Compact IGBT Modelling for System Simulation

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Compact IGBT Modelling for System Simulation

• Philip Mawby
• Angus Bryant

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Background

• Compact modelling of IGBTs and diodes
• Warwick and Cambridge Universities, UK
• Collaboration with University of South Carolina,
  USA
• Developed for MATLAB/Simulink, PSpice
• Integrated device optimisation parameter
  extraction in MATLAB
• Proven for a wide range of devices conditions
• Includes full temperature dependency

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Compact Device Models

• Excess carrier density modelled
• Critical to on-state and switching behaviour
• Ambipolar diffusion equation (ADE) describes
  carrier density distribution
• Fourier series used to solve ADE
• Boundary conditions set by depletion layers, MOS
  channel, emitter recombination, etc.
• Implemented in Simulink
• Block-diagram form (including circuit)
• Chopper cell circuit (inductive switching)

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Model Details

• Excess carrier density (stored charge) is
  one-dimensional for 90 of CSR.
• Fourier series solves 1D carrier density p(x,t)
  in CSR
• Fourier terms pk(t) solved by ordinary
  differential equations
• Boundary conditions CSR edges x1,x2 and
  gradients dp/dx (set by currents).
• Depletion layer voltage Vd2 provides feedback to
  keep p(x2)0.
• Classic MOS model used to determine e- current
  In2.

General arrangement of CSR and depletion layer
during turn-off
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Model Capabilities

• Temperature-enabled
• Proven capability from 150C to 150C.
• IGBT structures
• 2-D effects (gate structure) accounted for
• Buffer layer enabled choice of NPT/PT (including
  FS/SPT devices)
• Local lifetime control enabled

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IGBT Model Outline
Base region resistance (conductivity modulation)
Emitter recombination (injection)
Carrier storage region (CSR) with Fourier series
solution
Depletion layer equations
Classic MOSFET model
Miller capacitance
Kelvin emitter inductance
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Device Matching - 1

• Full chopper cell
• Initial fit by hand

• All parasitics required (especially stray
  inductances).
• Estimates of unknown parasitics and parameters.

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Device Matching - 2

• IGBT and diode parameter sets for compact models.

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Device Matching - 3

• Inductive switching shown here.
• IGBT turn-on (left), IGBT turn-off (right).

• Instantaneous power dissipations shown to
  validate switching energies.

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Device Matching - 4

• Inductive switching shown here.
• IGBT turn-on (left), IGBT turn-off (right).

• Instantaneous power dissipations shown to
  validate switching energies.

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Device Matching - 5

• On-state (forward voltage) shown here.

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Turn-on Waveforms

• Given at different temperatures and load currents
• x-axis is time (us)

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Turn-off Waveforms

• Given at different temperatures and load currents
• x-axis is time (us)

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Power Converter Modelling

• IGBT model used in full converter modelling
• Simulation of every switching event is too
  time-consuming.
• Look-up table of losses is used instead
• Generated from device models in MATLAB/Simulink.
• Gives losses as a function of load current and
  temperature.
• Simple converter/heatsink model then simulates
  device temperature.
• Rapid and accurate estimation of device
  temperature for whole load cycle.

Simulation controller
Converter simulation
Look-uptable
EXTERNAL CONDITIONS
LOSS DATA
Device temp.
Power diss.
Compact models
Heatsink model
System modelling
Device modelling
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Look-up Table of Losses

• IGBT power losses (W) for whole switching cycle
  plotted as a function of load current (A), duty
  ratio and temperature (C).

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Full System Simulation

• Example is hypothetical electric vehicle, running
  standard Federal Urban Driving Schedule.
• Simple drive model gives inverter electrical
  conditions.
• Resulting IGBT temperature profile plotted in
  relation to the vehicle speed.
• Peaks in temperature correspond to
  acceleration/deceleration.

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Conclusions

• Accurate modelling of device losses
• Temperature-enabled
• Proven over a wide range of conditions
• Model can be used to predict behaviour
• Already demonstrated with integrated
  optimisation.
• Integration with system simulation.
• Whole system runs in MATLAB and Simulink.
• Look-up table decouples device and system
  simulation.
• Future work will investigate device reliability
• Based on device temperature profiles and thermal
  cycling data for device packaging.