Suitable ac drive for multi-motor application

Hello,

I have four motors (each 15kw, 28.8A, 1470RPM, 400V, 50Hz) for extrusion machine. Each motor coupled to drive one gear. 

Currently the motors are driven by 75kw ABB drive in scalar mode (V/Hz). But this drive is failed and I want to change it by Siemens. 

Is there any drive best suitable for parallel connected multi motor application ? Does anyone have practical experience with siemens drives for multi motors? 

I appreciate if you suggest me with order codes.

Kind regards,

Hi,

As you mentioned shared gearbox this example might interest you: SINAMICS S: DCC Load Sharing

Or this article about multiple motor being controlled by a Micromaster: MICROMASTER 4 (MM4): Operation with more than one motor (multi motor) on an inverter.

Hi MicroMan, 

Thanks for your help. 

I think the basics of MM4 & Sinamics and other ac Siemens drives are the same. I am looking for if there is a drive specifically or best suits for multi-motor application.

desmul24

Hi MicroMan, 

Thanks for your help. 

I think the basics of MM4 & Sinamics and other ac Siemens drives are the same. I am looking for if there is a drive specifically or best suits for multi-motor application.

 

Basicaly all inverters have an IGBT output module /or/ every three phase contactor has 3 main contacts. If you connect  motors in paralllel, they will spin together. You can have best performance if you use same motors and cables of the same size.

Obviously, the sensorless vector control can't be adopted, V/f only. Therefore, there is no such inverter on the market that is specificaly built for parallel connnection of motors.

To make it clear I have attached the motors arrangement.

Sorry I should mention first that the drive failed frequently (the IGBT). 

I had done some investigation as follows: 

1. When the motors run the current display on the drive fluctuates fast like 58A - 80A - 110A.

2. Due to gears tooth gap, there is some lag in motors for example I had tried to rotate the motors by hand on the fan side, then if I rotate one motor 10 degree the other motors will not rotate till I rotate it to more than 10 degrees. 

3. Since it is only option to setup the drive V/Hz mode only, thus the motors runs in constant Hz and as I mention above, the position lag - lead problem I suspect that the motors are creating ripple each other, or the regenerated voltage on one motor is pulling or pushing the other.

4. I am thinking if these four motors are driven separate drive in vector mode with common torque reference, then the mechanical lag - lead might be compensated. But I have no idea how to network the four motors and I doubt the drives can handle very fast responses. 

Kind regards.

Hi,

So you need the motors to be in sync. See this:

SINAMICS S120 Gearing with DCC

Hi MicroMan,

The solution you suggest is already implemented by mechanical gear. My problem is a lag due to gear tooth gap, which is equivalent to integral time / response time of electronic gear. 

Let make ideal calculation (I might be wrong ). Let say the gears tooth gap is 5degrees and when the motors is running at 1470rpm then the rate of this error will be 1470*360deg/5deg/60sec= 1764 errors/sec =0.56ms/error. Now in order to overcome this error my controller (drive) should calculate and respond at least twice faster < 0.28ms. Moreover I don't want but if I include encoders and implement electronic gear solution then the error might be worse >> Electronic gear error + Mechanical gear error.

Thanks

You can take a risk of buying 4 inverters and put them into sensorless vector control, further look for droop compensation mode, I think is the only way to control without feedback.

Altrough I have never tried more inverters in droop.

maybe you have a problem with your cable length - a output reactor could help.

For example the new  SINAMICS PM240-2 powermodels has a new hardware structure, which improves the behavior with longer / parallel cables.

Normally the V/f mode should be the most stable mode for multimotor applications on one drive.