CEME708a_InvrtrDrvnIndctnMachn

7/30/2019 CEME708a_InvrtrDrvnIndctnMachn

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Design of Inverter Driven

Induction Machines

Daniel M. Saban, PE [email protected]


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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


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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


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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?


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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)


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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


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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


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IM design synthesis

Clean sheet

Single application

Product family

Existing laminations

Brute Hp vs. finesse


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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


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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


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Common Design Constraints

Rotor OD

Stator OD

Stack length

Machine construction

Cooling system


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Manual Iteration

IM design iteration

LP FE

matl propsdesign

constraints

mfg

constraintsobjectives


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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


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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 maximumdrive current


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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


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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

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CEME708a_InvrtrDrvnIndctnMachn