Question

Choose the most correct Voltage vs. Frequency plot of a 3-phase variable speed Induction motor drive at constant flux operation

• A. \includegraphics[width=2.5cm]{110.1.JPG}
• B. \includegraphics[width=2.5cm]{110.2.JPG}
• C. \includegraphics[width=2.5cm]{110.3.JPG}
• D. \includegraphics[width=2.5cm]{110.4.JPG}

Hint:

For constant flux in induction motors: Maintain \( \frac{V}{f} = \text{constant} \) up to rated frequency. Beyond rated frequency, operate in field weakening mode.

Answer 1

The Correct Option is D

For constant flux operation of an induction motor:
- Flux \( \phi \propto \dfrac{V}{f} \)
- To maintain constant flux, the voltage \( V \) must vary linearly with frequency \( f \) until rated conditions.
- After rated frequency, voltage is kept constant while frequency increases, leading to field weakening operation.
Thus, the correct plot is:
- A straight-line rise in \( V \) with \( f \) up to rated frequency,
- Followed by constant \( V \) for \( f>f_{\text{rated}} \)