IGBT modeling method and circuit simulation method

A circuit simulation method, in which an IGBT piece-wise line model is used to describe characteristics of a commutation loop, the method comprising:

• forming a two-port network based on an IGBT, a freewheel diode and stray inductance in a commutation loop, wherein voltages and currents of each of an input port and an output port of the two-port network is determined according to a direction of an output current:
• if the output current flows out of the two-port network, the voltage of the input port equals a direct current (DC) bus voltage VDC and the current of the input port equals the collector current ic, while the current of the output port equals a load current IL and the voltage of the output port equals VDC-vce, vce is a collector-emitter voltage;
• if the output current flows into the two-port network, the voltage of the input port equals the DC bus voltage VDC and the current of the input port equals ic-IL, while the current of the output port equals the load current IL and the voltage of the output port equals the collector-emitter voltage vce;
• obtaining a relationship between (vce, ic) and (VDC, IL, sw) in each period during a switching-on transient and a switching-off transient based on the IGBT piece-wise line model,
• wherein sw represents an IGBT switching signal, and
• the IGBT piece-wise line model is obtained by:
• creating first piece-wise line functions describing a collector-emitter voltage vce, a collector current ic and a gate-emitter voltage vge of the IGBT during a switching-on transient based on an internal structure of the IGBT and transient processes of the IGBT, wherein creating the first piece-wise line functions comprises:
• determining various periods during the switching-on transient of the IGBT, wherein the switching-on transient, which is after receipt of a turn-on signal and before a steady on-state, is divided into four on periods:
• a first on period starts when a gate drive sends the turn-on signal and ends when ic begins to rise, a second on period starts when ic begins to rise from 0 and ends when ic reaches a maximum value, a third on period starts when ic reaches the maximum value and ends when ic falls back to a load current, and a fourth on period ends when vce falls back to a saturation voltage;
• and
• determining starting values and ending values of each of the collector-emitter voltage vce, the collector current ic and the gate-emitter voltage vge during the four on periods of the switching-on transient and a duration of each of the first on period, the second on period, the third on period and the fourth on period based on the transient processes of the IGBT, thereby determining the collector-emitter voltage vce, the collector current ic and the gate-emitter voltage vge during each of the first on period, the second on period, the third on period and the fourth on period as a linear function or an exponential function, and
• creating second piece-wise line functions describing the collector-emitter voltage vce, the collector current ic and the gate-emitter voltage vge of the IGBT during a switching-off transient based on the internal structure of the IGBT and the transient processes of the IGBT, wherein creating the second piece-wise line functions comprises:
• determining various periods during the switching-off transient of the IGBT, wherein the switching-off transient, which is after receipt of a turn-off signal and before a steady off-state, is divided into four off periods:
• a first off period starts when the gate drive sends the turn-off signal and ends when vce begins to rise, a second off period starts when vce begins to rise from the saturation voltage and ends when vce reaches a DC bus voltage, a third off period starts when ic begins to fall from the load current and ends when ic falls to a tail current initial value, and a fourth off period ends when ic falls to 0;
• and
• determining starting values and ending values of each of the collector-emitter voltage vce, the collector current ic and the gate-emitter voltage vge during the four off periods of the switching-off transient and a duration of each of the first off period, the second off period, the third off period and the fourth off period based on the transient processes of the IGBT, thereby determining the collector-emitter voltage vce, the collector current ic and the gate-emitter voltage vge during each of the first off period, the second off period, the third off period and the fourth off period as a linear function or an exponential function;
• and
• adding the two-port network to a simulation circuit for computation.