need to Synchronize 2 VFDs driving 2 AC motors

[assadmahmood]

GREETINGS EVERYBODY!
I have 2 VFDs driving 2 different motors, each VFD is driving a single motor.

There is a little difference between both the motors.

I used potentiometer (variable resistor) in VFD to change the speed of the motor. for 2 VFDs 2 variable resistors are being used.

Now the thing is I have to control this all by a single variable resistor in such a manner that both motors should have same speed. Is there anyway to do so?

Many thanks for your kind consideration.

 

[chuckey]

Measure the voltage on each terminal of the pot with respect to earth. Most VFDs put out 10 V and earth across the pot with the centre connection feeding back the voltage , so 5V = 50%, 7V = 70 % etc. So ascertain what each VFD is feeding out and what it needs to be fed back in for any given speed. There might be some irregularities, i.e. 4 V = 38 % full speed on one and 43% full speed on the other, can you put up with this?.
Once you have understood what is required, the easiest way is to call one pot the master. Undo the connection to the slider contact and put a 10K resistor in series with the lead. Try out the master, it could be running a little bit slower, if its satisfactory, then connect the "voltage in" (slider) of the second VFD to the master slider via a 10 K resistor, with any luck it should work OK.
If the two VFDs use different voltages or their voltages are referred to some thing other then earth (say, 20V and 35 V with 1/2 speed = 27.5V), then a more complex solution would be required.
Frank

 

[FvM]

Feeding both VFDs with the same 0 - 10V setpoint signal will make them run at same nominal speed. Different motor parameters can be compensated by fine adjusting VFD parameters, e.g. setpoint scaling. But it's never exactly "synchronizing".

 

[nikhil90490]

Measure the voltage on each terminal of the pot with respect to earth. Most VFDs put out 10 V and earth across the pot with the centre connection feeding back the voltage , so 5V = 50%, 7V = 70 % etc. So ascertain what each VFD is feeding out and what it needs to be fed back in for any given speed. There might be some irregularities, i.e. 4 V = 38 % full speed on one and 43% full speed on the other, can you put up with this?.
Once you have understood what is required, the easiest way is to call one pot the master. Undo the connection to the slider contact and put a 10K resistor in series with the lead. Try out the master, it could be running a little bit slower, if its satisfactory, then connect the "voltage in" (slider) of the second VFD to the master slider via a 10 K resistor, with any luck it should work OK.
If the two VFDs use different voltages or their voltages are referred to some thing other then earth (say, 20V and 35 V with 1/2 speed = 27.5V), then a more complex solution would be required.
Frank

hey buddie can plz tell what will be the wiring diagram for this

 

[schmitt trigger]

GREETINGS EVERYBODY!
I have 2 VFDs driving 2 different motors, each VFD is driving a single motor.

There is a little difference between both the motors.

Do they have the same slip? Will they drive an IDENTICAL load?
Remember, an induction motor's mechanical speed will ALWAYS be lower than the rotation of the magnetic field.
That is the slip, and it varies with motor load. And the motor load itself may be nonlinear with speed.

Therefore, you could dial in the exact same control voltage, but still end up with several RPM difference.

 

[D.A.(Tony)Stewart]

Select the proper control mode.
VFD control mode choice greatly depends on the application.

The three VFD control modes are volts-per-Hertz (V/Hz), sensorless vector (sometimes called open-loop vector), and closed-loop.

Closed loop has the best speed regulation, but for perfect sync you need phase control and frequency control.