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Multi phase motor controller

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mikeb
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Username: mikeb

Post Number: 1149
Registered: 02-2008

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Posted on Tuesday, 17 March, 2015 - 12:12 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I am building the EPE motor controller to gain experience of motor control and play around with the control code (thanks EPE!!!).

Can anyone see a problem with adapting the single phase design to 3 phase.

The micro would now drive 3, 60 degree phase shifted signals, to 3 switching transistors, under the same 'rectified pwm' design as in the single phase.

The bells and whistles can then be added to the micro code ie direction, slow start, speed control, torque control, 'nudge' etc
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basementboy
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Post Number: 231
Registered: 05-2012

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Posted on Thursday, 19 March, 2015 - 10:32 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

It's definitely worth a try. I can't think of a logical reason why not, and it's exactly what I'd do.
It shouldn't need too much processor either, as the waveform is the same on each phase. Have you got enough timers to add the delay, or will you simply reset the same timer 3 times per cycle.
I got a scrapped alstom 3 phase controller a few years back. Quite a low power single processor, and a very nice IGBT block which I used to repair a large UPS. They used fibre optics to isolate the mains from the logic.
I seem to remember 'plugging' was another word for nudge.
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mikeb
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Post Number: 1150
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Posted on Thursday, 19 March, 2015 - 11:20 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Yep - thanks for confirmation. I am assuming that a 3 phase motor is simply three, universal motors (ie AC or DC), with a common return.

I think it will either work or there will be smoke, so I see plenty of low voltage testing at first.
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pebe
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Post Number: 171
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Posted on Thursday, 19 March, 2015 - 12:40 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

No. A 3 phase motor is for AC only. It uses a field wound in three sectors (one for each phase) in order to get a rotational field. The rotor is usually in the form of a 'squirrel cage'.
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mikeb
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Post Number: 1151
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Posted on Thursday, 19 March, 2015 - 01:29 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

This is where I am getting confused.

I would agree with pebe if it were a induction motor ie the rotor has is 'unpowered' (no commutator). The rotating magnetic field must be fully AC to effect the rotational motion.

But in a 'powered' 3 phase rotor (ie a rotor that has a commutator) aren't the polarity changes taken care of (the same reason that you can power a universal motor from AC or DC) ... or have I just got terribly lost .......
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mikeb
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Post Number: 1152
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Posted on Thursday, 19 March, 2015 - 02:27 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

OK - thanks all - finally I understand.

I saw a video of how its done. Basically the single phase is rendered into DC. Each of the AC output phases is digitally created by forming a OV rail and switching between +ve and -ve rails.
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basementboy
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Posted on Thursday, 19 March, 2015 - 04:03 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Got a link to the video Mike?
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mikeb
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Post Number: 1153
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Posted on Thursday, 19 March, 2015 - 11:26 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I should have tagged the videos - I cant find them now of course.

This video shows what I want to do. A dirty great hairy 3 phase motor, controlled by a 6 transistor bridge. It is light on theory.

https://www.youtube.com/watch?v=AkaUvVaplWg
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basementboy
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Post Number: 233
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Posted on Friday, 20 March, 2015 - 11:49 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

It certainly looks like a pro set up.
A few things I noticed :-
DC for the H bridge (not sure what the 3 phase version of H bridge is called) is derived from the 3 phase. Motor didn't look that big, but maybe that's the next step to 7kW.
The control board must be isolated from the mains, possibly by the RH transformer
To get around the problematic hi-side driver, each part of the bridge has its own transformer?

I'd imagine the transformers would go in any pro device.

I have a USB isolator I use to drive my programmer when working on boards that I want isolation with. Doesn't stop you getting a belt off the board, though.
Interesting project. Good luck.
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mikeb
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Post Number: 1154
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Posted on Friday, 20 March, 2015 - 01:53 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks basement - yep, I deduced much the same as yourself, except that it looks to me as though he is using a single phase supply (the large grey box with lcds is a multi DC power supply I think).

Well, I will finish off the EPE controller and then might play with 3 phases.

cheers

mb
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chippie
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Username: chippie

Post Number: 347
Registered: 11-2005


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Posted on Friday, 20 March, 2015 - 05:48 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Here's my twopenneth,
From experience of repairing single/three phase inverters/ vsd units, smaller than 1hp use either a dedicated thick film chip, such as IRAMX20UP60A or use a hi/lo driver and a CPV363M4KPBF, larger units use the hi/lo driver and discrete igbts.....

Single or three phase AC supply is rectified to give either 240/400 v dc to the three phase Half H bridges....
The gates are driven by a hi and lo side driver typically an IR2133....
The control side is by a small micro, the low voltage supplies are generated using either a fet switcher or maybe a Topswitch, TOP224Y....
Current limiting is done by sampling the volt drop across lo ohm resistor in the common feed to the hi side, using an opto coupler fed into an op amp, whose o/p feeds into the micro.....

(Message edited by Chippie on 20 March, 2015)
eccentric millionaire financed by 'er indoors
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chippie
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Post Number: 348
Registered: 11-2005


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Posted on Friday, 20 March, 2015 - 07:17 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Have a look at the data sheet for this.....
IKCS17F60B2A
eccentric millionaire financed by 'er indoors
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mikeb
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Post Number: 1155
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Posted on Friday, 20 March, 2015 - 10:12 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks for info chippie.

I have discovered the IR2133 from trawling through the web and utube.
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chippie
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Post Number: 349
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Posted on Saturday, 21 March, 2015 - 04:24 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Here's the package I was looking for....
7MBR30SA060

If you search on that, you'll get the data sheet for it...
600v units are for 240ac in 1-3 phase, or 1200 v for 3ph 415 ac in....
eccentric millionaire financed by 'er indoors
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mikeb
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Post Number: 1156
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Posted on Sunday, 22 March, 2015 - 11:33 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Its coming down to bit of cost engineering now. I am getting the EPE IGBT STGW40 at about £8 from ebay - 6 'o them say £50.

The 7MBR is £59 from a quick ebay look.

I think its getting a bit pricey for an experiment, unless I have a specific need.

A few of the guys at the chop shop have expressed the desire for 3 phase controllers (lathes, mills etc) but they are retailing for many hundreds ...... hmmmmm.

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