Assistance Needed – Negative Input Power in Simulink Model

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Fsquared
Fsquared 2025-9-22
回答： TARUN 2025-9-26
Hello everyone,
I am currently simulating a model of an induction motor in Simulink, but I am encountering an issue where the input power is showing negative values. I have attached the model for your reference.
Could you please help me understand what might be causing this behavior and suggest possible solutions to resolve it?
Thank you for your assistance.
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Walter Roberson
Walter Roberson 2025-9-23
Which scope output should we be focusing on, as evidence of the input power showing negative values?

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回答（2 个）

Sabin
Sabin 2025-9-25
The instantaneous power measurement assumes that both voltages and currents are referenced to the same point. However, in the attached model the computation is done using phase currents and line voltages. Therefore, the incorrect calculation.
TARUN
TARUN 2025-9-26
Hi @Fsquared,
The negative input power is due to a mismatch in your measurement signals. The instantaneous power block expects phase-to-neutral voltages with phase currents, but in your model, you’ve connected line-to-line voltages with phase currents, which leads to incorrect results.
To fix this, you can:
• Use phase-to-neutral voltages (Va, Vb, Vc) instead of line voltages.
• If only line voltages are available, convert them to phase voltages before feeding them into the power calculation.
This should give you the correct positive power that matches your motor’s shaft power (torque × speed).

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