Hi,
Power Electronics is not my normal forte however i have a small problem I hope you guys will point me into the right direction with.

I have 1 Inverter motor controller a Delta C2000 which controls up to 8 motors by switching (via an interface board) the a motor on and off. the motors can either be a standard 0.75kw 3 phase ac 50Hz motor or a 300Hz motor. The inverters carrier frequency is 8KHz (Default) but can be adjusted between 2KHz and 15KHz.

The control of the frequency is done via the inverter interface and the MCU (Beckhoff CX PLC).

My issue is my switching interface which consists of a standard relay.
The relay requires switching off 500ms after the inverter control signal is switched off or else I get arcing across the relay contacts which interferes with the etherCat system and causes frames to be missed affecting my servo motors.

As I require a faster switching system around 150-250ms rather than the 500ms at present can you suggest any way of creating a switching interface electronically that can switch these kinds of frequency and currents Triacs will not work at the carrier frequency.
Running current of both motors (when new) will draw between 1.0 and 1.5 amps when in normal operation.

Thanks in advance for any help

 

Generally it is not considered proper practice to switch the output of a VFD while output is present, there is usually interlocking implemented to ensure that the VFD is at zero output before switching the output to a different motor.
Max.

 

Generally it is not considered proper practice to switch the output of a VFD while output is present, there is usually interlocking implemented to ensure that the VFD is at zero output before switching the output to a different motor.
Max.

Hi, thanks for the reply however the VFD is switched off from the enable command, my issue is when i then switch the relay off I wait for 500ms before I efectively disconnect the motor via the relay off. I would like an electronic way of doing this
1) to reduce the time I can switch the "relay" off and
2) to remove the interference I get from arching on the relay contacts that interfere with the etherCat system.

The inverter cycle of 0.25 sec of decel with braking resister is still giving the arcing problem even at 400ms later when the relay switches off
What I am doing is good practice however I need to improve points 1) and 2).

 

I had a look at the Delta C2000 motor controller specs plus data sheets and everything in them says do not ever use them with a physical disconnect between the controller and the motor it drives. It will lead to catastrophic output stage damage if they are disconnected while the motor is still powered up.

If you need to switch between two motors use to controllers otherwise you will eventually damage the one you have and thusly have no controllers resulting in you needing to buy a second one anyway.

 

What I am doing is good practice however I need to improve points 1) and 2).

No. What you are doing is not good practice and it's well documented in the manuals.

 

No. What you are doing is not good practice and it's well documented in the manuals.

Hi thanks for the reply however again I emphasise the motor is switched off via the command signal and the relay is switched 500ms after the decel of the motor so therefore the motor has stopped and the cycle has finished ! the disconnection is complete 500ms after all of this and the motor is NOT running I am getting transient v/a from the motor I wish an electronic way of switching between motors to reduce all of this problem as explained in the post. If you believe I am not doing this the correct way please state the correct way which is not 2 controllers as in many industries this use of 1 inverter for many motors is common ie the water industry particularly however the time for switching is not as critical as the time situation i need.

 

What I am doing is good practice however I need to improve points 1) and 2).

I have done it a few times using identical motors on switching, but I used one of the configurable outputs set to At-Zero-Speed in order to interlock the change over and prevent any VFD problems.
Max.

 

I have done it a few times using identical motors on switching, but I used one of the configurable outputs set to At-Zero-Speed in order to interlock the change over and prevent any VFD problems.
Max.

Thanks max I have done the same too within the PLC on the inverter I monitor the speed and then allow switching I feel my issue is at the motor end with transients from both types of motors and with 8KHz carrier wave its no so easy to use a snubber circuit and triacs cant switch this fast my only other thought is IGBT's