Turn-on of the N-channel IGBT

Hello,

I am trying to simulate a very simple circuit consisting of a DC voltage source (300 V), a resistor (10 ohm) and an N-channel IGBT, the emitter of which is grounded. In the settings of the IGBT, I have selected Fundamental non-linear equations for I-V characteristics and I hace specified a gate-emitter threshold voltage of 6 V. The gate driver voltage varies between -15 V and 15 V and the switching frequency is 10 kHz. However, when gate-emitter voltage exceeds the voltage, the IGBT does not start to conduct. It starts to conducyt only in the Miller region. I do not understand why it is happening. Can you please explain why it is happening ? I have attached herewith the relevant waveforms.

Khaled

[Joel Van Sickel]

In the model you are showing, the IGBT does start conducting, but it is conducting at 10V instead of 6V, is that where the confusion lies? Can you share your model and the full list of parameters you used for the n-channel IGBT?

[Khaled]

Hi Joel,

Yes, this is where my confusion lies. I believe it should start conducting as soon as Vge crosses 6 V. Please find attached the model herewith. All the parameters are given in the IGBT (behavioural model).

Best regards,

Khaled

[Khaled]

Hi Joel,

Any update regarding my query ?

Best regards,

Khaled

[Mohsen Aleenejad]

Hi Khaled,

The IGBT switch turns on after a certain delay when Ve is reater than 6V (the red waveform below). I changed the Gate-emitter threshold voltage from 6V to 10V (the blue waveform), and there is the similar delay in here. I'l need to spend a little more time on this to figure out a relation that calculatesthis delay. I'll get ack to you soon.

Answer 1

[Mohsen Aleenejad]

Are you sure those parameters in the N-Channel IGBT were set properly?

This happens due to the parameters you set for your IGBT, I've used the default switch parameters and the V_ce start to fall down right when Vge==6V:

The orange is default switch, blue is your parameters.

[Khaled]

Hi Mohsen,

I think the orange/red line is for my parameters and the blue line is for the default parameters. Can you please tell me what the default parameters are ? My understanding is that the IGBT will start to conduct as soon as the Vge crosses the threshold, irrespective of the parameters, atlest in the circuit I have provided. Also, I have taken my parameters from a datasheet which I have attached herewith.

Best regards,

Khaled

[Mohsen Aleenejad]

Sorry for the confusion in the colors, the red V_ge and blue V_ce are the waveform with the default N-Channel IGBT parameters, the other two are with your datasheet parameters.

My understanding is that the IGBT will start to conduct as soon as the Vge crosses the threshold, irrespective of the parameters,

Not necessarily, at least not with the parameters you have used from the datasheet. There will be an internal gate resistance, RG, which in this case is 1.2 ohms, between the external gate node and the internal gate node.

The gate resistance and gate capacitance will construct an RC circuit. The IGBT will start to conduct when the voltage between the internal gate node and internal emitter node is greater than 6V.

Hence, you will see a delay for the IGBT to conduct from the external gate emitter node.

This behaviour is expected. The configuration of the IGBT block can be seen in the document below.

https://www.mathworks.com/help/sps/ref/nchanneligbt.html

I hope this answers your question.