[wingover]

In boat world, electric propulsion partisan, have to face heavy sarcasm for fuel fans, My EV...is in fact EB, slim 40 feet sailing trimaran.
EV forums are a peaceful places ! that's why i am here !

As regenerating is as important as the propulsion in a sailing boat, motor will run 24h/24h when sailing. 1000 hours of use is reached only in a few months, so i think PM brushless motors are almost compulsory for my application.
Looking at actual applications of this kind of motor and sensorless controllers, it seems they are used a lot in aerospace and military applications. This let me think it is a good technical choice for bulletproof applications.

Also, for a direct drive low revering (compulsory for efficency) of the propeller shaft i will use a 24 to 12 poles motor giving full speed at 900 to 1200 tr/mm. What will be the effect on the controller ? I guess this helps ?

My application runs under 50 volts and motor will be 4 to 5Kw, but for the moment i dont not know if it will be AC synchronous, asynchronous, PMAC...as it is a little confused in my head about advantages of each as far as efficency, weight and regeneration efficency. I found a 24 poles motor from Perm in Germany, but for the moment this motor is only qualified as a wind generator and they ask for time to do more test to use it as a motor. So if you have ideas about other motors...let me know !

The question i need to answer now, is about the performance of the controller for reading informations with the BEMF (Back ElectroMagnetic Force) from the motor and then giving the good orders. I have been told that all the controllers are not the same on this aspect . Some do it well, some get lost under certains situations...
Is it true ?
In what situation will the controller be lost or do not execute correctly the orders ?

I found this first answer that is giving usefull informations

Originally Posted by abudabit

Here is how it was explained to me:

With no hall sensors in the motor and the motor not turning there is no way for the controller to know the position of the rotor (as far as I know). The way controllers know the position of sensorless brushless motors is by detecting back emf in the various windings. When not turning there is no back emf. When slowly turning there is very little back emf. To detect the position during slow or no turning the controller cycles pulses through the windings in a circular pattern. This is very inefficient because it is basically blindly (but in a useful pattern) running electricity through the windings.

Once the back emf becomes large enough to detect then the sensored and sensorless can become equally efficient. But in stop and go traffic, or during a stall, or starting from a stop, or crawling extremely slowly, etc. it is massively less efficient. And those are the times you need efficiency the most because those are the highest torque applications in an ev.

I could be incorrect as I have never worked with an unsensored brushless.

What is your experience with sensorless motors ?
Is it preferable to forget about sensorless as the global reliability won't be affected using hall sensors ?

Thank's !

[Tesseract]

Originally Posted by wingover

...As regenerating is as important as the propulsion in a sailing boat, motor will run 24h/24h when sailing. 1000 hours of use is reached only in a few months, so i think PM brushless motors are almost compulsory for my application.
Looking at actual applications of this kind of motor and sensorless controllers, it seems they are used a lot in aerospace and military applications. This let me think it is a good technical choice for bulletproof applications.

Sensorless motors are tougher than ones with Hall Effect sensors in them, but not in a way that is relevant to a sailing vessel. Hall Effect sensors do not tolerate vibration very well (it causes piezoelectric effects) and they also have a fairly limited operating temperature range (to be military/aerospace qualified a part must function properly from -55C to +125C). A sailboat is about as low a vibration environment as I can imagine and the people on the boat will probably have a more restricted temperature range than any Hall Effect sensor so I would not restrict myself to only sensorless motors/controllers for this application.

That said, there's no reason to exclude sensorless motors/controllers, though, because while the information in the quoted post by abudabit is correct, a sailboat rarely reverses direction and changes speed very gradually (compared to an automobile, for example) so those concerns aren't really relevant in such an application.

Originally Posted by wingover

Also, for a direct drive low revering (compulsory for efficency) of the propeller shaft i will use a 24 to 12 poles motor giving full speed at 900 to 1200 tr/mm. What will be the effect on the controller ? I guess this helps ?

Yes - more poles means more BEMF for a given shaft RPM.

Originally Posted by wingover

My application runs under 50 volts and motor will be 4 to 5Kw, but for the moment i dont not know if it will be AC synchronous, asynchronous, PMAC...as it is a little confused in my head about advantages of each as far as efficency, weight and regeneration efficency. I found a 24 poles motor from Perm in Germany, but for the moment this motor is only qualified as a wind generator and they ask for time to do more test to use it as a motor. So if you have ideas about other motors...let me know !

You're not the only one confused by all the different types of "rotating machines". Broadly speaking, brushless DC motors are the same as synchronous AC motors but with permanent magnets in the rotor instead of a wound field and slip rings. Asynchronous AC motors (e.g. - what are commonly referred to simply as "induction" motors) are very easy to drive in all 4 quadrants - simply command a lower speed than the shaft is turning at and an induction motor automatically turns into a generator. Another plus is that induction motors work equally well as a generator or a motor because they do not have a fixed field position (the field is "induced" in the rotor by the currents flowing through the stator windings).

Anyway, one very well respected manufacturer of brushless motors here in the US is Mars Electric. See, for example, this page:

http://www.marselectricllc.com/burnishermotor.html


As for the rest of your post, I have not enough experience with brushless motors (except industrially, in servodrives) to really comment on which controllers work better, etc...

[wingover]

Tesseract your information are already a great help as it answers several questions i was asking myself !

Yes Mars brushless are great motors but for inboard boat application, a 2:1 to 3:1 mechanical reduction is compulsory, and i do not want this.

- First because i do not know where i can buy this reduction
- Second because i think i will lose 10 to 15 % in it.
- Third it means more parts, so more problems.
- Fourth Noise will be higher as a reduction will make noise

But to be honest reduction on a ship has a 2 advantages:
- motor choice is much wider, so this means lower cost
- Motor is in an upper position in the boat, so less exposed to water always present in a ship when sailing very heavy weather

So unless i would find a good quality, low loss, resonnable cost belt reduction i won't use reduction.

Belt drive reduction looks like this :
http://www.youtube.com/watch?v=GdEDZ...eature=related
http://www.youtube.com/watch?v=Bd4EI...eature=related

[Tesseract]

Originally Posted by wingover

Tesseract your information are already a great help as it answers several questions i was asking myself !

You are most welcome, monsieur.

I like toothed-belt drives. They can be very quiet and very efficient (95% efficiency is relatively easy to achieve) and, of course, they are a lot easier to fabricate yourself than a gear reduction and much more efficient than a v-belt or flat belt (a little noisier though).

This link has about the best explanation on how to design a belt drive I have come across:

http://www.sdp-si.com/D260/D260cat.htm

[etischer]

DCBL Motor is a DC motor which uses an encoder or some sort of feedback device for commutation. Typically an absolute encoder is used, the encoder must be precision aligned with the stator (by the factory).

AC Induction motor does not require commutation.

You have to put power into the AC induction motor to regen, there needs to be some magnetizing current to create a field. So if your battery is dead to the point you can't reach minimum voltage on the controller, you might just be SOL. Sensorless vector mode running on an AC induction motor is fine as long as you don't intend to spend alot of time at low speed (less than 5% base speed, or around 100 rpm)

[wingover]

Battery can't be dead unless accident as i also have solar panels, windmill and a "low voltage cut everything" security, but it was worth to point out this limit.

What happens exactly when i slow down too much the AC motor going close or under 5% or rated speed ? Do i loose efficiency or will i loose also control of the motor by loosing BEMF ?

"you might just be SOL" what means "SOL" ;-)

Another question coming to my mind, what will be the usual maximum frequency that will accept a sensorless controller, with positive and negative torque, that is to say when motoring and when regenerating ?
Ideally, 200 Hz would be great for positive, 250/300 for negative...Do i dream awake ?

Thank's !

For school time, here is an interesting paper about different motor technologies and drive solutions
http://www.lg-motion.co.uk/product%2...tors_04-05.pdf
And this one about regeneration
http://www.roboteq.com/how-to/unders...eneration.html

[etischer]

The low speed range of an AC motor running in sensorless vector may have a problem with stablity. This is only in sensorless vector or Volts/hz mode. Closed loop vector mode (using encoder feedback) should not have this problem. Your application should not have the problem in sensorless vector either, because you will be running in "Fan mode" not "Linear mode". Baiscally, you do not need high torque at low speed, your torque increases with speed.

For an electric car let's put it this way:

60 hz and 230 volts = 2000 RPM
30 hz and 115 volts = 1000 RPM

If you want to go 10 RPM you would need

0.3 hz and 1.15 volts

you cannot get much torque with 1.15 volts, so the AC controller will throw some dc offset in. this setting is called boost.

On flat ground to get 10 rpm, you may use 0.3 hz and 30 volts.
On a steep hill you may need to use 0.3hz and 50 volts.
For a boat, the boost setting should always be the same cause you cannot go up hill and the torque should always be the same (unless the prop is grounded or something).


Max speed on most AC controllers would be around 400 hz, or about 12,000 rpm.


SOL means sorry, out of luck. Also means S*** outta luck. It's a TLA

Originally Posted by wingover

Battery can't be dead unless accident as i also have solar panels, windmill and a "low voltage cut everything" security, but it was worth to point out this limit.

What happens exactly when i slow down too much the AC motor going close or under 5% or rated speed ? Do i loose efficiency or will i loose also control of the motor by loosing BEMF ?

"you might just be SOL" what means "SOL" ;-)

Another question coming to my mind, what will be the usual maximum frequency that will accept a sensorless controller, with positive and negative torque, that is to say when motoring and when regenerating ?
Ideally, 200 Hz would be great for positive, 250/300 for negative...Do i dream awake ?

Thank's !

For school time, here is an interesting paper about different motor technologies and drive solutions
http://www.lg-motion.co.uk/product%2...tors_04-05.pdf

[wingover]

About synchr motor speed versus frequency i thought that it was :

Rpm synchronous = (120 x Frequency)/ Number of poles

Is it correct, and what is the formula for torque ?

So in my case, just by choosing a 18 to 24 poles motor will give me the rpm range i want (and more in fact)

Originally Posted by etischer

For a boat, the boost setting should always be the same cause you cannot go up hill and the torque should always be the same (unless the prop is grounded or something).

In fact yes you are right for most of time , but no when you have very big waves, very long period, coming for thousand miles away. Then you go up and down hill, boat decelerating a lot and accelerating slightly less , and then... i usually puke.

[etischer]

I don't think you will ever find a 18 or 24 pole motor. Most are 4, some are 6, you might find one that is 8.

there is some slip involved, so RPM synchronus is never achieved. I believe slip is directly related to torque. Too much slip and the motor runs jerky and cogs. This is where boost comes in. Not enough boost, you slip and loose your synch. Too much boost and the motor is overshooting its position, and feels like it is cogging. When in closed loop mode using an encoder, the drive knows exactly how fast the motor is turning and can apply the right boost, volts and frequency.

Originally Posted by wingover

About synchr motor speed versus frequency i thought that it was :

Rpm synchronous = (120 x Frequency)/ Number of poles

Is it correct, and what is the formula for torque ?

So in my case, just by choosing a 18 to 24 poles motor will give me the rpm range i want (and more in fact)



In fact yes you are right for most of time , but no when you have very big waves, very long period, coming for thousand miles away. Then you go up and down hill, boat decelerating a lot and accelerating slightly less , and then... i usually puke.

[major]

Originally Posted by etischer

there is some slip involved, so RPM synchronus is never achieved.

Hi etischer,

He's talking about BLDC, so there is no slip. Synchronous RPM is a must. There is a torque angle, if I am not mistaken, like you have with a synchronous motor.

Regards,

major