ac pm motor starting

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djsharpe
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Post by djsharpe »

It is one of life's mysteries how the Prius & Insight start the engines.
I thought synchronous motors were not able to be started directly from AC power. The only possibility is a ramped up wave ie 0 V 0 Hz to operating volts. Any explanation?

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Post by woody »

Just guessing here: The Prius's motor controllers would be inverters - I.E. generate it's own sine waves from the DC battery voltage at whatever frequency and voltage* required, so you're right low voltage low frequency to start with. If a prius motor is generating, its controller would put DC current onto the bus / batteries.

*limited by the DC voltage.
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Post by Electrocycle »

you can start the AC drive to the motor from zero Hz :)
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Post by acmotor »

AC PM motors (synchronous AC, BLDC can run the same w/o commutation signals) are a bit notchy to start by just an AC waveform, however a PWMd low frequency low voltage waveform can do it quite smoothly. The sync AC motor can develop full torque from zero RPM as with induction motor.
The induction motor actually requires some slip to magnetise the rotor of course.
As with most emotors, torque is proportional to current. At low revs you only need a low voltage to push the required current to get the required torque.   

You will notice that the prius has (well disguised) notches at 1 or 2 kmph.

Most VFDs, such as mine, will operate sync AC motors as well as induction motors.

Image

edit: spelling (faulty keeboared I recon)
Last edited by acmotor on Sat, 14 Mar 2009, 11:47, edited 1 time in total.
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Post by Electrocycle »

my bike (PMAC motor) is seamless at very low speed, as long as you don't use too much throttle.
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Post by djsharpe »


Thanks for explanation.
Ive got a wind turbine PM alternator that I want to run as a high speed engine driven machine for my EV range extender. Commercial gen sets are all too heavy in my opinion as they have 50Hz alternators. My alternator is light as it will be much higher frequency than 50Hz. Ive got the Diesel but want to use the alternator to start the engine. Battery is 150V nominal. Perhaps a US (115V AC) VSD could be used to run it. Diesel was used to a 48V DC generator/motor and has no stater motor or ring gear for one. Any suggestions for a cheap VSD?

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Post by Johny »

Unfortunately 115 VAC is not a standard for 3 phase anywhere in the world (that I know of), so VFDs for 115 V are not available. The best you could do is a 240 V 3P VFD and hope that you could "trick" it into thinking the DC Bus voltage was OK - a bit risky though.

You don't mention the power of the generator.
VFD pricing, even 2nd hand, is proportional to the power rating.
I would expect, with a few months to look, that you could pick up a 240V 6kW off eBay for under AU$300.

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Post by Electrocycle »

given the short run time and specific load / rpm requirements of starting the generator, I'd say you could pretty easily build a controller for it.
Probably a 6 IGBT module would be the easiest way.
A small microprocessor could drive it, and you can just play with the drive settings until it works. It wouldn't need proper current limiting or complex monitoring because you can pre test all that and set it to only run within safe limits.
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Post by acmotor »

David,
I'm with Electrocycle.
Does the WT motor have the required torque to start the diesel ? If so then the voltage would be quite low at cranking speed ? (100RPM or less)(at high current, around the max for the WT motor).
Just thinking out loud here. A basic single frequency no feedback AC inverter could be built. Or even use one from an ebike if it had enough current. The voltage is likely to only be 36-48V max. Might be a problem in voltage once the diseasal starts though.

A 240V VFD expects 330VDC and shuts down at 270VDC from memory. SO not much good for you.
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Post by djsharpe »

This 3 ph would have enough torque to rotate the Diesel which is a Robins Subaru DY41 1 cyl with decomp lever. It actually lets the engine do a number of revs before allowing the exhaust valve to close. You must be able to get VSD to suit US voltages (1 ph 115 60Hz) and motors wound for same.
In Aus if 240V AC you buy a VSD and if you have a 3 ph IM with 6 wires and link box you connect from star to delta & away you go. Must be same philosophy in US.
Readers interested in this subject of a light weight range extender might be interested in what I have determined so far:
50Hz alternators are too heavy. Cheap petrol sets unless of the inverter type are unlikely to deliver rated power. You could probably power 3 NG3 Zivans off a suitable set but would need about 14kVA to do it. This would deliver 54A for a 144V battery enough to do 75-90 kph for a typical small EV.
1 cyl Diesels have large heavy flywheels. Multis have smaller ones. If the DY41 is not used I might go a Kubota or Yanmar 3 cyl 60-70 kgs bare.
High frequency alternators ie multi poles driven at 3000 RPM or more will be lighter but efficiency may suffer. Aircraft run their alternators (400Hz) at engine revs and are much lighter. Efficiency for this application and ours is not so important as getting the mass lower.
It is best to have an alternator that you couple direct to your battery via bridge rectifier and vary the speed to suit conditions. I would also change the alternator config from star to delta as the speed increases.    

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Post by acmotor »

I agree with the higher frequency / higher revs / revs not linked to Hz ideas for small gen sets specifically aimed at EV batery pack charging.

Inverter syle gen sets go a long way to addressing these points though.

Re VFDs
There are basically two voltage standards in the world ...
approx 115V single phase (100-120V) >> 200V 3 phase
and 240V single phase (220-240) >> 415V 3 phase
(there is also 50 and 60 Hz) I guess you know the countries.

Industrial VFDs for 3 phase power are made for the 200V 3 phase and 415V 3 phase market (and also some higher voltage units for bigger motors)
There is no 115V 3 phase anywhere so you can't buy an industrial 3 phase VFD for that voltage. It just happens that we in Oz can use a VFD designed for ~200V 3 phase and supply it with 240V single phase and run a small (<3kW) 3 phase motor off it(these small motors are available in Oz for ~230V in delta ~400V in star. This gives the caps and diode a harder time due to the increased ripple 100Hz vs 300Hz.

That is not to say that there are not some specialised VFDs for not off the mains applications out there for 144VDC.

Most VFDs will run almost any voltage motor as long as they have suitable output current. I can tell my Danfoss 30kW VLT to run a 50VAC motor of 100W if I like. However I must still have the normal DC bus voltage available >470VDC) supplied to the controller.

On that point Dave, what current and voltage does the PM motor require to start the diesel ? You could run it off a normal VFD to find this out.

What is your thinking re kW of range extender ?
It is a big step to put enough gen set on board to give continuous operation at say 90k. I was thinking that 4kW would give suitable range 'extention' if used from the start of the drive. 2 to 3 times range of city driving in my case.
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Post by djsharpe »

The original DC drive developed so much torque that it didnt need to engage the decomp lever. Ive never tested the set to just turn the engine with no compression. My plan is to see if I can drive to Perth next year (never done it before) with my EV and charge at any convenient spot. I wont try & organise anything like the EVent to Canberra. I do need to travel at 90ks though. This why the range extender might blow out to a 3 cylinder Diesel providing 8 kWs or more. I could stick it in the rear rather than a trailer, which will take more power to pull. I was thinking of building a false removeable firewall so that the noise is not so bad.

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Post by acmotor »

How many km per day would you plan ?
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Post by djsharpe »

It would work this way: If I found fuel stops would let me charge as well as get fuel, Id turn up with near flat traction battery & fuel both, but it might involve only 200ks per day in battery mode because each 100ks needs 3 hours charging even with my 2 NG3s (33 Amps).
Day 1 drive 100ks on bats 1.5 hrs followed by 300ks on fuel 3.5 hrs, refill tank charge bats 3 hrs (long lunch), 100ks bats 1.5 hrs 300ks on fuel 3.5 hrs Stay at camping ground onight charging. 800ks 13 hrs on the road. Engine revs would be adjusted to avoid too much charging en route. So Perth in 4 days, there are some people who do this much driving in a day in conventional cars . The alternative strategy of driving very slowly to get better mpg etc is not considered due to abject boredom factor. Id only go one way, train for me to Adelaide on return, cheaper direction. Ive got a country place 250ks from Melb on way to Adelaide which would be a charging locn for both directions.

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Post by acmotor »

Can you put some Wh/km numbers on that ?
First impression is it won't come out of a 10A socket ?

If you had a 10kW gen, just take a long lunch and let EV charge from that. (much that same as using the diesel gen at Nullabor, Madura and Caiguna etc.) BP border villiage is the only one (I noticed) that is solar/wind powered.

I would think to plan a 10 hour charge overnight at 2.4kW and size the gen to share the battery load and achieve range extention to km as required. i.e. run the gen from the start of each drive.

BTW, I have just purchased a 650kVA gen set, V12 twin turbo, for a work project I am involved in.   Image
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Post by djsharpe »

It will need two separate 10A circuits. The AC current is more like 15A but a 10A GPO will handle it as the 2.5mm2 wiring can do 20A. They do get warm though. Id say my combined 132Ahr pack goes to 20% remaining so needs around 150whrs per k. More like 200 ex grid. I hope to get this down with some aero mods and LRR tyres. The aim of the exercise is to use grid/local power to charge the bats when ever possible but I suppose your point is that if the local power is Diesel you may as well use your own. Maybe the bigger sets are more efficient. Wots your V12 going to be used for?

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Post by acmotor »

It may be worth, on that local power source issue, to map out just how much of the trip is outside interconnected power grids (so probably diesel gen anyway). It would be between Norseman in WA and Ceduna in SA at first thought. (1200km) Out of the total trip (3400km)

20kWh/3.75kW is still over 5 hours. That's a long lunch !

BTW, I've driven the 'bore 16 times (return trips) now and it is a lot better NOT to drive at night. (kangaroos,trucks,dipping headlights,lack of scenery,fatigue).

V12 is for use on our front lawn, for when the grid power goes off. Or any Friday / Saturday night that things are a bit quiet according to Andrew.

No, actually...

V12 is to run a 450kW Danfoss Image Image Image Image to run a 450kW 12 pole 3 phase motor (big mother) to run a turbine in a circulating tank to simulate wave and tide for offshore pipeline research. It will 'replay' recorded cyclone events via computer control.
I built a 1/10th scale model last year and the oil companies were so impressed they put up the $1M for the University (UWA) to build the full scale version on the spot.
Since then I have had fun buying the parts and arranging the build !
The Genset is because the local power authority would not supply the power (massive upgrades to infrastructure was the excuse). Rather than hold up the project, we decided to take a chance on this beast !

The 650kVA is an old Dorman diesel on a petbow alternator. Ex hospital backup power. Has very few hours on it. Runs smooth and loud (no muffler at test time !) I've load tested it to 400kW (all I could find a the time) Sweet !
Injectors and pump have been stripped and cleaned for fear of old fuel before starting.

I think you would call it a nice juxtaposition with EVs ! Image

650kVA Dorman V12 twin turbo aftercooled (~3m high) and rather loud.

Image

Image

Image

Man, was that off topic or what ?? Image
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Post by djsharpe »

Recharge time if 90Ahrs is used will be around 3 hrs not 5 as I have 2 Zivans and will ask for 2 separate circuits to charge from. I was originally going to use 3 Zivans (and 3 ph) but this an extravagance, might go a bad boy auto or variac plus bridge rect though with earth spike for EV. Dormans are very nice sets and once de rigeur when reliability was needed.

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Post by Johny »

Off topic or not, impressive machinery acmotor.

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Post by acmotor »

I could put it on a semi and follow DJ across the 'bore. It would solve the charging problems. Image

... Sorry, bad joke. Image
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Post by acmotor »

Oh, you meant the 450kW Danfoss (FC302 with braking) !

That's for Phil's bus when the research project is finished. Image
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Post by Bigglesworth »

Ahh, the Bus. It's still on the design board
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Post by Mesuge »

acmotor wrote: V12 is for use on our front lawn, for when the grid power goes off. Or any Friday / Saturday night that things are a bit quiet according to Andrew.


lol Image
Seriously, this is very interesting project you are doing for the university, I gather that the 1/10 scale model was also Danfoss powered, right?
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Post by acmotor »

Yep, I should have shares in Danfoss !

The 1/10 scale model runs a 5.5kW 2 pole motor and an 11kW Danfoss VLT2800 (a bit overkill but it was experimantal to test the concept). Control is simple 0-10V with reversing via a National Instruments DAQ card running Labview software.
Software can generate various waveforms including offsets and ramps or replay a 'storm' from a csv file.

You've heard of wave tanks, well this is a closed loop pipe full of water to experiment with the undercurrents on the seabed. There is a clear square test zone with flow laminators either end.

The 11kW Dan was too small for an EV anyway ! Image
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