Compact IGBT Modelling for System Simulation

Philip Mawby

Angus Bryant

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

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)

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.

0 12

1)(cos)(),(

kk xx

xxktptxp

General arrangement of CSR and depletion layer during turn-off

Model Capabilities

• Temperature-enabled• Proven capability from –150°C to +150°C.

• IGBT structures:• 2-D effects (gate structure) accounted for• Buffer layer enabled: choice of NPT/PT

(including FS/SPT devices)• Local lifetime control enabled

IGBT Model Outline

Carrier storage region (CSR) with Fourier series solution

Depletion layer equations

Classic MOSFET model

Miller capacitance

Base region resistance(conductivity modulation)

Emitter recombination (injection)

Kelvin emitter inductance

Device Matching - 1

• Full chopper cell • Initial fit by hand

• All parasitics required (especially stray inductances).

• Estimates of unknown parasitics and parameters.

Device Matching - 2• IGBT and diode

parameter sets for compact models.

Device Matching - 3

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

(right).

• Instantaneous power dissipations shown to validate switching energies.

Device Matching - 4

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

(right).

• Instantaneous power dissipations shown to validate switching energies.

Device Matching - 5

On-state (forward voltage) shown here.

Turn-on Waveforms

Given at different temperatures and load currentsx-axis is time (us)

Turn-off Waveforms

Given at different temperatures and load currentsx-axis is time (us)

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.

Look-uptable

LOSS DATASimulation controller

Compact models

Converter simulation

Heatsink model

Device temp. Power diss.

System modelling

Device modelling

EXTERNALCONDITIONS

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).

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.

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.