Design of Inverter Driven Induction Machines

1
Design of Inverter Driven Induction Machines

• Daniel M. Saban, PE PhD
• saban_at_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
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?)
• LPFE PC-IMD/FEA (SPEED), RMxprt (Ansoft)
• MCM ??
• FE Magnet (Infolytica), (Flux, Maxwell)
  Ansys/Ansoft
• System simulation Matlab/Simulink, Simplorer
  (Ansoft), Easy 5

14
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