Servo Drive and Motor Compatabilty

PCW

I think I understand the selection of the output inductor now, could you review please my conclusion?

To adapt the MR055K drive to the Servo Dynamics MTS30R4-42 servo

I will use the 195E30 part you suggested.


To adapt the MR0808 to the UGJMED-60 MA

I think the following is the correct choice

HAMMOND - 195G20 - DC REACTOR CHOKE, 5MH, 20A, 15%

195G20

The reasonaing I used is the following:

Table 2 Combination of Servopack with Servomotor and Reactor

I see in the in the 7th row 2nd column where UGJMED-60MA is listed the cell to the right specifies 5mh (although I don't know what the 14A relates to)

I see in table 3 Characteristics in Combination of Servopack and Servo Motor

I see in the in the 7th row 2nd column where UGJMED-60MA is listed the cell to the right specifies 19 Amps

That seems to fit the 195g20 specs:

Inductance: 5mH
DC Resistance Max: 0.025ohm
DC Current Rating: 20A

If I understand correctly this output inductor limits the current that can pass through the circut in some way that protects the motor.
I would wire this in series with the DC power through the motor.

In the worst case the motors might get overheated or burned out in which case I just get better matching ones later.

Is my understanding correct?

The thing I don't get is how you know what voltage is supplied to the motors.

Thanks for your help.

Jon Schmidt

What the inductor does is lower the AC PWM voltage supplied to the motor.

The PWM DC motor drives that you have take the supplied AC power, rectify it to supply a DC bus voltage and switch this DC voltage on an off at a constant high frequency (somewhere between 2 KHz and 50 KHz depending on the drive) The drive then varies the on and off times of this switched signal as required to vary the motor current. Since you have drives that run on 230V I would expect the actual switched DC voltage to be around 300V. This means that even if the drive is only supplying and average of 150V to the motors (1/2 on time) the peak motor voltage is still 300V. This may cause problems with motor insulation and commutation on a lower voltage drive. By adding a series inductor you can reduce the peak voltage the motor 'sees'. If th external inductor has the same inductance as the motor armature, the AC voltage will be reduced by a factor of 2.

The other important thing is to make sure that the motor armature inductance + external inductor have more that the minimum inductance required by the drive. This is more likely to be an issue when driving a lower voltage motor with a high voltage drive as the lower the motor voltage, the lower the motor inductance. Too much inductance is better than too little. (too much may lower dynamic performance a little, but too little will likely damage the drive (or prevent you from getting full current) or overheat the motor (due to current ripple).

Thank you for the detailed explanation, I think it will take me a few days to fully understand it.

Your mention of AC confuses me though:

What the inductor does is lower the AC PWM voltage supplied to the motor.

I was thinking that the series inductor would be installed in the DC line to the motor.
I must not be understanding something correctly, is it installed in the AC line to the drive or the DC line to the motor?

Did my part number selections seem reasonable?
I would like to order them but I am not confident that I have made the right choice, especially for the minertia motor UGJMED-60 MA .

If this works out it will be a huge savings and enable me to get to the cables challenge.

The inductor _is_ in series with the motor.

The drive output is not pure DC but pulsed DC which contains a high frequency AC component

I think 2.5 mH is adequate (if you choose a inductor with the same inductance as the motor you will
reduce the peak voltage by a factor of 2)

Note that it will likely work without the inductor, its just gentler on the drive and the motor with the inductor in place

OK thanks for explaining that; I never knew that there was AC within the DC, now it makes sense.

Do you happen to know if the wires going from the drive need to be anything special like twisted or shielded?
I have never taken a servo cable apart to see what is inside.

Thanks for all your help you have advanced my project by a couple months.

Often the motor wires are twisted and shielded,
as are the differential encoder wires.
That is the A, /A are twisted as are B, /B and Z, /Z

PCW,

I have the same exact machine and servodrives, but different Yaskawa motors. One motor I have is 64V, 2.3A, 5.0ohm. I cannot find the motor inductance rating.

Can I use an inductor that is 1/2 the rating of the motor, and then use the 64V motor with the 200V DC pwm servodrive?