# Help Finding Inverter Solution



## kennybobby (Aug 10, 2012)

It might help if you could provide more information about your motor, e.g. is it 3-phase, how many poles, is that a mechanical commutator frequency or the electrical frequency of the current waveform, etc. i've used a 300 hp Baldor industrial drive to run a large induction motor. DC buss voltage ~800, semikron switches rated ~600 A. There are large inverters available if you have the $$$.


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## joltron (Feb 24, 2014)

3 phase, 36 poles, electrical frequency. I requested the motor model so I can post it to have all information available. The coin$$$ for the drive isn't a big problem. I will post up a model when I get my hands on it from our ME. Thanks.


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## major (Apr 4, 2008)

joltron said:


> ....The coin$$$ for the drive isn't a big problem.


In that case, look at http://www.rinehartmotion.com/


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## joltron (Feb 24, 2014)

major said:


> In that case, look at http://www.rinehartmotion.com/


Do you have any insight into if they can handle a frequency of 1200-1500Hz? I have a couple PM100DX's we used on our Dyno (and have sold on here). I will contact them about their higher power modules and see what they have to say about the frequency. Thanks.


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## EVCan (Oct 11, 2012)

This one seems able with regards to current. What is the application?

http://www.tm4.com/products/motor-controllers/co150-motor-controller/


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## major (Apr 4, 2008)

joltron said:


> Do you have any insight into if they can handle a frequency of 1200-1500Hz?


No. Have to ask them. At your power, you may be in no-man's-land for that high frequency.


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## kennybobby (Aug 10, 2012)

*An interesting problem...*

So you have a 200 RPM motor that you want to run at 4000-5000 RPM. Maybe you already know the winding inductance and resistance at 60 Hz and at 1200-1500 Hz? Or the nameplate ratings at 60 Hz?


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## frodus (Apr 12, 2008)

*Re: An interesting problem...*

What motor are you looking to drive?


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## joltron (Feb 24, 2014)

I was on a short hiatus but was able to gather more information on the motor. The motor is custom made by a company I work with.

Motor Characteristics:

-32 poles (16 pole pairs) on the rotor assembly
-36 slots on the stator, with a 3 phase winding with a Series-Y connection.
-Maximum speed = 5500 RPM
-Maximum operating frequency = (5500/60) * (32/2) = 1467 Hz
-Expected coil operating temperature = 120 degrees C, so the following values reflect the parameters at this temperature.
-Direct axis inductance Ld = 72.2 micro-Henries line-line
-Quadrature axis inductance Lq = 91.2 micro-Henries line-line
-Stator resistance = 4.59 milli-Ohms line-line @ 120 degrees C
-Torque constant Kt = 1.35 Nm/A @ 120 degrees C
-Back emf constant Kb = 81.7 Vrms/krpm line-neutral @ 120 degrees C
-Maximum current = 670 Arms total to achieve 900 Nm at 120 degrees C.

With a significant bit of field weakening at high speeds, the Kt and the R values could be increased to reduce the maximum current draw.

I contacted TM4 and they might be able to work out a solution for us. We have been looking at rebuilding the motor to be 6 phase instead of 3 as well.


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## kennybobby (Aug 10, 2012)

36 slots in the stator does not make it a 36 pole motor, nor does 32 slots in the rotor mean it has 16 pole pairs (squirrel cage rotor has shorted end turns). It is most likely a 6-pole motor that runs at 1200 rpm on 3-phase, but can run up to 5500 rpm on 3-phase at 275 Hz.


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## joltron (Feb 24, 2014)

Those are the actual motor characteristics - this is a custom designed, high efficiency motor.


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## PStechPaul (May 1, 2012)

I just saw this, and if this is an induction motor then 36 stator slots can be wound with a maximum of 12 poles (6 pole pairs) for nominal 600 RPM. When I rewound a 36 slot ACIM I found that it ran at a synchronous speed of 300 RPM (actual speed about 250 RPM due to slip), because I had one winding reversed. I think this creates "interpoles" which give half speed but efficiency and torque are reduced.

I haven't done anything with my AC motor rewinding projects recently and I'm not an expert on detailed motor theory, but I was able to come up with a reasonable explanation of my observed performance. There has been some discussion as to why higher pole count motors tend to have less power for the same size, especially smaller ones with low stator slot counts. I have a 2HP 3600 RPM (2 pole), 1.5HP 1800 RPM (4 pole), and 1HP 900 RPM (8 pole), all the same frame size and similar weight. Larger motors seem to have closer to the same HP/size at least for 4 pole and 6 pole, but beyond that there really aren't many commercially available large motors with 8 poles or more.

My feeling is that this is due to the overlap of adjacent pole windings which increases with pole count, but is less for higher slot counts. I think most large motors (as this seems to be) have 48, 72, and more stator slots, while the smaller motors I've taken apart have 24 and 36. Some small single phase fan motors have just 6 slots (or maybe 12), and I have rewound them for three phase.

For a long time I had wanted to rewind a motor for high pole count and use higher frequency to get higher power/size, but after some research and the experience of others who have done it, the efficiency and practicality diminish above about 3x to 4x overclocking (180-240 Hz), and for motors designed to run at 400 Hz and higher, the laminations and other design parameters become very special and expensive.


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## major (Apr 4, 2008)

PStechPaul said:


> I just saw this, and if this is an induction motor .....


With these specs: 



joltron said:


> -Torque constant Kt = 1.35 Nm/A @ 120 degrees C
> -Back emf constant Kb = 81.7 Vrms/krpm line-neutral @ 120 degrees C


It appears to be a PMSM.


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## joltron (Feb 24, 2014)

Yep^^, P mag


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