Efficiency of stator oriented control

ProgramThyself · Nov 13, 2020

Lebowski explained that stator oriented control (SOC) gives better regen braking efficiency than field oriented control (FOC).

Lebowski said:
For me FOC means that (when powering) the motor current vector is lined up with the Back EMF vector, for max efficiency. During regen the current vector is lined up with the Stator voltage vector, again for max efficiency. This is called SOC, Stator Oriented Control.

It's hard to argue with the reasoning, but how much efficiency does this gain?

I guess there is a subtle difference between extracting from each amp of phase current the maximum mechanical braking power (FOC) vs. the maximum electrical power (SOC) because motors are lossy.

john61ct · Nov 13, 2020

Personally I think the energy recovery hardly justifies regen.

It's all about more efficient / effective braking, greater control on long descents with heavy loads afaic.

With saving brake pad wear in between.

thepronghorn · Nov 14, 2020

john61ct said:
Personally I think the energy recovery hardly justifies regen.

It's all about more efficient / effective braking, greater control on long descents with heavy loads afaic.

With saving brake pad wear in between.

Not sure what you mean by "personally," but there are definitely routes where it is possible to recover significant amounts of energy from regen...
https://endless-sphere.com/forums/viewtopic.php?f=16&t=9045

Balmorhea · Nov 14, 2020

thepronghorn said:
Not sure what you mean by "personally," but there are definitely routes where it is possible to recover significant amounts of energy from regen...

There are more situations where regen isn't worth the energy lost by not having freewheeling. Most people live in areas that became populated because they are relatively flat and easy to move around. Drag-free coasting can be much more valuable in many such places.

I choose low maintenance for my own bikes, meaning direct drive hub motors without regen. So I sacrifice a little efficiency on both counts, in favor of reliability.

ProgramThyself · Nov 14, 2020

john61ct said:
Personally I think the energy recovery hardly justifies regen.

It's all about more efficient / effective braking, greater control on long descents with heavy loads afaic.

With saving brake pad wear in between.

I agree that the energy recovered is modest, perhaps 5 % for me. Another benefit is reduced braking noise. If you want the highest stopping power (vs. recharging power) from the regen brake, I would expect FOC to be better than SOC.

john61ct · Nov 14, 2020

thepronghorn said:
john61ct said:

Personally I think the energy recovery hardly justifies regen

Click to expand...

Not sure what you mean by "personally," but there are definitely routes where it is possible to recover significant amounts of energy from regen...

I mean wrt my own decision-making, prioritizing among the myriad factors.

I set aside those "possible" energy savings as a decision factor, because they are not relevant to my use cases.

Similarly to slipstreaming / aerodynamic issues.

If I did not need drag braking down for long time periods descending steep slopes with heavy loads, then

I would not take ability to regen into account at all, unless it just happened to be easy, came along "for free" as a result of all the other choices following decisions based on the other factors.

thepronghorn · Nov 16, 2020

john61ct said:
thepronghorn said:

john61ct said:

Personally I think the energy recovery hardly justifies regen

Click to expand...

Not sure what you mean by "personally," but there are definitely routes where it is possible to recover significant amounts of energy from regen...

Click to expand...

I mean wrt my own decision-making, prioritizing among the myriad factors.

I set aside those "possible" energy savings as a decision factor, because they are not relevant to my use cases.

Similarly to slipstreaming / aerodynamic issues.

If I did not need drag braking down for long time periods descending steep slopes with heavy loads, then

I would not take ability to regen into account at all, unless it just happened to be easy, came along "for free" as a result of all the other choices following decisions based on the other factors.

Ok. I think you should clarify that this is what you mean before going around posting that you "think energy recover hardly justifies regen" since some people might think that you are talking about the general case instead of your specific use case.

thepronghorn · Nov 16, 2020

Balmorhea said:
thepronghorn said:

Not sure what you mean by "personally," but there are definitely routes where it is possible to recover significant amounts of energy from regen...

Click to expand...

There are more situations where regen isn't worth the energy lost by not having freewheeling. Most people live in areas that became populated because they are relatively flat and easy to move around. Drag-free coasting can be much more valuable in many such places.

I choose low maintenance for my own bikes, meaning direct drive hub motors without regen. So I sacrifice a little efficiency on both counts, in favor of reliability.

How do you figure regen to negatively affect reliability of a system?

Balmorhea · Nov 17, 2020

thepronghorn said:
Balmorhea said:

I choose low maintenance for my own bikes, meaning direct drive hub motors without regen. So I sacrifice a little efficiency on both counts, in favor of reliability.

Click to expand...

How do you figure regen to negatively affect reliability of a system?

Reversing reaction torque at the axle tends to loosen threaded fasteners. It's the same as fixed gear bikes having much more frequent problems with loose pedals and cranks than regular bikes-- force gets transmitted both ways through the interface, and things loosen as a result.

The reversing torque of regen also dramatically increases the likelihood of fatigue cracking and breakage of the axle.

thepronghorn · Nov 17, 2020

Balmorhea said:
thepronghorn said:

Balmorhea said:

I choose low maintenance for my own bikes, meaning direct drive hub motors without regen. So I sacrifice a little efficiency on both counts, in favor of reliability.

Click to expand...

How do you figure regen to negatively affect reliability of a system?

Click to expand...

Reversing reaction torque at the axle tends to loosen threaded fasteners. It's the same as fixed gear bikes having much more frequent problems with loose pedals and cranks than regular bikes-- force gets transmitted both ways through the interface, and things loosen as a result.

The reversing torque of regen also dramatically increases the likelihood of fatigue cracking and breakage of the axle.

Ahhh yes I didn't think of the axle and torque arm reliability. Good point. I would say there are other things you sacrifice too besides efficiency, but those are mostly personal preferences.

john61ct · Nov 17, 2020

thepronghorn said:
I think you should clarify that this is what you mean before going around posting that you "think energy recover hardly justifies regen"

That is also my opinion generally, not just for my use cases.

I was answering your question as to what I meant by "personally".

If measured accurately, it is rare for regen to actually recover much useful energy over 10, 15% very rare.

Do you consider that significant?

thepronghorn · Nov 17, 2020

john61ct said:
thepronghorn said:

I think you should clarify that this is what you mean before going around posting that you "think energy recover hardly justifies regen"

Click to expand...

That is also my opinion generally, not just for my use cases.

I was answering your question as to what I meant by "personally".

If measured accurately, it is rare for regen to actually recover much useful energy over 10, 15% very rare.

Do you consider that significant?

Yes I consider 10% range increase to be significant!

Efficiency of stator oriented control

ProgramThyself

100 mW

john61ct

1 TW

thepronghorn

1 kW

Balmorhea

100 kW

ProgramThyself

100 mW

john61ct

1 TW

thepronghorn

1 kW

thepronghorn

1 kW

Balmorhea

100 kW

thepronghorn

1 kW

john61ct

1 TW

thepronghorn

1 kW

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