif iqiq i kq i kd LlLl d-axis q-axis Previous work: dq model implemented in Simulink for study of balanced systems Stationary 3-axis synchronous machine model On-going work: Develop solution using Fortran 90/95/2003 Build code so that it can run on multi-processor machines Obtain solution on PC first Run on supercomputers with system model dq model of synchronous wound-field generator Inductance matrix: Modeling effort focuses on capturing and exploring fundamental assumptions as well as solution software

Ship Electric Power System UT Activities: Topic 9  Ship IPS components: 100 MJ Energy storage module Rectifier Alternator (wound-field w/ 2 dampers) Inverter (equations for 1 leg only) Flywheel dynamics Breaker Charging motor (Simple pm synchronous, no dampers) Detailed performance model valid for a range of applications

Ship Electric Power System UT Activities: Topic 9, cont.  Ship IPS components: Energy storage module Example run Component models provide good system understanding showing flywheel storage well suited for ship applications

Ship Electric Power System: UT Activities: Topic 10  MVDC, MVAC, and HFAC system simulation COTS baselines Work to be coordinated with ESRDC team members InverterRectifier PrimeMover PrimeMover DC/DC DC/AC Prop Motor Gen Aux Gen Energy Storage Charge Discharge Loads Main Power Distribution Ship Service Power High Pulse Power Loads Added to baseline 5 kVDC Fuel THE EXPLORATION OF MVDC REQUIRES ADDING PRACTICAL COMPLEXITY TO THE BASIC PROBLEM

Questions?