Author Topic: Do modern car/boat alternators use PFC circuits?  (Read 3964 times)

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Offline e100Topic starter

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Do modern car/boat alternators use PFC circuits?
« on: July 23, 2019, 03:44:12 am »
PFC cicuits are common on mains powered DC power supplies but I couldn't find much information about their use in low voltage systems such as the car alternators or wind turbine generators used on boats.
 

Offline NiHaoMike

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #1 on: July 23, 2019, 04:45:42 am »
An increasing number of cars are using switching power supplies for the 12V.
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Offline MosherIV

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #2 on: July 23, 2019, 06:56:54 am »
I doubt it.
Why (how) would you power factor correct dc voltage/current?
Car alternators are internally rectified to produce 13-14V dc to charge the car battery.
It is very difficult to get to the raw ac in a car alternator.

 

Online Kleinstein

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #3 on: July 23, 2019, 07:10:43 am »
The raw output of the alternator is usually AC and I understand the questing in the way weather the generators internally use a kind of PFC circuit instead of the a normal simple rectifier.

An extra PFC circuit in theory could increase the power rating by a little, however I don't think it is worth the trouble. A simple rectifier is just more reliable. Using a little more copper in the alternator may still be more cost effective than the extra electronics. So I don't think they use active PFC.
 

Offline tautech

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #4 on: July 23, 2019, 07:24:27 am »
PFC cicuits are common on mains powered DC power supplies but I couldn't find much information about their use in low voltage systems such as the car alternators or wind turbine generators used on boats.
Because there is zero need for it.

For a PSU especially SMPS one must limit its effects in the mains supply whereas power from an alternator originates from within it and it’s three phases are each full wave rectified for a HF ripple output where the R of the load (battery) further absorbs ripple. Other DC loads are always sourced from close to the battery so to source cleaner DC than directly from the alternator.
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Offline MagicSmoker

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #5 on: July 23, 2019, 10:30:33 am »
Given that the typical claw-pole rotor alternator is around 55%-60% efficient, it makes absolutely no sense to spend lots of money (relatively speaking) adding PFC to it when it would cost far less to simply change to a more efficient rotor design (the claw pole rotor does a very poor job of concentrating the flux from its field winding).

 

Offline T3sl4co1l

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #6 on: July 23, 2019, 06:01:40 pm »
It could be used, but it would greatly complicate a component that is otherwise very simple, not very efficient, and heavily stressed.  Engine bay components get very hot indeed.  It could be done with some difficulty with silicon parts, or perhaps less difficulty with GaN parts (or SiC if this were a high voltage system).  Nevermind the commercial availability (currently ~boutique) and cost of packaging those devices (200°C+, usually gold and ceramic), of course.

In short, all you gain is slightly less heating in the winding -- reduced harmonic currents.  Actually hmm, how much of that even is true, because, if the voltage ends up flat-topped, that's not instantly causing huge current spikes.  The output impedance isn't nearly as low as a proper generator is.  So that leaves slightly increased core heating due to the voltage harmonics, but that's really a small part of an already very toasty core -- due to the relatively high operating frequency and laminated iron construction.

Probably, significantly more efficiency would be saved through using thinner laminations, of higher quality material (lower losses, and maybe higher Bmax, though Bmax really only affects volts/turn at idle speeds), and tighter tolerances probably with a better salient-pole rotor configuration (as mentioned above).  All of which increase the cost, for a low ranking system (that is to say, the electrical power in an average ICE vehicle is a tiny fraction of the total available power).

This would be applicable to hybrids and electrics, but I'm guessing they usually use direct-drive inverters, so regenerative braking, and generation from the APU where applicable, is trivial in the sense that the power train (both electrical and mechanical), is all there.  (The control may be nontrivial, to get a controlled-power polyphase inverter system running, but that's just 1's and 0's; a solution exists, it's just engineering to find it.)

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Offline David Hess

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #7 on: July 23, 2019, 06:42:11 pm »
The output from the alternator is controlled by the field current so the output is high impedance; it operates like a current transformer with gain instead of a low impedance voltage source like with a power line.

So the conduction angle of the output rectifiers is much higher and the power factor is better than a line power operated rectifier and capacitor filter.  I am not sure there would be any improvement to be had by adding active power factor correction and given the currents involved, construction would be difficult.
 
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Offline NiHaoMike

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #8 on: July 24, 2019, 04:49:43 am »
Given that the typical claw-pole rotor alternator is around 55%-60% efficient, it makes absolutely no sense to spend lots of money (relatively speaking) adding PFC to it when it would cost far less to simply change to a more efficient rotor design (the claw pole rotor does a very poor job of concentrating the flux from its field winding).
The move is towards permanent magnet rotors, then stepping down the voltage with a switching power supply.
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Offline MagicSmoker

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #9 on: July 24, 2019, 11:44:14 am »
Given that the typical claw-pole rotor alternator is around 55%-60% efficient...
The move is towards permanent magnet rotors, then stepping down the voltage with a switching power supply.

Really? That's exceptionally stupid, even for an automotive OEM, which can usually be counted on to do things too cheaply, rather than the other way around. PM rotors are much more expensive and can't withstand even moderately high temperatures (some types of rare earth magnets start to suffer demagnetization at less than 100C), to say nothing of then needing an SMPS to provide voltage regulation and current-limiting. It would make far more sense to simply replace the crappy claw-pole rotor with a salient pole wound-field rotor as found on larger synchronous machines since it could use the same field current regulator design and 3-ph. bridge rectifier.

 

Offline duak

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #10 on: July 24, 2019, 06:30:53 pm »
An AC generator (alternator) equivalent circuit includes a series inductance Ls.  This can be a good thing for limiting peak currents such as those using rectifiers to convert to DC or should it be overloaded.  Automotive DC generators have current limit relays, but alternators don't.  I don't know what the value of Ls is for a typical alternator. I used an old alternator to test a PWM driver I was developing.  I recall Ls was in the low mH range but definitely not more than 10 mH. Ls provides a measure of PFC and I think you won't see the extreme current pulses that occur in a capacitor input offline supply.
 

Offline David Hess

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #11 on: July 24, 2019, 09:27:52 pm »
Low millihenries is what I remember for car alternators and about 3 or 4 ohms so 3 or 4 amps at 12 volts of excitation.

I once built a PWM switching regulator based control circuit for my car charging system and measured the alternator characteristics with an impedance bridge for modeling purposes which allowed me to get the pole-zero frequency compensation close on the first try.  Load regulation at the battery terminals was better than 10 microvolts for a 30 amp change in load current where the stock regulator was 100s of millivolts under the same conditions.
 

Offline NiHaoMike

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #12 on: July 25, 2019, 01:06:39 am »
Really? That's exceptionally stupid, even for an automotive OEM, which can usually be counted on to do things too cheaply, rather than the other way around. PM rotors are much more expensive and can't withstand even moderately high temperatures (some types of rare earth magnets start to suffer demagnetization at less than 100C), to say nothing of then needing an SMPS to provide voltage regulation and current-limiting. It would make far more sense to simply replace the crappy claw-pole rotor with a salient pole wound-field rotor as found on larger synchronous machines since it could use the same field current regulator design and 3-ph. bridge rectifier.
The added cost is offset by removing the need for a separate starter motor. Then add auto start/stop, to boost MPG and help otherwise conventional cars stay competitive with hybrids and EVs.
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Offline TheUnnamedNewbie

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #13 on: July 25, 2019, 05:44:15 am »
Given that the typical claw-pole rotor alternator is around 55%-60% efficient, it makes absolutely no sense to spend lots of money (relatively speaking) adding PFC to it when it would cost far less to simply change to a more efficient rotor design (the claw pole rotor does a very poor job of concentrating the flux from its field winding).
The move is towards permanent magnet rotors, then stepping down the voltage with a switching power supply.

I thought the general push was to a much higher voltage. I know this is already electric cars, but I think there is a big push to 48 volts for internal stuff. Now with better on-chip DC-DC capabilities, the reduced cost of wires (esp the weight gains) easily outweighs the cost of fancier DC/DC.

12 V used to just be nice with lead-acid (I think, don't know why you wouldn't want to put more lead-acid cells in series?). I think some bigger vehicles, like trucks use 24 V? .

SMPS technologies are really becoming cheaper, and the increase in EV stuff is only helping their price go down further (lots of research going into that). Same with GaN and SiC - their cost is coming down to the point where their increased cost can be justified for the benefits they offer in system design. 
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Offline MagicSmoker

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #14 on: July 25, 2019, 01:55:45 pm »
The added cost is offset by removing the need for a separate starter motor. Then add auto start/stop, to boost MPG and help otherwise conventional cars stay competitive with hybrids and EVs.

Ahh, yes. The mild hybrid/belted-alternator-starter thing. I was so fixated on conventional ICE vehicles changing their alternator design over to PM that I totally forgot about mild hybrid systems. I'm still not sure this makes any economical sense, but it is definitely true that mating a PM rotor alternator - that is, a PM synchronous motor/generator - to a 6-switch inverter with field-oriented ("vector") control allows the alternator to act as a motor or generator and with ideal power factor at all times. Whether the higher efficiency of the mild hybrid system offsets the vastly higher cost over the lifetime of the vehicle is another question altogether, though.


 

Offline Zbig

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #15 on: July 25, 2019, 02:17:40 pm »
An increasing number of cars are using switching power supplies for the 12V.
http://techno-fandom.org/~hobbit/cars/ginv/i1mech.html

Not saying they aren't (don't know) but the page you've linked talks about Toyota Prius (hybrid) specifically. Toyota Hybrid Synergy Drive uses completely different electrical system topology. You don't have a conventional alternator there: the 12V system and the 12V lead-acid battery (yes, there still is one) are powered from high voltage (c.a. 400V IIRC) DC coming from the High Voltage Battery or either of the two Motor-Generators via the Inverter-Converter.
 

Offline james_s

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #16 on: July 25, 2019, 03:57:09 pm »
Really? That's exceptionally stupid, even for an automotive OEM, which can usually be counted on to do things too cheaply, rather than the other way around. PM rotors are much more expensive and can't withstand even moderately high temperatures (some types of rare earth magnets start to suffer demagnetization at less than 100C), to say nothing of then needing an SMPS to provide voltage regulation and current-limiting. It would make far more sense to simply replace the crappy claw-pole rotor with a salient pole wound-field rotor as found on larger synchronous machines since it could use the same field current regulator design and 3-ph. bridge rectifier.
The added cost is offset by removing the need for a separate starter motor. Then add auto start/stop, to boost MPG and help otherwise conventional cars stay competitive with hybrids and EVs.

Those silly auto stop-start systems exist to exploit a loophole in the way idle emissions are calculated. They have a negligible impact on real world fuel economy and anecdotally they seem to have a very real impact on battery life. They certainly are annoying to drive a vehicle that has one too, especially the cheap ones that have an ordinary noisy starter that engages.
 

Offline soldar

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #17 on: July 25, 2019, 04:06:10 pm »
PFC circuits exist in devices connected to the mains because the energy (current) has to be transported hundreds or thousands of Km from generation to consumption and PFC provides a reduction in power wasted in transmission.

In a car it makes no sense.
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Offline Gyro

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #18 on: July 25, 2019, 04:45:29 pm »
An increasing number of cars are using switching power supplies for the 12V.
http://techno-fandom.org/~hobbit/cars/ginv/i1mech.html

Not saying they aren't (don't know) but the page you've linked talks about Toyota Prius (hybrid) specifically. Toyota Hybrid Synergy Drive uses completely different electrical system topology. You don't have a conventional alternator there: the 12V system and the 12V lead-acid battery (yes, there still is one) are powered from high voltage (c.a. 400V IIRC) DC coming from the High Voltage Battery or either of the two Motor-Generators via the Inverter-Converter.

We picked up our nice Kia Niro Hybrid earlier this week. Kia phased out (no pun intended) the 12V lead-acid battery in 2018 - It was there when the car was first released in 2016. It uses both the 32kW drive motor and the Engine belt coupled Hybrid Starter Generator (8kW) for regeneration. Both are hooked up to the high voltage battery (240-270V).

Apparently there is now a separate 12V auxiliary section in the main (LIPo) high voltage battery (there's a regenerate button to recharge it from the main battery if it gets low), but both of the motors, and the Aircon compressor too are 3-phase permanent magnet type, driven by the inverter module from high voltage battery.

It took me a while searching around the boot for the Aux battery compartment before I found a reference on the web to it being phased out. The earlier service manual reference that I have still had it included.

I can't get my head around these new 48V 'mild' hybrids! A tax / congestion area get-around?

I do like the belt drive starter generator though, pinion drive 12V starters are a really weak link for stop-start operation.
« Last Edit: July 25, 2019, 05:19:31 pm by Gyro »
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Online ejeffrey

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #19 on: July 25, 2019, 05:56:00 pm »
I can't get my head around these new 48V 'mild' hybrids! A tax / congestion area get-around?

I do like the belt drive starter generator though, pinion drive 12V starters are a really weak link for stop-start operation.

48 V mild hybrid is basically start-stop++.  You get a more powerful combined starter/generator that is attached directly to the drive shaft and replaces the starter and alternator.  It can restart the engine faster than a crappy 12V starter motor and also start to move the car forward while starting for impatient people who need to move *now* when the light turns green.  The 48 V system is also enough to power an electric AC compressor which means the compressor doesn't have to deal with the huge RPM range of the engine and also doesn't shut off when the engine stops at a traffic light.  The electric motor costs more than a pulley, but also gives the manufacturer more freedom in placement, and may allow complete elimination of the serpentine belt. You get a small amount of regenerative braking which still helps for stop/go city driving and if you can put some of the other higher power accessories on 48V you save a bit on copper costs.  Since 48V is still considered "safe" you don't have to implement the same emergency cutoff and auxillary battery systems that traditional hybrids have.

 
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Re: Do modern car/boat alternators use PFC circuits?
« Reply #20 on: July 25, 2019, 08:05:48 pm »
The latest Mercedes I6 has no serpentine belt and uses a 48 volt electrical system.

Some of the benefits explained...

https://youtu.be/7PkX-NH6bE0?t=263
 

Offline MagicSmoker

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #21 on: July 25, 2019, 08:06:31 pm »
PFC circuits exist in devices connected to the mains because the energy (current) has to be transported hundreds or thousands of Km from generation to consumption and PFC provides a reduction in power wasted in transmission.

In a car it makes no sense.

Yeah, excellent point... /discussion.
 

Offline schmitt trigger

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #22 on: July 25, 2019, 08:37:01 pm »
I drove for 8 years a 2005 Honda Civic Hybrid.

The main electrical motor (BLDC) was sandwiched between the CVT transmission and the gas engine.

The vehicle had a start/stop function, and since the HP rating of the electrical motor was a significant portion of the engine's HP rating, it would start immediately and effortlessly.
Even so, the start/stop function could become annoying. Fortunately, it could be disabled. And the MPG loss, to the best of my recollection, was negligible.

Thus, I agree with previous posters that start/stop function is only a gimmick that auto manufacturers employ to game the economy ratings.
 

Offline james_s

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #23 on: July 26, 2019, 12:21:24 am »
My partner has a Prius which shuts off the ICE when the car is stopped but it doesn't bother me too much on those. The electric motor is sufficient on its own to get the car rolling which gives the ICE plenty of time to fire up. I'm still not convinced that all that complexity is worth the gains however it's a 2002 model still running the original traction battery and it has surpassed my expectations, being impeccably reliable.

On a non-hybrid the stop-start system exists only to game the system. I hope that eventually the rating system catches up and closes these loopholes because driving a car that has one of those is a terrible experience. Especially the more primitive ones that don't disable stop-start when the AC is running, every time you stop at a light the vents start blowing warm muggy air until the thing chugs and lurches forward when you step on the gas.
 

Offline duak

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Re: Do modern car/boat alternators use PFC circuits?
« Reply #24 on: July 26, 2019, 04:17:47 am »
Which vehicles have belt start engines?  Do they have a conventional starter too?
 


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