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Design of Inverter Driven Induction Machines

Design of Inverter Driven Induction Machines

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Design of Inverter Driven Induction Machines

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  1. Design of Inverter Driven Induction Machines Daniel M. Saban, PE PhD saban@ieee.org

  2. Overview • The induction machine problem • Stakeholders & design drivers • Analysis & synthesis challenges • Design rules-of-thumb & constraints • Optimization and/or synthesis • Common tools • Selected approaches • Inverter system consideration • Opportunities

  3. Induction machine • Stakeholders and their perspectives • Customers • Sales & Marketing • Manufacturing Engineering & Operations • Application Engineering • Product Development • Opportunities • Materials: improved and exotic • Manufacturing processes and process control • Design, analysis and optimization tools • Size & Topology

  4. Induction machine • Temperature “is everything” • Material limits (life) • Insulation system • Bearing system • Material dependencies (performance) • Cooling system • Rules-of-thumb in design • Cost “is everything” • Operating cost: efficiency, power factor • Initial cost: better material, more material • Quality “is everything” • Performance “is everything”?

  5. IM analysis challenges • Non-linear: saturation, core losses • Winding harmonics • Rotor/Stator slotting & skewing • Material property variation (lot-to-lot) • Dimensional variation & shift • Manufacturing/assembly variation • Rotor resistance • End-leakage (consider frame) • High-frequency impedance (bearing currents)

  6. Proximity & Skin Effect • Fundamental current injected into conductors • 1 turn per coil; 4.0 kW loss/pole • 4 turns per coil; 2.5 kW loss/pole

  7. Slot Ripple Eddy Current • Current Sheet used to simulate total air-gap flux density • No current injected into conductors • Loss is due to induced eddy currents • Used to analyze effect of wire transposition and aspect ratio

  8. IM design synthesis • Clean sheet • Single application • Product family • Existing laminations • Brute Hp vs. finesse

  9. IM design synthesis challenges • Knowns • Full stator slots • High conductivity conductors • Small gap? • Unknowns • Rotor & stator aspect ratios • Slot shape details • Discrete values only • Pole count • Discrete wire sizes, non-linear cost function • Winding details: number of turns, coils, pitch • Integral numbers of slots, rotor/stator • Lamination material, grade, thickness

  10. Rules-of-thumb • Stator current density • 620 A/cm2 to 1 kA/cm2 • Highly dependant on cooling system • Revise after thermal modeling • Peak flux density of stator teeth, yoke • ~1.7T, ~1.6T • Revise upward for more power density • Revise lower for higher efficiency • Rotor current density • Gap flux density: 0.5T to 0.8T

  11. Common Design Constraints • Rotor OD • Stator OD • Stack length • Machine construction • Cooling system

  12. design constraints mfg constraints matl props objectives IM design iteration Manual Iteration LP FE

  13. IM design tools • In-house • Typically only lumped parameter (LP) • May be tied to manufacturing or operations • Some “special” versions of commercial software • Commercial • LP: PC-IMD (SPEED), VICA (support?) • LP+FE: PC-IMD/FEA (SPEED), RMxprt (Ansoft) • MCM: ?? • FE: Magnet (Infolytica), (Flux, Maxwell) Ansys/Ansoft • System simulation: Matlab/Simulink, Simplorer (Ansoft), Easy 5

  14. design constraints mfg constraints matl props objectives stand output file stand input file LP MCM geom trans addl output files FE IM design optimization Optimization engine

  15. IM design optimization • Inverter driven machines • Pole count is now a free variable • Stator & Rotor lamination design optimization can be decoupled • Skewing penalizes machine • Finesse approach • Size machine, ignore details & discrete values • Create response surface & narrow search space • Optimize rotor and stator separately • Second pass takes into account discrete values • Requires dedicated code • Key design points: torque corner point, max speed, max torque • Best motor will deliver maximum torque for maximum drive current

  16. IM-Inverter system optimization • Max torque-speed envelope (output) • different than constant torque/power/slip • power factor and efficiency variations • Optimal motor leakage • Harmonic ripple current • Chopping frequency • Fundamental AC current • Peak transistor frequency

  17. Opportunity • Simple tools • When to apply vs. other technologies (IM vs. PM) • Rough sizing: stack length, stator od, rotor od • Fit of test data for lamination family, or single design • Models of different manufacturing techniques/defects • Stray load loss - rotor/stator harmonic interaction • Stator conductor eddy currents; large copper cross-section, high frequency • Vehicle to adapt academic work into industrial setting • Open source • Widespread use • Extensible framework