A question about the SpeedFit simulation tool

HUST_Ma

When I use the simulation tool with the application of 'Three Phase 2-Level Inverter', and set the detailed parameters as the Fig.1 showing below, it can be seen that the RMS current is calculated to 21.487A. But actually, the phase current(RMS) of 3P2L inverter under the provided parameters should be 30.387A, which is consistent with the result in the Fig.2. So could you please tell me what is the RMS current 21.487A referred to, and how to get this calculation result? I will be pretty grateful if the technical expert can give me a reply. Thank you.

Fig.1

Fig.2

Forum_Moderator

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Mhusain

Hello,

You are correct that with your settings, the RMS phase current will be 30.387 A. However, it's important to note that the device conducts only for half of the time. Therefore, we can approximate that the current flowing through one device in a leg resembles a half sine wave.

For a half sine wave, the RMS value is given by Ipeak/2. In this scenario, the RMS current through the device can be calculated as:

RMS Device Current = (RMS Phase Current) / sqrt (2)

This results in:

30.387 A / sqrt (2) ~ 21.49A

Thus, the quantity mentioned in the SpeedFit's Devices section refers to the RMS device current. You can also see this reflected in the simulation section, where the MOSFET RMS current is recorded as 21.477 A.

If you have any further questions, please feel free to ask.

Best regards