AC induction motor - V/f control

In summary, if an error occurs in the voltage and frequency control of an AC induction motor while it is running, causing the stator frequency to drop below the rotor frequency for 1-2 seconds, the motor will attempt to return electrical power to its source, resulting in deceleration. The slip, or difference between the rotor and stator frequencies, will depend on the specific condition and formula used. Generally, a reduction in motor internal inductance due to frequency drop can cause a large current. This is similar to connecting an AC motor to a DC power supply. The presence of CEMF and the change in inductance due to stator frequency can also contribute to the current draw.
  • #1
earth_physics
7
0
What will happen if an ac inductions motor is running, an suddenly an error occurs in the voltage pr. hertz motor control so the stator frequency goes down below the rotor frequency for 1-2 sec?
 
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  • #2
the motor will attempt to return electrical power to its source, decelerating as it does so.

Keep your thinking simple.
What would be the slip under the condition you postulate?
What do yur formulas tell you about power vs slip?
 
  • #3
Okay thanks.
Let say the rotor frequency is 60Hz and the stator frequency suddenly become 2 Hz or 0 Hz(DC) in 1-2 sec the motor will generate a lot current?

Lets say your AC motor accelerate from stand still and your voltage and frequency is controlled properly, but suddenly the frequency (an error occur) is not proper compared to the voltage (V/f ratio). The stator frequency are still in front compared to rotor frequency. Do the AC motor draw a big current?
 
  • #4
Condition of rotor is not important in this case. When the frequency of power supply drops close to zero without any voltage reduction, this case is same that you connect an ac motor to the dc power supply. Generally reduction of motor internal inductance due to frequency drop (Xl=2*pi*f) can be caused a big current.
 
  • #5
Okay. if the this happens in 1 sec or less etc. Does the motor still draw a big current?

How about if this happens while the motor is running does it still draw a big current because now the motor produce CEMF? the inductance value does not only change by stator frequency.
 

1. What is an AC induction motor?

An AC induction motor is a type of electric motor that converts electrical energy into mechanical energy. It is commonly used in industrial and consumer applications, and is known for its reliability, simplicity, and low cost.

2. What is V/f control?

V/f control, also known as Volts-per-Hertz control, is a method of controlling the speed of an AC induction motor by adjusting the voltage and frequency of the power supply. This is done to maintain a constant ratio of voltage to frequency, which is necessary for the motor to operate efficiently.

3. How does V/f control work?

V/f control works by varying the frequency of the power supply to the motor in proportion to the voltage. This allows the motor to maintain a constant magnetic flux, which is necessary for the motor to operate at its rated speed. As the frequency increases, the motor will run faster, and as the frequency decreases, the motor will run slower.

4. What are the advantages of using V/f control?

There are several advantages to using V/f control for AC induction motors. It allows for smooth and precise control of motor speed, thereby improving the overall efficiency of the motor. It also helps to reduce wear and tear on the motor, leading to a longer lifespan. Additionally, V/f control is a cost-effective solution for speed control compared to other methods.

5. Are there any limitations to V/f control?

V/f control is not suitable for high-performance applications that require precise speed control, as it does not provide the same level of accuracy as other control methods such as vector control. It is also not recommended for use with variable torque loads, as it may result in motor overheating. Additionally, V/f control is not effective for controlling the direction of rotation of the motor, as it only controls the speed.

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