PULSED ALTERNATORS Scott Pish, Jon Hahne, Angelo Gattozzi Center for Electromechanics The University of Texas at Austin 8/14/17 Tutorial Objectives Iron-Core Compensated Pulsed Alternator • Provide a detailed understanding of rotating-machine-based pulsed power systems • Review the maturation of pulsed Twin Round-Bore alternator technology Railguns • Introduce technologies enabling SSFTP Pulsed Alternator increased power and energy density • Discuss shipboard integration Railgun & Resistive Load Presenters Mr. Scott Pish • Research Engineer, Program Manager • Manufacture & test of prototype rotating machines, • Design, analysis, & fabrication of composite structures • B.S. Mechanical Engineering 1996 Mr. Jon Hahne • Senior Engineering Scientist, Program Manager • Development, design, manufacture, and test of prototype rotating electrical machines. • B.S., Mechanical Engineering 1986 Dr. Angelo Gattozzi • Research Associate, IEEE Senior Member • Electric power system modeling and simulation, smart-grid/micro-grid systems, Navy power systems, high-speed motors/generators • Ph.D., Electrical Engineering and Applied Physics 1978 TECHNOLOGY BACKGROUND How We Got Here • Chinese technical literature credits the University of Texas researchers with the invention of the modern pulsed alternator • But pulsed alternators evolved, rather than were invented, through UT’s efforts to make rotating machines more power and energy dense (Motors, Generators, Energy storage) • Increasing power and energy density is a long term research objective of UT and requires advances in • Rotating machine design • Materials • Power electronics • Advanced controls All areas of traditional and growing expertise at UT’s CEM Power and Energy Density • Critical for ships and aircraft, both manned and unmanned, tracked and wheeled vehicles, & trains because the weight of the power system reduces the weight of the payload • Fundamental study of energy density by UT demonstrated that rotating machines most energy dense Energy Density Comparison Flywheel based on potential improvements using nano-composites Conventional composite flywheel From: “A FUNDAMENTAL LOOK AT ENERGY STORAGE FOCUSING PRIMARILY ON FLYWHEELS AND SUPERCONDUCTING ENERGY STORAGE” By: K.R. Davey R.E. Hebner Electric Energy Storage Applications and Technologies EESAT 2003 Conference Abstracts, SanFrancisco, California, U.S.A., October 27-29, 2003, Powering EM guns • EM guns have been successfully powered by • Rotating machines • Batteries • Capacitors • Inductors • The Army and Marines both developed EM guns for wheeled vehicles • Both were based on pulsed alternators as they provided the greatest power and energy density • The Navy chose a less power dense solution for their initial efforts • Likely that the Army pushed the power density beyond the Navy’s threshold CENTER FOR ELECTROMECHANICS UT-Austin Center for Electromechanics Prototype Manufacture and Assembly Over 140,000 ft2 of conditioned space for prototype manufacture & test EM Gun Research Provides Continuous Improvement • 9 MJ Task B Railgun • High-energy spin test bunker • 90mm bore, 10m long • Withstand 5 psi internal overpressure • 30” thick FRP reinforced concrete walls • Vertical Gun Range • SS mount structure, anchored to bedrock • 15 ft dia., 140 ft deep • 5M lb vertical & 20M ft-lb torque • Capacitor & rotating machine- • Gas Turbine Test Cell based PPS • EMI/RFI Screen Room for DAQ & controls Design and Testing of Power Systems 3MW, 15 krpm 4MW, 480MJ 2MW, 15 krpm Rotating Machines for Energy Storage Parameter NASA FESS ALPS System Bus System CHPS System Function Energy Storage Load Leveling Load Leveling Leveling/Pulsed Energy Stored (kWhr) 3.6 133 2 7 Peak Power (kW) 5 2,000 150 5,000 Typical Discharge Time 30 minutes ~ 3 minutes 30 seconds 3 seconds Rotational Speed (RPM) 53,000 15,000 40,000 20,000 Machine Weight (lbs) 250 19,000 450 1,100 Motor/Generator Permanent Magnet Induction Permanent Magnet Permanent Magnet Topology Partially Integrated Non-Integrated Partially Integrated Fully Integrated Cooling Cold Plate Air/Oil and Water Oil and Water Oil Bearings Homopolar Magnetic Hompolar Magnetic Homopolar Magnetic Homopolar Magnetic Backup Bearing Duty Limited Limited Significant Significant Gimbal NA (Torque Balanced) Required Required Required Flywheel Design CEM Cylindrical CEM Cylindrical CEM Cylindrical CEM Mass Loaded Rotor Tip Speed (m/s) 920 1,015 935 600 Safety RSL&NDE RSL & Containment RSL&Containment RSL Pulsed Power Testing Capacitor-based 12 MJ Pulse Forming Network (PFN) Railgun 4m long, 54mm square-bore Projectile Soft- Catch system Microgrid Facility Supports Navy and other research with new HIL & CHIL capability Providing solutions Prototype Navy EMALS generator developed at UT-CEM successfully transitioned to industrial partners for deployment • Developed system simulation models • Design, built, & tested the prototype generator • 20% lower mass & volume than commercially available power supplies PULSED ALTERNATOR TECHNOLOGY BASICS OVERVIEW Jon Hahne Center for Electromechanics The University of Texas at Austin 8/14/2017 Rotating Machines for Pulsed Power • Modular, multi-function systems • Combines Energy Storage + Pulse/Continuous Generation • High Power and Energy Density • Multiple pulse discharges with rapid recharge • Extended design/operational life • Technology Advancements Offer Potential for Higher Performance • Advanced composite materials • Composite arbors • Solid-state power electronics • Thermal management materials and techniques Core PA Technologies Extend to Other Rotating Machines Flywheel Topologies • ee Non-Integrated Topology Partially-Integrated Topology Fully-Integrated Topology • Larger than other topologies, but • Smaller and more efficient than non- • Most compact system may have most simple assembly integrated • Special purpose flywheel system • Maximum use of conventional M/G • Good use of available M/G technology, • Favors use of PM generator systems and technology but integration required • Heat generation on rotor requires • Flexible / adaptive design • Good design adaptability special engineering • Power generation outside of vacuum • Favors use of PM generator • Rotating magnets at large radius • Requires shaft seal and coupling • Heat generation on rotor requires careful engineering Non-Integrated Topology • Federal Railroad Authority – Advanced Locomotive Propulsion System • 480 MJ, 15 krpm flywheel • 3 MW motor/generator • Flex drive coupling interconnect UT-CEM Partially Integrated Topology • Transit Bus flywheel battery power system • 7 MJ, 40 krpm flywheel • 150 KW motor/generator • Flywheel & Electrical section • On common shaft • Inside vacuum enclosure UT-CEM Fully Integrated Topology • US Army Subscale Focused Technology Program pulsed alternator • 22 MJ, 12 krpm flywheel • Wound field coil • 2 GW peak delivered power • Energy storage in power generation section UT-CEM PULSED ALTERNATORS Pulsed Alternators Are: • A unique class of rotating electrical machines • Specifically designed for driving transient loads • A well-characterized and demonstrated technology • “Conventional” electrical devices with “Non-conventional” challenges • Mechanical design • Thermal design • Assembly processes Pulsed Alternator Options • Compulsator ?– Compensated Pulsed Alternator • Not all pulsed alternators are compensated • Specialized synchronous generators designed to minimize and control internal impedance • Inertial energy storage in spinning rotor • Capable of delivering MA output currents • Range of machine topologies enable flexible designs tailored for specific application(s) • Mission, platform, load • Design evolution primarily driven by need for higher power/energy density • Balance efficiency against power/energy density • Current SOA machines are self-excited, air core designs without explicit compensation Armature Compensation • Compensation: Methods used to control machine internal impedance • More critical for single phase, single-pulse machines • Determines output pulse characteristics • Three basic approaches to compensation: • Active – compensation provided by a secondary armature winding in series with the primary winding. This provides a sharp “peaky” pulse • Passive – compensation provided by continuous conductive shield between the field and armature windings; impedance independent of rotor position providing roughly sinusoidal output pulse • Selective Passive – compensation provided by shorted compensating windings; varying impedance with rotor position provides pulse shaping Compensation Increases Complexity and Technical Risk Multi-phase Air-Core Machines do not Require Explicit Compensation Synchronous Generator Operation • Voltage induced in each stator winding by passage of the rotating magnetic field created by the field winding 2 P As x B x L x D x w As – stator line current density B – air gap flux density L – length D – diameter w– angular velocity Brushless Synchronous Generator Exciter Field Voltage Regulator (Field Current Excitation Control) Power to Load Excitation Power Diesel Genset Input Gas Turbine Motor Power Input Steam Turbine Mechanical Torque • DC field excitation provided by exciter and rotating rectifier • Voltage regulator modulates exciter field current which in turn controls generator field current and thus the output voltage Brushed Synchronous Generator Voltage Regulator Excitation (Field Current Power Control) Input Power to Load Slip Rings And Brushes Diesel Gas Turbine Power Input Motor Mechanical Steam Turbine Torque