1. What does V/f mode mean?
The voltage V also decreases proportionally as the frequency decreases. This problem has been explained in answer 4. The proportional relationship between V and f is predetermined in consideration of the characteristics of the motor. Usually, there are several characteristics in the memory device (ROM) of the controller, which can be selected by a switch or a dial.
2. How does the torque of the motor change when V and f are changed proportionally?
When the frequency drops, the voltage is completely proportionally reduced, and the motor will tend to reduce the torque generated at low speeds. Therefore, given V/f at low frequencies, the output voltage is increased somewhat in order to obtain a certain starting torque, which is called an enhanced starting. It can be implemented in various ways, such as an automatic method, selecting a V/f mode, or adjusting a potentiometer.