David Sadey, Operation and Control of a Three-Phase Megawatt Class Variable Frequency (vf) Power Generation and Distribution System

David Sadey, Operation and Control of a Three-Phase Megawatt Class Variable Frequency (vf) Power Generation and Distribution System

• 1.
  DAVID SADEY, NASA Operationand Control of a Three-Phase Megawatt Class Variable Frequency (VF) Power Generation and Distribution System ILLUSTRATIONS BY WILLIAM CUTTER, VPL
• 2.
  OUTLINE • Fundamental Operationof a Doubly Fed Induction Generator (DFIG) • Terrestrial Application of the DFIG as a Frequency Converter • Standard Operation • Paralleling Procedure • Implementation of a 12MW VF Power System • Comparison vs. Standard VFDs • Conclusion
• 3.
  Fundamental Operation ofa DFIG • DFIG is a Wound Rotor Induction Machine (WRIM) • Fed Mechanical Shaft HorsePower (Hp) on the Rotor • Fed Electrical Power on the Rotor • Converts Both Rotor Power Quantities to Stator Power • Direction of Power Flow Can Vary Depending on Application
• 4.
  Fundamental Operation ofa DFIG • DFIG can be used as a Frequency Converter • Direct Control of the Shaft Speed allows for DFIG to act as a Frequency Transformer • Shaft Speed can be Controlled via DC Motor
• 5.
  Fundamental Operation ofa DFIG • Frequency Converter Examples (2-Pole) Rotor (Mech, RPM) Rotor (Elec, Hz) Stator (Elec, Hz) 0 RPM 60Hz CW 60Hz CW 3600RPM 60Hz CW 120Hz CW CW,(60Hz) 3600RPM 60Hz CW 0 CCW,(60Hz)
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  Fundamental Operation ofa DFIG • Rotor is Excited at a Constant Volts-per-Hertz (V/F) • Constant Flux ϕ in the Machine • Stator Output Voltage and Frequency Relationship Remains Constant over All Frequencies 𝑉𝑆1 𝑓𝑆1 = 𝑉𝑆2 𝑓𝑆2 = 𝑘𝑉𝑅 𝑓𝑅 ∝ ϕ VOLTS Hz
• 7.
  Terrestrial Application ofa DFIG as a Variable Frequency Drive • DFIG Fed 60 Hz Grid Power on the Rotor • DC Drive Motor Supplies Mechanical Shaft Hp and Regulates Rotor Speed • Process Load Machine is Speed Regulated by Frequency Regulation of the VF Bus. VFD LOAD
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  Power Capability ofTerrestrial Frequency Converter • Power Levels at the MW Level and Higher can be Obtained by Paralleling Multiple DFIGs • DFIGs Must Be of Equivalent Characteristics • Paralleling Achieved by Synchronization and Load Balance Procedures
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  Synchronizing Parallel Frequency Converters •Master DFIG is Selected, E.g. Master ‘A’ • Master Sequentially Drives Remaining ‘Slaves’ as Motors on VF Bus • DC Motors Speed Regulate Rotors for Synchronization on 60Hz Grid Side. Allows For Industrial Synchronizers to Be Used. • Synchronization Occurs When Voltage, Phase, and Frequency are Equal Across the Slave Synchronization Breakers.
• 10.
  Balancing Parallel FrequencyConverters • Synchronizing DFIGs does Not Guarantee Load Sharing • To Equally Share Load Among Generators, Armature Currents of the DC Drive Motors must be Equalized • Balanced within 1% of Master Rated Armature Current • Balancing Achieved by Bumping Slave Rotor(s) Accordingly • Armature Currents of Slaves are Actively Balanced at All Times after Initial Synchronization
• 11.
  Physical Implementation ofa 12MW Class VF Power System • NASA Glenn Research Center at Lewis Field has a 12MW Class VF DFIG Based Power System • System Consists of 10 1.2MW DFIGs which can be Run Individually or in Parallel • System Consists of Five Process Load Machines of Varying Hp
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  System One-Line Diagram
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  Variable Frequency Characteristics •*Converter Speed is Limited to -1100 RPM (5 Hz) • **Zero RPM (60 Hz) is Not Allowed
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  Loaded Test Results •Eight Machines Were Paralleled to Drive the Partially Loaded 15,000 Hp Machine
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  DC Armature CurrentBalance • DC Armature Currents of all Eight Machines Were Demonstrated to be in Balance During Operation
• 16.
  Rotor Current Balance •Acceptable Rotor Current Balance was Demonstrated
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  Stator Current (Output)Balance • Stator Current Balance was Demonstrated
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  Challenges and Limitations •Synchronizing and Paralleling Multiple DFIGs • Special Instrumentation is Needed In Certain Areas • Commercial Instrumentation has Bandwidth Limitations of 40-80Hz • Applies to Protective Relaying as Well • Low Frequency Machine Instability Limits System Frequency to 5Hz on Low End
• 19.
  Comparison with TraditionalVFDs • Pros vs. Traditional VFDs • System is Highly Configurable • Can Efficiently Run Multiple Sized Loads • Can Run Multiple Loads at any Given Time • System is Easily Expandable • Produces Pure, Three-Phase Power • No Harmonics on the VF Bus • Reduces Excess Heat and Torque Pulsations on Loads • Not Susceptible to rapid dV/dT and Wave Reflection Phenomenon
• 20.
  Comparison with TraditionalVFDs • Cons vs. Traditional VFDs • DFIG Based System is More Complex • Higher Maintenance and Operating Costs • Larger Footprint • V/F Ratio is Constant and Cannot be Altered • Fault Conditions Must Be Considered on Rotor Windings as Well as DC Drive Side
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  Conclusion and FutureWork • Unique Alternative to Standard VFD Technology • Can be Implemented for MW Class Systems and Higher • Expansion Easily Achieved by Adding Further DFIGs and by using Described Synchronizing and Paralleling Procedures • Effective for Systems with Multiple Large Hp Loads • Possible Alternative to Future Work on High Power Hybrid Electric Aircraft Systems
• 22.
  Questions? • Thanks toBill Cutter and Don Brown for Their Support and Contributions.