Design of Inverter Driven Induction Machines. Daniel M. Saban, PE PhD

Transcription

1 Design of Inverter Driven Induction Machines Daniel M. Saban, PE PhD

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 2

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 3

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? 4

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) 5

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 6

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 7

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

9 Knowns IM design synthesis challenges 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 9

10 Stator current density Rules-of-thumb 620 A/cm 2 to 1 ka/cm 2 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 10

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

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

13 In-house IM design tools 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 13

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

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 15

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 16

17 Simple tools Opportunity 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 crosssection, high frequency Vehicle to adapt academic work into industrial setting Open source Widespread use Extensible framework 17