IGBT

Implement insulated gate bipolar transistor (IGBT)

Library

Power Electronics

Description

The IGBT block implements a semiconductor device controllable by the gate signal. The IGBT is simulated as a series combination of a resistor Ron, inductor Lon, and a DC voltage source Vf in series with a switch controlled by a logical signal (g > 0 or g = 0)

The IGBT turns on when the collector-emitter voltage is positive and greater than Vf and a positive signal is applied at the gate input (g > 0). It turns off when the collector-emitter voltage is positive and a 0 signal is applied at the gate input (g = 0).

The IGBT device is in the off state when the collector-emitter voltage is negative. Note that many commercial IGBTs do not have the reverse blocking capability. Therefore, they are usually used with an antiparallel diode.

The IGBT block contains a series Rs-Cs snubber circuit, which is connected in parallel with the IGBT device (between terminals C and E).

The turnoff characteristic of the IGBT model is approximated by two segments. When the gate signal falls to 0, the collector current decreases from Imax to 0.1 Imax during the fall time (Tf), and then from 0.1 Imax to 0 during the tail time (Tt).

Dialog Box and Parameters

Resistance Ron

The internal resistance Ron, in ohms (Ω). The Resistance Ron parameter cannot be set to 0 when the Inductance Lon parameter is set to 0.

Inductance Lon

The internal inductance Lon, in henries (H). The Inductance Lon parameter is normally set to 0 except when the Resistance Ron parameter is set to 0.

Forward voltage Vf

The forward voltage of the IGBT device, in volts (V).

Current 10% fall time

The current fall time Tf, in seconds (s). This parameter is not modeled when the Enable use of ideal switching devices parameter of the Powergui block is selected.

Current tail time

The current tail time Tt, in seconds (s). This parameter is not modeled when the Enable use of ideal switching devices parameter of the Powergui block is selected.

Initial current Ic

You can specify an initial current flowing in the IGBT. It is usually set to 0 in order to start the simulation with the device blocked.

If the Initial Current IC parameter is set to a value greater than 0, the steady-state calculation considers the initial status of the IGBT as closed. Initializing all states of a power electronic converter is a complex task. Therefore, this option is useful only with simple circuits.

Snubber resistance Rs

The snubber resistance, in ohms (Ω). Set the Snubber resistance Rs parameter to inf to eliminate the snubber from the model.

Snubber capacitance Cs

The snubber capacitance in farads (F). Set the Snubber capacitance Cs parameter to 0 to eliminate the snubber, or to inf to get a resistive snubber.

Show measurement port

If selected, add a Simulink® output to the block returning the diode IGBT current and voltage.

Inputs and Outputs

g

Simulink signal to control the opening and closing of the IGBT.

m

The Simulink output of the block is a vector containing two signals. You can demultiplex these signals by using the Bus Selector block provided in the Simulink library.

Signal

Definition

Units

1

IGBT current

A

2

IGBT voltage

V

Assumptions and Limitations

The IGBT block implements a macro model of the real IGBT device. It does not take into account either the geometry of the device or the complex physical processes [1].

Depending on the value of the inductance Lon, the IGBT is modeled either as a current source (Lon > 0) or as a variable topology circuit (Lon = 0). The IGBT block cannot be connected in series with an inductor, a current source, or an open circuit, unless its snubber circuit is in use.

Use the Powergui block to specify either continuous simulation or discretization of your electrical circuit containing IGBT blocks. When using a continuous model, the ode23tb solver with a relative tolerance of 1e-4 is recommended for best accuracy and simulation speed.

The inductance Lon is forced to 0 if you choose to discretize your circuit.

Example

The power_igbtconvpower_igbtconv example illustrates the use of the IGBT block in a boost DC-DC converter. The IGBT is switched on and off at a frequency of 10 kHz to transfer energy from the DC source to the load (RC). The average output voltage (VR) is a function of the duty cycle (α) of the IGBT switch:

VR=11αVdc

In our example, α = 0.5 so that the theoretical value of VR is 200 V, assuming no voltage drop across the diode and the IGBT.

Run the simulation and observe the inductor current (IL), the IGBT collector current (IC), the diode current (ID), the IGBT device collector-emitter voltage (VCE), and the load voltage (VR).

The load voltage (197 V) is slightly lower than the theoretical value (200 V) mainly because of the forward voltage (Vf) of the diode (0.8 V) and of the IGBT (Vf = 1 V).

References

[1] Mohan, N., T.M. Undeland, and W.P. Robbins, Power Electronics: Converters, Applications, and Design, John Wiley & Sons, Inc., New York, 1995.

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