# switched reluctance motors and drives



## DawidvC (Feb 14, 2010)

Very Nice. Building an invertor for these should be easy - if it is a 4-phase motor, just get 4 dc drives, syncronised and hooked up.

Dawid


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## aeroscott (Jan 5, 2008)

DawidvC said:


> Very Nice. Building an invertor for these should be easy - if it is a 4-phase motor, just get 4 dc drives, syncronised and hooked up.
> 
> Dawid


I talked to LTI about 1 year ago , they gave me a great 1/2 hour on why they use them . there are some finner points to the programming . Another point is no shoot-threw is possible in the controller . did you check the links , they have ways to make them quieter and one is 95% eff. with driver losses (100 kw).


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## DawidvC (Feb 14, 2010)

We had an Oulton motor and drive at a company I worked for about 17 years ago. It was only rated for 5.5kw (about 7.5hp) and we eventually replaced it with an acim and drive. If I remember correctly we needed a 11kw motor (15hp) to give us the same torque - or so we thought.

The machine was a bottle-printing machine. The Oulton SR motor would break any botlle which happen to fall into the machine. The AC motor would simply stall, instead of breaking the bottles.

It still was a nice motor! Funny thing, everybody said they were oversize and slow when Oulton introduced them more than 20 years ago. All the modern SR motors seems optimised for high speed ( > 20krpm quoted in the links ). 

What I like about them is that they are lighter, can be rewound by a competent DIYer, and the drive does not need to be very complex - minimum 4 switches for a 4/6 phase SR motor. Of course, that is neither elegant nor efficient.  What about one of these ( or both ) http://www.srdrives.co.uk/green-propulsion.shtml

Maybe we should start Qer and Tesseract into building a SR Drive. Who knows??

Dawid


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## aeroscott (Jan 5, 2008)

good to hear from you , great to hear hands on experience . when I talked to LTI they said programing was the big issue (1 year ago ) , but now in this last year I see software and classes etc. So nothing stops the open source /diy development . ps many year ago I saw 6 phase aero motors wounder if they were sr's.


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## GerhardRP (Nov 17, 2009)

See also: http://www.e-driveonline.com/Conf-09/images/Emerson.pdf
One of the interesting features is that losses are all in the stator, so cooling is easy.


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## aeroscott (Jan 5, 2008)

GerhardRP said:


> See also: http://www.e-driveonline.com/Conf-09/images/Emerson.pdf
> One of the interesting features is that losses are all in the stator, so cooling is easy.


 Gearhard great find ,Emerson was one of the links but I got lost on the site.


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## DawidvC (Feb 14, 2010)

Some multiphase motor (if we use the term to refer to motors with *more* than 3 phase, and acim for 3 phases) are actually normal ac induction motors, wound with additional phase windings.

This is primarily done for higher torque or for efficiency, thus you will see it in the shipping industry and in the aircraft industry. There has been a resurgence of interest in these type of motors lately, because people are starting to realise that a 3 phase motor is the *minimum* requirement for selfstarting in ac motors. 6 phase motors are getting popular because they require the minimum redesign in ac motors.

A lot of SR motors have 4 phases, but they will be referred to as 4/6 pole motors. This is due to the fact that most companies specify the stator *and* rotor poles on these motors, making it a bit easier to distinguish between sr motors and ac motors

Regards
Dawid


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## MPaulHolmes (Feb 23, 2008)

It doesnt look too much tougher than an acim controller. Are the motors expensive?


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## DawidvC (Feb 14, 2010)

I have no idea of the current pricing on these motors. They would probably be more expensive than similar sized ACIM's due to smaller production runs. These motors are also much more difficult to optimise, so that would add another premium.

Controlling them is not very difficult, but the software can get very complex, about equal to field orientated control on acim. There are several modes of control depending on the speed of the motor and wether torque is controlled or uncontrolled. Torque control on its own is difficult, according to the papers I have seen about it. They normally control both speed and torque, which is actually better for use in an EV. There is no direct link between torque and current in these motors, so you have to rely on the controller calculations on what the actual torque is. The modern controllers can run without encoder feedback, in fact they seem to be able to run without any feedback as good as they can with feedback. Depending on the power section used the controller can use the windings to sense the position of the rotor.

There are a number of schemes to configure the power section, with different amounts of transistors needed per winding. Some three-phase SR motors can even be driven from a standard AC Drive, depending on the drive software. Transistor counts for normal SR drives range from 1xn to 2xn, where n is the number of phases of the motor. These power sections range from simple (see post #2) to quite complicated. Here is a sample of some cicuits to give an idea of how the *same* motor can be control by different control schemes.

























The last scheme is the best for using in an EV, but the first is workable, although there are a couple of things that argue against its use. The other scheme gives the most flexible use of these motors available. I will try and locate some of the papers available about the control of these motors so you guys can see the differences between the various control schemes. These motors are mechanically simple enough that people are building it for themselves, and with enough knowledge an acim can be turned into a SR motor. I will go hunt some URL's for those interested in the actual working of these motors.

Regards
Dawid


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## aeroscott (Jan 5, 2008)

dawid thanks , It will be interesting to study . Do you have any of those great links like the under volt acim from oz on sr ? ps; liked the idea of slower switching speeds .


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## DawidvC (Feb 14, 2010)

Hi Aeroscot

Here are a couple of links:
http://www.fleadh.co.uk/srm.htm
Sensorless Commutation Control of Shttp://www.jimhendershot.com/ac brushless sr motor comparison.pdfwitched Reluctance Motor
Microsoft PowerPoint - Theory of SR Motor Operation

Here is the wikipedia take on SR motors
http://en.wikipedia.org/wiki/Reluctance_motor

This one is a bit more specific on the type
http://openpdf.com/.../6-4-switched-reluctance-motor-ppt-pdf.html

This is for the people who can access non-free publications - please let me know if someone can access this - it looks interesting
http://linkinghub.elsevier.com/retrieve/pii/S0304885304016920

Regards
Dawid


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