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Download Compact Device Modelling for System Simulation - Mos-AK
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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: p( x, t ) k ( x x1 ) pk (t ) cos x x 2 1 k 0 • 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 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 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 Device Matching - 1 • Full chopper cell • All parasitics required (especially stray inductances). • Initial fit by hand • Estimates of unknown parasitics and parameters. Device Matching - 2 • IGBT and diode parameter sets for compact models. Device Matching - 3 • Inductive switching shown here. • Instantaneous power dissipations • IGBT turn-on (left), IGBT turn-off shown to validate switching (right). energies. Device Matching - 4 • Inductive switching shown here. • Instantaneous power dissipations • IGBT turn-on (left), IGBT turn-off shown to validate switching (right). energies. Device Matching - 5 On-state (forward voltage) shown here. Turn-on Waveforms Given at different temperatures and load currents x-axis is time (us) Turn-off Waveforms Given at different temperatures and load currents x-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. EXTERNAL CONDITIONS Converter simulation Device temp. System modelling Look-up table LOSS DATA Simulation controller Power diss. Heatsink model Device modelling Compact models 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.
